Feature analysis methods for intelligent breast imaging parameter optimisation using CMOS active pixel sensors

This thesis explores the concept of real time imaging parameter optimisation in digital mammography using statistical information extracted from the breast during a scan. Transmission and Energy dispersive x-ray diffraction (EDXRD) imaging were the two very different imaging modalities investigated. An attempt to determine if either could be used in a real time imaging system enabling differentiation between healthy and suspicious tissue regions was made. This would consequently enable local regions (potentially cancerous regions) within the breast to be imaged using optimised imaging parameters. The performance of possible statistical feature functions that could be used as information extraction tools were investigated using low exposure breast tissue images. The images were divided into eight regions of interest, seven regions corresponding to suspicious tissue regions marked by a radiologist, where the final region was obtained from a location in the breast consisting solely of healthy tissue. Results obtained from this investigation showed that a minimum of 82% of the suspicious tissue regions were highlighted in all images, whilst the total exposure incident on the sample was reduced in all instances. Three out of the seven (42%) intelligent images resulted in an increased contrast to noise ratio (CNR) compared to the conventionally produced transmission images. Three intelligent images were of similar diagnostic quality to their conventional counter parts whilst one was considerably lower. EDXRD measurements were made on breast tissue samples containing potentially cancerous tissue regions. As the technique is known to be able to distinguish between breast tissue types, diffraction signals were used to produce images corresponding to three suspicious tissue regions consequently enabling pixel intensities within the images to be analysed. A minimum of approximately 70% of the suspicious tissue regions were highlighted in each image, with at least 50% of each image remaining unsuspicious, hence was imaged with a reduced incident exposure

Towards combined x-ray and optical mammography

Optical contrast, dependent upon haemodynamics and thus providing physiological information, is complementary to radiographic contrast. Combined x-ray and optical mammography screening could provide increased specificity over either system alone. Medical imaging equipment is routinely characterised and tested using tissue equivalent phantoms. A novel phantom material is presented: a solution of polyvinyl alcohol in ethanol and water freeze-thawed to produce a solid yet elastically compressible gel. The x-ray attenuation, mechanical and optical properties of these gels can be accurately adjusted over appropriate ranges so as to mimic cancerous or healthy breast tissues. Modulated imaging in both optical and x-ray acquisitions is also considered. An x-ray system capable of optimising dose distribution has previously been developed at UCL. Overall images are obtained by aligning multiple images from smaller sensors. The effects that this type of acquisition has on spatial resolution are discussed. Two considerations are made: (i) is there a minimum size sensor whose modulation transfer function (MTF) can accurately be determined? (ii) does the MTF of an overall image differ significantly from those of its constituent images? The smaller a sensor becomes, the harder it is to determine its MTF accurately, and the resolution of overall images is slightly poorer than those of individual sensor images. Nonetheless these effects are small and should not hinder the development of such systems. Whilst similar dose considerations do not apply to optical tomography, modulated imaging still presents potential benefits. A method of visualising intensity data in order to localise regions of heterogenous absorption is presented using both simulated and experimental data. Objective functions designed to quantify the visibility of these heterogeneities are proposed and it is shown that optimal distributions of source power, that maximise these, can be found. It is proposed that such techniques might allow optical acquisitions to be performed more rapidly

Fabrication And Characterization Of Microcalcification Breast Phantom For Image Quality Analysis

This study aims to improve the early diagnosis of breast cancer through the application of image processing techniques based on the MATLAB algorithms to enhance the visibility of microcalcifications (MCs) in Full Field Digital Mammography (FFDM). Various polyvinyl alcohol (PVAL) composites phantoms were produced through freezing and thawing method to mimic the physical and radiological properties of different categories of breast tissue in line with the BIRADS classification. The density, elemental composition, effective atomic number (Zeff), electron density (ꝭeff), mass attenuation coefficients of the PVAL-based phantoms and MC features (CaCO3/graphite) were determined. The microstructure and CT number of the PVAL were also studied. The 50/50 water/ethanol-based 10 wt% PVAL (E50), the water-based 10 wt% PVAL (P10), 10 wt% PVAL mixed with 4% graphite powder (G4), and the heterogeneous phantom (H) had physical and radiological properties suitable to mimic BIRADS B, C, D, and a heterogeneous breast tissue respectively. Phantom E50, P10, G4, and H recorded densities of 0.952 ± 0.011 g/cm3, 1.056 ± 0.002 g/cm3, 1.081 ± 0.002 g/cm3, and 1.025 ± 0.006 g/cm3 respectively, their Zeff and ꝭeff ranged from 7.148 to 7.418 and 3.189 X 1023/cm3 to 3.209 X 1023/cm3 respectively