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*Ultrasound Physics* > Ch. 3 - Describing Sound Waves > Flashcards

Ch. 3 - Describing Sound Waves Flashcards

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0
Q

Wavelength is determined by what?

A

SS and medium

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1
Q

Period and frequency are determined by what?

A

SS

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2
Q

Amplitude, power, and intensity are determined by what?

A

SS

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3
Q

Speed is determined by what?

A

Medium

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4
Q

Which/what acoustic parameter(s) is/are determined by medium only?

A

Speed

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5
Q

Which/what acoustic parameter(s) is/are determined by SS only?

A

Period, Frequency

Amplitude, Power, and Intensity

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6
Q

Which/what acoustic parameter(s) is/are determined by SS and medium?

A

Wavelength

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7
Q

The time required to complete a single cycle is

A

Period

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8
Q

Give an example of period.

A

The period of class in hs is 50 minutes.

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9
Q

Can period be changed by the sonographer?

A

No

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10
Q

Period is determined by what?

A

SS

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11
Q

Typical values of a period are

A

0.06 - 0.5 microseconds (less than 1-millionth of a second)

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12
Q

Frequency is defined as

A

Number of certain events that occur during a particular time period.

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13
Q

Give an example of frequency

A

The frequency of presidential elections is once per four years

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14
Q

In US, the frequency of a wave is…

A

the number of cycles of an acoustic variable that occur in one second.

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15
Q

The unit for frequency is

A

Hertz (meaning “per second”)

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16
Q

Can frequency be changed by the sonographer?

A

No

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17
Q

What are the typical values of frequency?

A

2 MHz - 15 MHz

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18
Q

What does frequency affect in Us?

A

Penetration and axial resolution

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19
Q

A wave with a frequency exceeding 20,000Hz (so high it isn’t audible) is

A

Ultrasound

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20
Q

Sound heard by man between 20Hz and 20,000Hz

A

Audible sound

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21
Q

Sound with frequencies less than 20Hz are _____. And can they be heard by man?

A

Infrasound. No, so low it is inaudible.

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22
Q

Frequency and ______ are reciprocals.

A

Period

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23
Q

Frequency and period have a(n) _____ relationship.

A

Inverse

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24
Q

With frequency and period, units to be used are (2 examples)

A

Sec and Hz or microseconds and MHz

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25
Q

When period increases, frequency _________.

A

Decreases

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26
Q

What are the 3 bigness parameters (define and list)?

A

3 parameters that describe a sound wave.

Amplitude
Power
Intensity

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27
Q

What is defined as the difference between the average value and the max value of an acoustic variable?

A

Amplitude

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28
Q

List the 3 acoustic variables and their units.

A

Pressure - Pascals
Density - grams/cubic cm
Particle motion - m/s, mm/microsecond

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29
Q

The unit for amplitude is

A

Acoustic variables
Pressure - Pascals
Density - grams/cm^3
Particle motion - cm, m, distance

(And Decibels (dB))

30
Q

Can amplitude be changed by the sonographer?

A

Yes

31
Q

Amplitude ________(increases/decreases) as sound propagates through the body.

A

Decreases

32
Q

The difference between max and min values of an acoustic variable is called

A

Peak-to-peak amplitude

33
Q

Amplitude is ______ (fraction) of the peak-to-peak amplitude.

A

Half

34
Q

The rate of work performed, or the rate of energy transfer is

A

Power

35
Q

What is the unit for power?

A

Watts

36
Q

Can power be changed by the sonographer?

A

Yes

37
Q

Power ______(increases/decreases) as it propagates through the body.

A

Decreases

38
Q

Why are power and amplitude often described similarly?

A

Because they both describe “bigness”

39
Q

What is the relationship between power and amplitude?

A

Power is proportional to the wave’s amplitude squared

40
Q

If the amplitude is tripled, the power is

A

Increased by a factor of 9

41
Q

The concentration of energy in a sound beam is the definition of what?

A

Intensity

42
Q

The beam’s power divided by the beam’s cross-sectional area is another description of what?

A

Intensity

43
Q

Power (watts)
_____________
Beam area (cm^2)

is an equation for what?

A

Intensity

44
Q

What is the unit for intensity?

A

Watts/cm^2

45
Q

Can intensity be changed by the sonographer?

A

Yes

Since amplitude and power can be changed, the intensity can too

46
Q

Intensity _____ (increases/decreases) as sound propagates through the body.

A

Decreases

47
Q

What is the relationship between intensity and power?

A

Proportional or directly-related

48
Q

Intensity is proportional to the _______ of the wave (value).

A

Amplitude

Squared

49
Q

If amplitude is doubled, the intensity is

A

Increased by a factor of 4

2 x 2 = 4

50
Q

The length or distance of a single cycle is

A

Wavelength

51
Q

This is similar to a boxcar in a long train

A

Wavelength

52
Q

What is wavelength determined by?

A

SS and the medium

53
Q

Can wavelength be changed by the sonographer?

A

No

54
Q

What does wavelength influence in an US?

A

Axial resolution (image quality)

55
Q

What are the typical values of a wavelength?

A

0.1 - 0.8mm

56
Q

What is this equation of?

Propagation speed (mm/microseconds)
____________________________________
Frequency (MHz)

A

Wavelength

57
Q

What are the units for wavelength?

A

m, mm, or any measurement of length

58
Q

Do higher frequency waves have longer OR shorter wavelengths?

A

Shorter

59
Q

Do high frequency wavelengths have longer OR shorter periods?

A

Shorter

60
Q

In soft tissue, sound with a frequency of 1 MHz has a wavelength of _____.

In soft tissue, sound with a frequency of 2 MHz has a wavelength of _____.

A
  1. 54mm

0. 77mm

61
Q

This equation is for what?

1.54mm/microsecond
____________________
Frequency (MHz)

A

Wavelength

62
Q

The rate of sound travels through a medium is a definition for what? What is it also called?

A

Propagation speed

Velocity or speed

63
Q

What are the units for propagation speed?

A

m/s or mm/microsecond

64
Q

Propogation speed is determined by what?

A

Medium - density and stiffness

65
Q

Can propagation speed be changed by a sonographer?

A

No

66
Q

What are the typical values for propagation speed?

A

Average speed of sound in biologic tissue.

1,540m/s = 1.54km/s = 1.54mm/microseconds

67
Q

Lung, fat, soft tissue (incl. blood), air, bone, tendon - put these in order of slowest to fastest speed.

A

Air, lung, fat, soft tissue (incl. blood), tendon, bone

68
Q

Rule of thumb is

A

Stiffness and speed - same direction

Density and speed - opposite direction

69
Q

Stiffness is related to ________, Density is related to ________.

A

Change in shape/”squishability”

Weight

70
Q

What is the range for audible sound?

A

20Hz - 20,000Hz

71
Q

What are the typical values for power in US?

A

0.004 watts - 0.090 watts

72
Q

What are the typical values of intensity in US?

A

0.01 W/cm^3 - 300 W/cm^3

*Ultrasound Physics* (5 decks)

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