A Monte Carlo-based evaluation of sensitivity, count rate performance, and spatial resolution in circular vs....

The geometry of Positron Emission Tomography (PET) detector arrays directly influences system sensitivity, spatial resolution, and count rate performance, yet nearly all clinical whole-body scanners employ a circular arrangement. In this work, GATE Monte Carlo simulations were used to evaluate an alternative PET system geometry based on an elliptical detector arrangement that better matches the transverse cross-section of the human body. We compared a standard circular system with two elliptical configurations: Elliptical, where the detectors are tangent to the ellipse, and Focused Elliptical, where the seven most lateral blocks on each side are reoriented toward the geometric center of the ellipse. The elliptical systems feature a major axis of 81.64 cm (comparable to the diameter of the circular system) and a minor axis of 50.0 cm. We hypothesize that the reduced detector-to-source distance along the anteroposterior axis increases sensitivity through greater solid angle coverage, while the Focused Elliptical design mitigates potential resolution loss by redirecting lateral blocks toward the center. We evaluated system sensitivity, spatial resolution, and Noise Equivalent Count Rate (NEC). Images were reconstructed using 2D filtered back projection (FBP). The Focused Elliptical configuration achieved a mean sensitivity gain of 26% over the circular system, with lower variability across the field of view (FOV). NEC peak values were 11% higher for the elliptical systems, achieved at lower activity concentrations. Spatial resolution showed a direction-dependent response, with improvements in some transverse directions and degradation in others, while the axial response was strongly influenced by the Single Slice Rebinning (SSRB) procedure. These results, combined with a 22% reduction in the number of detector blocks, suggest that elliptical geometries are a promising alternative for further investigation, providing higher sensitivity and count-rate performance.