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Physics > Ultrasound > Flashcards

Ultrasound Flashcards

1
Q

What is Half Value Tissue Thickness in US?

A

Tissue thickness that decreases signal by 3 dB

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2
Q

What is Impedance?

A
  • Stiffness
  • Density X Speed of sound
  • Bigger impedance= bigger reflection
  • Units= Rayl
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3
Q

What is Refraction?

A

Bending of sound waves due to change in speed

-Depends on Speed and change in angle

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4
Q

Do smooth (specular) or Non specular surfaces depends on angle of incidence?

A

-Specular reflectors depend on angle of incidence

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5
Q

How does frequency affect scatter?

A

higher frequency–> Smaller wavelength–> Surfaces appear non specular–> More Scatter

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6
Q

How does frequency affect HVT?

A

Increased frequency–> Decreased HVT

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7
Q

Equation for attenuation?

A

0.5 (dB/cmMHz) X Frequency of Tranducer X Distance (round trip)

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8
Q

How does the crystal thickness relate to probe frequency?

A
  • Inversely proportional
  • Increased crystal Thickness= Lower Frequency (Increased Wavelength)
  • Decreased Crystal Thickness= Higher Frequency (Smaller Wavelength)
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9
Q

What is the Dampening Block?

A

Absorbs energy to change the SPL

  • Thin Block: Long Spatial Pulse Length, narrow bandwidth (Doppler)
  • Thick Block: Short SPL, Broad Bandwidth (better axial resolution)
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10
Q

What is the Matching layer?

A

Minimizes Acoustic Impedance between Transducer and Tissue

Optimal thickness if 1/4 Wavelength.

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11
Q

How does the transducer Frequency and Diameter affect the near field?

A

Increased Frequency= Longer Nearfield
Increased width= Longer Nearfield
Higher Frequency= Less DIvergence

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12
Q

What is the Spatial pulse length?

A

Number of Cycles emitted per pulse X Wavelength?

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13
Q

What is axial resolution?

A
  • Ability to discriminate two objects in the direction of the beam.
  • Two objects must be at least 1/2 SPL apart
  • Does not depend on depth
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14
Q

What is lateral resolution?

A
  • Ability to discriminate things perpendicular to the beam
  • Higher Frequency (longer near field and narrower focal spot)= better lateral resolution
  • Higher Scan Line Density= Better lateral resolution
  • Wider Transducer Width= Better lateral resolution
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15
Q

What is Elevational resolution?

A
  • Lateral resolution in the orthogonal plane
  • Smaller Transducer element height= Better Elevation resolution
  • Higher Frequency= Better elevational resolution
  • Better with 1.5 dimension array
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16
Q

How do you improve axial resolution?

A
  • Shorter SPL
  • Thick Dampening Crystal
  • Higher Frequency Probe (lower wavelength, lower SPL)
17
Q

What is Side Lobe Artifact?

A
  • Strong Reflector outside the main beam generates echos detectable by the transducer
  • Ex: GB Sludge
  • Assumption: All detected echos originate from the main beam
18
Q

What is Beam Width Artifact?

A
  • Object in the divergent field sends echos back to the main beam
  • Ex: Bladder Debris
  • Assumption: All detected echos originate from the main beam
  • Fix: Correct the focal spot or place the tranducer at the center of the image
19
Q

What is reverberation Artifact?

A
  • Two parallel reflectors bounce echos back and forth before returning to detector
  • Assumption: All echos return to detector after one reflection
20
Q

What is comet tail artifact?

A
  • Type of reverberation artifact
  • Assumption: All echos return to detector after one reflection
  • Triangle because later echos are more attenuated
21
Q

What is Ring Down Artifact?

A
  • Tetrahedron of air bubbles surround fluid and continuously send signal back
  • Assumption: All echos return to detector after one reflection
  • Ex: Air/Fluid in the duodenum
22
Q

What is mirror artifact?

A

-Hit a strong reflector and echos bounce back and forth
-Assumption: All echos return to detector after one reflection
Ex: Lung/Liver interface

23
Q

What is speed displacement Artifact?

A
  • Slower velocity in tissues will result in longer return echo time (speed is slower in fat)
  • Assumption: Velocity is same in all tissues
  • Ex: Fat in liver will make the liver border look discontinuous bc it took longer in that area for it to return
24
Q

What is Refracton Artifact?

A
  • Due to the angle change and speed change in different tissues
  • Assumption: All echos return to detector after one reflection
  • Ex: Duplicated SMA
25
Q

What causes posterior acoustic shadowing?

A
  • Hit a strong reflector that attenuates mroe
  • Assumption: Attenuation issue
  • Ex: Gallstones
26
Q

What causes posterior acoustic enhancement?

A
  • Hit a weak reflector that attenuates less
  • Assumption Attenuation issue
  • Ex: Cyst
27
Q

What is A Mode, B Mode and M Mode?

A
  • A Mode: Amplitude, Optho
  • B Mode: Brightness
  • M Mode: Motion
28
Q

What is the best doppler Angle?

A
  • Between 30-60
  • <30, too much aliasing and artifact
  • At 90 (perpendicular), flow will be 0
29
Q

What is power doppler used for?

A
  • Very sensitive to flow
  • No aliasing
  • No dependence on angle
30
Q

What is aliasing?

A
  • Wrap around of high flow to low Flow

- Occurs if doppler shift is greater than the Nyquist frequency= 1/2 PRF

31
Q

How do you decreased aliasing?

A

-Increase the Scale
-Increase the PRF
-Increase the Angle
-Decrease frequency of the Transducer
(SPAF)

32
Q

What is color bleed?

A
  • Color outside the vessel Wall

- Fix by decreasing color gain

33
Q

What is time gain compensation?

A

Increases the amplification based on the depth to create uniform brightness

34
Q

What is Harmonics?

A
  • Sending at one frequency and receiving at another frequency
  • Improves lateral resolution
  • Reduces reverberation
  • Loss of Depth Penetration
  • Can make something solid look like a cyst
35
Q

What is Compound imaging?

A
  • Electronic steering of US Beam in different directions
  • Sharpens the edges and decreases posterior acoustic shadowing
  • Can make a cyst look solid
36
Q

What is Intensity?

A
  • Power/Area
  • Smaller Beam (less area) means more intensity
  • Doppler> M Mode> B mode
37
Q

What is Thermal Index?

A
  • Maximum rise in temperature secondary to energy absorption
  • Varies per Tissue
  • No damage until threshold reached
  • Limit 1.0
38
Q

What is Mechanical Index?

A
  • Chance of Cavitation given frequency and peak rarefraction
  • More likely with low frequency and High wavelength
  • Limit 0.5
39
Q

What are specific parameters for OB?

A
  • TIS for Early Gestation, TIB for greater than 10 weeks
  • TI <0.7-1
  • Use M mode instead of spectral doppler

Physics (10 decks)

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