Traditional
Poster Session - Engineering |
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Click on
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the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
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2575. |
Design and construction of
a Halbach array magnet for portable brain MRI ![](poster.gif)
Clarisa Zimmerman1, Lawrence L Wald2,
Matthew S Rosen3, and James Blau4
1Electrical Engineering, Massachusetts
Institute of Technology, Cambridge, MA, United States, 2Department
of Radialogy, Athinoula A. Martinos Center for
Biomedical Imaging, Massachusetts General Hospital,
United States, 3Athinoula
A. Martinos Center for Biomedical Imaging, Massachusetts
General Hospital, United States, 4Athinoula
A. Martinos Center for Biomedical Imaging, United States
A Halbach array magnet was designed, modeled and
constructed for a portable brain MRI application. The
array consists of 20 radially magnetized NdFeB N42
magnets and is large enough to fit the human head. The
modeled field shows a roughly quadratic field profile
with a central Larmor frequency sufficient for imaging
(~3.3MHz). While the homogeneity is well below that of
superconducting magnets, it fits well with our
light-weight and portable concept if the inhomogeneities
are used in image encoding.
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2576. |
A practical insert design
for dreMR imaging in the human torso ![](poster.gif)
Chad Tyler Harris1, William B Handler1,
and Blaine A Chronik1,2
1Physics and Astronomy, University of Western
Ontario, London, Ontario, Canada, 2Imaging
Research Laboratories, Robarts Research Institute,
London, Ontario, Canada
Delta relaxation enhanced magnetic resonance (dreMR) is
a relatively new technology that allows for enhanced
signal specificity when using targeted MR contrast
agents. The method utilizes a supplementary “Bo insert
coil” to modulate the main magnetic field within an
otherwise unmodified superconducting system. Previously,
Bo inserts have been developed for small-animal imaging
and recently we have presented a practical insert design
for dreMR imaging of the human head. In this work, we
present a feasible design for an open-geometry Bo insert
coil capable of producing significant dreMR contrast in
the human torso.
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2577. |
Next Generation Delta
Relaxation Enhanced MRI with ±0.36T ΔB
Eddy SM Lee1, Ludovic de Rochefort2,
Gianni Ferrante3, and Brian K Rutt1
1Lucas Center, Stanford University, Stanford,
California, United States, 2Univ.
Paris-Sud, CNRS, UMR8081, IR4M, Orsay, Paris, France, 3STELAR
s.r.l., Mede, Italy
Delta relaxation-enhanced magnetic resonance (dreMR)
imaging is a B0-cycled MR technology that
produces contrast from intended targets only. Variable B0 was
produced with a next generation, insertable,
field-cycling magnet that enabled dreMR imaging with ΔB
of up to ±0.36T; the highest achieved to date. dreMR signal
was linearly enhanced as ΔB was increased, while
physiological background remain suppressed. Our results
demonstrate the advantage and proof-of-concept of
achieving dreMR imaging at high ΔB.
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2578. |
Magnetic filed shimming of
a high Tc superconducting
bulk magnet using a cylindrical single-channel shim coil ![](poster.gif)
Daiki Tamada1, Keisuke Maruyama1,
Katsumi Kose1, and Takashi Nakamura2
1Institute of Applied Physics, University of
Tsukuba, Tsukuba, Ibaraki, Japan, 2RIKEN,
Wako, Saitama, Japan
A cylindrical single-channel shim coil was developed for
a high critical temperature (Tc) superconducting bulk
magnet (4.7 Tesla) with a 23 mm diameter room
temperature bore. The single channel shim coil was
designed using circular current loops periodically
placed on the cylindrical surface. The magnetic field
distribution in a rectangular region (5 mm x 5 mm x 7
mm) was measured for various shim current values. As a
result, about 30% homogeneity improvement was achieved
for an optimal current value, which demonstrated
usefulness of our approach.
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2579. |
Magnetic field shimming of
a 2.0 T permanent magnet using a bi-planar single-channel
shim coil ![](poster.gif)
Daiki Tamada1, Katsumi Kose1, and
Tomoyuki Haishi2
1Institute of Applied Physics, University of
Tsukuba, Tsukuba, Ibaraki, Japan, 2MRTechnology,
Inc., Tsukuba, Ibaraki, Japan
In this study, we proposed a novel single-channel shim
coil design method using circular current elements to
correct higher order inhomogeneities. We succeeded in
decreasing PP value of the ĢB0 by 40%. In conclusion,
the novel SCSC design method is simple and useful for
shimming a ĢB0 including higher order terms.
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2580. |
Gradient Coil Induced
Joule Heating in a MRI magnet
Yihe Hua1, Longzhi Jiang2, Graeme
C Mckinnon3, Seung-Kyun Lee4, and
Anbo Wu1
1GE Global Research, Shanghai, China, 2GE
Healthcare, Florence, SC, United States, 3GE
Healthcare, Waukesha, WI, 4GE
Global Research, Niskayuna, NY, United States
In conductive cooling magnet, joule heating in 4K region
is critical due to the cold head capability limitation.
When a MRI scanner is operating, the current in gradient
coil will induce EC in magnet metal structure, which
will vibrate by the Lorentz force due to the main field.
The motion will further generate motional EC. In this
article Joule heating in cryostat, AC loss in
superconductive wires and dielectric loss in coil epoxy
are calculated for one 1.5T MRI magnet including full
metal VV, TS and coil former with 2D harmonic analysis.
The z-gradient coil is optimized towards heating
minimization.
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2581. |
Fringe field effects on
hyperpolarized 129Xe
for a continuous flow SEOP setup
Martin Kunth1, Christopher Witte1,
and Leif Schröder1
1Leibniz-Institut für Molekulare
Pharmakologie (FMP), Berlin, Germany
We studied the influence of fringe field effects on
hyperpolarized 129Xe
for a spin exchange optical pumping polarizer system
working in continuous flow mode when the magnetic
optical pumping field of the polarizer is in direct
proximity to the magnet of the spectrometer. The
configuration of the pumping field was modified to three
coils with a variable current of the center coil and a
single shot 129Xe
NMR spectrum was acquired every 2 seconds. Our data show
that the 129Xe
NMR signal can be optimized by modifying the net fringe
field.
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2582. |
Design and Optimization of
a Permanent Magnet for Small-sized MRI Based on Particle
Swarm Optimization Algorithm ![](poster.gif)
Yiyuan Cheng1, Ling Xia1, Wei He1,
Feng Liu2, and Stuart Crozier2
1Department of Biomedical Engineering,
Zhejiang University, Hangzhou, Zhejiang, China, 2The
School of Information Technology and Electrical
Engineering, The University of Queensland, Brisbane,
Australia
The main magnet, an important part of an MRI system, is
used to produce the static magnetic field in the imaging
area. In a permanent MRI magnet, there is a widespread
end effect that causes a non-uniform magnetic field
distribution and affects the imaging quality. In this
paper, we have designed an H-type permanent magnet for
small-sized MRI applications; in particular, the novel
design has been realized by adding a shimming ring
outside the pole piece to improve the magnetic field
uniformity. Particle swarm optimization (PSO) algorithm
is used to solve the complex and nonlinear optimization
problems. The simulation results show that the magnet
optimized by the proposed method generates a homogeneous
magnetic field that can be easily implemented in
practice and at a low cost.
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2583. |
Passive Shimming of MRI
Magnets with B0 >= 3T at Reduced Field
Yuri Lvovsky1, Zhenyu Zhang1,
Timothy Hollis2, and Ye Bai2
1GE Healthcare, Florence, SC, United States, 2GE
Healthcare, BeiJing, China
Method of passive shimming of MRI magnet is presented.
To reduce forces and torque during shim tray insertion /
removal, after the initial virgin map is taken at full
field the magnet is partially ramped down where coarse
iterations are performed using maps acquired at lower
field. Test results proved successful shimming of the
magnet.
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2584. |
Cryogen-Free 3T-MRI System
for Human Brain Research using Bi-2223 High-Temperature
Superconducting Tapes
Shin-ichi Urayama1, Osamu Ozaki2,
Hitoshi Kitaguchi3, Kazuyuki Takeda4,
Iwao Nakajima5, Naoki Ohnishi6,
Michael Poole7, Ken-ichi Sato8,
and Hidenao Fukuyama1
1HBRC, Kyoto University, Kyoto, Japan, 2Kobe
Steel, Ltd., Kobe, Japan, 3National
Institute for Materials Science, Tsukuba, Japan, 4Kyoto
University, Kyoto, Japan,5Takashima
Seisakusyo, Tokyo, Japan, 6Astrostage,
Inc., Tokyo, Japan, 7University
of Queensland, Queensland, Australia, 8Sumitomo
Electric Industries, Ltd., Osaka, Japan
The demand for the exhaustible natural resource helium
is increasing rapidly, with 20% of global production
used as the cryogen in superconducting MRI magnets.
High-temperature superconducting (HTS) materials show
great potential for realizing helium-less magnets. This
is the first report for a cryogen-free 3T-MRI scanner
for human brain research using Bi-2223 tapes operating
at a temperature of 20K.
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2585. |
Simulation of
Magneto-mechanical Coupling in a 3T Head-only Magnet Design
Dominic M Graziani1, Seung-Kyun Lee1,
Jean-Baptiste Mathieu1, Graeme C McKinnon2,
Thomas K Foo1, and John F Schenck1
1GE Global Research, Niskayuna, NY, United
States, 2Applied
Science Lab, GE Healthcare, Waukesha, WI, United States
We present an investigation on the effects of
magneto-mechanical coupling on the eddy current in a
prototype 3T head only scanner design. Transverse and
longitudinal actively shielded gradient coils were
modeled in COMSOL along with an aluminum cylinder, fixed
at both ends, representing a conducting surface of the
magnet. Magneto-mechanical resonance was observed for
both gradient designs at frequencies between 2-3.5 kHz.
At resonance, the peak gradient strength changed by up
to ~10% for the longitudinal gradient and ~1.5% for the
transverse gradient.
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2586. |
Development of a low-field
NMR unit using a crossed coil setup for calibration of a
PASADENA polarizer ![](poster.gif)
Robert Borowiak1, Elmar Fischer1,
Sebastien Bär1, Jochen Leupold1,
Frank Huethe2, Thomas Lange1, Jeff
Snyder1, Jürgen Hennig1, Dominik
von Elverfeldt1, and Jan-Bernd Hövener1
1Medical Physics, Dep. of Radiology,
University Medical Center Freiburg, Freiburg,
Baden-Württemberg, Germany, 2Neurozentrum,
scientific workshop, University Medical Center Freiburg,
Freiburg, Baden-Württemberg, Germany
Low-field NMR has received increasing attention in the
recent years as several new approaches were published.
As previous polarizers had no detection ability at B0 =
1.8 mT, we developed an apparatus specifically for the
fields required by SABRE and PASADENA (B0 = 1 – 6 mT),
suitable for RF calibration and the direct detection of
NMR signal. PASADENA and SABRE are unique liquid-state
hyperpolarization techniques which have achieved 13C NMR
signal enhancement of several orders of magnitude.
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2587. |
An Open Source Low-Cost
NMR System
Michael D Twieg1, Matthew J. Riffe2,
Natalia Gudino2, and Mark A. Griswold1,3
1Department of Electrical Engineering and
Computer Science, Case Western Reserve University,
Cleveland, OH, United States, 2Department
of Biomedical Engineering, Case Western Reserve
University, Cleveland, OH, 3Deptartment
of Radiology, Case Western Reserve University and
University Hospitals of Cleveland, Cleveland, OH
We present a low cost NMR system aimed for use in simple
NMR experiments. The system is based on an Arduino
microcontroller platform and a MATLAB interface. Most of
the RF chain is broadband, allowing it to be easily used
with a wide range of frequencies and transmit/receive
coils. The system is capable of several simple NMR
experiments, allowing the measurement of T1,
T2, ρ0, and self diffusion
coefficient (D). The total cost of the system,
neglecting a host computer and bench top power supplies,
is less than $400. Documentation on the project is open
source.
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Traditional
Poster Session - Engineering |
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Gradients, Shims & Field Monitoring
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2588. |
Design of High Performance
Gradient Coil for 3T Head Specialty Scanner
Jean-Baptiste Mathieu1, Bruce C Amm1,
Silke Lechner-Greite2, Seung-Kyun Lee1,
Ek Tsoon Tan1, Thomas K-F Foo1,
John F Schenck1, Matt A Bernstein3,
and John Huston3
1Diagnostics and Biomedical Technologies, GE
Global Research, Niskayuna, NY, United States, 2Diagnostics
and Biomedical Technologies, GE Global Research Europe,
Garching, Germany, 3Mayo
Clinic, Rochester, MN, United States
We report on the design of a head-only shielded gradient
prototype to be inserted in a specialty 3T head-only
magnet for high-performance neuroimaging. The gradient
is force- and torque- balanced, and employs asymmetric X
and Y gradient and symmetric Z gradient design. This
design delivers peak specifications of 88mT/m and
630T/m/s with a commercial gradient driver and a
linearity of 16.9% over a 26 cm diameter spherical
volume (DSV). The expected image distortion due to
gradient nonlinearity was evaluated with simulated brain
image with nonlinearity correction.
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2589. |
Conventional and Linked
Gradient Coil Designs: a Comparative Study ![](poster.gif)
Alice Borceto1, Andrea Viale2,
Leonardo Bertora2, Richard Bowtell3,
and Franco Bertora1
1Robotics Brain and Cognitive Science,
Istituto Italiano di Tecnologia, Genova, GE, Italy, 2Paramed
Medical System, Genova, Italy, 3University
of Nottingham, Sir Peter Mansfield Magnetic Resonance
Centre, Nottingham, United Kingdom
A comparative study of two different types of gradient
coil design (conventional and 3D or "linked" designs) is
presented. "Linked" coils generally have better
performance characteristics than conventional designs,
but they are more expensive to manufacture due to their
complexity. The analysis is performed by assessment of
inductive energy, resistive power dissipation and cost
factors for different coil geometries for three coil
configurations: (i) cylindrical, (ii) biplanar and (iii)
split. If high performance is needed, "linked" gradient
coils can be preferable. On the contrary, if lower
performance is sufficient, conventional gradient coils
provide better value for money.
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2590. |
Radial Multi-Coil Imaging
Christoph Juchem1, Terence W Nixon1,
and Robin A de Graaf1
1Yale University School of Medicine, New
Haven, CT, United States
Radial MR imaging is presented in which the linear
gradient fields are generated by a matrix of individual,
generic coils. The ability of this multi-coil concept
for magnetic field modeling to flexibly trade accuracy
for efficiency is applied to increase the available
gradient strength and imaging bandwidth multi-fold. MC
imaging bears the potential of providing an inexpensive
alternative for specialized imaging applications for
which maximum gradient strength and performance are not
required.
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2591. |
Design and Implementation
of High-Performance Non-Linear PatLoc Gradient Coil ![](poster.gif)
Maxim Zaitsev1, William Punchard2,
Andrew Dewdney3, Daniel Gallichan1,
Jason Stockmann4, Chris A. Cocosco1,
Sebastian Littin1, Anna Masako Welz1,
Hans Weber1, Piotr Starewicz2, and
Jürgen Hennig1
1University Medical Centre Freiburg,
Freiburg, Germany, 2Resonance
Research Inc., United States, 3Siemens
Healthcare, Germany, 4Yale
University, United States
To overcome present limitations on gradient performance
and investigate unconventional encoding topologies a
PatLoc (parallel imaging technique using localized
gradients) concept was proposed recently. PatLoc relaxes
requirements of gradient homogeneity and global
uniqueness of spatial encoding in favour of local
gradient strength. To date the proof-of-concept PatLoc
imaging has been performed with prototype hardware with
performance inferior to that of linear gradients. The
purpose of this project was to design and implement a
PatLoc head gradient insert capable of generating local
gradients exceeding those of proprietary linear gradient
inserts.
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2592. |
3D Gradient System for Two
B0 Field
Directions by Using Concomitant Fields in Earth Field MRI
Steffen Lother1,2, Uvo C. Hölscher1,
Peter M. Jakob1,2, and Florian Fidler1
1Research Center Magnetic-Resonance-Bavaria (MRB),
Wuerzburg, Bavaria, Germany, 2Department
for Experimental Physics 5 (Biophysics), University of
Wuerzburg, Wuerzburg, Bavaria, Germany
We built for our earth field MRI setup a gradient system
that is capable of dealing with two B0 field
directions. It is benefiting to have the opportunity to
orientate the prepolarizing field parallel and
perpendicular to the B0 field.
We were able to show with the help of the concomitant
fields the number of necessary coils can be reduced. We
spare two coils in comparison to two independent
gradient sets. These gradients can even be used for
further B0 field
directions and therefore this promise new applications
and results in more compact setups.
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2593. |
High Resolution 3D
TrueFISP images of Guinea Pig Inner Ear using the Composite
Gradient Systems on a Clinical 3T MRI System ![](poster.gif)
Seong-Eun Kim1, K Craig Goodrich1,
Richard Wiggins1, Jason Mendes1,
and Dennis L Parker1
1UCAIR Department of Radiology, University of
Utah, Salt Lake City, Utah, United States
Our composite system has the distinct advantage that
both of standard and insert gradient systems can be
operated simultaneously and/or independently. With
simultaneous acquisition, the gradient strength
available from either system alone can be increased. The
use of composite gradients will allow high resolution
SSFP images without increasing TR or bandwidth, allowing
for improved inner ear imaging. To test the utility of
this composite gradient system we scanned the temporal
bone of guinea pigs with the composite and body
gradients only and compared image quality.
