In nuclear medicine, a radionuclide is administered to a patient and a scintillation camera such as the Anger gamma camera, shown in U.S. Pat. No. 3,011,057, is used to produce a visual image of the distribution of the administered radionuclide within the target organ of the patient. Devices used to detect the emitted radiation utilize a collimator to selectively filter the passage of emitted radiation from the patient to a scintillation system which includes a scintillation crystal positioned behind the collimator. The crystal changes radiation to visible light during each scintillation.
The gamma rays that do not pass through the collimator do not contribute to the image. Spatial resolution is approximately proportional to the depth of the object, that is, the distance between the object and the face of the collimator. For planar imaging, this distance is minimized by placing the collimator as close as possible to the portion of the patient being imaged. To perform three dimensional imaging, such as emission computed tomography (ECT), it is necessary to have the detector portion of the radiation imaging device orbit the patient. Scintillation cameras capable of emission computed tomographic studies, such as Technicare's Omega 500, are arranged to have the scintillation detector orbit the patient in a circular path. Since people tend to have an elongated circumference at thorax level, a circular orbit will necessarily result in undesirable separation between the face of the collimator and the patient's chest (anterior position) and patient's back (posterior position). During these portions of the circular orbit, the patient-detector distance will be undesirably excessive. Hence, the resolution of the reconstructed tomographic image will be degraded relative to a tomogram acquired from an orbital path closely tracking the patient's perimeter.