Relative renal blood flow measurements with Rb-82 and a hybrid gamma camera using a pig model

We have successfully demonstrated with chronically implanted blood flow probes in a pig model that Rb-82 is indeed able to reflect acute alterations in renal blood flow. Two flow probes were placed around the left and right renal arteries in a surgical procedure nine weeks before the first Rb-82 measurements. Together with the flow probes, a flow restrictor was implanted around the left renal artery. This enabled us to regulate the flow to the left kidney and use the right kidney as a control for comparison. Single bolus infusions of 6 mCi Rb-82 were used to study the uptake in the kidneys approximately 7 minutes apart in hybrid-image limited-angle acquisitions (stationary camera heads posterior and anterior of the pig) while changing the flow to the left kidney between acquisitions. Acquisitions were repeated four times, each approximately a week apart. The acquired data were reconstructed into 7.5-second frames using a Maximum Likelihood (ML) list-mode reconstruction algorithm exploiting timing signals inserted into the list every 0.25 sec. Attenuation compensation was not done except for experiment 4 to study its effect in limited angle tomography. Reconstructed data were orientated to coronal views before regions of interest (ROI's) were drawn over both kidneys with a separate background region for each. The data represented are noisy due to the reconstructed 7.5-second frames, and the total imaging time of 5 minutes (or 8 Rb-82 half-lives). We were able to show a steady decline in uptake of Rb-82 in the left kidney with decreased flow. In addition, there is a difference in uptake when comparing the left and right kidney. This was also evident when we studied the Rb-82 uptake to the rabbit kidneys. During our intervention period of about 40 minutes, the restricted blood flow to the left kidney does not seem to affect the Rb-82 uptake to the right kidney adversely. However, comparing the baseline renal blood flow of the left kidney obtained before and after the intervention, indicate that some ischemia persists after blood flow was restored. Attenuation compensation better described the shape of the kidney but only scale the time activity curve without changing its shape.