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CMI 350 > Ch.3 Describing Sound Waves > Flashcards

Ch.3 Describing Sound Waves Flashcards

1
Q

What are the seven parameters that describe sound waves?

A

Period
Frequency
Amplitude
Power
Intensity
Wavelength
Propagation Speed

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2
Q

Period

A

is the time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle

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3
Q

Period:
Units
Typical values

A

units of time
microseconds (us),
0.06 to 0.5 us

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4
Q

Period:
Determined by
Adjustable

A

Sound Source ONLY
NOT medium
No

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5
Q

Frequency

A

is the number of particular events that occur in a specific duration of time

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6
Q

Frequency:
Units
Typical Values

A

units of per second
(1/sec, hertz, Hz)
(1 cycle/second = Hertz)
Approx. 2MHz to 15 MHz

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7
Q

Frequency:
Determined by
Adjustable

A

Sound Source ONLY
No

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8
Q

Sound Wave Spectrum:
Infrasound (infrasonic)

A

Less than 20 Hz
(NOT Audible)

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9
Q

Sound Wave Spectrum:
Audible Sound

A

Between 20 Hz and 20 kHz

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10
Q

Sound Wave Spectrum:
Ultrasound (ultrasonic)

A

Greater than 20 kHz
(Greater than 20,000 Hz)
(In audible to humans)

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11
Q

What is the relationship between frequency and period?

A

are inversely related
(Reciprocal = 1/f )
if one remains constant that the other remains the unchanged

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12
Q

What are the three bigness parameters?

A

Amplitude
Power
Intensity

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13
Q

Amplitude

A

is the “bigness” of a wave. It is the difference between the maximum value and the average or undisturbed values of an acoustic variable

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14
Q

Amplitude:
Units
Typical Values

A

any units from the acoustic variable
pascals
density
cm, inches
decibels (dB)
1 million pascals (MPa)
to 3 MPa

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15
Q

Amplitude:
Determined by
Adjustable

A

Sound Source only
Yes, a control on the system allows the sonographer to alter initial amplitude of a wave

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16
Q

What is the difference between amplitude and peak-to-peak amplitude?

A

Amplitude: is measured from the baseline to the maximum value or minimum value
Peak-to-Peak: is difference between maximum and minimum value of an acoustic variable. (Twice the value of the amplitude)

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17
Q

Power

A

is the rate of energy transfer or the rate at which work is performed

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18
Q

Power:
Units
Typical value

A

watts
0.004 to 0.090 watts
(4 to 90 milliwatts)

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19
Q

Power
Determined by
Adjustable

A

Sound Source ONLY
Yes, initial power like amp can be changed

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20
Q

Power decreases as _____ propagates through the body.

The rate at which power decreases as sound propagates depends on the characteristics of the _____ and the _____ .

A

sound
amplitude and wave

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21
Q

How are amplitude and power related?

A

power is proportional to the wave’s amplitude squared

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22
Q

If a sonographer increases the amplitude of a wave by a factor of 3. How has the power changed?

A

3 x 3 = 9
power increased by 9

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23
Q

If a sonographer decreases the amplitude of a wave to 1/2 of its original value, how has the power changed?

A

1/2 x 1/2 = 1/4
power decreases to 1/4th or 25% of its original value

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24
Q

Intensity

A

is the concentration of energy in a sound beam.
to calculate divide the beam’s power by the beam’s cross-sectional area.
relates to how the power in a wave spreads or is distributed in space
-depends on power and area

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25
Q

Intensity:
Units
Typical Values

A

Watts/square centimeter
W/cm^2
0.01 to 300 W/cm^2

26
Q

Intensity:
Determined by
Adjustable

A

Sound Source ONLY
(intensity changes as sound propagates thru body)
Yes allowed to alter the initial intensity of a wave

27
Q

The rate at which intensity changes as sound propagates depends on the characteristics of both the _____ and the ______

A

sound wave
medium

28
Q

How is intensity related to power?

A

proportional to power

29
Q

How is intensity and amplitude related?

