Comparison of ionic and nonionic Gd-DTPA in MR imaging of the genitourinary system

Ionic (Gd-dimeglumine-DTPA, Schering-Berlex) and non-ionic (Gd-bis[methylamide]-DTPA, Salutar) formulations of Gd-DTPA were used to perform dynamic contrast agent-enhanced MR imaging of normal rabbit kidneys. Twenty sequential gradient-echo images (repetition time msec/echo time msec = 30/15, flip angle = 250, field of view = 20 cm, two acquisitions, 256 X 256, 5-mm sections, 16 seconds per image) were acquired 0-5 minutes after injection. In the gradient-echo images of rabbit kidneys, the effect of the contrast agent was first observed in the cortex as a uniform band of hypointensity. In subsequent images, this dark ring appeared more centrally, such that a steady inward progression was demonstrated. The presence of the dark band and its time sequence of change were a reflection of intratubular concentration of Gd-DTPA. This pattern of signal change was demonstrated after injection of either Gd-DTPA formulation; however, it appeared more conspicuously after administration of the nonionic material. Although this distinction was subtle, it was reproducible and was a manifestation consistent with the nonionic compound's lower osmolarity