Contact

Dr. Nikolai Avdievitch

Address: Spemannstr. 41
72076 Tübingen
Room number: 1.B.03
Phone: +49 7071 601 713
Fax: +49 7071 601 702
E-Mail: Nikolai.Avdievitch

 

Picture of Avdievitch, Nikolai, Dr.

Nikolai Avdievitch

Position: Senior Research Scientist  Unit: Henning Scheffler

Optimization of Transmit and Receive Performance of a Transceiver Phased Array

Motivation

In spite of great benefits offered by ultra-high field (UHF, > 7T) MRI, its further developments toward clinical applications are associated with significant technical issues, which include low transmit (Tx) efficiency and strong inhomogeneity of the RF magnetic field, B1+ (1). To improve Tx-efficiency and provide for a full coverage of the human brain, UHF multi-element multi-row arrays (2-6) have to be used in combination with 3D RF shimming or parallel transmission (pTx). There are two major types of human head array coils currently developed for the full-brain imaging at UHF. First type, a so called transmit-only/ receive-only (ToRo) array, consists of two nested layers of elements (5). Inner layer, which is positioned closer to a head, contains multiple elements (commonly loops) used only during reception, i.e. receive (Rx)-only elements. Larger array, positioned in the outer layer, provides for local transmission. Second design, a so called transceiver (TxRx) array, consists of a single layer of elements used during both transmission and reception (2-4,6). The Rx-performance of a human head coil can be easier optimized within the frame of the ToRo-design. Current state of the art UHF ToRo-arrays contain 30 and more Rx-only elements (5), which is critical for high SNR and parallel Rx-performance. In turn, TxRx-arrays provide for more efficient transmission, B1+/√P, due to tighter fit and, thus, higher tissue loading. TxRx-design is also simpler then the ToRo-design since it does not require detuning of elements. However, a drawback of the TxRx-design is that the number of elements in an array is limited by the number of available high power RF Tx-channels (commonly 8 or 16). My work focuses on development of new UHF arrays, which combine benefits of both designs, i.e. provide for efficient transmission and the same time do not compromise SNR and parallel receive performance.

Transmit efficiency

Previously we demonstrated that at 400 MHz a 16-loop double-row (2x8) tight-fit human head TxRx-array can be well decoupled entirely by overlapping surface loops without any additional decoupling strategy (7). This based on our analytical findings that at 400 MHz the mutual resistance between adjacent overlapped loops combined within this specific array geometry is minimal, and both the mutual inductance and mutual resistance can be minimized at the same time (8). As a result, the constructed 2x8 array demonstrated very good decoupling, a full brain coverage, and Tx-efficiency, which was 50% higher than that of the larger ToRo-array of similar length (7). Adding two perpendicular TxRx-loops at the superior position of a head (Fig.1A) improves uniformity of the array transmit B1+ profile (Fig.2).

Receive Performance

In the next step we developed a method of increasing the number of Rx-elements in a TxRx-array without compromising the array’s Tx-performance (9). First, we constructed a human head array prototype, which consisted of a single row of 8 TxRx surface loops circumscribing a head, and 8 Rx-only “vertical” loops positioned in the center of each TxRx-loop such to produce B1+ field perpendicularly to magnetic field B0 (similarly as in Fig.1B). All vertical loops were actively detuned during transmission and preamplifier decoupled during reception. Evaluation of the new array demonstrated that neither Tx-efficiency nor maximum SAR was compromised due to addition of Rx-only vertical loops (9). At the same time SNR was substantially improved (~30% near the brain center). Following prototyping 16-loop array, we extended this idea by constructing 32-element tight-fit human head array consisted of 18 TxRx-loops (Fig.1A) and 14 Rx-only vertical loops (Fig.1B) with the total number of Rx elements equal to 32. The general idea of this approach is that the total number of array elements should not exceed the number of available Rx-channels, i.e. 32 in our case. During designing, first, the required number (e.g. 18, Fig.1A) of TxRx-loops is placed around the object tightly to provide for high Tx-performance. Then, the rest of the loops are used as Rx-only elements, which are positioned to minimize interaction with the TxRx-loops, e.g. “vertically” (Fig.1B). In comparison to the common ToRo-design, this method preserves tight fit of the TxRx-loops and, thus, does not compromise the Tx-performance. In addition, it minimizes the total number of array elements as well as the number of active detuning circuits, which are not required for the TxRx-elements. As seen from Fig.3, the ToRo-array still provides for somewhat higher peripheral SNR.

