Contact

Dr. Rolf Pohmann

Address: Spemannstr. 41
72076 Tübingen
Room number: 3.B.02
Phone: +49 7071 601 903
Fax: +49 7071 601 702
E-Mail: Rolf.Pohmann

 

Picture of Pohmann, Rolf, Dr.

Rolf Pohmann

Position: Project Leader  Unit: Scheffler

Magnetic Resonance Imaging at ultra high fields requires novel techniques, both concerning hardware and imaging sequences. At field strengths of 9.4 T (human) and 14.1 T (rodents), I investigate the capabilities of ultra high field MRI. Specifically, our aim is to

  • quantify the MR parameters at ultra high field strength,
  • find solutions to some of the major challenges involved in ultra high field MRI, like B1-homogeneity or safety,
  • develop techniques that take full advantage of the potential of the high field strength and assess the gain compared to conventional MR instruments
  • help in appying those techniques to medical or biological applications
  • help in combining ultra-high field MRI with other techniques to gain additional information in neuroscientific studies.

In addition, I assist other groups by developing or optimizing specialized techniques for their applications.

 


 

 

 

For a comprehensive overview over our projects, please see our project group web page.

Evaluation of Signal Gain and MR tissue parameters at ultra-high field

While the number of ultra-high field MR scanners is still growing rapidly, mainly due to the desired SNR gain with increasing fields, surprisingly little is known about the actual SNR that can be obtained with higher fields. In this project we compared the SNR and tissue parameters at 3 T, 7 T and 9.4 T. The same subjects were scanned with the same gradient echo sequence at all three fields, and the SNR of the resulting maps were corrected for the differences in relaxation times and transmit field. Since it is not easily possible to obtain reliable values for the sensitivity of the receive coils, arrays with similar number of elements and geometry were used. The SNR was found to increase supralinearily with the field strength, following a relation of SNR ≈ B01.65.

SNR (top) and relative SNR differences (bottom) at 3 T, 7 T and 9.4 T. Data are from the same subject at all fields. SNR increases supralinearily, growing by 3.3 from 3 T to 7 T and another factor of 1.67 from 7 T to 9.4 T.

 


 

Ultra-high Resolution Imaging with Acquisition Weighting

High spatial resolutions are one of the main goals of ultra-high field imaging. In this study we demonstrated the possibility to obtain images with voxel sizes down to 14 nl with sufficient SNR in an acceptable scan time by combining the ultra-high field with a highly sensitive 31 channel array coil and a special, SNR optimized imaging technique. By performing a k-space weighting during acquisition, it can be shown that this method not only avoids ringing artifacts, but also increases SNR by up to 36% without losses in spatial resolution or scan time (publication).

High resolution images (0.2 × 0.2 × 0.5) mm3 acquired with a conventional (top) and the acquisition weighted sequence (bottom). The weighted images show greater fine detail and a higher SNR.

 

High sensitivity perfusion imaging with Arterial Spin Labeling

Arterial Spin Labeling is a promising technique for quantitative perfusion imaging without the need for contrast agents. Since ASL generally suffers from a low signal-to-noise ratio, we concentrate on implementing and developing techniques with high sensitivity. To reach this goal, we follow several different approaches:

  • In contrast to the most commonly used techniques of pulsed arterial spin labeling, continuous arterial spin labeling has a considerably increased sensitivity, but also a higher complexity. We have implemented a number of different variants of continuous ASL, which are now used in neuroscientific and biological applications (publication).

    Perfusion images acquired with different CASL and a PASL technique.

  • In contrast to the cortex in the brain, which has a very high perfusion, the white matter or, even more, the skeletal muscle are only poorly perfused, making highly quantitative measurement difficult. For making it possible to obtain quantitative values of the perfusion from those tissues, a highly sensitive technique based on single-voxel spectroscopy was developed. This FAIRPRESS techniques has been successfully used to quantify the perfusion in the white matter as well as in muscels in the legs of rats and humans.
  • In addition to the gain in intrinisc signal-to-noise ration at ultra-high field, the longer longitudinal relaxation time will help to further improve the accuracy of perfusion images. Using the most sensitive CASL sequences is, however, hampered by the high SAR with is necessary to label the inflowing blood. Using a dual-coil CASL technique, that applies the labelling field with separate, local coils at the neck of the volunteer, it will be possible to reduce SAR far enough to be able to take full advantage of the improved signal at higher field.


