8.1 Introduction

The most frequently occurring malignancy in women is breast cancer, and its mortality rate is high. Predictions of new cases from the United States National Cancer Institute continue to rise. There are many breast imaging systems available on the market to facilitate the diagnosis of breast cancer. Some of them are used for screening, some for diagnosis, and most others are used for adjunctive evaluation. The most commonly used diagnostic modalities for breast cancer detection are mammography, ultrasound, and clinical breast examination (CBE). Mammography is currently the most widely used technique due to its effectiveness in detecting microcalcifications; however, in spite of its current popularity, mammography has its own limitations. In a study conducted by Carney et al., mammography recorded a sensitivity of 87% and specificity of 96.9% for women with fatty breasts. However, for younger women with extremely dense breasts, the sensitivity of mammography was only 62.9%, and the specificity was 89.1%. This indicates that mammographic sensitivity increases with age and decreases with breast density. Other limitations of mammography include risks of increased radiation exposure, possible inter-observer variability, and patient discomfort due to breast compression.

Though there are a number of other methods used for breast cancer detection in addition mammography, they also have their own limitations. By the time CBE detects a cancer, the disease is usually at an advanced stage. Breast ultrasound is frequently used to evaluate breast abnormalities that are found with screening or diagnostic mammography or CBE. In spite of ultrasound being less expensive, more comfortable for the patient, and radiation-free, it is not as efficient in imaging microcalcifications as mammography. Microcalcifications are often the first indication of breast cancer. Breast MRI is also radiation-free and has been found to be more sensitive than other modalities in detecting breast cancer in young women. However, it is more expensive, does not detect microcalcifications well, and is not suitable for evaluating patients with implants or metallic pieces embedded in their bodies. Computed tomography (CT) can effectively locate an abnormal mass but is not efficient in differentiating benign from malignant masses, or scar tissue from cancerous tissue. Positron emission tomography (PET) is effective in detecting metabolically active large tumors but is not capable of picking up microscopic metastatic foci, and is more expensive and time consuming. Other modalities include optical mammography, electrical impedance tomography, electrical impedance scanning, and thermography. These techniques have their own drawbacks as well.