What does the term "US" refer to in diagnostic procedures?

In the context of diagnostic procedures, the term "US" refers to ultrasound. Ultrasound is a non-invasive imaging technique that uses high-frequency sound waves to create images of structures within the body. It is commonly used in various medical applications, such as assessing the health of a fetus during pregnancy, examining the heart, and diagnosing conditions affecting organs like the liver, kidneys, and gallbladder. The technique is favored for its safety and effectiveness, as it does not involve ionizing radiation, differentiating it from other imaging modalities like X-rays or CT scans.

The other options do not align with the established medical terminology for diagnostic procedures. For instance, "Upper Shelf" and "Universal System" lack recognition in the context of medical diagnostics, while "Unilateral Supination" pertains to a movement or position related to joints and anatomy rather than a diagnostic imaging technique. This reinforces that "US" as ultrasound is the most appropriate interpretation in medical terminology.