Functional High Field MRI | Universitätsklinikum Freiburg

Experimental Radiology

Functional High Field MRI

To assess tissue function, we develop novel imaging pulse sequences and hardware for MRI at very high fields (B0 ≥ 3 T). Tissue oxygenation, metabolism and inflammation are studied using non-proton MRI techniques, and the oscillation of the vocal folds is imaged using novel MRI techniques with sub-millisecond temporal resolution. For the imaging experiments both the small animal imaging systems (7 T and 9.4 T Bruker) at AMIR and a 7 T whole body MR system at the DKFZ are used.

Research Projects

19F MRI for Tracking Myeloid Cells

Kian Tadjalli Mehr, Ali C. Özen, Simon Reiss, Michael Bock

Myeloid cells are involved in inflammatory healing processes during and after myocardial infarction and are therefore of interest for novel therapeutic approaches. Since they take up injected perfluorocarbons (e.g. perfluorooctyl bromide (PFOB)), these cells can be tracked using ¹⁹F MRI. This project focuses on developing ¹⁹F MRI imaging methods to maximize the signal gained from such tracers.

Combined ¹H and ¹⁹F image of a porcine spleen after PFOB injection

Cooperation Partners

Cardiology and Angiology I, Heart Center, Freiburg University and Faculty of Medicine, Freiburg, Germany

References

Özen AC, Spreter F, Schimpf W, et al. Scalable and modular 8-channel transmit and 8-channel flexible receive coil array for 19 F MRI of large animals. Magn Reson Med. 2023;89(3):1237-1250.

Grant support

Funded by DFG project number 415243609 and SFB 1425 project number 422681845.

Dynamic Imaging of the Vocal Fold Oscillation

Johannes Fischer, Paula Jordan

Conventional optical laryngoscopy is limited to a top down view of the vocal fold surface. This makes it insensitive to important physiological features such as the vocal fold contact area or the vertical oscillation amplitude. To reveal this dynamic behavior below and within the vocal folds, we develop MRI techniques than can resolve this rapid motion with sub-millisecond temporal resolution, by using time-optimized MRI pulse sequences. We have successfully imaged the motion in 1D and 2D and are currently working on a fully isotropic 3D implementation.

References

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.

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.

Fischer J, Özen AC, Ilbey S, Traser L, Echternach M, Richter B, Bock M. Sub-millisecond 2D MRI of the vocal fold oscillation using single-point imaging with rapid encoding. MAGMA. 2022 Apr;35(2):301-310.

Cooperation Partners

Institute for Musicians’ Medicine, Freiburg University and Faculty of Medicine, Freiburg, Germany

Grant Support

Funded by DFG project number 525074946.

Past Projects

17O-MRI to Assess Renal Metabolism of Donor Kidneys

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

CMRO2 Measurements with  17O MRI

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

MR Angiography

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

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)