At the same time, the new 32-channel tight-fit array has substantially (~30%) higher SNR near the center of the brain. It is well known that increasing the number of surface loops in a helmet human-head Rx-array only improves peripheral SNR, while SNR near the center practically doesn’t change (10,11). Combination of surface and vertical loops improves SNR near the center. Overall, the new tight-fit array demonstrates high SNR over the entire brain and a substantially more uniform SNR distribution than that of the ToRo-array. Both arrays provide for comparable Rx parallel performance.

References: 1) Vaughan JT et al, Magn Reson Med, 46:24-30, 2001. 2) Adriany G et al. Magn Reson Med 2010; 63(6):1478-1485. 3) Avdievich NI et al, Appl Magn Reson 2011, 41(2):483-506. 4) Gilbert KM et al, Magn Reson Med 2012;67:1487–1496. 5) Shajan G et al, Magn Reson Med, 71:870-879, 2014. 6) Avdievich NI et al, NMR in Biomedicine. 2017;30(2):1-12. 7) Avdievich et al, Proc. ISMRM 25, 2017, 759. 8) Avdievich et al, NMR in BioMed 2017, DOI: 10.1002/nbm.3759. 9) Avdievich et al, Proc. ISMRM 25, 2017, 4309. 10) Wiggins GC et al, Magn Reson Med 2009;62:754-762. 11) Vaidya MV et al, Conc Magn Reson Part B 2014; 44B(3):53–65.

Optimization of Transmit and Receive Performance of a Transceiver Phased Array

Motivation

In spite of great benefits offered by ultra-high field (UHF, > 7T) MRI, its further developments toward clinical applications are associated with significant technical issues, which include low transmit (Tx) efficiency and strong inhomogeneity of the RF magnetic field, B1+ (1). To improve Tx-efficiency and provide for a full coverage of the human brain, UHF multi-element multi-row arrays (2-6) have to be used in combination with 3D RF shimming or parallel transmission (pTx). There are two major types of human head array coils currently developed for the full-brain imaging at UHF. First type, a so called transmit-only/ receive-only (ToRo) array, consists of two nested layers of elements (5). Inner layer, which is positioned closer to a head, contains multiple elements (commonly loops) used only during reception, i.e. receive (Rx)-only elements. Larger array, positioned in the outer layer, provides for local transmission. Second design, a so called transceiver (TxRx) array, consists of a single layer of elements used during both transmission and reception (2-4,6). The Rx-performance of a human head coil can be easier optimized within the frame of the ToRo-design. Current state of the art UHF ToRo-arrays contain 30 and more Rx-only elements (5), which is critical for high SNR and parallel Rx-performance. In turn, TxRx-arrays provide for more efficient transmission, B1+/√P, due to tighter fit and, thus, higher tissue loading. TxRx-design is also simpler then the ToRo-design since it does not require detuning of elements. However, a drawback of the TxRx-design is that the number of elements in an array is limited by the number of available high power RF Tx-channels (commonly 8 or 16). My work focuses on development of new UHF arrays, which combine benefits of both designs, i.e. provide for efficient transmission and the same time do not compromise SNR and parallel receive performance.

Transmit efficiency

Previously we demonstrated that at 400 MHz a 16-loop double-row (2x8) tight-fit human head TxRx-array can be well decoupled entirely by overlapping surface loops without any additional decoupling strategy (7). This based on our analytical findings that at 400 MHz the mutual resistance between adjacent overlapped loops combined within this specific array geometry is minimal, and both the mutual inductance and mutual resistance can be minimized at the same time (8). As a result, the constructed 2x8 array demonstrated very good decoupling, a full brain coverage, and Tx-efficiency, which was 50% higher than that of the larger ToRo-array of similar length (7). Adding two perpendicular TxRx-loops at the superior position of a head (Fig.1A) improves uniformity of the array transmit B1+ profile (Fig.2).

