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MIDS 139 (Core Exam) > Ch 2a Sound Wave Principles > Flashcards

Ch 2a Sound Wave Principles Flashcards

1
Q

Is sound a traveling variation of acoustic variables?

A

Yes!

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2
Q

What are compressions?

A

Areas of high pressure + density

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3
Q

What are rarefactions?

A

Areas of low pressure + density

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4
Q

Differentiate b/w a mechanical + electromagnetic wave?

A

Mechanical: requires a medium to transport energy
(ex. sound waves are longitudinal mechanical waves)

Electromagnetic: can transfer energy through empty space or a medium

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5
Q

What are acoustic variables? List them all.

A

Quantities that vary in a sound wave:

-Pressure
-Density
-Particle motion
-Temperature

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6
Q

Do sound waves require a medium to travel through?

A

Yes!

(sound waves are longitudinal mechanical waves - meaning they travel parallel to wave motion + require a medium)

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7
Q

Differentiate b/w TRV (shear) waves + longitudinal waves?

A

TRV: particle motion is perpendicular to wave motion (ex. water ripples)

Long: particle motion is parallel to wave motion (ex. sound, u/s)

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8
Q

List 6 sound wave terms?

A

-Frequency (# cycles per sec)
-Period (time for 1 cycle to occur)
-Wavelength (length 1 cycle takes up)
-Propagation speed (speed wave moves through medium)
-Amplitude (how loud)
-Intensity (rate energy passes through area)

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9
Q

What is frequency?

A

-How often something happens
-# of cycles per second

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10
Q

What is a cycle?

A

1 complete variation in pressure or acoustic variable

(1 Hz = 1 cycle per sec)

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11
Q

How many Hz are in 1 kHz + 1 mHz?

A

1 kHz = 1000 Hz
1 mHz = 1,000,000 Hz

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12
Q

How many Hz is u/s?

A

> 20,000 Hz (20kHz)

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13
Q

How many Hz is human hearing?

A

20-20,000 Hz

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14
Q

U/s ranges b/w how many mHz for most applications?

A

B/w 2-20 mHz

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15
Q

What is the period?

A

Time it takes for 1 cycle to occur

(in microseconds)

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16
Q

What is wavelength?

A

Length of space 1 cycle takes up

(in mm)

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17
Q

What is propagation speed?

A

-Speed at which a wave moves through a medium
-Determined by stiffness of the medium

(in m/s or mm/microsec)

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18
Q

The average propagation speed in soft tissue is what?

A

1540 m/s (1.54 mm/microsec)

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19
Q

How would the propagation speed be in gases, liquids + solids?

A

Gases: lowest
Liquids: middle
Solids: highest

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20
Q

Do soft or stiff media have higher sound speeds?

A

Stiff media

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21
Q

What is bulk modulus?

A

The measure of how resistant a material (solid or fluid) is to compression

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22
Q

Mediums that are more stiff (ex. bone) will contribute higher or lower propagation speeds?

A

Higher

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23
Q

Mediums that have low stiffness (ex. liquid) will contribute higher or lower propagation speeds?

A

Lower

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24
Q

Is pulsed u/s continuously on?

A

No - a pulse is a few cycles of u/s that gets separated in time with gaps of no u/s (ringing + listening period)

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25
Q

Explain what the ringing + listening period is with pulsed u/s?

A

Ringing (transmission): periods of pulses of sound

Listening (receiving): gaps of no u/s

(1 scan line = 1 pulse transmitted/ringing + received/listening)

26
Q

Describe PRF, PRP, pulse duration, duty factor, spatial pulse length + bandwidth?

A

PRF: # of pulses occurring in 1 sec
PRP: time from start of 1 pulse to start of next
PD: actual time pulse is on
DF: fraction of time that pulsed u/s is on
SPL: length of space occupied by a pulse
Bandwidth: range of frequencies contained within a pulse

27
Q

If PRF decreases, what happens to the PRP?

