ARDMS SPI Acoustic Waves and Properties 5

Question 1

Which of the following acoustic wave types does diagnostic ultrasound primarily use for imaging?

Accepted Answer

Longitudinal (compressional) waves

Answer

Diagnostic ultrasound uses longitudinal waves in which particle displacement occurs parallel to the direction of wave propagation, as these travel efficiently through soft tissue.

Question 2

Total internal reflection of an ultrasound beam occurs when the angle of incidence exceeds:

Accepted Answer

The critical angle

Answer

When the incident angle exceeds the critical angle at an interface where speed increases, refraction is impossible and all energy is reflected back.

Question 3

Acoustic shadowing in ultrasound images is caused by:

Accepted Answer

Strong reflection or high attenuation by a structure, reducing echoes beyond it

Answer

Structures that strongly reflect or absorb sound (e.g., gallstones, bone) prevent beam transmission, creating a dark shadow posterior to them.

Question 4

The spatial pulse length (SPL) is determined by:

Accepted Answer

Number of cycles × wavelength

Answer

SPL = number of cycles per pulse × wavelength; shorter SPL (fewer cycles, shorter wavelength) means better axial resolution.

Question 5

Compared to soft tissue, fat has a propagation speed that is:

Accepted Answer

Lower (~1450 m/s)

Answer

Fat propagates sound at approximately 1450 m/s, slower than the 1540 m/s assumed by scanners, which can cause focal-zone registration errors.

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Practice Test

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Practice Test

ARDMS SPI Acoustic Waves and Properties 5