In ultrasound, the following events happen:
- The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe.
- The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone).
- Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected.
- The reflected waves are picked up by the probe and relayed to the machine.
- The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second).
- The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.
In a typical ultrasound, millions of pulses and echoes are sent and received each second. The probe can be moved along the surface of the body and angled to obtain various views.