Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Vascular 1 > Essentials of ultrasound physics > Flashcards

Essentials of ultrasound physics Flashcards

1
Q

What is acoustic pressure and its units?

A

Quantification of the strength of the wave
- units = Pascals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What determines speed of sound through a material?

A

c = Sqrt(K / p)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the difference between characteristic impedance and acoustic impedance?

A

They are practically the same

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the units for acoustic impedance?

A

Pressure per velocity per area
(or rayls)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is acoustic impedance and its equation?

A

The acoustic pressure divided by the resultant particle velocity
Z = pc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is Snell’s law?

A

The law for angle of refraction of an ultrasound beam

sin(theta2) / sin(theta1) = c2 / c1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What two conditions are required for refraction?

A
  1. Must be an incident angle between transducer and interface
  2. Must be 2 materials with different c
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the difference between specular and diffuse reflection?

A

Diffuse = all directions
Specular = one direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are Rayleigh scatterers?

A

Scatterers that are much smaller than the wavelength of sound
- scatter sound in all directions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the 3dB rule?

A

Whenever intensity changes by 3dB this corresponds to a doubling of the intensity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the two sources of attenuation in the body?

A
  1. Reflection and scatter at interfaces
  2. Absorption (conversion to heat)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is attenuation of ultrasound in tissue measured?

A

dB / cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the purpose of the backing layer?

A

Allows shorter pulse duration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the equation for pulse duration and frequency?

A

PD = n / f
n = No. of cycles
f = frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are both the near field length and the far field spread dependent on?

A

The transducer aperture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the interference of 2 waves 180 degrees apart?

A

Destructive - will cancel if they are the same sine wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are ultrasound transducer elements made of?

A

PZT (lead zirconate titanate)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How are PZT elements polarised?

A

They are heated above 365 degrees to allow particles to move.
A voltage is then applied across them and they are cooled with the voltage applied

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the main determinant of the resonant frequency of a PZT crystal?

A

The thickness of the element

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the purpose of backing material?

A

To provide damping needed for short pulses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are Huygen outlets?

A

An ultrasound transducer with a collection of point sources that fire coherently to produce a beam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is apodization?

A

Signal strength varies at different points on the transducer face - weaker at sides to reduce side lobe interference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Define focal zone?

A

The region over which the beam width is less than 2x the beam width at the focus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are the two main advantages of using arrays?

A
  1. Electronic beam steering
  2. Electronic focusing and beam forming
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How is electronic focusing achieved?

A

By exciting elements at different times - introducing delay

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What determines slice thickness for linear, curved or phased array transducers?

A

The fixed focal length lens attached to the entire array

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the duty factor?

A

The fraction of time the transducer actively transmits sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is demondulation?

A

When the receiver converts the amplified raw echo signal (pulses) into a single pulse spike

29
Q

What is persistence?

A

Signals for each pixel location are combined with previous signals from the same location

30
Q

What is the Doppler frequency?

A

fD = (2 v fT cos(theta)) / c

31
Q

What is a possible explanation of ISB?

A

Differences in Cos(theta) due to the difference in angle from the middle and edges of the transducer

32
Q

What are the 4 main pulsed doppler controls?

A
  1. Range gate position
  2. Gate or sample volume size
  3. Pulse duration
  4. Flow angle cursor
33
Q

How is a digital signal converted to a spectral waveform?

A

Fast Fourier Transform

34
Q

What can cause the filling of the spectral window?

A
  1. Turbulence
  2. Spectral broadening due to a wider range of doppler frequencies from the sample volume (wider range gate)
35
Q

How do you calculate pulsatility index?

A

PI = (PSV - EDV) / average

36
Q

How do you calculate resistive index?

A

RI = (max - min) / max

37
Q

When does aliasing occur?

A

When the PRF < two times the maximum frequency

38
Q

What is the Nyquist limit?

A

The condition when PRF = 2fD
- it defines the minimum sample rate for a signal before aliasing will occur

39
Q

What is the equation for maximum velocity detectable with pulsed Doppler?

