Attenuation, Reflection, and Refraction Flashcards

What artifact is produced when refraction causes the beam to miss its intended target?

Answer: Lateral displacement artifact

Refraction can displace the apparent position of a structure laterally, creating a lateral displacement artifact.

At normal incidence, what determines the fraction of sound intensity reflected at an interface?

Answer: The difference in acoustic impedance between the two media

The reflection coefficient at normal incidence depends solely on the acoustic impedances of the two media.

Which of the following interfaces reflects nearly 100% of incident sound energy?

Answer: Soft tissue–air interface

The acoustic impedance mismatch between soft tissue and air is extreme, causing nearly total reflection and no transmission.

The angle of refraction is related to the angle of incidence by:

Answer: Snell's law

Snell's law (sin θ₁/c₁ = sin θ₂/c₂) governs the relationship between the angle of incidence and angle of refraction.

Acoustic impedance (Z) is calculated as:

Answer: Density × propagation speed

Acoustic impedance Z = ρ × c, where ρ is the tissue density and c is the propagation speed.

Which artifact results from acoustic enhancement behind a fluid-filled cyst?

Answer: Posterior acoustic enhancement

Fluid attenuates sound less than surrounding tissue, so structures behind a cyst appear brighter — posterior acoustic enhancement.

If the acoustic impedance of two media are identical, what happens at their interface?

Answer: No reflection occurs

When Z₁ = Z₂, the reflection coefficient is zero, so all sound is transmitted with no reflection.