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2594. |
Performance Analysis of
Multi-Coil Magnetic Field Modeling
Christoph Juchem1, and Robin A de Graaf1
1Yale University School of Medicine, New
Haven, CT, United States
Magnetic field modeling based on individual generic
coils has been shown recently to enable the accurate and
flexible generation of a multitude of field shapes for
MR. Here, the analysis of fundamental performance
properties of the multi-coil (MC) concept is presented.
The results are compared to dedicated wire patterns for
the generation of magnetic field shapes that resemble
spherical harmonic functions. Improved magnetic field
homogeneity with MC shimming has been demonstrated
previously. Along with the higher efficiency for the
generation of shim fields as demonstrated in this work,
MC shimming bears significant potential to replace
conventional spherical harmonic shim systems.
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2595. |
Matrix Shimming for Whole
Body Gradient coils
Derek A. Seeber1, Timothy Bergfeld1,
Kevin Koch2, Richard Hackett1,
David Lee1, and William Einziger1
1GE Healthcare, Florence, SC, United States, 2GE
Healthcare, Waukesha, WI, United States
A matrix array shim coil system was designed to be
included into a widebore gradient coil consisting of 28
channels in a 7 circumferential by 4 axial coil matrix
array. The matrix shim coil is designed from multi-layer
Kapton circuit boards and is integrated into a gradient
coil between the inner and outer gradient coil.
Simulations from brain images were analyzed and
demonstrate improved performance over a traditional 3rd
order harmonic shim set.
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2596. |
Improvement of DTI
measurement using the Composite Gradient Systems on a
Clinical 3T MRI System ![](poster.gif)
Seong-Eun Kim1, K Craig Goodrich1,
J Rock Hadley1, Richard Wiggins1,
Eun-Kee Jeong1, and Dennis L Parker1
1UCAIR Department of Radiology, University of
Utah, Salt Lake City, Utah, United States
Our composite system has the distinct advantage that
both of standard and insert gradient systems can be
operated simultaneously and/or independently. With
simultaneous acquisition, the gradient strength
available from either system alone can be increased. The
composite gradient system can acquire better DTI
measurements with less artifacts in human studies than
can be obtained with insert or body gradient coils
alone. It can also provide high resolution fMRI datasets
with better imaging quality compared to data obtained
using the standard gradient system.
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2597. |
Study of concomitant
fields in multipolar PatLoc imaging ![](poster.gif)
Anna Masako Welz1, Frederik Testud1,
Jürgen Hennig1, Jan G. Korvink2,3,
and Maxim Zaitsev1
1Department of Radiology, Medical Physics,
University Medical Center Freiburg, Freiburg, Germany, 2Dept.
of Microsystems Engineering, IMTEK, University Freiburg,
Freiburg, Germany, 3Freiburg
Institute of Advanced Studies (FRIAS), University
Freiburg, Freiburg, Germany
FFor spatial encoding in magnetic resonance imaging only
the Bz component of the magnetic vector is of interest.
For linear gradients concomitant fields are well known
and investigated. With new imaging techniques, such as
PatLoc, using higher order harmonics the concomitant
fields of these gradients are in focus. Concomitant
fields calculated from the spherical harmonics potential
are compared and evaluated against a simplified model
since the effect of the concomitant fields on image
distortion and PNS is important especially for human
imaging.
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2598. |
Characterization of PatLoc
Gradient with a Field Camera ![](poster.gif)
Frederik Testud1, Daniel Gallichan1,
Christoph Barmet2, Johanna Vannesjö2,
Anna Masako Welz1, Christian A. Cocosco1,
Klaas Prüssmann2, Jürgen Hennig1,
and Maxim Zaitsev1
1Medical Physics, University Medical Center
Freiburg, Freiburg, Germany, 2Institute
for Biomedical Engineering, University and ETH Zurich,
Zürich, Switzerland
A field camera consisting of 16 proton based field
probes is used to characterize the Parallel Acquisition
Technique with Localised gradients (PatLoc) gradient
coil. Higher order magnetic field monitoring is
performed with a 16 channel proton field camera. The
recorded field dynamics are used to test the linearity
of the PatLoc gradient coil performance in combination
with standard linear gradients and to measure the
gradient impulse response functions of the five channel
gradient system.
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2599. |
Gradient Waveform
Pre-Equalization using the Magnetic Field Gradient Waveform
Monitor Method ![](poster.gif)
Frederic G. Goora1,2, Hui Han2,
Bruce G. Colpitts1, and Bruce J. Balcom2
1Department of Electrical and Computer
Engineering, University of New Brunswick, Fredericton,
New Brunswick, Canada, 2MRI
Research Centre, Department of Physics, University of
New Brunswick, Fredericton, New Brunswick, Canada
The accuracy of applied magnetic field gradients in
magnetic resonance imaging directly impacts the
corresponding image quality and measurements of
molecular motion. These distortions result from the
generation of eddy currents within the magnet structure
and from distortion of the magnetic field gradient coil
excitation current due to gradient current amplifier
limitations (such bandwidth and stability) and the
reactive gradient coil load which fundamentally limit
the minimum excitation current rise and fall times which
further distort the applied magnetic field gradient. We
present a method that utilizes the magnetic field
gradient waveform monitor method to measure the magnetic
field gradient waveform and determine a pre-equalized
gradient amplifier current excitation waveform such that
an optimal approximation of the desired / ideal magnetic
field gradient results.
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2600. |
Gradient waveform
measurement using prephased gradient moments.
Peter Latta1, Marco L. H. Gruwel1,
Vladimír Jellúš2, and Boguslaw Tomanek1
1Institute for Biodiagnostics, National
Research Council of Canada, Winnipeg, Manitoba, Canada, 2MR
Application Development, Siemens AG, Healthcare,
Erlangen, Germany
One of the commonly used methods for k-space
trajectory/gradient waveform characterization is based
on utilizing the FID phase evolution sampled from a thin
slice excited at a known distance. In many cases like
breast or extremity imaging, there is no source of
signal near the magnet’s isocenter. This introduces
problems with rapid phase accrual. Additional
complications arise from measuring high gradient
amplitudes when modification of this approach is
necessary to avoid problems with low signal amplitudes
caused by spin dephasing. Here we propose alternative
methods for gradient characterization based on the
gradient moment mapping.
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2601. |
Validation strategies for
NMR probes in field measurement applications
Saikat Sengupta1, John C. Gore1,
and E. Brian Welch1
1Radiology and Radiological Sciences,
Vanderbilt University, Nashville, TN, United States
Nuclear magnetic resonance probes can provide real time,
location specific, measurements of signal phase and
magnitude. Here, we propose and demonstrate three
different approaches to test the performance of NMR
probes in the scanner. The approaches are, (a) motion
simulation (b) spectrometer frequency offsets and (c)
higher order field perturbations using a real time
shim-switching module. Real time probe data is shown to
encode each of these different perturbations faithfully,
thereby demonstrating strategies for testing the
performance and characterization of the probes against
known and calibrated inputs.
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2602. |
Real-time control of
multiple coils for the generation of gradient and shim
fields
Stefan Wintzheimer1, Toni Drießle1,
Michael Ledwig1, Ralf Kartäusch1,
Peter Michael Jakob2,3, and Florian Fidler1
1Research Center Magnetic-Resonance-Bavaria,
Würzburg, Bavaria, Germany, 2Research
Center Magnetic-Resonance-Bavaria, 3Experimental
Physics 5, University of Würzburg
In this study a novel matrix gradient design is
presented, which is capable of generating both linear
gradient fields for imaging and at the same time high
order shim fields. Using a home-built 50-ch gradient
amplifier with a customized MR console allows real-time
control of fieldprofiles while measuring MR signal. This
system was used to create field profiles for shimming
complex field distrortions as well as imaging of an
sample object in a whole body magnet. Furthermore the
new design is able to switch every field order very fast
due to low inductivity of the coils.
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2603. |
Signal Considerations in
Slicewise Dynamic B0 shimming.
Saikat Sengupta1, E. Brian Welch1,
John C. Gore1, and Malcolm J. Avison1
1Radiology and Radiological Sciences,
Vanderbilt University, Nashville, TN, United States
Dynamic Shimming improves Bo field homogeneity compared
with global volume shimming. The most common approach
for estimating slice-wise shim values involves removing
the redundancy of functionally degenerate shim terms
from an in-plane field regression and assuming a linear
through plane inhomogeneity profile. This approach
yields excellent inplane inhomogeneity compensation but
compromises intravoxel signal recovery. Here, we present
a slice-wise shim calculation method based on maximizing
the voxel signal. Signal simulations and in vivo T2*
measurements are presented which demonstrate improved
signal recovery performance compared to both the
degeneracy analysis and static global shimming
approaches.
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2604. |
Echo Planar Imaging at 7T
with 3rd Order Slice-Wise Dynamic Shim Update (DSU) and Full
Eddy-Current Compensation (ECC) ![](poster.gif)
Ariane Fillmer1, Signe Johanna Vannesjo1,
Matteo Pavan1, Klaas Paul Pruessmann1,
Peter Boesiger1, and Anke Henning1
1Institute for Biomedical Engineering,
University and ETH Zurich, Zurich, ZH, Switzerland
The transition to ultra high field strengths yields
advantages as increased SNR and higher BOLD contrast,
but at the expense of decreased B1 and B0 homogeneity.
This work presents the application of Dynamic Shim
Updating (DSU) with full 3rd Order eddy-current
compensation to Echo Planar Images, which are the basis
for fMRI. Due to a highly accurate calibration of the
pre-emphasis very fast switching of shim terms during
the sequence is possible, without extending the scan
time. The presented results exhibit a significant gain
in image quality.
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2605.
![](MAGNA25.jpg) |
SEA imaging using a dual
planar array and fourth gradient coil for phase compensation ![](poster.gif)
John C. Bosshard1, Mary P. McDougall1,2,
and Steven M. Wright1,2
1Electrical & Computer Engineering, Texas A&M
University, College Station, TX, United States, 2Biomedical
Engineering, Texas A&M University, College Station, TX,
United States
Single Echo Acquisition (SEA) imaging is performed using
a fourth gradient coil to provide opposite coil phase
compensation for dual-planar or "sandwich" arrays having
an array plane directly above and below a sample,
allowing simultaneous imaging of dynamic or single-shot
events at the top and bottom boundaries of a sample.
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2606. |
A passive copper shield
for the split MRI system ![](poster.gif)
Limei Liu1, Hector Sanchez Lopez1,
Michael Poole1, Ewald Weber1, Feng
Liu1, and Stuart Crozier1
1the University of Queensland, Brisbane,
Queensland, Australia
the eddy currents generated by the switching gradient
fields produce undesired joule heating, noise and image
artefacts in the MRI system. It is found that these eddy
current effects are worsened in the split MRI system
which is designed for the hybrid PET-MRI technology to
provide high resolution images for the target tissues.
In this work, a passive copper shield was applied
outside of the split gradient coils to reduce the eddy
currents induced in the cryostat inner bore in order to
protect the contained helium vessel. The results show
that the passive copper shield can effectively reduce
the power heating in the cryostat inner bore. However,
it sacrifices the gradient linearity in the region of
interest.
|
2607. |
Evaluation of effects of
permanent magnet circuits on gradient field linearity ![](poster.gif)
Yasuhiko Terada1, Hirotaka Fujisaki1,
and Katsumi Kose1
1Institute of Applied Physics, University of
Tsukuba, Tsukuba, Ibaraki, Japan
We experimentally evaluated the effects of permanent
magnetic circuits on gradient field linearity. The
gradient field generated by a gradient coil set differed
when it was inserted in different magnetic circuits. For
a magnet with a wide gap compared with the coil gap, the
field linearity was as large as the calculated one. For
a magnet with a narrow gap close to the coil gap, the
gradient field linearity significantly decreased. This
is because of the mirror image currents flowing in the
pole pieces. This indicates that the design of gradient
coils requires consideration of the mirror current
effect.
|
2608. |
Towards Truly Quiet MRI:
Animal Scale Gradient as a Test Platform for Acoustic Noise
Reduction ![](poster.gif)
AbdEl-Monem M El-Sharkawy1, and William A.
Edelstein1
1Division of MR Research, Department of
Radiology, Johns Hopkins University, Baltimore, MD,
United States
MRI acoustic noise often exceeds 100 dB, causing patient
anxiety and discomfort, and is an obstacle to
interventional MRI procedures. Clinical MRI acoustic
noise reduction is a long-standing unsolved engineering
challenge made especially difficult because special
equipment and large-scale engineering test facilities
are needed for experiments. Our approach is to produce a
Truly Quiet (< 70 dB) small-scale animal imager. Results
serve as a test platform for acoustic noise reduction
measures that can be implemented in clinical scanners.
We have so far decreased noise in an animal scale system
from 108 dB to 81 dB, a 27 dB reduction.
|
|
|
Traditional
Poster Session - Engineering |
|
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2609. |
RF Coil Array for
Accelerated Excitation in Three Dimensions ![](poster.gif)
Jörg Felder1, Suk-Min Hong2, Avdo
Celik1, Joshua Park2, Frank
Geschewski1, Hong-Bae Jeong2,
Etienne Besançon1, Myung-Kyun Woo2,
Daniel Brenner1, Zang-Hee Cho2,
and N. Jon Shah1,3
1Institute for Neuroscience and Medicine - 4,
Forschungszentrum Jülich GmbH, Jülich, Germany, 2Neuroscience
Research Institute, Gachon University, Incheon, Korea, 3Department
of Neurology, Faculty of Medicine, JARA, RWTH Aachen
University, Aachen, Germany
We present a coil array for neuroimaging at 9.4T which
is capable of accelerated excitation and reception in
all three directions. It employs sixteen receive
elements while two coils are combined during
transmission due to the limited number of independent
transmitter channels. The array has been approved for
application in a clinical trial and first in vivo
experiments demonstrate its imaging capabilities.
|
2610. |
Impact of number of Tx
channels for RF shimming – an in vivo study
Alexander Childs1, Shaihan J Malik1,
Declan P O'Regan1, and Joseph V Hajnal1
1Robert Steiner MRI Unit,Imaging Sciences
Department, MRC Clinical Sciences Centre, Hammersmith
Hospital, Imperial College London, London, United
Kingdom
Multi-channel transmission allows individualised subject
specific RF shimming to be used to mitigate B1+
inhomogeneity and improve image signal and contrast
uniformity. Using a whole body 3T system with 8 transmit
channels, we have performed a systematic study in vivo
of RF shim performance in both the pelvis and thighs for
coil configurations with 1, 2, 4 or 8 independent
channels. As the number of channels was increased, B1+
homogeneity progressively and significantly increased,
while total RF power requirements for the same
homogeneity systematically decreased. T1w images also
showed perceptible progressive improvement with number
of channels used for shimming.
|
2611. |
B1-control
Receive Array Coil for Abdominal Imaging
Yukio Kaneko1, Yoshihisa Soutome1,
Masayoshi Dohata1, Hideta Habara1,
Hisaaki Ochi1, and Yoshitaka Bito1
1Central Research Laboratory, Hitachi Ltd.,
Kokubunji, Tokyo, Japan
B1 inhomogeneity increases as strength of magnetic field
increases. Various methods to reduce the B1
inhomogeneity have been developed. However, B1
inhomogeneity still remains in some cases of abdominal
imaging, and a more effective method is required. In
this study, a B1-control loop is combined with a receive
array coil by using PIN diodes for generating the
B1-control loop during the RF transmit period. A
12-channel gB1-control receive array coilh was
fabricated, and both its receive sensitivity and the
effect of B1 homogenization were confirmed
experimentally. The B1-control receive array coil can
improve B1 inhomogeneity, while maintaining receive
sensitivity.
|
2612. |
Simulation Study of
Parallel Transmit Arrays for 3T Body Imaging under Local and
Global SAR Constraints ![](poster.gif)
Bastien Guerin1, Matthias Gebhardt2,
Peter Serano1, Elfar Adalsteinsson3,4,
Michael Hamm2, Josef Pfeuffer2,
Juergen Nistler2, and Lawrence L. Wald1,4
1Martinos Center for Biomedical Imaging,
Dept. of Radiology, Massachusetts General Hospital,
Charlestown, MA, United States, 2Siemens
Healthcare, Erlangen, Germany, 3Dept
of Electrical Engineering and Computer Science,
Massachusetts Institute of Technology, Cambridge, MA,
United States, 4Harvard-MIT
Division of Health Sciences Technology, Cambridge, MA,
United States
Despite intense research in pTx hardware development
there has been little theoretical work on the benefit of
increasing the number of transmit channels. In this work
we compare the performance of three pTx arrays with 4, 8
and 16 channels using an HFSS/ADS co-simulation and a
pulse design algorithm constraining simultaneously
global/local SAR and average/maximum forward power. We
show that increasing the number of channels from 4 to 16
allows reduction of local SAR by as much as 90% for
constant excitation error and reduction of excitation
error by as much as 10% for constant local SAR (2 spokes
excitations).
|
2613. |
Comparison of 7+1ch tx
arrays and Implementation for torso imaging at 3T - Four
different coil geometries with phantom and human body
Yeun Chul Ryu1, Sukhoon Oh1,
Christopher Sica1, Wei Luo2, Yong-Gwon
Kim3, and Christopher M. Collins1,4
1Radiology, The Pennsylvania State
University, Hershey, PA, United States, 2Engineering
Science and Mechenics, The Pennsylvania State
University, University Park, PA, United States, 3Radiological
Science, Konyang University, Korea, 4Bioengineering,
The Pennsylvania State University, Hershey, PA, United
States
Here, we report a progress toward a case where 8
elements are placed in the space above the patient table
as transmit coil and additional receive coil (or array)
to get more intensive signal from the chest. The
8-channel tx body array was suggested. Through the
simulations, we compared 4 different 7+1 tx array
structures and showed the utilities of B1+ shimming in
multi-channel tx body imaging at 3T. This structure and
shimming over the body size phantom we propose provide
an enhanced homogeneous B1 field in large ROI imaging.
