Measurement of renal transit of gadopentetate dimeglumine with echo‐planar MR imaging

Times of peak gadolinium concentration ([Gd]) after intravenous (IV) and left ventricular (LV) bolus injection of gadopentetate dimeglumine were determined in renal cortex and medulla in normal rabbits and in rabbits after saline load (overhydration) or hemorrhage (dehydration). Magnetic resonance images were obtained with echo‐planar inversion‐recovery sequences, and signal intensity‐versus‐time curves in cortical and medullary regions of interest were converted to [Gd]‐versus‐time curves. Cortical perfusion measured with microspheres demonstrated that the three physiologic states were significantly different. There were three separate [Gd] peaks in both the cortex and medulla as the bolus moved from one anatomic compartment to the next. The first cortical peak occurred sooner after LV than after IV bolus injection (P <.05) and later in dehydrated than in normal and overhydrated rabbits (P <.05). The first medullary peak always followed the first cortical peak by about 6–10 seconds and mirrored the cortical patterns. The second and third cortical peaks were consistent with proximal and distal tubular transit. These peaks similarly showed faster response to LV than IV injection and were delayed by hemorrhage. The authors conclude that quantitative physiologic information can be obtained with dynamic contrast‐enhanced MR imaging of the kidney.