Final answer:
The pectoralis major muscle must be included in mammography images as an important anatomical landmark to ensure proper breast tissue positioning and to provide a consistent reference point for image comparison.
Step-by-step explanation:
In mammography, the muscle that must be included in the images is the pectoralis major. This thick, fan-shaped axial muscle covers much of the superior portion of the anterior thorax. Ensuring that the pectoralis major is visible in mammogram images is important because this muscle serves as a key anatomical landmark and helps in assessing the proper positioning of the breast tissue during the imaging process. It also provides a consistent reference point for comparing images over time for the detection of any changes. Other muscles, such as the serratus anterior, latissimus dorsi, and subscapularis, are also important for the movement and stability of the shoulder girdle but are not the primary focus in mammography images.