The acoustic variable distance is measured in units of?

• A. cm or mm
• B. m
• C. km
• D. in

Answer: (A)

Distances in an acoustic field inside the body fall on the centimeter to millimeter scale. In medical ultrasound, the depths encountered are typically a few centimeters, so depth measurements and imaging grids are given in centimeters (often with millimeter precision). Using meters would be unnecessarily large for tissue depths, and kilometers are far outside any anatomical context. Inches aren’t the standard units in clinical imaging either, since the metric system is the norm for ultrasound equipment and documentation. So the distance variable is expressed in centimeters or millimeters, making cm/mm the best fit.