Incidental Renal Findings during 99mTc-MDP Biological Distribution Assay. The Role of Small Animal Imaging.

Portillo, Mariano Gastón*, Tesán, Fiorella Carla, Giaquinta Romero, Diego, Zubillaga, Marcela Beatriz, Salgueiro, María Jimena
Radioisotope Laboratory, Physics Department, School of Pharmacy and Biochemistry, University of Buenos Aires, Buenos Aires, Argentina. 

A B S T R A C T
The present work aims to report an incidental renal finding during a bone scintigraphy performed as an additional exploratory study during a biological distribution assay as part of the quality control of 99mTc-labeled methylene disphosphonate (99mTc-MDP). Radiolabelling and quality control of 99mTc-MDP were performed according to the instructions of the manufacturer as well as to the USP monograph. After euthanasia and prior to dissection in the biological distribution, bone scintigraphy was carried on using a small field of view gamma camera. Finally, after dissection images of the kidneys were acquired. The uptake of 99mTc-MDP in the kidneys was calculated as the uptake of each kidney with regard to total renal uptake. Imaging analysis showed a remarkable difference in 99mTc-MDP uptake between right and left kidney (15.0% and 85.0% respectively). Lateral views confirmed anatomical positioning of kidneys and counting. Confirmation of the differential uptake in kidneys of the radiopharmaceutical was also achieved by ex vivo techniques [92.8% for left kidney and 7.2% for right kidney measured ex vivo in gamma camera; and 91.6% for left kidney and 8.4% for right kidney measured in a well-type gamma counter]. The present work clearly demonstrates that the comprehensive assessment of the biological behavior of radiopharmaceuticals assayed in experimental animals by using the small animal imaging approach, contributes more efficiently to the interpretation of the results. In this case, it was possible to detect incidental renal abnormalities that influenced the outcome of the biological distribution assay of 99mTc-MDP.
Keywords: 3Rs, 99mTc-MDP, biological distribution, radiopharmaceuticals, renal findings, small animal imaging.