review: Test2

Question 1

what is normal incidence?

(PORN)

Answer 1

perpendicular

orthogonal

right angle

ninety degrees

normal

Question 2

if an angle is anything other than 90°, what is it known as?

Answer 2

oblique

Question 3

acute

obtuse

Answer 3

acute-less than 90°

obtuse-more than 90°

both are oblique

Question 4

the sound wave’s intensity right before it strikes a boundary is known as?

Answer 4

incident intensity

Question 5

portion of the incident sound beam that, after striking a boundary, returns back is known as?

Answer 5

reflected intensity

Question 6

normal incidence means that the incident sound beam strikes the boundary at what?

Answer 6

90°

Question 7

the portion of the incident beam that, after striking a boundary, continues forward in the same general direction that it was traveling is what?

Answer 7

transmitted intensity

Question 8

what is the percentage of ultrasound intensity that bounces back?

Answer 8

intensity reflection coefficient (IRC)

Question 9

what is the percentage of ultrasound intensity that passesthrough the boundary?

Answer 9

intensity transmission coefficient (ITC)

Question 10

What are the units of IRC and ITC?

Answer 10

no units-percentage

Question 11

Large reflections will occur in normal incidence if the impedances are?

Answer 11

substantially different

Question 12

with greater impedance, differences between two media, the IRC and the amount of reflection do what?

Answer 12

IRC increases

reflection is greater

Question 13

specular reflection arrises from what type of interface?

Answer 13

a smooth boundary (mirror)

Question 14

what do we know about oblique incidence?

Answer 14

oblique incidence occurs when the incident sound beam strikes the boundary at any angle other than 90°

Question 15

two physical principles always apply to reflection with oblique incidence:

Answer 15

1) conservation of energy
2) reflection angle = incident angle

Question 16

what is Snell’s law?

Answer 16

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

Question 17

what is a reflection that arises from a rough boundary?

Answer 17

diffuse reflection (backscatter)

Question 18

what is considered a dominant contributor to attenuation?

Answer 18

absorption

Question 19

as path length increases, attenuation of ultrasound in soft tissue does what?

Answer 19

increases

Question 20

acoustic impedance is also known as:

Answer 20

characteristic impedance

Question 21

in order to have reflections occur, what do we have to have?

Answer 21

media on either side of the boundary have different impedances

Question 22

what type of probe would you use for abd images vs small parts?

Answer 22

higher frequency on parts closer to surface

lower frequency on parts that are deeper in the body

Question 23

what is the attenuation coefficient for soft tissue?

Answer 23

0.5 dB/cm/MHz

Question 24

how do we determine attenuation?

Answer 24

determined by 2 factors:

path length, frequency of sound

Question 25

decibels and intensities

Answer 25

3dB-double

10dB-ten times larger

• 3dB-half
• 10dB-one tenth

Question 26

what’s the difference between more and less attenuation in regards to frequency and distance?

Answer 26

more attenuation:

longer distances, higher frequencies

less attenuation:

shorter distances, lower frequencies

Question 27

what is sound going in all different directions?

Answer 27

scattering

Question 28

sound back to the transducer is created by:

Answer 28

reflection:

specular(mirror), diffuse(backscatter)

Question 29

what is Rayleigh scattering related to?

Answer 29

organized and omnidirectional

Rayleigh scattering always equals frequency⁴

when frequency doubles, Rayleigh scattering is 16 times greater

Question 30

what is the calculation for acoustic impedance?

Answer 30

acoustic impedance =

density(of a medium) x speed(at which sound travels in medium)

units-rayls(z)