As the result of B1 shimming with 4 different tx array
structure and with 2 different objects, the resultant B1
fields guarantee consistent homogeneity over a large ROI.
|
2614. |
Improving the Sensitivity
of Individually Shielded Elements of RF Transceiver Array
Coils Using Dielectric Materials in MRI ![](poster.gif)
Yunsuo Duan1, Bradley S Peterson1,
Feng Liu1, and Alayar Kangarlu1
1MRI Research, Psychiatry, Columbia
University/NYSPI, New York, NY, United States
Decoupling by individualy shielding coil elements
provides desired isolations between the coil elements of
transceiver array coils. However, it severely degrades
the sensitivity of the coil element. We propose to
improve the coil sensitivity by inserting dielectric
media between the coil elements and the shields. The
results shows that the sensitivity can be improved form
32% to 86% while maintaining the good isolation.
|
2615. |
Mode Matrix Tranceiver
Surface Coil
Taner Demir1, Esra Abaci Turk1,2,
and Ergin Atalar1,2
1UMRAM, Bilkent University, Ankara, Turkey, 2Electrical
and Electronics Engineering, Bilkent University, Ankara,
Turkey
The concept of a mode matrix tranceiver surface coil for
transmit array system is introduced. The coil
performance is experimentally tested and the concept of
mode matrix transmission is verified.
|
2616. |
Methodology for UHF
multichannel coil evaluation ![](poster.gif)
Lance DelaBarre1, Pierre-Francois van de
Moortele1, Carl Snyder1, Jinfeng
Tian1, Steen Moeller1, and J.
Thomas Vaughan1
1Center for Magnetic Resonance Research,
University of Minnesota, Minneapolis, MN, United States
Evaluating the performance and safety of high field RF
coils with multiple elements is necessary to improve
coil designs, but it is challenging due to the
complexity of the coil itself. A methodology to evaluate
coil performance is demonstrated using a 7T coil as an
example.
|
2617. |
B1+ and Coupling
Variability of Transmit Head Coils and Arrays for Ultra-High
Field MRI: Simulation Studies and Experiments
Narayanan Krishnamurthy1, Daniel Stough1,
Tiejun Zhao2, Shailesh Raval1,
Fernando Boada1, and Tamer S Ibrahim1
1University of Pittsburgh, Pittsburgh,
Pennsylvania, United States, 2Siemens
Medical Solutions
Variation of spin excitation in surface/TX array and
volume head coils were evaluated in these UHF MRI
experiments. Phantoms with varying conductive and
dielectric loads were used to evaluate the robustness of
the TX B1+ field of different MR coils.
|
2618. |
An analytical method to
optimize transmit efficiency for local excitation with a
transmit array
Giuseppe Carluccio1,2, Christopher Michael
Collins2, and Danilo Erricolo1
1Electrical and Computer Engineering,
University of Illinois at Chicago, Chicago, Illinois,
United States, 2Radiology,
Pennsylvania State University, Hershey, Pennsylvania,
United States
We present an analytically-based method for rapid
optimization of the local RF magnetic (B1+)
field intensity for a given RF power through a transmit
array. With knowledge of the B1+ field
distribution generated by each single coil of the array,
both the phases and the amplitudes of each coil current
are optimized to provide the maximum magnitude of the B1+ field
in a specific location of the body, and the minimum
power transmitted through the array and, consequently,
reducing the whole body SAR.
|
2619. |
Simultaneous tuning of
multiple modes for an RF transmit array
Mikhail Kozlov1, and Robert Turner1
1Max Planck Institute for Human Cognitive and
Brain Sciences, Leipzig, Saxony, Germany
We implement a dual-domain optimization approach, which
results in improved performance for 7 and 9.4 T head
arrays in multi-mode operation, without limiting the use
of static RF shimming and even pTX. For both 7 and 9.4T
arrays, dual-domain optimization resulted in negligible
Parray_refl (less than 3% of Ptransmit) for given modes
and nearly optimal transmit performance in all modes.
|
2620. |
Performance consequences
of broken cylindrical symmetry for a 7T head RF transmit
array
Mikhail Kozlov1, and Robert Turner1
1Max Planck Institute for Human Cognitive and
Brain Sciences, Leipzig, Saxony, Germany
We numerically simulated a transmit-only strip-line
8-channel 7T RF transmit coil array designed and built
by Vaughan. A non-split tuning resonance Sxx can be
obtained, despite relatively high (-6dB) adjacent
element coupling, but excitation uniformity can be very
poor when coupling is asymmetrical. By installing
different values at specific capacitor positions it is
possible to improve excitation uniformity, but reflected
power Parray_refl remains high. For CP mode excitation,
decoupling of array elements whilst simultaneously
equalizing currents through the front and end capacitors
significantly improves transmit performance without
improving inhomogeneity. Equalizing element currents
does not necessarily improve excitation homogeneity.
|
2621. |
Analysis of
Circumferential Shielding as a Method to Decouple
Radio-Frequency Coils for High-Field MRI
Jean-Guy Belliveau1,2, Kyle Gilbert1,
Mohamed Abou-Khousa1, and Ravi Menon1,2
1Robarts Research Institute, London, Ontario,
Canada, 2Biomedical
Engineering, University of Western Ontario, London,
Ontario, Canada
We perform an engineering analysis on common performance
metrics for circumferentially shielded radiofrequency
coils for MRI. Various circumferentially shielded
radiofrequency coils have previously been presented;
however, an in-depth analysis of the effect of shielding
on coil performance has not previously been undertaken.
Our analysis demonstrates that (1) shielding helps with
multiple element isolation; (2) the nature of the
shielding geometry can potentially increase local SNR
and decrease SAR; and (3) shielding has advantages for
B1+ shimming techniques and parallel imaging.
|
|
|
Traditional
Poster Session - Engineering |
|
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2622. |
Shared-conductor versus
overlapped-loop quadrature surface coils: which performs
better in human brain at 7T? ![](poster.gif)
Arthur W. Magill1,2, Martin Meyerspeer1,3,
and Rolf Gruetter1,4
1Laboratory of Functional and Metabolic
Imaging, Ecole Polytechnique Fédérale de Lausanne,
Lausanne, Switzerland, 2Department
of Radiology, Univeristy of Lausanne, Lausanne,
Switzerland, 3ZMPBMT,
Medizinische Universitaet Wien, Vienna, Austria, 4Department
of Radiology, University of Geneva, Geneva, Switzerland
The performance of two quadrature surface coil designs
is compared at 7 Tesla in the human head. The first
design is a traditional overlapped pair of loops; the
second is a pair of loops with a common the central
conductor.
|
2623. |
A Twisted Loop Coil for
High Field MRI ![](poster.gif)
Wolfgang Loew1, Randy Giaquinto1,
Scott Dunn1, Ronald Pratt1, Diana
Lindquist1, and Charles Dumoulin1
1Imaging Research Center, Cincinnati
Children's Hospital Medical Center, Cincinnati, Ohio,
United States
A novel RF coil design for a 7T animal scanner was
developed. The new approach uses a loop coil twisted
around a cylindrical former. The RF homogeneity of this
new design was compared to an identically-sized birdcage
using B1 mapping, and found to be more uniform. SNR
comparisons between the coils showed the expected
sensitivity ratio between a linear and quadrature coil.
The RF homogeneity and SNR characteristics of the new
coil were evaluated in in-vivo mouse images acquired
with the twisted loop design. The new coil has fewer
parts and is easier to tune than a comparably-sized
birdcage coil.
|
2624. |
Quadrature Transmit Coil
for Ultra High Field MRI
Zhiyong Zhai1, and Michael A. Morich1
1Philips Healthcare, Cleveland, Ohio, United
States
At ultra high fields such as 7T, B1 field distribution
is dominated by the tissue dielectric effects. A
transmit coil with uniform B1 remains a challenge
compared to 1.5T or 3T. Here we suggest a new type of
volume transmit coil for 7T and above - a birdcage
structure with discontinuous (or broken) rungs.
Simulations show that such a coil structure, when tuned
properly, can generate similar B1 to that of a birdcage
volume coil. It provides a new and more flexible way of
making volume transmit coil for ultra-high fields MRI.
|
2625. |
An Asymmetric Insert
Quadrature Birdcage Coil for Hyperpolarised 129Xe
Lung MRI at 1.5 T ![](poster.gif)
Xiaojun Xu1, Martin H Deppe1,
Nicola De Zanche2, and Jim M. Wild1
1Academic Radiology, University of Sheffield,
Sheffield, South Yorkshire, United Kingdom, 2Department
of Medical Physics, Cross Cancer Institute and
University of Alberta, Canada
A whole body asymmetric birdcage transmit receive coil
is demonstrated for hyperpolarised 129Xe
MR lung imaging. The objective was to develop an insert
body transmit-receive birdcage RF coil for imaging of
hyperpolarised 129Xe
in the lungs at 17.7 MHz at 1.5 T. The design makes
efficient use of the available bore space within a
clinical MR system, has homogenous B1 field
and is transparent to the 1H
body coil making anatomical 1H
imaging of the chest possible without moving the coil.
In future work, the coil will be used as a transmit-only
coil in conjunction with a custom receive array.
|
2626. |
Investigation of
fractal-shaped alternating impedance microstrip coil for 7
Tesla MRI ![](poster.gif)
Xia Li1,2, JuCheng Zhang1, WenLong
Xu1, XiaoFang Liu1,2, and BingQiao
Xu1
1China Jiliang University, Hangzhou,
Zhejiang, China, 2Zhejiang
University, Hangzhou, Zhejiang, China
This work presents the electromagnetic properties of
Koch fractal-shaped alternating impedance microstrip
coil for ultra high field MRI. Based on the fractal
theory, a first order Koch geometry microstrip coil was
modeled and simulated. A conventional and two
alternating impedance microstrip line coil was also
simulated for comparison. Results indicate that,
narrowing the width of high impedance sections will
enhance magnetic field quantity but lead to less
homogeneity. The Koch fractal-shaped alternating
impedance microstrip coil shows less discontinuous of
electric field at the joints of high-low impedance
sections and lower electric field emission. The magnetic
field peak of Koch fractal-shaped alternating impedance
microstrip coil was found to be broadened, which gives a
more uniform magnetic field distribution.
|
2627. |
A Double Resonant Solenoid
Coil for 35Cl/ 23Na Imaging of the Rat Brain at a Whole Body
7 Tesla MRI ![](poster.gif)
Manuela Rösler1, Reiner Umathum1,
Armin Nagel1, Yaron Gordon1, Peter
Bachert1, Wolfhard Semmler1, and
Florian Meise1
1Dept. of Medical Physics in Radiology,
German Cancer Research Center, Heidelberg, Germany
Sodium and Chlorine ions are central in the physiology
of living organisms. To detect them quasi-simultaneously
in a rat brain would improve the understanding of
(patho-) physiological processes. The aim of the study
was to design and characterize double resonant coils for
imaging 35Cl and 23Na in the rat brain. For all
measurements a 7Tesla whole body MRI was used to
simplify the translation of small animal experiments to
human applications.
|
2628. |
A High-pass Birdcage Coil
for Small Animal Imaging at 600MHz/14.1T ![](poster.gif)
Arthur W. Magill1,2, Hongxia Lei1,3,
and Rolf Gruetter1,2
1Laboratory of Functional and Metabolic
Imaging, Ecole Polytechnique Fédérale de Lausanne,
Lausanne, Switzerland, 2Radiology,
Univeristy of Lausanne, Lausanne, Switzerland, 3Radiology,
University of Geneva, Geneva, Switzerland
A high-pass quadrature birdcage coil was simulated,
built and tested for use at 600MHz (14.1T). The
resulting coil produces a highly homogeneous B1 field
over the the field-of-view, despite the short RF
wavelength.
|
2629. |
A Hybrid Design for
Dual-tuned Quadrature 13C/1H Volume Coil at High Field ![](poster.gif)
Xiaoliang Zhang1,2, Duan Xu1, Ye
Li1, Ilwoo Park1, Yong Pang1,
Peter Shin1, Kayvan Keshari1,
David Wilson1, and Daniel B Vigneron1,2
1Department of Radiology and Biomedical
Imaging, University of California San Francisco, San
Francisco, California, United States, 2UCSF/UC
Berkeley Joint Graduate Group in Bioengineering, San
Francisco and Berkeley, California, United States
In this work, we propose a hybrid technique for
double-tuned volume coil design by combing microstrip
coil design and conventional low pass birdcage design
for high field in vivo MR applications. This aims to
provide an efficient solution to diminishing technical
challenges in designing such coils at high fields, such
as the increased interaction between the two nuclear
channels, enlarged separation of the two resonance
frequencies, and issues caused by high operation
frequency required by proton.
|
2630. |
A 1H
and 23Na
Two Coil System Optimized for Imaging Mini-Pig Knee
Cartilage at a Whole Body 7 Tesla MRI
Florian M Meise1, Armin M Nagel1,
Tobias Gotterbarm2, Sebastian Hagmann2,
Manuela Rösler1, Marc-Andre Weber3,
Wolfhard Semmler1, and Reiner Umathum1
1Dept. of Medical Physics in Radiology,
German Cancer Research Center (DKFZ), Heidelberg, BW,
Germany, 2Dept.
of Orthopaedic Surgery, University Hospital Heidelberg,
Heidelberg, BW, Germany, 3Dept.
of Diagnostic and Interventional Radiology, University
Hospital Heidelberg, Heidelberg, BW, Germany
Investigation of integration and vitality of cartilage
transplants as well as the underlying cartilage matrix
are important to optimize therapeutic approaches for
cartilage damage. The aim of this study was to design an
SNR optimized coil system for co-registered 1H
and 23Na
imaging of mini-pig knee cartilage at a whole body 7
Tesla MRI scanner, without the common loss of
sensitivity due to a double resonant coil design.
|
2631. |
Double Resonant 1H/31P
Coil Configuration for 31P
MR Spectroscopy at a Whole Body 7 T MR Tomograph ![](poster.gif)
Andreas Korzowski1, Reiner Umathum1,
Peter Bachert1, and Florian Martin Meise1
1Dept. of Medical Physics in Radiology,
German Cancer Research Center (DKFZ), Heidelberg, BW,
Germany
The aim of this study was to find, implement, and test
the optimum double-resonant configuration for two
concentric surface coils at f0(31P)
= 120.3 MHz and f0(1H) = 297.15
MHz at an experimental 7-T whole-body MR tomograph.
|
2632. |
Helical microcoil system
for high resolution magnetic resonance imaging
Oliver G. Gruschke1, Nicoleta Baxan2,
Dominik von Elverfeldt2, Jürgen Hennig2,
Vlad Badilita3, and Jan G. Korvink1,4
1Lab. of Simulation, University of Freiburg -
IMTEK, Freiburg, Germany, 2Dept.
of Radiology Medical Physics, University Medical Center,
Freiburg, Germany, 3Lab.
for Microactuators, University of Freiburg - IMTEK,
Freiburg, Germany, 4Freiburg
Institute for Advanced Studies – FRIAS, University of
Freiburg, Freiburg, Germany
A solenoid wound wirebonded microcoil is integrated with
a custom-built transmit and receive switch and low noise
amplifiers. The system allows high resolution imaging in
a short period of time with a high SNR.
|
2633. |
STRUCTURAL MAGNETIC
RESONCNE IMAGING OF ZEBRAFISH BRAIN USING DEDICATED RADIO
FREQUENCY MICROCOILS ![](poster.gif)
Viktor Vegh1, Miriam Ariens1,
Jeremy Ullmann1, Nyoman Kurniawan1,
and David Reutens1
1Centre for Advanced Imaging, University of
Queensland, Brisbane, Queensland, Australia
We developed five different 5mm radio frequency solenoid
coils for ex vivo structural imaging of the zebrafish
brain. We investigated the use of different conductors
and coatings, and configuration of the radio frequency
electronic circuit. We analysed the five coils based on
signal-to-ratio maps. Using the best performing coil, we
were able to obtain images of the adult zebrafish brain
with six micron resolution. We compared our findings to
an image obtained using the scanner proprietary 5mm
radio frequency coil. A significant improvement in image
detail was evident with the use of the new coil.
