Design and physical characteristics of a small animal PET using BaF2 crystals and a photosensitive wire chamber

A small diameter Positron Emission Tomograph (PET) dedicated to animal imaging, using BaF2 crystals and a photosensitive wire chamber with tetrakis-dimethylamine-ethylene (TMAE), has been designed and built. It consists of a cylindrical ring with an inner diameter of 200 mm containing 2958 BaF2 crystals measuring 3 X 3 X 20 mm(3) each. The lack of septa in the design allows for 3D data acquisition and reconstruction. It is fully completed and operational. The first physics measurements show that the tomograph meets the design specifications: 1) the detection efficiency for one 511 keV photon is 38%, 2) the sensitivity as measured with a Ge-68 point source at the centre is 32 000 cps per Mbq, 3) the tangential resolution (FWHM) varies from 3 mm at the centre to 4.5 mm at a position 50 mm radially off centre, 4) the radial resolution (FWHM) varies from 3 mm at the centre to 6 mm at 50 mm radially off centre, and the axial resolution is 3.5 mm, 5) the coincidence time resolution (FWHM) is 29 ns, which allows the use of a time window of 50 ns. Sinogram data and the corresponding reconstructed image for a uniform Ge-68 cylinder 54 mm in diameter are also presented. These show that good uniformity can be achieved within the held of view.