| Receive Array Technology |
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Monday 20 April 2009 |
| Room 312 |
16:30-18:30 |
Moderators: |
James A. Bankson and Graham Wiggins |
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16:30 |
100. |
Cutting the Cord - Wireless
Coils for MRI |
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Oliver Heid1,
Markus Vester2, Peter Cork3,
Peter Hulbert3, David William Huish3
1H Technology and Concepts, Siemens, 91052
Erlangen, Germany; 2H IM MR PLM SC,
Siemens, 91052 Erlangen, Germany; 3Technology
and Innovation, Roke Manor Research, Romsey,
Hampshire, UK |
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MRI scanner workflow
improvement will result from replacing the existing
cable connection from patient coils to image
processing system with a cordless link. A multiple
input multiple output microwave link system is
proposed. Parametric upconverters in the patient
coils will convert Larmor signals from the coils to
microwave frequency. A transceiver array integrated
into the bore will provide the local oscillator and
receive functions. Parametric amplifiers implement
upconversion with gain in simple and cheap circuits.
Since only patient coils in the field of view are
active the system is ideally suited to whole body
scan. |
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16:42 |
101. |
A Generalized Analog
Mode-Mixing Matrix for Channel Compression in
Receive Arrays |
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Jonathan Rizzo
Polimeni1, Vijayanand Alagappan1,
Thomas Witzel2, Azma Mareyam1,
Lawrence Leroy Wald1,2
1A. A. Martinos Center for Biomedical Imaging,
Massachusetts General Hospital, Charlestown, MA,
USA; 2Harvard-MIT Division of Health
Sciences and Technology, Massachusetts Institute of
Technology, Cambridge, MA, USA |
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Highly parallel arrays
of small receiver coils enable dramatic gains in
both SNR and accelerated imaging performance, but at
a considerable cost in system complexity. Here we
present a general analog mode-mixing matrix that can
compress a large array coil into a small subset of
channels, while retaining most of the SNR of the
array. The matrix is calculated via SVD of the
whitened signal correlation matrix, and implemented
with phase shifters and programmable attenuators. By
combining data from a 32-element array into 8 modes
the mode-mixing matrix was able to retain 70% of the
full-array image SNR. |
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16:54 |
102. |
element Design for Increased
Sensitivity in 64-Channel Wide-Field-Of-View
Microscopy |
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Chieh-Wei Chang1,
Steve M. Wright2, Mary Preston McDougall1,2
1Biomedical Engineering, Texas A&M
University, College Station, TX, USA; 2Electrical
and Computer Engineering, Texas A&M University,
College Station, TX, USA |
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Single Echo Acquisition
(SEA) has decreased imaging time dramatically
through the implementation of 64 channel array
elements to provide spatial localization in the
phase encode direction. Previous versions of the
array coil employed a planar pair design. This coil
design does not afford the SNR values and imaging
depth needed to pursue high-resolution applications
such as wide-field-of-view microscopy. In this work,
a raised-leg coil design was implemented as a
variation of the planar pair coil, and improvements
in SNR and imaging depth were attained. Future coil
modifications will seek to maintain imaging speed
while moving into high-resolution applications. |
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17:06 |
103. |
Resonance Shift Decoupling: A
Potential Alternative to Low Input Impedance
Preamplifiers |
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Marc Stephen Ramirez1,
James Andrew Bankson1
1The Department of Imaging Physics, The
University of Texas M. D. Anderson Cancer Center,
Houston, TX, USA |
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Current minimization
schemes are critical to reduce inductive coupling
between non-adjacent elements in MRI phased arrays.
Traditionally, low input impedance preamplifiers
have been used to accomplish this. In this work, we
test an alternate method involving a transistor
amplifier that is built into the coil to minimize
loop current and maximize gain, while simultaneously
achieving low-noise operation. Design methodologies
involving low-noise, high-gain transistor impedance
matching and a shift in the resonance frequency due
to the parasitic capacitance of the transistor are
described. Initial results indicate the potential to
provide effective element decoupling for MRI phased
arrays. |
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17:18 |
104. |
Studies on MR Reception
Efficiency and SNR of Non-Resonance RF Method (NORM) |
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Xiaoliang Zhang1,2, Chunsheng Wang1,
Daniel Vigneron1,2, Sarah Nelson1,2
1Department of Radiology and Biomedical
Imaging, University of California San Francisco, San
Francisco, CA, USA; 2UCSF/UC Berkeley
Joint Graduate Group in Bioengineering, San
Francisco/Berkeley, CA, USA |
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Non-resonance method
(NORM) for MR signal excitation and reception has
been advocated due to its unmatched advantages in
multinuclear and parallel imaging applications. In
this work, the reception efficiency and SNR of the
NORM technology were validated. No statistical
difference in reception efficiency was observed
between NORM and the conventional resonance
technology. The advantages of NORM technology is not
a trade-off of MR sensitivity. |
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17:30 |
105. |
The Shielding of RF MRI Coils Using Double-Sided EMI
Shield |
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Ibrahim Abu El-Khair1,
Jan G. Korvink1, Juergen Hennig2,
Gerhard Moenich3
1Dept. of Microsystems Engineering–IMTEK,
University of Freiburg, Freiburg, Germany; 2Dept.
of Diagnostic Radiology, Medical Physics, University
Hospital Freiburg, Freiburg, Germany; 3Dept.
of Radio Frequency Technology, Technical University
of Berlin, Berlin, Germany |
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Radiation losses
associated with RF coils increase up to the fourth
power of frequency; it becomes significant at high
fields above 2 Teslas. Furthermore, loading an RF
MRI Coil with a sample leads to a shift in the
resonant frequency, f0 away from the one specified.
