Reconstruction of spectral CT images

Abstract: Abstract X-ray computed tomography (CT) is a medical imaging modality that allows reconstruction of the internal stucture of the human body from a large number of x-ray attenuation measurements. In recent years, the development of spectral CT, in which the energy dependence of the x-ray attenuation coe-cient is utilized, has attracted considerable interest. This thesis is concerned with a spectral CT system based on a photon-counting silicon strip detector which is being developed in our group. A computer model for photon counting spectral CT was developed and used for simulating the proposed CT system as well as a laboratory CT setup designed for testing purposes. The simulations were used to compare the performance of two reconstruction methods for spectral CT, image-based energy weighting and basis material decomposition. The study shows that the two methods perform equally well when the number of x-ray photons in each measurement is high, while basis material decomposition performs signcantly worse than energy weighting for data with few photons in each measurement. Also included in the thesis is a simulation study of the detrimental eects of electronic noise and thresold variations on image quality. It is shown that a proposed electronic noise reduction of 20% in the readout channels gives an improvement in mean   SDNR2 over many channels of only 1.8%. In addition, a scheme for countering electronic noise contamination of the lowest energy bins due to threshold variations is discussed. The nal chapter of the thesis describes an experiment which demonstrates that the CT detector design studied here can indeed be used to obtain high-quality images.