Gene Hilton Payne^1,2, Gaston Vergara^2,3, Ravi Ranjan^2,3, Kamal Vij⁴, Nelly Volland^1,2, Eugene Kholmovski^1,2, Sathya Vijayakumar^1,2, Josh Blauer^2,5, Kimberly Johnson^2,3, Greg Gardner^2,5, Glenn Meredith⁶, Tongbai Meng⁶, Rob MacLeod^2,5, and Nassir F Marrouche^2,3
1UCAIR, Department of Radiology, University of Utah, Salt Lake City, UT, United States, ²CARMA Center, University of Utah, Salt Lake City, UT, ³Department of Cardiology, University of Utah, Salt Lake City, UT, United States, ⁴SurgiVision, Inc., Irvine, CA, United States, ⁵SCI, University of Utah, Salt Lake City, UT, United States, ⁶Center for Applied Medical Imaging, Siemens Corporate Research, Princeton, NJ, United States

During an RF ablation procedure for treatment of atrial fibrillation, cardiac pacing is sometimes used to enforce a normal sinus rhythm at a specific rate. With the ultimate goal of performing this atrial fibrillation treatment inside an MR scanner, it will be necessary to perform pacing in this environment. Presented are the experimental setup and methods for safely pacing on a porcine subject inside a 3T MR scanner. Also presented are electrogram data that show effective pacing of the subject. The results indicated that pacing was safe and effective inside the MR scanner.

Kenneth Craig Goodrich¹, William Bradfield Handler², Seong-Eun Kim¹, John Rock Hadley¹, Ulrich A Rassner³, Blaine A Chronik², and Dennis L. Parker^1
1UCAIR, University of Utah, Salt Lake City, Utah, United States, ²Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, ³Radiology, University of Utah, Salt Lake City, Utah, United States

The purpose of this study was to test PNS levels associated with a novel gradient system that allows an insert gradient to be used simultaneously with whole-body gradient system. 5 volunteers underwent PNS testing using whole body gradients and a head/neck insert. Three gradient configurations were measured; body gradients, insert gradients, both systems operating synchronously. The pulse sequence consisted of 64, 1 msec trapezoid pulses with 400 microsecond slew time. The PNS threshold for composite gradients was higher than for the body gradients only. Composite gradients may allow increased gradient performance while decreasing PNS relative to whole body gradients alone.

Irving N Weinberg¹, Pavel Stepanov², Steven C Glidden³, Howard D Sanders⁴, Daniel Warnow⁴, Alan B McMillan⁵, Rao P Gullapalli⁶, Piotr M Starewicz⁷, Kai-Ming Lo⁸, Amnon Fisher⁹, J Patrick Reilly¹⁰, Michael S Niziol¹¹, and Stanley T Fricke^12
1Weinberg Medical Physics LLC, Bethesda, Maryland, United States, ²Weinberg Medical Physics LLC, ³Applied Pulsed Power Inc., Freeville, New York, United States, ⁴Applied Pulsed Power Inc.,⁵Radiology, University of Maryland, Baltimore, Maryland, ⁶Radiology, University of Maryland, Baltimore, ⁷Resonance Research, Inc, Billerica, Massachusetts, ⁸University of Maryland, ⁹Physics, Technion-Israel Institute of Technology, Haifa, Israel, ¹⁰Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, ¹¹Family Practice Associates, Dryden, New York, ¹²Radiology, Children's National Medical Center, Washington, DC

Prior clinical trials have examined peripheral nerve stimulation (PNS) for magnetic gradients with ramp times of 50 µs and higher. We conducted a prospective IRB-approved controlled clinical trial in which 26 volunteers were exposed to magnetic gradient pulses with ramp times as short as 3.5 microseconds. The data suggests that at 3.5 µs, the threshold of gradient dB/dt (unipolar pulses) for 50% PNS in the general population would be 128,000 T/s (with substantially lower thresholds for younger subjects), representing dB/dt and slew rate thresholds more than 1,000 times higher than in typical MRI scanners.

Neha Bharat Butala¹, Ramez Emile Necola Shehada¹, Peter Nabil Costandi¹, Ali Dianaty¹, and Kevin Jurkowski^1
1Cardiac Rhythm Management Division, St. Jude Medical, Sylmar, CA, United States

Active implantable medical devices (AIMD) in patients undergoing MRI, present a risk of tissue stimulation at gradient dB/dt rates lower than the imposed limits for direct stimulation. Additionally, the gradient amplifier noise, “ripple” could interfere with AIMD, compromising safety. The dB/dt and associated ripple were investigated in 1.5T MRI scanners. A total of 126 measurements were performed using Faraday coils in various scanners and bore locations, while running different clinical sequences. The magnitude and location of maximum dB/dt and ripple was identified. This information may be valuable for assessment of unintended gradient stimulation hazard to demonstrate MR compatibility of AIMD.

