Image-guided MR spectroscopy volume of interest localization for longitudinal studies

Longitudinal magnetic resonance spectroscopy (MRS) studies require accurate repositioning of the volume of interest (VOI) over which measurements are made. In this work we present and evaluate a method for the image-guided re positioning of brain volumes of interest. The point-based registration tech nique we developed allows the repositioning to be performed on-line (i.e. w hile the patient is in the scanner). MR image volumes were acquired from si x subjects, three scans each over the course of a month. During the first s can, two spectroscopy VOIs are visually selected: one in the frontal white matter, the other in the superior cerebellar vermis. The coordinates of 13 internal brain landmarks are also identified. During both subsequent scans, the same 13 landmarks are identified, and the transformation that register s the first set of landmarks to the subsequent set is computed. This result is used to automatically map the position of the spectroscopy VOIs from th e first volume to the current volume. For the six subjects evaluated to dat e, we show an average repositioning error of the spectroscopy VOIs in the o rder of 1 mm. This accuracy allows us to conclude that any variations in th e MR spectra are unlikely to be due to repositioning error. (C) 1999 Elsevi er Science Ltd. All rights reserved.