Receive Performance

In the next step we developed a method of increasing the number of Rx-elements in a TxRx-array without compromising the array’s Tx-performance (9). First, we constructed a human head array prototype, which consisted of a single row of 8 TxRx surface loops circumscribing a head, and 8 Rx-only “vertical” loops positioned in the center of each TxRx-loop such to produce B1+ field perpendicularly to magnetic field B0 (similarly as in Fig.1B). All vertical loops were actively detuned during transmission and preamplifier decoupled during reception. Evaluation of the new array demonstrated that neither Tx-efficiency nor maximum SAR was compromised due to addition of Rx-only vertical loops (9). At the same time SNR was substantially improved (~30% near the brain center). Following prototyping 16-loop array, we extended this idea by constructing 32-element tight-fit human head array consisted of 18 TxRx-loops (Fig.1A) and 14 Rx-only vertical loops (Fig.1B) with the total number of Rx elements equal to 32. The general idea of this approach is that the total number of array elements should not exceed the number of available Rx-channels, i.e. 32 in our case. During designing, first, the required number (e.g. 18, Fig.1A) of TxRx-loops is placed around the object tightly to provide for high Tx-performance. Then, the rest of the loops are used as Rx-only elements, which are positioned to minimize interaction with the TxRx-loops, e.g. “vertically” (Fig.1B). In comparison to the common ToRo-design, this method preserves tight fit of the TxRx-loops and, thus, does not compromise the Tx-performance. In addition, it minimizes the total number of array elements as well as the number of active detuning circuits, which are not required for the TxRx-elements. As seen from Fig.3, the ToRo-array still provides for somewhat higher peripheral SNR. At the same time, the new 32-channel tight-fit array has substantially (~30%) higher SNR near the center of the brain. It is well known that increasing the number of surface loops in a helmet human-head Rx-array only improves peripheral SNR, while SNR near the center practically doesn’t change (10,11). Combination of surface and vertical loops improves SNR near the center. Overall, the new tight-fit array demonstrates high SNR over the entire brain and a substantially more uniform SNR distribution than that of the ToRo-array. Both arrays provide for comparable Rx parallel performance.

References: 1) Vaughan JT et al, Magn Reson Med, 46:24-30, 2001. 2) Adriany G et al. Magn Reson Med 2010; 63(6):1478-1485. 3) Avdievich NI et al, Appl Magn Reson 2011, 41(2):483-506. 4) Gilbert KM et al, Magn Reson Med 2012;67:1487–1496. 5) Shajan G et al, Magn Reson Med, 71:870-879, 2014. 6) Avdievich NI et al, NMR in Biomedicine. 2017;30(2):1-12. 7) Avdievich et al, Proc. ISMRM 25, 2017, 759. 8) Avdievich et al, NMR in BioMed 2017, DOI: 10.1002/nbm.3759. 9) Avdievich et al, Proc. ISMRM 25, 2017, 4309. 10) Wiggins GC et al, Magn Reson Med 2009;62:754-762. 11) Vaidya MV et al, Conc Magn Reson Part B 2014; 44B(3):53–65.

WORK EXPERIENCE:

Feb 2017-Current

Senior Research Scientist (100%), Institute of Physics, Ernst-Moritz-Arndt University Greifswald, Greifswald, Germany.

 

May. 2017-Current

Senior Research Scientist (20%), Department for Ultra-High Field MRI (Department chair Prof. K. Scheffler), Max Planck Institute for Biological Cybernetics, Tübingen, Germany.

 

Jan. 2013- Feb. 2017

Senior Research Scientist, Department for Ultra-High Field MRI (Department chair Prof. K. Scheffler), Max Planck Institute for Biological Cybernetics, Tübingen, Germany.

 

July 2012- Dec 2012

Senior RF Engineer, Resonance Research Instruments, Inc., Billerica, MA, USA.

 

Jan. 2007-June 2012

Associate Research Scientist, Magnetic Resonance Research Center, Department of Neurosergery, Yale University, New Haven, CT, USA.

 

Oct. 2000-Dec. 2006

Associate in Radiology, Magnetic Resonance Research Center, Department of Radiology, Albert Einstein Medical College, Bronx, NY, USA.

