The development of ASPECT, an annular single crystal brain camera for high efficiency SPECT

A description is given of ASPECT, a totally digital annular SPECT (single-photon-emission computed tomography) camera system designed specifically for 3-D brain imaging. Its detector consists of a single-crystal NaI(Tl) ring (31-cm ID by 8-mm thick by 13-cm wide) coupled through an annular light pipe to a 21*3 array of 51-mm/sup 2/ photomultipliers. A unique multifield collimator system, consisting of set of six parallel-hole collimators oriented in an annular array, is designed to view the patient´s head from six angles simultaneously. This ring is rotated with high precision, concentric to the detector, through 2 pi radians to sample gamma-ray emissions for 3-D reconstruction over a 23-cm*9-cm field of view. Preliminary results indicate that central regions of the brain will be detected with an efficiency of about six times that of a conventional rotating parallel-hole camera SPECT system and an effective inherent transverse resolution of within 3.5 mm. The system is designed to achieve a reconstructed resolution FWHM within 7.5 mm at the center of the image field. It also features unique means for digital position analysis, calibration, and user quality control. With ASPECT´s precision rotating collimator, artifacts normally associated with detector motion, nonuniform sensitivity, and spatial nonlinearities are expected to be insignificant.<>