|
2634. |
DIFFUSION WEIGHTED IMAGING
OF ZEBRAFISH EMBRYOS USING DEDICATED RADIO FREQUENCY COILS ![](poster.gif)
Miriam Ariens1, Jeremy Ullmann1,
Nyoman Kurniawan1, Harriet Lo2,
David Reutens1, and Viktor Vegh1
1Centre for Advanced Imaging, University of
Queensland, Brisbane, Queensland, Australia, 2Institute
of Molecular Bioscience, University of Queensland,
Brisbane, Queensland, Australia
We investigated the use of dedicated radio frequency
solenoid coils of diameter 1.4mm for the purpose of
imaging zebrafish embryos 24 and 48 hours post
fertilization. We compared seven different coil
conductor materials with different coatings and
evaluated coil performance based on the signal-to-ratio
map we calculated. The best performing coil was chosen
for the diffusion imaging of zebrafish embryos. We were
able to achieve around 30 micron resolution and
delineate the developing spine.
|
2635. |
A Quadrature Volume
Transmit Coil for Breast Imaging and Spectroscopy at 7 Tesla ![](poster.gif)
Joseph V Rispoli1, Sergey Cheshkov2,3,
Ivan Dimitrov2,4, Craig Malloy2,3,
Steven M Wright1,5, and Mary Preston
McDougall1,5
1Biomedical Engineering, Texas A&M
University, College Station, Texas, United States, 2Advanced
Imaging Research Center, University of Texas
Southwestern Medical Center, Dallas, Texas, United
States, 3Radiology,
University of Texas Southwestern Medical Center, Dallas,
Texas, United States, 4Philips
Medical Systems, Cleveland, Ohio, United States, 5Electical
and Computer Engineering, Texas A&M University, College
Station, Texas, United States
A quadrature volume transmit coil for breast imaging and
spectroscopy at 7 Tesla is discussed. The
Helmholtz-saddle coil configuration utilizes "Forced
Current Excitation" to ensure equal current at the feed
point of each element in each array. Results demonstrate
excellent B1 homogeneity and validate the design for use
at 7T.
|
|
|
Traditional
Poster Session - Engineering |
|
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2636. |
A Digital Cartesian
Feedback Loop for the MRI Transmitter ![](poster.gif)
Klaus M. Huber1, Wünsch Christian2,
Seisenberger Claus3, Nisznansky Martin2,
Demharter Nikolaus2, and Vester Markus2
1Siemens Corporate Technology, Erlangen,
Germany, 2Siemens
Healthcare, Erlangen, Germany, 3Siemens
Corporate Technology, Munich, Germany
Functional MRI (fMRI) and Diffusion-weighted MRI (DWI/DTI)
are two important MR applications which are known to be
sensitive to random system instabilities. The RF power
amplifier and the transmit path usually are major
contributors to this non-perfect system behavior. We
implemented a feedback loop in the digital part of the
transmitter hardware which can be configured flexibly
according to application-specific needs. The
configuration is done by choosing the appropriate linear
combination of the measured and digitized complex wave
parameters as an actual value for the control loop.
Results for both control of the forward power and
control of the actual B1-field are presented.
|
2637. |
Low-loss adjustable
networks for automated matching of transmit coils ![](poster.gif)
Giorgos Katsikatsos1, and Klaas Paul
Pruessmann1
1Institute for Biomedical Engineering, ETHZ,
Zurich, ZH, Switzerland
A low-loss, high power handling, custom-made capacitor
is used a building unit for an automated
L-matching-network controlled by an external computer.
The capacitors are adjusted mechanically by
piezoelectric motors. Each L-network is characterized
completely by its S-matrix and those S-matrices are used
in the analytical solution of the invert problem. The
result is highly reproducible since it achieves matching
for arbitrary loads.
|
2638. |
An Envelope-Tracking
Transmit Array Amplifier
Pascal P Stang1, John M Pauly1,
and Greig C Scott1
1Electrical Engineering, Stanford University,
Stanford, CA, United States
Modern MRI pulse sequences demand high-fidelity RF
transmit reproduction at multi-kilowatt power levels.
Typical MRI power amplifiers are Class-AB architectures
which excel at predictable linear performance, yet
become inefficient when used at less than their peak
power. We present an envelope-tracking linear RF power
amplifier system to explore the potential efficiency
gain and performance impact of this method in the
context of MRI transmit arrays. The efficiency
improvement from envelope tracking varies with both
pulse shape and amplitude, however for sync pulses,
preliminary measurements show DC power consumption
reduced by 20-35% compared to operation at full supply
rail while delivering the same RF output.
|
2639. |
Shielded Current Sensors
for Monitoring Parallel Transmission ![](poster.gif)
Karl Edler1, Marie-France Hang1,
Alexis Amadon1, Nicolas Boulant1,
Martijn A Cloos1, and Christopher J Wiggins1
1NeuroSpin/I2BM/DSV/CEA, Gif-sur-Yvette,
France
Toroidal sensors were attached to the conductors of two
decoupled transmit loops and were used to monitor the
current during an RF-pulse. These non-resonant sensors
were approximately matched to 50 and
were also shielded to minimize their coupling to other
sources. During the transmit pulse the preamplifiers
were replaced with attenuators so that the received
signal would remain within the dynamic range of the
receiver channels. The results were also compared with
the forward power as measured by connecting the
directional couplers on the rear of the RF power
amplifiers to spare receiver channels.
|
2640. |
Active Decoupling for
Prostate MR Imaging and Spectroscopy with Extended Field of
View at 7T ![](poster.gif)
Catalina S. Arteaga de Castro1, Ozlem Ipek1,
Mariska P. Luttje1, Marco van Vulpen1,
Juus Noteboom1, Peter R. Luijten1,
Uulke A. van der Heide2, and Dennis W.J.
Klomp1
1University Medical Center Utrecht, Utrecht,
Netherlands, 2Netherlands
Cancer Institute, Amsterdam, Netherlands
Prostate imaging at higher magnetic fields like 7 Tesla
is challenging. Even after B1 shimming the B1 strength
at the prostate location remains low. Endorectal coils
are used to increase the receive sensitivity at the
prostate, but as transmitters they can substantially
increase the B1. In contrast from receive only coils
that need PIN diodes to be decoupled from the
transmitters, the ERC remains tuned when combined with
external coils. We use active decoupling as an
alternative to PIN diode decoupling by transmitting with
the ERC with an optimized amplitude and phase to
counteract the coupling caused by the field of the
external elements.
|
2641. |
Design and Evaluation of a
Dipole Antenna TX/RX element as a Building Block for
Combined MR imaging and RF Hyperthermia at 7.0 T
Celal Özerdem1, Lukas Winter1,
Werner Hoffmann2, Helmar Waiczies1,
Reiner Seemann2, Davide Santoro1,
Alexander Müller1, Abdullah Ok1,
Tomasz Lindel2, Bernd Ittermann2,
and Thoralf Niendorf1,3
1Berlin Ultrahigh Field Facility (B.U.F.F.),
Max-Delbrueck-Center for Molecular Medicine, Berlin,
Germany, 2Physikalisch
Technische Bundesanstalt (PTB), Berlin, Germany, 3Experimental
and Clinical Research Center (ECRC), Charité -
University Medicine Campus Berlin Buch, Berlin, Germany
Combining RF hyperthermia and MR imaging is conceptually
appealing to pursue spatially and temporally controlled
and monitored RF heating. The benefits of this approach
could be used as an adjunctive therapy for established
cancer treatments including radiotherapy and
chemotherapy , targeted drug delivery and targeted MR
contrast agent delivery. This study evaluates the design
of a bow tie dipole antenna building block both for MR
imaging and RF heating at 7.0T.
|
2642. |
A Millimeter Scale
Implanted Coil with an Integrated Wireless Amplifier for
Imaging of the Rodent Kidney
Chunqi Qian1, Stephen Dodd1, Der-Yow
Chen1, Joe Murphy-Boesch1, and
Alan Koretsky1
1LFMI/NINDS, National Institutes of Health,
Bethesda, MD, United States
An implantable resonator with an integrated parametric
amplifier has been constructed to provide enhanced
localized sensitivity of internal organs in the rodent.
The sample coil was one element of a non-linear double
frequency resonator that mixed the MR signal with a pump
frequency to produce an amplified output at the Larmor
frequency. The resonator/wireless amplifier was 3mm x
3mm x 7mm in size, and it enabled high resolution images
to be obtained to identify small vascular structures of
a rat kidney in vivo.
|
2643. |
A dipole antenna for
pelvis imaging at 7T ![](poster.gif)
Sedig S Farhat1, Daniel J Lee1,
Carolyn Costigan1, Penny A Gowland1,
and Paul M Glover1
1University of Nottingham, Nottingham,
Nottinghamshire, United Kingdom
There are very few surface coils that work well at 7T.
Up until now the majority of RF coils have been designed
as near field antennas. The aim of this work was to
design and build a transmit/receive dipole antenna for
imaging the human pelvis. The dipole antenna shows the
desired improvement in SNR and homogeneous coverage.
Coverage goes much further into the pelvis than is shown
in the image, indicating that the dipole antenna is
better suited for imaging structures deeper into the
body than loop or strip transmitting elements.
|
2644. |
A Novel Highly Homogeneous
Wireless Birdcage Resonator Coil ![](poster.gif)
Haoqin Zhu1, Mehran Fallah-Rad1,
Michael Lang1, Wayne Schellekens1,
Kirk Champagne1, and Labros Petropoulos1
1R&D, IMRIS Inc, Winnipeg, MB, Canada
In this paper, a wireless HP birdcage coil was
presented. The design of this coil can be extended to
low pass, bandpass or dual frequency configurations.
Simulated B1 field of the HP b-cage within the body coil
showed an increase of more than 15dB in magnitude
compared to B1 field of body coil only. SNR measurements
on phantom showed comparable numbers between the
wireless coil and the 12-channel OEM coil. Additionally,
volunteer head images were of similar quality and
uniformity between the two coils.
|
|
|
Traditional
Poster Session - Engineering |
|
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2645. |
A Compact 10-channel RF
Array Coil for MR Imaging of Mice
Chieh-Wei Chang1, Wen-Yang Chiang1,
Steven M Wright1,2, and Mary Preston
McDougall1,2
1Biomedical Engineering, Texas A&M
University, College Station, TX, United States, 2Electrical
Engineering, Texas A&M University, College Station, TX,
United States
Our 10-channel cardiovascular phased array and
transmitting volume coil without active detune is
presented. Parallel imaging techniques in MRI provide
the capability to reduce scan time based on the partial
or entire removal of phase-encoding steps, especially
offering benefit to cardiovascular MRI of the murine
model. Our 10-channel array, transmit coil, and a
modular 16-channel low impedance preamplifier board that
together constitute a compact parallel imaging of
system. The integrated anesthesia chamber provides
streamlined imaging capability. The dual plane pair
element design [9] described 1) ensures that no
coil-to-coil decoupling mechanism is needed other than
the preamplifiers and 2) inherently decouples from a
homogenous transmit field, eliminating the need for
active decoupling and 3) reduces, and in this case,
eliminates, the need for baluns and/or cable traps. The
transmit coil design described ensures an extremely
uniform sensitivity pattern, and the 16-channel
preamplifier board described is compact and modularized
for straightforward use with any array coil.
|
2646. |
Parallel imaging
capabilities of an 11-channel coil for MRgHIFU imaging. ![](poster.gif)
Emilee Minalga1, Allison Payne1,
Robb Merrill1, Nick Todd1, Sathya
Vijayakumar1, Dennis L. Parker1,
and J. Rock Hadley1
1Utah Center of Advanced Imaging Research,
University of Utah, Salt Lake City, UT, United States
This work describes the parallel imaging capabilities of
an 11-channel breast RF coil for magnetic resonance
guided high intensity focused ultrasound. The coil was
built to be compatible with a breast magnetic resonance
guided high intensity focused ultrasound treatment
cylinder and uses capacitive decoupling of adjacent
loops. The coil is evaluated for SNR performance,
temperature imaging performance, and parallel imaging
capabilities. The coil was found to give better SNR over
a single loop chest coil. This SNR increase translates
to better anatomy imaging and temperature measurements
and allows for the use of parallel imaging.
|
2647. |
31-Channel 3T Cardiac
Array Optimized for SNR and g-Factor
Scott B King1, Mike J Smith1,
Jarod Matwiy1, Hung-Yu Lin1, and
Boguslaw Tomanek2
1Institute for Biodiagnostics, National
Research Council of Canada, Winnipeg, Manitoba, Canada, 2Institute
for Biodiagnostics, National Research Council of Canada,
Calgary, Alberta, Canada
Most array coils used for body imaging utilize regular
shaped rectangular or circular surface coils evenly
distributed to cover the entire torso. The cardiac
region comprises a relatively small volume compared to
the entire human torso, therefore, an optimized cardiac
array coil should reflect this, to make the best use of
a limited number of receivers. Here, a 31-channel
cardiac array was designed and constructed for focused
performance within the cardiac region, providing
improved SNR in addition to better g-factor performance.
Up to 200% SNR gains and more aggressive reduction
factors were achieved relative a 12-channel OEM cardiac
array.
|
2648. |
A 16 Element Phased Array
Surface Coil for Time-Resolved CE-MRA at SENSE Accelerations
up to 12 ![](poster.gif)
Paul T. Weavers1, Chris C. Cline1,
Casey P. Johnson1, Phillip J. Rossman1,
Thomas C. Hulshizer1, and Stephen J. Riederer1
1MR Research Laboratory, Mayo Clinic,
Rochester, Minnesota, United States
A 16 element receive coil specifically designed for the
calves has been constructed. The design permits close
proximity of the coil to the anatomy even as the leg
narrows from knee to calf, and is flexible enough to fit
around a wide range of patient sizes. G-factor maps made
with the 16ch coil at R = 12 compare favorably to g-maps
produced with a previous 8ch coil at R = 8. In-vivo CE-MRA
results are demonstrated using an accelerated
acquisition with R = 12 2D SENSE providing 1mm3 resolution,
a 3.5 sec update time and a 12.4 sec temporal footprint.
|
2649. |
A localized 16-channel
linear planar array for 3T human brain imaging
Hsuan-Chung Niu1, Ying-Hua Chu1,
Jo Lee1, Wei-Chao Chen2, Wen-Jui
Kuo3, and Fa-Hsuan Lin1,4
1Institute of Biomedical Engineering,
National Taiwan University, Taipei, Taiwan, 2SDI
corporation, Changhua, Taiwan, 3Institute
of Neuroscience, National Yang Ming University, Taipei,
Taiwan, 4Athinoula
A. Martinos Center for Biomedical Imaging, Massachusetts
General Hospital, MA, United States
To provide localized sensitivity and to adapt to
spatiotemporal resolution enhancement by parallel MRI,
we develop a 16-channel linear planar array for brain
imaging at 3T. The size of the array is about 10 cm x 10
cm with 16 slim rectangular distributed over two sides
of a circuit board. Isolation between channels brought
by appropriate overlapping and pre-amplifier decoupling
is demonstrated with minimal noise correlation.
Preliminary experiment results demonstrate up to 4x
acceleration of human temporal lobe structure imaging
with 1 mm spatial resolution.
|
2650. |
A 3.0T Flexible Transmit
and 16 Channel Receive Array Shoulder Coil ![](poster.gif)
Tsinghua Zheng1, Matthew Finnerty1,
Xiaoyu Yang1, Paul Taylor1, and
Hiroyuki Fujita1,2
1Quality Electrodynamics, LLC, Mayfield
Village, Ohio, United States, 2Dept.
of Physics, Case Western Reserve University, Cleveland,
Ohio, United States
A flexible transmit and 16 channel receive shoulder
array coil for 3.0 Tesla was constructed and tested. The
coil uses one quadrature transmit coil for transmitting
and an array of sixteen receive elements for receiving.
Initial phantom and volunteer imaging demonstrated
excellent image quality and uniformity, and the coil
required significant less transmit power than receive
only shoulder coils.
|
2651. |
Open access 3-channel
receive-only coil for interventional brain imaging. ![](poster.gif)
Emilee Minalga1, Allison Payne1,
Nick Todd1, Robb Merrill1, Dennis
L. Parker1, and J. Rock Hadley1
1Utah Center of Advanced Imaging Research,
University of Utah, Salt Lake City, UT, United States
This work describes the design of an open access
3-channel brain RF coil for interventional MR imaging.