Kirk Champagne^1,2, Tim Hoeppner², David Weber², Ta-yung Liu¹, Mehran Fallah-Rad¹, and Mark Alexiuk^1,3
1IMRIS, Winnipeg, Manitoba, Canada, ²Electrical and Computer Engineering, University of Manitoba, Winnipeg, Manitoba, Canada, ³Institute of Industrial Mathematical Sciences, University of Manitoba, Canada

Intra-operative OR suite designs that employ a high field movable MRI scanner require that safety checks be integrated into the surgical workflow. Existing safety checks may be complemented by a wireless sensor network that monitors the OR for potential safety hazards. We demonstrate the feasibility of such a system using Hall effect sensors. Testing with a movable 1.5T Siemens Espree scanner shows good agreement to magnetometer readings. A standard RF noise test (with the system in operation) showed an elevated baseline signal intensity but no image artifacts. Novelty of this system includes software-based thresholds and enables integrated room control.

Mingfeng Li¹, Brent Rudd¹, Teik C Lim², and Jing-Huei Lee^3,4
1Mechanical Engineering, University of Cincinnati, Cincinnati, OH, United States, ²Mechanical Engineering, University of Cincinnati, Cincinnati, United States, ³School of Energy, Environment, Biological and Medical Engineering, University of Cincinnati, Cincinnati, OH, United States, ⁴Center For Imaging Reserch, University of Cincinnati, Cincinnati, OH, United States

Active noise control (ANC) for treating MRI noise effectively on a real life 4 T MRI scanner is presented in this study. Several MRI scanning sequences are used for demonstration. A dummy is equipped with an MRI compatible headset containing piezoceramic speakers with condenser microphones installed inside and outside the earpiece to measure the environmental sound in the immediate patient vicinity. During the in-situ test, the sound pressure level (SPL) was measured, both with and without the ANC. Results presented show the ANC system attained significant overall SPL reduction for all three scanning sequences tested.

Benjamin Anthony Coppola¹, Ramez Emile Necola Shehada¹, Peter Nabil Costandi¹, Kevin Jurkowski¹, and Ali Dianaty^1
1Cardiac Rhythm Management Division, St Jude Medical, Sylmar, CA, United States

Susceptibility artifacts due to metallic implants may affect the interpretability of an anatomical image. Such artifacts may be quantified using ASTM standard F2119-07. A new method is proposed using image correlation that addresses voids in the image as well as geometric distortion. To test this method, a pacemaker was imaged with gradient echo and spin echo sequences in a variety of orientations. The results show that a threshold correlation coefficient of 0.7 conservatively outlines the region comprised of void/distortion. This definition of the image artifact area facilitates improved clinical interpretation with reduced risk of false diagnosis.

Conrad Steven Martin¹, Tobias Frauenrath¹, Celal Özerdem¹, Wolfgang Renz^1,2, and Thoralf Niendorf^1,3
1Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine, Berlin, Germany, ²Siemens Medical Solutions, Siemens, Erlangen, Germany, ³Charité Campus Buch, Humboldt-University, Experimental and Clinical Research Center (ECRC), Berlin, Germany

The magnetic forces of fringe magnetic fields of MR systems on ferromagnetic components can impose a severe patient, occupational health and safety hazard. MRI accidents are listed as number 9 of the top 10 risks in modern medicine. With the advent of ultrahigh field MR systems including passively shielded magnet versions, this risk, commonly known as the missile or projectile effect is even more pronounced. A strategy employing magnetic field sensors which can be attached to ferromagnetic objects that are commonly used in a clinical environment is conceptually appealing for the pursuit of reducing the risk of ferromagnetic projectile accidents.

Jaane Rauschenberg¹, Jens Groebner¹, Wolfhard Semmler¹, and Michael Bock^1
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

The widely used intrauterine contraceptive devices (IUD) had been evaluated for MR-safety only up to field strengths of 1.5T. In this work we performed ASTM measurements of 5 different IUDs at 3T. Additionally, we estimate the potential risk at 7T examinations. The metal-free hormone-containing Mirena IUD has a magnetic retraction thread but it does not produce hazardous heating. For copper-alloy IUDs no magnetic force and no torque could be detected; however, the temperature rise due to RF was up to 3°C during 15 min at 3T. For 7T head examinations no potential risk could be detected with the hardware used.

