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

Preferences: 
References per page: Year: Medium:

  
Show abstracts

Talks (45):

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.
Tuzzi E, Hagberg G, Balla DZ, Loureiro J, Neumann M, Laske C, Pohmann R, Valverde M and Scheffler K (September-30-2016) Abstract Talk: Ex-vivo and in-vivo ultra-High-Field R2* and QSM microimaging in Alzheimer’s disease, 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) S144-S145.
Pohmann R (September-24-2016) Invited Lecture: Optical imaging with fMRI, Satellite Symposium "Multi-modal fMRI from photons to protons", 5th Biennial Conference on Resting State and Brain Connectivity, Wien, Austria.
He Y, Pohmann R, Scheffler K, Kleinfeld D, Rosen B and Yu X (September-2016) Abstract Talk: Map task-related and resting-state Vascular Network Connectivity in Rats and Humans, 17th Conference of Junior Neuroscientists of Tübingen (NeNa 2016): Neuroscience & Law, Schramberg, Germany 13.
Valverde Salzmann MF, Scheffler K and Pohmann R (May-11-2016) Abstract Talk: Concurrent fMRI and intrinsic optical imaging spectroscopy with high resolution at ultra high field (14.1T), 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore(0766).
Hagberg GE, Bause J, Ethofer T, Ehses P, Dresler T, Shajan G, Pohmann R, Herbert C, Fallgatter A, Laske C, Pavlova M and Scheffler K (May-9-2016) Abstract Talk: Consistent detection of age-dependent variations of the longitudinal relaxation time in cortical brain regions investigated by MP2RAGE at 9.4T: influence of correcting for a non-uniform transmit field, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore(0059).
Pohmann R (March-7-2016) Invited Lecture: Ultra-High Resolution Imaging of the Human Brain at 9.4 T Using Prospective Motion Correction, ISMRM Workshop on Ultra High Field MRI: Technological Advances & Clinical Applications, Heidelberg, Germany.
Shajan G, Bause J, Pohmann R and Scheffler K (October-2015) Abstract Talk: Choice of RF coils at 9.4T: SNR and B1+ of transceiver and transmit-only receive-only arrays, 32nd Annual Scientific Meeting ESMRMB 2015, Edinburgh, UK, Magnetic Resonance Materials in Physics, Biology and Medicine, 28(1 Supplement) S58-S59.
Chadzynski GL, Scheffler K, Bause J, Shajan G, Pohmann R and Ehses P (October-2015) Abstract Talk: Fast and efficient free induction decay proton MRSI in the human brain at 9.4 T, 32nd Annual Scientific Meeting ESMRMB 2015, Edinburgh, UK, Magnetic Resonance Materials in Physics, Biology and Medicine, 28(1 Supplement) S298-S299.
Bause J, Scheffler K and Pohmann R (October-2015) Abstract Talk: Simulation of Flow-Driven Adiabatic Inversion in Dual Coil Continuous ASL at 9.4 T, 32nd Annual Scientific Meeting ESMRMB 2015, Edinburgh, UK, Magnetic Resonance Materials in Physics, Biology and Medicine, 28(1 Supplement) S367-S368.
Pohmann R and Scheffler K (October-2015) Abstract Talk: Smart Averaging, 32nd Annual Scientific Meeting ESMRMB 2015, Edinburgh, UK, Magnetic Resonance Materials in Physics, Biology and Medicine, 28(1 Supplement) S103.
Hagberg GE, Bause J, Ethofer T, Dresler T, Herbert C, Pohmann R, Shajan G, Fallgatter A and Scheffler K (October-2015) Abstract Talk: T1 relaxometry and tissue segmentation of the human brain at 9.4T and 3T using MP2RAGE, 32nd Annual Scientific Meeting ESMRMB 2015, Edinburgh, UK, Magnetic Resonance Materials in Physics, Biology and Medicine, 28(1 Supplement) S234-S235.
