Axial resolution is measured in?

• A. mm
• B. cm
• C. units of distance
• D. seconds

Answer: (A)

Axial resolution is the smallest separation along the direction of the ultrasound beam that can be distinguished as two separate reflectors. It is a distance measurement, not a time measurement, so the appropriate units are units of length. In clinical practice, this detail is expressed in millimeters because the level of detail is typically fractions of a centimeter. Shorter spatial pulse lengths—achieved with higher-frequency transducers or broader bandwidths—improve axial resolution, further explaining why millimeters is the standard unit used to describe it. Seconds would be inappropriate since they measure time, and while centimeters are a distance unit, they are less precise for typical axial-detail values, making millimeters the best fit.