SPI-Lecture 6 Flashcards

1
Q

When sound hits a boundary, it may be:

A

Transmitted
Reflected
Scattered
Refracted

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2
Q

Ultrasound can be used for imaging because:

A
  • Reflection and scattering at organ boundaries

- Scattering in heterogeneous tissues.

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3
Q

Specular Reflection

A
  • Arise from large smooth boundaries.
  • Similar to your reflection in mirror.
  • Sound must encounter boundary at a 90 degree angle (perpendicular)
  • Produces stronger echos than non-specular reflectors.
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4
Q

Scattering

A
  • Occurs when sound encounters irregular, rough, heterogeneous, or small (equal to or smaller than wavelength) boundary or tissue.
  • Sound is redirected into many directions.
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5
Q

2 types of Scattering:

A
  • Backscatter (Non-specular - large, rough surface) - sound returns toward transducer.
  • Rayleigh Scatter (small,
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6
Q

Incident Sound

A
  • Sound that is coming from the sound source and going into the medium.
  • Incident sound = Transmitted Sound + Reflected Sound.
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7
Q

Transmitted Sound

A
  • Sound that continues to propagate in the direction it was going, after hitting a boundary or interface.
  • Majority of sound is transmitted.
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8
Q

Reflected Sound

A
  • Sound that is reflected at the boundary or interface and returns to the transducer.
  • Only 1% or less of sound is reflected at a soft tissue interface.
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9
Q

Ways that Incident Sound can encounter the interface:

A

Perpendicular - Normal, orthogonal, 90 degree incidence, right angle incidence. The direction of sound travel is perpendicular (at 90 degrees) in relation to boundary.

Oblique- Sound does not encounter the boundary at 90 degrees.

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10
Q

Incident Intensity

A

The intensity of the sound just after it encounters a boundary or and interface and is reflected.

Incident Intensity = Reflected Intensity + Transmitted Intensity.

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11
Q

Transmitted Intensity

A

The intensity the sound has after it encounters a boundary or an interface and continues to travel.

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12
Q

Intensity Reflection Coefficient (IRC)

A

The percentage of the sound’s intensity that is reflected when sound hits a boundary or tissue interface between two media.

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13
Q

Intensity Transmission Coefficient (ITC)

A

The percentage of the sound’s intensity that is transmitted when sound hits a boundary or tissue interface between two media.

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14
Q

IRC and ITC Relationship

A

ALL sound must be accounted for so:

IRC and ITC MUST equal 100% of original intensity.

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15
Q

Two factors required for reflection to occur:

A
  1. Angle at which sound strikes the boundary must be at 90 degrees.
  2. The two tissues or media must have different acoustic impedances.
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16
Q

IRC Equation

A

R = (Z2 - Z1)² Watts/cm²
—————
(Z2 + Z1)² Watts/cm²

IRC = Reflected Intensity
(medium 2 impedance - medium 1 impedance)²
DIVIDED BY
Incident Intensity
(medium 2 impedance + medium 1 impedance)²

Reflection depends on impedance difference!

17
Q

ITC Equation

A

ITC = 1 - IRC

18
Q

Examples of impedance mismatch:

A
  • Highest IRC occurs between an air/soft tissue interface. (99%)
  • Lower IRC occurs between a soft tissue/bone interface. (50%)
  • Lowest IRC occurs between 2 similar soft tissue interfaces, such as the liver and kidney.