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Physics 1 > Test 4 > Flashcards

Test 4 Flashcards

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1
Q

What is the region in an unfocused beam that extends from the transducer surface to an axial distance where the field begins to diverge?

A

Fresnel Zone

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2
Q

Which change will make the near zone become longer?

A

Increased diameter of crystal

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3
Q

The near field length (blank) with increasing frequency

A

Increases

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4
Q

Which change will increase the rate of far field divergence?

A

decrease in frequency

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5
Q

For an unfocused transducer, what is the approximate beam width at the focal distance and twice the focal distance, given the crystal diameter of 5 mm?

A

2.5 mm, 5 mm

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6
Q

The transmitted beam diverges at which zone?

A

Fraunhofer Zone

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7
Q

True/False

If the number of cycles in the pulse are increased the axial resolution improves.

A

False

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8
Q

What will happen to the crystal if you heat a transducer above the Curie point?

A

it becomes depolarized

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9
Q

What is used to make most crystals in modern diagnostic sonographic transducers?

A

Lead zirconate titanate

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10
Q

Why is the piezoelectric effect employed in diagnostic medical ultrasound ?

A

To generate sound waves from electrical waves.

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11
Q

True/False

Intensity is uniform throughout the beam

A

False

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12
Q

What is the use of the transducer lens ?

A

Used to help focus the beam

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13
Q

What is the use of the transducers’ matching layers?

A

Lowers acoustic impedance mismatch between the transducer and patient

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14
Q

What is the use of the transducers piezoelectric material?

A

converts electrical to mechanical energy

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15
Q

What is the use of the transducers backing material?

A

Used to decrease the SPL, improve AR, increase transducer BW, & decrease transducer sensitivity

(Match response)

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16
Q

What is the most common natural piezoelectric material?

A

Quartz

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17
Q

The matching layers are cut to _____ the ______ of the crystal

A

1/4 the wavelength

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18
Q

An advantage of multiple transmit foci per line is improved _________ resolution.
However, ________ resolution will degrade.

A

Lateral resolution improves
Temporal resolution degrades

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19
Q

The velocity of sound waves is primarily dependent on the ?

A

Material in which the sound is being transmitted

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20
Q

One benefit of composite piezoelectric elements over natural elements is:

A

Acoustic impedance closer to that of soft tissue

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21
Q

True/False

The crystals in linear sequenced array transducers are fired off in groups to create a longer near zone.

A

True

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22
Q

True/False

If a crystal is damaged in a phased array transducer there will be a black line on the screen corresponding to that specific crystal

A

False

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23
Q

Huygen’s principle states that:

A

Numerous
wavelets that are produced form a new wave front using constructive interference

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24
Q

What primarily determines the operating frequency of an ultrasonic transducer?

A

Thickness of the crystal

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25
Q

In a real time scanner, the frame rate is influenced by…

A

Number of transmit focal regions
Number of lines per frame
Speed of sound in tissue
Depth of tissue examined

Note: NOT “Frequency bandwidth of the transducer”

26
Q

True/False

Continuous wave probes have broad bandwidths due to their long pulse lengths

A

False

27
Q

True/False

Electronic focusing is accomplished by delaying the electrical pulses to each crystal to cause the wave fronts to converge at variable focal points

A

True

28
Q

What mode has NO grayscale image? It only has spikes representing how strong the retuning signal is.

A

A mode

29
Q

This mode tracks the position of the transducer to place a dot on the screen corresponding to the transducer position (X, Y location), thus creating the 2-D image

A

B mode

30
Q

True/False

Increasing the number of scan lines also increases the spatial resolution

A

True

31
Q

True/False

For pulse wave imaging we want there to be a low Q factor

A

True

32
Q

True/False

Mechanical transducers are steered with a motor and are focused by either internal or external methods.

A

True

33
Q

What are the two other names for the operating frequency?

A

resonant and natural

34
Q

The matching layer(s) are commonly composed of what in epoxy resin?

A

Aluminum powder

35
Q

What is the pulse repetition period is the pulse repition frequency is 5 kHz?

A

0.2 ms

(Note: NOT 0.2 microsec)

36
Q

If the number of cycles in a pulse is increase, but the wavelength remains the same, what is being increased or decreased?

A

The pulse duration is increased

37
Q

What is the term for the time from the beginning of one pulse to the beginning of the next pulse?

A

Pulse repetition period

38
Q

How does increasing the depth of effect the SPL?

A

No change

39
Q

How does increasing the depth of effect the duty factor?

A

Decrease

40
Q

How does increasing the depth of effect the Pulse repetition period ?

A

Increase

41
Q

How does increasing the depth of effect the pulse duration?

A

No change

42
Q

How does increasing the depth of effect the propagation speed?

A

No relation

43
Q

How does increasing the depth of effect the number of cycles?

A

No relation

44
Q

What change will cause the pulse duration to increase?

A

Frequency decreases

45
Q

If the pulse repition period is 330 microseconds, what is the pulse repetition frequency?

A

3 kHz

46
Q

What is the fraction of time the sound is actually on?

A

Duty factor

47
Q

In diagnostic medical sonography, the beam would reach a reflector of approximately _______ deep in 20 microseconds

A

3 cm

48
Q

In DMs, what is the most common unit for SPL?

A

mm

49
Q

What is the unit for duty factor?

A

Unitless

50
Q

What is the SPL if the wavelength is 2mm and there are 3 cycles in the pulse?

A

6 mm

51
Q

PRF is the number of _______ occurring in 1 second

A

Pulses

52
Q

If the Pulse Repetition Frequency decreases then what would happen as well?

A

Duty factor decreases

53
Q

It took the beam 45.5 microseconds to reach the reflector. How deep did the beam travel?

A

7 cm

**typed

54
Q

You are scanning with a 4 MHz transducer that has 2 cycles per pulse. You note a mass that is at a distance of 8 cm. What is the pulse repetition frequency ?

A

9.57 kHz

**typed

55
Q

What is the relationship of frequency to absorption?

A

If the frequency is doubled, the absorption is doubled.

56
Q

True/False

Continuous wave differs in that the probe has only one crystal to send and receive signals and pulse wave probes have two crystals

A

False

57
Q

What determines the number of cycles in a pulse?

A

Backing layer

58
Q

True/False

A longer spatial pulse length yields better image resolution.

A

False

59
Q

What can the sonographer do to obtain the best image specular reflector?

A

The sonographer can turn their probe perpendicular to the interface.

**typed

60
Q

What does a duty factor of 1 mean?

A

The machine is always on

**typed

61
Q

You are scanning with a 3 MHz transducer that has 2 cycles per pulse. You note a mass that is at a distance of 11 cm. What is the pulse repetition frequency?

Round to two decimal places

A

6.96 kHz

**typed

Physics 1 (5 decks)

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