Electronic Posters : Engineering
Click on to view the abstract pdf and click on to view the video presentation.
Transmit Arrays: Coil Design

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 70

14:00 3827.   8-Channel Transmit Body Array for Homogeneous Excitation of the Thorax at 3T 
Yeun Chul Ryu1, Sukhoon Oh1, Christopher T Sica1, Chien-ping Kao1, Yong-Gwon Kim2, and Christopher M Collins1
1Radiology, The Pennsylvania State University, Hershey, Pennsylvania, United States, 2Radiological Science, College of Medical Science, Konyang University, Daejeon, Korea, Republic of

For experiments with transmit arrays in combination with existing receive-only arrays and without significant modification of an MR system that requires use for multiple purposes, we explore the use of a transmit array where all elements are in the region of the clear bore above the patient bed. Even with this severe constraint, using RF shimming at 3T it is possible to get much better homogeneity in the thorax than with a quadrature birdcage coil, and possible to achieve homogeneities approaching that with an array having elements spaced equidistantly around the entire bore.

14:30 3828.   Design and Application of 5 Channel Tx/Rx Coil for High Spatial Resolution Laryngeal MRI at 7 Tesla 
Jan Rieger1, Christof Thalhammer1, Wolfgang Renz1,2, Tobias Frauenrath1, Lukas Winter1, Andreas Goemmel3, and Thoralf Niendorf1,4
1Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine, Berlin, Germany, 2Siemens Medical Solutions, Erlangen, Germany, 3Chair of Structural Statistics and Dynamics, RWTH, Aachen, Germany, 4Experimental and Clinical Research Center (ECRC), Charité Campus Buch, Humboldt-University, Berlin, Germany

MRI of larynx is a clinically relevant topic for assessment of tumor progression and evaluation of processes in human phonation. Dedicated 5 channel transmit/receive coil was proposed, simulated and designed to address the challenges of laryngeal MRI at 7 T. The coil was tested on volunteers and found out to exhibit an SNR advantage that allowed acquisition of images with sub-millimetre spatial resolution ( 0.25x0.25x0.2 mm3). We anticipate using this setup in further studies to gather reference data to be used in a finite-element model of phonation functions as well as in clinical research to study laryngeal tumors.

15:00 3829.   Improved B1+ field using a 16-channel Transmit Head Array and an 8-channel pTx System at 7T 
Kyoung Nam Kim1, Niravkumar Darji2, Tim Herrmann1, Johannes Mallow1, Zang-He Cho3, Oliver Speck2, and Johannes Bernarding1
1Department of Biometry and Medical Informatics, OvG University Magdeburg, Magdeburg, Saxony-Anhalt, Germany, 2Chair of Biomedical Magnetic Resonance, OvG University Magdeburg, Magdeburg, Saxony-Anhalt, Germany, 3Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea, Republic of

At 7T, parallel transmission (pTx) systems provide still significant challenges for the design and implementation of RF-coils for dedicated transmit channels and their integration into existing pTx systems. This work was focused on the construction of a 16-channel head-array for available combined 8-channel and individual 16-channel transmission systems, resulting in a RF-coil with a total of 8-channel pTx system. Flip angle (FA) maps of an oil and water phantom were acquired using this prototype. For 16 individual FA maps for odd-even channels and 8 combined FA maps of 16-channel head-array were compared with RAPID Biomedical 8-ch. Tx/Rx head-array at 7T.

15:30 3830.   A Fully Tested Head Coil for 7T Compatible with a Dome Gradient Set 
Daniel James Lee1, Arthur W Magill2,3, and Paul M Glover1
1Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom, 2LIFMET, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 3Radiology, University of Lausanne, Lausanne, Switzerland

A new head coil for 7T imaging has been designed, built and tested. This coil is designed to fit within dome shaped gradients (which allow stronger gradients to be applied) and to generate less SAR in the shoulders. SAR simulations, B1 maps and images are presented which validate this coil design.

Tuesday May 10th
  13:30 - 15:30 Computer 70

13:30 3831.   The inductively decoupled transceiver array: simulations and performance at 7T 
Jullie W Pan1, Nikolai Avdievich1, Tamer S Ibrahim2, and Hoby P Hetherington1
1Neurosurgery, Yale University School of Medicine, New Haven, CT, United States, 2Bioengineering, University of Pittsburgh, United States

The transceiver array has been shown to achieve excellent homogeneity and B1 amplitude at ultra-high field for head studies. However, as a set of decoupled surface coil elements there has been uncertainty as to its performance consistency. Under in vivo conditions, the largest variable between volunteers is the distance between the element(s) and head, with both coil loading and decoupling affected by this gap. We simulate this effect on variable loading and decoupling at 7T and compare it to experimental data.

14:00 3832.   An Easily Integrated Eight Channel Parallel Transmit System for Transmit SENSE Applications 
Neal Anthony Hollingsworth1, Katherine Lynn Moody2, Jon-Fredrik Nielsen3, Douglas C. Noll3, Mary Preston McDougall1,2, and Steve M. Wright1,2
1Electrical and Computer Engineering, Texas A&M University, College Station, TX, United States, 2Biomedical Engineering, Texas A&M University, 3Biomedical Engineering, University of Michigan

Development of complex RF pulses has driven interest in parallel transmit techniques(e.g. Transmit SENSE). These have, in turn, driven the development of multichannel transmit systems. We have constructed an eight channel parallel transmit system that can be easily integrated with an existing MR system. Each channel has independent amplitude and phase control and uses an RF current source as the output stage. By using this in conjunction with a series resonated loop array coil for transmit we have obtained good inter element coil isolation. This has allowed for the synthesis of a uniform excitation pattern.

14:30 3833.   Versatile Volume Coil Implementation Using a Constellation Coil 
Yudong Zhu1, Ryan Brown1, Cem Murat Deniz1, Bei Zhang1, Leeor Alon1, Graham Wiggins1, Hans-Peter Fautz2, Bernd Stoeckel3, and Daniel K Sodickson1
1Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, United States, 2Siemens Medical Solutions, Erlangen, Germany,3Siemens Medical Solutions USA Inc, New York, NY, United States

A constellation coil uses a continuous RF structure and distributed ports to support generally sophisticated current patterns responsible for the ultimate spin excitation and signal detection performance allowed by electrodynamics. Given its inherent simplicity and versatility, one implementation meaningful in certain applications or MR systems is to use constellation coil in place of a conventional volume transmit coil, creating a customizable configuration where, in emulation mode, the coil uses a single Tx channel and emulates the conventional volume coil, and, in parallel mode, the coil conducts parallel Tx / Rx. This study investigated the feasibility of such an implementation.