 

Feb. 1998-Oct. 2000

Electron Spin Resonance (ESR) Lab Manager, ESR Research Resource Center, Department of Physiology & Biophysics, Albert Einstein Medical College, Bronx, NY, USA.

 

1994-Feb. 1998

Postdoctoral Associate, Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.

 

1993-1994

Researcher, Laboratory of Spin and Magnetic Phenomena, International Tomography Center, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

1992-1993

Researcher, Laboratory of Magnetic Phenomena, Institute of Chemical Kinetics and Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

1987-1992

Junior Researcher, Laboratory of Magnetic Phenomena, Institute of Chemical Kinetics and  Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

1985-1987

Engineer, Laboratory of Physical Methods of Chemical Kinetics, Institute of Chemical Kinetics and Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

1983-1985

Research Technician, Laboratory of Physical Methods of Chemical Kinetics, Institute of Chemical Kinetics and Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

EDUCATION:

1993

Ph.D. in Physical Chemistry, Institute of Chemical Kinetic and Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

1985

M.S., Chemical Physics, Department of Physics, Novosibirsk State University, Novosibirsk, Russia.

1983

B.S., Radiophysics, Department of Physics, Novosibirsk State University, Novosibirsk, Russia.

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Show abstracts

Articles (51):

Bagryanskaya EG, Grishin YA, Avdievich NI, Sagdeev RZ and Molin YN (July-1986) Studies of various mechanisms of nuclear polarisation due to a resonant high-frequency field in radical reactions Chemical Physics Letters 128(2) 162–167.

Conference papers (2):

Chang Y-C, Avdievich N and Henning A (August-2014) System Identification and Signal Processing for PID Control of B0 Shim Systems in Ultra-High Field Magnetic Resonance Applications, 19th World Congress of the International Federation of Automatic Control (IFAC World 2014), Pergamon Press, Oxford, UK, IFAC Proceedings Volumes, 47(3), 7517-7522.
pdf
Kozlov M, Turner R and Avdievich N (October-2013) Investigation of decoupling between MRI array elements, 43rd European Microwave Conference (EuMC 2013), IEEE, Piscataway, NJ, USA, 1223-1226.

Contributions to books (2):

Avdievich NI: Quadrature Transverse Electromagnetic (TEM) Surface Coils, 51-61. In: RF Coils for MRI, (Ed) J.T. Vaughan, Wiley, Chichester, UK, (2012).
Avdievich NI: Transverse Electromagnetic (TEM) Surface Coils for Extremities, 185-195. In: RF Coils for MRI, (Ed) J.T. Vaughan, Wiley, Chichester, UK, (2012).

Posters (63):

