Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
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
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.
2011. , 60 p.