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Flat-panel, cadmium telluride (CdTe) photon counting detectors (PCDs) are of interest for contrast-enhanced spectral mammography (CESM). Modelling of the frequency-dependent imaging performance of CdTe PCDs is useful for optimization of technique parameters. The purpose of this work is to experimentally validate a Monte-Carlo-based model of the frequency-dependent imaging performance of a CdTe PCD for contrast-enhanced breast imaging. Our Monte-Carlo model accounts for the basic physics of x-ray detection by PCDs, including the finite range of photo-electrons, characteristic emission and subsequent reabsorption, the finite size of charge clouds due to diffusion and Coulomb repulsion, electronic noise and energy thresholding. We validated the model using a two-bin CdTe PCD with charge summation for charge-sharing correction. The detector consists of a 750-um-thick CdTe converter with 100 um pixels. Our model was used to predict both the modulation transfer function (MTF) and the normalized noise power spectrum (NNPS) of both energy bins, in addition to the cross NPS between energy bins. Validation was performed for 40 kVp, 45 kVp and 50 kVp tube voltages. For each tube voltage, we validated for energy thresholds that resulted in photon ratios between the two energy bins of 1:2, 1:1 and 2:1. In all cases, our model predicted the MTF of both energy bins within 3%. The modelled NNPS was 5% to 15% of the measured NNPS. We conclude that the Monte-Carlo-based model can be used to model the frequency-dependent signal and noise properties of contrast-enhanced spectral mammography implemented with CdTe PCDs.
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