Jaane Rauschenberg¹, Jens Groebner¹, Angela Heinrichs², Anne Szostek², Patric Meyer², Frauke Nees², Georgios Paslakis³, Maria Gilles³, Michael Bock¹, Michael Deuschle³, Herta Flor², and Wolfhard Semmler^1
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany, ²Department of Cognitive and Clinical Neuroscience, Central Institute of Mental Health, Mannheim, Germany, ³Department of Psychiatry and Psychotherapy, Central Institute of Mental Health, Mannheim, Germany

Up to now, no sufficient experimental data about the exposure especially to movements in the stray field of MR systems are available. In this study the neurobehavioral effects is measured during the exposure to static fields and during controlled movements in the stray fields of different field strength. For this purpose we designed a magnetic field dosimeter, a motion system, a 7T compatible presentation tool, and a 0T MR system for control measurements. It could be shown that the experimental design is suitable for this complex study. First results show no significant effects on the exposure to static magnetic fields.

Valentina Hartwig¹, Rossana Tortorelli², Nicola Vanello², Giulio Giovannetti¹, Vincenzo Positano³, Luigi Landini², and Maria Filomena Santarelli^1
1Institute of Clinical Physiology - CNR, Pisa, Italy, ²Department of Information Engineering, University of Pisa, Italy, ³Fondazione Toscana Gabriele Monasterio, Pisa, Italy

Occupational workers operating magnetic resonance imaging (MRI) and spectroscopy (MRS) are repetitively and lengthy exposed to large static magnetic fields and to low frequency time varying magnetic fields. In 2004, the European Union adopted the Physical Agents (Electromagnetic Fields) Directive 2004/40/EC on the health and safety requirements for exposure to electromagnetic fields in the workplaces, which introduces significant restrictive limits on the use of clinical MRI. In this work a novel tool to estimate the induced current density due to worker movements in static magnetic field is presented. This tool represents a valid instrument to find the worst-case exposures situations.

Maarten J. Versluis^1,2, Wouter M. Teeuwisse^1,2, Hermien E. Kan^1,2, Andrew G. Webb^1,2, and Matthias J.P. van Osch^1,2
1Radiology, Leiden University Medical Center, Leiden, Netherlands, ²C.J. Gorter Center for high field MRI, Leiden University Medical Center, Leiden, Netherlands

Patient tolerance for high field MRI examinations (7 Tesla) is important for the successful clinical introduction of these systems. The first 102 subjects that participated as volunteers in MRI examinations were asked to fill out a questionnaire to assess comfort and side effects, such as dizziness, metallic taste and overall comfort. Our results show that neuro MRI examinations at 7 Tesla are well tolerated, with only 3% of subjects rating the examination as unpleasant. Most mentioned complaints are dizziness moving in and out of the scanner and scanner noise.

Daniel Güllmar¹, Lucas A Bitzer^1,2, and Jürgen R Reichenbach^1
1Medical Physics Group, Jena University Hospital, Jena, Thuringia, Germany, ²School of Physics and Astronomy, Friedrich-Schiller-University, Jena, Thuringia, Germany

In this work we have evaluated the application of a template driven, adaptive, active noise cancellation system in order to reduce the acoustic noise, which accompanies each MR image acquisition. The system was tested offline using self-written Matlab software code and consists of a modified feed-forward ANC-System. The overall acoustic noise level reduction (frequency range 0-3000 Hz) was between 10 to 15 dB without and more than 25 dB with continuous adaptation. These achievements were obtained using parameter optimization of the LLMS algorithm and will be implemented in the future on DSP hardware for online acoustic noise cancellation.

Peter Brunecker¹, Claudia Kunze¹, Anja Grebe¹, Chao Xu¹, Ivana Galinovic¹, and Jochen B Fiebach^1
1Center for Stroke Research Berlin (CSB), Charité, Berlin, Germany

Monitoring of long-term alterations in MRI scanner parameters is essential for observational studies extending over several years. However, during this time intentional adjustments of the scanner hardware can actively introduce changes on a mid-term scale. To investigate this, daily phantom measurements were performed over a time period of 20 months and mean signal magnitude, signal-to-noise ratio, and uniformity were estimated. We found that sudden alterations of the absolute signal magnitude in our data were triggered by technical maintenance. We suggest that using a correction based on the stepwise constant behavior of scanner hardware parameters in time could prevent such alterations.

William Bradfield Handler¹, Chad Tyler Harris¹, and Blaine Alexander Chronik^1
1Physics & Astronomy, University of Western Ontario, London, Ontario, Canada

The heating of a metal due to an oscillating magnetic field has been characterized to better understand the effects of gradient heating of implants and devices used inside the scanner bore. The results can guide the engineering of implants and devices, and there safe use within the MR environment.

