Imaging of striatal dopamine D-2 receptors with a PET system for small laboratory animals in comparison with storage phosphor autoradiography: A validation study with F-18-(N-methyl)benperidol

Several groups have developed high-resolution PET systems and shown the fea sibility of in vivo studies on small laboratory animals. In this investigat ion, one of these systems was validated for the performance of receptor ima ging studies. For this, the radiotracer concentrations obtained in the same animals with PET and with autoradiography were quantified, and the corresp ondence between both methods was assessed by means of correlation analysis. Methods: Striatal radioactivity was measured in 10 Sprague-Dawley rats aft er injection of 60 +/- 10 MBq of the dopamine D-2 receptor ligand F-18-(N-m ethyl)benperidol in 6 time frames of 6 min each. On completion of the scans , animals were killed, and their brains were removed and sectioned using a cryostat microtome. Coronal slices were subjected to storage phosphor autor adiography with BaFBr:Eu2+-coated imaging plates. Striatal radioactivity wa s quantified in both modalities using reg ion-of-interest analysis and acti vity standards. Results: After partial-volume correction, the median of str iatal radioactivity concentration measured with PET was 0.40 MBq/cm(3) (25t h percentile, 0.32; 75th percentile, 0.44). Radioactivity concentrations de termined by means of storage phosphor autoradiography amounted to 0.42 MBq/ cm(3) (25th percentile, 0.24; 75th percentile, 0.51). Correlation of striat al radioactivity values yielded a Pearson correlation coefficient of 0.818 (P = 0.002). Radioactivity accumulation in Harder's glands led to an overes timation of striatal activity concentrations by approximately 5%. The media n of striatal radioactivity concentration after spillover correction decrea sed slightly to 0.38 MBq/cm(3) (25th percentile, 0.30; 75th percentile, 0.4 3). Correlation of striatal radioactivity values after spillover correction yielded a Pearson correlation coefficient of 0.824 (P = 0.002). Conclusion : The results show a significant positive correlation between radioactivity values obtained with PET and storage phosphor autoradiography used as the gold standard. quantified in the target region, we may infer that in vivo r eceptor binding studies will be possible in small laboratory animals.