Giapitzakis I-A, Avdievich N and Henning A (October-21-2017): Characterization of macromolecular baseline of human brain using metabolite cycled semi-LASER at 9.4 T, 34th Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2017), Barcelona, Spain, Magnetic Resonance Materials in Physics, Biology and Medicine, 30(Supplement 1) S475-S476.
Avdievich N, Giapitzakis I and Henning A (October-20-2017): Double-Row 16-element Tight-Fit Transceiver Phased Array with High Transmit Performance for Whole Human Brain Imaging at 9.4T, 34th Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2017), Barcelona, Spain, Magnetic Resonance Materials in Physics, Biology and Medicine, 30(Supplement 1) S256-S257.
Fichtner N, Giapitzakis I-A, Avdievich N, Mekle R, Zaldivar D, Henning A and Kreis R (April-27-2017): Magnetization exchange between water and downfield metabolites in human brain at 9.4T, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Avdievich N, Giapitzakis I and Henning A (April-26-2017): Double-Row 16-element Tight-Fit Transceiver Phased Array with High Transmit Performance for Whole Human Brain Imaging at 9.4T, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Avdievich N, Giapitzakis I and Henning A (April-25-2017): Effect of Mismatching on the Transmit and Receive Performance of a Human Head 9.4T Tight-Fit Transceiver Phased Array, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Avdievich N, Giapitzakis I and Henning A (April-25-2017): Optimization of the Receive Performance of a Tight-Fit Transceiver Phased Array for Human Brain Imaging at 9.4T, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Shao T, Avdievich NI and Henning A (May-12-2016): 3D volumetric parallel excitation at 9.4T using the trajectory container concept, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Fichtner ND, Giapitzakis IA, Avdievich N, Henning A and Kreis R (May-11-2016): Downfield spectra of human brain obtained with and without water suppression at 9.4T, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Pfrommer A, Avdievich NI and Henning A (May-11-2016): Effect of the RF Shield on the Mutual Coupling Between Adjacent and Non-Adjacent Array Elements, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Zoelch N, Hock A, Avdievich NI and Henning A (May-11-2016): In vivo metabolite quantification using ERETIC with corrections for changes in the RF transmission and recepetion field, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Avdievich NI, Pfrommer A, Giapitzakis IA and Henning A (May-10-2016): Analytical Modeling of the Coupling within a Human Head Surface Loop Transmit Phased Array at Ultra-High Fields, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Fichtner N, Henning A, Giapitzakis I, Zoelch N, Avdievich N, Boesch C and Kreis R (March-31-2016): Downfield MR Spectroscopy at Ultrahigh Magnetic Fields, 11th Annual Meeting Brain Connectivity, Bern, Switzerland.
Avdievich NI, Walzog J, Steffen T and Henning A (October-2015): Development of a low cost multi-channel tune and match device for transceiver arrays at high magnetic fields, 32nd Annual Scientific Meeting ESMRMB 2015, Edinburgh, UK, Magnetic Resonance Materials in Physics, Biology and Medicine, 28(1 Supplement) S452-S453.
Giapitzakis IA, Nassirpour S, Avdievich N, Kreis R and Henning A (June-4-2015): Metabolite cycled single voxel 1H spectroscopy at 9.4T, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Avdievich NI, Giapitzakis IA and Henning A (June-2-2015): Novel Splittable N-Tx/2N-Rx Transceiver Phased Array to Optimize both SNR and Transmit Efficiency at 9.4 T, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Kuehne A, Laistler E, Eschelbach M, Henning A, Moser E and Avdievich NI (June-1-2015): Analytical Performance Evaluation and Optimization of Resonant Inductive Decoupling (RID), 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Avdievich NI, Giapitzakis IA and Henning A (June-1-2015): Asymmetric Transceiver Phased Array for Functional Imaging and Spectroscopy of the Visual Cortex at 9.4 T, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Shao T, Avdievich NI, Chang P, Hoffmann J, Scheffler K and Henning A (June-1-2015): Systematic investigation of influence factor on parallel transmit pulse performance at 9.4 Tesla, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Giapitzakis IA, Nassirpour S, Kreis R, Avdievich NI and Henning A (March-19-2015): Metabolite cycled proton magnetic resonance spectroscopy at 9.4T, 10th Annual Meeting of the European Society for Molecular Imaging (EMIM 2015), Tübingen, Germany.
Chang Y-C, Eschelbach M, Avdievitch N, Scheffler K and Henning A (May-15-2014): Fast Method for Parametric System Identification of Gradient Systems, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.
Giapitzakis IA, Shao T, Avdievich N, Kreis R and Henning A (May-15-2014): Optimisation of Asymmetric Adiabatic Pulses for Single Voxel Metabolite Cycled 1H-MRS in the Human Brain at 9.4 Tesla, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.
Pfrommer A, Avdievich N and Henning A (May-12-2014): Four Channel Transceiver Array for Functional Magnetic Resonance Spectroscopy in the Human Visual Cortex at 9.4 T, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.
