Chapter 3: Attenuation (ultrasound physics)

the loss of amplitude, power, and intensity

what is attenuation?

absorption, reflection, and refraction

what are the three parts of attenuation?

absorption

what is the dominant form of attenuation in soft tissue?

direct and nonlinear

how does absorption change when frequency increases or decreases?

large smooth and flat, large rough, and small

what are the surface characteristics of reflection?

perpendicular relationship

what relationship does a ray and wavefront have?

true

true or false: every compression is a wavefront

incident ray

what is an incoming ray called?

reflected wave

what is the wave going back called?

angle of incident

what is the angle called between the normal line and incident ray?

contact angle

what is the angle called between the incident ray and the boundary layer?

large and flat

the incident angles are equal in what surface?

normal incidence

what produces the brightest reflections and is at 90 degrees?

specular

which reflection type is the strongest?

specular

what kind of reflection occurs on a large flat surface?

oblique incidence

what is it called when an incidence is coming at an angle?

impedence

what is it called when sound continues to travel through similar mediums?

Z=pxc

what is the impedence equation?

true

true or false: the bone causes a lot of reflection

intensity reflection coefficient

what is the % of sound intensity that’s reflected

IRC=reflected intensity/incident intensity

what is the equation for IRC when intensities are given?

IRC=(z2-z1)/z2+z1)²

what is the equation for IRC when impedences are given?

true

true or false: % reflection + % transmission = 100%

ITC=transmitted intensity/incident intensity

what is the equation for ITC?

large rough

what type of surface produces non-specular reflections (scatter)

backscatter

what kind of scatter is diffuse?

rayleigh scatter

what type of reflection occurs on a small surface?

rayleigh scatter

what is the weakest of all reflection that includes red blood cells?

refraction

what is the change of direction of sound when crossing a boundary?

oblique incidence and different propagation speeds

what are the two things that MUST occur for refraction?

propagation speed

the medium with the highest _____ has the larger angle

ci/ct=sin(oi)-sin(ot)

what is the snell’s law formula

(new angle-old)/old angle x 100

what is the percent change formula?

the critical angle

what is it called when there is total internal reflection with refraction?

anechoic

what is it called when there is no echos and no reflection

hypoechoic

what is it called when the echos are comparative, less bright?

isoechoic

what is it called when the echos are even with the same amount of echos are surrounding?

hyperechoic

what is it called when the echos are brighter then other tissues?

acoustic enhancement

what is it called when there is a stream of brightness and lots of reflection