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Physics 1 > Quiz 5 > Flashcards

Quiz 5 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

What change while make the near zone become longer?

A

Increased diameter of crystal

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3
Q

Which statement regarding the near field or the far field zones is true?

A

The near field length increases with increasing frequency

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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 a crystal diameter of 5mm ?

A

2.5 mm, 5 mm

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6
Q

The transmitted beam diverges is 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

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

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 effect?

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, and decrease transducer sensitivity.

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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 of the wavelength

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18
Q

An advantage to multiple transmit foci per line is improved _____ resolution, however, ______ resolution will degrade.

A

Lateral, temporal

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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 composit 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 phase array transducer there will be a black line on the screen corresponding to that specific crystal.

A

False

23
Q

Huygens principle states that:

A

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

24
Q

What primarily determines the operating frequency of an ultrasonic transducer?

A

Thickness of the crystal

25
Q

In a real-time scanner, the frame rate is influenced by all of the following:

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

At a frame rate of 2 FPS, what is the time for a single frame to occur?

A

0.05 second

(20 frames/1second = 1frame / x second)

28
Q

True/False:

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

A

True

29
Q

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

A

a mode

30
Q

Which 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

31
Q

True/False

Increase in the number of scan lines also increases the spatial resolution

A

True

32
Q

True/False:
For pulse wave imaging we want there to be a low Q factor.

A

True

33
Q

Your crystal diameter is 9 mm and your frequency is 4 MHZ, what is the near zone length?

A

54 mm

34
Q

True/False:
Mechanical transducers are steered with a motor and are focused by either internal or external methods

A

True

35
Q

Written
What are the two other names for the operating frequency?

A

Resonant and natural

36
Q

written
The matching layers are commonly composed of what in epoxy resin?

A

Aluminum powder

37
Q

In which of the following is the amplitude height of the echo proportional to its strength?

A

A-mode

38
Q

In M-mode, the vertical axis represents:

A

Depth

39
Q

The ‘A’ in A-mode stands for:

A

Amplitude

40
Q

If the echo amplitude increases, the echo brightness:

A

Increases

41
Q

What is determined by the range equation?

A

Depth of the reflector

42
Q

The number of frames generated per second is called:

A

Frame Rate

43
Q

The major limitation in scanning speed is:

A

Time it takes for the sound wave to propagate through tissue

44
Q

The ability to resolve two events related by times is:

A

Temporal resolution

45
Q

Higher frame rate and temporal resolution are:

A

Directly related

46
Q

Frame rates can be improved by:

A

Decreasing the depth

47
Q

Maximum depth x line per frame x number of focal zones x frame rate is less than:

A

77,000

48
Q

The image depth controls the:

A

PRF

49
Q

The relationship between the spatial resolution and temporal resolution can be described as:

A

Indirectly related

50
Q

Another name for the depth control is:

A

Field of view

51
Q

What organ is scanned with the highest temporal resolution?

A

Pediatric heart

52
Q

Spatial resolution includes…

A

-longitudinal resolution
-elevational resolution
-lateral resolution

(Note: NOT temporal resolution)

53
Q

How many microseconds does it take for the ultrasound instrument to put an echo 6cm deep on the image?

A

78

54
Q

A voxel is a 3-D picture element which includes all of the following:

A

-length
-width
-thickness

Physics 1 (5 decks)

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