Assessment of rapid changes in renal blood flow with (191m)Ir, an ultra-short-lived radionuclide

We investigated the feasibility of using (191m)Ir (half-life, 5 s) to measure rapid dynamic alterations in differential renal blood flow. A nonobstructive constant renal pelvic pressure model was used. The renal pelves of 6 New Zealand White rabbits were drained by use of bilateral catheters, and increased hydrostatic pressure was achieved by raising 1 catheter to 16, 25, 30, or 35 cm above the level of the renal pelvis. The contralateral kidney served as the control. (191m)Ir first-pass angiograms were obtained at baseline, after the induction of elevated pressure in the renal pelvis, and after the pressure was returned to normal. A minimum of 3 sequential angiograms were obtained at each point. The differential blood flow values (mean +/- SD) were 47.5% +/- 7.3% at baseline, decreased to 42.3% +/- 2.6% when the renal pelvic pressure was elevated (P = 0.001), and returned to 51.1% +/- 4.0% after the pressure was returned to normal (P = 0.0017). There was no significant difference between baseline and postcompression values (P = 0.4807). It is possible to use (191m)Ir first-pass angiography to evaluate rapid dynamic changes in differential renal blood flow in an experimental animal model.