SIGNAL PROFILE MEASUREMENTS FOR EVALUATION OF THE VOLUME-SELECTION PERFORMANCE OF ISIS

High-resolution signal profiles obtained with a test phantom were used in this study to evaluate the volume-selection performance of an impl ementation of ISIS (Image Selected In vivo Spectroscopy), The phantom simulated the brain with regard to volume and loading of coil. A remot ely controlled, movable signal source inside the phantom was filled wi th orthophosphoric acid, Signal profiles of the volume of interest (VO I) were measured in three perpendicular directions, Special interest w as focused on the transition zones, the position of the profiles, and the effects of off-resonance and T-1 smearing, The transition zones we re on average 5.6 mm wide and the full width at half maximum (FWHM) wa s 35 mm for a VOI of 40 X 40 X 40 mm(3), The positions of the centre o f the signal profiles were x=3.2, y=-0.7 and z=3.3 mm off-centre, The deviation of the volume position could be explained by off-resonance e ffects during imaging and spectroscopy, These data illustrate the impo rtance of detailed knowledge of the volume-selection performance when attempting precision measurements using image-guided in vivo MRS.