Biomedical NMR Research

Our research is devoted to the further development and application of magnetic resonance imaging (MRI) and localized magnetic resonance spectroscopy for noninvasive studies of animals and humans. Current projects range from advanced methods that monitor the dynamics of myocardial functions and blood flow in real time to neurofeedback training in humans by functional brain mapping. The use of genetically modified animals allows us to link molecular and genetic information to MRI-accessible functions at the system level.

Our recent breakthrough towards real-time MRI is based on the use of non-Cartesian spatial encoding, pronounced data undersampling, and image reconstruction by regularized nonlinear inversion. Pertinent techniques bear the potential to alter the future of (clinical) MRI. They allow for movie recordings of speech production, turbulent flow or the beating heart – without synchronization to the ECG and during free breathing. The computational demand is met by a parallelized algorithm and multiple graphical processing units which could be fully integrated into the software framework of a commercial MRI system.

A second area of research focuses on studies of the functional organization of the human brain and its axonal connectivity. Diffusion MRI provides information about the orientational dependence of the anisotropic water mobility in brain tissue and may be exploited for three-dimensional reconstructions of nerve fiber tracts. In order to overcome limitations of the standard echo-planar imaging technique we developed a single-shot stimulated-echo MRI sequence which is now further extended by radial undersampling and nonlinear inverse reconstruction. Functional brain mapping deals with the neural encoding of sensorimotor functions. Our results for fine-scale finger somatotopy in humans indicate consistent intra-digit topographic maps for the little but not the index finger within the primary somatosensory cortex. Neurofeedback training of brain activity is a potential treatment option for psychiatric diseases offering access to arbitrary structures. Our aim is to investigate the role of fMRI-based neurofeedback in the anterior mid-cingulate cortex which relates to higher-order cognitive processes.

Animal MRI research addresses the pathophysiologic mechanisms underlying human brain disorders. The development of MRI techniques for transgenic mice allows for structural, metabolic, and functional assessments of the mouse brain at high spatial resolution. An observation of utmost importance is the high but reversible elevation of brain lactate in response to volatile anesthetics. The metabolite responses to various neuromodulators indicate a stimulation of adrenergic pathways as well as an inhibition of the respiratory chain. Corresponding findings in conditional Cox10 mutant mice, in which oligodendrocytes suffer from impaired oxidative energy metabolism, suggest the use of lactate as brain energy source, so that oligodendrocytes survive by enhanced nonoxidative glucose consumption which in turn secures the maintainance of myelin as well as long-term axonal integrity.