Andreas Senn¹, Andreas Peter¹, and Jan G. Korvink^1,2
1Department of Microsystems Engineering (IMTEK), University of Freiburg, Freiburg, Baden-Württemberg, Germany, ²Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg, Baden-Württemberg, Germany

Application of CRLH metamaterial transmission lines in MR coil design.

Krishna N Kurpad^1
1Radiology, University of Wisconsin, Madison, WI, United States

Solenoids are known to be inherently high SNR coils that also generate highly homogeneous radio frequency magnetic (B1) fields. Traditional solenoidal coils generate B1 field that is parallel to the static magnetic (B0) field. Here, we present a novel variant of the solenoid coil, the Orthogonal Double Solenoid (ODS) coil that generates transverse B1¬ field when placed with its axis parallel to the B0 field in dedicated high field small animal horizontal bore systems. We conclude that the performance of a linear ODS coil is comparable to commercial quadrature birdcage coils with sufficient head room for further improvement.

Daniel Papoti¹, Edson Luis Gea Vidoto¹, Mateus José Martins¹, Alfredo O Rodríguez², and Alberto Tannús^1
1Instituto de Física de São Carlos, São Carlos, São Paulo, Brazil, ²UAM Iztapalapa, DF, Mexico, Mexico

Small animal MR imaging and spectroscopy, where spatial resolution is a limiting factor, requires the use of distinct transmit and receive coils. This approach makes easier the optimization of the RF field homogeneity for transmit-only coils and signal-to-noise ratio for receive-only coils. It also requires that RF coils should be electrically decoupled, commonly using PIN diodes. This work describes the development and double crossed coil operating in the transceiver mode for magnetic resonance imaging of rodents at 2T. Experimental and theoretical comparisons of coil performance were carried out using a standard birdcage coil.

Marc Stephen Ramirez¹, Yunyun Chen², Stephen Y Lai², and James Andrew Bankson^1
1The Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, United States, ²The Department of Head and Neck Surgery, The University of Texas M. D. Anderson Cancer Center, Houston, TX, United States

The traditional multimouse MRI methodology in which volume coils are dedicated to many mice must be reconsidered for short routine imaging protocols due to unnecessary complication of preparing and scanning many animals simultaneously. Instead we propose imaging a more manageable number of mice faster by dedicating phased arrays to each mouse and employing parallel imaging (PI) techniques. An array consisting of five transmit and 15 receive coils was selected as a throughput-optimized configuration for the next generation of 16-channel small-animal MRI systems. Details of the fabrication, testing, and in vivo use of the system for PI-accelerated multiple-mouse MRI are described.

Jun Dazai¹, Michael Wong¹, Christine Laliberté¹, and R Mark Henkelman^1
1Mouse Imaging Centre, The Hospital for Sick Children, Toronto, Ontario, Canada

Anatomical abnormalities, especially in neuroanatomy, are important indicators of human disease and their respective mouse models. Using magnetic resonance imaging (MRI) and subsequent image analysis, minute abnormalities in the mouse brain and embryos can be detected. Using a custom-built 16-coil solenoid array, 16 mouse brains were imaged concurrently to produce high-resolution, ex vivo 3D datasets with an effective throughput of less than 45 minutes per sample.

Rupeng Li¹, Phillip Bishop², Andrzej Jesmanowicz², Andrew Nencka², J,B, Stephenson IV³, Christopher Pawela², Ji-Geng Yan³, Anthony G Hudetz⁴, Hani Matloub³, and James S Hyde^1
1Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States, ²Biophysics, Medical College of Wisconsin, ³Plastic Surgery, Medical College of Wisconsin, ⁴Anesthesiology, Medical College of Wisconsin

A more-sensitive approach to whole-brain acquisition of the rat is showed here. It consists of an array of coils on the upper surface in combination with intra-oral coils supported on a bite bar. The intra-oral coil is customized with the coil surface directly contacted to the upper palate. This novel coil array design voids the tissue interference from the side and the bottom of the rat brain, and minimizes the signal drop off. This two coil array also causes apparent improvement in the SNR. This design could also be used for other small animal studies.

Azma Mareyam¹, James Blau¹, Jonathan Polimeni^1,2, Boris Keil^1,2, Reza Farivar^1,2, Thomas Benner^1,2, Wim Vanduffel^1,2, and Lawrence L Wald^1,3
1A.A Martinos Center for Biomedical Imaging, Dept. of Radiology, Massachussetts General Hospital, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Division of Health Sciences and Technology, Harvard-MIT, Cambridge, MA, United States

High-field functional MRI of non-human primates provides elevated BOLD contrast but requires an optimized coil design to boost the SNR, facilitate image acceleration, and maintain mechanical and electrical stability during the awake primate experiment. We present an 8-channel receive-only coil array optimized for high-resolution whole-brain imaging of the awake primate. Imaging performance is compared with other available 3T and 7T arrays.

Elmar Fischer¹, Raghad Aal-Braij², Andreas Peter², Jürgen Hennig¹, Jan Gerrit Korvink^2,3, and Maxim Zaitsev^1
1Radiology, University Medical Center Freiburg, Freiburg, Germany, ²Microsystems Engineering – IMTEK, University of Freiburg, Freiburg, Germany, ³Freiburg Institute of Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany

This work is on the implementation and successful test of a self-built RF coil arrangement inside a PatLoc gradient coil for experiments inside a 9.4 T Bruker small-animal scanner. An eight-leg high-pass birdcage resonator with a very thin wall of only 0.5 mm wall thickness around the sensitive volume has been constructed and was successfully tested in transceive mode on a silicon oil phantom. Using the resonator in combination with an in-house built eight-channel receive array coil, experiments inside a PatLoc gradient coil in the bore of the 9.4 T Bruker small animal scanner could be performed. In-vivo experiments on mice are planned.

Jose Antonio Muniz^1,2, Malathy Elumalai^1,3, Ihssan S Masad^1,2, William W Brey¹, Petr L. Gor'kov¹, and Samuel Colles Grant^1,2
1National High Magnetic Field Laboratory, The Florida State University, Tallahassee, FL, United States, ²Chemical & Biomedical Engineering, The Florida State University, Tallahassee, FL, United States, ³Electrical & Computer Engineering, The Florida State University, Tallahassee, FL, United States

The use of ultra-high magnetic fields for magnetic resonance imaging has the ability to produce data with increased SNR, higher spatial resolution and/or reduced imaging times. In order to take advantage of these benefits, the efficient design of RF coils is crucial, especially at higher frequencies. The goal of this work is to construct a transmit-receive quadrature driven saddle pair array that will provide improved SNR over similarly sized single loop surface coils and volume coils at 21.1 T. Further, the implementation of multi-channel configurations may extend these benefits to include improved homogeneity and reduced imaging times.

Marc Filipe Carias¹, John G Sled¹, Mark R Henkelman¹, and Brian J Nieman^1
1Mouse Imaging Centre, Hospital for Sick Children, Toronto, Onratio, Canada

Multiple-mouse MRI (MMMRI) accelerates preclinical studies by imaging multiple mice simultaneously. We explored two possible transmit coil configurations for a MMMRI set up with separate transmit and receive coils: one with individual transmit coils for each mouse and one with a single large transmit coil for all mice. We observed that a single large transmit coil offered excellent image quality and some SNR benefit over the multiple transmit coil case. The large transmit coil is also appropriate for most imaging applications where high B1 field strength is not a requirement.

Meng-Chi Hsieh^1,2, San-Chao Hwang³, Hsu Chang³, and Jyh-Horng Chen^1,2
1Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, ²Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, ³Division of Medical Engineering Research, National Health Research Institutes, Zhunan, Taiwan

In this work, a high resolution whole mice body image using mechanically sliding coil array was demonstrated for interventional MR. Three fixed coil arrays were situated on the bottom of mice body while the mechanically mobile small coil loop with high S/N, was put on the top of mice head to perceive higher S/N on the volume of interest (VOI). One high SNR quality image of mice head captured by mobile loop and three homogenous quality images of mice body acquired by associated fixed rectangular coils were acquired and used for image reconstruction using parallel imaging to speed up imaging time. Compared with conventional array coils, this design offers more freedom for target detection and offers higher SNR on the target area.

Sairamesh Raghuraman^1,2, Joachim Schrauth¹, Daniel Weber¹, Frank Resmer², Peter Michael Jakob¹, Titus Lanz², and Daniel Haddad^3
1University of Wuerzburg, Wuerzburg, Germany, ²RAPID Biomedical GmbH, Rimpar, Germany, ³MRB Research Centre, Wuerzburg, Germany

Dynamic imaging of the cruciate ligaments in the complex curvature of minipig's knee is achieved using a multi-channel receive array and a movement device synchronised with sequence. Characterization of the coil along with static images and snapshots from dynamic images are presented.

Barbara L Beck^1,2, Joshua E Slade¹, and Huadong Zeng^1,2
1McKnight Brain Institute, University of Florida, Gainesville, FL, United States, ²National High Magnetic Field Laboratory, Tallahassee, FL, United States

PIN diodes are a basic component used in MRI coils to control decoupling circuits, allowing operation of either transmit-only or receive-only coils. A PIN diode driver is necessary to send out the appropriate forward bias current and reverse bias voltage for the diode to function properly. However, small animal MRI systems may not be configured with PIN diode drivers and commercial PIN drivers are very expensive. As an alternative, we have developed a low cost driver that can output the required forward bias current and reverse bias voltage to successfully drive multiple PIN diodes.

