Resolution improvement in x-ray imaging with an energy-resolving detector

In x-ray imaging, irnproving spatial resolution an important goal, but developing dctectors with smaller is technically challenging. We demonstrate a technique for improving the spatialesolution by utilizing the fact that linear attenuation coefficients of all substances within the human body can be expressed, to a good approximation, as a linear combination of two basis functions, or three if there is iodine contrast present in the image. When the x rays pass an interface parallel to the beam direction, the exponential attenuation law makes the linear attenuation coefficient measured by the detector a nonlinear combination of the linear attenuation coefficients on each side of the interface. This so-called nonlinear partial volume effectcauses the spectral response to be dependent on the steepness of interfaces in the imaged volume. In this work, we show how this effect can be used to improve the spatial resolution' spectral)jec ion x-ray imaging and quantify the achievable resolution improvement. We simulate x-ray transmission imaging of sharp and gradual changes in the projected path length of iodine contrast with an ideal ettergy-resolving photon -counting detector and demonstrate that the slope of the transition can be determined from the registered spectrum. We simulate piecewise-linear transitions and show that the algorithm is able to reproduce the transition profile on a subpixel scale. The FWHM resolution of the method is 5-30 % of the pixel width. The results show that an energy -resolving detector can be used to improve spatial resolution when imaging interfaces of highly attenuating objects.