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PTE Masters + A Practical Approach to Transesophageal Echocardiography > Physics of Ultrasound 1-4 > Flashcards

Physics of Ultrasound 1-4 Flashcards

1
Q

What is A mode?

A

Amplitude Mode

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2
Q

What is B-Mode?

A

Brightness Mode

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3
Q

What is M-Mode?

A

Motion Mode

(B-Mode vs. Time)

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4
Q

Which ultrasound mode has the best temporal resolution?

A

M-Mode

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5
Q

What correlates to the strength of the echo on ultrasound?

A

Brightness of the image

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6
Q

When you look at an M-mode example, what do you see on the:
X-axis?

Y-axis?

A

X-axis = Time

Y-axis = Depth

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7
Q

What is seen in this M-Mode clip?

A

Early closure of the aortic leaflets

HOCM

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8
Q

Draw an EKG comparing Systole and Diastole

A
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9
Q

Draw what you would expect a normal Aortic Valve Appears like in M-mode in AV LAX.

A

See image

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10
Q

Draw what you would expect a bicuspid Aortic Valve Appears like in M-mode in AV LAX.

A

See image

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11
Q

What is the period in terms of ultrasounds?

A

Time it takes to complete a single cycle

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12
Q

What is frequency?

A

Number of cycles per second

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13
Q

What is the pulse duration?

A

Time to complete a single pulse

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14
Q

What is the pulse repetition period?

A

Time is takes to go from pulse to pulse

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15
Q

What is the pulse repetition frequency?

A

Inverse of Pulse repetition period

OR

Number of pulses per second

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16
Q

What is 1/2 of the Pulse Repetition Frequency?

A

Nyquist Limit

(Max doppler shift before aliasing occurs)

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17
Q

What is a spatial pulse length?

A

Length of a single pulse

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18
Q

What is a wavelength

A

Length (distance of one cycle)

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19
Q

What resolution correlates to spatial pulse length?

A

Axial Resolution

Axial resolution = 1/2 of the Spatial Pulse Length

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20
Q

What is amplitude?

A

Difference between the average acoustic variable and the peak acoustic max variable

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21
Q

What is Power?

A

Amount of Work per unit time

Measured in: Watts or (Joules / second)

Said another way…….

Rate of Energy transfer = Rate at which work is performed

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22
Q

What is intensity?

A

Power per unit area (Watts/cm2)

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23
Q

What resolution does the pulse repetition frequency determine?

A

Temporal Resolution

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24
Q

What sound property is important for bioeffects of ultrasound?

A

Intensity

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25
Q

What is spatial resolution?

A

Ability to discern the correct space (place) of a structure

Said another way….
Ability to accureately create images of small structures in their correct anatomic position

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26
Q

What are the three types of spatial resolution?

A
  1. Axial
  2. Lateral
  3. Elevational
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27
Q

Axial resolution is proportional to …?

A

Pulse Length

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28
Q

Lateral resolution is proportional to …?

A

Beam Width

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29
Q

Elevational resolution is proportional to …?

A

Beam Height

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30
Q

What is the equation for axial resolution?

A

Axial resolution = 1/2 of the Pulse Length

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31
Q

What is the relationship for higher frequency ultrasound for:

Spatial Pulse Length* and *Axial Resolution?

A

Higher Frequency = Shorter Spatial Pulse Length = Better Axial Resolution

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32
Q

What is Ultrasound in hertz?

A

>20,KHz

1 KHz = 1 Kilo Hertz = 1000 Hz

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33
Q

What does increasing frequency do to attenuation?

A

Increased frequency = Increased attenuation

As the ultrasound beam travels through the body it loses energy. The intensity and amplitude of the sound wave decreases, and this process is known as attenuation.

The amount of attenuation that occurs will depend on the type of tissue the sound wave is traveling through. Where the molecules of the tissue are densely packed (such as bone), attenuation will be much greater than in less densely packed tissue (such as fat). Different tissues have different attenuation coefficients depending on the amount of attenuation occurring in the beam of sound.

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34
Q

How does attenuation change with increasing depth

A

Decreases (See image)

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35
Q

What is temporal resolution?

A

Abiltiy to accurately determine the position of a structure at a particular instant in time

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36
Q

What is frame rate?

A

The number of framees/sec = # images /sec

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37
Q

How does the pulse repetition frequency correlate to frame rate?

A

Proportional (Directly)

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38
Q

What are the 4 acoustic variables of a sound wave?

A
  1. Pressure
  2. Density
  3. Temperature
  4. Distance
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39
Q

What are the 3 mechanisms for Bioeffects?

A
  1. Thermal Effects
  2. Cavitation
  3. Physical Vibration
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40
Q

What is maximal heating related to?

A

Spatial peak temporal average (SPTA) intensity

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41
Q

What temperature flux do we want to limit the U/S exposure to produce in local tissue temperature?

