MRI image plane nonuniformity in evaluation of ferrous sulphate dosimeter gel (FeGel) by means of T-1-relaxation time

MR image nonuniformity can vary significantly with the spin-echo pulse sequ ence repetition time. When MR images with different nonuniformity shapes ar e used in a T-1-calculation the resulting T-1-image becomes nonuniform. As shown in this work the uniformity TR-dependence of the spin-echo pulse sequ ence is a critical property for T-1 measurements in general and for ferrous sulfate dosimeter gel (FeGel) applications in particular, The purpose was to study the characteristics of the MR image plane nonuniformity in FeGel e valuation, This included studies of the possibility of decreasing nonunifor mities by selecting uniformity optimized repetition times, studies of the t ransmitted and received RF-fields and studies of the effectiveness of the c orrection methods background subtraction and quotient correction. A pronoun ced MR image nonuniformity variation with repetition and T-1 relaxation tim e was observed, and was found to originate from nonuniform RF-transmission in combination with the inherent differences in T-1 relaxation for differen t repetition times. The T-1 calculation itself, the uniformity optimized re petition times, nor none of the correction methods studied could sufficient ly correct the nonuniformities observed in the T-1 images. The nonuniformit ies were found to vary considerably less with inversion time for the invers ion-recovery pulse sequence, than with repetition time for the spin-echo pu lse sequence, resulting in considerably lower T-1 image nonuniformity level s. (C) 1999 Elsevier Science Inc.