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Physics I > Intensity and Power > Flashcards

Intensity and Power Flashcards

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1
Q

Measurement of Intensity

Intensity

Determining Acoustic Output

–_____

– Radiation Force _____/_____

–_____

–_____

A

Hydrophone
Balance, Scale
Calorimeter
Thermocouple

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2
Q

Intensity

_____ is the amount of power divided by the area

The rate at which _____ is transmitted by the wave over a small area

Units - mW/cm^2 , W/cm^2

I = P/A

A

Intensity

energy

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3
Q

Intensity is _______ as the sound travels through a medium

Increasing intensity =
—Particle distribution in compression zone becomes more _______

—Peak acoustic pressure is _______

—-Length of particle oscillations _______

—-Maximum particle velocity _______

A 
Reduced
Dense
Higher
Increase
Increases
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4
Q

Intensity

_______, _______, and acoustic _______ of an US beam are NOT affected by a change in intensity

_______ is linked to the study of potential bioeffects

_______ intensity wave is more disruptive to living tissues

A 
Frequency 
Wavelength
Velocity
Intensity
High
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5
Q

A sonographer can vary _______ by adjusting the output power/acoustic output

A

Intensity

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6
Q

Instantaneous intensity

I = P^2/pc

Where:

I = instantaneous \_\_\_\_\_\_\_
P = acoustic \_\_\_\_\_\_\_
p = medium \_\_\_\_\_\_\_
c = acoustic \_\_\_\_\_\_\_
A

Intensity
Pressure
Density
Velocity

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7
Q

Intensity

Frequently the pulsed-wave US is characterized by a peak _____ pressure, a.k.a., peak rarefactional pressure

US instruments produce peak rarefactional pressure amplitudes from ___-___ megapascals (50 times greater than atmosphere pressure

A

negative

  1. 5
  2. 5
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8
Q

Intensity

Free-field Conditions

Pressure in measured in _____ without reflectors or other disturbances to the US field

Pressure and corresponding intensity in water is converted to intensity in tissue by applying correction (derating) factors for attenuation

Free-field measurements do not assess:

  • –_____ by tissue
  • –_____ by anatomic structure
  • –Production of standing _____
  • –Effects of _____ bodies
A 
water
attenuation
focusing
waves
reflecting
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9
Q

Determining Acoustic Output

Hydrophones

Very specialized equipment; usually used by the manufacturer

a.k.a. _____

Used in two forms:
—A small transducer element < __ mm in diameter mounted on the end of a hollow needle

A

microprobe

1

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10
Q

Determining Acoustic Output

Hydrophones

Used in two forms:
—A large _____ membrane with small electrodes on both sides

PVDF is used to make probe _____ and membrane

_____ floride has a wide bandwidth

A

piezoelectric
tip
polyvinylidene

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11
Q

Determining Acoustic Output

Hydrophones

—Receive sound from all directions without altering the sound by their presence

Period, PRP, and PD can be determined
—From these _____, _____, _____ can be calculated

Pressure _____ can be determined

_____, _____ and _____ can be calculated

A 
frequency 
PRF
DF
amplitude
wavelength
SPL
intensities
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12
Q

A radiation force ______ or radiation force ______ measures the intensity or power of the sound beam by measuring the force the sound beam exerts on the scale or balance

A

Balance

Scale

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13
Q

Determining Acoustic Output

______ is calibrated to measure total power in a sound beam through process of absorption

______ is a tiny electric thermometer placed into beam and temperature is measured; temp rise directly related to amount of power; power measured at specific area in beam

A

Calorimeter

Thermocouple

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14
Q

Intensity Descriptors

______ dependence (time)

______ dependence (area that the beam is hitting (space))

Intensity values for various operating modes

Common intensities

A

Temporal

Spatial

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15
Q

Temporal Dependence

______ peak

Pulse ______

Pulse ______

A

Temporal
Peak
Average

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16
Q

Temporal Dependence

Considerations:

Temporal Average and Peak Intensities

______ values are used to describe the intensity over time

Intensity is NOT uniform over ______; therefore, several intensities are used

A

Temporal

Time

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17
Q

Temporal Dependence

The peak values over time occur when the beam is on, temporal ______ (TP)

The temporal ______ (TA) value averages the intensity during on and off time

A

Peak

Average

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18
Q

Temporal Dependence

For pulse ultrasound, pulse ______ (PA) is the average intensity that occurs within the pulse during the pulse duration

A

Average

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19
Q

Temporal Dependence

Related to the Duty Factor; aka: Duty ______

The DF is to time what the SP/SA factor is to ______

Unit less

Max = 1.0 (100%) = CW

Min = 0.0 (0%)

DF = PD/PRP

A

Cycle

Space

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20
Q

Spatial dependence

Spatial ______

Spatial ______

A

Peak

Average

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21
Q

Spatial dependence

Considerations:

Spatial average and peak intensities

Intensities are important for discussing bioeffects

Intensity is NOT uniform over ______; therefore, several intensities are used

______ values are used to describe intensity as it relates to distance or space across the beam

A

Space

Spatial

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22
Q

Spatial dependence

Intensity is measured at its peak value, spatial ______ (SP)

Intensity is measured at its average value, spatial ______ (SA)

A

Peak

Average

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23
Q

Spatial dependence

Related to the beam uniformity ratio or coefficient; aka: BUR, BUC, or SP/SA factor

The SP/SA factor is to space what the DF is to ______

BUR = SP/SA

Unitless

Minimum value of 1.0

If SA decreases —- BUR ______

A

Time

Increases

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24
Q

Temporal and Spatial dependence

By combining spatial and temporal values, six intensities can be measured (see chart in PowerPoint)

A

(See chart in PowerPoint for six intensities)

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25
Q

Intensity Values for Various Operating Modes

______ (intensity) values for various modes are found in equipment operator’s manual

Typical SPTA Intensity values include:

Gray Scale = 1 - ___mW/cm^2

M-mode = 70-___mW/cm^2

PW Doppler = 20 - ___mW/cm^2

Color Scale = 10 - ___mW/cm^2

A 
SPTA
200
130
290
230
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26
Q

Common Intensities

______ - is the lowest of all intensity measurements used in diagnostic US

______ - has the highest values of all intensity measurements used in diagnostic US and is the intensity that exists at the spatial peak when the sound beam is on

A

SATA

SPTP

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27
Q

Common Intensities

______ - Spatial peak, temporal average intensity is used to describe pulsed US intensities and to measure biological effects

______ average intensity at the position of the spatial peak

Intensity that is referred to when discussing data concerning biological effects

Equal to SATA x SP/SA

A

SPTA

Time

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28
Q

Common Intensities

______ - Spatial Peak, pulse average is the intensity averaged over the duration of the pulse

The spatial ______ pulse average (SPPA) and spatial ______, pulse average (SAPA) are used only in pulsed US

A

SPPA
peak
Average

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29
Q

Common Intensities

Im - maximum intensity is the average intensity over the most intense half cycle of the pulse; its values are similar to the ______ intensity
(less than the SP)

A

SPTP

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30
Q

Common Intensities

For CW US, the following intensities are equal:

SPTP = \_\_\_\_\_\_
SATP = \_\_\_\_\_\_

The TP is always equal to the TA for CW due to the continuous generation of cycles

A

SPTA

SATA

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31
Q

Power

The rate at which work is performed

______ transmitted per unit time, summed over the entire cross-sectional area of the beam

Until
—(mW) - Measured in Watts
— Joules/sec

A

Energy

32
Q

Power

Typical Power Values for various operating modes

Gray scale = 1 - _____ mW

M-mode = 1 - ____ mW

PW Doppler = 2 - ____ mW

Color scale = 2 - ____ mW

A

20
5
20
20

33
Q

Power

Power / Intensity / Amplitude

Power and intensity are ______

Power and intensity are proportional to ______ squared

If you double the amplitude the power or intensity will increase ______ times

A

Proportional
Amplitude
Four

34
Q

Logarithms

Logarithms are especially useful as they compress a large range of numbers into a smaller range.

In diagnostic US the range of signal ______ (strength) which are reflected from the body is enormous relative to the range of amplitudes that can be displayed on a monitor and interpreted by the human eye.

Definition : the power to which a base must be raised to get the desired number

A

Amplitudes

35
Q

Logarithms

So what?

_____ are good units for comparing the relationships between various measured sound levels and the threshold of human hearing

Used for measuring _____, _____, _____ range, and _____

Units Attenuation (loss of signal strength) = _____ = dB
When US waves travels through a medium (tissue) they LOSE _____/weaken
may be annotated as -dB

A 
Decibels
attenuation
output
dynamic
gain
Decibels
strength
36
Q

Logarithms

Decibels involve logarithms (log)

RULES OF THUMB:

3 dB of _____ = intensity reduction of 1/2

3 dB of _____ = intensity increase x 2

A

attenuation

gain

37
Q

Logarithms

Initial intensity x intensity ratio (of 6dB) = remaining intensity

100 mW/cm^2(1/4) = 25 mW/cm^2

A

Formula

38
Q

Attenuation

The reduction in the intensity (_____) of an US beam as it travels through a medium, the weakening of sound as it propagates

Encompasses _____, _____, and some say _____

The depth of penetration becomes less as frequency is _____, and the ability to observe deep-lying structures is forfeited (axial resolution)

A 
amplitude
absorption
scattering
reflection
increased
39
Q

Attenuation

_____ limits imaging depth and must be compensated for

Attenuation is affected by
_____ - directly

_____ - directly

_____ Type (Soft tissue)

A

attenuation
frequency
depth
medium

40
Q

Attenuation

Loss of intensity by attenuation in different media

_____ = 0.9995

_____ = 0.96

_____ = 0.87

_____ Tissue = 0.83 - 0.89

_____ = 0.01

_____ = 0.0001

A 
Water
Blood
Fat
Soft 
Skull
Lung
41
Q

Attenuation

_____ are good units for comparing relationships between various measured sound levels and the threshold of human hearing