The coil was built to be compatible with a head
stereotactic device and uses capacitive decoupling of
adjacent loops. The coil is evaluated for SNR
performance, temperature imaging performance, and a
comparison of anatomy scans. The coil was found to give
better SNR over both the body coil and a 12-channel
commercial coil. This SNR increase translates to better
anatomy imaging and temperature measurements.
|
2652. |
An Eight-element Phased
Array Coil for Carotid Artery Imaging at 3 Tesla ![](poster.gif)
Yong-Qin Zhang1, Hua-Bin Zhu2,
Ben-Sheng Qiu3, and Xin Liu3
1Paul C. Lauterbur Research Centre for
Biomedical Imaging, Shenzhen Institutes of Advanced
Technology, Chinese Academy of Sciences, Shenzhen,
Guangdong Province, China, 2Suzhou
Zhongzhi Medical Technology Co., Ltd., 3Paul
C. Lauterbur Research Centre for Biomedical Imaging,
Shenzhen Institutes of Advanced Technology, Chinese
Academy of Sciences
To improve the penetration depth, coverage and
signal-to-noise ratio (SNR) of carotid coil in clinical
applications and its suitability for different people,
we designed a bilateral eight-channel receive-only
phased array coil for use at 3T. The SNR map and
g-factor map of the proposed coil is given in the
results. And simultaneously preliminary comparison
demonstrates that the SNR of the new design is much
higher than commercially available 4-element carotid
coils in most cases. The quantitative and qualitative
performance comparison between two carotid coils will be
done in further studies.
|
2653. |
A Novel Phased Array Coil
for Limb Imaging Incorporating 3D Coil Overlaps ![](poster.gif)
Randy Giaquinto1, Wolfgang Loew1,
Suraj Serai1, Jean Tkach1,
Kathleen Emery1, and Charles Dumoulin1
1Imaging Research Center, Cincinnati
Children's Hospital Medical Center, Cincinnati, Ohio,
United States
Single channel flex coils or adult sized knee/wrist
coils are currently used for imaging the pediatric
elbow. This frequently results in uncomfortable patient
positioning, patient motion, poor fat suppression and
degraded images. Furthermore, the use of single loop or
simple volume coils prevent the use of accelerated
imaging based upon parallel imaging strategies. In this
work, we present a novel eight-channel phased array coil
built on a lightweight polycarbonate frame. This coil
has improved SNR over flex coils used in our institution
and overcomes the challenges of cross-coil coupling in a
three-dimensional array construction.
|
2654. |
Sensitivity Simulation of
16ch Spine/Torso Array Coil at 3T
Yoshihisa Soutome1, Masayoshi Dohata1,
Hisaaki Ochi1, and Yoshitaka Bito1
1Central Research Laboratory, Hitachi Ltd.,
Kokubunji, Tokyo, Japan
To improve the workflow efficiency of scans by
decreasing the frequency of coil exchange, we have
designed a 16-channel spine/torso array coil, and
investigated its sensitivity at 3T with a torso phantom
using numerical simulations with method of moments. We
also compared the sensitivity of the designed coil with
that of the traditional spine and torso array coils, and
evaluated the performance of a 32-ch torso array
consisted of two designed coil. Simulation results
suggest that the designed coil can be commonly used as a
spine array coil and a posterior torso coil.
|
2655. |
A Two-part 16-Channel
Receive Phased Array for Imaging of Rabbit Heart and Aorta
on a 3T Clinical MRI System ![](poster.gif)
Stefan Fischer1, Mark Schuppert1,
Maxim Terekhov1, Stefan Weber1,
Andrei L. Kleschyov2, and Laura Maria
Schreiber1
1Section of Medical Physics, Department of
Diagnostic and Interventional Radiology, University
Medical Center of the Johannes Gutenberg University,
Mainz, Germany, 2II-Medical
Department, University Medical Center of the Johannes
Gutenberg University, Mainz, Germany
In this study a dedicated rabbit heart/aorta 16-channel
receive array was developed to achieve high SNR in the
relevant anatomical region. A split design with two 8-ch
parts was chosen. To validate the array SNR and g-factor
maps were evaluated. Compared with a 15-ch knee coil the
SNR of the 16-ch rabbit array was 50% higher in the
center of a 2 liter bottle phantom und 2.3-fold higher
in the peripheral area. The two-part design allows
minimizing array-to-object distance for rabbit MRI and
also simultaneously imaging of two objects with eight
channels each increasing the throughput.
|
2656. |
A Monte Carlo simulation
study on receiver gain variation of linear combined MRI coil
array ![](poster.gif)
Liang Liu1, Faiz Ikramulla1,
Velibor Pikelja1, Jonathan Nass1,
and Ashok Menon1
1Invivo, Philips Healthcare, Pewaukee, WI,
United States
Combiners/splitters have been widely used in MRI phased
array for channel reduction and mode selection. Unlike
uncombined MRI coil array where signals are weighted
differently by the associated noise level in image
reconstruction, combined MRI channels use RF switch and
combiner circuits to merge received signals directly and
both the magnitude and phase of the signals require
finely tuning prior combining. For coils with the
combiner circuits built after the preamplifiers stage,
the gain variations of these preamplifiers have
significant impact on the performance of final combined
signals. A Monte Carlo simulation was tested based on
real preamplifier data to investigate this effect and
aimed to help determine specifications for coil
designers.
|
2657. |
A New RD Coil Design for
Prostate MRI
Seunghoon Ha1, Mark Jason Hamamura1,
Werner W Woeck1, and Orhan Nalcioglu1,2
1Center for Functional Onco-Imaging,
University of California Irvine, Irvine, California,
United States, 2Department
of Cogno-Mechatronics Engineering, Pusan National
University, Pusan, Korea
Despite increasing the number of receiver coils and
upgrading to higher magnetic fields, prostate MRI using
the conventional torso-pelvic RF coil does not provided
sufficient image quality to clearly visualize all
features of interest due to the extended distance from
the coil elements to the prostate region. The endorectal
RF coil provides a higher SNR due to its close proximity
to the prostate region, but involves invasive
positioning and carefully patient monitoring to prevent
excess RF power deposition. In this study, we propose a
new non-invasive coil with a competitive SNR for
prostate MRI and compare its performance against other
commercial coils.
|
2658. |
A carbon receive array of
8 elements, interoperable with proton scanning, for human
temporal lobe
James Tropp1, Paul Calderon2,
Lucas Carvajal3, Fraser Robb2, P.
E. Z. Larson3, P. Shin3, D. B.
Vigneron3, and S. J. Nelson3
1Global Applied Science Lab, GE Healthcare
Technologies, Fremont, CA, United States, 2GE
Healthcare Technologies, 3University
of California San Francisco
We describe the design, construction, and test of an
array receive coil intended for carbon imaging of human
temporal lobe, in particular with hyperpolarized
substrates. Preliminary images of an oil phantom are
shown.
|
2659. |
Phased array probehead for
magnetic resonance
Oliver G. Gruschke1, Elmar Fischer2,
Maxim Zaitsev2, Jürgen Hennig2,
and Jan G. Korvink1,3
1Lab. of Simulation, University of Freiburg -
IMTEK, Freiburg, Germany, 2Dept.
of Radiology Medical Physics, University Medical Center,
Freiburg, Germany,3Freiburg Institute for
Advanced Studies – FRIAS, University of Freiburg,
Freiburg, Germany
The integration of a Helmholtz coil with our previously
published phased array of microcoils, allows creating a
high-resolution probehead. Increasing the usability and
creating the option for a future use in a MR scanner
with a small bore diameter.
|
2660. |
Multi-element wireless
stacked phased array coil ![](poster.gif)
Haoqin Zhu1, Grace Wang1, and
Labros Petropoulos1
1R&D, IMRIS Inc, Winnipeg, MB, Canada
A novel wireless stacked decoupled phased array was
presented. It was shown that this coil can greatly
improve image quality in terms of SNR and penetration.
SNR improvements of 35% were measured compared with a
single element coil of similar size. Such coil design
will allow to increase the number of elements on the
phased array design without increasing the overall coil
dimensions. The wireless technology will allow for user
friendly lighter coils without sacrificing image
quality. This design can be extended for standard phased
array coils combined with preamplifier decoupling to
further enhance the isolation between the adjacent
elements.
|
2661. |
An Implanted 8-channel
array coil for high-resolution macaque MRI at 3T ![](poster.gif)
Thomas Janssens1, Boris Keil2,
Jennifer A. McNab2, Reza Farivar2,
Annelies Gerits1,2, Jonathan R. Polimeni2,
Lawrence L. Wald2,3, and Wim Vanduffel1,2
1Laboratory for Neuro- and Psychophysiology,
K.U.Leuven, Leuven, Belgium, 2A.A
Martinos Center for Biomedical Imaging, Department of
Radiology, Massachusetts General Hospital, Harvard
Medical School, Charlestown, Massachusetts, United
States, 3Harvard-MIT
Division of Health Sciences and Technology, Cambridge,
Massachusetts, United States
Close proximity of a phased-array surface coil results
in increased SNR and improved performance during
accelerated imaging, two characteristics that are
essential for high-resolution macaque MRI. Here, a
receive-only 8-channel phased-array coil was developed
and implanted on top of the skull of a monkey underneath
the head fixation post. The data show a 5.4- and
3.6-fold increase in SNR in the brain periphery compared
to, respectively, an external single and 4-channel coil.
Even for very high resolutions, high SNR and image
quality in anatomical, functional, and diffusion images
was obtained, indicating the advantage of an implanted
phased-array coil approach.
|
2662. |
A 6-channel brain coil for
MR guided high intensity ultrasound. ![](poster.gif)
Emilee Minalga1, Robb Merrill1,
Nick Todd1, Allison Payne1, Dennis
L. Parker1, and J. Rock Hadley1
1Utah Center of Advanced Imaging Research,
University of Utah, Salt Lake City, UT, United States
This work describes design and evaluation of a 6-channel
brain RF coil for magnetic resonance guided high
intensity focused ultrasound. The coil was built to be
compatible with a head stereotactic device and a brain
magnetic resonance guided high intensity focused
ultrasound treatment system. The coil used capacitive
decoupling of adjacent loops. The coil is evaluated for
SNR performance, temperature imaging performance, and
anatomy imaging. The coil was found to give better SNR
over both the body coil and a 12-channel commercial head
coil. This SNR increase translates to better anatomy
imaging and temperature measurements.
|
|
|
Traditional
Poster Session - Engineering |
|
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2663. |
In silico electromagnetic
simulation of a murine glioma model at 7T MRI conditions
Jose I Rey1, Eduardo G Moros2,
Robert J Gillies1, and Gary V Martinez1
1Cancer Imaging, Moffitt Cancer Research
Center, Tampa, FL, United States, 2Radiation
Oncology, Moffitt Cancer Research Center, Tampa, FL,
United States
In silico study
of mouse glioma animal model under 7T MRI conditions.
Includes analysis of electric field intensities (E),
currents (J), and specific energy absorption (SAR) in
normal, brain and tumor tissue. FDTD simulations show
that glioma tumors have distinct dielectric properties
that confer significant variations in electromagnetic
response. This study is relevant to preclinical MR
method scenarios leading to clinical translation.
|
2664.
![](SUMMA25.jpg) |
Fast MR thermometry using
phase referenced asymmetric spin-echo EPI for high field ![](poster.gif)
Markus Nikola Streicher1, Andreas Schäfer1,
Dimo Ivanov1, Laurentius Huber1,
Bibek Dhital1, Enrico Reimer1,
Dirk Müller1, Andre Pampel1,
Robert Trampel1, and Robert Turner1
1Max Planck Institute for Human Cognitive and
Brain Sciences, Leipzig, Germany
The proton resonance frequency shift MR-thermometry
method is inherently very sensitive to magnetic field
perturbations in time. We show an improved referenced
spin-echo EPI sequence which enables paired water and
fat image acquisition in 100 ms, and allows correction
for almost all causes of in-vivo field drift, such as
breathing. Frequency-selectivity of the spin-echo
sequence is achieved by using reversed gradient
amplitudes for excitation and refocusing. With an
appropriate choice of parameters, the technique provides
not only fat and water separation, but immediate
acquisition of the reference map at the same slice
position and with maximum signal amplitude.
|
2665. |
Improving SNR in small
temperature change MR Thermometry to acquire SAR Maps of a
pair of ASL Labelling Coils
Aaron Oliver-Taylor1, Chris Randell2,
Roger J Ordidge3, and David L Thomas4
1Department of Medical Physics and
Bioengineering, University College London, London,
England, United Kingdom, 2PulseTeq
Products Division, Renishaw PLC, United Kingdom, 3Centre
for Neuroscience, University of Melbourne, Melbourne,
Victoria, Australia, 4Institute
of Neurology, University College London, London,
England, United Kingdom
Presented is a method to acquire SAR maps of a pair of
ASL labelling coils using proton resonance shift MR
thermometry. Accurate SAR measurements can only be made
from the linear initial temperature change when RF
heating commences, however due to the low power of the
ASL coils (1W) this temperature change is small and
consequently suffers from low SNR. Regular EPI phase
images were acquired over an extended period of RF
heating, and the time series of each voxel fit to a
suitable function to improve SNR. Resultant SAR maps are
accurate and reproducible.
|
2666. |
From 7T to 10.5T: B1+, SAR
and Temperature Distribution for Head and Body MRI ![](poster.gif)
Jinfeng Tian1, Devashish Shrivastava1,
John Strupp1, Jay Zhang1, and
Thomas Vaughan1
1U. of Minnesota, Minneapolis, MN, United
States
Spurred by the success of 7T whole-body MRI, whole-body
MRI systems of 9.4T or above were installed or will be
installed to push the boundary. In this abstract, the RF
performance of a 16-ch TEM array at 7T and 10.5T are
compared with FDTD simulation. Results showed the head
is a power sink absorbing the propagating EM waves at 7T
and 10.5T torso MRI, thus creating high B1 and SAR in
the head. The major RF artifacts, the high SAR and
temperature rise in the head at 7T, are all seen and
more sever at 10.5T.
|
2667. |
Patient-specific SAR
estimation for the 8-channel radiative antenna array at 7 T
prostate MRI ![](poster.gif)
Ozlem Ipek1, M de Greef2, A
Raaijmakers1, P.R. Luijten3, J.
J.W. Lagendijk1, and C.A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht,
Netherlands, 2Image
Science Institute, UMC Utrecht, Utrecht, Netherlands, 3Radiology,
UMC Utrecht, Utrecht, Netherlands
The patient-specific worst-case local SAR with 8 channel
radiative antenna array is studied in 3 different
patient models, by calculation of the largest eigenvalue
of the Q-matrix for each voxel. The models that we used
vary both in size and fat/muscle ratio. In this way,the
probability of a generic model is investigated for
worst-case local SAR estimation of an external surface
array. A generic model is not found in 3 models due to
huge variance in fat/muscle ratio.
|
2668. |
Fast Subject-Specific SAR
Calculation for Multi-Channel RF Transmission
Shumin Wang1
1Auburn University, Auburn, AL, United States
Safety assessment for multi-channel RF transmission
systems requires the analysis of specific absorption
rate (SAR) in a subject-specific manner. Since SAR
depends on individual subject anatomy and on the
multi-channel excitation scheme, traditional approaches
that rely on generic subject models and worst-case
scenario evaluations may result in excessive
overestimations. With the advancement of computational
electromagnetics techniques, fast full-wave simulations
of actual subject models have been proposed. In this
study, we demonstrate that high simulation accuracy can
be achieved with these techniques in real time.
|
2669. |
From Single Element
Complex B1 Mapping to Local SAR Estimation using
Multi-channel Transceiver Coil at 7T ![](poster.gif)
Xiaotong Zhang1, Jiaen Liu1, and
Bin He1
1Biomedical Engineering, University of
Minnesota, Minneapolis, Minnesota, United States
Quantitative patient-specific local SAR estimation is
highly desired in UHF MRI applications. In this work,
using a 16-channel transceiver head coil at 7T, based on
previously proposed method, we report our simulation
study from single element complex B1 mapping to in-vivo
local SAR estimation on a realistic geometry head model.
Promising simulation results suggest its feasibility and
reliability. Establishment of real-time EPT technique
may have a significant impact on patient-specific SAR
management in parallel transmission at UHF.
|
2670. |
Radio-Frequency Heating in
Swine due to a 3T (123.2 MHz) and 7T (296 MHz) Head Coil ![](poster.gif)
Devashish Shrivastava1, Lynn Utecht1,
Jinfeng Tian1, Timothy Hanson2,
and JT Vaughan1
1University of Minnesota, Minneapolis, MN,
United States, 2University
of South Carolina
Radio-frequency (RF) heating was measured using
fluoroptic probes in the scalp; 5 mm, 10 mm, 15 mm, 20
mm and 25 mm in the brain; and rectum in eight
anesthetized swine due to a continuous wave power
deposition from a 15 rung, 3T head coil and an 8
channel, 7T head coil (N=4 for each coil). The heating
was simulated using the analytical generic bioheat
transfer model (GBHTM) and the empirical ‘gold standard’
Pennes’ bioheat transfer equation (BHTE). The RF power
induced temperature changes did not achieve plateau. The
GBHTM simulated the heating more accurately than the
Pennes’ BHTE.
|
2671. |
Implications of posture
changes on local SAR and B1+ homogeneity in RF shimming at
3T
Desmond Teck Beng Yeo1, Zhangwei Wang2,
and Ileana Hancu1
1Diagnostics and Biomedical Technologies, GE
Global Research, Niskayuna, NY, United States, 2GE
Healthcare Coils, Aurora, OH, United States
Predicting local SAR risks in multi-channel transmit MR
systems is a challenging task. One approach uses EM
simulations to predict local SAR while optimizing the
voltage feeds’ complex weights to obtain a uniform
excitation profile. The weights are then applied to the
coils’ voltage sources and the RF waveforms monitored to
ensure they conform to the calculated weights. This
approach provides some information about local SAR
risks. Our work uses EM numerical computations and a
posable HBM to investigate how B1+ homogeneity and local
SAR may change when optimized weights are applied after
a subject is repositioned following RF shimming
optimization.
|
2672. |
Effect of Body Type,
Tissue Conductivity and Body Location within the RF Coil on
Tangential Electrical Fields in 1.5T MRI ![](poster.gif)
Shiloh Sison1, Xiaoyi Min2, Yan
Liu3, Kevin Feng3, Ji Chen3,
John Nyenhuis4, Gabriel Mouchawar2,
and Jon Dietrich2
1St. Jude Medical, Sunnyvale, CA, United
States, 2St.
