A landmark-based approach for the quantitation of receptor and transporter binding in the rat using small animal SPECT and PET

A retrospective image fusion method is presented for the quantitation of receptor and transporter binding in cerebral regions using small animal SPECT and PET. To obtain images of bone metabolism, tissue perfusion and brain perfusion rats were injected ^99mTc-labeled DPD, tetrofosmin (TF) or HMPAO. Further rats were applied dopamine transporter (DAT) or D₂ receptor ligands (¹²³I-FP-CIT, ¹²³I-IBZM, ¹⁸F-FMB). DAT or D₂ blockade was induced by methylphenidate (MP) and haloperidol (HAL), respectively. Scanning was performed with small animal SPECT or PEL Striatal, cortical and cerebellar regions were defined on sets of fusion images allowing the localization of the target regions relative to the sites of specific accumulation of metabolism and perfusion markers. For validation, mean striato- and corticocerebellar ratios were computed for blocked and unblocked DAT and D₂ binding. DPD, TF and HMPAO scans provided quasi-anatomical information, which facilitated the identification of striatum, cortex and cerebellum relative to the localization of cranium and orbitae with Harder´s glands. This was crucial in MP- and HAL-treated rats with reduced intracerebral radioactivity accumulations. Quantitative data obtained with this method lay within the order of magnitude previously reported in literature. The study shows the feasibility of fusing receptor and transporter with bone metabolism and perfusion scans. Our method represents a nuclear medical alternative to morphological coregistration with dedicated CT or MRT.