X-Ray Diffraction Imaging for Breast Tissue Characterization

dc.contributor.advisor

Kapadia, Anuj J

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Xiao, Jeffery

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2020-06-09T17:45:34Z

dc.date.available

2020-06-09T17:45:34Z

dc.date.issued

2020

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Medical Physics

dc.description.abstract

Although mammography is the gold standard for early screening for breast cancer, there is a need in improving its specificity. X-ray diffraction (XRD) has shown the ability to detect cancer based on its molecular properties; however, most commercial XRD systems focus on very thin targets using very low x-ray energies. To improve the imaging capabilities for thicker targets, we have developed XRD imaging systems capable of running at diagnostic X-ray energies. In this work, we evaluate the performance of our XRD system at two source configurations: 20 keV (mammography) and 60 keV (radiography), to understand and quantify the trade-off of between higher Rayleigh scatter cross section versus reduced penetration depth.

An XRD system was built using a Bremsstrahlung X-ray source, an energy discriminating X-ray detector, and customizable geometry. XRD scans were performed using adipose, fibroglandular, and carcinoma surrogate targets at two mean energies – 20 keV and 60 keV. The 20 keV configuration used a molybdenum filter and 2-mm collimated beam, whereas the 60 keV configuration used a tungsten filter with 1-mm diameter X-ray beam. Each target was scanned 5-10 times to evaluate measurement uncertainty. XRD spectra, normalized to mAs, were extracted from the detected signal and compared against known diffraction data for each material. System performance was evaluated using signal-to-noise ratio (SNR), average-percent-difference (APD) and uncertainty in each measurement.

An analytical calculation was done to test the effects of attenuation on the 20 keV and 60 keV configurations using elastic scatter coefficients and total attenuation coefficients excluding elastic scatter for each energy for breast tissue. Using the mean-free-path and the calculated exponential attenuation, an estimate of the surviving fraction of x-rays that undergo Rayleigh scatter was calculated.

The 20 keV configuration showed 8.25 SNR, 95.96% accuracy, and 1.46% uncertainty. The 60 keV configuration showed 7.05 SNR, 94.72% accuracy, and 0.96% uncertainty. Overall, the 20 keV configuration showed 13.21% improvement in SNR compared to the 60 keV configuration. The analytical estimation of the surviving fraction of x-rays having undergone Rayleigh scatter showed that at the average compressed breast thickness of 4.4 cm – 4.8 cm, the 20 keV system performed on par with the 60 keV system while the surviving fraction of Compton scatter, which is detrimental for XRD analysis, has decreased with energy. Calculating the ratio of the surviving fraction of Rayleigh scattered x-rays to Compton scattered x-rays to estimate the SNR with depth, 20 keV x-rays showed a consistent advantage. Through this, we demonstrated the viability of low-energy XRD imaging for characterizing breast tissues. The 20 keV configuration presents a viable method to characterize breast tissues at energies relevant to mammography, representing a potential method to improve specificity in mammography.

dc.identifier.uri

https://hdl.handle.net/10161/20798

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Physics

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X-ray Diffraction

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X-Ray Diffraction Imaging for Breast Tissue Characterization

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Master's thesis

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