15:00 3834.   Plug and play multi transmit head coil with integrated receiver arrays for clinical 7T MRI. 
Hans Hoogduin1, Ingmar Voogt2, Giel Mens3, Hugo Kroeze2, Peter Luijten2, and Dennis Klomp4
1University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, 2University Medical Center Utrecht, 3Philips Medical Systems, 4University Medical Center Utrecht, Utrecht, Netherlands

Multi transmit features control of SAR and B1, while multi receive can provide optimal SNR and acceleration. When these are merged into transceivers, compromises in image quality can be substantial. We therefore propose the use of an enlarged separate transmit array that fits an optimized receiver array for MRI of the human brain at 7T. Using pick-up probes integrated to the MR system, full control of the RF coupled coil is feasible while calibration procedures take less than 5 minutes. We therefore think that this setup will bring 7T MRI closer to clinical practice.

Wednesday May 11th
  13:30 - 15:30 Computer 70

13:30 3835.   Investigation of 7 Tesla Spine MRI with a 5-Channel Stripline Array and an 8-Channel Loop Array 
Oliver Kraff1,2, Stephan Orzada1,2, Philipp Dammann1,3, Marc Schlamann1,2, Mark E Ladd1,2, Harald H Quick1,4, and Andreas K Bitz1,2
1Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany, 2Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany, 3Clinic for Neurosurgery, University Hospital Essen, Essen, Germany, 4Institute of Medical Physics, Friedrich-Alexander-University Erlangen-Nuernberg, Erlangen, Germany

The feasibility of 7 Tesla MRI of the human spine has recently been demonstrated. However, for a clinical assessment, RF coils need further optimization. In this study, two established transmit/receive RF coil concepts were investigated: a 5-channel stripline array and an 8-channel loop array. Additionally, a combination of these two arrays with separated transmit and receive channels was assessed. Coil characterization was performed in vivo, in phantom measurements as well as using numerical simulations. This study may serve as a basis for further optimization of RF coils for MRI of the human spine at 7 Tesla.

14:00 3836.   Actively Detunable 8-channel Small Animal Transceive Volume Array for 9.4T MRI systems 
Ewald Weber1, Yu Li1, BingKeong Li1, Feng Liu1, and Stuart Crozier1
1School of ITEE, The University of Queensland, Brisbane, QLD, Australia

In this work we discuss the development of a 9.4T, 8-channel actively detunable small animal transceive volume array, capable of operating in transmit and/or receive mode. All individual coil elements are actively detunable for operation with independent receiver coils. A prototype was constructed and tested in a Bruker 9.4T Biospec MRI system. Experimental results presented herein demonstrate the potential of the design.

14:30 3837.   B1-control Loop Array for Reduction of B1 Inhomogeneity 
Yukio Kaneko1, Hideta Habara1, Yoshihisa Soutome1, Hisaaki Ochi1, and Yoshitaka Bito1
1Central Research Laboratory, Hitachi Ltd., Kokubunji-shi, Tokyo, Japan

We have proposed a new method of B1 homogenization: using a B1-control loop array combined with RF shimming. The loop, which has sufficiently lower resonance frequency than the transmit RF frequency, exhibits inductive characteristics. The inductive loop can change the magnetic flux because of an electrical counter current flow. The spatial distribution of the flux density around the loop has a potential to compensate the B1 inhomogeneity. Both FDTD simulation and experiments were conducted, and we found that the B1-control loop array, used with RF shimming, was more effective in reducing B1 inhomogeneity than RF shimming alone.

15:00 3838.   A 3T linear phase volume excitation coil 
Rock Hadley1, Dennis Parker1, and Glen Morrell1
1Radiology - UCAIR, University of Utah, Salt Lake City, Utah, United States

This work uses lumped element distributed capacitors to increase the electrical line length of non-resonant microstrip transmission lines. These line elements are combined to form an 8-element circular array volume coil with circularly polarized central magnetic field. Because of the phase change down the length of each element, a linear phase rotation occurs along the central axis of the volume coil making it ideally suited for parallel transmission, SAR reduction, and gradient-less imaging applications. Increasing the electrical line length of these devices using distributed capacitors enables these devices to become useful for 3T imaging.

Thursday May 12th
  13:30 - 15:30 Computer 70

13:30 3839.   Combinations of Weighted First and Second-order Clockwise CP Modes To Improve Image Homogeneity with a 16-Channel Head Array at 7 Tesla 
Kyoung Nam Kim1, Tim Herrmann1, Johannes Mallow1, Zang-He Cho2, and Johannes Bernarding1
1Department of Biometry and Medical Informatics, OvG University Magdeburg, Magdeburg, Saxony-Anhalt, Germany, 2Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea, Republic of

Inhomogeneous B1+ fields are still challenging at 7T. To evaluate new approaches to reduce B1+ inhomogeneity a 16-channel transmit head-array was constructed and connected to a 16x16 and an 8x8 Butler Matrix network by a pTx system with 8 RFPA for excitation. This served for sequential excitation of different circularly polarized (CP) phase modes. The CP+1 (first-order clockwise CP) as the dominant mode proved to be the most important mode to get a homogeneous image. Weighted combinations of CP+1 mode and selected clockwise higher CP modes images were found to additionally mitigate B1+ field inhomogeneity.

14:00 3840.   Constellation Coil Design 
Yudong Zhu1, Bei Zhang1, Ryan Brown1, Cem Murat Deniz1, Leeor Alon1, Hans-Peter Fautz2, and Daniel K Sodickson1
1Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, United States, 2Siemens Medical Solutions, Erlangen, Germany

The essence of RF system performance optimization can be described as one of maximizing |B1|/|E|. Further, the RF current carried by the coil structure is the means by which an MR scanner implements and optimizes RF fields. Constellation coil, a new approach to RF coils, targets a supportive structure for ideal RF current patterns and thereby the ultimate performance. The approach’s support for highly parallel Tx/Rx can also play a central role in overall scan performance enhancement. This study explores constellation coil designs. Full wave simulations as well as parallel Tx and Rx MR experiments were used to evaluate prototypes.

14:30 3841.   Self-decoupling elements of 8-channel 7T head antenna 
Hideta Habara1, Yoshitaka Bito1, Hisaaki Ochi1, Yoshihisa Soutome1, Yukio Kaneko1, Masayoshi Dohata1,2, Hiroyuki Takeuchi2, and Tetsuhiko Takahashi2
1Central Research Lab., Hitachi Ltd., Kokubunji, Tokyo, Japan, 2Hitachi Medical Corporation, Kashiwa, Chiba, Japan

Multichannel transmit antennas are important for higher field MRI because the RF shimming and transmit sense methods are very effective for correcting B1 inhomogeneity. However, decoupling of the multichannel antenna to the neighborhood channels is difficult. To overcome this problem, we propose to replace linear conductive elements with meandering or snaking ones. An 8-channel 7T head antenna was modeled and the S-parameters and B1+ map were calculated using electromagnetic field simulation. An ordinary microstrip line antenna was also modeled for comparison. The S12 parameter of the snaking elements achieved -12 dB without any decoupling capacitor.

