The High-Density Avalanche Chamber for Positron Emission Tomography

The development of wire chambers for positron emission tomography continues at CERN. In its present form, the basic detector is called a HIgh Density Avalanche Chamber (HIDAC). Owing to the Penning effect, electron avalanche multiplication is obtained in the gamma-ray converter: coincidence time resolution is reduced to 20 ns and stable chamber operation is achieved with a safe, non-polymerizing gas mixture. Spatial resolution remains at 2-3 mm FWHM. A rotating camera consisting of two 20 × 20 cm chambers has now been under evaluation at Geneva Hospital for one year. Multilayer printed-circuit techniques are now used to construct chambers with multiple converters, thus raising detection efficiency from 7.5 to 20%. Read-out electronics and back-projecting memory are being developed to handle the high data rate from these chambers. A four-chamber positron camera designed to achieve 100,000 coincidences s-1 is nearing completion.