Dimitrios Sakellariou¹, Cedric Hugon¹, Angelo Guiga¹, Aubert Guy¹, Sandrine Cazaux¹, and Philippe Hardy^1
1CEA Saclay, Gif sur Yvette, Essonne, France

We introduce a cylindrical permanent magnet design that generates a homogeneous and strong magnetic field having an arbitrary inclination with respect to the axis of the cylinder. The analytical theory of 3 D magnetostatics has been applied to this problem, and a hybrid magnet structure has been designed. This structure contains two magnets producing a longitudinal and transverse component for the magnetic field, whose amplitudes and homogeneities can be fully controlled by design. A simple prototype has been constructed using inexpensive small cube magnets, and its magnetic field has been mapped using Hall and NMR probe sensors. This magnet can, in principle, be used for magic angle field spinning NMR and MRI experiments allowing for metabolic chemical shift profiling in small living animals.

Ran Zhang¹, Feng Liu², Xiuhe Wang¹, and Stuart Crozier^2
1School of Electrical Engineering, Shandong University, Jinan, Shandong, China, People's Republic of, ²School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, Queensland, Australia

The design and optimization of quench protection circuit for magnetic resonance imaging (MRI) superconducting magnets require extensive and accurate information about quench behaviors under the action of different quench protection systems. Conventional quench simulation with analytical approach has difficulty in dealing with nonlinear problems. In this study, a commercial three dimension FEM software OPERA-3D/QUENCH is employed to address the quench characteristics of actual 1T clinical MRI magnets with both symmetric and asymmetric configurations. Passive and active protection systems are involved to identify the influence of different protection circuit on the quench performances. The modeling process and setup for the solving are discussed in detail. Critical safety-related quantities such as maximum temperature, current and voltage of superconducting coils and the variation of fringe field during the transition are provided comparatively. By comparing the correspondent simulation results, it is concluded that the one type of quench protection system is not applicable for all the superconducting magnets and the selection of quench protection circuit demands considerable investigation.

Gareth Reynold Davies¹, Kerrin James Pine¹, David John Lurie¹, and Fred Goldie^2
1Bio-medical Physics, University of Aberdeen, Aberdeen, Aberdeenshire, United Kingdom, ²Tesla Engineering Ltd., Storrington, United Kingdom

We are studying the unique contrast that is available from the variation of proton relaxation in different magetic field strengths. This is accessable through the use of fast field cycling magnet systems which can switch form zero field to 0.5 T, and anywhere in between, in 15 ms.

Kerrin James Pine¹, Fred Goldie², and David John Lurie^1
1Aberdeen Biomedical Imaging Centre, University of Aberdeen, Aberdeen, Scotland, United Kingdom, ²Tesla Engineering Ltd, Storrington, West Sussex, United Kingdom

Relaxometric properties of tissue vary greatly depending on the field strength at which they are measured. This is endogenous information not available from conventional imagers with fixed magnetic field strengths. One appealing approach is the "insert coil": a compact, portable addition to a conventional imager which can offset the main magnetic field B₀ over a volume of interest. We describe the parameters of such a coil and its integration with a body-sized system. The coil is used in conjunction with a volume-localised inversion-recovery pulse sequence to plot T₁dispersion in a human volunteer’s fingers over a range of field strengths.

William Bradfield Handler¹, Brian Dalrymple¹, Craig K Goodrich², Dennis L Parker², Timothy John Scholl^3,4, Frank Van Sas¹, and Blaine Alexander Chronik^1
1Physics & Astronomy, University of Western Ontario, London, Ontario, Canada, ²University of Utah, U.C.A.I.R., Salt Lake City, Utah, United States, ³Robarts Research Institute, Imaging Research Laboratories, London, Ontario, Canada, ⁴Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada

Innovations in gradient coil construction techniques, both mechanical and computational will be presented with an example which is a head gradient coil built for UCAIR, Salt Lake City.

Wesley M Skeffington¹, Franco M Martinez-Seantiesteban², Bruce D Collick³, Andrew Alejski², Brian K Rutt⁴, Luis J Garces¹, and Paul M Szczesny^1
1GE Global Research, Niskayuna, NY, United States, ²Robarts Research Institute, University of Western Ontario, London, Ontario, Canada, ³GE Healthcare, Waukesha, WI, United States,⁴Radiology Department, Stanford University, Stanford, CA, United States

Insert or specialty gradient coils enhance the capabilities of whole-body MRI systems. Use of the system’s gradient amplifiers without modification on insert coils can result in poor waveform fidelity, leading to reduced image quality. A method for using direct impedance measurements of a gradient coil to program a digitally controlled amplifier for operating on both whole-body and specialty gradient coils is presented. Use of the measured coil model resulted in a 93% reduction in coil current error and improved image quality.