Jude Medical, 3University
of Houston, 4Purdue
University
The body type, conductivity and location within an RF
coil partially determine the maximum tangential electric
field along implantable cardiac rhythm device lead
paths. The simulation conditions which have the
possibility of generating the largest temperature rise
at the electrodes of the lead are an obese male with
tissue conductivity 80% of nominal and landmark Z ~0mm.
Around this Z landmark the effect of 20mm to 50mm shifts
in the X and Y direction are negligible. The IEC limit
of 3.2 W/kg for head SAR may result in a whole body SAR
of less than 2 W/kg for some landmarks.
|
2673. |
Design and SAR Estimation
of a Segmented Loop for Dual Coil CASL at 9.4 T ![](poster.gif)
Jonas Bause1, G. Shajan1, Jens
Hoffmann1, Klaus Scheffler1, and
Rolf Pohmann1
1MR Center, Max-Planck Institute for
biological Cybernetics, Tuebingen, Germany
Dual-Coil Continuous Arterial Spin Labeling (DC-CASL)
can reduce magnetization transfer and increase SNR. Here
a balanced detunable segmented loop coil for DC-CASL in
humans at 9.4T was developed and FDTD simulations were
performed to estimate the optimal phase shift as well as
the local SAR. The simulations showed that sufficient
labeling is possible without exceeding the IEC limits
when the duty cycle is limited to 25 %. An additional
safety margin of 37 % was included in the SAR
calculations to account for deviations in the position
of the coils.
|
2674. |
Maximum SAR Estimation of
a Multiple Channel Travelling Wave System based on Waveguide
Theory ![](poster.gif)
Jan Paška1, David O Brunner2,
Juerg Froehlich1, and Klaas P Pruessmann2
1Laboratory for Electromagnetic Fields and
Microwave Electronics, ETH Zurich, Zurich, Switzerland, 2Institute
for Biomedical Engineering, University and ETH Zurich,
Zurich, Switzerland
Waveguide theory was used to analyze a travelling wave
multiple channel setup. This allowed us to reduce the
size of the numerical domain and increase the model
resolution, allowing a more precise estimation of the EM
fields. The SAR was calculated in the worst case, under
the condition that 1W is dissipated in the human body.
MR images based on the derived power limit were
acquired, with the travelling wave multiple channel
system in transceive mode.
|
2675. |
Matrix and Model Order
Reduction Approach for Rapid Safety Prediction and
Supervision of Local and Global SAR in Parallel Transmit
Coils ![](poster.gif)
Esra Neufeld1, Maximilian Fütterer1,
Matthias Gebhardt2, Michael Oberle1,
and Niels Kuster1,3
1IT'IS Foundation for Research on Information
Technologies in Society, Zurich, Switzerland, 2Imaging
& Therapy Division, Siemens AG, Erlangen, Germany, 3Swiss
Federal Institute of Technology (ETHZ), Zurich,
Switzerland
Parallel transmit coils can lead to high local SAR thus
posing a safety issue even when the total energy
deposition is monitored. A method based on pre-computed
matrices and model order reduction is presented to allow
efficient safety prediction and online supervision,
provided a mapping of the patient to a reference model
can be established. The method has been applied to a
detailed anatomical model with variable BMI. Rapid,
conservative estimations with known overestimation can
be provided for any set of steering parameters. The
impact of position, posture and anatomy remains to be
investigated.
|
2676. |
Influence of Skin Tissue
and Air Cavities on Local SAR Estimation in Parallel MR
Excitation ![](poster.gif)
Ara Yeramian1, Stefanie Buchenau1,
Chris A. Cocosco1, Matthias Gebhardt2,
Dirk Diehl3, Jürgen Hennig1, Jan
Korvink4, and Maxim Zaitsev1
1Medical Physics, University Medical Center
Freiburg, Freiburg, BW, Germany, 2Healthcare
Sector, Siemens AG, Erlangen, Germany, 3Corporate
Technology, Siemens AG, Erlangen, Germany, 4IMTEK,
Freiburg, Germany
Whole-body Specific Absorption Rate (SAR) estimation and
hot spot detection in parallel excitation is achieved
through EM simulations of RF parallel excitation coils
and virtual whole-body models. It has been proposed that
whole-body models comprising fat, muscle, and lung
tissues only (essential tissues) are sufficient for
accurate SAR estimation. In addition to these essential
tissues, due to their dielectric properties contrasts
with their surroundings, we investigate the influence of
skin tissue and air cavities in the head, pharynx,
trachea, bronchi, and the intestines on local SAR in an
8-channenl pTx environment.
|
|
|
Traditional
Poster Session - Engineering |
|
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2677. |
Electromagnetic Field
Evaluations Inside a Body-Tissue-Simulating Cylinder Phantom
Excited by an Ideal First-Order Circularly Polarized Mode
Andreas Rennings1, Le Chen1,
Friedrich Wetterling2, Mark E. Ladd3,
and Daniel Erni1
1General and Theoretical Electrical
Engineering (ATE), Faculty of Engineering, Univ. of
Duisburg-Essen, Duisburg, Germany, 2Computer
Assisted Clinical Medicine, Faculty of Medicine, Univ.
of Heidelberg, Mannheim, Germany, 3Erwin
L. Hahn Institute for Magnetic Resonance Imaging, Univ.
of Duisburg-Essen, Essen, Germany
The RF field excitation homogeneity problem of MRI at
high resonance frequencies is investigated on the basis
of the simplest two-dimensional setup including a
cylinder phantom with spatially constant but
frequency-dependent material parameters and an impressed
surface current distribution between the phantom’s
surface and a surrounding perfect electric conductor (PEC)
shield. This simple arrangement has been chosen
intentionally in order to reduce the set of parameters
to a minimum and therefore maximize the physical
insight, which allows quite general and helpful
statements about the B1+ pattern quality for the widely
used first-order circularly polarized (CP) excitation
mode. The coefficient of variation (CoV) of the B1+
distribution is most suited as a figure of merit for the
homogeneity, since it normalizes the standard deviation
to the mean value of the field pattern. Only two
parameters of the arrangement have been varied – the
excitation frequency ranging from 30°MHz up to 450°MHz
and the diameter of the phantom ranging from a few
centimeters up to 40 cm, which covers more or less every
MR imaging scenario. A characteristic B1+ pattern will
be introduced, which indicates the transition between a
regime with the well-known central brightening and
another one without.
|
2678. |
Dgital Beam Forming in the
MRI
Anand Gopinath1, Emad Ebbini1,
Lance DelaBarre2, and Tommy Vaughan2
1Department of Electrical and Computer
Engineering, University of Minnesota, Minneapolis,
Minnesota, United States, 2Center
for Magnetic Resonance Research, University of
Minnesota, Minneapolis, Minnesota, United States
In high field MRI systems, B0 of 7T and above,
inhomogeneity in the RF B1+ field is mitigated by RF
shimming in which multi-channel coil elements are
excited with different magnitude and phases to obtain a
uniform field in a region of interest (ROI). This
process is termed analog beam –forming. The alternative
is to digitize the receive signals and perform digital
beam forming: to focus on a single ROI, or multiple
closely spaced ROIs, perform element pattern correction
to exclude mutual coupling effects, perform nulling in a
specific region and other applications. This paper
provides a discussion of digital beam forming.
|
2679. |
RF signal incoupling into
multi-layered dielectric media: the role of surface waves ![](poster.gif)
Ozlem Ipek1, I.J Voogt2, P.R.
Luijten2, J. J.W. Lagendijk1, and
C.A.T van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht,
Netherlands, 2Radiology,
UMC Utrecht, Utrecht, Netherlands
The role of the surface waves at ultra high field
imaging is investigated for a loop coil and a dipole
antenna. Loop coil represents a magnetic dipole, which
is placed vertically and horizontally along B0 direction
while the dipole antenna represents the electric dipole
placed on a dielectric half-space. Surface waves
measured in the water substrate which is placed on a EG
gel phantom at 7 T MRI. They may lead to a larger
lateral FOV of an RF coil then expected.
|
2680. |
Development and Stability
Testing of an MRI Compatible Isolated Tissue System ![](poster.gif)
Simon Richardson1,2, Bernard Siow2,
Andrew Batchelor3, Mark F. Lythgoe1,
and Daniel D.C. Alexander2
1UCL Centre for Advanced Biomedical Imaging,
Division of Medicine and Institute of Child Health,
University College London, London, United Kingdom, 2Centre
for Medical Image Computing, Dept of Computer Science,
University College London, London, United Kingdom, 3Wolfson
Inst for Biomedical Research, University College London,
London, United Kingdom
We have developed an MRI compatible isolated tissue
maintenance chamber and tested its performance in
maintaining rat optic nerve functionally and
structurally for 10 hours. Electrophysiology, electron
microscopy and detailed diffusion MRI have been used to
assess the tissue stability within this system. The
chamber is versatile, controllable and reliable and can
be used with any horizontal bore MRI system. This is the
first temporal validation of tissue functional,
structural and MR stability in an MRI compatible
isolated tissue system.
|
2681. |
On The Direct MRI of
Histological Tissue Section: Expanding Standardized
off-the-shelf Sample Mounting from Coverslips To Glass ![](poster.gif)
Dung Minh Hoang1,2, Chao Zhang1,
Evelyn Voura1,3, Latifa Fakri-Bouchet4,
and Youssef Zaim Wadghiri1
1Radiology, NYU - School of Medicine, New
York, New York, United States, 2Radiology,
NYU - Medical Center, New York, New York, United States, 3Neurosurgery,
NYU - School of Medicine, New York, New York, United
States, 4University
Lyon 1 - Claude Bernard, Lyon, France
A set of five histological coils were designed and
tested to accommodate standard off-the-shelf mounting
commonly used for tissue examination under a microscope
with sizes enabling a wide range of tissue on either
coveslips or glass slides. We compared the sensitivity
of all the coil sizes designed in-house with a 7T system
acquired during overnight scans (8-hours). Our results
show that samples with sizes as small as 10x10mm and as
thin as 5um thick can be imaged with excellent
anatomical details
|
2682. |
Consistent Phase Contrast
Volumetric Imaging from a Set of 2D Slices ![](poster.gif)
Andrzej Jesmanowicz1, and Robert W. Cox2
1Biophysics, Medical College of Wisconsin,
Milwaukee, WI, United States, 2National
Institute of Mental Health, National Institutes of
Health, Bethesda, MD, United States
A new RF pulse synthesizer that is based on the Texas
Instruments DAC5688 chip was used to create a consistent
volumetric phase contrast imaging from the set of 2D
slices. This DAC chip has a sufficient quality to create
coherent transmit pulses and their reference waveforms
for compensating the phase of different slices.
|
|
|
Traditional
Poster Session - Engineering |
|
Receive Efficiency & Noise Mitigation
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2683. |
Software-based
optimization of coil geometries for decoupling a pair of
loop and Fo8 elements: does separation between coil elements
matter? ![](poster.gif)
Volkan Emre Arpinar1, and L Tugan Muftuler1,2
1Department of Neurosurgery, Medical College
of Wisconsin, Milwaukee, WI, United States, 2Center
for Imaging Research, Medical College of Wisconsin,
Milwaukee, WI, United States
In this study we developed a software that uses FEM
based RF electromagnetic field modeling to simulate the
coils and a Least Squares approach to automatically
calculate the optimal geometries of a pair of loop and
Fo8 coil elements to minimize coupling. We also
investigated how the relative dimensions change for
maximum decoupling when the distance between those
elements was increased.
|
2684. |
Calibration of
electromagnetic field simulations of MR coil arrays for
accurate quantitative comparison with the measured image SNR ![](poster.gif)
Christopher Stumpf1, Robert Rehner2,
Sebastian Martius3, Markus Vester2,
Rainer Engelbrecht1, and Lorenz-Peter Schmidt1
1Chair for Microwave Engineering, University
of Erlangen-Nuremberg, Erlangen, Bavaria, Germany, 2Siemens
Healthcare, Erlangen, Germany, 3Siemens
Corporate Technology, Erlangen, Germany
A new method for comparing simulated electromagnetic
field results of local receive antennas to measured SNR
images is shown. Electromagnetic field simulation is a
powerful tool for designing MR antennas. Simulation
results cannot be compared directly to measured SNR
images due to system properties like e.g. magnetization
of the investigated sample or receiver bandwidth. The
new calibration method allows a quantitative comparison
of simulated field results to measured SNR images of an
arbitrary antenna structure. In this work the theory of
this method is given and results are shown with an
example of a 4-element antenna array.
|
2685. |
A high-power RF switch for
arterial spin labelling with a separate tagging coil ![](poster.gif)
Arthur W. Magill1,2, Hongxia Lei1,3,
and Rolf Gruetter1,3
1Laboratory of Functional and Metabolic
Imaging, Ecole Polytechnique Fédérale de Lausanne,
Lausanne, Switzerland, 2Department
of Radiology, Univeristy of Lausanne, Lausanne,
Switzerland, 3Department
of Radiology, University of Geneva, Geneva, Switzerland
A high-power RF switch is demonstrated, designed to
switch an RF power amplifier between imaging and tagging
coils in an arterial spin labelling setup. The
improvement offered by resonating the diodes with a
parallel inductor is shown.
|
2686. |
298MHz Micro miniature 2KW
Transmit Receive Switch for 7.0 Tesla TR Arrays
Ronald D. Watkins1, Robert H Caverly2,
and William E. Doherty3
1Radiology, Stanford University, Stanford,
California, United States, 2ECE
Department, Villanova University, Villanova, Pa., 3RF
Devices, Microsemi Corp, Lowell, Ma., United States
This work will present the time domain modeling, design,
and packaging of a micro miniature 2KW Transmit Receive
switch for 7 Tesla proton imaging. It will demonstrate
significant advances in packaging and low magnetic
susceptibility packaging, all with commercial readily
available parts. These miniaturized switches are a
critical subsystem circuit needed for high element count
TR array at ultra high field and can be mounted directly
to the coil and reside within the image field of view.
|
2687. |
Multi-Slice N-fold
Acceleration with Scalable Digital Transmit and Receive
Systems ![](poster.gif)
Andrzej Jesmanowicz1, and William J O’Reilly2
1Biophysics, Medical College of Wisconsin,
Milwaukee, WI, United States, 2Tornado
Medical Systems, Toronto, ON, Canada
A System is presented that demonstrates a fully digital
transmit and receive system for multislice EPI
acceleration. The transmit system is based on a TI
DAC5688 chip, which provides superior tailored pulse
generation with almost two orders of magnitude lower
spurious inter-modulated frequencies. A 32 channel coil
is used to measure the 4-slice separation of
simultaneous axial slice excitation.
|
2688. |
On the Optimum Source
Impedance for MRI Phased Array Coils
Paul Joseph Cassidy1
1School of Engineering, Griffith University,
Gold Coast, QLD, Australia
Analytical expressions are presented for MRI phased
array preamplifiers in terms of blocking impedance, S21
decoupling, minimum noise factor and gain based on CMOS
common-source inductively degenerated low noise
amplifiers. These expressions support the idea of using
a source impedance greater than 50 Ohms for enhanced
decoupling and minimum noise factor at the expense of
gain.
|
2689. |
SNR Degradation in Receive
Arrays Due to Preamplifier Noise Coupling and A Method for
Mitigation
Graham Charles Wiggins1, Ryan Brown1,
Bei Zhang1, Marcus Vester2, Stefan
Popescu2, Robert Rehner2, and
Daniel Sodickson1
1The Bernard and Irene Schwartz Center for
Biomedical Imaging, NYU Medical Center, New York, NY,
United States, 2Siemens
Healthcare, Erlangen, Germany
Neighboring elements in a receive array can be decoupled
by various means. However next nearest neighbors still
exhibit substantial inductive coupling, which is usually
mitigated through the use of preamplifier decoupling. It
is commonly assumed that any remaining coupling effects
can be removed by characterizing the coupling through
measurement of the noise correlation matrix and
application of optimum SNR reconstruction.
|
2690. |
Mitigation of inductive
coupling in array coils by wideband port matching
Markus Vester1, Stephan Biber2,
Robert Rehner2, Graham Wiggins3,
Ryan Brown3, and Daniel Sodickson3
1HIM MR PLM SD HW, Siemens Healthcare,
Erlangen, Germany, 2HIM
MR PLM HW, Siemens Healthcare, Erlangen, Germany, 3Radiology,
NYU Medical Center, New York, United States
We suggest a method for mitigating the effects of coil
coupling. It is based on a wideband matching technique
which can be implemented by a simple circuit
modification. The reduced effective reflection will
result in less degradation of preamp noise figure in a
receive array, and in lower power loss in the
transmitter isolators in a parallel transmit system.
