Ultra-high resolution brain metabolite mapping at 7 T by short-TR Hadamard-encoded FID-MRSI.
MRSI in the brain at ≥7 T is a technique of great promise, but has been limited mainly by low B0/B1+-homogeneity, specific absorption rate restrictions, long measurement times, and low spatial resolution. To overcome these limitations, we propose an ultra-high resolution (UHR) MRSI sequence that provides a 128×128 matrix with a nominal voxel volume of 1.7×1.7×8mm3in a comparatively short measurement time. A clinically feasible scan time of 10-20min is reached via a short TR of 200 ms due to an optimised free induction decay-based acquisition with shortened water suppression as well as parallel imaging (PI) using Controlled Aliasing In Parallel Imaging Results IN Higher Acceleration (CAIPIRINHA). This approach is not limited to a rectangular region of interest in the centre of the brain, but also covers cortical brain regions. Transversal pulse-cascaded Hadamard encoding was able to further extend the coverage to 3D-UHR-MRSI of four slices (100×100×4 matrix size), with a measurement time of 17min. Lipid contamination was removed during post-processing using L2-regularisation. Simulations, phantom and volunteer measurements were performed. The obtained single-slice and 3D-metabolite maps show the brain in unprecedented detail (e.g., hemispheres, ventricles, gyri, and the contrast between grey and white matter). This facilitates the use of UHR-MRSI for clinical applications, such as measurements of the small structures and metabolic pathologic deviations found in small Multiple Sclerosis lesions.
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Austria.
Gilbert
G
Hangel
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Austria.
Bernhard
B
Strasser
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Christian Doppler Laboratory for Clinical Molecular MR Imaging, Austria.
Michal
M
Považan
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Austria.
Eva
E
Heckova
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Austria.
Lukas
L
Hingerl
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Austria.
Roland
R
Boubela
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Austria.
Stephan
S
Gruber
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Christian Doppler Laboratory for Clinical Molecular MR Imaging, Austria.
Siegfried
S
Trattnig
High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Austria. Electronic address: wolfgang.bogner@meduniwien.ac.at.
Wolfgang
W
Bogner
D000328:Adult; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D008297:Male; D059906:Neuroimaging / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D019047:Phantoms, Imaging
7 T; Brain; Hadamard encoding; Parallel imaging; Proton magnetic resonance spectroscopic imaging; Ultra-high resolution spectroscopic imaging