Multiband fMRI in animal studies

High temporal resolution is a crucial factor in many fMRI studies. Multiband imaging is a novel technique to increase the speed of fMRI acquisition by using parallel imaging methods to obtain the signals from two or more slices simultaneously. While this technique is already used frequently in human fMRI, it has so far not been applied in animal studies. We have implemented multiband EPI on an animal scanner and evaluated its performance with different fMRI protocols.

fMRI data from a rat forepaw stimulation experiment at 7 T, acquired with a conventional sequence (left) and a dual-band EPI with double temporal resolution.


Measurement of MR imaging parameters at ultra high field

When increasing the field strength, MR relaxation times, magnetization transfer effects, and susceptibility-induced field variations will change. We have measured and quantified those parameters at field strengths up to 16.4 T and analysed the effects of those changes on SNR and contrast of the resulting images (publication).

The relaxation times T1, T2 and T2* were measured with high accuracy and spatial resolution using inversion recovery, single spin echo and gradient echo sequences, respectively, with varying delays. The MTR was measured by off-resonance irradiation at different frequencies and power levels and the resulting values were used to determine the parameters of a two-pool model [2] to allow for comparison to other field strengths. Local frequency variations were deduced from phase changes in gradient echo images with varying echo time.

With values between 1834 ms (white matter ) and 2376 ms (hippocampus), T1 was significantly increased compared to lower fields, while T2 and T2* are relatively low (corpus callosum: 20 ms / 13.6 ms, cortex: 24 ms / 21 ms). The MTR varies between 51% and 61% and thus is considerably stronger than at lower field. Image phase shows distinct differences between different anatomical structures and can be a valuable contrast mechanism at high field. In all parameter maps, all major anatomical structures were clearly visible.

Comparisons to publications at lower field show an increase in contrast-to-noise ratio with field strength for all contrast mechanisms. Especially phase and T2* imaging have great potential for use in neuroscientific and preclinical applications.


 

Flip angle mapping

Highly accurate, fast, and simple mapping of the excitation field is a crucial requirement for ultra high field MR imaging. In an extensive study, we are comparing the accuracy and precision of the most popular flip angle mapping techiques, both theoretically and in experiments under different settings. The results will be used to further improve the performance of these sequences to enable highly accurate shaping of the transmit field using B1-shimming or Transmit SENSE (publication).


 

For information about the other projects in our group, please see  our project group web page.

Current Position:

Group Leader Ultra High Field MRI

at the Max-Planck-Institute for Biological Cybernetics

Education:
1988-1995

University studies in physics at the universities Würzburg, Germany and Buffalo, New York.

Diploma thesis on 'Theoretical Analysis of the quality of spectroscopic NMR imaging techniques'

1995-1999 PhD thesis at the University Würzburg on "Techniques for spatially resolved NMR-spectroscopy"
1999-2002 Deparment for Mission Planning at the German Space Operation Center (GSOC) at the German Center Aerospace Center (DLR) in Oberpfaffenhofen, Germany
2002-2005 Preclinical MRI/MRS Lab at Roche Pharmaceuticals in Basle, Switzerland.
since 2006 Max-Planck Institute for biological Cybernetics, Tübingen, Germany
scientific awards:

Wilhelm-Conrad-Röntgen Wissenschaftspreis 2001

of the University of Würzburg

Scientific award 2003 of the unterfränkischen Gedenkjahrstiftung für Wissenschaft

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Articles (55):

Pohmann R, Künnecke B, Fingerle R and von Kienlin M (January-2006) Fast perfusion measurements in rat skeletal muscle at rest and during exercise with single-voxel FAIR (flow-sensitive alternating inversion recovery) Magnetic Resonance in Medicine 55(1) 108-115.
Pohmann R and von Kienlin M (May-2001) Accurate phosphorus metabolite images of the human heart by 3D acquisition-weighted CSI Magnetic Reonance Imaging 45(5) 817–826.
Pohmann R, Rommel E and von Kienlin M (December-1999) Beyond k-Space: Spectral Localization Using Higher Order Gradients Journal of Magnetic Resonance 141(2) 197-206.
Pohmann R, von Kienlin M and Haase A (December-1997) Theoretical Evaluation and Comparison of Fast Chemical Shift Imaging Methods Journal of Magnetic Resonance 129(2) 145-160.
Jakob PM, Kober F, Pohmann R and Haase A (March-1996) Single-Shot Spectroscopic Imaging (SISSI) Using a PEEP/BURST Hybrid Journal of Magnetic Resonance: Series B 110(3) 278-283.

