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Why do ultrasonic waves reflect at boundaries between different body tissues?

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Ultrasonic waves reflect at the boundaries between different body tissues because of changes in tissue density. As these high-frequency sound waves travel through the body, they encounter interfaces where the physical properties of the medium change, such as the border between two different organs.12

This reflection occurs due to differences in acoustic impedance, which is a measure of how much a medium resists the transmission of sound waves. When waves strike a boundary where the impedance changes, a portion of the sound energy is reflected back toward the source. An electronic apparatus then detects these echoes to determine the intensity and position of the tissue, allowing for the creation of detailed images of the body's internal structures.342