Abstract
ObjectMagnetic resonance spectroscopic imaging (MRSI) is increasingly used in medicine and clinical research. Previous reliability studies have used small samples and focussed on limited aspects of variability; information regarding 1.5T versus 3T performance is lacking. The aim of the present work was to measure the inter-session, intra-session, inter-subject, within-brain and residual variance components using both 1.5T and 3T MR scanners.Materials and methodsEleven healthy volunteers were invited for MRSI scanning on three occasions at both 1.5T and 3T, with four scans acquired at each visit. We measured variance components, correcting for grey matter and white matter content of voxels, of metabolite peak areas and peak area ratios.ResultsResidual variance was in general the largest component at 1.5T (8.6–24.6%), while within-brain variation was the largest component at 3T (12.0–24.7%). Inter-subject variation was around 5%, while inter- and intra-session variance were both generally small.ConclusionMultiple variance contributions associated with MRSI measurements were quantified and the performance of 1.5T and 3T MRI scanners compared using data from the same group of subjects. Residual error is much lower at 3T, but other variance components remain important.
Highlights
Exploitation of the 1H chemical shift effect permits quantitative mapping of metabolite signals across the brain and within other organs of the body
Residual variance was in general the largest component at 1.5T (8.6–24.6%), while withinbrain variation was the largest component at 3T (12.0–24.7%)
This may result from greater radiofrequency transmit and receive inhomogeneity at 3T, as well as differences in chemical shift displacement of the excitation volume and the pulse excitation and refocussing profiles; these effects should be reduced for metabolite signal ratios; the higher proportion of retained voxels at 3T (43% versus 31%) could contribute
Summary
Exploitation of the 1H chemical shift effect permits quantitative mapping of metabolite signals across the brain and within other organs of the body. MRSI sequences are widely available as standard on 1.5T and 3T clinical MRI scanners. A number of test-retest reliability studies have been published [2,3,4,5,6,7,8,9,10,11], most are based on small sample sizes or focus on a limited number of variance components; while 3T MRI is often regarded as essential for clinical research involving MRS, there is little comparative information available regarding reproducibility at 1.5T versus 3T [6, 12]. We measured inter-subject, within-brain (to account for variance due to anatomy, coil sensitivity inhomogeneity etc.) and residual (e.g. variability due to scanner noise) variances
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