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PTE Masters + A Practical Approach to Transesophageal Echocardiography > Physics of Ultrasound Part 5-11 > Flashcards

Physics of Ultrasound Part 5-11 Flashcards

1
Q

What phenomenon occurs when the reflectors dimensions are much smaller than the wavelength of the ultrasound beam?

  • When this occurs the sound wave is redirected equally in all directions.
  • Clinically this is seen wiht the interaction of RBCs with an ultrasound beam
A

Raleigh Scattering

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2
Q

What phenomenon occurs when U/S reflections off an irregular surface radiate in more than one direction?

A

Diffuse Reflection = Backscatter

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3
Q

Which of the following is most responsible for the conversion of U/S energy to heat?

A. Absorption

B. Reflection

C. Refraction

D. Acoustic Vibration

E. Cavitation

A

Absorption

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4
Q

Which of the following is improved by lowering frequency of an ultrasound beam?

A. Penetration

B. Axial resolution

C. Lateral resolution

D. Temporal resolution

E. Longitudinal resolution

A

Penetration

Lower frequency ultrasound* has *less attenuation and better penetration

Distractor = Axial resolution improved by higher frequency ultrasound with a higher SPL

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5
Q

Which of the following properties of the media influences acoustic impedence?

A. Velocity

B. Density

C. Elasticity

D. Stiffness

E. All of the above

A

All of the above

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6
Q

What is the formula for Acoustic Impedence = ?

A

Acoustic Impedence = Velocity * Density

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7
Q

What is the definition of these respective angles;

Obtuse

Acute

Oblique

A

Obtuse = 90 - 180

Acute = < 90

Oblique = Not normal (Acute or obtuse, but not 0 or 90)

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8
Q

What does the matching layer do in terms of acoustic impedence?

A

Matching layer helps to

decrease the change in acoustic impedence from the crystal to the tissue (Helps decrease massive reflections in the probe)

  • prevents a large reflection at interface of musosa and TEE probe
  • PZT > Matching layer > Gel > Mucosa
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9
Q

What is are the formulas for near field length?

A

Near field length = (radius)2 / Wavelength

Near field length = (diameter)<span>2</span> / 4* Wavelength

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10
Q

The ability to accurately identify structures that lie close together when one is in front of the other (one deeper than the other) (in tandem) is called:

A

Longitudinal resolution

Also known as L.A.R.D. (Longitudinal, Axial, Range or Radial, Depth)

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11
Q

What type of resolution is the ability to accurately identify structures that lie close together when one is on top of the other (Along Y axis) (along vertical width of the beam)?

A

Elevational resolution

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12
Q

What is the relationship between line density and temporal resolution?

A

Inversely proportional

Increase in temporal resolution = Decrease in line density

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13
Q

What is the definition of line density?

A

of scan lines / image

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14
Q

What is the relationship between line density, frame rate, and temporal resolution?

A

Increase line density = Decreased frame rate = Increased temporal resolution

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15
Q

Does decreasing imaging depth affect line density?

A

No

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16
Q

What is the advantage of a focused ultrasound beam in terms of which resolution and in near/far field?

A

Improved lateral resolution in the near field

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17
Q

What is the disadvantage of a focused ultrasound beam in terms of which resolution and in near/far field?

A

Decreased lateral resolution in the far field

(more divergence in the far field)

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18
Q

What is the maximum spatial peak temporal average intensity recommended by the American institute of U/S in medicine to avoid thermal injury for unfocused ultrasound beams is what?

A

1 Watt / cm2

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19
Q

What is the maximum spatial peak temporal average intensity recommended by the American institute of U/S in medicine to avoid thermal injury for FOCUSED ultrasound beams is what?

A

Focused = Lower limit because energy isn’t spread out

100 milliwatts (mW)/cm2

= 0.1 W/cm2

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20
Q

What ultrasound modality is an obsolete form of U.S which plots amplitude (Y axis) vs. Depth (X axis)?

