Hans F. Wehrl: “PET/MR Brain Imaging in Small Animals”
CiNet 1F Conference Room
Werner Siemens Imaging Center, Functional and Metabolic Brain Imaging (FMBI) Group, University of Tuebingen, Germany
The combination of Positron-Emission-Tomography (PET) and Magnetic Resonance (MR) allows to image metabolic and functional processes at the same time.
PET/MR has become increasingly popular in the clinical but also the preclinical imaging setting. In this talk I will focus on the use of combined PET/MR to study brain metabolism in rodents. After a short introduction into PET/MR technology and its challenges application examples will be described. In the domain of brain tumors, choline metabolism could be studied with [11C]choline-PET as well as MR spectroscopy, indicating a mismatch between these two modalities, even if supposedly the same metabolite was assessed. This mismatch was further assessed using ex vivo methods such as histology and secondary ion mass spectrometric imaging. In the area of brain function, combined PET/MR was used to study stimulus evoked changes in the BOLD-fMRI signal relative to cerebral blood flow changes assessed by [15O]H2O-PET and glucose metabolism measured by [18F]FDG-PET. Aside from a shift between activation foci between BOLD-fMRI and PET, [18F]FDG-PET additionally revealed some brain regions to be activated, that appear not to be significantly active in the BOLD-fMRI signal. This mismatch could indicate that in certain brain areas, changes are too small or on a too slow time scale to be picked up by BOLD-fMRI.
Finally also combined PET/MR studies of the resting brain will be presented.
Here major networks in the brain (e.g. a default mode like network in the
rat) can be identified not only using resting state fMRI techniques but also from metabolic PET data. This new approach of metabolic brain connectivity mapping based on PET could ultimately lead to the new field of Cometomics which combines MR based connectivity measurement methods (Conectomics) with PET based metabolic imaging. Cometomics could offer the promise to be in some respects more specific, sensitive and quantitative in comparison to fMRI based connectivity measurements, and could therefore yield new insights into the brain.