15:00 3842.   Modelling Study of a Hybrid Loop-Sheet Coil Structure for a 8-channel Small Animal Transceive Array at 9.4T 
Yu Li1, Feng Liu1, Jin Jin1, Ewald Weber1, BingKeong Li1, and Stuart Crozier1
1School of ITEE, The University of Queensland, Brisbane, QLD, Australia

Conventionally, loop coils are used for the construction of small animal transceive arrays. However, as the number of coil elements increases the size of each coil has to be reduced, since the available space is generally restricted, to comply with MRI-system specifications. As a result the RF penetration depth will be compromised. In this work, a 9.4T shielded 8-channel hybrid loop-sheet coil transceive array for small animal MRI is proposed to overcome the low RF penetration depth issue.

Electronic Posters : Engineering
Click on to view the abstract pdf and click on to view the video presentation.
Multichannel Transmit Monitoring & Simulation
Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 71

14:00 3843.   A Robust Concept for Real-Time SAR Calculation in Parallel Transmission 
Hanno Homann1, Peter Börnert2, Olaf Dössel1, and Ingmar Graesslin2
1Institute of Biomedical Engineering, Karlsruhe Institute of Technology, Karlsruhe, Germany, 2Philips Research Europe, Hamburg, Germany

The specific absorption rate (SAR) depends on the individual patient anatomy. Hence, it is required to calculate the SAR for different body models to obtain a robust estimation of the worst-case SAR. In parallel transmit MRI, the SAR also depends on the multi-channel RF waveform such that real-time calculations of the SAR are required. In this study, a fast method for local SAR estimation in multiple body models is proposed. In this approach, the calculation time is almost independent of the number of models used. This allows using a high number of different models for robust SAR estimation.

14:30 3844.   Ultra-Fast Calculation of SAR-induced Temperature Increase 
Giuseppe Carluccio1, Sukhoon Oh2, and Christopher Michael Collins2
1Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, Illinois, United States, 2Radiology & Bioengineering, Pennsylvania State University at Hershey, Hershey, Pennsylvania, United States

We developed a method to drastically reduce computation time for solving the Pennes’ Bioheat equation, the most common equation used to estimate temperature in tissues due to SAR absorption. Given the geometry of the body and the SAR spatial distribution, the algorithm sequentially applies a digital filter to the solution of the Bioheat equation with the thermal conductivity neglected. The role of the filter is to estimate the effect of thermal conduction. Compared to temperature calculation methods based on FDTD methods, the algorithm can provide reasonably accurate results in a time about 60 times shorter.

15:00 3845.   Simulation Tool for 3T/7T Subject-Specific Multi-Transmission Applications without RF Measurements 
Tamer S Ibrahim1, Lin Tang2, and Yik-Kiong Hue3
1University of Pittsburgh, Pittsburgh, PA, United States, 2University of Oklahoma, 3University of Pittsburgh

This work presents a modeling mechanism that can accurately perform subject-specific B1 shimming and account for local/global SARs (without performing RF field measurements.) This model is capable of 1) maximizing the intensity of the B1+ field in an ROI, 2) homogenizing the distribution of the B1+ field in an ROI, 3) minimizing the average SAR over the whole load, and 4) minimizing the local SAR over the whole load. The technique was successfully tested on 3T and 7T whole-body systems equipped with multi-Tx array excitation systems and using both coupled and decoupled transmit arrays.

15:30 3846.   Patient Adapted SAR Calculation on a Parallel Transmission System 
Ingmar Graesslin1, Hanno Homann2, Sven Biederer3, Peter Börnert1, Giel Mens4, and Paul Harvey4
1Philips Research Laboratories, Hamburg, Germany, 2Institute of Biomedical Engineering, Karlsruhe Institute of Technology, Germany, 3Institute of Medical Engineering, University of Lübeck, Lübeck, Germany, 4Philips Healthcare, Best, Netherlands

Real-time SAR estimation is essential for efficient in vivo applications in parallel transmit MRI. In this work, a safety concept comprising two scan modes was implemented on an eight-channel 3T MRI system. In the first mode, a worst case SAR model is applied, representing multiple patient anatomies and body positions. Based on patient-specific information from the host of the scanner and a survey scan, a patient-adapted SAR model is selected. In the second mode, the selected SAR model is applied for improved SAR prediction accuracy. This mode facilitates increased scan efficiency of the parallel transmit MR system.

Tuesday May 10th
  13:30 - 15:30 Computer 71

13:30 3847.   Simple Approaches to Current Control for Transmit Array Elements at 7 Tesla 
Steven M Wright1,2, Mary Preston McDougall1,2, Ivan Dimitrov3, Sergey Cheshkov3, and Craig Malloy3
1Electrical Engineering, Texas A&M University, College Station, TX, United States, 2Biomedical Engineering, Texas A&M University, College Station, TX, United States,3University of Texas Southwestern Medical Center, Dallas, TX, United States

This abstract examines some very simple approaches for controlling current and/or phase on multiple element arrays using a single transmit channel. For decoupled elements, conventional power splitters and phase shifters can be easily constructed from passive components to give adjustable phase control. This is demonstrated with a completely printed two-element array. For coupled elements, forced current excitation can be used to enforce either in-phase or out-of-phase currents with reasonable insensitivity to coil configuration and coupling. This is demonstrated by using a three-element, co-axial array of strongly coupled loop elements to simulate a solenoid coil.

14:00 3848.   Threshold criteria for real time RF monitoring in 7T parallel transmit system 
Borjan Gagoski1, Himanshu Bhat2, Philipp Hoecht2, Khaldoun Makhoul3,4, Ulrich Fontius5, Josef Pfeuffer5, Franz Schmitt5, Michael Hamm2, Joonsung Lee1, Kawin Setsompop3,4, Lawrence L Wald3,6, and Elfar Adalsteinsson1,6
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Siemens Healthcare, Charlestown, MA, United States, 3A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 4Harvard Medical School, Boston, MA, United States, 5Siemens Healthcare, Erlangen, Germany, 6Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States

To guard against run-time deviations in parallel transmission RF waveforms that may result in violation of SAR limits, real-time RF waveform monitoring serves an important role. In this work we investigated subject-to-subject variation in excitation coil array monitoring parameters and use these findings to propose threshold criteria to detect a mismatch between ideal and observed RF signals. Calibration of the cut-off values needed in the threshold algorithm was done empirically by monitoring the RF signals in 15 in-vivo acqisitions. The performance of the proposed algorithm was then tested for different types of RF pulses in undisturbed and purposely disturbed acquisitions.

