Comparative efficacy of and sequence choice for two oral contrast agents used during MR imaging

OBJECTIVE. Our objective was to compare the efficacy of a positive and a ne gative oral contrast agent and to determine the optimal sequence choice for use in pelvic MR imaging. SUBJECTS AND METHODS. We undertook a prospective randomized trial of 57 pat ients with pelvic cancer who were examined with MR imaging after oral admin istration of a positive contrast agent (27 patients) or a negative contrast agent (30 patients). T1- and T2-weighted breath-hold and non-breath-hold g radient-recalled echo and turbo spin-echo sequences were obtained. Using th e hard-copy images, we graded filling and distention of the small bowel, bo wel wall conspicuity, delineation of normal and pathologic structures, and artifacts. RESULTS. Good or excellent small-bowel filling and distention was obtained in 17 patients (63%) receiving the positive agent and in 26 patients (87%) receiving the negative agent, and bowel wall conspicuity was graded good or excellent in 19 patients (70%) and 20 patients (67%), respectively. Normal and pathologic structures were better delineated with the negative agent ( 20 patients [74%] and 27 patients [90%], respectively; p =.02). Breath-hold gradi ent-recalled echo T1-weighted images were preferred for the positive agent (78%), and breath-hold T2-weighted images were preferred for the neg ative agent (93%). Contrast artifacts were more frequently seen with the ne gative agent (11% and 93%, respectively; p =.0001), and such artifacts were eliminated using T2-weighted sequences. CONCLUSION. Both contrast agents were effective in pelvic MR imaging, but d elineation of normal and pathologic structures was better with the negative agent, Gradient-recalled echo T1-weighted sequences are recommended for po sitive contrast agents, and breath-hold T2-weighted sequences are recommend ed for negative contrast agents.