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Breast cancer is the most frequently diagnosed cancer in women, with an estimated number of 226,870 new cases of invasive breast cancer occurring among women in the US during 2012. In addition, breast cancer also ranks second as a cause of cancer death in women (after lung cancer). Thus, even modest improvements in breast cancer screening, diagnosis, and therapy monitoring can have a significant impact in improving women’s health. Accurate detection and characterization of breast tumors is required for breast cancer screening and diagnosis, whereas therapy monitoring provides valuable information about cancer treatment efficacy. X-ray mammography, a common breast cancer screening technique, has high false negative rates in women under fifty and also uses harmful ionizing x-ray radiation. Techniques such as ultrasound and MRI are sometimes employed in addition to x-ray mammography but have limitations such as high cost, low throughput, limited specificity (MRI) and low sensitivity (ultrasound). Thus, new methods are required to detect earlier stages of cancers and cancers missed by mammography, and to monitor tumor growth during cancer therapy. Diffuse optical imaging (DOI) is an emerging noninvasive medical imaging modality that is especially suitable for breast imaging. It can be divided into several categories, namely diffuse correlation spectroscopy (DCS), diffuse optical spectroscopy (DOS), and diffuse optical tomography (DOT). In terms of spectroscopic techniques, DCS is typically used to measure relative blood flow in deep tissues, whereas DOS can provide information about absorption and scattering properties within tissues. On the other hand, DOT makes use of optical transmission measurements on the sample surface to reconstruct 3D maps of optical properties within the sample, namely the absorption and scattering coefficients. In addition, low tissue absorption in the 650- to 900- nm wavelength range allows us to convert optical property maps into concentration maps of intrinsic chromophores, such as oxy- (HbO2) and deoxy-haemoglobin (Hb), water and lipid, and extrinsic agents such as fluorescent dyes. 3D maps of the parameters mentioned above can aid in tumor detection and characterization. For instance, tumor position has been shown to be strongly correlated with total haemoglobin concentration via angiogenesis. This is especially valuable in breast cancer imaging, since the breast is a relatively homogeneous tissue. Thus, DOI provides physiological information directly related to tumor oxygenation and vasculature, while utilizing cost-effective, nonionizing, rapid, portable and noninvasive instrumentation at the same time.
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