Journal Article

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

Trattnig, Siegfried, Heckova, Eva, Strasser, Bernhard, Považan, Michal, Gruber, Stephan, Boubela, Roland, Hingerl, Lukas, Hangel, Gilbert, Bogner, Wolfgang

2018

Overview

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.

• Publisher: Elsevier Inc,Elsevier Limited
• Subject: 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