Real-time motion correction in LASER localized spiral 1H-MRSI

Proton magnetic resonance spectroscopic imaging (1H-MRSI) enables the non-invasive assessment of local changes in brain metabolism that underlie most brain diseases. It provides detailed metabolic information in healthy and pathologic tissue, which cannot be obtained by standard imaging methods. However, the utility of MRSI is limited due to reduced spatial coverage, low spatial resolution, long measurement times, and localization artifacts, if commonly available MRSI sequences on standard MR systems are used. To unfold its full potential, available MRSI methods have to provide: (i) coverage of the whole pathologic region within a 3D volume; (ii) accurate localization; (iii) short measurement times; and (iv) robustness to motion. Commonly used MRSI sequences are often limited to the acquisition of single 2D MRSI slab. Novel MRSI techniques based on echo planar imaging or spiral acquisition significantly improve measurement speed and provide coverage of well localized 3D volumes. Subject motion during MRSI scans does not always cause observable artifacts and as such may go completely unnoticed. To allow robust acquisition of MRSI data, real-time correction of motion induced artifacts significantly improves spectral quality. To improve the utility of MRSI, these approaches have to be properly combined. In the course of this project we aim (i) to combine a LASER localized spiral 3D-MRSI sequence with the acquisition of navigator images to monitor subject movement; (ii) to use the navigator images for real-time correction of B0 shimming and localization adjustments; and (iii) to evaluate the robustness of this method in healthy volunteers and patients at a standard 3T MR scanner (with option for additional 7T optimization). Such a fast and robust technique for 3D mapping of brain metabolites provides a solid basis for further studies of the human brain and can be readily extended to investigations of other body regions (i.e. breast, prostate).

Magnetic resonance spectroscopic imaging (MRSI) of the brain provides valuable information (i.e., the concentration of several important chemical compounds of low concentration) in healthy and pathologic brain tissue, which cannot be obtained by standard imaging methods and would otherwise require invasive biopsy. However, commonly available MRSI methods have several technical limitations that include long measurement times, the coverage of only a reduced area of the brain, localization artifacts, and artifacts caused by motion and MR scanner instabilities. To unfold the full potential of MRSI, the aim of our project was to improve the utility of MRSI, by combining several advanced imaging approaches. In particular, (i) we improved the localization accuracy by a novel method termed LASER, which allows to determine the amount of chemical substances more accurately; (ii) we reduced the measurement time from ~15-20 min to 2-4 min by using faster image encoding; (iii) this fast acquisition allowed to cover much larger regions of the brain in the same MR scan; (iv) we detected any occurring head motion and temporal instrument instabilities of the MR scanner in real-time and corrected the acquired MR data simultaneously using the knowledge of the detected head motion. To investigate the advantages of our new method, MR data were acquired and evaluated in healthy volunteers and patients at a standard clinical 3T MR scanner. Our new MRSI method is a robust tool for any neuro research and clinical application where changes in spatial distributions of chemical substances such as related to metabolism, neural cell density, neurotransmitter, and others provide important insight into disease processes. It can, therefore play an important role in the characterization of the major brain diseases such as neurological diseases, brain tumors, and psychiatric diseases. Further improvements may also allow its use for whole-body applications.