A

A-mode

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21
Q

What does frame rate depend on?

(Name 4 things)

A
  1. Line density (# scan lines per image)
  2. # of foci
  3. Imaging Depth
  4. Sector Width
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22
Q

What is the purpose of matching layer in an ultrasound transducer?

A

Reduces reflection at the tissue transducer interface

(Facilitates improved transmission from probe to the tissue)

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23
Q

What is a piezoelectric crystal made of?

A

Lead Zirconate Titanate

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24
Q

What is the term for the high temperature at which a piezoelectric crystal loses its function?

A

Curie Temperature

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25
Q

What is the disadvantage of the backing material?

A

Decreases sensitivity to reflected echoes

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26
Q

How does the backing material affect axial resolution?

A

Improves Axial Resolution by decreasing SPL (Spatial pulse length)

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27
Q

How does backing material affect Q factor?

A

Q Factor = RF / BW

Q factor = (V / 2*Thickness) / BW

Decreases Q factor because it increases bandwidth

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28
Q

How would adjusting PRF affect temporal resolution?

A

Increase PRF* = *Increase Temporal Resolution

Higher PRF = More images can be formed per second therefore higher fraame rate = # images / second

Increasing frame rate = Increasing temporal resolution

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29
Q

How does pulse duration affect bandwidth?

A

Shorter pulse = Wider bandwidth

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30
Q

How does damping material affect bandwidth?

A

Damping material increases bandwidth (BW = range of frequency of the pulses)

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31
Q

What is duty factor?

A

Unitless number describes amount of time (0% - 100%) U/S machine is producing sound

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32
Q

What is the formula for duty factor?

A

Pulse Duration* / *Pulse Repetition Period

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33
Q

What is the Q factor?

A

Unitless number which describes quality of the ultrasound pulse

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34
Q

What is the formula for Q-factor?

A

Resonant Frequency* / *Bandwidth

Imaging transducers tend to produce short U/S pulses with wide bandwidths, high resonant frequencies and small Q factors

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35
Q

How does the thickness of the piezoelectric crystal increases, how does this affect the frequency and wavelength?

A

Thicker = Increased frequency* and Smaller *wavelength

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36
Q

How are frequency and attenuation related?

A

Decreased frequency = Decreased Attenuation

High frequency probes = Can’t penetrate because of attenuation

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37
Q

What is the intensity reflection coefficient?

A

% of ultrasound intensity that is reflected at the interface of two media

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38
Q

What is the intensity transmission coefficient?

A

% of ultrasound intensity that is transmitted (Passes forward through the interface of the two media)

39
Q

What is the formula of the Intensity reflection coefficient?

A

[Z2 - Z1 / Z2+Z1]2 x 100

Z = Acoustic Impedance

40
Q

What is the formula for acoustic impedance?

A

Density of medium * Velocity of U/S in the medium

41
Q

What is the order of acoustic impedances of materials in the ultrasound?

A

PZT ~ Backing layer* > *Matching layer* > *Gel* > *Skin

42
Q

What does the piezeoelectic crystal determine about the wavelength of PWD doppler?

A

1/2 wavelength = Thickness of crystal

piezoelectric crystals are cut to a thickness that is 1/2 the desired radiated wavelength

43
Q

The frequency of the CWD ultrasound beam is determined by?

The frequency of the PWD ultrasound beam is determined by?

A

CWD = Electrical frequency of the excitation voltage applied to the crystal

PWD = Thickness of Piezoelectric crystal and the velocity of sound through the crystal

RF = Velocity / (2*Thickness)

44
Q

What is the formula for near field length?

A

radius2 / wavelength

45
Q

In general, do you want a low or a high Q factor?

A

Low Q factor = Better & Higher quality of pulse

46
Q

How does the focus change when you have high frequency, short wavelength* transducers vs. *low frequency, long wavelength transducers?