A

Vmax = ( c * PRFmax) / 4f
- as frequency is on the bottom, lower frequencies will allow a higher vmax to be detected

40
Q

What does high PRF mode do?

A

Creates multiple range gates

41
Q

What is PRF the same as?

A

Scale

42
Q

What are colour packets?

A

The multiple pulse-echo signals that are required for colour flow imaging

43
Q

What is colour hue?

A

The attribute of colour that allows it to be classified as red, yellow, green, blue or an intermediate
- hue is associated with wavelength of light

44
Q

What is a pure hue?

A

A completely saturated colour with only 1 wavelength associated with it

45
Q

What causes a less saturated colour?

A

The presence of more white light
- white light is composed of many wavelengths

46
Q

What does the colour of power mode doppler depend on?

A

The strength of Doppler signal, number of reflecting moving targets

47
Q

What are advantages of Power doppler?

A
  1. It is less impacted by angular effects
  2. It has more sensitivity than standard colour imaging
  3. If aliasing is present it does not affect energy mode display
48
Q

What are disadvantages of power doppler?

A
  1. Image build up and image rates tend to be lower than colour
  2. There are greater amounts of flash artefact
49
Q

What is a specular reflector?

A

Reflection at a smooth surface

50
Q

What are diffuse reflectors?

A

Reflectors that scatter sound in all directions

51
Q

What are 3 main assumptions of an ultrasound scanner?

A
  1. Reflectors giving rise to echoes lie along the beam axis
  2. The speed of sound is constant
  3. The echo strength indicates echogenicity
52
Q

When can spectral mirroring occur?

A
  1. When gain is too high
  2. When Doppler beam approaches 90 degrees to the vessel axis
53
Q

How can beam width artefacts occur?

A
  1. Small objects are broadened - appear as lines
  2. Smearing of echo information
54
Q

In which direction is beam width widest?

A

Perpendicular to the image plane (in the slice thickness direction) has greater thickness than the image plane

55
Q

What is acoustic power?

A

The rate at which energy is transmitted from the transducer to the medium being scanned

56
Q

What is a hydrophone?

A

A device used to measure acoustic pressure and intensity

57
Q

How does intensity relate to pressure?

A

Intensity is proportional to square of pressure

58
Q

How do time average and pulse average intensities compare?

A

Pulse average are often much higher (1000x) than time average

59
Q

What is thermal index?

A

TI is the ratio of acoustic power produced by the transducer to the power required to raise the temperature in tissue by 1 degree.

60
Q

What does a TI value of 1 mean?

A

When the probe is stationary, it has the potential to raise tissue temperature by 1 degree

61
Q

What is cavitation?

A

The activity of tiny gas bubbles in tissue in the presence of ultrasound waves
- ultrasound can generate tiny bubbles from dissolved gas in fluid

62
Q

What is mechanical index?

A

The likelihood of a transducer causing cavitation

63
Q

What is MI proportional to?

A

The peak rarefactional pressure

64
Q

What is MI inversely proportional to?

A

The sqrt (f)
- if frequency increases, MI decreases

65
Q

What are the advantages of ultrasound safety indices?

A
  1. Standardization of output specification information between manufacturers
  2. Presentation of output quantities relevant to potential bioeffects from ultrasound
  3. Information is available for users to implement ALARA
66
Q

When can MI and TI be underestimated?

A

When a large fraction of the path between transducer and isonified region contains fluid e.g. bladder or amniotic fluid.

67
Q

What is the biological effect concerned with TI?

A

Heating, caused by absorption of energy from the ultrasound beam

68
Q

What are the two types of cavitation?

A
  1. Stable cavitation - creation of bubbles that oscillate with the ultrasound beam
  2. Transient (or inertial) cavitation - oscillations grow so strong that bubbles collapse - producing very intense, localised effects
69
Q

What are non-cavitation mechanical effects?

A

Bioeffects caused by particle displacements

Vascular 1 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions