What portion of the breast is excluded during the MLO projection?

In the MLO (mediolateral oblique) projection, the medial portion of the breast is typically excluded in the visualization. This projection is designed to optimize the imaging of the upper outer quadrant of the breast, which is a common area for the detection of abnormalities, including breast cancer. By angling the x-ray beam at a 30 to 60-degree angle from vertical, the MLO projection captures a larger portion of the breast tissue while excluding the medial section.

This exclusion occurs because the angle of the beam allows for better visualization of the outer quadrants, and the positioning effectively pushes the medial portion of the breast away from the imaging plane. Consequently, the medial area is not well-represented in the resulting mammogram, focusing instead on areas that are clinically significant for screening and diagnosis. Understanding this anatomical exclusion helps radiologists interpret mammograms accurately and recognize the limitations of the imaging technique.