Medical ultrasound scanners use high-energy pulses to probe the human body.
It can be shown that the radiation force resulting from the impact of such
pulses to the object can vibrate the object, producing a localized
high-intensity noise in the audible range. When the scanner is used in a
maternal examination, and the beam is directed toward the fetal head, this noise
can disturb the fetus and cause it to move vigorously [J. Ultrasound Med. 20,
883--889 (2001)]. Here, a theoretical model for the audio noise generated by
ultrasound scanners is presented. This model describes the temporal and spectral
characteristics of the noise. It has been shown that the noise has rich
frequency components at the pulse repetition frequency and its harmonics.
Experiments have been conducted in a water tank to measure the noise generated
by a clinical ultrasound scanner. Results indicate that the noise pressure level
at the focal point of the ultrasound beam on a reflective object can reach up to
120 dB relative to 20