A

1 degree Celcius

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42
Q

What is the Maximum Spatial peak temporal average (SPTA) intensity for Unfocused beam?

A

<1 Watt / cm2

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43
Q

What is the Maximum Spatial peak temporal average (SPTA) intensity for Focused beam?

A

< 100 milli Watt/cm2 (0.1 Watts)

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44
Q

What is the mechanical index of an ultrasound?

A

Strength of Ultrasound beam and the ability of the beam to produce cavitation (Bursting of bubbles) of contrast material

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45
Q

What is the formula for mechanical index?

A

Peak negative pressure / (Frequency) 1/2

46
Q

What do high mechanical index ultrasound. beams cause?

A

Microbubbles of contrast materal to be compressed and expand significantly and to even burst (Cavitation)

47
Q

What does the shrinking and expanding of bubbles create?

A

New frequencies (Harmonic freqencies) different from the frequency of the original sound beam so the ultrasound transduce will receive echos containing the original frequency and the new harmonic frequency

48
Q

What two variables does the mechanical index depend on?

A
  1. Frequency
  2. Pressure
49
Q

How does the mechanical index changes given:

  1. Changes in frequency?
  2. Changes in pressure?
A

MI increases with lower frequency

MI increases with stronger (higher pressure variation)

50
Q

When are the strongest harmonic frequencies produced under ultrasound?

A

Mechanical Index (MI) of >1

51
Q

No harmonics are seen at what Mechanical index value?

A

MI < 0.1

Linear beahvior of bubble shrinking and expanding and this produces no harmonics but instead produces only backscatter

52
Q

What are the two types of harmonics?

A
  1. Tissue harmonics
  2. Contrast harmonics
53
Q

Tissue harmonics only exist at … (what)?

A

Deeper depths

Center main axis

54
Q

What is resonance in terms of harmonics?

A

Uneven shrinking and expanding of bubbles

55
Q

When you have a MI >1,

what is present?

A

Strong resonance and Cavitation (Lots of harmonics)

56
Q

When you have a MI 0.1 0 1

what is present?

A

Resonance (harmonics generated)

57
Q

When you have a MI < 0.1,

what is present?

A

No harmonics

58
Q

What is different from the Pulse Duation to Pulse Repetition Period?

A

Pulse Repititon Period = Pulse Duration + Listening time

59
Q

What is velocity of an ultrasound determined by?

A

Medium only

(Not the source)

60
Q

What are main properties of the medium that determine velocity of the medium?

A
  1. Stiffness
  2. Density
61
Q

How does stiffness of the medium affect velocity?

(Of ultrasound waves)

A

More stiff = higher velocity

62
Q

How does density of the medium affect velocity?

(Of ultrasound waves)

A

Increasing density = Decrease velocity

(

63
Q

Why do sound waves tend to travel faster in more dense materials?

*Tommy Burch describes this paradox*

A

Sound travels faster in higher density material because they are more stiff because stiffness differences among materials are usually larger than density differences

64
Q

What is the relationship between frequency and attenuation?

A

Frequency increases = Attenuation increases

65
Q

What is impedance?

A

Acoustic resistance to sound traveling through a medium

66
Q

What is the formula for acoustic impedance?

A

Z = P x V

Z = Acoustic Impedance

P = Density

V = Velocity

67
Q

What is acoustic impedance dependent on:

Source or Medium?

A

Medium Only

68
Q

What does a transducer do in its simplist definition?

A

Convert one from of energy to another

69
Q

What is the function of piezoelectric crystals?

A

Convert voltage to ultrasound

70
Q

What is the Curie Temperature?

A

Threshold temperature in which the piezoelectric crystals are dead

71
Q

What is the backing material on an ultrasound?

Function?

A

Backing material = Damping material = Deceases “ringing” of crytals

Function = Decreases spatial pulse length and improves axial resolution and decreases sensitivity to reflected echoes

72
Q

What is Q factor?

A

Unitless number that represents the ability of the machine to emit a “clean” pulse with a narrow beam length

73
Q

What is the formula for Q factor?

A

RF / Bandwidth

74
Q

Which transducers have a low QF?

Which transducers have a high QF?

A

Low QF (Imaging transducers) i.e. high bandwidth and short SPL

High QF (Therapeutic transducers)

75
Q

For continuous wave doppler, what is the frequency determined by?

A

Electrical frequency of the voltage

76
Q

For pulse wave doppler, what is the frequency determined by?

A

U/S System

Resonant Frequency

77
Q

What is the resonant frequency formula?

A

RF (Resonant Frequency) = V / 2T

V = Velocity

T = Thickness

78
Q

What is the bandwidth?

A

Difference between highest and lowest frequency pulse

79
Q

What phenomenon will increase your bandwidth?

A

Damping

80
Q

How does SPL correlate to bandwidth?

A

Shorter SPL = Higher BW

81
Q

How does QF relate to RF and Bandwidth?

A

QF = RF / Bandwidth

82
Q

What is the focus of an ultrasound beam?

