3D performance of a small diameter positron emission tomograph for scanning small animals

A small diameter positron emission tomograph has been constructed from commercially available bismuth germanate detectors and detection electronics. The tomograph has a diameter of 115 mm and an axial field of view (FOV) of 50 mm and was designed specifically for scanning small animals. The absence of interplane septa allows all possible lines of response to be acquired and a 15 plane image set is reconstructed from the 3D sinogram. The physical characteristics of the tomograph operating in 3D have been measured and a preliminary investigation of two scatter correction techniques has been completed. The transaxial resolution was measured as 2.4 mm full width half maximum (FWHM) at the centre of the transaxial FOV, degrading to 7.0 mm (radial) and 4.6 mm (tangential) FWHM at 40 mm from the centre of the transaxial FOV. The axial resolution was measured as 4.6 mm FWHM at the centre of the transaxial FOV, increasing to 5.1 mm FWHM at 40 mm radial distance. The measured sensitivity was 3.57×10⁴ counts.s^-1.MBq^-1 at 380-850 keV. A scatter fraction of 21.9% at 380-850 keV was determined from a central ¹⁸ F line source in a 60 mm diameter water-filled cylinder. The noise equivalent count performance in 3D indicated that 380-850 keV was the optimum energy window for routine data acquisition