Diuretic-enhanced gadolinium excretory MR urography: comparison of conventional gradient-echo sequences and echo-planar imaging

The aim of this study was to investigate the utility of different gadoliniu m-enhanced T1-weighted gradient-echo techniques in excretory MR urography. In 74 urologic patients, excretory MR urography was performed using various T1-weighted gradient-echo (GRE) sequences after injection of gadolinium-DT PA and low-dose furosemide. The examinations included conventional GRE sequ ences and echo-planar imaging (GRE EPI), both obtained with 3D data sets an d 2D projection images. Breath-hold acquisition was used primarily. In 20 o f 74 examinations, we compared breath-hold imaging with respiratory gating. Breath-hold imaging was significantly superior to respiratory gating for t he visualization of pelvicaliceal systems, but not for the ureters. Complet e MR urograms were obtained within 14-20 s using 3D GRE EPI sequences and i n 20-30 s with conventional 3D GRE sequences. Ghost artefacts caused by ure teral peristalsis often occurred with conventional 3D GRE imaging and were almost completely suppressed in EPI sequences (p < 0.0001). Susceptibility effects were more pronounced on GRE EPI MR urograms and calculi measured 0. 8-21.7% greater in diameter compared with conventional GRE sequences. Incre ased spatial resolution degraded the image quality only in GRE-EPI urograms . In projection MR urography, the entire pelvicaliceal system was imaged by acquisition of a fast single-slice sequence and the conventional 2D GRE te chnique provided superior morphological accuracy than 2D GRE EPI projection images (p < 0.0003). Fast 3D GRE EPI sequences improve the clinical practi cability of excretory MR urography especially in old or critically ill pati ents unable to suspend breathing for more than 20 s. Conventional GRE seque nces are superior to EPI in high-resolution detail MR urograms and in proje ction imaging.