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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Posters (81):

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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Wiesner HM, Pohmann R, Balla DZ, Chen W, Ugurbil K and Uludag K (May-12-2011): Measurement of CMRO2 changes by somatosensory stimulation in rat using oxygen-17 at 16.4 T, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada.
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Budde J, Mühlbauer F, Shajan G, Zaitsev M and Pohmann R (May-11-2011): Human fMRI at 9.4 T: Preliminary Results, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada.
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Pohmann R (May-10-2011): An experimental comparison of B1-mapping Techniques at two field strengths, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada.
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Deistung A, Budde J, Schweser F, Hoffmann J, Pohmann R and Reichenbach JR (May-10-2011): High Resolution Quantitative Susceptibility Mapping 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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Valverde Salzmann MF, Logothetis NK and Pohmann R (May-10-2011): High-Resolution Imaging of Vessels in the Isolated Rat Brain, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada.
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Gottschalk S, Balla DZ, Pohmann R and Engelmann J (November-2010): Molecular imaging of pancreatic islets in mice with a newly developed beta-cell specific superparamagnetic contrast agent at the ultra high field of 16.4T, 2010 World Molecular Imaging Congress (WMIC), Kyoto, Japan, Molecular Imaging and Biology, 12(Supplement 2) S750.
Angelovski G, Mamdeov I, Engelmann J, Gottschalk S, Balla DZ, Pohmann R and Logothetis NK (November-2010): The Use of Gadolinium-based Contrast Agents for Molecular and Cellular MRI: Quantitative Considerations, 2010 World Molecular Imaging Congress (WMIC), Kyoto, Japan, Molecular Imaging and Biology, 12(Supplement 2) S768.
Moisa M, Pohmann R, Siebner H and Thielscher A (June-2010): Interleaved TMS/CASL: State Dependence of Repetitive TMS Effects on the Dorsal Premotor Cortex, 16th Annual Meeting of the Organisation for Human Brain Mapping (HBM 2010), Barcelona, Spain.
Leitão J, Thielscher A, Werner S, Pohmann R and Noppeney U (June-2010): Investigating the effect of IPS TMS-stimulation on auditory and visual processing: A TMS-fMRI Study, 16th Annual Meeting of the Organisation for Human Brain Mapping (HBM 2010), Barcelona, Spain.
Shajan G, Hoffmann J, Balla DZ and Pohmann R (May-6-2010): A 700MHz Receive Array using Patch Antenna for Spin Excitation, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Hoffmann J, Shajan G and Pohmann R (May-6-2010): Capacitively Tunable Patch Antenna for Human Head Imaging at 9.4 Tesla, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Hoffmann J, Budde J, Shajan G and Pohmann R (May-6-2010): Slice-Selective B1 Phase Shimming at 9.4 Tesla, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Balla DZ, Wiesner HM, Shajan G and Pohmann R (May-5-2010): Functional MRI in the rat at 9.4 T and 16.4 T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Hong S-T, Balla DZ, Shajan G, Choi C, Ugurbil K and Pohmann R (May-5-2010): Localized in Vivo 1H NMR Spectroscopy of the Rat Brain at 16.4T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Nair T, Pohmann R and Gach M (May-4-2010): Aliasing, Off-Resonance Saturation, and Residual Signal Analysis for PCASL, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Pohmann R (May-4-2010): Contrast at Ultra-High Field: Relaxation Times in the Rat Brain at 16.4 T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Hoi C-B, Hong S-T, Kim S-Y, Woo D-C, Choe B-Y, Ryu K-N, Kang EH, Yim S-V, Lee D-W and Pohmann R (May-4-2010): Differential neurochemical responses in the rat striatum with isoflurane or ketamine/xylazine anesthesia: In vivo proton MRS study at 16.4 T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Budde J, Shajan G, Mühlbauer F, Hoffmann J, Ugurbil K and Pohmann R (May-4-2010): Human T2* and Phase Imaging at 9.4 T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Hong S-T, Choi C-B and Pohmann R (May-4-2010): Measurement of the Effects of Different Anesthetics in the Rat Thalamus by in Vivo 1H NMR Spectroscopy at 16.4T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Hong S-T, Balla DZ, Shajan G, Choi C and Pohmann R (May-4-2010): Regional Variations of Metabolite Concentrations in the Rat Brain Assessed with in vivo 1H MR Spectroscopy at 16.4T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Gottschalk S, Balla DZ, Pohmann R and Engelmann J (May-4-2010): Towards in vivo visualization of pancreatic beta-cells in the mouse: Molecular imaging at 16.4T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Hong S-T, Balla DZ, Choi C and Pohmann R (May-3-2010): Evaluation of Minimum Scan Time for High Quality Quantitative in vivo 1H MR Spectroscopy at 16.4T, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Moisa M, Pohmann R, Siebner H and Thielscher A (May-3-2010): Interleaved TMS/CASL: State Dependence of Repetitive TMS Effects on the Dorsal Premotor Cortex, ISMRM-ESMRMB Joint Annual Meeting 2010, Stockholm, Sweden.
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Dhingra K, Mishra A, Engelmann J, Schüz A, Canals S, Pohmann R, Beyerlein M, Maier ME and Logothetis NK (February-2010): Development of Bio-responsive Contrast Agents for Magnetic Resonance Imaging: Potential Applications of a Novel Precursor, 2009 World Molecular Imaging Congress (WMIC), Montréal, Canada, Molecular Imaging and Biology, 12(Supplement 1) S44.
Angelovski G, Chauvin T, Fousková P, Mamedov I, Canals S, Pohmann R, Tóth É and Logothetis NK (October-2009): Smart Calcium-sensitive MRI Agents, 442. Wilhelm und Else Heraeus-Seminar "Molecular Imaging", Bad Honnef, Germany.
Moisa M, Uludag K, Pohmann R and Thielscher A (July-2009): Interleaved TMS/CASL: Comparison of different rTMS protocols, 15th Annual Meeting of the Organisation for Human Brain Mapping (HBM 2009), San Francisco, CA, USA, NeuroImage, 47(Supplement 1) S170.
Hong S-T, Balla DZ, Shajan G, Ugurbil K and Pohmann R (April-22-2009): Highly Accurate Quantification of Proton MR Spectroscopy in Rat Brain in Vivo at 16.4 T, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA.
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Balla DZ, Wiesner HM, Shajan G, Faber C and Pohmann R (April-22-2009): TurboCRAZED BOLD imaging detects specific activation in the rat brain after somatosensory stimulation at 16.4 Tesla, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA.
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Seeger M, Nickisch H, Pohmann R and Schölkopf B (April-21-2009): Optimization of k-Space Trajectories by Bayesian Experimental Design, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA.
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Pohmann R, Budde J, Auerbach E, Adriany G and Ugurbil K (April-21-2009): Theoretical and experimental comparison of different techniques for continuous arterial spin labelling, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA.
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Balla DZ, Wiesner HM, Shajan G and Pohmann R (April-20-2009): Functional MRI in the rat brain with single-shot gradient echo EPI at 16.4 T, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA.
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Klarhöfer M, Lenz C, Haas T, Scheffler K and Pohmann R (April-20-2009): Perfusion Measurements During Reactive Hyperemia in Human Soleus Muscle, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA.
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Wiesner HM, Balla DZ, Pohmann R, Chen W, Ugurbil K and Uludag K (October-15-2008): In-vivo T1 and T2* tissue-relaxation rates of H2O17 at 16.4 Tesla, ISMRM Workshop on High-Field Systems and Applications 2008: "Whats special about 7T+?", Roma, Italy.
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Shajan G, Balla DZ, Hoffmann J and Pohmann R (October-2008): A Microstrip Resonator for Animal MRI at 16.4 T, ESMRMB 2008 Congress: 25th Annual Meeting, Valencia, Spain, Magnetic Resonance Materials in Physics, Biology and Medicine, 21(Supplement 1) 449-450.
Moisa M, Pohmann R, Uludag K and Thielscher A (July-2008): Interleaved TMS/CASL: A motor cortex study, Brain Stimulation, 1(3) 290-291.
Moisa M, Pohmann R, Ugurbil K and Thielscher A (May-8-2008): A new hardware-software coil positioning system for interleaved TMS/fMRI: A motor cortex stimulation study, 16th Scientific Meeting and Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM 2008), Toronto, Canada.
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Balla DZ, Hong S-T, Shajan G, Pohmann R and Ugurbil K (May-6-2008): Single Voxel MR Spectroscopy with Echo Times Below 2 ms at 16.4 T in the Rat Brain: First in vivo Results, 16th Scientific Meeting and Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM 2008), Toronto, Canada.
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Pohmann R and Ugurbil K (May-21-2007): Acquisition-Weighted CSI with a Small Number of Scans, 2007 Joint Annual Meeting ISMRM-ESMRMB, Berlin, Germany.

