Room: Room 207
Purpose: Evaluate linearity and pulse pile-up in XCounterâ€™s Actaeon Photon Counting Detector (PCD) at high fluence rates.
Methods: Diagnostic imaging with photon counting CdTe detectors can offer superior contrast, spectral accuracy, and spatial and temporal resolution. However, this promising technology has its drawbacks including charge sharing between adjacent pixels and event losses due to pulse pile-up. The Actaeon PCD from XCounter has four image acquisition modes including the High Sensitivity with Anti-Coincidence (ACC-On) mode which does the charge sharing correction. An Actaeon detector with a pixel pitch of 100 Âµm, was used to acquire flat field images and checked for linearity with varying exposure rates in the angiographic range from 260 ÂµR/frame to 2500 ÂµR/frame at 10 frames per second, pulse duration of 12.5 ms, with all four of its imaging modes. A non-paralyzable detector model was used to find the pile-up time.
Results: Three of the modes: High Sensitivity without Anti-Coincidence, High Flux and High Power exhibit linear behavior in all considered ranges of exposure rates. For these imaging modes the PCD saturates even before pulse pile-up becomes an issue. However, the ACC-On mode exhibits evidence for pulse pile-up by deviating from ideal linear behavior at high fluence rates. The pile-up time was found to be 4.5 Âµs for the ACC-On mode after modelling the count rates with a standard non-paralyzable detector model. Pulse pile-up in the ACC-On mode could be attributed to the time delay in implementing the eight next nearest-neighbor anti-charge sharing correction.
Conclusion: For the Actaeon PCD, only the ACC-On mode shows evidence of pulse pile-up for a range of angiographic exposure rates. For high resolution CdTe PCDs, as pixel size is reduced for improved spatial resolution, pulse pile-up will be less of a concern whereas the charge sharing correction will be increasingly important.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by Canon Medical Systems Corporation
Photon Detectors, Coincidence Counting, Deadtime