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How are ultrasonic echoes used to create images inside the body?

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Ultrasonic imaging creates internal body images by utilizing high-frequency sound waves, typically above one megahertz, which are generated by a piezoelectric transducer.12

When these waves are directed into the body, they travel through tissues and encounter boundaries where there are changes in acoustic impedance or density. At these interfaces, the waves are reflected back as echoes. An electronic apparatus receives these echoes, analyzing their intensity and time delay to determine the position and nature of the internal structures.12

Different scanning modes are used to visualize this data:
* B-scan: Uses a linear array of transducers to produce a two-dimensional plot of a body plane.2
* A-scan: Uses a single transducer to plot echoes against time, often to measure organ size.2
* M-scan: Records the motion of internal organs, such as the heart.2

Because ultrasound is a nonionizing mechanical vibration, it provides a safe, real-time method for diagnostic imaging, offering excellent contrast between various soft tissues without the risks associated with ionizing radiation.12