Semiconductor based photon-counting detectors for x-ray CT have a number of advantages over energy integrat ing detectors, including reduced electronic and Swank noise, increased dynamic range, capability of spectral CT for material decomposition, and improved SNR characteristics through energy weighting. Quite a few clinical applications could benefit from high-resolution spectral CT. For example, in breast CT the visualization of mi crocalcifications and assessment of tumor microvasculature after contrast enhancement require spatial resolution on the order of 100 μm or better. A straightforward approach to increasing spatial resolution by decreasing the detector pixel size, leads to two major problems: 1) fabricating circuitry with small pixels becomes very costly, and 2) inter-pixel charge spreading can obviate any improvement in spatial resolution. In this study, we have used computer simulations to investigate position estimation algorithms that utilize charge sharing to achieve sub-pixel position resolution. To study these algorithms, we model a simple detector geometry with a pixellated
5 x 5 anode array, and use conditional probability functions modeling electron-hole charge transport in CZT. We used COMSOL Multiphysics software to map the distribution of charge pulses in the detector. Performance of two x-ray interaction position estimation algorithms were evaluated: 1) method of maximum likelihood, and
2) a fast, practical algorithm that can be realistically implemented in a readout ASIC, providing identification
of the quadrant of the pixel in which interaction occurred. Both methods exhibit good sub-pixel resolution performance, however their actual efficiency is limited by electronic noise.