Characterization and Optimization of Silicon-strip Detectors for Mammography and Computed Tomography

The goal in medical x-ray imaging is to obtain the image quality required for a given detection task, while ensuring that the patient dose is kept as low as reasonably achievable. The two most common strategies for dose reduction are: optimizing incident x-ray beams and utilizing energy information of transmitted beams with new detector techniques (spectral imaging). In this thesis, dose optimization schemes were investigated in two x-ray imaging systems: digital mammography and computed tomography (CT). In digital mammography, the usefulness of anti-scatter grids was investigated as a function of breast thickness with varying geometries and experimental conditions. The general conclusion is that keeping the grid is optimal for breasts thicker than 5 cm, whereas the dose can be reduced without a grid for thinner breasts. A photon-counting silicon-strip detector developed for spectral mammography was characterized using synchrotron radiation. Energy resolution, ∆E/Ein, was measured to vary between 0.11-0.23 in the energy range 1540 keV, which is better than the energy resolution of 0.12-0.35 measured in the state-of-the-art photon-counting mammography system. Pulse pileup has shown little effect on energy resolution. In CT, the performance of a segmented silicon-strip detector developed for spectral CT was evaluated and a theoretical comparison was made with the state-of-the-art CT detector for some clinically relevant imaging tasks. The results indicate that the proposed photon-counting silicon CT detector is superior to the state-of-the-art CT detector, especially for high-contrast and high-resolution imaging tasks. The beam quality was optimized for the proposed photon-counting spectral CT detector in two head imaging cases: non-enhanced imaging and Kedge imaging. For non-enhanced imaging, a 120-kVp spectrum filtered by 2 half value layer (HVL) copper (Z = 29) provides the best performance. When iodine is used in K-edge imaging, the optimal filter is 2 HVL iodine (Z = 53) and the optimal kVps are 60-75 kVp. In the case of gadolinium imaging, the radiation dose can be minimized at 120 kVp filtered by 2 HVL thulium (Z = 69).