A Clinical Multiwire Proportional Chamber for Low Energy Radionuclides

A sealed, single-atmosphere xenon-methane imaging proportional chamber has been constructed specifically for clinical use with 125I-fibrinogen in the legs. The detector weighs approximately 7Kg, has a window of 10cm×30cm and yields an intrinsic spatial resolution of 2.85 mm FWHM at 27keV. It has a detection efficiency of 20%, and, when collimated with orthogonally-aligned pair of x-ray antiscatter grids, yields a system resolution of 6mm FWHM at the collimator face and an overall sensitivity of 1.3×10-4. A recirculating purification system using molecular sieve and a gettering furance serve to remove gas contaminants. The system was evaluated using 125I, in phantoms and animals and has seen preliminary clinical use.