A study of the effects of detector width and depth on spatial resolution in Positron Emission Tomography

As scintillation crystals used in Positron Emission Tomography (PET) cameras are made smaller to improve resolution, there is a loss of resolution at the edges of the field of view (FOV). This loss can be eliminated by the determination of the depth of interaction of photons within each crystal. A 4 mm black band around a {dollar}30times10times3{dollar} mm Bismuth Germanate (BGO) crystal painted at 10 mm along its length divides the crystal into two regions of equiprobable interaction. By collecting scintillation light from the front side of such a detector, it is possible to differentiate between photon interactions in front of and behind the band. The effectiveness of the technique for single and multiple detector blocks was studied.; More than half the annihilation photons incident upon the BGO crystals are Compton scattered before being absorbed photoelectrically in the crystal. The effect of scatter upon the aperture function (AF) of five {dollar}25times10{dollar} mm BGO crystals with widths increasing from 1 mm to 3 mm in steps of 0.5 mm was studied. The AF dependence upon the crystal depth was also investigated.