14:30 3849.   RF monitoring of the complex waveforms of an 8-channel multi-transmit system at 7T utilizing directional couplers and I/Q demodulators 
Irina Brote1,2, Klaus Solbach3, Stephan Orzada1,2, Oliver Kraff1,2, Stefan Maderwald1,2, Mark E. Ladd1,2, and Andreas K. Bitz1,2
1Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany, 2Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany, 3High Frequency Engineering, University Duisburg-Essen, Duisburg, Germany

RF real time monitoring is a major concern for multi-channel transmit systems. Here an approach is proposed which incorporates online monitoring of both the RF phase and amplitude by use of directional couplers and I/Q demodulators; the forward and reflected signals can be monitored. Furthermore, this set-up enables the direct assessment of the complex scattering matrix of the loaded coil array in just 10 s for an 8-channel system. The implemented monitoring system can be utilized for transmit SENSE applications to monitor the full waveform (phase and amplitude) of the multi-dimensional pulses.

15:00 3850.   Method for monitoring safety in parallel transmission systems based on channel-dependent average powers 
Nicolas Boulant1, Martijn Cloos1, Michel Luong2, Guillaume Ferrand2, Christopher Wiggins1, and Alexis Amadon1
1NeuroSpin, CEA Saclay, Saclay, France, 2Irfu, CEA Saclay, Saclay, France

We present a method for SAR monitoring based only on the average power for each channel of a Tx array. The corresponding SAR estimation still is conservative in the sense that all phase information is ignored. Given the simplicity of the technique, it is readily implementable on a lot of systems and does not require real-time amplitude monitoring of the RF waveform. It is shown that the cost in SAR using that technique is mild compared to the SAR result that would be obtained if the true RF amplitude waveforms were taken into account.

Wednesday May 11th
  13:30 - 15:30 Computer 71

13:30 3851.   Tailoring RF Power Distribution for Body Torso MRI at 300MHz 
Jinfeng Tian1, Anand Gopinath2, and J. T Vaughan2
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, 2University of Minnesota

Simulation and image experiments suggested low |B1+|/Power in 7T body-torso imaging, partly due to radiation and undesired power losses in the rest of the body. Three dielectric methods were proposed based on the electromagnetic wave incidence theory, and verified with Finite-Difference-Time-Domain simulation, with a 16-channel body-size TEM array. λ/4 or thin dielectric pads with proper εr substantially improved the |B1+|/Power by reducing RF reflection or/and destructive phase interferences. Thin layers of dielectric boards increased the body torso power deposition percentage to 93% from the original 36.91%. Combining the boards with the pads, the mean |B1+| in the heart jumped from 0.032µT to 0.1128uT or above.

14:00 3852.   B1-based local SAR estimation for a parallel transmit system at 3T: A simulation study 
Stefanie Buchenau1, Martin Haas1, Daniel Nicolas Splitthoff1, Juergen Hennig1, and Maxim Zaitsev1
1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany

The main challenge of estimating specific absorption rate via post-processing of measured B1maps is to find good assumptions on the not directly measurable components of the magnetic field and to correct for the influences by an additional phase resulting from the receive process that can physically not be separated from the transmit phase. Within this study an extension of this method is proposed that takes advantage of the multiplicity of B1maps measured with a multi-transmit array designed for parallel transmission experiments at 3T. Sufficiently good reconstruction of SAR distributions is demonstrated.

14:30 3853.   Feasibility of a local SAR monitoring for a 7 T body transmit array with single element power monitoring 
Ozlem Ipek1, Alexander J.E. Raaijmakers1, Dennis W.J. Klomp2, Alessandro Sbrizzi1, Peter R Luijten2, Jan J.W. Lagendijk1, and Cornelis A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands

7 T prostate imaging with a radiative antenna (single-side adapted dipole antenna) surface array was simulated with FDTD to investigate the worst-case local SAR compared to the SAR distribution of each individually simulated element. Worst- case SAR is calculated from sum of magnitudes of E fields of individually driven elements of the array. There is a correlation between the SAR hotspots for the single element and a worst case combination of all elements: 1) the location is identical 2) the single element values correlate with worst case combination but a maximum under estimation of 80% is possible.

15:00 3854.   Volumetric Local SAR Mapping for Parallel Transmission 
Leeor Alon1, Cem Murat Deniz1, Jian Xu2,3, Ryan Brown1, Daniel K Sodickson1, and Yudong Zhu1
1Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, United States, 2Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, United States, 3Siemens Medical Solutions, Malvern, PA, United States

In this work, we present a custom automated pulse sequence that volumetrically maps local SAR for parallel transmit systems with minimal manual intervention. This sequence combines MR thermometry and RF heating to determine the local electric field covariance matrix〖 Λ〗_r and thereby to calibrate a robust local SAR model. Once the model is calibrated, SAR maps specific to the particular geometry of the coil array and content of the imaged body can be obtained for any pulse shape/RF shimming combination. This sequence is particularly useful for assessing local SAR in phantoms for parallel transmission arrays and matching results with simulations.

Thursday May 12th
  13:30 - 15:30 Computer 71

13:30 3855.   Fast patient specific estimation of electric fields for a transmit array from B1+ measurements 
Alessandro Sbrizzi1, Hans Hoogduin1, Gerard L.G. Sleijpen2, Jan J. Lagendijk1, Peter Luijten1, and Cornelis A.T. van den Berg1
1Imaging Division, UMC Utrecht, Utrecht, Netherlands, 2Department of Mathematics, Utrecht University, Utrecht, Netherlands

An outstanding challenge of parallel transmission is to obtain patient specific information about the electric fields. In this work we describe how information about the electric fields in a body can be gained from standard transverse B1+ magnitude measurements. The novel method exploits the close relationship between electric and B1+ fields when they are expressed in terms of a Bessel/Fourier expansion. This approach allows a patient specific estimation of the electric fields and, in addition, requires only some seconds of computation time. The novel method is validated by means of FDTD simulations and in vivo measurement.

14:00 3856.   A fast algorithm to optimize transmit efficiency for local excitation with a transmit array 
Giuseppe Carluccio1, Christopher Michael Collins2, and Danilo Erricolo1
1Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, Illinois, United States, 2Radiology & Bioengineering, Pennsylvania State University at Hershey, Hershey, Pennsylvania, United States

We present a fast algorithm to optimize the transmitted field in a localized region with a transmit array at high B1+ field strengths. With knowledge of the B1 field distribution generated by each single coil of the array, we suggest a fast way to set the phase of each coil current to provide the maximum constructive interference in a localized region, and the amplitude of each coil current to increase the magnitude of the B1+ field and to minimize the power generated by the array.