Conference papers (5):

Song H, Liu W, Ruan D, Pohmann R, Stenger VA, Fernandez-Seara MA, Jung S and Gach HM (April-2015) Free-breathing perfusion MRI using multislice pCASL, 12th IEEE International Symposium on Biomedical Imaging (ISBI 2015) IEEE, IEEE, Piscataway, NJ, USA, 1474-1477.
Balla DZ, Ehses P, Pohmann R, Budde J, Mirkes C, Shajan G, Bowtell R and Scheffler K (July-2013) Functional QSM at 9.4T with single echo gradient-echo and EPI acquisition, 2nd International Workshop on MRI Phase Contrast & Quantitative Susceptibility Mapping (QSM 2013), 1-4.
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Chadzynski G, Gunamony S, Kolb R, Pohmann R, Scheffler K and Klose U (September-2012) In-vivo Proton Chemical Shift Imaging at 9.4 Tesla: preliminary study, 43. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP 2012), Deutsche Gesellschaft für Medizinische Physik, Jena, Germany, 60-63.
Seeger MW, Nickisch H, Pohmann R and Schölkopf B (June-2009) Bayesian Experimental Design of Magnetic Resonance Imaging Sequences In: Advances in neural information processing systems 21, , Twenty-Second Annual Conference on Neural Information Processing Systems (NIPS 2008), Curran, Red Hook, NY, USA, 1441-1448.
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Zoeschinger G, Pohmann R, Braun A and Wickler M (October-2002) Mission Planning in a Web Environment In: SpaceOps 2002 Conference, , 7th International Symposium on Space Mission Operations and Ground Data Systems (SpaceOps 2002), American Institute of Aeronautics and Astronautics, Reston, VA, USA, 1-11.

Contributions to books (3):

Pohmann R: Physical Basics of NMR, 3-21. In: In vivo NMR Imaging: Methods and Protocols, (Ed) L. Schröder, Springer Science, Totowa, NJ, USA, (September-2011).
Pohmann R: Spatial Encoding: Basic Imaging Sequences, 23-43. In: In vivo NMR Imaging: Methods and Protocols, (Ed) L. Schröder, Springer Science, Totowa, NJ, USA, (September-2011).
Kienlin M and Pohmann R: Spatial Resolution in Spectroscopic Imaging, 3-20. In: Spatially Resolved Magnetic Resonance: Methods, Materials, Medicine, Biology, Rheology, Geology, Ecology, Hardware, (Ed) P. Blümler, Wiley-VCH, Weinheim, Germany, (1998).

Posters (75):

