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Basic Ultrasound Physics > Describing Sound Waves > Flashcards

Describing Sound Waves Flashcards

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1
Q

Name the seven acoustic parameters

A

Frequency/Period, Amplitude/Power/Intensity, Wavelength/Propagation Speed

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2
Q

Define period

A

Time necessary to complete a single cycle

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3
Q

What are the units of period?

A

any time units

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4
Q

What are the typical values of period?

A

0.06 - 0.5 microseconds
0.00000006 - 0.0000005 seconds
6x10^-8 - 5x10^-7 seconds

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5
Q

Period is determined by?

A

the sound source

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6
Q

Is period adjustable by the sonographer?

A

No

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7
Q

Define Frequency

A

The number of cycles that occur in one second

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8
Q

What are the units of frequency?

A

Hz (1 cycle per second)

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9
Q

What are the typical values of frequency?

A

2-15 MHz
2 million - 15 million cycles per second

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10
Q

What is the frequency determined by?

A

the sound source

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11
Q

Is the frequency adjustable by the sonographer?

A

No (assuming everything remains constant)

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12
Q

Infrasound is less than _______ Hz

A

20

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13
Q

Range of frequencies for audible sound

A

20 Hz - 20,000 Hz (20 MHz)

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14
Q

Ultrasound has frequencies higher than ______.

A

20,000 Hz (20 MHz)

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15
Q

Frequency and period have an ________ and _______ relationship.

A

Inverse; reciprocal

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16
Q

Period x frequency = ?

A

1

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17
Q

What are the bigness parameters?

A

Amplitude, Power, Intensity

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18
Q

What do the bigness parameters describe?

A

The size, magnitude, or strength of sound waves

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19
Q

What is amplitude?

A

The difference between the maximum/minimum value and the average of an acoustic variable

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20
Q

What are the units for amplitude?

A

any of the acoustic variable units (Pa, g/cm^3, cm)

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21
Q

What are the typical values of amplitude?

A

1 million pascals - 3 million pascals
1MPa - 3 MPa

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22
Q

What is amplitude determined by?

A

the sound source

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23
Q

What is amplitude determined by?

A

the sound source and eventually the medium

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24
Q

Can amplitude be adjusted by the sonographer?

A

Yes

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25
Q

Define power

A

the rate of energy transfer

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26
Q

What are the units of power?

A

watts

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27
Q

What are the typical values of power?

A

0.004 - 0.090 watts
4 - 90 milliwatts

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28
Q

What is power determined by?

A

sound source

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29
Q

Is power adjustable by the sonographer?

A

Yes

30
Q

Amplitude and power have a _______ relationship

A

direct

31
Q

Power is proportional to amplitude ______.

A

squared

32
Q

If amplitude was increased by a factor of 3, the power would be increased by a factor of?

A

9 (3 x 3)

33
Q

If the amplitude is decreased by a factor of 1/2, the power is decreased by a factor of?

A

1/4 (1/2 x 1/2)

34
Q

Define intensity

A

The concentration of energy in a sound beam

35
Q

What are the units of intensity?

A

watts/cm^2

36
Q

What are the units of intensity?

A

watts/cm^2

37
Q

What are the typical values of intensity?

A

0.01 - 300 W/cm^2

38
Q

What are the typical values of intensity?

A

0.01 - 300 W/cm^2

39
Q

What is intensity determined by?

A

The sound source

40
Q

Is intensity adjustable by the sonographer?

A

Yes (b-mode or TGCs)

41
Q

Intensity is ______ to power

A

Proportional

42
Q

When a waves power doubles, intensity will _____.

A

double

43
Q

Intensity is proportional to amplitude ______.

A

squared

44
Q

When a wave’s amplitude is increased by a factor of 2, the intensity is increased by ______.

A

4

45
Q

Define wavelength

A

the distance or length of one complete cycle

46
Q

What are the units of wavelength?

A

mm, cm, m

47
Q

What are the typical values of wavelength?

A

0.1 - 0.8 mm (in soft tissue)

48
Q

What is the wavelength determined by?

A

the source and medium

49
Q

Which is the only parameter determined by both the source and medium?

A

wavelength

50
Q

Is the wavelength adjustable by the sonographer?

A

no

51
Q

Wavelength and frequency have an _______ relationship.

A

inverse

52
Q

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

A

1.54 mm

53
Q

Propagation speed in soft tissue is?

A

1,540 m/s, 1.54 km/s, 1.54 mm/microsec

54
Q

True or False: A sound wave with a short wavelength and a high frequency produce high quality images

A

True

55
Q

Define Propagation speed

A

The rate at which a sound wave travels through a medium

56
Q

What are the units of propagation speed?

A

m/s, mm/ms

57
Q

What are the typical values of propagation speed?

A

1.54 mm/microsec
range: 500 m/s - 4000 m/s

58
Q

Propagation speed is determined by?

A

the medium only

59
Q

Is propagation speed adjustable by the sonographer?

A

No

60
Q

When does propagation speed change?

A

Only when going from one medium to the next

61
Q

What is the speed of sound in air?

A

330 m/s

62
Q

What is the speed of sound in metals?

A

2,000 - 7,000 m/s

63
Q

What two characteristics of the medium affect speed?

A

stiffness, density

64
Q

Define stiffness?

A

The ability of an object to resist compression

65
Q

Stiffness is also called?

A

bulk modulus

66
Q

Stiffness and speed have a _______ relationship

A

direct

67
Q

What is the opposite of stiff?

A

Elasticity or compressibility

68
Q

What is density?

A

the relative weight of a material

69
Q

Density and speed are ______ related.

A

inversely

70
Q

What is the formula for frequency?

A

prop. speed / wavelength

71
Q

What is the formula for wavelength?

A

prop. speed / frequency

72
Q

What is the formula for prop. speed?

A

wavelength x frequency

Basic Ultrasound Physics (6 decks)

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