A

proportional to the wave’s amplitude squared

30
Q

Wavelength
units

A

is the distance or length of one complete cycle
mm, meters, or other unit of length

31
Q

Wavelength:
Typical Values
Determined by
Adjustable

A

0.1 to 0.8 mm
By BOTH source and medium (only parameter)
NO

32
Q

What is the difference between wavelength and period?

A

Wavelength refers to the length or distance of a single cycle
Period refers to the time that it takes to complete a single cycle

33
Q

What is the relationship between wavelength and frequency?

A

As long as a wave remains in one medium, wavelength and frequency are inversely related

34
Q

As frequency increases , wavelength ________ .
The lower the frequency, the _____ the wavelength.

A

decreases
longer

35
Q

What is the wavelength of 1 MHz sound in soft tissue?

A

Has a wavelength of 1.54 mm

36
Q

If sound has a frequency of 2 MHz, which is the wavelength in soft tissue?

A

1.54 mm / 2
= 0.77 mm

37
Q

Why is wavelength important in diagnostic ultrasound?

A

Wavelength plays an important role in image quality
-Shorter wavelengths are created by high frequency sound, which usually produces higher quality images with great detail

38
Q

Propagation Speed
units

A

is the rate at which a sound wave travels through a medium
-meters per second
-mm/us

39
Q

Propagation Speed:
Typical Values
Determined by
Adjustable

A

500 m/s to 4000 m/s
depending on the tissue
Medium ONLY
NO (Speed changes only when the wave travels from one medium to a different medium

40
Q

What is the speed of sound in soft tissue?

A

1,540 m/s
(1.54 mm/us)

41
Q

Sound travels fastest in what materials?

A

Solids
Liquids
Gases (slowest)

42
Q

What is the formula for the speed of sound in other media?

A

Speed (m/s) = frequency (Hz) x wavelength (m)

43
Q

What characteristics of a medium determine the speed of sound in that medium?

A

Stiffness and Density

44
Q

Stiffness

A

describes the ability of an object to resist compression
-retain its shape

45
Q

Density

A

describes the relative weight of a material.

46
Q

How does stiffness affect speed?

A

Stiffness and speed are directly related
-As materials become stiffer, the speed of sound in the material increases

47
Q

How does density affect speed?

A

Density and speed are inversely related
-As materials become more dense (heavier), the speed of sound decreases

48
Q

If two media are equally stiff, the dense medium will have a _____ speed.

A

lower

49
Q

Stiffness increases, Speed ____

A

Increases

50
Q

Density increases, speed _____

A

Decreases

51
Q

Materials that are stiff but not dense will have the ____ speed.

A

fastest
Ex: Bone

52
Q

Materials that are not stiff and very dense will have the ________ speed.

A

slowest

53
Q

Although both stiffness and density affect propagation speed, _______ has the greatest influence on speed

A

Stiffness
Ex: Air has an exceedingly low stiffness, so sound travels slowly in it.

54
Q

Period:
Adjustable
Units
Determined by
Typical value

A

NOT adjustable
seconds, us
source
0.06 to 0.5 us

55
Q

Frequency:
Adjustable
Units
Determined by
Typical Value

A

NOT adjustable
per second, Hz
source
2 to 15 MHz

56
Q

Amplitude:
Adjustable
Units
Determined by
Typical Value

A

Yes adjustable
pascals, cm, g/cm^3, dB
source
1 MPa to MPa

57
Q

Power:
Adjustable
Units
Determined by
Typical value

A

Yes adjustable
Watts, dB
Source
4 to 90 mW

58
Q

Intensity:
Adjustable
Units
Determined by
Typical value

A

Yes adjustable
Watts/cm^2, dB
Source
0.01 to 300 W/cm^2

59
Q

Wavelength:
Adjustable
Units
Determined by
Typical value

A

NOT adjustable
mm, distance
BOTH source & medium
0.1 to 0.8 mm

60
Q

Speed:
Adjustable
Units
Determined by
Typical value

A

NOT adjustable
m/s
medium
1,500 to 1,600 m/s

61
Q

What three parameters can be adjusted by the sonographer?

A

Amplitude
Power
Intensity

CMI 350 (11 decks)

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