The performance of a multiwire proportional chamber positron camera for clinical use

The Rutherford Appleton Laboratory clinical positron camera consists of two opposed multiwire proportional chambers (MWPCs) mounted on a rotating gantry capable of performing routine nuclear medicine studies. The system has operated since the end of 1986 with complete reliability. It has a sensitivity of 37 kcps MBq^-1 cm³ per axial cm for a 20 cm diameter uniformly filled cylinder of activity. The best spatial resolution obtainable is about 6 mm, although in practice images are smoothed in order to reduce statistical noise with a corresponding decrease in resolution. Cross-plane rays are utilised during image reconstruction and the resulting three-dimensional images exhibit the same spatial resolution in three orthogonal directions over a large cylindrical field of view 15 cm high by 30 cm in diameter. The maximum data-taking rate is limited to 1.5 to 2 kcps at present due to deadtime in the read-out system. The performance of the system is described with particular reference to the problems of imaging with the large fractions of random and scattered events which are a consequence of using large-area detectors. Images of phantoms and patients are presented and proposed modifications to the camera are described.