Rapid MR imaging of renal perfusion: a comparative study of GdDTPA, albumin-(GdDTPA), and magnetite.

MR contrast agents injected intravenously reach the kidney very rapidly. Modification of a gradient recalled echo sequence allowed acquisition of 32 sequential MR images each 3.9 s apart on a 1.5 T clinical imager. This sequence was then used to observe the renal accumulation of contrast agent following an intravenous bolus of 100 microns/kg GdDTPA, 60 microns/kg albumin-(GdDTPA) or 9.6 and 40 mg/kg of 0.7 mu magnetic latex microspheres in rats or rabbits. Serial changes in image intensity were obtained with 3.9 s temporal and 0.08 ml spatial resolution. The renal cortical response to GdDTPA was similar to changes in blood 1/T1, but the medulla showed first a signal enhancement owing to the initial increased T1 relaxation followed by loss of signal as increased concentrations caused T2 relaxation to become predominant. Changes in intensity caused by magnetite and albumin-(GdDTPA) correlated with the 1/T1 changes observed in blood samples consistent with the predominantly intravascular location of these two agents. We conclude that MRI provides high spatial resolution with sufficient temporal resolution to record tissue response to an intravenous bolus of MR contrast agents.