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Physics 110 Exam 2 > Intensities > Flashcards

Intensities Flashcards

1
Q

If you double the amplitude, what happens to intensity? Amplitude x3 means… ?

A

It is increased x4 (due to the exponent).

Intensity x9

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2
Q

What is power?

What are the units for power?

A

Energy per unit time.

Watts

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3
Q

What is sound intensity?

What are the units for intensity?

What are the (usual) ultrasound units for intensity?

A

Power per unit area.

W/m2

mW/cm2

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4
Q

What is the equation for intensity?

A

Intensity = power/area,

OR: Intensity = amplitude2 /2pV

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5
Q

True or false:

Amplitude and frequency are dependent on each other.

A

False, they are independent of each other.

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6
Q

What are the two basic parameters in measurements of intensity?

A

Space and Time

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7
Q

What are the two types of measurements of intensity?

A

Peak and Average

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8
Q

Which measurement will be higher?

Peak or Average?

A

Peak

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9
Q

What does peak refer to?

A

The maximum value

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10
Q

What does average refer to?

A

The mathematical middle value

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11
Q

What does temporal refer to?

A

To all time, Transmit (pulse duration) and Receive. .

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12
Q

True or false:

A pulsed ultrasound beam does not have the same intensity at different times.

A

True

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13
Q

What does pulsed refer to?

A

Only to the transmit time (pulse duration).

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14
Q

True or false:

A pulsed ultrasound beam has the same intensity at different times during the pulse.

A

False: It has does not have the same intensity at different times during the pulse.

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15
Q

Pulsed is the average intensity for what?

A

For the pulse duration only. (Ignore listening time).

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16
Q

If TP = TA, what kind of ultrasound is it?

A

Continuous wave: always on.

So, peak intensity = average intensity.

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17
Q

What is Im?

A

Another type of intensity measurement.

It’s the average intensity measured at the most intense half-cycle.

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18
Q

What is pulse average, PA?

And what type of measurement is it?

A

The average intensity for the duration of the pulse itself.

It is a measurement of time.

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19
Q

What does spatial refer to?

A

Location or space. (Distance)

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20
Q

What is spatial peak intensity, (Isp)?

A

The average intensity at the location where it is maximum. (the maximum in space)

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21
Q

What is spatial average intensity, (Isa)?

A

The average intensity across the beams cross sectional area.

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22
Q

True or false:

Spatial average intensity, or Isa, is always higher than spatial peak intensity, or Isp.

A

False. Spatial peak intensity is always higher.

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23
Q

What is this all about?

Why do we care?

A

Sound energy.

We don’t want our sound waves to damage tissue.

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24
Q

What is beam uniformity coefficient (BUC)?

A

Another intensity related measurement.

Sometimes called: SP/SA)

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25
Q

Why is a BUC closer to 1.00 optimal?

A

It suggests a uniform intensity across the area.

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26
Q

What does a higher peak intensity relative to average intensity mean?

A

A higher BUC.

Less uniformity of intensity.

27
Q

What is the lowest possible BUC?

What are the units for BUC?

A

1.00

None. BUC is unitless.

28
Q

What does it mean if the peak intensity isn’t very different from the average?

A

The distribution of intensity is pretty uniform across the area.

29
Q

What does it mean if there is a significantly higher peak intensity than the average?

A

The uniformity isn’t very good.

30
Q

What is dosimetry?

A

The study of effects of exposure of the body to signals used in diagnostic testing, such as ultrasound, X-ray, MRI, etc. (aka: Bioeffects)

31
Q

What are the two bioeffects of ultrasound?

A

Heat and Cavitation

32
Q

With respect to bioeffects, what is heat?

A

The energy dissipated as ultrasound travels through the tissue.

33
Q

What is the best index for heat?

A

SPTA is the best index.

34
Q

With respect to bioeffects, what is cavitation?

A

It is the creation of little spaces due to movement of particles.

35
Q

What is the best index for cavitation?

A

Temporal peak is the best index.

36
Q

When is significant heat production good?

A

Therapeutic ultrasound

37
Q

True or false:

Therapeutic ultrasound uses a higher frequency and lower intensity than diagnostic ultrasound.

A

False: Therapeutic ultrasound uses a lower frequency and higher intensity.

38
Q

AIUM found no bad effects with unfocused beams at _______?

A

100 mW/cm2

(Greater than this is bad)

39
Q

AIUM found no bad effects with a focused beam at _______ ?

40
Q

What is it we are really doing with intensity conversions?

A

We are converting space and time units.

41
Q

How do we convert pulse average to temporal average, PA to TA, using duty factor?

A

SPPA x DF = SPTA

(i.e., PA x proportion of time actually making sound)

42
Q

What are the units for duty factor, DF?

A

None. DF is unitless.

43
Q

How do you solve for DF when you are given SPPA and SPTA?

A

DF = TA/PA

(Ignore the SP in front)

44
Q

How do we convert spatial peak to spatial average using BUC?

A

SA = SP/BUC

45
Q

How do you solve for BUC when you are given SP and SA?

A

BUC = SP/SA

46
Q

When working temporal conversions use _____ .

A

Duty factor.

DF relates peak to average over time.

47
Q

When working spatial conversions use ______ .

A

Beam uniformity coefficient.

BUC relates peak to average over space.

48
Q

What is BUC about?

49
Q

What is DF about?

50
Q

What is the most relevant intensity with respect to tissue heating?

51
Q

List the intensities from highest to lowest.

(There are seven)

A

SPTP, Im, SPPA, SPTA, SATP, SAPA, SATA

52
Q

What does BUC describe?

What are its units?

What is its value?

A

The spread of a beam in space.

It is unitless.

It has a value of 1 or greater.

53
Q

What does DF describe?

What are its units?

What is its value?

A

The relationship of beam intensities with time.

It is unitless.

It has a value between 0 and 1.

54
Q

When pulsed and continuous wave sound beams have the same SPTP intensities, which beam has the higher SPTA intensity?

A

Continuous wave

55
Q

When pulsed and continuous wave sound beams have the same SATP intensities, which beam has the higher SATA intensity?

A

Continuous wave

56
Q

What is temporal peak intensity, or Itp?

A

Maximum intensity in time

57
Q

What is temporal average intensity, or Imax or Im?

A

The average intensity during the PRP.

(both the on and off times)

58
Q

Of all the temporal intensities, which is the highest?

A

Temporal peak is the highest.

59
Q

Of all the temporal intensities, which is the lowest?

A

Temporal average is the lowest.

60
Q

Why is temporal average the lowest of the temporal intensities?

A

Because it includes both the on and off time.

61
Q

What is pulse average intensity, or Ipa?

A

Taking the average intensity during the pulse duration, the transmit time.

62
Q

List the temporal intensities from largest to smallest.

A

Itp, Imax, Ipa, Ita

63
Q

This is an example of what? And what is it measuring?

A

Temporal peak intensity. TP

It is the maximum itensity Im derived from the most intense half cycle in the pulse.

64
Q

The shorter line above is an example of what and it measures when?

The longer line below is an example of what and

it measures when?

A

Pulse average, PA; Is measured during

transmit time only.

Temporal average, TA; Is measured during

both the transmit and receive times.

Physics 110 Exam 2 (6 decks)

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