Oakley Clark
About
My research project
A methodology for breast density measurement using the HEXITEC pixellated spectroscopic technologyBreast tissue is a mixture of adipose tissue and glandular tissue. Breast density is defined as the volume fraction of glandular tissue within the breast. Having a higher breast density has been shown to increase the likelihood of developing breast cancer. It is therefore important to measure breast density, in order to identify those who are at greatest risk (to screen them more often) and those who are at less risk (to screen them less often, saving resources).
The HEXITEC detector registers the position and energy of X-rays incident upon it. This projects aims to utilize the energy information provided to differentiate between adipose and glandular tissue within a breast, in order to measure breast density.
Supervisors
Breast tissue is a mixture of adipose tissue and glandular tissue. Breast density is defined as the volume fraction of glandular tissue within the breast. Having a higher breast density has been shown to increase the likelihood of developing breast cancer. It is therefore important to measure breast density, in order to identify those who are at greatest risk (to screen them more often) and those who are at less risk (to screen them less often, saving resources).
The HEXITEC detector registers the position and energy of X-rays incident upon it. This projects aims to utilize the energy information provided to differentiate between adipose and glandular tissue within a breast, in order to measure breast density.
Publications
A Monte Carlo model was developed to simulate the response of a pixelated hyperspectral CdZnTe (CZT) X-ray detector. The first part of the simulation was carried out using Geant4 to obtain a list of energy depositions inside the CZT crystal. The second part of the simulation used charge transport equations to calculate the size of the electron charge cloud, as it drifts under the influence of an electric field to be read out. Experimentally acquired data from an Am-241 source with the high energy X-ray imaging technology (HEXITEC) detector were compared to simulated data, and good agreement was found. The model was used to investigate the energy dependence of fluorescence and charge-sharing effects. The probability of producing an escaped fluorescence photon was quantified as a function of primary photon energy. As expected, at primary photon energies just above the K-edge of Cd, there was a greater chance of producing an escaped fluorescence photon, and this probability decreased as the primary photon energy increased. The probability of an event being shared across multiple pixels as a function of primary photon energy was quantified. It was found that as the primary photon energy was increased, there was a greater chance of producing an event shared across multiple pixels. The detector response to a Bremsstrahlung spectrum was simulated. Using previous results, fluorescence and charge-sharing effects were corrected for, giving a corrected spectrum in good agreement with the input spectrum.
A Monte-Carlo model was developed to simulate the response of a pixelated hyperspectral CZT X-ray detector. The first part of the simulation was carried out using Geant4, to obtain a list of energy depositions inside the CZT crystal. The second part of the simulation used charge transport equations to calculate the size of the electron charge cloud, as it drifts under the electric field to be read out. Experimentally acquired data from an Am-241 source with the HEXITEC detector were compared to simulated data, and good agreement was found. The model was used to investigate the energy dependence of fluorescence and charge sharing effects. Firstly, the probability of producing an escaped fluorescence photon was quantified as a function of primary photon energy. As expected, at primary photon energies just above the K-edge of Cd, there is a greater chance of producing an escaped fluorescence photon, and this probability decreases as the primary photon energy increases. Secondly, the probability of an event being shared across multiple pixels as a function of primary photon energy was quantified. It was found that as the primary photon energy is increased, there is a greater chance of producing an event shared across multiple pixels. The detector response to a Bremsstrahlung spectrum was simulated. Using previous results, fluorescence and charge sharing effects were corrected for, giving a corrected spectrum in good agreement with the input spectrum.