echoes Flashcards by abbie anderson

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

reflection

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why do reflections occur?

Impedance changes cause reflections to occur.
.

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define impedance

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

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

what is the avg in soft tissue?

what is its formula?

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

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what are these?

impedances of selected tissue

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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

reflection

Interface

Reflector

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what is the impedance change in each image?

1st one is no impedance change

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

specular

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

Scatter (Diffuse, non- specular)

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

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

Specular

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

diffuse

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what is raleigh scattering

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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what are Specular Reflectors -

what types are there?

Incidence

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

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___ is the – angle that strike interface

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

Types of incidence

perpendicular

oblique

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The greater the change of impedance the ____ the reflection

stronger

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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

perpendicular

reflection comes straight back to transducer

sound that continues

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what is IRC?

what is its formula?

what is it measured in?

Intensity Reflection Coefficient – fraction or percent of sound reflected

IRC = [Z2 –Z1 / Z2 + Z1]2

unitless

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

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

what is reflected intensity?

what is the formula?

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

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%)


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%)

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%)

what is intensity transmitted coefficient it's formula? it's unit?

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

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?

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?

able to calculate based on specular and perpendicular only

What is the intensity transmitted coefficient at this bile (water) – gall stone (bone) interface?  Already calculated IRC of .46

If Z is = then no reflection  Large difference in Z, large IRC and strong reflected intensity (bone; air)

perpendicular incidence

what happens w/ oblique incidence?

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.

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?

1 and angle of r = angle of i

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.

\<90

what is rarefraction? what law provides the formula? what is it?

 Refraction - Change in direction of sound on passing from one medium to another  Snell’s law  Sine (remove sine for our puposes)

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?

 Refraction causes \_\_\_\_because transmitted sound changes direction

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

what is a rarefraction mirror image

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

what is this? how can u tell?

rarefraction mirror image

what does this describe? Missing reflections – large shadow

Grazing Incidence (critical angle)

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?

90 degrees

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

describe diffuse reflectors. what is another name for these?

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

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

Back scatter

what are diffuse reflectors dependent upon? how?

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

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?

Rayleigh