In vivo radionuclide uptake quantification using a multi-pinhole SPECT system to predict renal function in small animals

Purpose: In vivo quantification of radiopharmaceuticals has great potential as a tool in developing new drugs. We investigated the accuracy of in vivo quantification with multi-pinhole single-photon emission computed tomography (SPECT) in rats. Methods: Fifteen male Lewis rats with different stages of renal dysfunction were injected with 50 MBq Tc-99m-dimercaptosuccinic acid. Four to six hours after injection, SPECT of the kidneys was acquired with a new four-headed multi-pinhole collimator camera. Immediately after imaging the rats were sacrificed and the kidneys were counted in a gamma-counter to determine the absorbed activity. SPECT data were reconstructed iteratively and regions of interest (ROIs) were drawn manually. The absolute activity in the ROIs was determined. Results: Uptake values ranging from 0.71% to 21.87% of the injected activity were measured. A very strong linear correlation was found between the determined activity in vivo and ex vivo (r(2)=0.946; slope m=1.059). Conclusion: Quantification in vivo using this multi-pinhole SPECT system is highly accurate.