Preliminary results from the new large-area PETRRA positron camera

The PETRRA positron camera is based on the use of BaF/sub 2/ scintillators interfaced to large area multiwire proportional chambers filled with a photo-sensitive vapour (TMAE). The camera consists of two 60 cm/spl times/40 cm annihilation photon detectors mounted on a rotating gantry. Initial measurements with the camera show that the spatial resolution is /spl sim/6.5/spl plusmn/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 /spl sim/30% per detector. The count rates obtained, by using a 20 cm diameter by 11 cm long water filled phantom containing /sup 18/F, were /spl sim/1.35/spl times/10/sup 6/ singles and /spl sim/1.2/spl times/10/sup 5/ 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//spl mu/Ci/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.