Peter T. While¹, Michael Poole², Hector Sanchez Lopez², Larry K. Forbes¹, and Stuart Crozier^2
1School of Mathematics and Physics, University of Tasmania, Hobart, TAS, Australia, ²ITEE, University of Queensland, Brisbane, QLD, Australia

Excessive heating is a considerable problem in gradient coil operation. An improved analytical model is presented for simulating the spatial steady-state temperature distribution for cylindrical gradient coils. The model includes resistive power deposition by current density, thermal conduction through a number of cylindrical layers and radial cooling via convection and radiation. Simulations are shown to compare well to experimentally measured temperature distributions for two coils of inherently different winding structure. Additionally, rise-times to reach thermal equilibrium are predicted. Many coil parameters and thermal material properties may be varied and the model provides a good utility prior to manufacture.

Sebastian Littin¹, Anna Masako Welz¹, Daniel Gallichan¹, Gerrit Schultz¹, Christian Cocosco¹, Jürgen Hennig¹, Willem de Boer², and Maxim Zaitsev^1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Institute of Experimental nuclear Physics, KIT, Karlsruhe, Germany

We present a concept study of a planar gradient system for MR imaging with non-linear gradients, similar to the previously developed PatLoc system. This planar gradient system consists of 3 independent gradient channels with force and torque balance and will be integrated in our modified whole-body scanner equipped with 6 gradient channels. Simulations of the gradient system and image-reconstruction have been performed, showing that the coil achieves extended FOV for 2D imaging by combining three of its channels. Availability of such a gradient system will open new perspectives for flexible region-specific encoding in different body regions.

Daniel Truhn¹, Fabian Kiessling¹, and Volkmar Schulz^1,2
1Institute of Experimental and Molecular Imaging, RWTH Aachen, Aachen, NRW, Germany, ²Philips Research Europe, Aachen, Germany

We demonstrate that a multiple shell setup exhibits favourable advantages over a single shell shielding enclosure in the context of simultaneous PET/MR imaging. It is shown that effects on the MR gradient fields can be reduced without compromising the shielding at high frequencies.

Chad Tyler Harris¹, William B Handler¹, Jamu K Alford², and Blaine A Chronik^1
1Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, ²Martinos Center for Biomedical Imaging, Massachusetts General Hospital/Harvard Radiology, Boston, MA, United States

Delta relaxation enhanced magnetic resonance (dreMR) is a new technology, which allows the specific detection of targeted agents only after they have chemically bound to their target molecule. This method utilizes an electromagnet insert coil in order to alter the main magnetic field as a function of time in an otherwise standard MR scanner. Previously, we have developed dreMR insert coils specifically for small animal imaging. In this study, we present a practical, actively shielded, dreMR coil insert design suitable for imaging of the human head.

Andreas Bungert^1,2, Christopher Chambers¹, and John Evans^1
1Cubric, School of Psychology, Cardiff University, Cardiff, Cardiff, United Kingdom, ²Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

In concurrent TMS/fMRI, susceptiblity effects of the mostly diamagnetic TMS-coil cause field inhomogneities and image artefacts. We demonstrate that these artefacts can be reduced using stainless steel attached to the TMS coil for passive shimming. An MR-compatible figure-of-8 TMS coil was used and the steel was distributed on the back of the coil, approximately along the wire. Field maps of the effects of the coil with and without the shim on B₀ were acquired. Also the artefacts in EP-images were studied in a phantom and a human. The shim reduced field inhomogeneities by 50-70% and improved the EP-images significantly.

David Otto Brunner¹, Christoph Barmet¹, Maximilian Haeberlin¹, Bertram Jacob Wilm¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Monitoring of gradient waveforms significantly enhances the quality of reconstructed MR images especially in case of fast read-out schemes. For this the geometrical positions of the sensors have to be calibrated, which is typically done in a dedicated preparation. This becomes unmanageable if the probe positions are changing during scanning. Here we propose a novel approach that uses small signal tones on the gradients occupying portions of the FM spectrum that are otherwise unused in order to autocalibrate the monitoring setup during acquisition. These tones have marginal influence on the trajectory and no impact on the sequence.

