Semester of Graduation
Master of Science (MS)
Physics and Astronomy
Purpose: Modulated Phase Grating (MPG) interferometry has been shown in theory and simulations to produce observable fringes on a clinical detector without requiring fluence absorbing analyzer. In this work, we will experimentally show that the MPG X-ray system produces observable fringes and multi-modal X-ray images.
Motivation:Nearly 1 in 8 women in the US will develop invasive breast cancer in their lifetime, accounting for approximately 40,000 deaths each year [1-2]. In order to pursue the best treatment option available, cancer itself must be adequately imaged and staged, based on size and level of metastasis, on the order of Stage I-IV. Currently, the most used imaging modality for breast cancer screening is mammography. Along with the traditional x-ray absorption images from mammography, the effects created from scattered x-rays at small angles (SAXS) can be utilized in the creation of multiple modalities generated from the same scan. Incorporating phase-shift and SAXS images in addition to the traditional attenuation images allow for an overall increase in contrast and the better detection of micro-calcifications, a risk factor for breast cancer. The advantage of MPG over prevalent Talbot Lau interferometry system is that MPG does not require fluence absorbing analyzer and therefore dose to patient can be maintained similar to conventional X-ray. Thus, MPG can be used for breast cancer screening mammography.
Methods: Experiments were performed with 8 keV test MPG gratings as well as two 25 keV MPG gratings, all manufactured by Microworks, GmbH. At LSU’s CAMD, the 8keV beamline was used to test the preliminary8 keV grating. We implemented both a deconvolution and linear optimization estimation method to remove the G0 grating effects seen in the detected fringe patterns. Experiments at Pacific Northwest National Lab (PNNL) were done using 25 keV design energy gratings placed in a X-ray tomography machine to test various constraints and limits of the proposed MPG system, leading us to the Pennington Biomedical Research Center (PBRC, LSU) experiments. Here, the Keck x-ray tomography machine (at PBRC) was used to measure the visibility at various set-up distances and imaged various samples (anchovy, chicken bone, seeds).
Results: For the CAMD experiments, we successfully removed the G0 effects to get similar results from the deconvolution and linear optimization methods. The PNNL experiments showed the limit of larger detector pixel size for MPG system set-up. The PBRC experiments showed that we were again able to view fringe patterns of MPG, calculate visibility and also see attenuation and small angle X-ray scattering images of samples.
Conclusion: The CAMD experiments yielded recovered fringe patterns with period lengths of 208𝜇𝑚 − 264𝜇𝑚, roughly twice the period of the MPG used. At the PBRC, the visibility calculations illustrated that the farther the MPG is from the detector, the more the visibility increased. We obtained attenuation, differential phase and small angle x-ray scattering images of samples. The triangular MPG also yielded better results than the rectangular MPG used.
Carr, Sydney B., "Experiments and Data Analysis for Modulated Phase Gratings in X-rays" (2023). LSU Master's Theses. 5796.