Our group is engaged in the development of methods for magnetic resonance imaging (MRI) and spectroscopy (MRS) including pulse sequences, RF hardware and image processing. Their applications aim at a quantitative characterization of brain tissue composition or physiological processes to understand the anatomy of the brain, its metabolism, and its activity as well as the biophysical processes underlying image contrast.
Available PhD projects
1. Arterial spin labeling (ASL) techniques allow to map tissue perfusion non-invasively without exogenous contrast agents. They are based on magnetically labeling the arterial blood water by application of suitable RF pulses. To improve ASL techniques at 7T we will design a multi-channel transmit RF coil that supports RF shimming for separately optimizing the labeling efficiency in brain-feeding arteries and imaging cerebral blood flow (CBF) in an extended region of interest. The transmit coil, consisting of multiple rows of loops and/or dipoles, will exploit the 16-channel transmit capabilities of our 7T MAGNETOM Terra scanner. Optimization and investigation of safety aspects will include circuit and EM field simulations in the numerical domain as well experimental validation. An existing 31-channel array will be integrated for reception. Multi-channel transmit concepts will be integrated in an existing pulse sequence for pseudo-continuous ASL. Ideally, the obtained solution should achieve CBF-based functional experiments on a sub-millimeter spatial scale.
2. Neural connections via axons and synapses are characterized by connection strength and delay. To study these properties, we will use diffusion-weighted (dw) magnetic resonance imaging (MRI) acquired at high spatial and angular resolution and multiple diffusion times. Additional information can be obtained from measurements of relaxation times T1, T2, and T2* as well as from quantitative susceptibility mapping (QSM). Such data can be combined to gain information on profiles of MRI parameters along fiber tracts.
3. A number of physical properties that can be used for tissue characterization show an apparent dependence on the orientation of the object in the main magnetic field. Examples include the exchange of magnetization between water and macromolecules (also known as "magnetization transfer") or the local bulk magnetic susceptibility. An analysis of the underlying physics (e.g., of dipolar couplings between proton spins or of the heterogeneity of contributions to magnetic susceptibility within a tissue) allows to model these effects for obtaining more specific information on tissue microstructure/composition or achieves a better understanding of image contrast. Another aspect is an integration of machine-learning concepts to support faster acquisition strategies and/or data analysis of orientation-dependent effects.