|
2691. |
Broadband damping of cable
modes
Ed B Boskamp1, Masahiro Fujimoto1,
Arslan Amjad1, and Michael Edwards1
1GE Healthcare, Waukesha, WI, United States
Currents induced on coaxial cable shields are common in
MRI due to the E fields present in the bore during the
RF pulses. These cable modes can increase SAR. Cable
modes can result from coupling between cable and any
coil. They affect the tuning and isolation. The standard
method to eliminate cable modes is a balun. We present a
different method to damp the cable modes using
conductive plastics. This method is broadband, and
inexpensive.
|
2692. |
Stand Alone Apparatus for
Measuring Noise Correlation of Phased Array Coils Outside of
Magnetic Field ![](poster.gif)
Sergei Obruchkov1,2, and Kenneth Bradshaw2,3
1School of Chemical and Physical Sciences,
Victoria University, Wellington, New Zealand, 2System
Design Engineering, University of Waterloo, Waterloo,
Ontario, Canada, 3Hologic
(Sentinelle Devision), Toronto, Ontario, Canada
Presently, the performance of a coil is tested through
both bench and scanner tests. Scanner tests tend to be
expensive in time and in resources. Scanner tests also
introduce variation in the results due to the difference
in the scanners themselves. It is an objective of this
paper to show that a coil’s actual performance can be
determined not with an expensive MRI scan but with a
newly designed bench tester.
|
|
|
Traditional
Poster Session - Engineering |
|
Travelling Wave & Dielectric Padding
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2693. |
Traveling Wave MRI in a
Vertical Bore 21.1-T System ![](poster.gif)
Alexey A Tonyushkin1,2, Jose Antonio Muniz3,4,
Samuel Colles Grant3,4, and Andrew J M
Kiruluta1,2
1Radiology, Massachusetts General Hospital,
Boston, MA, United States, 2Physics,
Harvard University, Cambridge, MA, United States, 3Center
for Interdisciplinary Magnetic Resonance, National High
Magnetic Field Laboratory, Tallahassee, FL, United
States, 4Chemical
& Biomedical Engineering, The Florida State University,
Tallahassee, FL, United States
Originally implemented clinically at 7 T, traveling wave
nuclear magnetic resonance is a far-field imaging
technique that relies on successful mode propagation in
a waveguide. However, for higher field magnets with
smaller bores, hollow waveguides are below cut-off
requirements for mode propagation. This work
demonstrates the first traveling wave MRI experiments on
a 21.1-T (900-MHz) vertical widebore magnet. Coupled
with a simple transceive loop coil, the setup utilizes a
high dielectric material within a cylindrical waveguide
to achieve a traveling wave regime that allows the
propagation of numerous modes (TEmn, TMmn and HEmn).
|
2694. |
A Travelling Wave Antenna
with Matched Waveguide for Head Imaging at 7 T: Simulation
Results ![](poster.gif)
Daniel James Lee1, and Paul M Glover1
1Physics and Astronomy, University of
Nottingham, Nottingham, Nottinghamshire, United Kingdom
The travelling wave approach to MRI uses an antenna to
propagate a TW through the bore of a 7T+ scanner. Using
a waveguide to match the incident wave into the head a
stronger B1+ can be generated. This has been simulated
and assessed using SEMCAD X. This design is compatible
with the use of local receive coils and local shim
coils. This work indicates that this setup is capable of
generating B1+ in the head with increased efficiency
compared to normal TW methods. Multiple modes can be
generated allowing for a multi-transmit approach to
improve B1+ homogeneity across the brain.
|
2695. |
Travelling-Wave Excitation
for Primate MRI at 7T Whole Body MRI-System ![](poster.gif)
Johannes Mallow1, Tim Herrmann2,
Judith Mylius3, Joerg Stadler3,
and Johannes Bernarding1
1Department of Biometry and Medical
Informatics, OvG University Magdeburg, Magdeburg,
Germany, 2Department
of Biometry and Medical Informatics, OvG University
Magdeburg, Magdeburg, Saxony-Anhalt, Germany, 3Leibniz-Institute
for Neurobiology, Magdeburg, Germany
fMRI for primates at 7T whole body MRI is still a big
challenge because no body-coil is provide and the
necessary fixation unit does not fit into commercial
volume coils. This study shows how the travelling-wave
concept can be optimized to work as an efficient
body-coil replacement. By simulating the RF-system
including the complete 7T whole body scanner it was
possible to consider all the important parameters of the
experiment. Directional characteristics, distance to the
object, and the excitation parameters of the constructed
patch antenna were optimized A phased array coil was
designed for primate fMRI of macaques.
|
2696. |
Multimodal travelling wave
MRI with two coaxial modules ![](poster.gif)
Stefan Alt1, Reiner Umathum1,
Wolfhard Semmler1, and Michael Bock1,2
1Dept. of Medical Physics in Radiology,
German Cancer Research Center (DKFZ), Heidelberg,
Germany, 2Radiology
- Medical Physics, University Hospital Freiburg,
Freiburg, Germany
To provide a "body coil" for high-field MRI systems,
FDTD simulation results of a novel travelling wave setup
are shown, that used two coaxial modules. The setup is
able to excite higher-order modes of wave propagation
enclosed in a defined imaging area. While this creates
diverse distributions of the transverse magnetic field
for B1-shimming, the transmission efficiency
remains inferior to resonant structures.
|
2697. |
Optimization of dielectric
substrate for a 7 T radiative antenna: role of surface waves ![](poster.gif)
Ozlem Ipek1, J. J.W. Lagendijk1,
and C.A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Utrecht,
Netherlands
The radiative antenna is optimized in terms of size and
dielectric properties of the substrate. The role of
surface waves is studied as a function of the thickness
of the dielectric substrate and the relative electrical
permittivity. As a result, optimal in-coupling of RF
signal is strongly determined by the surface waves.
|
2698. |
Imaging with dielectric
waveguide approach for 3T MRI
Alexey A. Tonyushkin1,2, Norman B. Konyer3,
Michael D. Noseworthy3,4, and Andrew J.M.
Kiruluta1,2
1Radiology Dept., Massachusetts General
Hospital, Harvard Medical School, Boston, MA, United
States, 2Physics
Dept., Harvard University, Cambridge, MA, United States, 3Imaging
Research Centre, St. Joseph's Healthcare, Hamilton,
Ontario, Canada, 4Electrical
and Computer Engineering Dept., McMaster University,
Hamilton, Ontario, Canada
Recent developments in ultra-high field MRI have allowed
researchers to explore the traveling wave regime. While
traveling wave MRI is uncommon due to engineering
constraints, it holds promise in a future to solve
various RF transmission issues. Unfortunately, the
traveling wave approach is forbidden for clinical MR
systems due to their much lower field, and therefore,
hard-to-fulfill cut-off requirements. We demonstrate a
possible solution for the traveling wave approach at
relatively low field clinical 3T system using a high
dielectric insert inside an unmodified MRI. We show
simulations and experimental MR images, which were
generated using our propagating mode approach.
|
2699. |
MRI Signal Enhancement via
High-Permittivity Material Pads
M D Ketterman1, Q X Yang2,3, A G
Webb4, Z G Herse2, T Neuberger5,
G Carluccio6, and M Lanagan1
1Materials Research Laboratory, The
Pennsylvania State University, University Park,
Pennsylvania, United States, 2Radiology,
The Pennsylvania State University College of Medicine,
Hershey, Pennsylvania, United States, 3Bioengineering,
The Pennsylvania State University College of Medicine,
Hershey, Pennsylvania, United States, 4Radiology,
Leiden University Medical Center, Leiden, Netherlands, 5High
Field MRI Facility, The Pennsylvania State University
College of Medicine, University Park, Pennsylvania,
United States, 6Electromagnetics
Laboratory, University of Illinois, Illinois, United
States
High permittivity pads have recently been used to
increase signal to noise in 3 and 7 tesla neuroimaging.
A model, using multi-regional travelling-wave analysis
within the near-field, has been constructed to account
for the improved impedance matching local to the pads.
|
2700. |
Improved material for
passive RF shimming with high dielectric pads ![](poster.gif)
Wei Luo1, Yeun Chul Ryu2, Sukhoon
Oh2, Zachary Herse2, Ketterman
David Matthew1, Qing X Yang2,
Lanagan T Michael1, and Christopher M Collins2
1Department of Engineering Science and
Mechanics, The Pennsylvania State University, University
Park, PA, United States, 2Radiology,
The Pennsylvania State University, Hershey, PA, United
States
High dielectric materials (HDM) have been successfully
used to improve the sensitivity and homogeneity of the
RF magnetic field (B1+ and B1- field) in human MRI.
Previously an HDM of a suspension made by calcium
titanate (CaTiO3) powder in distilled or deuterated
water was found advantageous for use in human brain MRI
due to the strong effect of a minimal amount of this HDM.
In this study, we developed and characterized a
composite material using distilled water and sintered
beads of BaTiO3. The bead/water composite showed a
higher dielectric constant and lower conductivity
compared to the BaTiO3 suspension, which should result
in an even a higher effect per amount of material
compared to the powder/water slurry.
|
2701. |
High Dielectric Constant (HDC)
Pad for High Field MRI: Reducing SAR and Enhancing SNR
Zhangwei Wang1, Mike Lanagan2, and
Qing X Yang3
1Coils, GE Healthcare, Aurora, OH, United
States, 2Electrical
Engineering, The Pennsylvania State University,
University Park, PA, United States, 3Radiology
and Neurosurgery, The Pennsylvania State University,
Hershey, PA, United States
Motivated by exciting experimental data demonstrated
previously at 7T, this computer modeling study explored
the potential utilization of high dielectric constant (HDC)
material in between the targeted region of the sample
and coil elements for ultra-high field human head
imaging. The computation experiments show that placement
of HDC pad introduced large changes in B1+ field and
reduced average SAR, although local peak SAR increase a
little
|
2702. |
MRI Enhancement via high
dielectric constant (εr = 510) pad at 3T: brain imaging
Qing Yang1,2, Chris Collins3,
Michael Lanagan4, Zachary Herse3,
Sebastian Rupprecht3, Wei Luo3,
Yeun Chul Ryu3, Megha Patel3, and
Jeff Vesek3
1The Penn State College of Medicine, Hershey,
Pennsylvania, United States, 2Neurosurgery,
The Penn State College of Medicine, Hershey,
Pennsylvania, United States, 3The
Penn State College of Medicine, 4The
Penn State University
High dielectric constant (HDC) pads provide a simple,
effective, low-cost method for improving the quality and
safety of MRI in a number of applications at 3T. Our
results indicate that when HDC-pads (filled with barium
titanate (BaTiO3)and deuterium oxide (D2O) are placed
bilaterally along the sides temporally of the head,
axial T2 Turbo Spin Echo (TSE) scans of the brain show
an increase in SNR (28-42%), reduced RF power (23.7%),
and an enhanced clarity of the temporal lobes. This data
suggests that not only do the scans provide clinicians
with an enhanced view of the temporal lobes to further
aid diagnoses, but the time required to scan is
decreased along with the amount of RF power needed per
scan.
|
2703. |
Numerical analysis on
effects of high dielectric material with 4-channel phase
array ![](poster.gif)
Wei Luo1, Giuseppe Carluccio2,3,
Sukhoon Oh3, and Christopher M Collins3
1Department of Engineering Science and
Mechanics, The Pennsylvania State University, University
Park, PA, United States, 2Department
of Electrical and Computer Engineering, University of
Illinois at Chicago, Chicago, IL, United States, 3Radiology,
The Pennsylvania State University, Hershey, PA, United
States
The effects of high dielectric material (HDM) in human
MRI have been studied intensively in recent years. Most
of the effort has been made to understand the effect of
HDM from the aspect of the transmit EM field. In this
study, we took consider also the receive EM field in
simulation of a 4-channel phase array. The transmit EM
field analysis was done to validate the simulation,
followed by the receive EM field analysis. The knowledge
of the effect of HDM on the receive EM field will
provide us a complete picture of the overall behavior of
HDM in human MRI, providing better insight to HDM design
and better performance of MRI.
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Traditional
Poster Session - Engineering |
|
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2704. |
Analysis of radio
frequency heating induced by a coronary stent at 7.0 T ![](poster.gif)
Davide Santoro1, Alexander Müller1,2,
Lukas Winter1, Wolfgang Renz1,3,
Andreas Grässl1, Celal Özerdem1,
Valeriy Tkachenko4, Jeanette Schulz-Menger4,
and Thoralf Niendorf1,4
1Berlin Ultra-High Field Facility (BUFF), Max
Delbrück Center for Molecular Medicine (MDC), Berlin,
Germany, 2Department
of physics, Humboldt-Universität zu Berlin, Berlin,
Germany, 3Siemens
Healthcare, Erlangen, Germany, 4Working
Group on Cardiovascular Magnetic Resonance, Experimental
and Clinical Research Center (ECRC), Medical University
Berlin, Charité Campus Buch, Berlin, Germany
The advantage of ultrahigh field MRI holds the promise
to enhance spatial and temporal resolution. Such
improvements could be advantageous for several
applications in cardiovascular MRI. However,
intracoronary stents used for treatment of coronary
artery disease are currently considered to be
contra-indications for CMR at 7.0 T. The antenna effect
induced by a metallic implant in combination with RF
wave lengths could increase the RF power deposition at
7.0 T and induce local heating which might cause
myocardial tissue damage, influence coagulation or
endothelial function. For all these reasons it is
essential to carefully assess RF induced heating in
coronary stents commonly used in percutaneous coronary
intervention. This work examines RF induced heating of a
copper tube and a coronary stent in agarose phantoms
using electromagnetic field simulations, fiber optic
temperature measurements and MR thermometry at 7.0 T.
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2705. |
Influence from Static
Magnetic Fields on Fiber-Optical Temperature Probes -
Effects on Safety Measurements at 7T
Jens Groebner1, Moritz Cornelius Berger1,
Wolfhard Semmler1, and Jaane Rauschenberg1
1Dept. of Medical Physics in Radiology,
German Cancer Research Center (DKFZ), Heidelberg,
Germany
Fiber-optical temperature probes are commonly used in MR
safety measurements on implants. In this work it could
be shown that fiber-optical temperature measurements are
B0-dependant and exhibit non-linear
temperature dependence: A temperature drop of 2.6°C at
7T compared to the earth magnetic field and relative
temperature differences of 0.30°C between 20°C and 60°C
at 7T were observed.
|
2706. |
Realistic MHD modeling
based on MRI blood flow measurements. ![](poster.gif)
Julien Oster1, Raul Llinares2,
Zion Tse3, Ehud Schmidt3, and Gari
Clifford1
1Department of Engineering Science,
University of Oxford, Oxford, United Kingdom, 2Departamento
de Comunicaciones, Universidad Politecnica de Valencia,
Valencia, Spain, 3Department
of Radiology, Brigham & Women’s Hospital, Harvard
Medical School, Boston, MA, United States
Electrocardiogram (ECG) recordings, required during MRI
for both triggering and monitoring, are distorted by the
MagnetoHydroDynamic (MHD) voltage induced from the blood
flow through the aorta. The MHD effect makes clinical
ECG analysis difficult and reduces triggering quality in
high field MRI. We propose a MHD model, based on MRI
blood flow measurements. The MHD induced body potential
was computed with an aorta model of 15 cylindrical
sections inside a torso model. The model exhibited a
good consistency compared to a real MHD signal. The
proposed MHD model may allow assessment of new ECG/MHD
separation and denoising techniques.
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2707. |
A Novel MRI-compatible
Tactile Stimulator for Cortical Mapping of Foot Sole
Pressure Stimuli with fMRI
Ying Hao1, Brad Manor1,2, Jing Liu3,
Lewis Lipsitz2, Vera Novak2,
Xiaoying Wang3, Jing Fang1,4, and
Jue Zhang1,4
1Academy for Advanced Interdisciplinary
Studies, Peking University, Beijing, Beijing, China, 2Department
of Medicine, Beth Israel Deaconess Medical Center,
Harvard Medical School, Boston, MA, United States, 3Department
of Radiology, Peking University First Hospital, Beijing,
Beijing, China, 4Department
of Engineering, Peking University, Beijing, Beijing,
China
Foot sole somatosensory feedback is critical to the
motor control of standing and walking. To enable study
of cortical networks underlying foot sole
somatosensation, their relationship to motor control,
and mechanisms of neural adaptation that optimize
behavior in the presence of sensory impairment, we
developed a pneumatic tactile stimulator capable of
producing straight-line oscillations with preset
frequency, magnitude and surface area over which
pressures are applied to the foot sole. Image tests
(anatomical/functional/field map) of a phantom
demonstrated that the device is compatible with 3T MRI.
