What relationship is indicated by the term "impedance" in ultrasound?

Impedance in ultrasound refers specifically to the resistance a medium provides against the transmission of sound waves. It is defined as the product of the density of the medium and the speed of sound within that medium. The significance of impedance lies in its role in determining how much sound will be transmitted versus how much will be reflected when sound waves encounter an interface between two different media.

When sound waves travel from one medium to another, the difference in acoustic impedance between the two mediums influences the amount of reflection and transmission. A high difference in impedance at the interface leads to greater reflection and less transmission, while a small difference promotes more transmission. This concept is crucial for understanding how ultrasound images are formed and how sound propagates through different tissues with varying densities and acoustic properties.

The other choices do not accurately capture the essence of impedance. Compression of sound waves relates more to wave propagation rather than their resistance. Propagation speed is important but does not define impedance itself. Similarly, while the intensity of reflected sound at an interface is influenced by impedance differences, it doesn't encapsulate what impedance is fundamentally about. Understanding this relationship is essential for effective interpretation and application in sonography.