An electronically collimated gamma camera for single photon emission computed tomography. Part I: Theoretical considerations and design criteria

The detection and imaging characteristics of a new type of gamma camera for single photon emission computed tomography have been investigated. Unlike conventional gamma cameras which use mechanical collimation, the new gamma camera utilizes electronic collimation which is obtained from a sequential interaction of gamma radiation with a dual position-and-energy sensitive detection system. Coincident counting between the two detectors provides localization of activity upon a multitude of conical surfaces throughout the object, wherefrom the three-dimensional activity distribution can be reconstructed. Not only does electronic collimation provide simultaneous multiple views of the object, but a large gain in sensitivity is also indicated over a conventionally collimated gamma camera under conditions of similar spatial resolution. Detector optimization studies have been performed to design a prototype system comprising a 33 X 33 array of high-purity germanium detectors coupled to an uncollimated conventional scintillation camera. The cumulative signal-to-noise ratio in projection images obtained with this system is expected to be about a factor of 4 higher (sensitivity about a factor of 15 higher) than that obtained in a corresponding projection image with a conventional gamma camera for imaging a uniformly distributed Tc-99m source in a 20-cm-diam X 20-cm-tall cylinder. A similar gain is expected in the tomographic images.