Author: Frank F. Dong, Megan C. Jacobsen, Ke Li, Xinming Liu, John Rong 👨🔬
Affiliation: UT MD Anderson Cancer Center 🌍
Purpose: We aimed to understand the physical performance of a CdTe PCD-based detector system within a whole-body PCD-CT scanner, with the goal of optimizing its clinical application. Instead of relying on raw detector counts, which are typically not accessible to end-users, we evaluated the detector using a novel approach based on reconstructed PCD-CT images.
Methods: After acquiring total-energy-bin PCD-CT images from a NAEOTOM Alpha scanner under the Expert mode, we calculated the 3D NPS using ROIs within 5 cm of the iso-center. The mean number of output counts per detector pixel was estimated by fitting the measured NPS to a previously validated parametric model. The mean input photon count was derived from exposure and beam-quality measurements and the TASMIP spectrum model. The ratio of output to input quanta provided the zero-frequency DQE (DQE0). The detector NPS was estimated by scaling Z-component of the 3D PCD-CT NPS according to magnification and detector sampling rate. The PCD’s deadtime was assessed by analyzing the dependence of PCD-CT image variances on mA levels, which ranged from 10 to 1200.
Results: For the Alpha detector system, including the anti-scatter grid, the protective cover, and electrodes, the DQE₀ was found to be 63.6% (range: [63.0%, 64.6%]). No significant dependence of DQE₀ on kV was observed. The estimated PCD deadtime is 12.6 ns. The PCD NPS is nearly flat across the frequency axis, decreasing by only 7% at the detector Nyquist frequency.
Conclusion: Results of this work suggest that: 1) DQE₀ of the Alpha scanner's detector system is primarily influenced by the geometric efficiency of the anti-scatter grid and pixelated electrodes, rather than the thickness of the CdTe sensor; 2) Alpha’s PCD is extremely fast with negligible pileup count losses under typical clinical conditions; 3) Cross-talk between PCD pixels is negligible based on the flat detector NPS.