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Dr. Rolf Pohmann

Adresse: Spemannstr. 41
72076 Tübingen
Raum Nummer: 3.B.02
Tel.: 07071 601 903
Fax: 07071 601 702
E-Mail: Rolf.Pohmann

 

Bild von Pohmann, Rolf, Dr.

Rolf Pohmann

Position: Projektleiter  Abteilung: 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 16.4 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

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.

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.


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).


Evaluation of 9.4T MR

While the field strength of 7 T has become a standard for ultra-high field MR, the trend towards even higher field strengths continues. However, the more unfavorable relaxation times, the increasing inhomogeneity of the transmit field as well as the more difficult coil design pose the question, whether the expected increase in intrinsic SNR with field strength can actually be realized at 9.4 T. In this project, we perform a direct comparison between 3 T, 7 T and 9.4 T and assess differences in relaxation times, B1-inhomogeneity, transmit efficiency, SNR and g-factor.


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

Präferenzen: 
Referenzen pro Seite: Jahr: Medium:

  
Zeige Zusammenfassung

Artikel (37):

Rauscher I , Bender B , Grözinger G , Luz O , Pohmann R Person, Erb M , Schick F und Martirosian P (November-2014) Assessment of T1, T1ρ, and T2 values of the ulnocarpal disc in healthy subjects at 3 Tesla Magnetic Resonance Imaging 32(9) 1085–1090.
Hoffmann J Person, Shajan G Person, Scheffler K Person und Pohmann R Person (Oktober-2014) Numerical and experimental evaluation of RF shimming in the human brain at 9.4 T using a dual-row transmit array Magnetic Resonance Materials in Physics, Biology and Medicine 27(5) 373-386.
Grözinger G , Pohmann R Person, Schick F , Grosse U , Syha R , Brechtel K , Rittig K und Martirosian P (Oktober-2014) Perfusion measurements of the calf in patients with peripheral arterial occlusive disease before and after percutaneous transluminal angioplasty using Mr arterial spin labeling Journal of Magnetic Resonance Imaging 40($) 980–987.
Chadzynski GL Person, Pohmann R Person, Shajan G Person, Kolb R , Bisdas S , Klose U und Scheffler K Person (September-2014) In vivo proton magnetic resonance spectroscopic imaging of the healthy human brain at 9.4 T: initial experience Magnetic Resonance Materials in Physics, Biology and Medicine Epub ahead.
Balla DZ Person, Schwarz S Person, Wiesner HM Person, Hennige AM und Pohmann R Person (Juli-2014) Monitoring the stress-level of rats with different types of anesthesia: A tail-artery cannulation protocol Journal of Pharmacological and Toxicological Methods 70(1) 35-39.
Rauschenberg J , Nagel AM , Ladd SC , Theysohn JM , Ladd ME , Möller HE , Trampel R , Turner R , Pohmann R Person, Scheffler K Person, Brechmann A , Stadler J , Felder J , Shah NJ und Semmler W (Mai-2014) Multicenter Study of Subjective Acceptance During Magnetic Resonance Imaging at 7 and 9.4 T Investigative Radiology 49(5) 249-259.
Loktyushin A Person, Nickisch H Person, Pohmann R Person und Schölkopf B Person (April-2014) Blind multirigid retrospective motion correction of MR images Magnetic Resonance in Medicine Epub ahead.
Shajan G Person, Kozlov M , Hoffmann J Person, Turner R , Scheffler K Person und Pohmann R Person (Februar-2014) A 16-channel dual-row transmit array in combination with a 31-element receive array for human brain imaging at 9.4 T Magnetic Resonance in Medicine 71(2) 870–879.
Budde J Person, Shajan G Person, Scheffler K Person und Pohmann R Person (Februar-2014) Ultra-high resolution imaging of the human brain using acquisition-weighted imaging at 9.4 T NeuroImage 86 592–598.
Budde J Person, Shajan G Person, Zaitsev M , Scheffler K Person und Pohmann R Person (Januar-2014) Functional MRI in human subjects with gradient-echo and spin-echo EPI at 9.4 T Magnetic Resonance in Medicine 71(1) 209–218.
Mirkes CC Person, Hoffmann J Person, Shajan G Person, Pohmann R Person und Scheffler K Person (Januar-2014) High-resolution quantitative sodium imaging at 9.4 tesla Magnetic Resonance in Medicine Epub ahead.
Loktyuschin A , Nickisch H Person, Pohmann R Person und Schölkopf B Person (Dezember-2013) Blind Retrospective Motion Correction of MR Images Magnetic Resonance in Medicine 70(6) 1608–1618.
Balla DZ Person, Gottschalk S Person, Shajan G Person, Ueberberg S , Schneider S , Hardtke-Wolenski M , Jaeckel E , Hoerr V , Faber C , Scheffler K Person, Pohmann R Person und Engelmann J Person (Dezember-2013) In vivo visualization of single native pancreatic islets in the mouse Contrast Media & Molecular Imaging 8(6) 495-504.
Hoffmann J Person, Shajan G Person, Budde J Person, Scheffler K Person und Pohmann R Person (Mai-2013) Human brain imaging at 9.4 T using a tunable patch antenna for transmission Magnetic Resonance in Medicine 69(5) 1494–1500.
Leitão J Person, Thielscher A Person, Werner S Person, Pohmann R Person und Noppeney U Person (April-2013) Effects of Parietal TMS on Visual and Auditory Processing at the Primary Cortical Level: A Concurrent TMS-fMRI Study Cerebral Cortex 23(4) 873-884.
