Kidane, Ghirmay; (2001) Breast tissue characterisation using low angle X-ray scattering. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis presents the application of a Low-angle x-ray scattering system based on an energy dispersive technique to the characterisation of breast tissues. Low angle scatter of x-rays at diagnostic energies is predominantly coherent. This coherence gives rise to interference effects resulting in x-ray diffraction patterns that are characteristic of the scattering material. The shapes of scattering distributions for low atomic number media such as breast tissues exhibit one or more intense peaks close to the transmission direction. The position and the shapes of the peaks depend upon the interatomic and intermolecular configurations of the soft tissues. The measurements of the scattering properties of breast tissues, some animal tissues, and tissue substitute materials have been carried out using an energy dispersive x-ray diffraction system over the momentum transfer range of 0.70 to 3.50 nm-1. One hundred and twenty one samples of excised female breast tissues, eight animal tissues, and test objects such as perspex, polyethylene and water have been used. Results from the diffraction system have been compared with those from histological analysis for all human tissues. It has been found that tissue types can be characterised on the basis of shape of the scatter spectrum and on its relative intensity. The shapes are significantly different between tissue types in the range from 1.0 per nm to 1.8 per nm-1. This suggested that differences in the distribution of coherently scattered photons in breast tissues would allow better discriminating signals in breast imaging if particular values of momentum transfer are monitored. A new technique is described which produces images based on selective momentum transfer region. The system uses a mammographic x-ray tube to acquire diffraction data at scatter angle of ~90. Images are reconstructed from the diffraction data, which represent the coherent-scatter intensity in the momentum transfer space around 1.1 nm-1. At this momentum transfer value the coherent-scatter intensity ratio of diseased tissue to healthy tissue was minimised. This system permits the x-ray diffraction properties of small inclusions embedded in large tissue sizes to be measured in-vitro. In this study images obtained by transmission methods and by coherent scattering technique have been recorded for several inclusions in blocks of human breast tissues and animal tissues. Smaller inclusions that are less distinguishable with transmission images have been clearly identified with the diffraction technique.

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