Robustness of Optimal Energy Thresholds in Photon-counting Spectral CT
2018
An important question when developing photon-counting detectors for computed tomography is how to select energy thresholds. In this work thresholds are optimized by maximizing signal-difference-to-noise ratio squared (SDNR2) in a silicon-strip detector and a cadmium zinc telluride (CZT) detector, factoring in pileup in both detectors and charge sharing in the CZT detector. To investigate to what extent one single set of thresholds could be applied in various imaging tasks, the robustness of optimal thresholds with 2 to 8 bins is examined with the variation of anatomies and tissues. In contrast to previous studies, the optimal threshold locations don't always increase with increasing anatomies if pileup is included. Optimizing the thresholds for a 30 cm phantom yields near-optimal SDNR2 regardless of anatomies and tissues in both detectors. Fixing that set of thresholds and including pileup, with 2 bins, up to 23% of SDNR2 is lost; and with 6 to 8 bins, the loss of SDNR2 is 5% in the silicon-strip detector and 8% in the CZT detector. Having more than 2 bins reduces the need for changing the thresholds depending on anatomies and tissues. Using around 6 bins may give near-optimal SDNR2 without generating an unnecessarily large amount of data.
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