| Περίληψη: | The current thesis is focused on breast implants and their imaging with the use of x-rays. During the last years the number of breast augmentations with silicone implants is increasing, especially in America. More and more women want to have breast implants either for esthetic reasons or for physiological reasons after mastectomy. On the other hand, several characteristics of silicone gel implants and the techniques of their placement affect the x-ray based imaging of the breast. In addition, the presence of silicone gel-filled implants interferes with standard mammography, since silicone is a radiopaque material.
The aim of this research is to explore the effects of silicone gel implant insertion in breasts and how the thickness of an implant as well as the incident beam energy interfere with the detectability of high and low contrast lesions. This study also aims in the investigation of non-conventional imaging techniques in case of augmented breasts in order to improve the detectability of lesions and the quality of breast images.
For the purpose of this study a wide number of software phantoms with homogeneous and heterogeneous texture were constructed for simulation studies with the use of the XRayImagingSimulator. A breast hardware phantom consisting of materials mimicking breast lesions was also constructed and used at the ELETTRA synchrotron facilities in Trieste, Italy for experiments performed with synchrotron radiation. Mammography and breast tomosynthesis were investigated as conventional breast imaging modalities in the incident beam energy range 20 KeV to 30 keV. Moreover, alternative imaging modalities like Dual Energy subtraction mammography, Dual Energy subtraction breast tomosynthesis, tomosynthesis with a discontinuous acquisition arc and In-Line phase contrast imaging were studied as potential modalities for augmented breast imaging.
This study established upper silicone gel thickness limits in the conventional beam energy range for both mammography and tomosynthesis above which microcalcifications could not be detected. Comparisons between tomosynthetic and mammographic images showed that the latter have superior CNR values compared to those calculated for tomosynthesis. Alterations of energy in the interval of 20 keV to 30 keV led to improved detectability of microcalcifications overlapped by silicone, while the opposite stands for breast masses. Although tomosynthesis resulted in inferior image quality in terms of CNR, it demonstrated an advantage in visualizing a larger breast area and small low contrast lesions because of non-overlaps. Moreover it was shown that DE mammography improves the detectability of high contrast features overlapping with high silicone gel thicknesses but gives marginal CNR values. Dual Energy breast tomosynthesis resulted in a superior image quality compared with the rest of the imaging modalities studied, when the visualization of both high and low contrast lesions in the neighborhood of silicone is needed. Breast tomosynthesis with an alternative acquisition arc succeeded to visualize microcalcifications under high thicknesses of silicone gel with sufficiently high CNR. This indicates that tomosynthesis with an appropriate acquisition arc might resolve the lack of contrast appearing in breast images with silicone gel insertion. Finally, simulations as well as experimental studies showed that phase contrast imaging improves the image quality resulting in higher CNR values and in a strong edge enhancement of features, which may be useful in augmented breasts imaging.
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