Many nuclear imaging procedures are currently limited by the bulk, cost, complexity, and fragility of scintillation cameras, which employ large NaI crystals and large banks of photomultiplier tubes. We propose to develop a gamma camera based on xenon gas proportional tubes oriented parallel to incident radiation and operated at high pressure. In Phase I studies, high quality proportional gas response has been obtained with pure xenon gas to a pressure of over 50 atm. At this pressure, the detection efficiency for Tc- 99m is 90% of that of a l cm NaI crystal, and the energy resolution (8% FWHM) is superior. This same detector can image Tl-201 with nearly 100% efficiency and with an energy resolution (10% FWHM) which is substantially better than that of NaI. Therefore, this new technology can provide imaging of the two dominant nuclear medicine imaging isotopes which is competitive in spatial resolution and sensitivity and superior in scatter rejection. In Phase II, improvements in tube performance will be pursued and are expected to increase the operating pressure and sensitivity to even higher levels, and a working prototype camera, complete with readout system, will be constructed. This camera will have a resolution element (tube dimension) of 4.8 mm, an active area of 25 x 25 cm2, a peak count rate of> 1,000,000 cps, and energy resolution of <8% at 140 keV. In.addition to improved imaging performance, this new camera technology will provide a much more compact and light weight package and freedom from distortions and instability produced by the phototube drift in scintillation cameras. Among other applications, highly portable, general purpose cameras will be feasible, and modular multiview cameras can be conceived. It is also likely that the basic high pressure xenon tube element will also have applications in diverse fields of radiation detection outside of nuclear medicine. PROPOSED COMMERCIAL APPLICATIONS: This project carries significant commercial potential and could be used in numerous applications. The proposed technology could displace the current NaI crystal scintillation detector which is widely used for gamma imaging throughout nuclear medicine. In particular, nuclear cardiology, the primary subspecialty of nuclear medicine, could benefit enormously since the proportional tube gamma camera could serve as a lower cost means of performing cardiac perfusion studies. The technology also could be applied towards general radiation detection applications, such as for survey monitors or well counters.