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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
Explain what the ringing + listening period is with pulsed u/s?
Ringing (transmission): periods of pulses of sound Listening (receiving): gaps of no u/s (1 scan line = 1 pulse transmitted/ringing + received/listening)
26
Describe PRF, PRP, pulse duration, duty factor, spatial pulse length + bandwidth?
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
If PRF decreases, what happens to the PRP?
It increases (inversely proportionate: PRF = 1/PRP)
28
Can PRF + PRP be adjusted by the sonographer?
Yes - by changing depth
29
Does a shallow image have a high or low PRF?
High PRF
30
Does a deep image have a high or low PRF?
Low PRF
31
If PRP increases, what happens to the imaging depth?
It increases - more listening time (proportionate)
32
If PRP decreases, what happens to the imaging depth?
It decreases - less listening time (proportionate)
33
What 2 things control PRP?
-Depth -Speed of sound in soft tissue
34
Is PRP or PRF the ringing + listening time?
PRP
35
Explain pulse duration?
-Time for pulse to occur + actual time pulse is ON -Is the ringing (transmission) of pulse
36
Explain the variables in the following formula: PD = n x T
PD: pulse duration n: # of cycles in pulse T: period
37
U/s pulses are typically how many cycles long?
2 or 3 cycles long (shorter pulses improve quality of images)
38
Doppler pulses are typically how many cycles long?
5-30 cycles long
39
Can PD be changed by the sonographer?
Nope
40
List the pulse duration for B-mode imaging, 3D imaging, PW + CW doppler?
B-mode: 2-5 cycles 3D: 3-5 cycles PW: 5-30 cycles CW: non stop
41
What is the typical duty factor for sonography + for doppler u/s?
Sono: 0.1-1% Doppler: 0.5-5%
42
Does duty factor have a unit?
No, unitless
43
SPL increases when what increases?
Number of cycles in a pulse increases
44
SPL decreases when what increases?
Frequency (inversely related)
45
Do shorter or longer pulses create higher image quality?
Shorter
46
As frequency increases what happens to the wavelength, penetration + spatial resolution?
Wavelength: decreases Penetration: decreases Resolution: increases Higher frequency = shorter wavelength = less penetration
47
As frequency decreases what happens to the wavelength, penetration + spatial resolution?
Wavelength: increases Penetration: increases Resolution: decreases Lower frequency = longer wavelength = greater penetration
48
What is frequency?
Number of cycles in a wave per second
49
Do pulsed u/s gaps exist b/w pulses with CW or PW doppler?
PW - meaning there are cycles missing
50
The shorter the pulse, the broader or smaller the bandwidth?
Broader
51
Amplitude + intensity are indicators of what?
The strength of the sound
52
Define amplitude, power + intensity of sound in simple terms?
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
What is amplitude?
-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
Amplitude of a pulse is determined by what?
How hard the crystals of the probe are struck (displayed as a % or in dB)
55
What is power?
The rate of energy transfer over time from 1 location to another (energy that travels along the u/s beam)
56
Other terms for amplitude?
-Transmit voltage -Output power (shown on our u/s machines)
57
If the amplitude is doubled, what will happen to the power?
Quadrupled (power is 2x amplitude)
58
How can we change beam intensity?
By changing our focus
59
If amplitude is halved, what happens to the intensity?
It decreases by a factor of 4
60
If amplitude is doubled + power is quadrupled, what happens to intensity?
It is also quadrupled

MIDS 139 (Core Exam) (16 decks)

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