Which term refers to the bounce-back of ultrasound waves when they encounter a boundary?

The term that refers to the bounce-back of ultrasound waves when they encounter a boundary is reflection. This occurs when the ultrasound waves hit a different medium or tissue interface, such as the transition from fluid to soft tissue or tissue to bone. The varying acoustic properties between these materials cause some of the ultrasound energy to be reflected back, which is critical for creating sonographic images. The degree of reflection depends on the density and acoustic impedance of the tissues involved.

Understanding reflection is essential in sonography because it allows technicians to visualize internal structures, thereby aiding in diagnosis. It is the principle that enables ultrasound machines to construct images based on the echoes that are returned after hitting boundaries within the body.