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. Detection efficiency for annihilation photons is ~30% per detector. The count rates obtained, by using a 20 cm diameter by 11 cm long water filled phantom containing ¹⁸F, were ~1.35×10⁶ singles and ~1.2×10⁵ cps raw coincidences 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 in the field of view of 10-100 MBq (0.27-2.7 mCi) with a timing gate of 20 ns. Initial results show that the randoms corrected sensitivity is >3-4 kcps/kBq/ml (120-150 kcps/μCi/ml) for activities up to 30 MBq (0.81 mCi) in a 20 cm diameter water-filled phantom. However, these values include a high (60%) scatter fraction due to detector support structures. The camera has not yet been fully optimised and it is expected that the performance will substantially improve by further tuning and a reduction in the scattering structures. With a 40 cm axial FoV the camera is ideally suited to whole-body imaging in oncology