Used for measuring _____, _____ range, and _____

_____ involve logarithms

Log of a number = number of tens that must be multiplied together to result in that number

A 
decibels
output
dynamic
gain
decibels
42
Q

Attenuation
Level (dB) = 10 log base 10 (I/I base O)

I = intensity at point of interest
I base O = Original or reference intensity

___ dB of attenuation = intensity decrease to 1/2 the original intensity

___ dB of attenuation = intensity decrease to 1/4 the original intensity

___ dB of attenuation = intensity decrease to 1/10, or 0.1 the original intensity

___ dB of attenuation = intensity decrease to 1/100, or 0.01 the original intensity

A

3
6
10
20

43
Q

Attenuation

Attenuation Units = Decibels = dB

for ST:

1/2 x frequency(MHz) x pathlength(cm)

or

Attenuation coefficient x pathlength

as frequency increases, attenuation _____
as pathlength increases, attenuation _____
as attenuation coefficient increases, attenuation _____

A

increases
increases
increases

44
Q

so WHAT’S AN ATTENUATION COEFFICIENT

AC(db/cm) = Attenuation dB/Separation between two points (cm)

The attenuation per unit _____of sound travel

The attenuation for each _____ of sound travel

Numerical values that express how different materials will attenuate an US beam per path length

Different materials have _____attenuation coefficients

A

length
cm
different

45
Q

SO WHAT’S AN ATTENUATION COEFFICIENT?

The average attenuation coefficient for soft tissue is one-____ the frequency in MHz

A

half

46
Q

Attenuation- Half-Value Layer

1/2 x cm x frequency

The amount (depth in cm) of material required to reduce the intensity by _____ of its original value

A half-value layer results in a ___-dB reduction in intensity

A

half

3

47
Q

Absorption

The only process whereby sound energy is dissipated in a medium.

_____ (conversion of sound to heat) is normally the dominant contribution to attenuation (in ST)

Other modes of interactions (_____ ,_____, _____ and _____) decrease beam intensity by redirecting its energy

A 
absorption
reflection 
refraction
scatting
divergence
48
Q

Absorption

Strongly dependent on _____
-Rate of absorption is _____ related, if frequency doubles, absorption _____

Related to the viscosity and _____ time of the medium

  • As viscosity increases, absorption _____
  • The longer the relaxation time, absorption _____
A 
frequency
doubles
relaxation
increases
increases
49
Q

Regions of lower pressure and density are called

A

rarefactions

50
Q

The rate at which energy passes through a unit area is called

A

intensity

51
Q

As sound travels, the reduction in amplitude and intensity of the wave is called

A

attenuation

52
Q

If beam power increases, intensity _____

A

increases

53
Q

If the beam area decreases, the intensity _____

A

increases

54
Q

Attenuation increases with increasing _____

A

frequency

55
Q

Amplitude and intensity are indicators of the sound wave’s _____

A

strength

56
Q

The attenuation coefficient for soft tissue using a 10 MHz transducer is _____

A

5 dB/cm

57
Q

Impedance is equal to density multiplied by _____ _____

A

propagation speed

58
Q

The unit for impedance is _____

A

rayl

59
Q

What does 3 dB of attenuation mean?

A

one half the original intensity

60
Q

The proportion of intensity to amplitude is _____

A

squared

61
Q

Attenuation encompasses (3)

A

absorption, scattering, and reflection

62
Q

What units are used to quantify attenuation?

A

dB

63
Q

Intensity is equal to the power of a wave divided by the _____ over which the power is spread.

A

area

64
Q

Amplitude is the maximum variation that occurs in an acoustic _____

A

variable

65
Q

_____ is the dominant factor contributing to attenuation of ultrasound in soft tissue.

A

absorption

66
Q

For each centimeter of distance, the pulse round-trip travel time is equal to _____

A

13 microseconds

67
Q

Amplitude and intensity describe the strength of sound.

TRUE or FALSE

A

true

68
Q

Cycle, period, and frequency are examples of acoustic variables.
TRUE or FALSE

A

false

69
Q

Sound is a mechanical longitudinal wave.

TRUE or FALSE

A

True

70
Q

Stiffer media have higher sound speeds.

TRUE or FALSE

A

true

71
Q

Imaging depth increases with increasing frequency.

TRUE or FALSE

A

false

72
Q

Attenuation increases with an increase in wavelength.

TRUE or FALSE

A

false

73
Q

The impedances of the media determine how much of the incident sound wave is reflected and transmitted into the second medium.
TRUE or FALSE

A

true

74
Q

The average attenuation coefficient for soft tissue is 1.0 dB/cm for each megahertz of frequency.
TRUE or FALSE

A

false

75
Q

Attenuation limits imaging depth

TRUE or FALSE

A

True

76
Q

Sound having a frequency of 10,000 Hz or higher is called ultrasound.
TRUE or FALSE

A

false

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