Deck 23: Diagnostic Ultrasound Imaging

Question 1

Which of the following is the Doppler effect?

A)When the source of a sound approaches the listener, the pitch becomes higher.
B)When the source of a sound approaches the listener, the pitch becomes lower.
C)When the source of a sound moves away from the listener, the sound is emitted with a higher pitch.
D)When the source of a sound moves away from the listener, the sound is emitted with a lower pitch.

Answer 1

When the source of a sound approaches the listener, the pitch becomes higher.

Question 2

Which of these statements describes a Doppler shift?

A)change in velocity of a wave as it passes the interface of two materials with different densities
B)change in wavelength of a wave as it passes the interface of two materials with different densities
C)change of a frequency of an emitted wave due to relative motion of a source and an observer
D)change of perceived frequency of a wave according to an observer due to relative motion of a source and the observer

Answer 2

change of perceived frequency of a wave according to an observer due to relative motion of a source and the observer

Question 3

Which of the following factors does the acoustic impedance depend on?

A)the frequency of the sound
B)the mass of the medium
C)the volume of the medium
D)the density of the medium

Answer 3

the density of the medium

Question 4

Under which of these conditions would you observe NO change in perceived frequency of sound?

A)if the source is moving with a speed v and the observer moves away in the opposite direction with the same speed v
B)if the source is moving with a speed v and the observer is chasing it in the same direction with the same speed v
C)if the source is moving with a speed v and the observer moves away in the opposite direction with twice the speed v
D)if the source is moving with a speed v and the observer is chasing it in the same direction with twice the speed v

Question 5

In which of these materials is ultrasound the least absorbed?

A)blood
B)brain
C)bone
D)muscle

Question 6

For an ultrasound wave with incident intensity 6.5 × 10^-2 J cm^-2 s^-1, what is the intensity of a beam reflected off a flat interface between muscle tissue and bone? The acoustic impedance value for muscle is Z_m = 1.66 × 10⁶ rayl, and for bone Z_b = 6.73 × 10⁶ rayl.

A)10.8 × 10^-2 J cm^-2 s^-1
B)3.93 × 10^-2 J cm^-2 s^-1
C)1.66 × 10^-2 J cm^-2 s^-1
D)0.60 × 10^-2 J cm^-2 s^-1

Question 7

Which of the following factors governs the intensity of the transmission and the intensity of the reflection of a sound on an interface?

A)the frequency of the sound
B)the mass of the medium
C)the volume of the medium
D)the density of the medium

Question 8

Which of the following is the definition of half-value thickness (HVT)?

A)It is the distance from the source at which absorption drops by half.
B)It is the distance from the source at which absorption increases by half.
C)It is the distance from the source at which the attenuation is half the intensity.
D)It is exactly halfway between the source and the receiver of the sound.

Question 9

How long does it take from emitting an ultrasonic signal until its return as an echo from a flat interface between a soft tissue and a muscle, if the thickness of a soft tissue is 2.5 cm? Assume that the speed of sound in soft tissue is 1450 m/s.

A)17.2 ìs
B)34.5 ìs
C)1.72 ms
D)3.45 ms

Question 10

What is the loss of intensity in decibels if an ultrasound beam is attenuated by 99%?

A)1 dB
B)10 dB
C)20 dB
D)99 dB

Question 11

What is the Doppler shift frequency in soft tissue, in which the speed of sound is 1540 m/s, if the transmitted frequency is 2 MHz, and the velocity of a reflector is 20 cm/s?

A)520 Hz
B)260 Hz
C)52 Hz
D)26 Hz

Question 12

We use an ultrasound signal to explore the layer of tissue in which sound travels at a speed of 1450 m/s. If the echo arrives with a delay of 37 ìs, what is the thickness of that layer of the tissue?

A)5.4 cm
B)2.7 cm
C)3.7 mm
D)1.9 mm

Question 13

For an ultrasound wave with an incident intensity of 6.5 × 10^-2 J cm^-2 s^-1, what is the intensity of a beam transmitted through a flat interface between fat tissue and muscle tissue? Acoustic impedance value for fat is Z_f = 1.33 × 10⁶ rayl, and for muscle Z_m = 1.66 × 10⁶ rayl.

A)19.2 × 10^-2 J cm^-2 s^-1
B)6.57 × 10^-2 J cm^-2 s^-1
C)6.42 × 10^-2 J cm^-2 s^-1
D)1.60 × 10^-2 J cm^-2 s^-1

Question 14

Which of these conclusions can be accurately drawn for frequencies used in ultrasound imaging?

A)When we use lower frequencies of ultrasound, we gain lower spatial resolution, and we can image to greater depth.
B)When we use higher frequencies of ultrasound, we gain lower spatial resolution, and we can image to greater depth.
C)When we use lower frequencies of ultrasound, we gain higher spatial resolution, and we can image to greater depth.
D)When we use higher frequencies of ultrasound, we gain higher spatial resolution, and we can image to greater depth.

Question 15

When we observe the motion of blood using Doppler shift of ultrasound, the targets are blood cells. Which of the following best describes the method?