Benjamin Emanuel Dietrich¹, Christoph Barmet¹, David Brunner¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Zurich, Switzerland

In current magnetic field monitoring systems acquisition duration is limited by the dephasing of the NMR field probes either by T2 decay, internal field variation or externally induced fields. Thus prohibiting field monitoring of scans with strong dephasing gradients (as applied in diffusion MRI) or long coherence trains (such as balanced SSFP). To alleviate these problems very short coherence times (T2,T1~ms) can be chosen. A new method based on short lived T/R-NMR probes enables real-time, continuous field monitoring. This is achieved by an interleaved excitation of sets of probes and rapid T/R switching.

Ariane Fillmer¹, Johanna Vannesjö¹, Christoph Barmet¹, Peter Boesiger¹, Klaas P. Pruessmann¹, and Anke Henning^1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

We present a fast iterative pre-emphasis calibration approach applied to a 3rd order DSU system, using spatio-temporal field monitoring to determine the ideal pre-emphasis settings. The major advantage of this technique compared to FASTERMAP based approaches is the higher time resolution and the significantly decreased expenditure of time.

Anna Masako Welz¹, Daniel Gallichan¹, Andrew J Dewdney², Walter R Witschey¹, Christian A Cocosco¹, Hans Weber¹, Jürgen Hennig¹, Jan G Korvink^3,4, and Maxim Zaitsev^1
1University Medical Center Freiburg, Department of Radiology, Medical Physics, Freiburg, Baden-Württemberg, Germany, ²Siemens Medical Solutions, Erlangen, Germany, ³Dept. of Microsystems Engineering – IMTEK, University of Freiburg, Freiburg, Germany, ⁴Freiburg Institute of Advanced Studies (FRIAS), University Freiburg, Freiburg, Germany

PatLoc imaging with non-linear quadrupolar gradients has been developed and realised for rapid MR imaging. This gradient coil is driven within a clinical 3T scanner with 6 gradient channels for simultaneous use of the linear and PatLoc gradients. For rapid imaging the gradient coil performance and accuracy is especially important. This abstract describes the measurement procedure and the compensation of eddy currents from around 300Hz to 30Hz, which improves image quality significantly.

Glen Morrell¹, Joshua Kaggie², K. C. Goodrich², Seong-Eun Kim², Sung Man Moon², and Dennis Parker^2
1Radiology, University of Utah, Salt Lake City, Utah, United States, ²Utah Center for Advanced Imaging Research, Salt Lake City, Utah, United States

We demonstrate a method of mapping the field patterns of insert gradient coils in a composite gradient system. Composite gradient systems allow the simultaneous use of whole body gradient coils and localized insert gradient coils within the same pulse sequence. These systems combine the speed of nonlinear local insert gradient coils for readout with the desirable linearity of slower whole body gradients for slice selection. Correction of image distortion requires accurate maps of the nonlinear insert gradient fields used for readout. Our method provides distortion-free maps of the gradient insert fields over the entire imaging volume in reasonable imaging time

Vivek R Bhatia¹, and Luis Hernandez-Garcia^1
1Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States

We present a new measurement for oscillating magnetic fields in the KHz frequency range using magnetic resonance imaging. The method uses non-linear iterative minimization techniques to estimate the field map. We deomnstrate our technique by simulations and in vitro experiments.

Frederik Testud¹, Christoph Barmet², Martin Haas¹, Denis Kokorin¹, Juergen Hennig¹, Klaas P. Pruessmann², and Maxim Zaitsev^1
1Medical Physics, Dept. of Radiology, University Medical Center Freiburg, Freiburg, Germany, ²ETH and University, Zurich, Institute for Biomedical Engineering, Zurich, Switzerland

Field probes have been used in the last years for dynamic magnetic field monitoring in order to reduce image artifacts by using the measured field dynamics in the reconstruction. Parallel spatially selective Excitation allows inner volume imaging where only specifically regions of interest are excited. This relies on exact matching of multidimensional RF pulses and the simultaneously traversed k-space trajectory. Four ¹H field probes were used for calibrating k-space trajectories used during transmit. The measured trajectories were then used to calculate RF pulses which were then applied to excite target patterns.

Emre Kopanoglu^1,2, Burak Akin¹, Vakur B. Erturk², and Ergin Atalar^1,2
1National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey, ²Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey

Slice-profile is related to the frequency-spectrum of an RF envelope through the gradient field, which is conventionally linear. Although a rectangular pulse is more efficient as far as SAR is concerned, apodized sinc envelopes are widely used for excitation because the slice-profile of a rectangular pulse is not desirable. In this study, a method that employs non-linear gradients to modify the slice-profile of a rectangular pulse into a feasible one is proposed. As a sample study, the method is compared to an apodized sinc envelope, and showed 41% reduction in SAR as well as an increase in correct excitation in the region of interest from 71% to 94%.