Fat subtraction protocol for wide-angle x-ray scatter analysis of breast biopsies

Abstract

Breast cancer detection often involves the use of mammography to locate sus- picious lesions followed by extraction of some tissue within the lesion via a biopsy procedure. The gold standard method for determining whether the extracted tis- sue is malignant or benign is an histological analysis. However, complimentary x ray methods such as x-ray uorescence (XRF), small-angle x-ray scatter (SAXS) and wide-angle x-ray scatter (WAXS) have been investigated by various groups. The focus of this dissertation was to develop a WAXS fat subtraction protocol for the WAXS analysis of breast tissue biopsies. The WAXS signals of breast tissue could become an additional source of diagnostic information. Healthy breast tissue is composed of fat and broglandular ( brous) tissue. Com- parisons of the WAXS signals of broglandular and cancerous tissue are di cult be- cause biopsies of either type usually contain some fat tissue. The ability to look at WAXS signals independent of the fat contribution could be informative. The goal of this work was to validate a WAXS fat subtraction protocol using an animal tis- sue sample consisting of a mixture of fat and brous tissue. The di erential linear scattering coe cient d s=d of a region of interest (ROI) within the sample was measured via energy dispersive x-ray di raction measurements using a custom built CdTe di ractometer. The mean fractional volume of fat ( fat) within the ROI was estimated using a digital x ray imaging system. The transfer of the sample from the iii WAXS system to the digital system required accurate knowledge of the ROI. The use of fat in a WAXS fat subtraction model then allowed the d s=d of brous tissue to be estimated. The signals obtained via the subtraction protocol agreed well with the signals obtained using pure tissue samples. The scattering coe cient d s=d is a function of the momentum transfer argu- ment x = 1= sin( =2), a variable that combines the dependence of scatter on photon and scatter angle . Accessing a larger x space could provide more information about the nature of breast tissue. Modi cations to the custom built di ractometer were implemented in order to access a larger x space. Speci cally, the capability to measure signals at smaller and the use of higher kV beams were the outcomes. Pre- liminary results obtained with water, polymethyl methacrylate, and polycarbonate samples were promising, yet suggested that better collimation is required between the sample and the detector in order to reduce scatter contamination from objects located downstream from the sample.