Randoms distributions for triple-head gamma-camera PET systems

Understanding the effects of random coincidences in PET is important to the analysis of emission images. The noncircular detector structure of triple-head systems gives rise to different randoms distributions than ring tomographs. Using a simulation method, it is found that the shape of the randoms distributions for triple-head systems is more sensitive to the configuration of the detector heads than to the source distribution. The distribution for triple-head systems is spread across the field-of-view, peaking off-center; the dual-head case peaks in the center of the FOV. We also discuss the difference in the axial distribution for 2D and 3D acquisition and rebinning; the introduction of septa and an axial acceptance angle reduces randoms, illustrating an important trade-off between imaging with and without axial septa.