Introduction to Mammography: The Basics

How Is a Mammogram Performed?

Standard Views

The routine mammogram consists of two complementary standard views for each breast: the craniocaudal (CC) view and the mediolateral oblique (MLO) view ( Table 1.1 ). Based on standard mammographic terminology, each projection describes the direction of the x-ray beam. The first letter in the projection refers to the location of the x-ray source and the second refers to the location of the image receptor. For example, in the CC view the x-ray beam travels superior to inferior, from the cranial to caudal direction.

When performing the CC view, the patient faces toward the mammography unit, and the image receptor is placed inferior to the breast. The inferior breast is relatively mobile and allows the inframammary fold to be elevated when the technologist lifts and pulls the breast forward onto the positioning platform. This maneuver allows greater visualization of the posterior and superior breast tissue. The breast is then compressed in the axial plane, perpendicular to the x-ray beam ( Fig. 1.1 ). The CC view includes most of the breast tissue except for the far lateral and far posterior breast.

In the MLO projection, the x-ray beam travels from superomedial to inferolateral. The breast compression plane is along the angulation of underlying pectoralis major muscle, usually at 45 degrees ( Fig. 1.2 ). However, angulation of the compression plane varies with patient anatomy and may range from 40 to 60 degrees; thinner body habitus may need a slightly steeper obliquity, and shorter or heavier body habitus may need a slightly flatter obliquity. The course of the pectoralis muscle can be approximated by drawing an imaginary line between the ipsilateral shoulder to the mid sternum. When properly positioned, the MLO view includes nearly the entire breast including the axillary tail.

These two standard views are complementary. The MLO view visualizes the most amount of breast tissue. It is the best for viewing the posterior, upper-outer quadrant, axillary tail, and lower-inner quadrant of the breast. However, there may be considerable breast tissue overlap, often with limited compression of the more anterior structures. Also, the far superior-medial breast tissue (upper-inner quadrant) may sometimes be excluded from the MLO view. The CC view allows for better visualization of the medial and posteromedial tissue, as well as better compression of the subareolar and central breast.

Standardized Labeling

Standardized image labeling is important for consistency, allowing mammograms to be accurately identified and interpreted even outside of the performing institution. According to the Mammography Quality Standards Act (MQSA), the patient identification label is required to include the patient’s name, unique identification number and/or date of birth, facility name and location, examination date, technologist’s initials, cassette (screen) number for screen-film and computed radiography images, and mammographic unit identification (if there is more than one unit in the facility) ( Box 1.2 ). The view and laterality label should be placed near the axilla on all mammograms. The laterality should be listed first, followed by technique (e.g., magnification, implant displacement) and projection (e.g., CC).

What Is Acceptable Quality?

Before interpreting a mammogram, it is important to first assess whether the mammogram is technically adequate ( Box 1.3 ). Suboptimal image quality compromises mammographic evaluation and may lead to missed cancers.