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Title: Hyperspectral X-ray imaging : a comparison of iodinated and gold nanoparticle contrast media for the application of contrast-enhanced digital mammography
Author: March, Louise M.
ISNI:       0000 0004 7972 3286
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2019
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Dual energy imaging (DE) is a potential alternative breast imaging modality for patients with dense breasts. It utilises intravenous injection of contrast agent (CA) to highlight structures of interest, such as tumours. Following CA administration, images are acquired at two different energies, such that the change in attenuation of the CA across the energy range differs significantly from that of the background material, such as across its K-edge. Implementation of DE on a conventional detector requires two separate exposures, leading to a higher dose and possible patient movement between exposures, which can lead to incomplete background removal. The novelty of this work is the implementation of the DE algorithms using a hyperspectral energy-sensitive detector, HEXITEC, which gives a whole spectrum per pixel. This allows multiple energy images to be obtained simultaneously by integrating appropriate bands of the spectra acquired by each individual pixel, thereby providing a single-shot approach to DE. The ability to access a whole array of possible image combinations from a single exposure provides a powerful tool in determining the optimum beam parameters and energy ranges to produce the DE images. Two different contrast agents were compared: a clinical iodinated contrast agent and gold nanoparticles (AnNPs), which have the potential to be preferentially absorbed by tumours through targeting and functionalisation. Imaging performance was assessed for both contrast agents via reconstructed concentration calculations and CNR. The cell toxicity of each CA was also investigated using clonogenic assays to generate a cell survival curve following exposure to CA and radiation between 0-5 Gy. Both iodine and AuNPs showed good agreement with nominal values in terms of reconstructed concentration for a range of nominal concentrations (the reconstructed concentration of 200 mg/ml CA was 189 ±10 and 216 ±8 mg/ml for AuNPs and iodine respectively). Iodine outperformed AuNPs in terms of CNR. Toxicity results indicated a statistically significant decrease at the 68% confidence level in the alpha parameter of the linear quadratic dose curve with the addition of AuNPs but not with the addition of iodine, suggesting an increased toxicity with AuNPs (alpha values were found to be 0.46±1, 0.40 ±1 and 0.19±1/Gy⁻¹ for no CA, iodine and AuNPs respectively). Iodine outperformed AuNPs overall, but further work is required (including optimisation of the energy spectra) to allow the full potential of AuNPs to be determined.
Supervisor: Pani, Silvia Sponsor: Engineering and Physical Sciences Research Council (EPSRC) ; National Physical Laboratory
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral