Ultrasound physics midterm review

A pair of waves are in phase. What occurs when these waves interfere?

constructive interference

Which of the following cannot be considered a unit of frequency?

cycles

As an ultrasound wave travels though the body, its amplitude usually:

decreases

Two waves arrive at the same location and interfere. The resultant sound wave is smaller than either of the 2 original waves. What is this called?

destructive interference

How are scores on the ultrasound board exams related to study time?

directly

What conditions are necessary for refraction to occur at a boundary between 2 media?

dissimilar propagation speeds and oblique incidence at the boundary

Which of the following actions would cause a PZT crystal to lose its special properties?

exposing to high temperatures

True or false? Lower frequency sound creates higher quality images with greater detail.

false

True or false? The acoustic impedance of the skin is greater than the acoustic impedances of both the matching layer and the piezoelectric element.

false

Ultrasound waves traveling through lung tissue attenuate to a ___ extent than when traveling through soft tissue

greater

The attenuation of an acoustic wave traveling through bone is ___ its attenuation through soft tissue.

greater than

How thick is the active element of a 3 MHz pulsed wave transducer?

half the wavelength of the sound wave in PZT

The speed of sound traveling through bone is ____ tissue.

higher than

If the ___ of 2 media are different and sound strikes a border between the media at 90˚ incidence, then reflection will occur.

impedances

Which of the following terms does not belong with the others?

increased duty factor

A wave of acoustic energy is leaving soft tissue and transmitting into fat with an 86˚ incident angle. What is true of the angle of transmission?

it is less than 86˚

Mathematically, when a number is squared, the number is multiplied by:

itself

Sound traveling through blood attenuates to a ___ extent than when traveling through soft tissue.

lesser

The scale associated with decibel notation is ___?

logarithmic

Acoustic impedance is a property of the ___ and has units of ___.

medium, Rayls

Which of the following units are appropriate to describe the period of an acoustic wave?

minutes

To calculate acoustic impedance of a medium, one should ___ the ___ by the ___.

multiply, density, propagation speed

Which of the following describes an angle with a measure of 123˚?

obtuse

Attenuation is determined by which of the following factors?

path length and frequency of sound

What is the pulse duration equal to?

period multiplied by the number of cycles in the pulse

Decibel notation is a/the ___ between 2 numbers.

ratio

What event does Snell's law govern?

refraction

What are the units of PRF?

seconds

Sound is best described as _____?

series of compressions and rarefactions

What determines the initial intensity of an ultrasound beam?

the source of the sound wave

What establishes the frequency of an ultrasound wave?

the transducer

What does a 3 dB change in a value intensity mean?

the value has doubled

True or false? The PRF and the frequency are unrelated.

true

True or false? The purpose of the backing material of an ultrasound transducer is to shorten the pulses, thereby creating images with better image quality.

true

What helps to determine the frequency of the sound produced by the transducer of a continuous wave ultrasound system?

ultrasound system electronics

What are the units of pulse duration?

units of time

What is the name of the horizontal axis of a graph?

x-axis

What is the vertical axis of a graph called?

y-axis

To which of the following is Rayleigh scattering related?

frequency⁴

Which of the following terms best describes the relationship between frequency and wavelength for sound traveling in soft tissue?

inverse

What happens to the intensity when the power in an ultrasound beam in unchanged, and at the same time, the beam area doubles?

is halved

In the case of pulsed ultrasound, what is the maximum value of the duty factor?

less than 100%

Infrasound is defined as a sound with a frequency of _____

less than 20 Hz

Which term has a meaning other than normal incidence?

oblique incidence

Compressibility describes a characteristic of a medium. Which 2 terms describe the same property as compressibility?

stiffness and elasticity

Which component of an ultrasound transducer is made from a slab of epoxy embedded with tungsten particles?

the damping material

The speed at which a wave travels through a medium is determined by:

the mediums properties only

What are the units of the intensity reflection coefficient?

- W/cm² - watts - dB - none of the above none of the above

The wavelength of an ultrasonic wave is determined by:

- the sound source - the medium through which the wave travels

In diagnostic imaging, what determines the spatial pulse length?

-the ultrasound system -the medium through which the pulse travels

What results when the intensity transmission coefficient and the intensity reflection coefficient are added together?

1.0

The final amplitude of an acoustic wave is reduced to ½ of its original value. The final power is ____ the original power.

1/4

What is the reciprocal of 5?

1/5

What is the value of the duty factor for continuous wave ultrasound?

100 1% 1000 % none of the above -none of the above

How long does it take for sound to make a round trip to and from the skins surface to a reflector depth of 1 cm in soft tissue?

13 µs

A sound beam travels 9cm in soft tissue. The attenuation coefficient is 3 dB/cm. What is the total attenuation that the sound beam experienced?

27 dB

Assume that the frequency of sound with the greatest power emitted by a transducer is 5 MHz. However, the pulse contains acoustic energy with frequencies as low as 3.5 MHz and as high as 6.5 MHz. What is the bandwidth of the transducer?

3.0 MHz

A sack contains 6 pounds of flour. The contents of the bag are increased by a factor of 5. How much flour is in the bag?

30 (6x5)

In soft tissue, sound travels to a reflector and back to the transducer in 39 µs. How deep is the reflector?

3cm

In soft tissue, sound travels to a reflector and back to the transducer in 39 µs. What is the total distance that the pulse traveled?

6cm

When a sonographer increases the maximum imaging depth during an exam, what happens to the PRF?

PRF decreases

Which of the following lists orders the impedance from highest to lowest?

PZT, matching layer, gel, skin

What is the uniform dispersion of a sound wave in many different directions after striking a very small particle?

Rayleigh scattering

Which of the following is true of all waves?

all carry energy from one site to another

A longitudinal wave propagates from east to west at a speed of 2 MPH. What is the direction of motion of the particles within the wave?

alternately from east to west then west to east

What is the amount of attenuation per cm that a sound wave undergoes called?

attenuation coefficient

A sound wave reaches a rough or irregular border between 2 media. Under these explicit circumstances, which process is most likely to occur?

backscatter reflection

What term is used to describe the effects of an ultrasound wave on living tissue?

biological effects