Short‐echo, single‐shot, full‐intensity proton magnetic resonance spectroscopy for neurochemical profiling at 4 T: Validation in the cerebellum and brainstem

Abstract

A short echo-time (TE = 24ms) semi-adiabatic LASER sequence was designed and optimized for full intensity 1H MRS at 4T. The sequence was combined with VAPOR water suppression and three dimensional outer-volume-suppression (OVS) for improved localization and suppression of unwanted coherences. Artifact-free, single-shot spectra were obtained from the human brain with a spectral pattern almost identical to that obtained with an ultra-short echo (TE = 5ms) STEAM sequence as a result of the train of adiabatic refocusing pulses in semi-LASER that reduce the apparent TE. Approximately twofold higher signal intensity relative to STEAM was demonstrated in phantoms and the human brain. To test the performance of the sequence in clinically relevant brain regions with a volume coil, semi-LASER spectra were acquired from three cerebellar and brainstem volumes-of-interest (VOI) in 23 healthy subjects. Ultra-short echo STEAM spectra were acquired from the same VOI to compare neurochemical profiles obtained with semi-LASER to those obtained with STEAM. Neurochemical profiles of the cerebellum and brainstem acquired by these two techniques were nearly identical, validating the accuracy of the metabolite concentrations obtained with semi-LASER at the longer TE relative to STEAM. A high correlation between metabolite concentrations obtained by these two MRS techniques indicated the sensitivity to detect inter-subject variation in metabolite levels.

Multi‐center reproducibility of neurochemical profiles in the human brain at 7 T

“…It was first introduced in spectroscopic imaging mode (7), and shown to be reliable and reproducible at 3T (8). Additional technical adjustments (improved water suppression, phase cycling and outer volume suppression) enabled a successful single voxel implementation of the technique (9) with excellent 2-site reproducibility at 3T (10). The sequence was further demonstrated to perform better than other available spin- and stimulated-echo techniques for single voxel MRS at 7T (11).…”

The separation of Gln and Glu in STEAM: a comparison study using short and long TEs/TMs at 3 and 7 T

“…Besides the STEAM technique, other 1 H-MRS techniques have also been previously applied at 3 or 4 T for in vivo Gln and Glu detection, such as MEGA-PRESS spectral editing [37], semi-adiabatic LASER [38], and 2D J-resolved PRESS [39]. Kakeda et al [37] used MEGA-PRESS with TE = 68 ms to acquire Gln and Glu signals in human frontal lobe and parieto-occipital lobe regions at 3 T. The quantified Glu/Gln ratio was 1.1 with CRLBs of 70 and 11 for Glu and Gln estimation, respectivley.…”

“…Kakeda et al [37] used MEGA-PRESS with TE = 68 ms to acquire Gln and Glu signals in human frontal lobe and parieto-occipital lobe regions at 3 T. The quantified Glu/Gln ratio was 1.1 with CRLBs of 70 and 11 for Glu and Gln estimation, respectivley. Öz et al [38] applied the semi-adiabatic LASER sequence with a short TE = 24 ms for full signal intensity to measure human cerebellum spectra at 4 T. A mean Glu/Gln ratio of 2.6 was obtained. In addition, as suggested by Henry et al [40], 2D J-resolved PRESS is an effective and stable technique for in vivo Gln and Glu acquisitions.…”

MR Spectroscopy in Health and Disease

“…There are regional differences in neurochemical levels within the cerebellum as well (Pouwels and Frahm 1998;Ö z et al 2010a, 2011bÖ z and Tkáč 2011). Note for example the differences between the spectral patterns, that is, the ratios of the major resonances, obtained in the cerebellar vermis and a hemisphere voxel that primarily contains white matter (Fig.…”

“…29.1). These differences are a result of higher tCr, myo-inositol, glutamate and glutamine levels in the vermis relative to hemispheric white matter (Ö z et al 2010a;Ö z and Tkáč 2011).…”