Avdievich NI, Pan JW and Hetherington HP (April-25-2013): Densely-Populated Transceiver Surface Coil Array for the Human Brain Studies at 7T, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
Hetherington HP, Avdievich NI and Pan JW (April-25-2013): Improved Volume Localization for MRSI at 7T Using RF Shimming and RF Multiplexing, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
Lee J-H, Norris M, Fugate EM, Avidievich NI and Hetherington HP (April-24-2013): A Novel Double Tuned 4T 1H/17O Head Volume Coil, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
Hetherington HP, Avdievich NI and Pan J (April-24-2013): Reducing SAR and Imaging Time at 7T Using RF Multiplexing and Transceiver Arrays at 7T, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
Avdievich NI, Pan JW and Hetherington HP (May-7-2012): Novel Inductive Decoupling for Single- and Double-Tuned Transceiver Phased Arrays to Compensate for both Reactive and Resistive Components of the Mutual Impedance, 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012), Melbourne, Australia.
Avdievich NI, Pan JW and Hetherington HP (October-2011): Double Tuned 31P/1H Elliptical Transceiver Phased Array for the Human Brain Studies at 7T, 28th Annual Scientific Meeting ESMRMB 2011, Leipzig, Germany, Magnetic Resonance Materials in Physics, Biology and Medicine, 24(Supplement 1) 421-422.
Hetherington HP, Avdievich NI, Gonen O and Pan JW (May-9-2011): Hadamard Encoded 3D MRSI of Human Brain at 7T, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada.
Pan JW, Avdievich NI and Hetherington HP (May-9-2011): Thalamic and subcortical GABA in human brain at 7T, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada.
Pan JW, Avdievich N, Ibrahim TS and Hetherington HP (May-9-2011): The inductively decoupled transceiver array: simulations and performance at 7T, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada.
Oh S, Avdievich NI, Pan JW, Hetherington HP and Collins CM (May-6-2010): Enhanced RF Excitation Homogeneity by Combining TEM and Counter Rotating Current Surface Coil Array: Numerical Simulations and Experiments at 4.0 T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
Avdievich NI, Pan JW and Hetherington HP (May-5-2010): Double Tuned 31P/1H Elliptical Transceiver Phased Array for the Human Brain Studies at 7 T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
Hetherington HP, Avdievich NI and Pan JW (May-5-2010): An 8 Element Inductively Decoupled Transceiver Array for 1H MR of the Brain at 7T: Performance Characteristics Across 82 Subjects, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
Pan JW, Avdievich NI and Hetherington HP (May-5-2010): J Refocused Coherence Transfer Spectroscopic Imaging at 7T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
Avdievich NI, Pan JW, Kuznetsov AM and Hetherington HP (April-21-2009): Variable Geometry Elliptical Transceiver Phased Array for Imaging of the Human Brain at 7 T, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA.
Avdievich NI, Peshkovsky AS and Hetherington HP (May-21-2007): Comparison of Transceive Phased Array with TEM Volume Coil for Human Brain Imaging at 4 T, 2007 Joint Annual Meeting ISMRM-ESMRMB, Berlin, Germany.
Avdievich NI and Hetherington HP (May-10-2006): 4T Actively-Detunable Double-Tuned 1H/31P TEM Head Volume Coil and Four-Channel 31P Phased Array for Human Brain Spectroscopy, 14th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2006), Seattle, WA, USA.
Avdievich NI, Bradshaw K, Lee J-H and Hetherington HP (May-10-2006): 4T Split TEM Volume Head and Knee Coils for Improved Sensitivity and Patient Comfort, 14th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2006), Seattle, WA, USA.
Avdievich NI and Hetherington HP (May-10-2006): Improved Homogeneity of the Transmit Field Due to Simultaneous Transmission with Phased Arrays and Volume Coils, 14th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2006), Seattle, WA, USA.
Hetherington HP, Avdievich NI and Pan JW (May-11-2005): Improved Spectral Editing for Measurements of Cerebral GABA, 13th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2005), Miami Beach, FL, USA.
Avdievich NI and Hetherington HP (May-10-2005): Experimental Comparison of TEM and Birdcage Small Animal Volume Coils at 9.4 T, 13th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2005), Miami Beach, FL, USA.
Avdievich NI, Peshkovsky A, Kennan RP and Hetherington HP (May-19-2004): SENSE imaging with quadrature half-volume TEM coil at 4T, 12th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2004), Kyoto, Japan.
Avdievich NI and Hetherington HP (May-17-2004): 4T Human Brain Spectroscopic Imaging with Four-Channel Phased Array, 12th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2004), Kyoto, Japan.
Peshkovsky A, Kennan RP, Fabry ME and Avdievich NI (May-17-2004): Open volume TEM quadrature coil for high-field imaging, 12th Scientific Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM 2004), Kyoto, Japan.
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