infusion on a Picker PRISM 3000 XP (Cleveland, OH) SPECT camera. The PRISM 3000 XP is a 3-headed camera equipped with a low energy, ultra-high resolution fanbeam collimator (photopeak window, 159 keV ± 10%; matrix 128×128) with a uniform sensitivity across the field of view. A 57Co-distributed source was measured with each experiment to control for day-to-day variation in camera sensitivity. The axial resolution (full width at half maximum) is 12.2 mm, measured with a 123I line source in water in a cylindrical phantom. Blood was drawn prior to injection and at the beginning and end of the emission scans for analysis of plasma total parent and free fraction of parent tracer in plasma (fP, free fraction). The chemical fate of [123I]5-IA post injection was assessed in plasma as previously described51. Briefly, plasma total parent was assessed by acetonitrile protein denaturation, while free fraction was determined by ultrafiltration using Centrifree units.
