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Physics > Test 1 > Flashcards

Test 1 Flashcards

1
Q

Define sound

A

Sound is a travelling pressure / density variation

Compressions and rarefactions

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2
Q

What are acoustic variables? Give examples

A

Quantities that vary in a sound wave

  1. Pressure
  2. Density
  3. Particle motion/vibration
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3
Q

Compression

A

Regions of high pressure / density

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4
Q

Rarefaction

A

Regions of low pressure / density

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5
Q

Longitudinal wave

A

Vibration parallel to direction of wave

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6
Q

Frequency

A

Cycles per second
Hz
KHz
MHz

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7
Q

Audible sound

A

20Hz - 20 KHz

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8
Q

Ultrasound range

A

20 KHz - 160 KHz

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9
Q

Period

A

Seconds per cycle

Unit: us (microsecond)

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10
Q

Wavelength

A

Cycle length

Unit: mm

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11
Q

Acoustic velocity /

Prop speed

A

The speed at which a wave moves through a medium

Unit:
m/s
mm/us

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12
Q

Propagation speed is dependent on

A

The medium through which the wave travels

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13
Q

Wavelength formula

A

Lambda = c/f

c= mm/us
f= MHz
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14
Q

Propagation speed units

A

mm/us

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15
Q

What is stiffness

A

Resistance of a material to compression

AKA Bulk modulus (B)

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16
Q

Propagation speed formula

A

Square root of :

Bulk modulus (N/m^2)
/
Density (kg/m^3)

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17
Q

Propagation speed through solid liquid gas - what is the order

A

Solid is highest

Gas is lowest

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18
Q

Acoustic velocity in soft tissue

A

1540 m/s

1.54 mm/us

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19
Q

Propagation speed in:
bone
Fat

A

Bone: 3-5 times higher
Fat: slightly lower than ST

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20
Q

Compressibility and elasticity are related how?

How are they related to stiffness

A

They represent the same thing. Both inversely related to stiffness

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21
Q

Stiffness is ____ to propagation speed

A

Directly related to

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22
Q

How is stiffness related to bulk modulus

A

Directly proportional

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23
Q

Describe pulse echo technique in the use of ultrasound

A

Pulse separated by a gap because ultrasound needs to receive and process the information

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24
Q

Describe harmonics production

A

You send out one frequency, and you get back several higher frequencies.
Therefore harmonics allows us to achieve higher frequency waves and which allows for better image quality

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25
Q

Continuous wave

A

Sinusodal waveform where cycles repeat indefinitely

26
Q

Pulse repetition frequency

A

Number of pulses per second

Unit: KHz

27
Q

What does PRF depend on?

A

Pulse repetition frequency depends on the instrument

28
Q

Pulse repetition period

A

Time from beginning of one pulse to beginning of next

Unit: ms

29
Q

If PRF increases, what happens to PRP

A

Inversely proportional, so PRP decreases

30
Q

What is pulse duration and it’s unit

A

Time for one pulse to occur

Unit: us

31
Q

Typical numbers of cycles in an ultrasound pulse

A

2-3 cycles long

32
Q

Typical number of cycles in a Doppler pulse

A

5-30 pulses

33
Q

If frequency increases, what happens to PD? Why?

A

Frequency increases
Period decreases because inversely proportional
Therefore pulse duration decreases because period and PD are directly proportional :

PD = n x T

34
Q

PD units

A

us (because T is us)

35
Q

What is the advantage of shorter PD?

A

Improves the quality of images

36
Q

What is DF? It’s unit? It’s equation?

A

Fraction of time the pulsed ultrasound is ON

Unit is a decimal or %

DF = PD (us) / PRP (us)

37
Q

If pulse duration increases what happens to DF?

A

Increases because the sound is on more % of the time

DF = PD (us) / PRP (us)

38
Q

What is SPL? Unit? Significance?

A

SPL is the length of the pulse
Unit: mm

SPL(mm) = n x wavelength (mm)

39
Q

If frequency increases, what happens to SPL?

A

Frequency increases therefore wavelength decreases (because wavelength is inversely proportionate). So if wavelength decreases SPL decreases

40
Q

Anechoic

A

Without internal echoes

41
Q

Echogenic

A

With internal echoes

42
Q

Heterogeneous

A

Not smooth

43
Q

Homogeneous

A

Smooth

44
Q

Hyperechoic

A

Brighter echoes than surrounding tissue

45
Q

Hypoechoic

A

Darker echoes than surrounding tissues

46
Q

Isoechoic

A

Similar echoes to surrounding tissues

47
Q

Grey scale US

A

Pulse-echo technique

48
Q

Doppler US

A

Pulse-echo + Doppler effect

49
Q

Bandwidth

A

Range of frequencies produced by a transducer

50
Q

Bandwidth is seen only in

A

Pulsed ultrasound

51
Q

What happens to bandwidth with a shorter pulse?

A

Larger bandwidth
Thus lower Q factor

All of these improve image quality

52
Q

What is the range of fractional bandwidth in most transducers

A

50-100%

53
Q

What happens to quality factor if fractional bandwidth goes down

A

It increases

54
Q

Amplitude is

A

The strength of a sound wave

Unit: pressure (N/m^2) or voltage

55
Q

Power is

A

The rate at which energy is transferred

Unit: W or mW

56
Q

Intensity is

A

The rate at which energy passes through a unit area
Unit:
mW/cm^2
Power/area

57
Q

What is the relationship between intensity and amplitude

A 
I = Amp^2
Amp = 1/I^2
58
Q

What is the relationship between power and amplitude

A 
P = Amp^2
Amp = 1/P^2
59
Q

Waves

A

Transfer energy from one location to another

Cyclical

60
Q

Amplitude units

A

Pressure - N/m2
Density - kg/m^3
Voltage - V

61
Q

Nonlinear propagation

A

Propagation in which speed depEnds on pressure and the shape of the wave changes

Physics (9 decks)

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