Popular Scientific Articles (2):

Buckenmaier K, Shajan G, Chadzynski G, Hoffmann J, Pohmann R and Scheffler K: Magnetresonanztomografie bei ultrahohen Feldstärken - Forschungsbericht 2014 Max-Planck-Institut für biologische Kybernetik, Jahrbuch der Max-Planck-Gesellschaft 2014.
Pohmann R: Ultrahohe Magnetfelder in der Magnetresonanz-Bildgebung: Lohnt es sich? - Forschungsbericht 2011 Max-Planck-Institut für biologische Kybernetik, Jahrbuch der Max-Planck-Gesellschaft 2011.

Talks (41):

Tuzzi E, Hagberg G, Balla D, Loureiro J, Neumann M, Laske C, Pohmann R and Valverde M (April-27-2017) Abstract Talk: In-vivo and ex-vivo R2* and Quantitative Susceptibility Mapping in Alzheimer’s Disease at Ultra-High Magnetic Field compared to Histology, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA 677-678.
He Y, Pohmann R, Scheffler K, Kleinfeld D, Rosen B and Yu X (April-25-2017) Abstract Talk: Mapping the task-related and resting-state vascular dynamic network connectivity in rats and humans, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA 304-305.
Loureiro J, Hagberg G, Tuzzi E, Himmelbach M, Ethofer T, Grodd W, Martin P, Valverde M, Pohmann R and Scheffler K (October-1-2016) Abstract Talk: In-vivo ultra-high resolution structural imaging of the human superior colliculus at 9.4T: validation with ex vivo measurements at 9.4T and 14T, 33rd Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2016), Wien, Austria, Magnetic Resonance Materials in Physics, Biology and Medicine, 29(Supplement 1) S376-S377.
Martirosian P, Pohmann R, Schraml C, Schwenzer N, Schmidt H, Schwarz M, Scheffler K, Nikolaou K and Schick F (October-1-2016) Abstract Talk: Perfusion and transit-time quantification in the human liver using pseudo-continuous arterial spin labeling MR imaging, 33rd Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2016), Wien, Austria, Magnetic Resonance Materials in Physics, Biology and Medicine, 29(Supplement 1) S284-S285.
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Last updated: Monday, 22.05.2017