14:30 3857.   SAR consequences of optimization strategy for a 7T RF transmit loop array in CP mode 
Mikhail Kozlov1, and Robert Turner1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony, Germany

We numerically investigated SAR consequences of optimization strategy for a 7T RF transmit loop array in CP mode. If the non-conservative RF electric field is generally dominant, even a significant variation of the array’s current distribution due to changes in array geometry and different tuning/matching/decoupling has a very weak influence on the ratio mean B1+ over the entire human brain to square root of maximum of 10 gram average SAR , although the SAR profile varies. As a result, the same MRI RF pulse sequence may produce nearly the same SAR10g for different loop arrays, as long as similar B1+ maps are generated.

15:00 3858.   A method for calibrating multi-channel RF systems 
Francesco Padormo1, Shaihan J Malik1, Giel Mens2, and Jo V Hajnal1
1Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, United Kingdom, 2Philips Healthcare, Best, Netherlands

There is growing interest in parallel transmit architectures and in the use of low cost systems that may display significant non-linearity in response. We describe a system level calibration approach that can generate a full set of calibration tables for multi-channel RF systems. The method is simple to set up and provides compensation for frequency drifts during the calibration process.

Electronic Posters : Engineering
Click on to view the abstract pdf and click on to view the video presentation.
RF Modeling

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 72

14:00 3859.   Fast Full Wave RF Simulation Scheme for MRI 
Tamer S Ibrahim1, and Gary Boerger2
1University of Pittsburgh, Pittsburgh, PA, United States, 2University of Oklahoma

Electromagnetic simulations in MRI can take significant calculation (CPU) time. Not only this can dampen the progress of evaluating the performance of the coil, it renders these methods impracticable for real time applications such as multi-transmission methods. This work aims at overcoming this obstacle through developing a stable and fast implicit finite difference time domain scheme that is suitable for MRI RF calculations. Very good correlation was attained for the B1+ field distribution obtained through calculations using standard FDTD and implicit FDTD methods, and through MRI experimental measurements.

14:30 3860.   Electro-Dynamic Inverse Method for High-Field RF Transmit Coil Design 
Shumin Wang1, Jeff Duyn2, and Alan Koretsky2
1NIH, Bethesda, Maryland, United States, 2NIH

Radio-frequency transmit coils need to produce homogeneous transverse magnetic fields. At low field strengths, this is typically accomplished by birdcage-like transmitters. At high field strengths, it is believed that due to destructive wave interferences, producing homogeneous fields by a single resonator is no longer possible. Here we present a general full-wave electro-dynamic approach that allows one to find the desired current distribution on any surfaces that generate homogeneous filed distributions on any specified locations inside a human-shaped phantom.

15:00 3861.   On The Consequences of Wrapping Patients with RF Shielding Materials 
Paul R. Harvey1, and Johan S. van den Brink1
1Philips Healthcare, Best, Netherlands

Electromagnetic field simulations have been used to evaluate the effect on SAR and RF power demand during normal RF exposure, using the system body coil, for a human body model partially wrapped with a carbon (graphite) sleeve intended to shield parts of the body against the applied RF field. The presence of an RF absorbing/shielding sleeve creates an additional load inside the body coil which causes re-distribution of the E-field and requires increased input power together resulting in elevated global and local SAR.

15:30 3862.   Investigation of RF penetration in humans at ultrahigh magnetic fields 
Yong Pang1, Daniel Vigneron1,2, and Xiaoliang Zhang1,2
1Radiology & Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, 2UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco & Berkeley, CA, United States

Radiofrequency penetration is not only determined by the coil itself, but also related to the electromagnetic properties (e.g. permittivity, conductivity) and geometry of imaging samples. In this work, the RF field penetration of surface coils in human liver and brain imaging at 7T is studied numerically. Due to conductivity effects in human liver and its irregular shape, RF penetration decreases while in the brain RF penetration increases due to “dielectric resonance” effect. Therefore, it is necessary to have larger size coils for liver than for brain to achieve the required penetration/coverage in ultrahigh field MRI.

Tuesday May 10th
  13:30 - 15:30 Computer 72

13:30 3863.   In-vivo Human Forearm Temperature Mapping for Correspondence with Numerical SAR and Temperature Calculations 
Sukhoon Oh1, Yeun Chul Ryu1, Andrew Webb2, and Christopher M Collins1
1Radiology, College of Medicine, The Pennsylvania State University, Hershey, PA, United States, 2Radiology, The Leiden University Medical Center, Netherlands

In this study, we report recent progress towards a validation of in-vivo temperature change (Capital Greek DeltaT) of a human forearm, since in-vivo Capital Greek DeltaT is greatly moderated by perfusion. We acquired MR Capital Greek DeltaT map, then built a FDTD model from anatomical images to simulate SAR. Finally, we calculate Capital Greek DeltaT from the simulated SAR to validate the experimental Capital Greek DeltaT. In the Capital Greek DeltaT calculation, we considered the perfusion rate as a function of temperature, temperature decrease during acquisition of the second gradient-echo image, and the tuning condition of the RF heating coil. Qualitatively, the simulated Capital Greek DeltaT distribution appears very similar to the experimental one.

14:00 3864.   A Detailed Quantitative Analysis of B1 Components at 1.5T and 3T 
Xin Chen1, and Michael Steckner1
1Toshiba Medical Research Institute USA, Inc., Mayfield Village, OH, United States

While SAR is crucial for the RF safety control of an MR scan, B1rms (root mean square of the total B1 field ) serves as a supplemental safety metric. For example, B1rms is useful for defining the MR conditional labeling of implants. An unloaded quadrature driven (QD) birdcage coil generates nearly perfect B1 with circular polarization: B1+ (the tipping component) is homogeneous and B1- (the component rotating counter to the spin precession) is zero and thus |B1-|<<|B1+| is usually assumed. Loading the coil distorts the B1 field, causing B1+ and B1- components. While only B1+ is useful for MRI purposes, both components contribute to RF power deposition. In this work we use FDTD (Finite Difference Time Domain) numerical simulations to demonstrate that B1- should not be ignored in loaded coils at either 1.5T or 3T.

14:30 3865.   A Comparison of FDTD-Solvers for Simulation of a 31P Birdcage Coil at 1.5 T 
Andre Kuehne1, Helmar Waiczies1,2, Sairamesh Raghuraman3, Tobias Wichmann4, Titus Lanz4, Frank Seifert1, and Bernd Ittermann1
1Physikalisch-Technische Bundesanstalt, Berlin, Germany, 2Experimental and Clinical Research Center (ECRC), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany, 3MRB Research Centre, Würzburg, Rimpar, Germany, 4Rapid Biomed, Rimpar, Germany

FDTD simulations are an important tool to calculate SAR values required for safe coil operation limits. After being presented with discrepancies between simulations using different software packages, the coil in question, a 31P birdcage coil, was simulated using three different FDTD programs (XFdtd, MWS, SEMCAD) and the results compared throughout the simulation volume. Possible sources of error, mainly different standards for scaling to different input power measures, are identified. When identical scaling standards are applied, the obtained results match very closely.

