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SPPI > echoes > Flashcards

echoes Flashcards

1
Q

___ is an Echo, a Portion of sound returned from a media boundary or interface that create our image

A

reflection

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2
Q

why do reflections occur?

A

Impedance changes cause reflections to occur.
.

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3
Q

define impedance

A

Impedance – an acoustic property of a medium that is related to its density and propagation speed

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4
Q

___ is Directly proportional to density and propagation speed. what is it measured in?

what is the avg in soft tissue?

what is its formula?

A

impedance rayles

Average for soft tissue is 1,630,000 R (1.63 MR)

Z (r) = Density (kg/m3) x C (m/s)

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5
Q

What is the impedance of a medium if the density is 1000 kg/m3 and the propagation speed is 1540 m/s?

A
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6
Q

what are these?

A

impedances of selected tissue

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7
Q

Greater the change of impedance, greater the _____

_____ is point where impedance changes and a reflection occurs. AKA Boundary

____ is the media boundary that produces a reflection

A

reflection

Interface

Reflector

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8
Q

what is the impedance change in each image?

A

1st one is no impedance change

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9
Q

____ is reflection from a large (relative to the wavelength), flat, smooth boundary

A

specular

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10
Q

____ is – diffusion or redirection of sound in several directions upon encountering a particle suspension (small boundaries) or a rough surface

A

Scatter (Diffuse, non- specular)

e.g. light off a mirror = specular; light off a white wall = diffuse

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11
Q

____ have Reflectors larger than wavelength
Wavelength small compared to reflector
Examples: diaphragm, wall of vessel, femur, heart valve
Cause more artifacts
Angle dependant

A

Specular

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12
Q

____ are Reflectors are smaller than wavelength
Wavelengths large compared to reflector
Examples: liver, kidney, placenta, muscle
Cause less artifacts
Angle independent

A

diffuse

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13
Q

what is raleigh scattering

A

Sound scattering in all directions
“Back scatter” the sound that returns to the transducer to create the image
Often referred to with Doppler and blood

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14
Q

what are Specular Reflectors -

what types are there?

A

Incidence

Perpendicular incidence (normal, orthagonal)
 Oblique incidence (non- perpendicular)
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15
Q

___ is the – angle that strike interface

Calculate strength of reflection with _____
Calculate angle of reflection with _______

A

Types of incidence

perpendicular

oblique

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16
Q

The greater the change of impedance the ____ the reflection

A

stronger

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17
Q

what type of incidence

Beam hits interface at 90 degree

what is Reflected intensity - ?
Transmitted intensity – ?

Will calculate these by determining the “fraction” or “percent” of sound reflected

A

perpendicular

reflection comes straight back to transducer

sound that continues

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18
Q

what is IRC?

what is its formula?

what is it measured in?

A

Intensity Reflection Coefficient – fraction or percent of sound reflected

IRC = [Z2 –Z1 / Z2 + Z1]2

unitless

19
Q

What is the intensity reflection coefficient if medium one has an impedance of 1 MR and medium two has an impedance of 2 MR?

A
20
Q

What is the intensity reflection coefficient at this bile (water) – gall stone (bone) interface

A
21
Q

what is reflected intensity?

what is the formula?

A

Intensity of reflection (reflected intensity)
IR mW/cm2 = II mW/cm2 x IRC

22
Q

What is the reflected intensity if medium one has an impedance of 1 MR and medium two has an impedance of 2 MR and the incident intensity is 100 mW/cm2?

Already calculated IRC to be .09 (or 9%)

A
23
Q


What is the reflected intensity if medium one has an impedance of 1 MR and medium two has an impedance of 4 MR and the incident intensity is 100 mW/cm2?

Already calculated IRC to be .36 (or 36%)

A
24
Q

What is the reflected intensity if medium one has an impedance of 1 MR and medium two has an impedance of 4 MR and the incident intensity is 200 mW/cm2?

Already calculated IRC to be .36 (or 36%)

A
25
Q

what is intensity transmitted coefficient

it’s formula? it’s unit?

