Project Leader

Dr. Rolf Pohmann
Phone: +49 7071 601-903
Fax: +49 7071 601-702
Opens window for sending emailRolf.Pohmann[at]

Current and former Lab members

  • Hardware and B1 shaping:
      Gunamony, Shajan (engineer)
      Jens Hoffmann (PhD student)

  • Anatomical and functional Imaging:
      Dr. Matthias F. Valverde Salzmann (Postdoc)
      Dr. Juliane Budde (former PhD student)
      Dr. David Balla(former Postdoc)
      Dr. Tram Nguyen (former PhD student)

  • Spectroscopy:
      Dr. Sung-Tak Hong (former PhD student)
      Morteza Bakhtiary (PhD student)
      Marlon Arturo Perez Rodas (PhD student)
  • 17O Imaging
      Hannes Wiesner (former PhD student)

  • Perfusion Imaging:
      Jonas Bause (PhD student)
      Dr. Mustafa Cavasoglu (former PhD student)


Ultra High Field Magnetic Resonance

Human venogram acquired at 9.4 T (left) and image of the rat brain from 16.4 T.
The High-Field MR and Methodology group focuses mainly on the development of MR techniques, with emphasis on MR imaging and spectroscopy at ultra high field. In addition, the characteristics and advantages of ultra high magnetic fields are investigated.
With a 9.4 T MR scanner for humans and a 14.1 T instrument for small animals, our institute has a unique instrumentation that makes it a pioneer in the investigation of ultrahigh field imaging. Thus, the main goals of our group are to develop imaging techniques to make it possible to fully take advantage of the high magnetic field. In addition, the special properties of MR imaging at those field strengths are investigated and applications for which especially high gains are expected are implemented and characterized.

High magnetic field strengths have a high potential for magnetic resonance imaging and spectroscopy: The signal-to-noise ratio increases, the longitudinal relaxation time - and thus the potential to store additional information -  grows, the sensitivity to detect small local changes in the magnetic properties of tissue gets stronger and the spectral dispersion and thus the information contained in an NMR spectrum increases. Simultaneously, however, the physical properties of the MR signal change drastically as the field gets higher, requiring novel approaches in both hardware and measuring techniques.
We aim to develop the technology that make it possible to fully take advantage of the expected gain at ultra high field:
  • Evaluation of the potential advantages and limitations imposed by using high magnetic fields,
  • Development of optimized measuring techniques with the aim of taking full advantage of the improved imaging characteristics,
  • Combine MRI with other technologies to enhance the significance of neuroscientific studies.
  • Support of other groups within the department by developing and optimizing imaging techniques adapted to their applications.

The main projects currently are:

Anatomical Imaging

The high field strengths used in our scanners open the potential of increased SNR with different or even novel contrast mechanisms. A systematic comparison between human brain imaging at 3 T, 7 T and 9.4 T has shown a distinctly supralinear SNR gain with field strength, giving rise to a more than five times higher SNR at 9.4 T than at 3 T. Even at 16.4 T, our investigations have shown considerably improved image quality in images with contrast based on the relaxation times as well as on image phase and magnetization transfer [2]. In spite of the high T1 values of around 2250 ms in gray matter at that field, the SNR gain still increases rapidly with the field strength.
With T2* and image phase, excellent contrast can be obtained with very high spatial resolutions in a way that is exclusive to high field. In human imaging at 9.4 T, inplane resolutions down to 130 μm were possible using an SNR optimized imaging technique. A high amount of anatomical information iscontained in T2*-images, which can be used to detect large strains of nerve fibers or regions with high iron content. Even higher gains are possible by taking advantage of the phase of the image: phase imaging makes intra-cortical structures visible that cannot be observed with other imaging techniques. With susceptibility-weighted imaging (SWI) it is possible to visualize venous structures at very fine detail with SNR increasing drastically with magnetic field strength when compared to similar data acquired at 3 T (Fig. 2). Measurements at 16.4 T have shown that in addition, the highly enhanced effect of magnetization transfer can serve as an additional means for contrast enhancement. Here, the high SNR allows for isotropic spatial resolutions below 50 μm can easily be obtained in ex vivo measurements, while in vivo experiments in the abdomen of living mice reached a voxel size of 66 × 66 × 100 μm3 within ten minutes in spite of the rapid motion due to breathing.

Functional Imaging

In functional imaging, isotropic spatial resolutions of 1 mm for humans and 150 μm in rats were reached with high signal variations due to brain activation. Using a special EPI sequence with correction of image distortions due to field inhomogeneities, it was possible to accurately overlay phase information, which distinctly shows the positions of veins, and functional activation maps with the aim of comparing the main BOLD-signal contributions with the venous architecture. For fMRI based on gradient-echo EPI, it could be shown that the major signal contributions arise from the draining veins as expected from theoretical predictions. It will have to be shown whether the expectation of improved weighting of the small vasculature in comparison to larger veins for spin-echo based imaging realizes the promises for improved spatial specificity at high field strengths.


In addition to the high sensitivity, in vivo MR spectroscopy profits from the increased spectral dispersion, causing the expectation of an especially high gain at ultra high field. Thus, proton spectroscopy in the rat brain at 16.4 T was implemented and optimized acquisition and quantification techniques were developed. A localized STEAM sequence with short echo times and improved water suppression was established and a novel, improved algorithm to take the signals of macromolecules into account was developed. With these techniques, the high sensitivity and spectral dispersion made it possible to quantify up to 20 metabolites, including glycine and acetate (Fig. 3). Additional studies verified the high precision and accuracy of these measurements even in short experiments or from difficult deep brain regions, like the medulla oblongata or the cerebellum [3]. Applications in different rat strains or brain regions showed the capability of detecting even small variations in the concentration of single metabolites [4].

Perfusion measurements

Quantifying the perfusion in the brain or other organs without the need to use contrast agent is challenging due to the low amplitude of the signal obtained with Arterial Spin Labeling techniques. We concentrate on increasing the sensitivity of ASL measurements by developing and applying highly sensitive techniques like continuous ASL or a specially developed technique for quantifying low perfusion, as in muscle or in white matter brain tissue. In addition, using ultra-high field ASL will yield improved perfusion images due to the high intrinsic sensitivity at high field and the increased longitudinal relaxation time.

Last updated: Tuesday, 10.02.2015