The shadow behind a renal stone is primarily due to which interaction?

The shadow behind a renal stone is primarily due to which interaction?

• A. Reflection
• B. Refraction
• C. Destructive Interference
• D. Cavitation

Answer: (A)

When ultrasound meets a renal stone, the dominant interaction is reflection at the stone’s surface. The stone has a much higher acoustic impedance than surrounding tissue, so most of the incident energy is reflected back toward the transducer and little energy is transmitted beyond the stone. The energy that does pass through is also strongly attenuated by the stone, so the tissue behind it receives almost no sound and appears as a dark shadow. Refraction, destructive interference, and cavitation aren’t the primary causes of this posterior shadow.

When ultrasound meets a renal stone, the dominant interaction is reflection at the stone’s surface. The stone has a much higher acoustic impedance than surrounding tissue, so most of the incident energy is reflected back toward the transducer and little energy is transmitted beyond the stone. The energy that does pass through is also strongly attenuated by the stone, so the tissue behind it receives almost no sound and appears as a dark shadow. Refraction, destructive interference, and cavitation aren’t the primary causes of this posterior shadow.