A

It increases

(inversely proportionate: PRF = 1/PRP)

28
Q

Can PRF + PRP be adjusted by the sonographer?

A

Yes - by changing depth

29
Q

Does a shallow image have a high or low PRF?

A

High PRF

30
Q

Does a deep image have a high or low PRF?

A

Low PRF

31
Q

If PRP increases, what happens to the imaging depth?

A

It increases - more listening time

(proportionate)

32
Q

If PRP decreases, what happens to the imaging depth?

A

It decreases - less listening time

(proportionate)

33
Q

What 2 things control PRP?

A

-Depth
-Speed of sound in soft tissue

34
Q

Is PRP or PRF the ringing + listening time?

A

PRP

35
Q

Explain pulse duration?

A

-Time for pulse to occur + actual time pulse is ON
-Is the ringing (transmission) of pulse

36
Q

Explain the variables in the following formula: PD = n x T

A

PD: pulse duration
n: # of cycles in pulse
T: period

37
Q

U/s pulses are typically how many cycles long?

A

2 or 3 cycles long

(shorter pulses improve quality of images)

38
Q

Doppler pulses are typically how many cycles long?

A

5-30 cycles long

39
Q

Can PD be changed by the sonographer?

A

Nope

40
Q

List the pulse duration for B-mode imaging, 3D imaging, PW + CW doppler?

A

B-mode: 2-5 cycles
3D: 3-5 cycles
PW: 5-30 cycles
CW: non stop

41
Q

What is the typical duty factor for sonography + for doppler u/s?

A

Sono: 0.1-1%
Doppler: 0.5-5%

42
Q

Does duty factor have a unit?

A

No, unitless

43
Q

SPL increases when what increases?

A

Number of cycles in a pulse increases

44
Q

SPL decreases when what increases?

A

Frequency

(inversely related)

45
Q

Do shorter or longer pulses create higher image quality?

A

Shorter

46
Q

As frequency increases what happens to the wavelength, penetration + spatial resolution?

A

Wavelength: decreases
Penetration: decreases
Resolution: increases

Higher frequency = shorter wavelength = less penetration

47
Q

As frequency decreases what happens to the wavelength, penetration + spatial resolution?

A

Wavelength: increases
Penetration: increases
Resolution: decreases

Lower frequency = longer wavelength = greater penetration

48
Q

What is frequency?

A

Number of cycles in a wave per second

49
Q

Do pulsed u/s gaps exist b/w pulses with CW or PW doppler?

A

PW - meaning there are cycles missing

50
Q

The shorter the pulse, the broader or smaller the bandwidth?

A

Broader

51
Q

Amplitude + intensity are indicators of what?

A

The strength of the sound

52
Q

Define amplitude, power + intensity of sound in simple terms?

A

Amplitude: how loud (represented by the height of the wave)
Power: time required to transfer energy
Intensity: rate that energy passes through a unit area

53
Q

What is amplitude?

A

-Max variation that occurs in an acoustic variable (pressure, density, particle motion, temp)

-How much the acoustic variable changes as the sound wave travels through a medium

54
Q

Amplitude of a pulse is determined by what?

A

How hard the crystals of the probe are struck

(displayed as a % or in dB)

55
Q

What is power?

A

The rate of energy transfer over time from 1 location to another (energy that travels along the u/s beam)

56
Q

Other terms for amplitude?

A

-Transmit voltage
-Output power (shown on our u/s machines)

57
Q

If the amplitude is doubled, what will happen to the power?

A

Quadrupled

(power is 2x amplitude)

58
Q

How can we change beam intensity?

A

By changing our focus

59
Q

If amplitude is halved, what happens to the intensity?

A

It decreases by a factor of 4

60
Q

If amplitude is doubled + power is quadrupled, what happens to intensity?

A

It is also quadrupled

MIDS 139 (Core Exam) (16 decks)

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