A

ITC – fraction or percent of sound transmitted

Will be everything that was NOT reflected

1 = IRC + ITC
ITC = 1 – IRC

Unitless
IT mW/cm2 = II mW/cm2 x ITC
IT mW/cm2 = II mW/cm2 –IR mW/cm2

26
Q

What is the intensity reflection coefficient if medium one has an impedance of 1 MR and medium two has an impedance of 2 MR?

IRC was .09 (or 9%)

What is the intensity transmitted coefficient?

A
27
Q

What is the reflected intensity if medium one has an impedance of 1 MR and medium two has an impedance of 4 MR and the incident intensity is 200 mW/cm2?

IRC is .36 (36%)
IR is 72 mW/cm2

What is the transmitted intensity?

A

able to calculate based on specular and perpendicular only

28
Q

What is the intensity transmitted coefficient at this bile (water) – gall stone (bone) interface?

Already calculated IRC of .46

A
29
Q

If Z is = then no reflection

Large difference in Z, large IRC and strong reflected intensity (bone; air)

A

perpendicular incidence

30
Q

what happens w/ oblique incidence?

A

Beam hits interface at < 90 degree

Can not calculate intensities – too complex

Will calculate angle of reflection and transmission

Causes artifacts – missing reflector, mirror image, anisotropy, etc.

31
Q

Beam hits interface at < 90 degree describe the difference.

Angle of Incidence ( 
Angle of reflection ( 
Angle of transmission (

what does the angle of r always equal?

A

1

and angle of r = angle of i

32
Q

When angle of incidence is ___degrees the reflection may not return to the transducer

Results in missing reflectors

Results in diminished or missing reflection (hypoechoic) esp. when involving tendons, ligaments, muscles referred to as anisotropy.

A

<90

33
Q

what is rarefraction?

what law provides the formula? what is it?

A


Refraction - Change in direction of sound on passing from one medium to another

Snell’s law

Sine (remove sine for our puposes)

34
Q

If the angle of incidence is 45o at an interface between medium one with a propagation speed of 1.3 mm/us and medium two with a propagation speed of 1.7 mm/us. What is the angle of reflection and angle of transmission?

A
35
Q


Refraction causes ____because transmitted sound changes direction

A

edge shadows

hits the edge, changes direction, wave doesn’t bounce back.
refraction of the beam when it hits a specular reflector w/ 2 mediums w/ different propagation speeds at an obliqued angle

36
Q

what is a rarefraction mirror image

A

goes through rectus abdominous muscle which is a specular reflector . which bends the beam. in this case as it bounces back it hits the sac causing a refraction. another beam hits the sac straight on allowing the beam to travel back hence you have 2 sacs

37
Q

what is this? how can u tell?

A

rarefraction mirror image

38
Q

what does this describe?

Missing reflections – large shadow

A

Grazing Incidence (critical angle)

39
Q

If the angle of incidence is 60o at an interface between medium one with a propagation speed of 1.0 mm/us and medium two with a propagation speed of 1.5 mm/us. What is the angle of reflection and angle of transmission?

A

90 degrees

40
Q

If oblique incidence and change in propagation speed = refraction Need to image specular reflectors at __ degrees to see them

A

90

41
Q

describe diffuse reflectors. what is another name for these?

A

scatter or rayleigh scattering

Rough surfaces and small reflectors

Scatterers

Rayleigh scattering - redirection of sound in all directions by the diffuse reflectors

Often used to describe scattering from RBC

Wavelength of 5MHz .3 mm, RBC .008 mm

42
Q

___ is – sound that returns to transducer to create image. Able to image diffuse reflectors at any angle and it looks the same

A

Back scatter

43
Q

what are diffuse reflectors dependent upon? how?

A

frequency


Increased frequency = increased scatter b/c

Increased frequency = smaller wavelength; therefore
Wavelength is < reflector

An 8 MHz transducer will create more scatter than a 4 MHz

44
Q

Scattering from___ scatterers increased to the 4th power of frequency

Doubling the frequency = increases scattering by 16 times (24)
How much will the scattering increase when changing from a 2 MHz to a 8 MHz?

A

Rayleigh

SPPI (5 decks)

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