A

high frequency, short wavelength = Deep focus

low frequency, long wavelength = Shallow focus

47
Q

What is the frequency of audible sound?

What is the frequency of ultrasound?

A

Audible sound = 20 Hz - 20,000 Hz

Ultrasound > 20,000 Hz

48
Q

Selective depth dependent amplificiation is achieved by altering which of the following?

A

Time Gain Compensation

TGC increases receiver gain with increasing arrival time of echoes to compensate for ultrasound attenuation

  • Hence, deeper structures have weaker echos and require more gain for optimal visualization
49
Q

What is the formula for line density?

A

of scan lines per image

50
Q

What is the post image processing method used for CW and PW doppler analysis?

A

Fast Fourier Transform

51
Q

How does changing the PRF change the duty factor?

A

Increase PRF = Increase Duty Factor

(If you increase PRF, you increase the # of pulses per second therefore increase duty factor)

52
Q

SPL is determined by:

Source?
Medium?

Both?

A

Both medium and source

53
Q

What are the components of ultrasound that are determined by sound source only?

A

“Sound = Seconds”

Period, Frequency, PRF, PRP, Duty Factor, etc

Anything related to time

54
Q

What are the components of ultrasound that are determined by medium only?

A
  1. Velocity
  2. Acoustic Impedence (density * velocity)
55
Q

Does a high frequency transducer produce higher quality images because of:

A high or low SPL?

A

Low SPL

You want this low so that you will improve axial resolution (You want resolution number as small as possible!)

  • Paradoxical but true
56
Q

What is the primary component of attenuation in soft tissue?

A

Absorption

57
Q

What ultrasound parameters are determined by sound source & medium?

A

Parameters with Length (Wavelength), Spatial Pulse Length

58
Q

In order for refraction to occur, what two componets must be present?

A
  1. Oblique Incidence
  2. Velocity media 1 cannot = Velocity media 2
59
Q

Rank the following media in order of increasing (Highest velocity last) velocity.

Air

Bone

Fat

Lung

Soft Tissue

A

(Slowest) Air < Lung < Fat < Soft Tissue < Bone (Fastest)

60
Q

What is Power doppler tell you?

What is is not tell you?

A

+/- Presence of a Doppler shift

No speed or direction

61
Q

What are the synonyms of Power Doppler (Name 2 of them)

A
  1. Energy Mode
  2. Color Angio
62
Q

What are 3 advantages of Power Doppler?

A
  1. Increased sensitivity to low flow
  2. Unaffected by angle unless 90 degrees
  3. Unaffected by aliasing since velocity is ignored
63
Q

What are 3 disadvantages of Power Doppler?

A
  1. Lower frame rates than conventional color flow doppler
  2. No measure of velocity or direction
  3. Susceptible to motion of the transducer, patient, or soft tissues which may result in a burst of color or flash artifact
64
Q

What is shown at the green dot in the image?

What does this signify?

A

L wave

Signifies diastolic dysfunction with impaired relaxation and Elevated LAP

65
Q

What are the 5 functions of the receiver?

A
  1. Amplification
  2. Compensation
  3. Compression
  4. Demodulation
  5. Rejection
66
Q

What is the difference between rejection in post image processing vs. Low Pass Wall filters?

A

Rejection = 2D amplitudes are eliminated

Low Pass Wall filters = Eliminates large doppler shifts (high frequency signals)

67
Q

Absorption is responsible for what % of attenuation seen in soft tissue?

A

>80%

68
Q

What frequencies do most echocardiography machines operate?

A

2-10 MHz

69
Q

What intensity is the maximum spatial peak temporal averate intensity (SPTA intensity) recommended for focused ultrasound beams?

A

100 mW/cm2

70
Q

What intensity is the maximum spatial peak temporal averate intensity (SPTA intensity) recommended for unfocused ultrasound beams?

A

1 W / cm2

71
Q

For every “x” cm will your amplitude be decreased by 1/2?

