Charge-cloud-based micrometer resolution in deep-silicon photon-counting CT.

PURPOSE: We are developing a monolithic deep-silicon photon-counting sensor targeting spatial resolution on the order of 1    μ m . This work investigates how pixel pitch, noise level, threshold number, and threshold placement affect the achievable tangential and wafer-thickness resolution to guide the CMOS electronics and sensor design. APPROACH: Allpix Squared simulations were used to evaluate pixel pitches with two noise levels and two threshold-placement schemes over varying threshold numbers. Interaction position was estimated in both dimensions using lookup tables trained on the thresholded pixel output, and performance was quantified using the MTF. RESULTS: Decreasing pixel pitch strongly improved tangential resolution for Compton interactions, whereas photoelectric interactions showed a weaker dependence on pixel pitch and threshold placement. Equal-counting thresholds approached the achievable resolution with fewer thresholds than equidistant thresholds. For eight equal-counting thresholds, the 10% MTF across the studied pixel sizes ranged from 1284   lp / cm to 2452   lp / cm in the tangential direction and from 15 to 71    lp / cm in the wafer-thickness direction for Compton interactions, compared with 409 to 507    lp / cm and 18 to 79    lp / cm , respectively, for photoelectric interactions. RMSE analysis further showed that some interactions for the 25    μ m pitch reached below 2    μ m tangentially and a few tens of micrometers in the wafer-thickness direction. CONCLUSIONS: Spatial resolution improved with a threshold number up to about 8 to 10, beyond which additional programmable thresholds gave only modest gain. The achieved tangential resolution also suggests that analyzer-free phase-contrast imaging is feasible for realistic geometries and expected interference patterns.