A)The blood cells are moving receivers; the transducer is a stationary source.
B)The blood cells are stationary emitters; the transducer is a moving source.
C)The blood cells are first receivers, and then they are emitters of an echo; source and receiver are moving toward each other.
D)The blood cells are first receivers, and then they are emitters of an echo; source and receiver are moving away from each other.

Question 16

Which of these qualities do we aim for when we choose a high frequency of ultrasound for imaging?

A)imaging to greater depth
B)better spatial resolution of the image
C)faster imaging
D)lower attenuation

Question 17

If transmission of ultrasound through the interface between two tissues is large, which of the following statements applies?

A)The two tissues are similar, and little contrast is recorded.
B)The two tissues are very different, and little contrast is recorded.
C)The two tissues are very different, and large contrast is recorded.
D)The two tissues are similar, and large contrast is recorded.

Question 18

Which of the properties of ultrasound used for images is not affected by the characteristics of the tissue through which the ultrasound passes?

A)amplitude
B)frequency
C)velocity
D)wavelength

Question 19

What is the unit for acoustic impedance, Z (the rayl)?

A)kg m^-3
B)kg m s^-2
C)kg m^-2 s^-1
D)kg m² s^-2

Question 20

If the reflection of ultrasound through the interface between two tissues is 48.7%, what is the value for transmission?

A)We cannot calculate this without knowing the acoustic impedances of the two tissues.
B)We cannot calculate this without knowing the densities of the two tissues.
C)51.3%
D)1.3%

Question 21

A large attenuation coefficient means that a sound is quickly weakened as it passes through a medium.

Question 22

Acoustic impedance is larger for gases than for solids.

Question 23

The sound absorption coefficient depends on the medium, and is the same at all frequencies.

Question 24

A bat wants to locate a stationary obstacle while moving toward it at 4 m/s and emitting sound pulses at a frequency of 80 kHZ. What is the fractional of change of the echo's frequency? The speed of sound in air is 343 m/s.

Question 25

You are standing near train tracks when you hear the whistle of an approaching train. The frequency you are hearing is at 580 Hz. As the train passes you and moves away from you, you hear sound at a frequency of 544 Hz. What is the speed of the train? The speed of sound in air is 343 m/s.

Question 26

In Fig. 23.1, tissue 1 is fat. How long does it take from emitting the signal until its return as an echo from interface In₁ if the thickness of the fat tissue is l₁ = 2.5 cm? Assume that the speed of sound in soft tissue is 1450 m/s.

Question 27

If transmission of ultrasound through the interface between two tissues is large, then the two tissues are similar.

Question 28

A horseshoe bat is most sensitive at a frequency of 76 kHz and is flying toward a moth at 6 m/s; the moth is flying away at 3 m/s. What is the sound the bat needs to emit in order to hear the echo back at the same frequency? The speed of sound in air is 343 m/s.

Question 29

A horseshoe bat is most sensitive at a frequency of 76 kHz. What is the sound it needs to emit while flying toward a target at 5 m/s in order to hear the echo back at that frequency? The speed of sound in air is 343 m/s.

Question 30

In Fig. 23.1, if the echo arrives with a delay of 43 ìs, what is the thickness, l₁, of a layer of fat under the skin? The speed of sound in fat is 1450 m/s.

Question 31

In ultrasound imaging, when we use lower frequencies of ultrasound, we gain higher spatial resolution, but we cannot image to greater depth.

Question 32

In ultrasound imaging, when we use higher frequencies of ultrasound, we gain higher spatial resolution.

Question 33

The sine of the angle of a wave front with a flat interface is inversely proportional to the speed of sound in that medium.

Question 34

Explain conceptually the difference between the following two expressions describing a wave:
(i) D = Asin(ùt - kx), and (ii) D = Ae^-ãxsin(ùt - kx)

Question 35

Dolphins use ultrasound to locate obstacles and prey in murky water. A dolphin is chasing a squid. If the dolphin swims at 39 km/h while emitting a sound at a frequency of 135.0 kHZ, and receives an echo at a frequency of 135.5 kHz, what is the relative speed of the dolphin with respect to squid? Is the dolphin moving toward or away from the squid? The speed of sound in the sea is 1560 m/s.

Question 36

The sine of the angle of a wave front with a flat interface is proportional to the wavelength of a sound in that medium.

Question 37

When a receiver is chasing a source of sound and is catching up with it, the perceived pitch of the sound is higher than the actual pitch of the emitted sound.

Question 38

The sound attenuation coefficient depends on the medium, and is the same at all frequencies.

Question 39

For an ultrasound wave with an incident intensity of 7.5 × 10^-2 J cm^-2 s^-1, calculate the intensity reflection R, and the intensity transmission T at a flat interface between a muscle tissue and a bone. Acoustic impedance value for muscle is 1.66 × 10⁶ rayl, and for bone 6.73 × 10⁶ rayl.

Question 40

Figure 23.1 The figure shows ultrasound measurement. Interface In₁ is l₁ below the skin. The interface separates two media with acoustic impedances of Z₁ and Z₂.
In Fig. 23.1, l₁ = 2.5 cm. What is the intensity loss of a signal before interface In₁? The sound attenuation coefficient is á_fat = 1.0 dB cm^-1 MHz^-1.