Mammography

Medical imaging in general, and mammography in particular, lets physicians evaluate a specific area of the body of a patient which might be externally visible. In fact, the New England Journal of Medicine [45] regards medical imaging as one of the most important medical developments of the past thousand years, basically due to the fact that it provides physicians with physiology and functionality of organs and cells inside human bodies.

Among the different imaging modalities used for breast cancer detection, mammography remains the key screening tool for the detection of breast abnormalities. In a recent study, Vacek et al. [182] show that the proportion of breast tumours that were detected in Vermont (US) by screening mammography increased from $2\%$ during $1974-1984$ to $36\%$ during $1995-1999$ . However, it is also well known that expert radiologists can miss a significant portion of abnormalities [12,13]. In addition, a large number of mammographic abnormalities turn out to be benign after biopsy [5,63].

Mammograms capture the low energy X-rays which passes through a compressed breast. Depending on the viewpoint of the X-rays, the images are classified into different categories. Figure  shows the two most used viewpoints for extracting mammograms: the Medio-Lateral Oblique view (MLO) and the Cranio-Caudal view (CC). Figure (a) shows physically the viewpoints' directions, while Figures (b) and (c) show an example of each mammogram view. It is important to notice that in the MLO views there is one region corresponding to a portion of the pectoral muscle which may be present in the left or the right upper corner of the image. Moreover, some annotations and labels can appear in the images. For instance, the R symbol which appears in Figure  is used to mark the mammogram as right breast.

Figure 1.1: In mammography there are different viewpoints of the same breast: (a) shows the direction of the two most used views, which produce images like (b) the Cranio-Caudal view, and (c) the Medio-Lateral Oblique view. Note the presence of the pectoral muscle in the upper right corner of image (c).

(a)	(b)	(c)