15:00 3866.   SAR comparison for infant due to different positioning within an MRI head coil 
Zhangwei Wang1, Owen Arthurs2, Desmond T.B. Yeo3, and Fraser Robb1
1GE Healthcare Coils, Aurora, OH, United States, 22University of Cambridge, Cambridgeshire, United Kingdom, 3GE Global Research, Niskayuna, NY, United States

Pediatric body MR imaging is limited by the lack of dedicated coils. Many infants are typically imaged using adult head or knee coils, but the SAR consequences are unknown. Compared to adults, infants have several unique physiological and physical characteristics that may influence the thermal risk during RF exposure. In this work, we use EM numerical modeling to evaluate the local SAR deposition in an infant body model irradiated imaged by an adult head coil. SAR comparisons are performed for the infant model with infant-specific versus adult-specific electrical properties, and placed at different landmark positions.

Wednesday May 11th
  13:30 - 15:30 Computer 72

13:30 3867.   Comparison of deviations in SAR prediction between highly detailed and proper simplified human models at 7T 
Sebastian Wolf1, and Oliver Speck1
1Dept. Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany

In this work, deviations in the SAR prediction caused by simplification of the model are compared to deviations between highly detailed models, which do or do not reflect the actual patient. It will be shown, that model simplifications such as reduced extension and reduction of tissue types that may allow the creation of human models, which are more similar to the actual subject are feasible.

14:00 3868.   Method and Tool for Improved, Rapid N-gram Average SAR Determination 
Sukhoon Oh1, Giuseppe Carluccio2, and Christopher M Collins1
1Radiology, College of Medicine, The Pennsylvania State University, Hershey, PA, United States, 2Department of Electrical and Computer, University of Illinois at Chicago, IL, United States

According to prescription (such as 10-gram SAR for comparison to IEC limits), it possibly results an artificially high N-gram SAR region near air interfaces. Here, we implement a simple method for meaningful N-gram SAR calculation and provide a GUI for performing such calculations given an unaveraged SAR distribution. The tool was developed as a companion to a versatile MRI simulator (PSUdo MRI) which we recently released for public use, but also can be used with any unaveraged SAR dataset given in the right format. In comparison to the conventional 10-gram SAR calculation, our result shows smooth and actual 10-gram SAR.

14:30 3869.   Optimization of Composite Pulses Considering Pulse Duration, Excitation Uniformity and SAR 
Bu S Park1,2, J McGarrity2, Z Cao2, K Sung3, S Oh2, and C M Collins2
1NIH, Bethesda, MD, United States, 2Radiology, The Pennsylvania State University, Hershey, PA, United States, 3Radiology, Standford University, Stanford, CA, United States

Except for RF shimming, transmit array pulses are generally expected to require more time than their quadrature-drive, single-pulse counterparts. Although many transmit array pulses can achieve better excitation uniformity than a simple pulse (including RF shimming), to do so in the same time duration with no significant increase in SAR is a challenge. Here we explore the effect of pulse duration in an array-optimized composite pulse (ACP) and in RF shimming designed to both improve excitation uniformity in the whole brain and reduce SAR using an 8-channel transmit head array, and compare results with the conventional quadrature drive at 7T. Minimum RF excitation time having better excitation uniformity and less SAR than the conventional quadrature drive for each pulse is presented.

15:00 3870.   RF shimming with regularization of maximum and mean RF power 
Ulrich Katscher1, Kay Nehrke1, Peter Vernickel1, Ingmar Graesslin1, and Peter Börnert1
1Philips Research Europe, Hamburg, Germany

RF shimming is able to compensate wave propagation effects at high main fields. The targeted B1 homogeneity has to be counterbalanced by the corresponding mean forward RF power required, which can be described by "regularized" RF shimming. However, this procedure frequently results in heterogeneous power distributions over the different transmit channels, which is disadvantageous for multi-channel RF amplifier design. To achieve comparable power requirements for all transmit channels, this study investigates "double-regularized" RF shimming, minimizing the mean as well as the maximum RF power. The approach was tested successfully in vivo for a whole-body, 8-channel TX/RX system at 3T.

Thursday May 12th
  13:30 - 15:30 Computer 72

13:30 3871.   How to reach the full potential of the B1+ efficiency for a 7 T body transmit array? 
Ozlem Ipek1, Alexander J.E. Raaijmakers1, Dennis W.J. Klomp2, Johannes m Hoogduin2, Peter R Luijten2, Jan J.W. Lagendijk1, and Cornelis A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands

The discrepancy if the B1+ value at prostate in measurement (10 µT ) and simulation (20 µT) is studied for 8 elements radiative antenna transmit surface array. The phase shimming was determined to obtain constructive B1+ interference in the prostate from the voltage phases of individual simulations. As the phase of the transmitted B1+ field of an element is not proportional to the feeding voltage but to the total current in an element we determined in simultaneously-driven elements, the voltage sources settings that would result in current phase setting from individual-driven elements. This solved the discrepancy problem.

14:00 3872.   Ultrahigh Field Body Transmit Arrays Using Non-resonance Method: A Feasibility Study 
Xiaoliang Zhang1,2, Chunsheng Wang1, Sarah Nelson1,2, and Daniel Vigneron1,2
1Dept 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 investigate the feasibility and advantages of ultrahigh high field body transmit array design using non-resonance method. With their features of uniform current and field distributions and frequency-insensitive, the proposed technique can be used for proton and multinuclear excitations with one single coil, providing a promising method to large-sized body coil designs at ultrahigh fields.

14:30 3873.   Electromagnetic simulations of high dielectric materials at 7 Tesla 
Wouter M Teeuwisse1, Chris M Collins2, Nadine B Smith1, and Andrew G Webb1
1Radiology, Leiden University Medical Center, Leiden, Netherlands, 2Radiology, Hershey Medical College

This work presents the results of electromagnetic simulations to study the effects of different high dielectric materials, size, geometry and position on the RF field distribution within the head at 7 Tesla. Local increases in signal-to-noise from materials with high dielectric constant are balanced by much smaller global decreases further away from the material. Splitting up the dielectric into several smaller subunits reduces the very strong wavelike behaviour that can occur when using materials with very high dielectric constants.

15:00 3874.   Simulation-Based Phased-Array Optimization Using an Efficient Method for Realistic Coil Modeling 
Matthias Korn1, Simon Lambert1, Xavier Maître1, and Luc Darrasse1
1IR4M (UMR8081), Université Paris-Sud XI - CNRS, Orsay, France

An efficient procedure for modeling and simulating phased-array coils is presented. The method uses a full wave EM simulation to calculate the EM-fields, while the effect of the port circuitry is substituted by the impedance of a discrete impedance. The value of this impedance is derived directly from the reflection coefficient of the preamplifier input and the coil impedance. The presented approach also includes sample losses, distributed capacitors, and geometrical and capacitive element decoupling. The method is demonstrated on a 6-channel receive-only coil to compare baseline sensitivity and g-factor performance of three different geometrical element configurations (gap, shared-conductor and overlap design).

