Physics Review Ch. 5, 6, 7 Flashcards Preview

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Flashcards in Physics Review Ch. 5, 6, 7 Deck (63)
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1

How do you calculate intensity?

a beam's power divided by its area.
units: W/cm^2

2

What are other names for normal incidence?

perpendicular
orthogonal
right angle
90 degrees

3

Difference between normal and oblique incidence

normal incidence strikes the boundary at exactly 90 degrees
oblique incidence strikes the boundary at any angle other than 90 degrees (acute and obtuse)

4

Define incidence intensity

The sound waves intensity immediately before it strikes a boundary

5

Define reflected intensity

Is the intensity of the portion of the incident sound beam that, after striking a boundary, returns back from where it came

6

Define transmission intensity

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

7

IRC

Intensity Reflection Coefficient; the percentage of intensity that bounces back, after it strikes the boundary between 2 media. (1%)

8

ITC

Intensity Transmission Coefficient; the percentage of intensity that passes in the forward direction between 2 media. (99%)

9

Define Impedance

The acoustic resistance to sound traveling in a medium. Calculated by multiplying the density of a medium by the speed at which sound travels in the medium.
Units: rayls; Z

10

Impedance-what is takes to achieve reflection

Reflection of an ultrasound wave depends upon the difference in acoustic impedances of the two media at a boundary.

11

Define specular reflectors

When the boundary is smooth, the sound is reflected in only on direction in an organized manner

12

Conservation of energy

Applies at the boundary between two media.
IRC + ITC = 100%

13

Reflection and transmission with oblique incidence

We cannot predict; it's too complex

14

Define Refraction

Is a change in direction of wave propagation when traveling from one medium to another

15

Refraction occurs only when there is what?

1. Oblique Incidence. (not normal)
2. Different Propagation speeds between the media.

16

What is refraction associated with?

Transmission

17

Attenuation

The decrease in intensity, power, and amplitude as sound travels.
Units: dB

18

Attenuation is determined by?

1. Path length
2. Frequency of sound

19

What three processes contribute to attenuation?

1. Reflection
2. Scattering
3. Absorption

20

What is impedance determined by?

Medium

21

Define scattering

Is the random redirection of sound in many directions. (Disorganized and chaotic)

22

Define Rayleigh scattering

Is a special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength. (Organized and omnidirectional)
*omnidirectional-in all directions

23

Relationship between scattering and frequency

directly related; Rayleigh scattering is proportional to frequency^4

24

Formula for Impedance

Impedance (rayls) = density (kg/m^3) * prop. speed (m/s)

25

Formula for IRC and ITC

100% = IRC + ITC

26

What are other names for decibel notation?

relative measurement
comparison
ratio
logarithmic

27

Half-Value Layer

Is the depth of tissue that results in 3 dB of attenuation to the intensity.
May be called: penetration depth, depth of penetration, and half-boundary layer
Units: cm

28

Half-value layer thickness depends on what two factors?

1. The medium
2. The frequency of sound

29

Half-Value Layer conditions

Thin Half Value:
-High frequency sound
-Media with high attenuation rate
Thick Half Value:
-Low frequency sound
-Media with low attenuation rate

30

Five key words that are related to intensity

1. Spatial
2. Peak
3. Average
4. Temporal
5. Pulsed