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Physics > Module 1 Physics > Flashcards

Module 1 Physics Flashcards

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1
Q

What is the equation for medium impedance? (and measurement)

A

AI = density x velocity (raylz)

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2
Q

What is the speed of EM waves?

A

3.0x10^8 m/s = FAST

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3
Q

What does it mean to be ionizing?

A

it can knock of electrons from atoms resulting in free radicals in the body which is not good

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4
Q

EM waves from short wavelength/high freq –> long wavelength/lowfreq

A

gamma ray, x-ray, UV, visible, infrared, microwave, radio

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5
Q

What are the acoustic variables?

A
  1. Pressure
  2. Density
  3. distance
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6
Q

Diagnostic Ultrasound Hz levels

A

1-15 MHz

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7
Q

What are the 4 sound wave parameters

A
  1. Freq and period
  2. Wavelength
  3. Amplitude (power/intensity)
  4. Prop. velocity
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8
Q

Define stress and strain

A

Stress - a change in pressure applied

Strain - % of change in volume from the stress

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9
Q

What is an acoustic variable

A

A mechanical change in a medium

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10
Q

What happens when we increase our overall gain?

A

we are increasing the voltage of already returned echoes that have been converted back into the electrical signal = increased amplitude = increased brightness and contrast

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11
Q

What is the measurement of attenuation? Why?

A

dB - large non linear energy changes occur

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12
Q

Relationship between frequency and amplitude?

A

No direct relationship but related through attenuation. Increase freq = increase attenuation = decrease amplitude

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13
Q

What has the longest pulse duration?

A

Continuous wave - continuous never stops

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14
Q

Smallest FOV

A

Sector

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15
Q

Lowest DF vs Highest DF

A

Lowest - B mode

Highest - Continuous wave, has a DF of 100

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16
Q

What is duty factors relations to bioeffects

A

Increased DF = increased bioeffects

17
Q

Why wont we lose a lot of energy when going through skin even though it has a high attenuation?

A

because its so thin

18
Q

What is the attenuation calculation

A

medium coefficient x frequency x distance (2)

19
Q

What does 3dB of intensity attenuation represent?

A

1/2

20
Q

What does 6dB of amplitude attenuation represent?

A

1/2

21
Q

3 types of reflectors

A

Specular - large, flat, and smooth
Scatter - small and rough
Rayleigh scatter - very small

22
Q

Specular reflections are highly dependent on what? And therefore independent from what?

A

highly angular dependent, and frequency independent

23
Q

What could cause a loss of the bright reflection in a specular reflector?

A

loss of the perpindicular angle (angular dependent)

24
Q

Scatter reflectors are dependent on what?

A

frequency dependent - increase freq = smaller wavelength = smoother reflector

25
Q

degree of rayleigh scatter =

A

f^4

26
Q

What kind of frequency does Doppler use?

A

Very low frequency to scan blood as an increased freq would increase friction and therefore loss of energy to heat and absorption
so wouldnt be able to see rayleigh

27
Q

Impedence formula

A

impedence = density x prop speed

28
Q

What is the Z value of Crystals

A

38 MRayls

29
Q

Z value of tissue?

A

2 MRayls

30
Q

In what cases will retraction occur

A
  • an oblique angle of incidence

- when the speeds at the boundary are different on either side

31
Q

What is the unit of amplitude

A

Pascals (Pa)

32
Q

What is the unit of power

A

Watts (W) or mW

33
Q

Relationship between power and amplitude

A

Power= amplitude squared

34
Q

Relationship of power and intensity

A

equal Power = intensity therefore intensity also = amplitude squared

35
Q

What is the Duty Factor

A

Displays the % of time the ultrasound system is producing sound
Its is the reinging period over the ringing and listening period
PD/PRP

36
Q

what does dampening the sound beam do?

A

it reduces the length of the “ring” therefore decreases the SPL

37
Q

What is the unit of density

A

kg/cm3

38
Q

What is snells law?

A

describes the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media (refraction)

39
Q

What is the total attenuation equation? How do you get this to amplitude form

A

medium coefficient (dB/cm-Mhz) X freq (MHz) X Distance (2) (cm)

Amplitude form - dB (attenuation amount) X 20 X log (Af/Ai)

Physics (12 decks)

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