A Positron Camera by Use of a Focal Detector of Hexagonal Multi-Crystal Array

Abstract

A new positron camera consisting of a focal detector of hexagonal multi-crystal array and a conventional Anger type scintillation camera was made. Annihilation γ-ray pair can be picked up among numerous ‘single’ γ-ray events by use of a fast coincidence circuit. A coarse collimator of long focus was designed and adopted to prevent incidence of ineffective ‘single’ γ-rays into scintillation camera, which otherwise limit high counting rate characteristics of the system. This collimator was also so designed that it improves the spatial uniformity of the detection efficiency. Some characteristics of the positron camera are; (1) maximum attainable high counting rate is about 2.5-5 kcps, (2) detection efficiency is 0.6-0.9 dots/sec/μCi, (3) spatial resolution is 6-9 mm (FW HM) (those figures depend on the distance from the collimator surface of the γ-camera to source), (4) area of uniform sensitivity is about 20 cm in diameter at the depth of 20 cm from collimator surface.