What does "acoustic impedance" refer to?

• A. The pressure of sound waves in the air
• B. The resistance of a medium to the passage of sound waves
• C. The speed at which sound travels
• D. The intensity of sound waves

Answer: (B)

Acoustic impedance refers to the resistance of a medium to the passage of sound waves. It is a crucial concept in ultrasound physics, as it influences how sound waves travel through different tissues and how they reflect off tissue boundaries. The acoustic impedance is determined by the density of the medium and the speed of sound within it.

When sound waves encounter a boundary between two different media, such as soft tissue and bone, the difference in acoustic impedance can affect how much of the sound wave is reflected back versus transmitted into the next medium. High acoustic impedance differences lead to greater reflection, which is essential for creating images in diagnostic medical sonography. Understanding acoustic impedance helps sonographers estimate how well ultrasound waves will penetrate various tissues, aiding in visualization and diagnosis.