Magnetic resonance imaging-based compartmentation and its application to measuring metabolite concentrations in the frontal lobe

Partial volume mixing of water compartments within a spectros-copy voxel (e.g. cerebrospinal fluid within a 'brain' voxel) may, if not corrected for, lead to underestimation of brain metabolite concentrations. To correct for this source of bias, a new imaging-based method of compartmentation analysis is presented. Brain water, cerebrospinal fluid and solid matter content were obtained from proton density- and T₂-weighted images of the brain and an external standard in 10 healthy young males (21 to 30 years), and results compared with a previously-described technique based on spectroscopy. Mean (SD) fractional water content (β(MR)) of the 2 x 2 x 2 cm³ voxel in the frontal lobes was 0.79 (0.03) by imaging, slightly but significantly (p = 0.03) smaller than the value of 0.83 (0.03) obtained by spectroscopy. From water-suppressed spectra recorded at five echo times, using β(MR) determined by imaging, the T₂-corrected concentrations of compounds containing N- acetylaspartate, creatine, choline and myo-inositol were 10.6 (1.0), 8.0 (0.9), 1.6 (0.3) and 3.7 (0.7) mmol.l^-1 of brain, respectively. Imaging- based compartmentation is a rapid and straightforward technique, and can be performed on standard MR systems.