Pohmann R Person, Shajan G Person, Hoffmann J Person, Budde J Person, Hagberg G Person, Bieri O , Bisdas S , Ernemann U , Weigel M , Ehses P Person, Hennig J , Chadzynski G und Scheffler K Person (April-2013) Imaging and Spectroscopy at 9.4 Tesla: First Results on Patients and Volunteers MAGNETOM Flash 2013(2) 58-67.
Pohmann R Person und Scheffler K Person (März-2013) A theoretical and experimental comparison of different techniques for B1 mapping at very high fields NMR in Biomedicine 26(3) 265–275.
Cavusoglu M Person, Pohmann R Person, Burger HC Person und Uludag K Person (Februar-2013) Regional effects of magnetization dispersion on quantitative perfusion imaging for pulsed and continuous arterial spin labeling Magnetic Resonance in Medicine 69(2) 524–530.
Hong S-T Person und Pohmann R Person (Januar-2013) Quantification issues of in vivo 1H NMR spectroscopy of the rat brain investigated at 16.4 T NMR in Biomedicine 26(1) 74–82.
Shajan G Person, Hoffmann J Person, Balla DZ Person, Deelchand DK , Scheffler K Person und Pohmann R Person (Oktober-2012) Rat brain MRI at 16.4T using a capacitively tunable patch antenna in combination with a receive array NMR in Biomedicine 25(10) 1170–1176.
Moisa M Person, Siebner HR , Pohmann R Person und Thielscher A Person (Mai-2012) Uncovering a context-specific connectional fingerprint of human dorsal premotor cortex Journal of Neuroscience 32(21) 7244-7252.
Ziegler A , Kunth M , Mueller S , Bock C , Pohmann R Person, Schröder L , Faber C und Giribet G (Dezember-2011) Application of magnetic resonance imaging in zoology Zoomorphology 130(4) 227-254.
Pohmann R Person, Shajan G Person und Balla D Person (Dezember-2011) Contrast at high field: Relaxation times, magnetization transfer and phase in the rat brain at 16.4 T Magnetic Resonance in Medicine 66(6) 1572-1581.
Hong ST Person, Balla DZ Person, Choi C und Pohmann R Person (Dezember-2011) Rat strain-dependent variations in brain metabolites detected by in vivo (1) H NMR spectroscopy at 16.4T NMR in Biomedicine 24(10) 1401-1407.
Shajan G Person, Hoffmann J Person, Budde J Person, Adriany G , Ugurbil K und Pohmann R Person (August-2011) Design and Evaluation of an RF Front-End for 9.4 T Human MRI Magnetic Resonance in Medicine 66(2) 594–602.
Hong S-T Person, Balla D Person und Pohmann R Person (Juli-2011) Determination of regional variations and reproducibility in in vivo (1) H NMR spectroscopy of the rat brain at 16.4 T Magnetic Resonance in Medicine 66(1) 11-17.
Keliris A Person, Ziegler T , Mishra R Person, Pohmann R Person, Sauer M , Ugurbil K und Engelmann J Person (April-2011) Synthesis and Characterization of a Cell-Permeable Bimodal Contrast Agent Targeting β-Galactosidase Biorganic & Medicinal Chemistry 19(8) 2529-2540.
Angelovski G Person, Chauvin T , Pohmann R Person, Logothetis NK Person und Toth E (Februar-2011) Calcium-responsive paramagnetic CEST agents Bioorganic and Medicinal Chemistry 19(3) 1097-1105.
Budde J Person, Shajan G Person, Hoffmann J Person, Ugurbil K und Pohmann R Person (Februar-2011) Human imaging at 9.4 T using T2*-, phase-, and susceptibility-weighted contrast Magnetic Resonance in Medicine 65(2) 544-550.
Hong S-T Person, Balla DZ Person, Shajan G Person, Choi C , Ugurbil K und Pohmann R Person (Januar-2011) Enhanced neurochemical profile of the rat brain using in vivo 1H NMR spectroscopy at 16.4 T Magnetic Resonance in Medicine 65(1) 28-34.
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Pohmann R Person (Oktober-2010) Accurate, localized quantification of white matter perfusion with single-voxel ASL Magnetic Resonance in Medicine 64(4) 1109-1113.
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Joshi R Person, Mishra R Person, Pohmann R Person und Engelmann J Person (April-2010) MR contrast agent composed of cholesterol and peptide nucleic acids: Design, synthesis and cellular uptake Bioorganic and Medicinal Chemistry Letters 20(7) 2238-2241.
Pohmann R Person, Budde J Person, Auerbach EJ , Adriany G und Ugurbil K (Februar-2010) Theoretical and Experimental Evaluation of Continuous Arterial Spin Labeling Techniques Magnetic Resononance in Medicine 63(2) 438-446.
Moisa M Person, Pohmann R Person, Uludag K Person und Thielscher A Person (Januar-2010) Interleaved TMS/CASL: Comparison of different rTMS protocols NeuroImage 49(1) 612-620.
Seeger M Person, Nickisch H Person, Pohmann R Person und Schölkopf B Person (Januar-2010) Optimization of k-Space Trajectories for Compressed Sensing by Bayesian Experimental Design Magnetic Resonance in Medicine 63(1) 116-126.
Mishra R Person, Su W Person, Pohmann R Person, Pfeuffer J Person, Sauer MG , Ugurbil K und Engelmann J Person (September-2009) Cell-Penetrating Peptides and Peptide Nucleic Acid-Coupled MRI Contrast Agents: Evaluation of Cellular Delivery and Target Binding Bioconjugate Chemistry 20(10) 1860-1868.
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Moisa M Person, Pohmann R Person, Ewald L und Thielscher A Person (Januar-2009) New coil positioning method for interleaved transcranial magnetic stimulation (TMS)/functional MRI (fMRI) and its validation in a motor cortex study Journal of Magnetic Resonance Imaging 29(1) 189-197.

