Optimizing energy settings in CdTe, CZT, and Si photon-counting CT for material separation and detection

Objective. The performance of photon-counting CT (PCCT) depends on how detector energy thresholds or bins (collectively referred to as energy settings) are defined. This study aimed to identify optimal energy settings for various PCCT technologies to enhance spectral separability and spatial detectability of materials relevant to diagnostic imaging.Approach. We modeled vendor-neutral PCCT scanners with cadmium telluride (CdTe), cadmium zinc telluride (CZT), and silicon (Si) based detectors using anin-silicoimaging framework. The scanner models incorporated scanner geometries and spatio-energetic detector responses to account for inter-pixel and inter-energy crosstalk and noise correlation. Using these models, we imaged two sizes of a cylindrical phantom containing inserts with various concentrations of calcium, iodine, and gadolinium across various energy settings and two dose levels. Other settings were held constant, including tube voltage (120 kV), pitch (1), gantry rotation speed (0.5 rot s^-1), and reconstruction settings. Image quality was quantified in terms of separability index (s') and contrast-to-noise ratio. The scanner-specific optimal energy settings were determined by ranking the measureds' values using a rank-sum method and evaluating them with the Friedman test.Main results.The optimal energy settings varied primarily with the phantom size and material pairs to separate (Ca-I, Ca-Gd, I-Gd) rather than the dose level. When aggregated across all imaging tasks and conditions, the optimal energy settings were 30-65 keV and 20-35-50-70 keV for two- and four-threshold CdTe-, 20-35-50-70 keV for four-threshold CZT-, and 5-35-50-80-120 keV for four-bin Si-based PCCT systems. Optimization of energy settings significantly improved material decomposition accuracy for Ca, I, and Gd across PCCT systems, particularly under low-concentration conditions, reducing percent differences from as high as 422.0% to within 17.0%.Significance.This work presents a simulation-based framework for optimizing energy settings of photon-counting detectors used in PCCT scanners, providing clinically translatable insights towards clinical adoption for accurate and standardized spectral imaging.