Contrast agents are often crucial in medical imaging for disease diagnosis. Novel
contrast agents, such as gold nanoparticles (AuNPs) and lanthanides, are being ex-
plored for a variety of clinical applications. Preclinical testing of these contrast agents
is necessary before being approved for use in humans, which requires the use of small
animal imaging techniques. Small animal imaging demands the detection of these contrast agents in trace amounts at acceptable imaging time and radiation dose. Two
such imaging techniques include x-ray fluorescence computed tomography (XFCT)
and photon-counting CT (PCCT). XFCT combines the principles of CT with x-ray
fluorescence by detecting fluorescent x-rays from contrast agents at various projections to reconstruct contrast agent maps. XFCT can image trace amounts of AuNPs
but is limited to small animal imaging due to fluorescent x-ray attenuation and scatter. PCCT uses photon-counting detectors that separate the CT data into energy
bins. This enables contrast agent detection by recognizing the energy dependence of
x-ray attenuation in different materials, independent of AuNP depth, and can provide
anatomical information that XFCT cannot. To achieve the best of both worlds, we
modeled and built a table-top x-ray imaging system capable of simultaneous XFCT
and PCCT imaging.
We used Monte Carlo simulation software for the following work in XFCT imaging of AuNPs. We simulated XFCT induced by x-ray, electron, and proton beams
scanning a small animal-sized object (phantom) containing AuNPs with Monte Carlo
techniques. XFCT induced by x-rays resulted in the best image quality of AuNPs,
however high-energy electron and medium-energy proton XFCT may be feasible for
on-board x-ray fluorescence techniques during radiation therapy. We then simulated
a scan of a phantom containing AuNPs on a table-top system to optimize the detector
arrangement, size, and data acquisition strategy based on the resulting XFCT image
quality and available detector equipment. To enable faster XFCT data acquisition,
we separately simulated another AuNP phantom and determined the best collimator
geometry for Au fluorescent x-ray detection.
We also performed experiments on our table-top x-ray imaging system in the lab.
Phantoms containing multiples of three lanthanide contrast agents were scanned on
our tabletop x-ray imaging system using a photon-counting detector capable of sustaining high x-ray fluxes that enabled PCCT. We used a novel subtraction algorithm
for reconstructing separate contrast agent maps; all lanthanides were distinct at low
concentrations including gadolinium and holmium that are close in atomic number.
Finally, we performed the first simultaneous XFCT and PCCT scan of a phantom
and mice containing both gadolinium and gold based on the optimized parameters
from our simulations.
This dissertation outlines the development of our tabletop x-ray imaging system
and the optimization of the complex parameters necessary to obtain XFCT and PCCT
images of multiple contrast agents at biologically-relevant concentrations. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/12308 |
| Date | 04 November 2020 |
| Creators | Dunning, Chelsea Amanda Saffron |
| Contributors | Bazalova-Carter, Magdalena |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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