Analyzing the effect of timing accuracy on NECR performance for dedicated breast PET

Limited geometric sensitivity and activity outside the field-of-veiw (FOV) may reduce lesion detection accuracy by reducing noise performance in breast PET (BPET) systems. In this work, the effect of scanner geometry and coincidence window (0.5, 1, 2, 3 and 4.5 ns) on noise performance characteristics has been evaluated for breast phantom models using GATE Monte Carlo simulation techniques. Cylindrical BPET systems with 25 cm transaxial FOV and 20, 15 and 11 cm axial FOV have been modeled to evaluate their noise characteristics. The detector was modeled with LYSO crystal of 2×2 mm
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tangential dimension and 2 cm depth for improved sensitivity. The sensitivity in detecting point sources at different axial extent were evaluated. A breast volume of 14 cm diameter and 11 cm axial length was modeled analytically using a cylindrical-spherical geometry for noise performance evaluation. Contribution of counts from non-breast anatomy such as heart and torso has been incorporated. The effect of detection timing resolution for singles (176, 354, 760, 1061 and 1591 ps) and activity concentration (0.01-0.05, 0.1-1.0 uCi/cc) on noise performance has been evaluated. Increasing the axial extent of the detector produced improved detection sensitivity for lesions away from chest wall. Reducing the coincidence window (CW) improved the NECR by reducing the randoms rate (randoms rate decreased by 77% at 1 ns CW compared to 4.5 ns CW). The primary contribution to the scatter rate was observed to originate from activity inside the FOV, while the primary contribution to the randoms rate originated from activity located outside the FOV.