Effect of the Image Detector Response in the Identification of Low-Level X-ray Scattering Signals from Image Subtraction

This work is part of an investigation on the potential use of X-ray scattering patterns in diagnostic imaging. It is motivated by the interest of contrasting numerical simulations with experimental measurements of scattering patterns. The scatter image is obtained by means of a subtraction method, where the signal of interest corresponds to the difference between images measured with and without the presence of the scattering medium, using a collimated beam. The acquired image contains a wide range of signal intensities (high intensity in the transmission region and very low intensity in the scattering region) covering almost the whole dynamic range of the detector. This work aims to assess the effects of the signal transfer property (STP) of a digital detector on the scatter imaging derived from the subtraction method. The STP of a RadEyel EV detector was measured showing a deviation from linearity particularly at low exposures. Therefore the STP was modeled by a piecewise quadratic-linear function. This model was applied to Monte Carlo simulated images that consider the interference effects in coherent scattering. Simulations were performed with the PENELOPE code. The loss in signal intensity due to the detector nonlinear response was in very good agreement with the scatter image measured using a mammographic X-ray tube and the characterized detector.