Magnetic resonance imaging (MRI) has become an important clinical diagnostic method since its first experimental application about 40 years ago. Unlike other medical imaging techniques such as computed tomography (CT) and positron emission tomography (PET), it allows for a high soft tissue contrast and does not require the use of ionizing radiation.
The research group develops MR acquisition techniques to characterize metabolic and functional processes. The focus of our research is on the field of ultra-high field (7 Tesla) and the so-called X-nucleus MRI. "X" stands for any atomic nucleus with nuclear spin, except 1H.
In our research group, methods are developed to mesaure, for example, in vivo images of sodium (23Na), potassium (39K), chloride (35Cl), oxygen (17O) or phosphorus (31P). These nuclei are interesting for medical research, as they play an important role in many physiological processes. The 23N-, 39K- and 35Cl-concentrations are tightly linked to the physiological state of the cell, and 17O MRI can be used to non-invasively study cellular oxygen turnover.
Several challenges need to be overcome to measure these nuclei. Most of the X nuclei have a nuclear spin > 1/2 and thus have an electric nuclear quadrupole moment, which leads to short transverse relaxation times. In addition, the in-vivo concentration of the X-nuclei is several orders of magnitude lower than the 1H concentration. On the other hand, the physical properties of the quadrupoles (e.g. 17O, 23Na, 35Cl, 39K) can be exploited to create special image contrasts (e.g. triple quantum filtered imaging).
A relatively new technique we use to detect metabolic processes is Chemical Exchange Saturation Transfer (CEST) imaging. In addition, we develop parallel transmission techniques (ptx) for homogenizing the transmission field at 7 Tesla and procedures for visualizing the arterial blood flow.
The research group is working on the development of quantitative methods in magnetic resonance imaging.
One focus is on the development of new methods for measuring water diffusion in the tissue. The measurement of diffusion allows statements about tissue structure or tissue integrity and is used clinically, for example, in stroke diagnostics and in the diagnosis of prostate cancer. Our research focuses on the measurement of anisotropic diffusion (diffusion tensor imaging), non-Gaussian diffusion processes (e.g. Kurtosis imaging, IVIM imaging), the determination of tissue microstructure (e.g. diffusion pore imaging) and the development of high-gradient methods (e.g. dedicated breast gradients, G > 1 T/m). In order to enable a quantitative evaluation, suitable validation and reference objects, so-called phantoms, are also being developed.
Another focus is on quantitative susceptibility mapping (QSM). Different biological tissues differ in their magnetic susceptibilities, which can be measured and quantified using appropriate MRI techniques. QSM can be used, for example, to differentiate calcifications and bleeding.