Pohmann R, Bause J, Mirkes C, Eschelbach M, Engel E-M and Scheffler K (October-2015) Abstract Talk: Ultrahigh resolution anatomical brain imaging at 9.4 T using prospective motion correction, 32nd Annual Scientific Meeting ESMRMB 2015, Edinburgh, UK, Magnetic Resonance Materials in Physics, Biology and Medicine, 28(1 Supplement) S155.
Chadzynski GK, Hagberg G, Bause J, Shajan G, Bisdas S, Pohmann R and Scheffler K (June-5-2015) Abstract Talk: In-vivo proton MR spectroscopic imaging of the human brain gliomas at 9.4 Tesla: evaluation of metabolite coordinates, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada(0763).
Shajan G, Mirkes C, Hoffmann J, Scheffler K and Pohmann R (May-14-2014) Abstract Talk: A Three-Layered Coil Arrangement for Sodium Imaging of the Human Brain at 9.4T, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy(0620).
Hoffmann J, Mirkes C, Shajan G, Scheffler K and Pohmann R (May-13-2014) Abstract Talk: A 3-Port Traveling-Wave Antenna in Combination with TIAMO for the Acquisition of Void-Free Brain Images at 9.4 Tesla, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy(0399).
Mirkes C, Hoffmann J, Shajan G, Pohmann R and Scheffler K (October-5-2013) Abstract Talk: Quantitative Sodium Imaging at 9.4 T, 30th Annual Scientific Meeting ESMRMB 2013, Toulouse, France, Magnetic Resonance Materials in Physics, Biology and Medicine, 26(Supplement 1) 370.
Hoffmann J, Shajan G, Scheffler K and Pohmann R (October-4-2013) Abstract Talk: Combination of Multimode Traveling-Wave Excitation and TIAMO for Human Brain Imaging at 9.4 T, 30th Annual Scientific Meeting ESMRMB 2013, Toulouse, France, Magnetic Resonance Materials in Physics, Biology and Medicine, 26(Supplement 1) 192.
Bause J, Shajan G, Scheffler K and Pohmann R (October-4-2013) Abstract Talk: High Resolution Arterial Spin Labeling in the Human Brain at 9.4 T: Initial Results using FAIR, 30th Annual Scientific Meeting ESMRMB 2013, Toulouse, France, Magnetic Resonance Materials in Physics, Biology and Medicine, 26(Supplement 1) 257.
pdf
Loktyushin A, Nickisch H, Pohmann R and Schölkopf B (October-4-2013) Abstract Talk: Multi-rigid motion correction of MR images, 30th Annual Scientific Meeting ESMRMB 2013, Toulouse, France, Magnetic Resonance Materials in Physics, Biology and Medicine, 26(Supplement 1) 176.
Pohmann R (June-25-2013) Invited Lecture: MR sequence development for perfusion and structural imaging at 3T and 9.4T, Danish Research Centre for Magnetic Resonance (DRCMR), Hvidovre, Denmark.
Hoffmann J, Shajan G, Scheffler K and Pohmann R (April-23-2013) Abstract Talk: RF Shimming Capabilities at 9.4 Tesla using a 16-channel Dual-Row Array, 21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013), Salt Lake City, UT, USA 901.
pdf
Shajan G, Hoffmann J, Scheffler K and Pohmann R (October-2012) Abstract Talk: A 31-Element Receive Array for Human Brain Imaging at 9.4T, 29th Annual Scientific Meeting ESMRMB 2012, Lisboa, Portugal, Magnetic Resonance Materials in Physics, Biology and Medicine, 25(Supplement 1) 265-266.
Chadzynski GI, Shajan G, Kolb R, Pohmann R, Klose U and Scheffler K (October-2012) Abstract Talk: In-vivo Proton Chemical Shift Imaging at 9.4 T: initial results, 29th Annual Scientific Meeting ESMRMB 2012, Lisboa, Portugal, Magnetic Resonance Materials in Physics, Biology and Medicine, 25(Supplement 1) 270.
Shajan G, Hoffmann J, Scheffler K and Pohmann R (May-8-2012) Abstract Talk: A 16-Element Dual-row Transmit Coil Array for 3D RF Shimming at 9.4 T, 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012), Melbourne, Australia(308).
