What unit is used to measure wavelength in ultrasound?

The unit used to measure wavelength in ultrasound is typically expressed in millimeters. Wavelength is defined as the distance between successive peaks of a wave, and in the context of ultrasound, it refers to the spatial period of the ultrasound wave traveling through a medium. Given that ultrasound frequencies are commonly in the range of megahertz (MHz), which correspond to wavelengths in the millimeter range, using millimeters allows for a more practical representation of the dimensions involved in the propagation of ultrasound waves.

While centimeters, micrometers, and inches are also units of measurement that could theoretically be used for wavelengths, millimeters are most appropriate in the context of medical ultrasound where the wavelengths are generally small (on the order of millimeters). This makes them more convenient and relevant for the scales typically encountered in clinical settings.