GRE-EPI images of seven healthy young adults using a
typical block-design stimulation protocol revealed
significant sensorymotor activation.
|
2708. |
Acoustic noise control
during auditory fMRI using a DSP system - first initial in
vivo results ![](poster.gif)
Daniel Güllmar1, Markus Hädrich1,2,
and Jürgen R Reichenbach1
1Medical Physics Group / IDIR I, Jena
University Hospital, Jena, Thuringia, Germany, 2University
of Applied Sciences Jena, Jena, Thuringia, Germany
We implemented a template driven active noise
cancellation algorithm on a DSP system in order to
attenuate the acoustic noise which accompanies
especially fmri acquisitions. Employing acoustic
stimuli, we found that stopping filter adaptation during
stimulus presentation yields to much better activation
in terms of HRF amplitude in the auditory cortex,
whereas without noise control at all, no activation was
detected in the auditory cortex, although the stimuli
were detected.
|
2709. |
Evaluation of ISO/IEC JWG
Tier 3 Approach for RF Heating in 1.5 MRI with Implantable
Cardiac Rhythm Devices ![](poster.gif)
Yan Liu1, Kevin Feng2, Ji Chen2,
Xiaoyi Min3, Shiloh Sison3,
Gabriel Mouchawar3, and Jon Dietrich3
1University of Houston, Houston, TX, United
States, 2University
of Houston, 3St.
Jude Medical
The ISO/IEC Joint Working Group developed tiers to
establish the worst case RF heating for active
implantable devices. Tier 3 utilizes the maximum
simulated tangential electric field (Etan) along lead
paths. Tier 3 was evaluated in five human body models by
comparing Etan and maximum of rms tangential electrical
fields over lead paths (Erms). Tier 3 can overestimate
the effective E by more than a factor of 2 (factor of 4
in heating). Knowing tier 1 and tier 2 are more
stringent than tier 3 indicates that the ISO/IEC JWG
tiers 1-3 are over conservative for implantable cardiac
rhythm devices.
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2710. |
Using transmission line
theory to analyze RF induced tissue heating at implant lead
tips ![](poster.gif)
Daniel Zemann1, and Karin Moertlbauer1
1Institute of Ion Physics and Applied
Physics, University of Innsbruck, Innsbruck, Tirol,
Austria
We present a method to analyze the RF induced tissue
heating at the lead tip of medical implants. This is
done by applying the theory of field-to-transmission
line interaction to a single insulated wire embedded in
a tissue-like medium. A comparison of calculations with
FDTD simulations was done. With our approach it is
possible to analyze the effect of characteristic
transmission line impedance, wire bending and/or
electric field configuration on the current distribution
of conducting leads.
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2711. |
Sound Level Comparison
between Insert, Whole Body, Composite Gradients
K Craig Goodrich1, Seong-Eun Kim1,
Robb Merrill1, Yong Wang2, Richard
Wiggins1, J Rock Hadley1, and
Dennis L Parker1
1UCAIR, University of Utah, Salt Lake City,
Ut, United States, 2Otolaryngology,
University of Utah, Salt Lake City, Ut, United States
This work is a comparison of Sound Pressure Levels (SPL)
using three gradient modes: 1) Head/neck insert
operating alone, 2) Whole body gradients operating
alone, and 3) Composite mode gradients where the
gradient fields of the first 2 modes are superimposed.
SPL of three pulse sequences (GRE, CISS and EPI) for the
three gradient modes were measured. Then for GRE SPL as
a function of receiver bandwidth, slew rate and field of
view were explore. Then SPL for increased insert
proportion of gradient field strength was measure up to
maximum composite mode gradient strength. Attempts were
made to attenuate SPL of the composite system.
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2712. |
MR testing of
gradient-induced vibrations using an optical contact-free
sensor within the switched gradient magnetic field of a 1.5
Tesla MR system. ![](poster.gif)
Gregor Schaefers1, Michael Scholten2,
Pascal Bartnik3, Amin Douiri3, and
Wolfgang Görtz3
1MR Safety Testing Laboratory, MR:comp GmbH,
Gelsenkirchen, NRW, Germany, 2MR:comp
GmbH, Germany, 3MR:comp
GmbH
A likely, but less investigated interaction of the
switched gradient field with medical implants is
vibration. Vibrations are caused by induced
eddy-currents in electrically conductive structures of
medical devices. Measurement of vibrations in an MR
environment is a complex experiment. It seems that
optical systems will be the best choice for minmizing
interferences due to measurement. By placing an optical
sensor in the magnet bore, near to different test
objects it was feasible detecting gradient-induced
vibrations quantitatively and contact-free.
|
2713. |
Optimized methodology for
worst-case determination of orthopedic implants for magnetic
resonance safety testing ![](poster.gif)
Bruno Camps-Raga1, Wolfgang Görtz1,
Amin Douiri1, Michael Scholten1,
Mark J. Pawlenka1, and Gregor Schaefers1
1MR:comp GmbH, MR Safety Testing Laboratory,
Buschgrundstr. 33, 45894 Gelsenkirchen, Germany
A methodology for worst-case selection through computer
simulation techniques to be used as an input to
determine worst-case object and position in subsequent
RF heating tests following ASTM2182-09 is described.
|
2714. |
Simultaneous EEG-fMRI:
evaluating the effect of the cabling configuration on the
gradient artefact. ![](poster.gif)
Muhammad E.H. Chowdhury1, Karen J Mullinger1,
and Richard W Bowtell1
1SPMMRC, School of Physics and Astronomy,
University of Nottingham, Nottingham, Nottinghamshire,
United Kingdom
EEG data recorded during simultaneous fMRI are
compromised by large gradient artefact (GA) voltages.
The GA is usually corrected using average artefact
correction, but any change in the GA during data
acquisition significantly reduces the efficacy of
correction. Here we characterise the GA contribution
from the cabling between the EEG cap and amplifier for
two cable configurations: a ribbon cable and a cable
bundle. We demonstrate that the GA amplitude and its
sensitivity to cable movement can be reduced by
minimising cabling wire loop areas. Use of a cable
bundle consisting of twisted wires is recommended for
future EEG/fMRI studies.
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2715. |
Design of an fMRI-compatible
analogue and digital joystick ![](poster.gif)
Jonathan Howard1, and Rexford Newbould2
1Imanova Ltd, London, United Kingdom, 2Imanova
Ltd, London, London, United Kingdom
A wide variety of neuroscience experiments require the
use of an fMRI-compatible joystick. Several commercial
models are available, generally using fibre-optic
position and switch detection. However, these devices
can be cost-prohibitive, especially for smaller fMRI
studies without large funding levels. Further, fibre-optic
devices often contain a limited number of fiber-optic
sensor components, resulting in a dramatically reduced
resolution of the analogue position signal. In this
work, an inexpensive 2-DOF analogue and digital joystick
for neuroscience studies in an MRI/fMRI environment is
designed. This design can readily be replicated at low
cost.
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|
|
Traditional
Poster Session - Engineering |
|
Click on
to view
the abstract pdf. Click on
to view
the poster (Not all posters are available for viewing.)
Monday 7 May 2012
Exhibition Hall |
14:15 - 16:15 |
|
|
2716. |
Simultaneous Diffusion,
Perfusion MRI and FET-PET ![](poster.gif)
Ke Zhang1, Irene Neuner1,2,
Christian Filss1, Karl-Josef Langen1,
Hans Herzog1, and Nadim Joh Shah1,3
1Institute for Neuroscience and Medicine
Medical Imaging Physics, Medical Imaging Physics
(INM-4), Forschungszentrum Jülich, Jülich, Germany, 2Faculty
of Medicine, Department of Psychiatry and Psychotherapy,
JARA, RWTH Aachen University, Aachen, Germany, 3Faculty
of Medicine, Department of Neurology, JARA, RWTH Aachen
University, Aachen, Germany
PET with metabolic imaging is the clinical established
technique for the diagnosis of cerebral gliomas.
Diffusion MRI is the anatomical tool to demonstrate the
plasticity of the brain. Perfusion MRI can precisely
investigate the angiogenesis in the tumour and help
classify and grade brain tumours. In this study,
diffusion, perfusion MRI and FET-PET were simultaneously acquired
using a hybrid 3T MR-PET scanner. Using the hybrid
approach, data from two representative human brain
tumour cases are presented. The results demonstrates
that hybrid technique offers fast, complete and valuable
information for diagnosis and neurosurgery of brain
tumours.
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2717. |
Simultaneous PET/MR Hybrid
Imaging: MR based continuous valued attenuation map
generation and its effect on quantitative PET imaging ![](poster.gif)
Krishnan Bharath Navalpakkam1, Harald Braun2,
Susanne Zeigler2, Harald H Quick2,
Joachim Hornegger1, and Torsten Kuwert3
1Pattern Recognition Lab,
Friedrich-Alexander-Universität Erlangen-Nürnberg,
Erlangen, Germany, 2Institute
of Medical Physics, Erlangen, Germany, 3Clinic
of Nuclear Medicine, Friedrich-Alexander-Universität
Erlangen-Nürnberg, Erlangen, Germany
MR-based attenuation correction for PET images is till
an open issue. An accurate attenuation correction is
needed for PET quantification. In this work, we generate
a continuous valued CT-like attenuation map from
Ultrashort Echo Time and two-point DIXON VIBE sequences
using ε-insensitive Support Vector Regression (ε-SVR).
Further, we compare the PET quantification accuracy
using attenuation maps from a segmented CT and predicted
CT with respect to a patient CT as the gold standard.
Results show that a continuous estimation of attenuation
values outperforms a segmentation based attenuation map.
|
2718. |
Identifying appropriate
contrast MR images to construct a digital head phantom for
functional near infrared spectroscopy
Hiroshi Kawaguchi1, Takayuki Obata1,2,
Kazuki Kurihara3, Yosuke Takahashi3,
Eiji Okada3, and Hiroshi Ito1
1Molecular Imaging Center, National Institute
of Radiological Sciences, Chiba, Japan, 2Research
Center for Charged Particle Therapy, National Institute
of Radiological Sciences, Chiba, CHiba, Japan, 3Department
of Electronics and Electrical Engineering, Keio
University, Yokohama, Japan
Functional near-infrared spectroscopy (fNIRS) requires a
realistic three-dimensional digital head phantom (based
on the segmentation of anatomical head images) to
improve the accuracy of image reconstruction and
visualization of image data. We test several MR imaging
protocols, i.e. T2-weighted (T2W), Fat saturated
proton-density (FSPDW) and FIESTA image, for their
suitability to extract the scalp, skull and CSF in the
subarachnoid space to construct a digital head phantom
for fNIRS. The combination of FIESTA and FSPDW produced
more accurate results when segmenting the superficial
tissues. Furthermore, the combined acquisition time of
FIESTA and FSPDW is shorter than that of T2W.
|
2719. |
Sequential integrated
PET/CT-MR system: Comparison of image registration accuracy
of PET/CT versus PET/MR ![](poster.gif)
Felix Pierre Kuhn1, Florian Wiesinger2,
Scott Wollenweber3, Andrei Samarin1,
Gustav von Schulthess1, and Daniel Schmid1
1Radiology, University Hospital, Zurich,
Switzerland, 2GE
Global Research, Munich, Germany, 3GE
Healthcare, Waukesha, United States
Multi-modality imaging combines morphological and
functional information originating from different
imaging platforms and is based on the critical
assumption of accurate registration. In the presented
work a tri-modality PET/CT+MR system is used to
investigate the hardware registration performance
between sequential PET and MR versus gold standard
PET/CT.
|
2720. |
MR-based FoV Extension in
Whole-Body MR/PET Using Continuous Table Move ![](poster.gif)
Jan Ole Blumhagen1,2, Ralf Ladebeck1,
Matthias Fenchel1, Klaus Scheffler2,3,
and Harald H. Quick4
1Magnetic Resonance, Siemens Healthcare,
Erlangen, Bavaria, Germany, 2Division
of Radiological Physics, University of Basel Hospital,
Basel, Switzerland, 3MRC
Department, Max Planck Institute for Biological
Cybernetics, Tübingen, Germany, 4Institute
of Medical Physics, Friedrich-Alexander-University
Erlangen-Nürnberg, Erlangen, Germany
In whole-body MR/PET attenuation correction, an MR-based
FoV extension is of emerging interest. However, gradient
nonlinearities and B0 inhomogeneities
often hamper an accurate spatial encoding at the edges
of large FoVs. Recently, we proposed a method to axially
extend the FoV by determining an optimal readout
gradient field which locally compensates B0 inhomogeneities
and gradient nonlinearities. In this work a combination
of the mentioned axial FoV extension and Continuous
Table Movement is presented. In experiments on
volunteers a significant distortion reduction has been
achieved at off-center positions of up to 300 mm off
from the iso-center.
|
2721. |
Effects of Simultaneous
Operation on the Biograph mMR ![](poster.gif)
Sebastian Fürst1, Isabel Dregely1,
Stephan Nekolla1, Markus Schwaiger1,
and Sibylle Ziegler1
1Department of Nuclear Medicine, Technische
Universität München, Munich, Bavaria, Germany
The introduction and immediate success of combined
positron emission tomography (PET) and computed
tomography (CT) scanners in the clinical environment
have significantly increased interest in other
multimodal imaging systems and accelerated their
development, with PET and MR being in the centre of the
efforts. Previous studies already showed that the
performance of the first integrated whole-body PET/MR
machine, the Biograph mMR, compares well to the one of
stand-alone PET and MR scanners. The aim of the present
work was to investigate the effects of MR sequences on
PET data acquisition with a focus on energy spectra and
count rates.
|
2722. |
Systematic Evaluation of
Phantom Fluids for Simultaneous PET/MR Hybrid Imaging ![](poster.gif)
Susanne Ziegler1, Harald Braun1,
Philipp Ritt2,3, Jens U. Krause1,
Carsten Hocke3, and Harald H. Quick1
1Institute of Medical Physics, University of
Erlangen-Nuremberg, Erlangen, Germany, 2Pattern
Recognition Lab, University of Erlangen-Nuremberg,
Erlangen, Germany, 3Clinic
for Nuclear Medicine, University Hospital Erlangen,
Erlangen, Germany
With the recent advent of PET/MR hybrid systems the need
for simultaneous PET and MR phantom measurements arises.
However, phantom fluids that are used in MRI are not
necessarily applicable in PET, and vice versa. In this
study different fluids were systematically evaluated in
regard to their usability for phantom measurements in
simultaneous PET/MR hybrid imaging. Crucial were the
criteria: homogeneity of RF excitation in MRI,
miscibility with FDG for PET imaging and compatibility
with the plexiglas material of the phantom. Our results
show that triethylene glycol represents a viable fluid
for simultaneous PET and MR phantom measurements.
|
2723. |
MR-based FoV Extension of
Human Attenuation Correction in Whole-Body MR/PET Hybrid
Imaging ![](poster.gif)
Jan Ole Blumhagen1,2, Ralf Ladebeck1,
Matthias Fenchel1, Harald H. Quick3,
and Klaus Scheffler2,4
1Magnetic Resonance, Siemens Healthcare,
Erlangen, Bavaria, Germany, 2Division
of Radiological Physics, University of Basel Hospital,
Basel, Switzerland,3Institute of Medical
Physics, Friedrich-Alexander-University Erlangen-Nürnberg,
Erlangen, Germany, 4MRC
Department, Max Planck Institute for Biological
Cybernetics, Tübingen, Germany
In whole-body MR/PET, the human tissue attenuation
correction (AC) of PET data can be based on the MR data.
However, the MR FoV is limited due to B0inhomogeneities
and gradient nonlinearities. Therefore, the human AC map
may be truncated and thus the PET reconstruction may be
biased. In this work we explored extending the MR-based
AC map using a purely MR-based FoV extension. We applied
this method to whole-body MR/PET examinations on
patients and evaluated the impact on the PET
reconstruction. The reported bias was reduced and the
PET reconstruction was in good agreement with a PET/CT
reference measurement.
|
2724. |
Building a combined
cyclotron and MRI facility: implications for interference ![](poster.gif)
Mark BM Hofman1, Joost PA Kuijer1,
Jan Willem de Ridder1, Lars R Perk2,
and Rudolf M Verdaasdonk1
1Physics and Medical Technology, VU
University Medical Center, Amsterdam, Netherlands, 2BV
Cyclotron VU, Amsterdam, Netherlands
With the introduction of hybrid PET/MRI systems, it has
become more likely that cyclotron and MRI systems will
be located close to each other. This study considered
the theoretical interference of a cyclotron facility on
a MRI system. Measurements and simulation showed that
the magnetic field of a cyclotron can be considered a
magnetic dipole field. In a specific case of an 18 MeV
cyclotron and a 3T superconducting whole body MR system
a minimum distance of 11-21 m (depending on location and
criteria applied) has to be considered to prevent
interference.
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2725. |
New Insights into PET
Count Rate Reduction during Simultaneous MR-PET Measurements
Daniel Brenner1, Christoph Weirich1,
Jürgen Scheins1, Etienne Besancon1,
Lutz Tellmann1, Hans Herzog1, and
N. Jon Shah1,2
1Institute of Neuroscience and Medicine - 4,
Forschungszentrum Jülich, Jülich, Germany, 2JARA
- Faculty of Medicine, RWTH Aachen University, Aachen,
Germany
Minor influences of MRI on the PET detectors during
simultaneous MR-PET measurements with the 3T MR-BrainPET
have been observed and shown to result in a drop of the
measured count rate of up to three percent. This study
analyses the distortions generated in the output signal
of the PET detector by the time varying MR gradients.
Pronounced effects are visible at start and beginning of
the gradient ramps while an increased noise level was
observed during the gradient flat top.
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