Beiträge zu Tagungsbänden (2):

Balla DZ Person, Ehses P Person, Pohmann R Person, Budde J Person, Mirkes C Person, Shajan G Person, Bowtell R und Scheffler K Person (Juli-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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Seeger MW Person, Nickisch H Person, Pohmann R Person und Schölkopf B Person (Juni-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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Beiträge zu Büchern (2):

Pohmann R Person: 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 Person: 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).

Poster (58):

Mirkes CC Person, Shajan G Person, Hoffmann J Person, Brenner D , Pohmann R Person und Scheffler K Person (Mai-15-2014): Sodium B1 mapping at 9.4 T, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.
Pohmann R Person und Scheffler K Person (Mai-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 Person, Ehses P Person, Shajan G Person, Scheffler K Person und Pohmann R Person (Mai-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 Person, Ehses P Person, Pohmann R Person, Budde J Person, Mirkes C Person, Shajan G Person, Bowtell R und Scheffler K Person (Juli-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 Person, Shajan G Person, Hoffmann J Person, Scheffler K Person und Pohmann R Person (April-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 Person, Hoffmann J Person, Shajan G Person, Pohmann R Person und Scheffler K Person (April-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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Mirkes C Person, Hoffmann J Person, Shajan G Person, Pohmann R Person und Scheffler K Person (April-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 Person, Bisdas S , Hagberg G Person, Pohmann R Person, Shajan G Person, Kolb R , Klose U und Scheffler K Person (April-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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Chadzynski G Person, Pohmann R Person, Shajan G Person, Kolb R , Klose U und Scheffler K Person (April-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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Last updated: Dienstag, 18.11.2014