Preliminary results from the new large-area PETRRA positron camera

The PETRRA positron camera is based on the use of BaF2 scintillators interf aced to large area multiwire proportional chambers filled with a photo-sens itive vapour (TMAE). The camera consists of two 60cm x 40cm annihilation ph oton detectors mounted on a rotating gantry. Initial measurements with the camera show that the spatial resolution is similar to 6.5+/-1mm FWHM all th rough the field-of-view, and the timing resolution is between 7ns and 10ns FWHM. Detection efficiency for annihilation photons is similar to 30% per d etector. The count rates obtained, by using a 20cm diameter by 11cm long wa ter filled phantom containing F-18, were similar to 1.35 x 10(6) singles an d similar to 1.2 x 10(5)cps raw coincidences at which point data-rates are limited by the dead-time in the readout system. The randoms rate varies bet ween 5 and 50% with activity in the geld of view of 10-100MBq (0.27-2.7mCi) with a timing gate of 20ns. Initial results show that the randoms correcte d sensitivity is >3-4kcps/kBq/ml (120-150kcps/mu Ci/ml) for activities up t o 30MBq (0.81mCi) in a 20cm diameter water-filled phantom. However, these v alues include a high (60%) scatter fraction due to detector support structu res. The camera has not yet been fully optimised and it is expected that th e performance will substantially improve by further tuning and a reduction in the scattering structures. With a 40cm axial FoV the camera is ideally s uited to whole-body imaging in oncology.