Monte Carlo simulation of photon-counting breast CT system: from implementation to image quality evaluation

Photon-counting detectors (PCD) are an emerging technology that has the potential to improve the image quality and material characterization capabilities in breast CT (bCT) compared to energy-integrating detectors (EID). This work focuses on implementing a Monte Carlo (MC) model to simulate PCD, using a previously validated Geant4-based MC code. MC simulations of bCT acquisitions, using both PC and EI detection technologies, were performed to investigate image quality improvement. To evaluate PCD simulation performance, a 50 keV beam was simulated with an energy threshold of 20 keV and four energy bins. The detection efficiency was 88%, with 24% of the counts corresponding to the incorrect energy channel due to partial energy deposition and charge-sharing effects. For image quality evaluation, projection images for bCT were simulated using anthropomorphic breast phantoms with an added iodinated spherical lesion and a W/Cu (0.257 mm) at 65 kV x-ray spectrum. 225 projections were simulated, and CT images were reconstructed using IMPACT method. Image quality was evaluated using the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). Comparing the simulated projections, the SNR and CNR increased, respectively, by up to 88/95% and 31/35% for single/multichannel PCD vs. EID. For the reconstructed images, the improvements were up to 27%/9%. It was observed a better accuracy and precision of linear attenuation coefficient estimation for PCD (PCD: 4.4% and 3.0%, and EID: 6.7% and 3.3%, on average, respectively). Overall, the PCD detector provides improved image quality and more accurate tissue characterization compared to the EID detector for bCT.