Mass Segmentation Using Two or More Images

The comparison of different mammographic images of the same woman is a commonly used practice in breast radiology. Usually, this comparison is between:

• Left and right mammograms.
• Two mammographic views (CC and MLO) of the same breast.
• Same view mammograms taken at different times.

This practice is justified from a clinical point of view by many studies. Kopans, for example, makes two important observations when comparing different mammograms of the same woman [94]:

• Though one breast may be larger than the other, internal structures are quite symmetric over broad areas.
• Overlapping tissue structures that form summation shadows and normal tissue variations on the mammogram highlight unimportant asymmetries.

In order to distinguish masses and asymmetric breast tissue, clinicians take a range of characteristics of abnormal areas, such as size, density, and shape into account.

The following subsections provide a more detailed description of the various approaches to mass segmentation from multiple mammographic images.