Empirical detector model for simulated breast exams with a dedicated breast CT scanner

This work proposes an empirical model for tuning spatial resolution and noise in simulated images in virtual clinical trials in x-ray breast imaging. In extending previous studies performed for direct conversion a-Se detectors used in digital mammography and digital breast tomosynthesis, this work introduces the model for the case of cone-beam computed tomography dedicated to the breast that uses a indirect conversion flat-panel detector. In the simulations, the detector is modeled as an absorbing layer whose material and thickness reflect those of the scintillator of the detector of a clinical scanner. The simulated images are then computed as a dose deposit map. The detector response curve, modulation transfer function (MTF) and noise power spectrum (NPS) were measured on a real detector. The same measurements were replicated in-silico for the simulated detector and scanner. The comparison of simulated and measured detector response curves permits to recover pixel values at the clinical scale. The difference between the simulated and measured MTFs permitted to introduce a linear filter for compensating simulated model simplification that determines a better spatial resolution in the simulated images with respect to real images. This filter presented a Gaussian shape in the Fourier domain with a standard deviation of 1.09 mm-1, derived from those of the measured and simulated MTF curves, of 0.86 mm-1 and 1.41 mm-1, respectively. Finally, the analysis of the NPS permits to compensate for noise characteristics due to the simulated model simplifications. The model applied to the simulated projection images produced MTF and normalized NPS in simulated 3D images, comparable to those obtained for the clinical scanner.