Lecture 10 Flashcards
Perpendicular incidence involves (3)
Pulse echo technique
Transmission
Impedance difference
Oblique incidence involves (5)
Angle of incidence Angle of reflection Angle of transmission Refraction Propogation speed differences
Both oblique incidence and perpendicular incidence are examples of
Specular incidence
Sepecular reflector translates to
Mirror like
What boundaries in the body are specular reflectors
Smooth and large
(Diaphragm
What happens with the sound to a specular reflectors
Sound will bounce back to the transducer and produce a strong echo
What occurs when there is not a smooth large boundary
Scattering occurs
What is scattering
Redirection of sound in many directions
What is a rougher surface ?
Heterogenous tissue (liver)
What does a object have to be to be considered large
Comparable or large than the wavelength
Specular reflection has ____ wavelength and ____ object
Small
Large
Does scattering help us, why?
Yes
Gives us a good vis of the tissue parenchyma
Scattering depends on ____ and _____
Operational frequency and scatterer size (wavelength)
Higher operational frequency and less scatterer size (wavelength)
More specular reflection (comes straight back to the transducer )
Increase intesity of echo
The object will be larger than the wavelength
What is back scatter
The echo info that comes back to the transducer
More frequency more specular refreaction is not true for ______
Rayleigh scattering
Rayleigh scattering
Happens when the object is much much smaller than the wavelength
We get more information from red blood cells because
They have lots of scattering
Scattering intensity is proportional to frequency to the power of
4
During speckle, scattering echo sound waves….
Take different paths on the way back to the transducer
Speckle Waves coming back can either come back _____ or _____
Constructively or destructively
Constructive speckle wave
Reinforce each other
Destructive speckle wave
Partially or totally cancel each other
Constructive interference is aka
In phase
Consructive interferance leads to _____ intensity
Stronger
Destructive interferance also known as
Out of phase
In order for wave to be constructive, they have to line up ______
Perfectly
Some scattered beams coming back in phase and others out of phase can cause
Multiple intensities within one tissue (produces grainy appearance aka speckle)
Acoustic speckle is a form of
Acoustic noise
Acoustic speckle is the result of
Constructive and deconstrustive interference of staterred sound waves
