B0-adjusted and sensitivity-encoded spectral localization by imaging (BASE-SLIM) in the human brain in vivo

Abstract

Spectral Localization by Imaging (SLIM) based magnetic resonance spectroscopy (MRS) provides a new framework that overcomes major limitations of current MRS techniques, which allow only rectangular voxel shapes that do not conform the shapes of brain structures or lesions. However, the restrictive assumption of compartmental homogeneity in SLIM can lead to localization errors, thus its applications have been very limited to date. SLIM-based localization is subject to errors due to inhomogeneous B0 and B1 fields, particularly in organs with complex compartmental geometry including the human brain. The limitations of SLIM were overcome through the development and implementation of B0-Adjusted and Sensitivity-Encoded SLIM (BASE-SLIM) that includes corrections for inhomogeneities of both B0 and B1 fields throughout the volume of interest. In this study, we demonstrate significantly improved localization accuracy in compartments with arbitrary shapes and reliable quantification of metabolite concentrations in gray and white matter of the human brain using the BASE-SLIM technique.

Imaging based magnetic resonance spectroscopy (MRS) localization for quantitative neurochemical analysis and cerebral metabolism studies

“…The recently proposed B0-Adjusted Sensitivity Encoded SLIM (BASE-SLIM) successfully reconstructed GM and WM spectra from the human brain (Fig. 2), demonstrating the unique spectral patterns of GM and WM [58, 59]. Neurochemical concentrations in GM and WM quantified from BASE-SLIM reconstructed data were consistent with those determined from regression analysis of CSI data with GM fractions of each CSI voxel.…”

“…Various approaches have been proposed to overcome the limitation of SLIM and extend its capabilities. These approaches include GSLIM [51], SLOOP [52], BSLIM [53], SPLASH [54], SLAM [55, 56], starSLIM [57], and BASE-SLIM [58, 59]. …”

“…Several approaches have been proposed to correct for B0 field inhomogeneity, primarily involving a time-dependent SLIM-like matrix formulated as a function of a spatially-dependent phase evolution term [53, 59, 71]. …”

Region-specific aging of the human brain as evidenced by neurochemical profiles measured noninvasively in the posterior cingulate cortex and the occipital lobe using 1 H magnetic resonance spectroscopy at 7 T

“…In both voxels, the percentage of GM decreased and the percentage of WM increased with age. If known concentrations of the five commonly observed neurochemicals in GM and WM (Adany et al, 2016) are consulted, the changes in concentrations due only to difference in VOI composition would be relatively small (1 to 4%) for all except Glu, which has been reported to have 2 times higher concentration in GM than WM (Srinivasan et al, 2006). Except tCho, the expected outcome would be decrease in the metabolite concentration.…”

Quantitativein vivoneurochemical profiling in humans: where are we now?

“…The signal of total creatine has been widely used as an internal reference. However, this approach does not fulfil the criteria for 'absolute' quantification, because the tCr content differs between brain regions 22 and between grey and white matter 41 , and may change due to neurodegenerative processes. 42 Using unsuppressed water signal as a reference appears to be the best available approximation for metabolite quantification because it is H MR spectrum acquired from the human brain at 7 T (STEAM, TE ¼ 6 ms, TR ¼ 5 s, NT ¼ 160, grey-matter-rich occipital cortex).…”