Separation of 23Na Compartments and Semi-Quantitative Determination of the Intracellular Sodium Concentration Using Ultra High Field Magnetic Resonance Imaging

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The aim of the current project is the non-invasive separation of different sodium compartments in vivo and the semi-quantitative determination of the intracellular sodium concentration. Different sequences for ultra-high field magnetic resonance imaging (MRI) (7 Tesla) will be developed and evaluated.First, a new sequence that allows for shorter acquisition time and SNR- and SAR-efficient detection of the bi-exponential weighted sodium signal will be developed. To separate different sodium compartments the exact knowledge of the relaxation times is inevitable. Thus, a triple-quantum-filtered (TQF) single voxel spectroscopy (SVS) sequence will be implemented that allows for a rapid measurement of the local (e.g. in tumor tissue) bi-exponential relaxation times.To provide sufficient accuracy and reproducibility for the determination of signal intensities of the different 23Na-MRI techniques, several corrections have to be performed. In addition to the correction of inhomogeneities of the static magnetic field (B0) and the sensitivity profiles of the radiofrequency coils (B1), high resolution information from 1H-MRI will be used to enable a better quantification of the 23Na-MRI signals. In the human body sodium is dissolved in water. Therefore, the tissue sodium concentration should be normalized to the local water content. Thus, a technique for quantitative water mapping will be implemented. In muscular diseases fatty infiltration are often present. The sizes of these structures are often smaller than the spatial resolution of 23Na-MRI. Therefore, a quantitative determination of the muscular fat content and a highly resolved visualization of the fat infiltrations is necessary the correct for partial volume effects. Furthermore, prior knowledge from 1H-MRI data (e.g. bone tissue gives no 23Na-signal) will be incorporated to enable a better 23Na-MR image quality regarding SNR and spatial resolution. Based upon the newly developed techniques and the sequences that are available from prior work, models that allow for a semi-quantitative determination of the intracellular sodium concentration will be developed. After a successful check of the developed method in measurements of well suited phantoms, in vivo evaluation in healthy subjects will be performed. Models for the semi-quantitative determination of the intracellular sodium concentration will be provided for brain and muscle tissue.Finally, examinations of patients with well-defined muscular channelopathies as model diseases will be performed. In these diseases provocation (cooling and muscle exercise) leads to an increase of the intracellular sodium concentration. This increase can be provoked with high reproducibility. Measurements before and after provocation of the muscle tissue will be performed to evaluate the potential to visualize an increase of the intracellular sodium content with the developed methods.