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Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 73

14:00 3875.   Experimental Comparison of Array Coil Overlap Strategies for Maximal SNR 
Tyler Charlton1, Adam Maunder1, B. Gino Fallone1,2, and Nicola De Zanche1,2
1Dept. of Oncology, University of Alberta, Edmonton, Alberta, Canada, 2Dept. of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada

Three 8-channel array designs are compared at 3T: a) a gapped array; b) a standard overlapped array with zero mutual inductance between nearest neighbors; and c) a gapped array with mutual-inductance-nulling transformers between nearest neighbors. Preamp decoupling was used for all three. The gapped array provided the best SNR performance (respectively 18% and 24% better) since it had the lowest noise covariance.

14:30 3876.   Physical insights from ideal current patterns resulting in ultimate intrinsic SNR: efficacy of traditional coil designs at low field strength and the need for new designs at high field 
Riccardo Lattanzi1,2, and Daniel K Sodickson1,2
1Center for Biomedical Imaging, New York University Langone Medical Center, New York, NY, United States, 2Radiology, New York University Langone Medical Center, New York, NY, United States

Using a rigorous full-wave electrodynamic formulation based on dyadic Green’s functions (DGF), we calculate ideal current patterns that result in the highest possible signal-to-noise ratio (SNR) in homogeneous spherical and cylindrical samples, and compare the resulting patterns to familiar coil designs. Our results demonstrate the natural emergence of quadrature birdcage-like reception current patterns for imaging near the center of the object, as opposed to distributed loop-butterfly surface quadrature patterns for locations closer to the surface. Ideal current patterns become more complex at high field, indicating that innovative coil designs may be needed in order to approach the optimal performance.

15:00 3877.   Optimum SNR Data Compression for Complex Arrays 
Scott B. King1, Mike J Smith1, and Boguslaw Tomanek2
1Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada, 2Institute for Biodiagnostics (West), National Research Council of Canada, Calgary, Alberta, Canada

The number of receive channels on clinical MRI systems is now as high as 128, allowing the possibility for highly accelerated parallel MRI and increased SNR. To lessen the demands for data handling and processing, data compression methods are being explored. Here eigenmode channel compression was investigated for complex volume array designs revealing that significant (N/2) channel compression is possible while retaining >95% SNR and showing that symmetric, uniformly distributed array elements, as in the 24-channel head array, leads to more degeneracy and quad/antiqued pairs, and ultimately, whole-volume channel compression is possible, making permanent hardware channel compression an option.

15:30 3878.   Ultimate Intrinsic Signal-to-Noise Ratio of the Human Head at 9.4T 
Jörg Felder1, and Nadim Joni Shah1,2
1Institute of Neuroscience and Medicine-4, Forschungszentrum Juelich GmbH, Juelich, NRW, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

Ultimate intrinsic SNR has been introduced to establish an upper limit for physically achievable SNR in MRI. Up to now, due to computational complexity, ultimate intrinsic SNR solutions have only been presented for highly symmetric and homogeneous phantoms. Using 3D field simulations, we have evaluated ultimate intrinsic SNR for the human head at 9.4T allowing comparison of novel conductor arrangements for high field, parallel imaging coils and evaluating experimental performance in an absolute measure. Simulation results using a human head model (Ella) are presented.

Tuesday May 10th
  13:30 - 15:30 Computer 73

13:30 3879.   Predicting potential SNR gain for high field body imaging at 7 Tesla using radiative coil array element sensitivity patterns 
Alexander J.E. Raaijmakers1, Cornelis A.T. van den Berg1, and Dennis W.J. Klomp2
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 2Radiology, UMC Utrecht, Utrecht, Netherlands

Body imaging at 7 Tesla is hampered by the increased B1 signal attenuation at higher frequencies. The question therefore arises whether the potential gain in SNR by moving towards higher magnetic field strengths is diminished by the reduced sensitivity of receive coils. In this study, we compare potential receive array element designs and how their sensitivity patterns depend on the B1 frequency. It is shown that when the imaging target is located in the far-field of the antenna, the coil sensitivity does not decrease with magnetic field strength. This results in a quadratic increase in SNR with magnetic field strength.

14:00 3880.   Investigating Parallel Imaging Performance of the 8-Channel Transceiver Array With Tilted Microstrip Elements 
Yong Pang1, Bing Wu1, Daniel Vigneron1,2, and Xiaoliang Zhang1,2
1Radiology & Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, 2UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco & Berkeley, CA, United States

The rapid development of parallel imaging requires high performance RF coil arrays with excellent decoupling performance. In this study, parallel imaging performance for a new 8-channel volume transceiver array with tilted microstrip elements was investigated in terms of reconstructed image quality, noise correlation matrix and g-factor. In vivo human knee images were obtained using a 7T whole body MR scanner. Commonly used parallel imaging methods – SENSE and GRAPPA – were utilized to perform accelerated image reconstructions. The results demonstrate excellent parallel imaging performance for our proposed tilted microstrip array.

14:30 3881.   Effect Of Receive Only Array Inserts on B1+ Field and Specific Absorption Rate (SAR) 
Narayanan Krishnamurthy1, and Tamer S Ibrahim1
1University of Pittsburgh, Pittsburgh, PA, United States

A receive coil can distort the transmit field and cause local increased SAR. We seek to investigate the effects of a detuned and thin 32- loop receive-only head insert on transmit coil performance at 7 Tesla.

15:00 3882.   Effects of channel numbers on Signal-to-Noise Ratio in multi T/Rx coils at 7.0 Tesla 
Hongbae Jeong1, Suk-Min Hong1, Joshua Haekyun Park1, Myung-Kyun Woo1, Young-Bo Kim1, and Zang-Hee Cho1
1Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea, Republic of

This study is designed to compare the channel numbers of multi channel T/Rx coils performace at 7.0 Tesla. 2,4,6 and 8 channel multi T/Rx coils are constructed with same dimension on 270mm diameter of acryl case. The 6 channel coil showed the best SNR in central and peripheral area compared to 4 and 8 channel coils. For parallel imaging techinique, we prefer to use the 8 channel coil which displays similar SNR with 6 channel coil, and the 6 channel coil may have benefit of some angiography studies which requires more contrast diference in central area. The 2 channel coil has no specific advantage in terms of both SNR and Tx power consumption.

