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

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Abstract
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.

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