Balla DZ, Merkle H, Hennel F, Steudel T, Murayama Y, Pohmann R, Scheffler K and Logothetis NK (September-29-2016): Fast fMRI in nonhuman primates at 4.7T with multiband EPI and a 4 Tx/Rx + 1 Rx phased-array concept, 33rd Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2016), Wien, Austria.
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Savić T, Gündüz S, Pohmann R, Logothetis NK, Scheffler K and Angelovski G (May-11-2016): A Ratiometric Bioresponsive MRI Contrast Agent for Rapid Monitoring of Biological Processes, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Chadzynski GL, Bause J, Shajan G, Pohmann R, Scheffler K and Ehses P (May-11-2016): Fast and efficient free induction decay MRSI at 9.4 T: assessment of neuronal activation-related changes in the human brain biochemistry, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Pérez Rodas MA, Engelmann J, Merkle H, Pohmann R and Scheffler K (May-11-2016): Towards fast and highly localized spectroscopy using miniaturized coils in a 14.1T animal scanner, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Pohmann R and Scheffler K (May-10-2016): Smart Averaging: SNR Improvement by Retrospective Filtering, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Martirosian P, Pohmann R, Schraml C, Schmidt H, Schwenzer NF, Schwartz M, Scheffler K, Nikolaou K and Schick F (May-9-2016): Measurement of Liver Perfusion using Pseudo-Continuous Arterial Spin Labeling with Background Suppression: Approaches to Separate Portal-Venous and Arterial Perfusion, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Chadzynski GL, Ehses P, Bause J, Shajan G, Pohmann R and Scheffler K (January-15-2016): A novel approach to assess an extended biochemical profile of the human brain by the means of fast and efficient in-vivo proton Magnetic Resonance Spectroscopic Imaging at 9.4 Tesla, Forschungskolloquium 2016 der Medizinischen Fakultät, Tübingen, Germany.
Bause J, In M-H, Ehses P, Shajan G, Speck O, Pohmann R and Scheffler K (June-3-2015): Distortion-Corrected High Resolution Zoomed fMRI at 9.4 T, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Shajan G, Hoffmann J, Scheffler K and Pohmann R (June-2-2015): An interface to connect a 16-channel transmit array to an 8-channel parallel transmit system, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Balla DZ, Pohmann R, Shajan G, Ehses P, Nauerth A, Steudel T, Murayama Y, Oeltermann A, Munk MH, Merkle H, Beyerlein M, Evrard HC, Logothetis NK and Scheffler K (June-2-2015): 500 ms temporal and 750 μm spatial inplane resolution for whole-brain fMRI applications in the macaque at 7T, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
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Shajan G, Balla DZ, Steudel T, Ehses P, Merkle H, Logothetis NK, Pohmann R and Scheffler K (June-1-2015): A 7T transmit and receive array combination for simultaneous investigation of electrophysiology and fMRI in non-human primates, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Shajan G, Mirkes C, Pohmann R and Scheffler K (June-1-2015): Phosphorus 3D CSI at 9.4 T using a 27-channel Receiver array, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Hoffmann J, Shajan G, Mirkes C, Shao T, Henning A, Pohmann R and Scheffler K (June-1-2015): Towards routine application of dynamic parallel transmission for whole-brain imaging at 9.4 Tesla, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Chadzynski G, Hagberg GE, Bause J, Shajan G, Bisdas S, Pohmann R, Engelmann J and Scheffler K (March-20-2015): Assessment of human brain tumors with proton magnetic resonance spectroscopic imaging at 9.4 Tesla, 10th Annual Meeting of the European Society for Molecular Imaging (EMIM 2015), Tübingen, Germany.
Chadzynski G, Bause J, Hagberg GE, Shajan G, Pohmann R, Engelmann J and Scheffler K (March-19-2015): Free induction decay proton magnetic resonance spectroscopic imaging in the healthy human brain at 9.4 Tesla: initial results, 10th Annual Meeting of the European Society for Molecular Imaging (EMIM 2015), Tübingen, Germany.
Mirkes CC, Shajan G, Hoffmann J, Brenner D, Pohmann R and Scheffler K (May-15-2014): Sodium B1 mapping at 9.4 T, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.
Pohmann R and Scheffler K (May-12-2014): Brain Imaging with 7T Vs. 9.4T: A Direct Comparison of MR Parameters and SNR, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.
Bause J, Ehses P, Shajan G, Scheffler K and Pohmann R (May-12-2014): Functional ASL at 9.4 T: a comparison between balanced SSFP and GRE-EPI readout, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.
Balla DZ, Ehses P, Pohmann R, Budde J, Mirkes C, Shajan G, Bowtell R and Scheffler K (July-2013): Functional QSM at 9.4T with single echo gradient-echo and EPI acquisition, 2nd International Workshop on MRI Phase Contrast & Quantitative Susceptibility Mapping (QSM 2013), Ithaca, NY, USA.
