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Department of Radiology - Medical Physics

Experimental Radiology

Ultra High Field MRI

In this research group, novel imaging pulse sequences and hardware for MRI at very high fields (B0 > 3 T) are being developed. For the imaging experiments both the department’s small animal imaging systems (7 T and 9.4 T Bruker) and a 7 T whole body MR system at the DKFZ are being utilized.

Research Projects

Hao Song, Ali Özen, Johannes Fischer

CMRO2 quantitatively represents the rate of oxygen consumption by metabolic processes in brain tissue. Dynamic 17O MR imaging is used to measure it directly and noninvasively through inhalation of isotope-enriched 17O gas (in coop. with Nukem Isotopes). The MR signal change is monitored using dedicated coil hardware, pulse sequences and post-processing methods. Currently, all measurements are performed at a clinical field strength of 3 Tesla in order to apply this technology in patients in the future.

References

Kurzhunov, D., Borowiak, R., Reisert, M., Özen, A.C., Bock, M., 2018. Direct estimation of 17O MR images (DIESIS) for quantification of oxygen metabolism in the human brain with partial volume correction. Magnetic Resonance in Medicine 80(6), 2717-2725.

Kurzhunov, D., Borowiak, R., Hass, H., Wagner, P., Krafft, A.J., Timmer, J., Bock, M., 2017. Quantification of oxygen metabolic rates in human brain with dynamic 17O MRI: profile likelihood analysis. Magnetic Resonance in Medicine 78(3), 1157-1167.

Kurzhunov, D., Borowiak, R., Reisert, M., Krafft, A.J., Özen, A.C., Bock, M., 2017. 3D CMRO2 mapping in human brain with direct 17O MRI: comparison of conventional and proton-con-strained reconstructions. NeuroImage 155, 612-624.

Borowiak, R., Reichardt, W., Kurzhunov, D., Schuch, C., Leupold, J., Krafft, A.J., Reisert, M., Lange, T., Fischer, E., Bock, M., 2017. Initial investigation of glucose metabolism in mouse brain using enriched 17O-glucose and dynamic 17O-MRS. NMR in Biomedicine 30, e3724.

Borowiak, R., Groebner, J., Haas, M., Hennig, J., Bock, M., 2014. Direct cerebral and cardiac 17O-MRI at 3 Tesla: initial results at natural abundance. Magnetic Resonance Materials in Physics, Biology and Medicine 27, 95-99.

Hoffmann SH, et al. Direct 17O MRI with partial volume correction: first experiences in a glioblastoma patient. MAGMA 2014;27(6):579-587

Cooperation Partners

NUKEM Isotopes GmbH

Hao Song, Jeffry Omega Prima, Ali C. Özen

Direct 17O-MRI can be used to observe the dynamics of renal metabolism in kidney transplants. In this work 17O-MRI methods are developed in a porcine kidney in an organ transplantation setup at 3T. To obtain stable SNRs above 20 over time while maintaining a spatial resolution below 8 mm, we investigated the influence of nominal spatial resolution, bandwidth and acquisition time window of a UTE-sequence with golden-angle acquisition pattern on SNR. Signal increase of up to 25% per liter of 17O-gas was observed in a pilot experiment.

To increase SNR further, a dedicated 17O Rx array was designed that fits into a perfusion box used for functional metabolism tests of the donor kidneys. The increased filling ratio resulted in higher SNR compared to the volume and surface Tx/Rx coils. In combination with a Tx-only birdcage 17O coil for homogeneous excitation, the 4-element Rx array also enables parallel imaging.

Top: Anatomical, isotropic 1H-MPRAGE image of the perfused porcine kidney (left) and the corresponding interpolated 17O-magnitude data (right), which were averaged over the entire scan time. Both images are intrinsically registered since 1H-data were acquired by the body coil while the 17O-coil was inserted.


References

Yanis Taege, Johannes Fischer, Ali Çağlar Özen, Hao Song, Christian Schuch, Rianne Schutter, Cyril Moers, Ronald JH Borra, and Michael Bock. Protocol Optimization for Functional 17O-MRI of Donor Kidneys at 3T. ISMRM 27th Annual Meeting & Exhibition 2019.

Cooperation Partners

Nukem Isotopes GmbH

Groningen group, University of Groningen

Johannes Fischer, Ali C. Özen

Imaging of the vocal folds oscillation is difficult with MRI as it requires a temporal resolution below 1 ms, which is not feasible with conventional encoding schemes. In this new approach to ultra-fast MRI we use only the phase encoding (PE) gradient to encode the one-dimensional motion, effectively reducing the temporal resolution to the duration of the PE gradient. For the retrospectively gated reconstruction, an electroglottogram (EGG) is simultaneously acquired using customized and MR-safe electrodes. Complementary to laryngeal stroboscopy, this technique allows for a look below the surface of the tissues in motion.

References

Fischer, J, Abels, T, Özen, AC, Echternach, M, Richter, B, Bock, M. Magnetic resonance imaging of the vocal fold oscillations with sub‐millisecond temporal resolution. Magn Reson Med. 2020; 83: 403– 411.

Özen, A.C., Traser, L., Echternach, M., Dadakova, T., Burdumy, M., Richter, B. and Bock, M. (2016), Ensuring safety and functionality of electroglottography measurements during dynamic pulmonary MRI. Magn. Reson. Med., 76: 1629-1635.


Past Projects

Maddalena Strumia, Wilfried Reichardt

To differentiate between abnormal tumor vessels and regular brain vasculature using new quantitative measures in time-of-flight (TOF) MR angiography (MRA) data (in cooperation with the DKTK)

References

Strumia M, Reichardt W, Staszweski O, Heiland DH, Weyerbrock A, Mader I, Bock M. Glioma vessel abnormality quantification using time-of-flight MR angiography. MAGMA. 2016 Oct;29(5):765-75.

Radio-frequency coils and pulse sequence technologies for parallel signal reception and excitation (pTx) developed for both animal and human-sized MR systems (in cooperation with IMTEK  and QED)

Prof. Dr. Michael Bock
Director of Experimental Radiology

Tel. +49 761 270-94140
Fax +49 761 270-93790
E-Mail: michael.bock@uniklinik-freiburg.de

University Medical Center Freiburg
Dept. of Radiology · Medical Physics
Killianstr. 5a
79106 Freiburg, Germany
 

Tracey Webb-Kolbinger
Administrative Assistant
Tel. +49 761 270-93840
Fax +49 761 270-93790
E-Mail: tracey.webb-kolbinger@uniklinik-freiburg.de