Preliminary results from the new large-area PETRRA positron camera

The PETRRA positron camera is based on the use of BaF₂ scintillators interfaced to large area multiwire proportional chambers filled with a photo-sensitive vapour (TMAE). The camera consists of two 60 cm×40 cm annihilation photon detectors mounted on a rotating gantry. Initial measurements with the camera show that the spatial resolution is ~6.5±1 mm FWHM all through the field-of-view, and the timing resolution is between 7 ns and 10 ns FWHM. A detection efficiency for annihilation photons is ~30% per detector. With singles count rates of ~1.35×10⁶, raw coincidences are ~1.2×10⁵ cps at which point data-rates are limited by the dead-time in the readout system. The randoms rate varies between 5 and 50% with activity for 10-100 MBq (0.27-2.7 mCi) with a timing gate of 20 ns. Initial results show that the randoms corrected sensitivity is >3-4kcps/kBq/ml (120-150 kcps/μCi/ml) for activities up to 30 MBq (0.81 mCi) in a 20 cm diameter water-filled phantom. The camera has not yet been fully optimised and it is expected that the performance will substantially improve by further tuning. At the present time, the camera, which can be produced at a price similar to a double-headed gamma camera, has a performance close to that of a 2D multi-ring BGO system such as the ECAT EXACT. With a 40 cm axial FoV the camera is ideally suited to whole-body imaging in oncology