Compton and Proximity Imaging of Ac In Vivo With a CZT Gamma Camera: A Proof of Principle With Simulations

In vivo imaging of 225Ac is a major challenge in the development of targeted alpha therapy radiopharmaceuticals due to the extremely low injected doses. In this article, we present the design of a multimodality gamma camera that integrates both proximity and Compton imaging in order to achieve the demanding sensitivities required to image 225Ac with good image quality. We consider a dual-head camera, each of the heads consisting of two planar cadmium zinc telluride detectors acting as scatterer and absorber for Compton imaging, and with the scatterer practically in contact with the subject to allow for proximity imaging. We optimize the detector’s design and characterize the detector’s performance using Monte Carlo simulations. We show that Compton imaging can resolve features of up to 1.5 mm for hot-rod phantoms with an activity of 1 $\mu $ Ci, and can reconstruct 3-D images of a mouse injected with 0.5 $\mu $ Ci after a 15-min exposure and with a single bed position, for both 221Fr and 213Bi. Proximity imaging is able to resolve two 1 mm-radius sources of less than 0.1 $\mu $ Ci separated by 1 cm and at 1 mm from the detector, as well as it can provide planar images of 221Fr and 213Bi biodistributions of the mouse phantom in 5 min.