A new technology for medical imaging: Silicon Drift Detectors
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چکیده
Introduction Although breast cancer awareness was raised over the last two decades and breast cancer funding has risen strongly, the United States has one of the highest breast cancer rates in the world. Each year 180,000 women are diagnosed and 44,000 women will die of breast cancer. The even more alarming statistic is that about fifty years ago the probability for a woman to be diagnosed with breast cancer during her lifetime was one in fifty (0.2%), whereas today the probability is an alarming one in eight (12.5%). The situation is particularly critical for younger women because the cancer develops faster in younger tissue. The five-year survival rate for localized breast cancer (malignance size less than 15 mm) is over 95% after treatment, whereas the five year survival rate drops to less than 20% for metastatic cancer after treatment. The key is early detection when the malignancies are still sufficiently localized. Presently around 85% of all localized malignancies are detectable with x-ray mammography, and an optimized digital mammography device will be able to further reduce the minimum detectable malignance size. The use of digital radiographic equipment in the medical imaging field is becoming more and more relevant, simply because a digital device allows a lower and shorter exposure phase at similar or even superior resolutions than traditional film/screen devices. It also enables the physician to process and analyze the recorded digital information in a more efficient and computer guided way. Another strong advantage of digital mammography is that the achievable position resolutions (< 20 micron) allow us to measure microcalcifications very effectively. These small deposits of Calcium are the only indication of tumor formation in a large fraction of all cases. The deposits generally do not exceed a spread of more than 1 mm and thus a spatial resolution of better than 50 micron is required for good detection. The main concern of a widespread application of x-ray mammography is the radiation dose that each patient receives per image. A preliminary study in Europe indicates that x-ray mammography is an effective prevention tool for women of age 50 and older, whereas in younger women the effect of the radiation (potential cell mutations) offsets the benefits of early detection. This cutoff age is obviously directly linked to the actual radiation dose per screening, which was set to 20 mGy/image for women of age 50 and older. In young women the breast tissue is generally denser which reduces the contrast to cancerous tissue and thus a successful mammography session requires higher exposure rates. One of the potential advantages of digital mammography over conventional x-ray mammography is the lower dose requirement.
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