Acoustic Waves and Properties Flashcards

Snell's Law in ultrasound describes the relationship between:

Answer: Incident and refracted beam angles at a tissue boundary

Snell's Law states that the sine of the angle of incidence to the sine of the angle of refraction equals the ratio of propagation speeds in the two media.

What is the approximate average propagation speed of ultrasound assumed by diagnostic scanners in soft tissue?

Answer: 1540 m/s

Diagnostic ultrasound machines assume 1540 m/s (1.54 mm/µs) as the average soft-tissue propagation speed for depth calculation.

The reflection coefficient at a tissue interface is primarily determined by the difference in:

Answer: Acoustic impedances of the two media

The intensity reflection coefficient depends on (Z2 − Z1)² / (Z2 + Z1)², where Z1 and Z2 are the acoustic impedances of the two media.

Increasing the amplitude of an ultrasound wave will directly increase its:

Answer: Acoustic power and intensity

Amplitude is proportional to pressure variation; acoustic intensity is proportional to amplitude squared, so larger amplitude means greater power and intensity.

A sound wave with frequency of 5 MHz traveling through soft tissue (c = 1540 m/s) has a wavelength of approximately:

Answer: 0.31 mm

λ = c / f = 1540 m/s ÷ 5,000,000 Hz = 0.000308 m ≈ 0.31 mm.

What happens to the transmission of sound energy when two tissues have identical acoustic impedances?

Answer: There is no reflection; all energy is transmitted

When Z1 = Z2, the impedance mismatch is zero, producing no reflection and allowing complete transmission of the ultrasound beam.

Which of the following best defines the acoustic property 'stiffness' of a medium in the context of sound propagation?

Answer: The medium's resistance to being compressed

Stiffness (bulk modulus) is the medium's resistance to compression; stiffer media transmit sound faster because they restore disturbed particles more quickly.