This also leads to a very poor reception at f0. A
double-sided EMI (ElecroMagnetic Interference)
shield using the CTLM (Coaxial Transmission Line
Modeling) technique of shielding restores f0, and
eliminates the radiation loss. The mutual capacitive
coupling among the neighboring coils within an
array, and associated electronics, is also
eliminated. |
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17:42 |
106. |
A
30 Channel Receive-Only 7T Array for Ex Vivo
Brain Hemisphere Imaging |
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Azma Mareyam1,
Jonathan Rizzo Polimeni1, Vijayanand
Alagappan1, Bruce Fischl1,2,
Lawrence L. Wald1,3
1A. A. Martinos Center for Biomedical Imaging,
Dept. of Radiology,MGH, Charlestown, MA, USA; 2CSAIL,
MIT, Cambridge, MA, USA; 3Harvard-MIT
Division of Health Sciences and Technology ,
Harvard-MIT , Cambridge, MA, USA |
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High-field MRI of ex
vivo samples provides 3D image encoding at
resolutions capable of resolving laminar and
myeloarchitectonic features, thus providing a
potential replacement for the technically
challenging task of whole-brain histological
sectioning. Here we present a 30-channel
receive-only coil array for high-resolution
whole-cerebral-hemisphere imaging. With this array,
whole-hemisphere acquisitions of 150 µm voxel size
in which laminar details are clearly detectable are
possible within six hours. Considerations for
satisfying the many constraints imposed by ex vivo
imaging on surface coil are discussed, and imaging
performance is compared with other available 3T and
7T arrays. |
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17:54 |
107. |
Multi-Purpose Flexible
Transceiver Array at 7T |
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Bing Wu1,
Chunsheng Wang1, Roland Krug1,
Douglas Kelley2, Yong Pang1,
Duan Xu1, Sharmila Majumder1,3,
Sarah Nelson1,3, Daniel Vigneron1,3,
Xiaoliang Zhang1,3
1Radiology&Biomedical Imaging, University of
California, San Francisco, San Francisco, CA, USA;
2GE Healthcare, San Francisco, CA, USA;
3UCSF/UC Berkeley Joint Group Program in
Bioengineering, San Francisco & Berkeley, CA, USA |
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A multi-purpose flexible
transceiver array was designed for ultra-high field
MRI using a mixing technique of primary and 2nd
harmonic microstrips. Besides the coil geometry, the
number of coil elements in the proposed design is
also selectable for different applications. The
feasibility of this multi-purpose flexible array has
been demonstrated by 7T MR imaging for human wrist,
knee, head and liver. |
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18:06 |
108. |
A 32-Channel Receive Array
Coil for Pediatric Brain Imaging at 3T |
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Vijayanand Alagappan1,2,
Graham Charles Wiggins3, Jonathan Rizzo
Polimeni3, Lawrence Leroy Wald3,4
1Department of Radiology, A.A Martinos Center
for Biomedical Imaging, Charlestown, MA, USA; 2Department
of Biomedical engineering, Tufts University,
Medford, MA, USA; 3Department of
Radiology, A.A Martinos Center for Biomedical
Imaging, Charlestown, MA, USA; 4Health
Science and Technology, MIT, Cambridge, MA, USA |
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We describe a 32 channel
receive-only 3T phased array head coil for the
pediatric population. The 32-channel coil was built
on a close fitting fiberglass helmet with
soccer-ball element geometry. SNR gains of 4 and 2
times in the cortex and 1.2 and 2 times in the
center of the head were observed when compared to a
commercial 32-channel adult head coil and a
12-channel adult head coil. The Maximum G factors
were also reduced significantly with the 32-channel
coil optimized for the pediatric head imaging. |
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18:18 |
109. |
Hole-Slotted Phased Array at 7
Tesla |
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Marcos A. Lopez1,2,
Philipp Ehses1, Felix Breuer2,
Daniel Gareis1, Peter Michael Jakob1,2
1Experimental Physics 5, University of
Wuerzburg, Wuerzburg, Bavaria, Germany; 2Research
Center Magnetic Resonance Bavaria, Wuerzburg,
Bavaria, Germany |
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The hole-slot magnetron
is used as a HF oscillator in radar applications. A
surface coil based on the hole-slot magnetron’s
geometry was introduced showing deeper RF
penetration than a conventional coil at 1.5 and 4
Tesla. Four different conventional coil geometries
were compared with a hole-slotted coil at 7 Tesla.
Furthermore a hole-slotted array was built and
evaluated. The hole-slotted loop improves RF
penetration depth compared to the different loops
showing a improved SNR in the second half of the
phantom. The images acquired with the hole-slotted
array show high SNR as well as good homogeneity and
RF penetration depth. |
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