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Ultrasound Physics > Sound We Don’t Hear Pt.1 > Flashcards

Sound We Don’t Hear Pt.1 Flashcards

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1
Q

Frequency

A

number of cycles in a wave in 1 sec

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2
Q

Rarefactions

A

Low pressure and low density

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3
Q

Compressions

A

High pressure and high density

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4
Q

Longitudinal wave

A

compressional wave with back and forth particle motion that is parallel to the direction of wave travel

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5
Q

Acoustic variables

A

Pressure
Density
Particle motion

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6
Q

Frequency units

A

Hz
kHz
MHz

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7
Q

Infrasound

A

Less than 20 Hz
Too low for human hearing

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8
Q

Ultrasound

A

20,000Hz or higher

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9
Q

Human hearing

A

20-20,000Hz

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10
Q

Period (T)

A

Time it takes for one cycle to occur

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11
Q

Duty factor

A

percentage of time that pulsed ultrasound is on

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12
Q

The relationship between period and frequency

A

Period decreases and frequency increases

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13
Q

Wavelength (cycle length)

A

the length of space one cycle takes up from front to back

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14
Q

Propagation speed (c)

A

The speed a wave moves through a medium

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15
Q

What does wavelength depend on?

A

It depends on frequency and propagation speed.

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16
Q

Detailed resolution improves with…

A

Increasing frequency because the wavelength decreases

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17
Q

Propagation speed is determined by…

A

Stiffness of the medium

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18
Q

Stiffness

A

Resistance of a material to compression

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19
Q

Propagation speeds are highest in..

A

Solids

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20
Q

Propagation speed is lowest in..

A

Gases

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21
Q

Harmonics

A

Frequencies that are even and odd multiples of the fundamental frequency.

Continuous wave

Nonlinear propagation

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22
Q

Nonlinear propagation

A

Higher pressure portions of the wave travel faster than lower pressure portions

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23
Q

Average longitudinal propagation speed in soft tissues

A

1540 m/s

24
Q

Fundamental frequency

A

Original frequency

25
Q

Continuous wave

A

Cycles repeat indefinitely

26
Q

Pulsed ultrasound

A

Pulses separated by gaps in time

27
Q

Pulses

A

a few cycles that travel together, separated by gaps in time

28
Q

2 components of pulsed US

A

Transmit time (send,on)
Receive time (listening, off)

29
Q

Pulse Repetition Frequency (PRF)

A

number of pulses that occur in 1 sec

30
Q

Pulse Repetition Period (PRP)

A

the time from the beginning of one pulse to the beginning of the next

Includes pulse duration and listening time

31
Q

The PRP ____ while PRF increases. Why?

A

decreases. When more pulses occur in a second, the time between them decreases.

32
Q

Pulse duration

A

the time it takes for one pulse to occur 

33
Q

How does the number of cycles and frequency affect pulse duration?

A

Pulse duration decreases when number of cycles in a pulse is decreased or if the frequency is increased (reducing T)

34
Q

Which pulse durations improve image quality?

A

Shorter

35
Q

What affects the duty factor?

A

Longer pulses increase DF because the sound is on more of the time.

36
Q

What increases DF? Why?

A

Higher PRFs because there is less listening time between pulses

37
Q

What happens when DF increases?

A

Pulse duration increases

38
Q

What happens when PRF increases?

A

PRP decreases and DF increases

39
Q

What happens when wavelength decreases?

A

Frequency increases

40
Q

What happens when frequency is increased?

A

Period is decreased, reducing pulse duration

41
Q

Spatial pulse length

A

the length of a pulse from front to back

42
Q

What increases spatial pulse length?

A

wavelength and the number of cycles in a pulse

43
Q

With SPL what improves resolution?

A

Shorter pulse lengths

44
Q

Bandwith

A

a range of frequencies

45
Q

Which bandwidth has a large range of frequencies?

A

Broad

46
Q

Which pulses have a broad bandwidth?

A

Short pulses

47
Q

Fractional bandwidth

A

bandwidth divided by operational frequency

48
Q

Wavelength is the length of ____ over which one cycle occurs.

A

space

49
Q

The ___ and ___ of a medium determine propagation speed.

A

density, stiffness

50
Q

Propagation speed increases if ____ is increased.

A

stiffness

51
Q

Classifications of matter in order of increasing sound propagation speed

A

gas, liquid, solid

52
Q

Wavelength in soft tissues ___ while frequency increases.

A

decreases

53
Q

Propagation speed in bone is ____ that in soft tissues.

A

higher than

54
Q

Sound travels faster in ____.

A

solids

55
Q

Solids have higher propagation speeds than liquids because they have greater _____.

A

stiffness

56
Q

Sound travels most slowly in _____.

A

gases

57
Q

Sound is a ______ _______ wave.

A

mechanical longitudinal

Ultrasound Physics (2 decks)

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