Absolute quantitation of brain metabolites with respect to the CSF fraction in ¹H-MR spectroscopic volumes

Abstract

This work describes an approach to extract absolute metabolic concentrations, estimated by proton magnetic resonance spectroscopy in the brain with respect to heterogeneous tissue distributions within the spectroscopic volume. Single voxel PRESS ¹H MR spectra were acquired on a clinical 3 T MR scanner in the anterior insular cortex of five healthy volunteers in combination with T1-weighted high resolution anatomic 3D-imaging of the whole brain. Spectra were reconstructed by a weighted linear combination of multichannel data of a head matrix phased array coil. Weighting factors were determined by using an SVD (Singular Value Decomposition) method. Absolute concentrations of NAA, Cr, Cho, mIns and Glu were quantified with the LCModel using the internal water reference approach. Concentrations were corrected for the individual cortical spinal fluid (CSF) fraction within the ¹H-MRS voxel by co-registration of the segmented anatomic whole brain data with the MRS data. Extracted concentrations without CSF correction were found to be lower by 10.5±0.1% on average compared to the corrected values for all investigated metabolites (p≤0.002). Except for mIns and Glu, the corrected concentrations revealed lower variances of up to 200% over all volunteers.