A

Most narrow portion of an ultrasound sound beam

said another way

Focus = Location of the Minimum diameter of the beam

83
Q

What is the near field of a sound beam?

A

Space between near field and focus of a sound beam

84
Q

What is the far field of an ultrasound beam?

A

Space between far field and focus of a sound beam

85
Q

What is another name for the far field or far zone of the sound beam?

A

Fraunhofer Zone

86
Q

What is the formula for the near field length?

A

Ln = r2/wavelength

Ln = Near Field Length

r = Radius of the crystal

87
Q

What is another term for near field length?

A

Focal Length

88
Q

If you have a higher frequency, how will this affect the focal length?

A

Longer focal length

(Higher frequency = Lower wavelength)

89
Q

What are the three types of spatial resoluation?

A
  1. LARD - longitudinal, axial, radial, range, and depth resolution
  2. LATA - Lateral, Angular, Transverse and Azimuthal.
  3. Elevational
90
Q

What is the formula for axial resolution?

A

1/2 Spatial Pulse Length

91
Q

What is range resolution?

A

Descibes the ability to discern the specific depth (range ~ location) of a reflector (Describes pulsed U/S)

92
Q

What is the doppler equation?

A

Change in Frequency = v * cos(Angle) * 2Ftransmitted / C

Change in Frequency = Doppler shift

v = 1540 m/s

93
Q

What is fast fourier transform?

A

Current method of PW and CWD analysis

94
Q

What are the 5 functions of a receiver?

A
  1. Amplification
  2. Compensation
  3. Compression
  4. Demodulation
  5. Rejection
95
Q

What does amplification of the receiver do?

A

Enlargement of the returning signals

AKA
Receiver gain = Overall gain

96
Q

What does compensation do?

A

Makes all echos from similar structures appear with similar brightness

AKA
Time Gain Compensation

Depth Gain Compensation

Swept gain compensation

97
Q

What does compression do?

A

Reduces the total rnage of signals from smallest to largest

Dynamic range.= Range of signals that can be processed by the ultrasound machine

Compression decreases the dynamic range

98
Q

What is the function of demodulation?

A

Changes the shape of the electrical signal to make it recognizable by the image screen

99
Q

What are the 2 steps of demodulation?

A
  1. Rectification (Turn all negative voltages positive)
  2. Smoothing - smoothes out signals
100
Q

What is the purpose of rejection?

A

Low level signals are ignored (Noise)

101
Q

What are the other two names for rejection?

A
  1. Threshold
  2. Suppression
102
Q

What is the sound of speed in m/s?

A

1540 m/s

103
Q

What is the sound of speed in mm/microsecond?

A

1.54 mm/microsecond

104
Q

What are the two types of reverberation?

A

Ring down artifact

Comet Tail

Image shows Ring down and comet tail artifact

105
Q

What is seen at the green arrow?

A

Reverberation artifact

Comet Tail seen here

106
Q

Why can we not see the septal wall (Green arrows)?

A

Thick calcified mitral valve causes Acoustic Shadowing

107
Q

What is the formula for resonant frequency (RF) of a piezoelectric crystal?

A

RF = Velocity / (2*Thickness)

**Remember, the more thin the crystal, the higher the resonant frequency**

108
Q

Which of the following is associated with cavitation of microbubbles present in an ultrasound contrast agent?

A. High frequency ultrasound

B. Low pressure ultrasound

C. High mechanical index (MI) ultrasound

D. High velocity ultrasound

E. Low intensity ultrasound

A

High mechanical index (MI) ultrasound

Mechanical index is an indication of an ultrasound beam’s ability to cause cavitation-related bioeffects, and this is currently thought a reasonable proxy for micromechanical damage. It is “strictly a cavitation index,” but is meant to be interpreted more broadly as tissue mechanical stress/damage.

109
Q

An ultrasound contrast agent is exposed to an ultrasound beam with a high mechanical index (MI >1). Which is the following is more likely true?

  1. The sound beam has high frequency
  2. The sound beam has a low peak negative pressure
  3. The strength of the sound beam is low
  4. The contrast agent will experience bubble disruption and production of strong harmonic frequencies
A

D = The contrast agent will experience bubble disruption and production of strong harmonic frequencies

110
Q

Which of the following is true with regard to harmonic imaging using contrast agents?

A. Harmonic are only produced when the mechanical index > 0.1

B. The harmonic signals are stronger than tissue harmonics

C. Harmonic signals result from microbubble disruption

D. Harmonic signals result from microbubble resonance

E. All of the above

A

All of the above

111
Q

Which of the following is true with regard to tissue harmonic imaging?

A. Tissue harmonics are created during transmission through tissues

B. Tissue harmonics are NOT present as sound leaves the transducer but are only present deeper in the tissue

C. Tissue harmonics are weaker than the harmonics created by contrast agents

E. All of the above

F. None of the above

A

All of the above

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