Rapid renal single-photon emission tomography by continuous infusion of iridium-191m

Continuous infusion of iridium-191m (t(1/2) = 5 s), produced with an Os-191 /Ir-191 generator, was used to obtain rapid high-resolution single-photon e mission tomography (SPET) of renal blood flow in the rabbit. SPET scans of the abdomen were obtained with a triple-detector SPET system (MS3, Siemens Gammasonics). The generator was eluted at a flow rate of 3 ml/min, which de livered a steady-state dose of 170 MBq (4.5 mCi) of Ir-191m. The total Os-1 91 breakthrough was 850 kBq (23 mu Ci). A 5-min SPET acquisition recorded a total of 2.8 million counts, resulting in images of high technical quality . Volume-rendered images clearly showed the abdominal aorta, splenic artery , spleen, renal arteries, kidneys and splanchnic vasculature. Tomographic s lices through the kidneys revealed tracer primarily within the renal cortic es without visualization of the collecting system. The estimated effective dose equivalent for a 5 min infusion of Ir-191m at a steady-state dose of 1 70 MBq is 0.74 mSv compared with 2.7 mSv from a 170 MBq dose of Tc-99m-DMSA . This study demonstrates the feasibility of high-resolution SPET of region al renal perfusion in the rabbit by continuous intravenous infusion of Ir-1 91m. The renal distribution of continuously infused Ir-191m is largely with in the cortices, with minimal or no detectable activity in the region of th e renal pelvicalyceal system. Using this technique, cortical renal SPET can be completed much more rapidly (<5 min) than with conventional renal corti cal imaging agents, which suggests that this technique could be applied to the observation of rapid changes in renal perfusion such as those resulting from pharmacologic intervention, obviating the need for the patient to ret urn for additional visits. Additional studies are required to (a) validate the methodology in larger animals prior to considering the potential for us e in human beings, (b) optimize the generator design for continuous infusio n, and (c) evaluate the changes in the distribution of Ir-191m that occur i n animal models of altered renal perfusion.