Quad-Detector Arrangement and Sampling Characteristics in Rotary Positron Tomography: POSITOLOGICA II

This paper clarifies that a method of rotary positron-emission computed tomography (PCT) with quad (tri or bi)-detector units can provide the satisfactory sampling characteristics with negligible sacrifice (less than 1 percent) of the detector packing ratio. This paper also presents the array design of quad-BGO (bismuth germanate) units and the sampling characteristics of a rotary PCT system named POSITOLOGICA II. In the rotary PCT, detector units are mounted unequally spaced on a ring so as to provide fine and uniform linear sampling during a 360 degrees rotation of the ring around its center. This principle was applied to a system named POSITOLOGICA I, but it has unidetector units [one detector-one photomultiplier tube (PMT)]. The quad-detector unit consists of four BGO crystals, two PMT's, and a circuit positioning the address of the crystal by which a gamma ray is detected. Merits of the quad units are an effective coupling between rectangular crystals and a photocathode of PMT and reduction of the number of PMT's.