Budde J, Shajan G, Zaitsev M, Scheffler K and Pohmann R (May-8-2012) Abstract Talk: Human functional imaging at 9.4 T: Spin echo and gradient echo EPI, 20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012), Melbourne, Australia(327).
Balla D, Gottschalk S, Shajan G, Ueberberg S, Schneider S, Pohmann R and Engelmann J (May-12-2011) Abstract Talk: In vivo visualization of pancreatic islets in the mouse, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada 648.
pdf
Hoffmann JO, Shajan G and Pohmann R (May-9-2011) Abstract Talk: Human Brain Imaging at 9.4 Tesla Using a Combination of Traveling Wave Excitation with a 15-Channel Receive-Only Array, 19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), Montréal, Canada 157.
pdf
Pohmann R (January-14-2011) Invited Lecture: Technical Challenges of Ultra-High Field Imaging, 1st International Workshop on MRI Phase Contrast & Quantitative Susceptibility Mapping (QSM 2011), Dornburg, Germany.
Pohmann R (September-2010) Invited Lecture: Cortical structure observed by phase contrast at high fields, IVth European Conference of Medical Physics on Advances in High Field Magnetic Resonance Imaging 2010, Udine, Italy 46.
Pohmann R (September-2010) Invited Lecture: Travelling Wave MR, IVth European Conference of Medical Physics on Advances in High Field Magnetic Resonance Imaging 2010, Udine, Italy 19.
Pohmann R (March-2010) Invited Lecture: MR-Bildgebung bei 9,4 T, Arbeitskreis Magnetresonanzverfahren der DGMP: 45. Arbeitskreissitzung, Ettlingen, Germany.
Pohmann R (October-1-2009): Accurate, localized quantification of white matter perfusion with ASL, ESMRMB 2009 Congress: 26th Annual Meeting, Antalya, Turkey, Magnetic Resonance Materials in Physics, Biology and Medicine, 22(Supplement 1) 94-95.
Wiesner HM, Balla DZ, Pohmann R, Chen W, Ugurbil K and Uludag K (April-21-2009) Abstract Talk: 17 O T1/T2* tissue-relaxation rates with anatomical contrast in the rat brain at 16.4 T, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA(354).
pdf
Budde J, Pohmann R, Shajan G and Ugurbil K (April-20-2009) Abstract Talk: Susceptibility Weighted Imaging of the Human Brain at 9.4T, 17th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2009), Honolulu, HI, USA(43).
Seeger M, Nickisch H, Pohmann R and Schölkopf B (November-20-2008) Invited Lecture: Bayesian Optimization of Magnetic Resonance Imaging Sequences, Workshop Machine Learning Approaches to Representational Learning and Recognition in Vision, Frankfurt a.M., Germany.
Pohmann R and Budde J (October-4-2008) Abstract Talk: Theoretical and experimental comparison of different techniques for continuous arterial spin labelling, ESMRMB 2008 Congress: 25th Annual Meeting, Valencia, Spain, Magnetic Resonance Materials in Physics, Biology and Medicine, 21(Supplement 1) 205.
Pohmann R and Gemballa S (October-3-2008) Abstract Talk: Shark Imaging, ESMRMB 2008 Congress: 25th Annual Meeting, Valencia, Spain, Magnetic Resonance Materials in Physics, Biology and Medicine, 21(Supplement 1) 109.
pdf
Balla DZ, Faber C, Schneider JT, Shajan G and Pohmann R (October-2-2008) Abstract Talk: Strong BOLD-effect with TurboCRAZED MRI following hyperoxia in the rat brain at 16.4 T, ESMRMB 2008 Congress: 25th Annual Meeting, Valencia, Spain, Magnetic Resonance Materials in Physics, Biology and Medicine, 21(Supplement 1) 36-37.
Page:  
1, 2, 3, 4

Export as:
BibTeX, XML, Pubman, Edoc, RTF
Last updated: Monday, 22.05.2017