Ultra-high resolution brain metabolite mapping at 7 T by short-TR Hadamard-encoded FID-MRSI

• Published in: NeuroImage (Orlando, Fla.) Fla.), 2018-03, Vol.168, p.199-210
• Main Authors: Hangel, Gilbert, Strasser, Bernhard, Považan, Michal, Heckova, Eva, Hingerl, Lukas, Boubela, Roland, Gruber, Stephan, Trattnig, Siegfried, Bogner, Wolfgang
• Format: Article
• Language: English
• Subjects: 7 T; Adult; Brain; Brain - diagnostic imaging; Brain - metabolism; Brain cancer; Brain mapping; Brain research; Brain slice preparation; Contamination; Cortex; Feasibility Studies; Female; Hadamard encoding; Humans; Image processing; Image Processing, Computer-Assisted - methods; Lipids; Localization; Magnetic Resonance Spectroscopy - instrumentation; Magnetic Resonance Spectroscopy - methods; Magnetic Resonance Spectroscopy - standards; Male; Metabolism; Metabolites; Multiple sclerosis; Neuroimaging; Neuroimaging - instrumentation; Neuroimaging - methods; Neuroimaging - standards; Parallel imaging; Phantoms, Imaging; Protocol; Proton magnetic resonance spectroscopic imaging; Spatial discrimination; Substantia alba; Therapeutic applications; Ultra-high resolution spectroscopic imaging
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2016.10.043

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 1.7×1.7×8mm3 in 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. [Display omitted] •Ultra-high resolution MRSI (128×128 in-plane matrix) at 7 T.•Parallel imaging and short TR of 200ms make UHR-MRSI clinically feasible (10–20min).•Pulse-cascaded Hadamard encoding provides 3D-MRSI coverage.