The wide band gap semiconductor Cadmium Zinc Telluride (CZT) is of recent
interest for medical imaging at room temperature. A number of properties, including
superior energy resolution, 3D photon position sensitivity, compact size, direct
photon conversion and energy-resolving capability, make CZT a promising candidate
for positron emission tomography (PET) and photon-counting X-ray imaging systems.
Despite these advantages, drawbacks, such as low mobility of holes, hole trapping,
charge sharing effect and characteristic X-ray escape degrade the performance of
large volume CZT detectors.
In this research, characterization and evaluation of single-crystal CZT photon
detector using simulation and experimental studies were done. First, a comprehensive
analytical model was developed and implemented by using Monte Carlo simulation
and finite element analyses. This model includes the generation and transportation of
charge carries within CZT detectors, and it provides useful guidance in optimizing the
electrode design and associated readout circuits.
Second, the performance of a 20×20×5mm3
CZT crystal with 8×8 pixel anodes
and a planar cathode was integrated with readout electronics that can be used to build
a PET system was studied. The experiments demonstrate an energy resolution of
~2.26±0.84% full width half maximum (FWHM) at 662 keV and 19±3 ns
coincidence time resolution with planar parallel field configuration. A novel
algorithm based on charge sharing effect and transient signal analysis targeting the
improvement of spatial resolution, was proposed. The sub-pitch spatial resolution is
found to be ~30 µm and ~250 µm under signal-to-noise ratio of ~17, for inside and
outside the valid range of charge sharing, respectively.
Finally, the feasibility of CZT in photon-counting Computed Tomography (CT)
was studied by using monoenergetic sources, with a special attention paid to energy
degradation due to characteristic X-ray escape and the charge sharing effect. The
effects of detector configuration and incident beam location were also investigated.
The results show that the pixel size can be reduced to 500 µm without significant
count loss (~5%) and charge loss (~15%) for the photo-counting X-ray applications. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/23880 |
| Date | January 2017 |
| Creators | Zheng, Xiaoqing |
| Contributors | Deen, M. Jamal, Electrical and Computer Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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