High resolution x-ray imaging by measuring the induced charge distribution

Abstract: Computed tomography (CT) is a medical imaging technique used to create cross-section images of human bodies based on x-rays. The emerging photon-counting CT detector shows several advantages compared with the traditional energy integrating detector. This thesis is based on the new generation deep silicon photon-counting CT detector developed by KTH Medical Imaging group, with a 12×500μm^2 pixel size. A method is proposed to achieve high spatial resolution with low computation resource consumption.A Monte Carlo simulation has been done to simulate the photon interaction along with the charge transport process in the detector. The charge cloud distribution and induced current are used to make a precise estimation of the interaction position in the direction along the collecting electrodes. The feasibility of such a method under estimated electronic noise and other detector geometries has been checked. By having a high spatial resolution of around 1μm in one direction, it could be beneficial in phase contrast imaging.Besides the small pixel geometry, simulations on current photon-counting detector geometry, similar to what is used in clinics, have also been carried out, with a study of the charge carrier transport behavior and charge sharing possibility. The result shows that although the charge sharing event could be used to help estimate interaction position, its low proportion among total events leads to little resolution improvement. Another study on the induced current as a function of time has been presented. By reducing the electrode width while keeping the same pixel width, the induced current signal peak appears to be sharper.