The 123 annotation method refers to measuring distance from which reference line?

• A. Nipple projection line
• B. Chest wall
• C. Midline
• D. Inferior breast fold

Answer: (A)

Localization of a breast lesion on ultrasound relies on a stable reference line to describe where the lesion sits. In the 123 annotation method, the reference line used is the nipple projection line—the line projected from the nipple across the skin surface. Measuring distances from this line provides a reproducible way to describe the lesion’s position within the breast, which is helpful for follow-up and surgical planning. Other lines like the chest wall, midline, or inferior breast fold are not the reference in this method because they’re less consistent across imaging sessions or less standardized for this particular annotation system. So the distance is measured from the nipple projection line.