A

1 cm

Not sure how he did this calculation

72
Q

What modality utilizes two or more sample volumes along a scan line which decreases aliasing artifact but introduces range ambiguity?

A

High pulse repetition frequency PWD

Note: The answer is not CWD

73
Q

What is the processing method used for modern PWD and CWD analysis?

A

Fast Fourier Transform

74
Q

The thickness of tissue required to reduce the intensity by a factor of 0.5 is referred to as the half value thickness layer.

This represents how many decibels (dB) of attenuation?

A

3 dB

75
Q

calculate the thickness of tissue required to decrease the power of a 12 MHz TEE by half (half power distance).

A

Answer = 0.5 cm

76
Q

What angle of incidence will provide the best 2D gray scale TEE images?

A

90 degrees

77
Q

Focused U/S beam improves which type of resolution (Axial, Lateral, Elevational) in which field (Near or Far)?

A

Improved lateral resolution in the near field

78
Q

How does line density affect frame rate?

A

As line density increases, frame rate decreases (Worsens temporal resolution)

Line density = Spacing between sound beams

Line density increases the number of pulses per image

79
Q

How does the damping material affect the Q factor?

A

Decreases it

(Increases bandwidth * Decreases Resonant frequency)

80
Q

What is the formula for attenuation coefficient?

A

Attenuation coefficient = 1/2 * Frequency

81
Q

Calculate the attenuation expected to occur at a depth of 7cm when using a 10 MHz TEE probe.

A
  1. Calculate attenuation coefficient = 1/2 * (Frequency) = 1/2 * (10Hz) = 5 Hz
  2. Multiple AC * Path length (7 cm)

3. Answer is 35 dB of attenuation

82
Q

Selective depth dependent amplification is achieved by altering which of the following?

A

Time gain compensation* AKA *Depth gain compensation

This increases the receiver gain with increasing arrival of echos to compensate for ultrasound attenuation.

  • Deeper structures have weaker echos and require more gain for optimal visualization
  • This function compensates for the attenuation that occurs with increasing depth

-

83
Q

An ultrasound system with a decrease in output by 1/10th the original power can be represented by what decibel reading?

A

Answer = 10 dB

84
Q

What determines the frequency of a PWD ultrasound beam?

A

Thickness of PZT crystal and velocity of sound through crystal

85
Q

What determines the frequency of a CWD ultrasound beam?

A

Electrical frequency of the excitation voltatge applied to the PZT crystal

86
Q

What is the best angle of incidence for 2D TEE images?

What is the best angle of incidence for doppler?

A

2D images = 90 Degrees

Doppler = 0 degrees where (Cos is 0)

87
Q

An unfocused CW U/S beam has near zone length of 10cm. At the focus, the beam is 4mm wide. What is the diameter of the PZT crystal in the transducer?

A

Answer = 8mm

Formula: Unfocused transducer in continuous mode**

Focus diameter (4mm) = [Transducer diameter (In PZT) / 2]

Transducer diameter = 4mm x 2 = 8 mm

88
Q

What are the formulas for:

Pressure

Amplitude

Power

Intensity

A

See image

89
Q

What transducer is capable of creataing multiple focal zones per scan line?

A

Phased Array Transducer

  • Increasing the number of focal zones per scan line will improve lateral resolution
90
Q

What two words best describe the motion of particles in a medium as sound passes through it?

A
  1. Compression
  2. Rarefaction
91
Q

What phenomenon is responsible for the doppler determinations of blood flow velocities?

A

Rayleigh Scattering

92
Q

What is the relationship of a wavelength and an RBC during Raleigh Scattering?

A

When Wavelength >> RBC (In terms of length) then Rayleigh scattering occurs

93
Q

Most TEE Probes are what subtype of array probes?

A

Linear Phased Array transducers

Newer 3d Probes = Matrix phased aray capable of 3d imaging

PTE Masters + A Practical Approach to Transesophageal Echocardiography (55 decks)

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