Wednesday May 11th
  13:30 - 15:30 Computer 73

13:30 3883.   Do We Need Preamplifier Decoupling? 
Arne Reykowski1, Charles Saylor1, and G. Randy Duensing1
1ACD, Invivo Corporation, Gainesville, FL, United States

Noise coupling theory suggests that preamp decoupling methods may simplify coil tuning but have no impact on combined SNR. Based on this theory, the authors conducted two experiments involving a set of coupled receive coils. In the first experiment, both coils were matched using conventional preamp decoupling. In the second experiment, both coils were matched at resonance. While the individual channel signals for both cases were quite different, the combined SNR was very similar; this indicates that the theory is valid.

14:00 3884.   Investigating the Use of Carbon Nanotubes in MRI Receiver Coils 
Mohamed Aly Saad Aly1, Nibardo Lopez1, Daniel Weyers2, Sarbast Rasheed1, Eihab M Abdel-Rahman1, and Arsen Hajian2,3
1System Design Engineering, University of Waterloo, Waterloo, Ontario, Canada, 2Tornado Medical Systems, Waterloo, Ontario, Canada, 3System Design Engineering, University of Waterloo, Waterloo, ontario, Canada

The possibility of integrating single-wall carbon nanotubes (SWCNT) in RF receivers was investigated in this work. We have approached this by two methods; replacing copper in copper coils by SWCNT and coating copper coils with sufficient thickness layer of SWCNT. Replacing copper with Single-wall carbon nanotubes shows promising results with some challenges. These hurdles are; high DC resistance and low impedance values. Using different CNT grades might help to overcome these challenges. Because of the high DC resistance of the CNT layer, coating copper with SWCNT layer did not affect the coil performance in terms of resistance, impedance, or quality factor.

14:30 3885.   7T Imaging of the head and neck region: B0 and B1+ challenges 
Johanna Jacoba Bluemink1, Anna Andreychenko1, Astrid L.H.M.W. van Lier1, Marielle Phillippens1, Jan J.W. Lagendijk1, Peter R. Luijten2, and Cornelis A.T. van den Berg1
1Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands, 2Radiology, University Medical Center Utrecht, Utrecht, Netherlands

The head and neck (H&N) region is challenging to image due to air cavities that distort the B0 field. At 7T better a SNR can be obtained, but susceptibility effects are increased and for the H&N region no commercial 7T transmit coils are available. Two setups, a volume T/R coil placed near the neck and a traveling wave setup are compared in transmit performance. With the volume T/R coil sufficient B1+ can be obtained for SE in the nasopharynx and the oropharynx. The traveling wave setup can cover a larger volume, but the maximum B1+ obtained was only 3ìT.

15:00 3886.   Fast automatic matching control: technical advances and initial results of SNR optimization 
Matteo Pavan1, Roger Lüchinger1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Noise reduction is an important issue for SNR (Signal to Noise Ratio) maximization in MR measurements. Automatic Matching Networks (AMN) have been introduced and are a great tool to overcome notoriously difficult matching situation such as coil arrays, mechanically adjustable coils and in general coils that see different loading conditions. In this work a new automatic matching network has been implemented and tested, it allows automatic SNR measurements over thousands points in a short time, in a repeatable and robust way. An initial study of the behavior of the SNR has been done.

Thursday May 12th
  13:30 - 15:30 Computer 73

13:30 3887.   Theoretical determination of the dielectric constant for passive RF shimming at high field 
Mohan Lal Jayatilake1,2, Judd Storrs1,3, Wen-Jang Chu1,3, and Jing-Huei Lee1,4
1Center for Imaging Research, University of Cincinnati, Cincinnati, OH, United States, 2Department of Physics, University of Cincinnati, Cincinnati, OH, United States,3Department of Psychiatry and Behavioural Neuroscience, University of Cincinnati, Cincinnati, OH, United States, 4School of Energy, Environmental, Biological, and Medical Engineering, University of Cincinnati, Cincinnati, OH, United States

Optimal image quality for MRI at high field requires a homogeneous RF (B1) field; however, dielectric properties of the human brain cause B1 field inhomogeneities in the periphery of the head. Selecting the appropriate permittivity and the quantity of material for B1 shim is essential. In this work we introduce a theoretical framework for determining the requisite dielectric constant of the passive shim material.

14:00 3888.   SVD-based Hardware Concept to Drive N Transmit Elements of a Phased Array Coil with Mless than or equal toN channels for High Field MRI 
Guillaume Ferrand1, Michel Luong1, Martijn A Cloos1,2, Alain France1, Alexis Amadon2, Nicolas Boulant2, and Luc Darrasse3
1IRFU/SACM, CEA-Saclay, Gif s/ Yvette, France, 2I2BM/Neurospin, CEA-Saclay, Gif s/ Yvette, France, 3IR4M (UMR8081), Univ Paris-Sud, CNRS, Orsay, France

In high field MRI, a phased array coil comprising a large number of transmit elements appears more attractive with respect to local SAR reduction and to B1 inhomogeneity mitigation using parallel transmission. However, if each element were driven by a dedicated channel consisting of a concatenation of signal modulator and high power amplifier, the system cost would increase linearly with the number of transmit elements. It would be the same for the acquisition time of B1 maps necessary for parallel transmission. Here, we propose a new hardware scheme based on the singular value decomposition (SVD) to drive N elements with M channels, where M less than or equal to N. The proof of concept is provided by numerical simulations of the whole process.

14:30 3889.   A Novel Method for Amplitude and Phase Mapping of RF Transmit and Receive Fields 
Alessandro Sbrizzi1, Hans Hoogduin1, Gerard L.G. Sleijpen2, Astrid L Van Lier3, Jan J. Lagendijk1, Peter Luijten1, and Cornelis A.T. van den Berg1
1Imaging Division, UMC Utrecht, Utrecht, Netherlands, 2Department of Mathematics, Utrecht University, Utrecht, Netherlands, 3UMC Utrecht

In this work we present a new approach for extracting complete complex information about the transmit and receive fields of a RF transmit coil from a B1+ amplitude measurement. The method is based on a Bessel/Fourier modes expansion of the B1+ and B1- maps. The results obtained from FDTD simulations and in vivo measurements confirm the validity of the novel approach.

15:00 3890.   SAR reduction through Dark modes excitation 
Kawin Setsompop1,2, and Lawrence L Wald1,3
1Radiology, A. A. Martinos Center for Biomedical Imaging, MGH, Charlestown, MA, United States, 2Harvard Medical School, Boston, MA, United States, 3Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States

We propose a strategy which employs the “dark modes” of excitation coil array to cancel local E-fields that produce SAR hotspots. The method is based on the observation that some modes of an array coil (e.g. birdcage with the wrong circular polarization) produce E-fields but not useful excitation of MR magnetization (i.e. no B1+). We can therefore energize these “dark modes” exclusively with the goal of cancelling local SAR hot-spots. While this will not lower SARglobal (since more power will be used), our goal is local SAR reduction at a few hot spots where local SAR is the limiting factor.