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Bakhtiary M, Shajan G, Hoffmann J, Scheffler K and Pohmann R (April-25-2013): 31P-spectroscopy on humans at 9.4 T in combination with a patch antenna for proton imaging: Initial results, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
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Mirkes C, Hoffmann J, Shajan G, Pohmann R and Scheffler K (April-25-2013): Combination of a sodium birdcage coil with a tunable patch antenna for B0 shimming and anatomical localization at 9.4 T, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
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Chadzynski G, Pohmann R, Shajan G, Kolb R, Klose U and Scheffler K (April-25-2013): Gradient Induced Sideband Artifacts in non Water-Suppressed Proton CSI of the Human Brain at 9.4 T, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
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Mirkes C, Hoffmann J, Shajan G, Pohmann R and Scheffler K (April-23-2013): Amide Proton Chemical Exchange Saturation Transfer at 9.4 T with Optimized RF Transmit Field Through B1 Shimming, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
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Chadzynski G, Bisdas S, Hagberg G, Pohmann R, Shajan G, Kolb R, Klose U and Scheffler K (April-23-2013): First Proton CSI of a Human Brain Tumor at 9.4T, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
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Budde J, Shajan G, Scheffler K and Pohmann R (April-23-2013): Ultra-High-Resolution Imaging of the Human Brain at 9.4 T Using k-Space Weighted Acquisition, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA.
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Budde J, Shajan G, Scheffler K and Pohmann R (March-4-2013): k-Space Weighted Acquisition for Ultra-High-Resolution Imaging of the Human Brain at 9.4 T, ISMRM Workshop Ultra High Field MRI: What is in Full Bloom & What is Sprouting?, Noordwijk aan Zee, Netherlands.
Pohmann R and Scheffler K (October-2012): K-Space Weighted Acquisition for High-Resolution Imaging, 29th Annual Scientific Meeting ESMRMB 2012, Lisboa, Portugal, Magnetic Resonance Materials in Physics, Biology and Medicine, 25(Supplement 1) 511-512.
Bakhtiary M, Pohmann R, Guanmony S and Scheffler K (June-8-2012): NMR phosphorus spectroscopy at 9.4 Tesla using construted Quadrature surface coil, 3rd Scientific Symposium on Ultrahigh Field MR, Berlin, Germany.
Loktyushin A, Nickisch H, Pohmann R and Schölkopf B (May-9-2012): Blind Retrospective Motion Correction of MR Images, 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012), Melbourne, Australia.
Cavusoglu M, Pohmann R and Uludag K (May-9-2012): Magnetization dispersion effetcs on quantitative perfusion imaging for pulsed and continuous arterial spin labeling, 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012), Melbourne, Australia.
Bause J, Shajan G, Hoffmann J, Scheffler K and Pohmann R (May-7-2012): Design and SAR Estimation of a Segmented Loop for Dual Coil CASL at 9.4 T, 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012), Melbourne, Australia.
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Martirosian P, Grözinger G, Rauscher I, Würslin C, Pohmann R, Springer F and Schick F (May-7-2012): Relaxometry of tendons, ligaments and menisci in the knee joint at 3 T, 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012), Melbourne, Australia.
Grözinger G, Pohmann R, Claussen CD, Schick F and Martirosian P (May-2012): Kontrastmittelfreie quantitative Messung der Perfusion der Unterschenkelmuskulatur mittels MR-Spektroskopie-basierter Arterial Spin Labeling (ASL) Technik: FAIR-PRESS, 93. Deutscher Röntgenkongress der DRG, Hamburg, Germany, RöFo: Fortschritte auf dem Gebiet der Röntgenstrahlen und der bildgebenden Verfahren, 184(S 01) VO204_1.
Blecher W, Pohmann R, Schölkopf B and Seeger M (October-2011): Model based reconstruction for GRE EPI, 28th Annual Scientific Meeting ESMRMB 2011, Leipzig, Germany, Magnetic Resonance Materials in Physics, Biology and Medicine, 24(Supplement 1) 493-494.
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Loktyushin A, Nickisch H and Pohmann R (October-2011): Retrospective blind motion correction of MR images, 28th Annual Scientific Meeting ESMRMB 2011, Leipzig, Germany, Magnetic Resonance Materials in Physics, Biology and Medicine, 24(Supplement 1) 498.
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Engelmann J, Keliris A, Ziegler T, Mishra R, Pohmann R, Sauer MG and Ugurbil K (June-2011): A cell-permeable, β-galactosidase targeted contrast agent for optical and MR imaging, 6th European Molecular Imaging Meeting (EMIM 2011), Leiden, The Netherlands.
Shajan G, Hoffmann J and Pohmann R (May-12-2011): A 15-Channel Receive Array & 16-Channel Detunable Transmit Coil for Human Brain Imaging at 9.4T, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada.
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Last updated: Tuesday, 18.11.2014