review: Test2 Flashcards
what is normal incidence?
(PORN)
perpendicular
orthogonal
right angle
ninety degrees
normal
if an angle is anything other than 90°, what is it known as?
oblique
acute
obtuse
acute-less than 90°
obtuse-more than 90°
both are oblique
the sound wave’s intensity right before it strikes a boundary is known as?
incident intensity
portion of the incident sound beam that, after striking a boundary, returns back is known as?
reflected intensity
normal incidence means that the incident sound beam strikes the boundary at what?
90°
the portion of the incident beam that, after striking a boundary, continues forward in the same general direction that it was traveling is what?
transmitted intensity
what is the percentage of ultrasound intensity that bounces back?
intensity reflection coefficient (IRC)
what is the percentage of ultrasound intensity that passesthrough the boundary?
intensity transmission coefficient (ITC)
What are the units of IRC and ITC?
no units-percentage
Large reflections will occur in normal incidence if the impedances are?
substantially different
with greater impedance, differences between two media, the IRC and the amount of reflection do what?
IRC increases
reflection is greater
specular reflection arrises from what type of interface?
a smooth boundary (mirror)
what do we know about oblique incidence?
oblique incidence occurs when the incident sound beam strikes the boundary at any angle other than 90°
two physical principles always apply to reflection with oblique incidence:
1) conservation of energy
2) reflection angle = incident angle
what is Snell’s law?
quantifies the physics of refraction
sin(transmission angle)/sin(incident angle) = speed of medium2/speed of medium1
medium1-defined as the medium in which the sound is currently traveling
medium2-defined as the medium into which the sound is entering
what is a reflection that arises from a rough boundary?
diffuse reflection (backscatter)
what is considered a dominant contributor to attenuation?
absorption
as path length increases, attenuation of ultrasound in soft tissue does what?
increases
acoustic impedance is also known as:
characteristic impedance
in order to have reflections occur, what do we have to have?
media on either side of the boundary have different impedances
what type of probe would you use for abd images vs small parts?
higher frequency on parts closer to surface
lower frequency on parts that are deeper in the body
what is the attenuation coefficient for soft tissue?
0.5 dB/cm/MHz
how do we determine attenuation?
determined by 2 factors:
path length, frequency of sound
decibels and intensities
3dB-double
10dB-ten times larger
- 3dB-half
- 10dB-one tenth
what’s the difference between more and less attenuation in regards to frequency and distance?
more attenuation:
longer distances, higher frequencies
less attenuation:
shorter distances, lower frequencies
what is sound going in all different directions?
scattering
sound back to the transducer is created by:
reflection:
specular(mirror), diffuse(backscatter)
what is Rayleigh scattering related to?
organized and omnidirectional
Rayleigh scattering always equals frequency4
when frequency doubles, Rayleigh scattering is 16 times greater
what is the calculation for acoustic impedance?
acoustic impedance =
density(of a medium) x speed(at which sound travels in medium)
units-rayls(z)
