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Thrall > Physics > Flashcards

Physics Flashcards

1
Q

When were x-rays discovered?

A

Nov 8, 1985

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2
Q

What is the only distinction between x-rays and gamma rays?

A

Their source.

X-rays are from electrons

Gamma are from the nucleus.

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3
Q

What is the velocity of electromagnetic radiation?

A

C (speed of light) = frequency(s) x wavelength (m)

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4
Q

What is the energy of an electromagnetic radiation?

A

Energy = Planck’s constant x (C/wavelength)

Otherwords: Energy is inversely proportional to wavelength.

Unit = eV or electron volts.

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5
Q

What is the amount of energy in an x-ray is needed to ionize something?

A

15eV

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6
Q

What is exposure to radiation measured in?

A

Roentgen

C/kg

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7
Q

What is the unit for absorbed dose?

A

Rad

Gray

1Gy = 100rads

The difference in tissue absorption is what make radiographs

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8
Q

Dose Equivalent is measured in?

A

Sieverts

Rem

1Sv = 100 rem

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9
Q

What is the difference between deterministic effects and stochastic effects?

A

Deterministic - Has a threshold.

Stochastic - No dose, can happen at any time.

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10
Q

What is the #1 example of deterministic effects?

A

Cataracts

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11
Q

What is the maximum permissible dose?

A

The maximum absorbed dose that can be delievered to the whole body or a organ still be safe.

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12
Q

What is the primary international body focusing on protection against ionizing radiation?

A

International Commission on Radilogical Protection (ICRP)

Non-governmental.

Provides recommendations.

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13
Q

What is the whole body limit recommended by the ICRP?

A

20 mSv per year, averaged over 5 years and no one year should exceed 50mSv.

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14
Q

What is the governing body of the USA radiation protection?

A

National Council on Radiation Protection (NCRP)

THIS BODY RECOMMENDS.. no enforcement power!

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15
Q

What is the recommended whole-body limit set by NCRP?

A

50mSv per year with a lifetime accumulation not exceeding 10mSv.

No one under 18 should have occupational exposure.

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16
Q

What is the max monthly exposure for a fetus?

A

0.5mSv

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17
Q

Max radiation exposure to the general public (no including diagnostic imaging and radiation therapy)?

A

1mSv (0.1 rem)

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18
Q

What is the largest contributor to the general population due to background radiation?

A

Radon gas

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19
Q

What caused the largest increase in exposure to ionizing radiation in the general public of the USA?

A

CT scans.

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20
Q

Who defined ALARA?

A

National Regulatory Commission (NRC)

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21
Q

What are the three variables that affect ALARA or dose?

A

Distance

Shielding

Time

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22
Q

How do modern film badges work?

A

The are made of Al oxide or lithium fluoride crystals

They trap electrons that are energized by incoming radiation and then that is quantified.

Should be analyzed quarterly

23
Q

Two ways x-rays are created?

A

Characteristic (collisional)

Brehmstralung (radiative)

24
Q

How many x-rays can be produced by a incoming electron using brehmies?

A

Multiple braking events makes multiple x-rays.

25
Q

What is the process of eliminating the negative phase of the alternating current called? This is done in order to get a nice even flow of x-rays?

A

Rectification

26
Q

What is the diffference between the actual focal spot and the effective focal spot?

A

Actual focal is what hits the anode

Effective focal spot is based off the angle of incidence.

27
Q

What is the disadvantage of a small filament?

A

Unable to use high mA

28
Q

What are the relevant three interactions with matter?

A

Coherent scatter

Compton scattering

Photoelectric effect

29
Q

What is coherent scatter?

A

The photon direction is changed but nothing happens to its energy.

5% of the interaction

30
Q

What is the photoelectric effect?

A

The striking x-ray is completely absorbed.

It ejects a photoelectron from the INNER SHELL! This will be absorbed in the tissues.

Characteristic x-rays given off are absorbed as well.

Probablility of the this happeninig based on Z3

And 1/E3 (energy)

This is most important for radiograph making.

31
Q

What is compton scatter?

A

High energy photon ejects an outside electron (recoil electron) and continues at different angle

Probability depends on physical density (grams/cm3)

Increases until 1.02 MeV and then drops

32
Q

What does scatter x-rays create if they strike the cassette?

33
Q

What creates image blackness?

A

mAs - directly related.

kVp

focal film distance.

34
Q

What is the inverse square law?

A

I1/I2 = (d2)2/ (d1)2

Reason for decreased exposure and decreased blackness

The I’s can be changed to mAs

…. Then it is just the “Square law” no inverse

mAs1/mAs2 = (d1)2/(d2)2

35
Q

What affects detail or sharpness?

A

Motion

Focal spot size - problem is overheating with large mAs

36
Q

What is the penumbra in rads?

A

The edge unsharpness on large focal spots.

37
Q

What are intensifying screens?

A

Turns x-rays into light and therefore the need for a ton of x-rays is not needed.

38
Q

Intensfying screens are made from what materials?

A

CaWO4 or calcium tungstate

Rare-earth - Greater x-ray to light conversion = lower mAs

39
Q

The thicker an intensifying screen is the…what?

A

The faster it is because more absorbtion of x-rays happen thus making light faster with less x-rays

BUT

less detail because the diffusion of the light is more due to the thicker material and there for more distance for the light to diffuse.

DYE is placed in the screen to soak up some of this diffusion but that means more mAs is needed. Thus increased dose.

40
Q

In general mAs should be increase by a factor of what when a grid is used?

A

2-3 times.

41
Q

Patients of what size need a grid?

A

10 cm or thicker

42
Q

What is the grid ratio?

A

Height vs distance between the strips

43
Q

What effect does lines/inch of grid strips have on technique (mAs)?

44
Q

What is distortion?

A

The unequal magnification of the part being radiographed.

45
Q

What are the factors affecting contrast?

A

kVp

mAs

fogging/scatter (thickness, physical density, atomic number, beam energy)

46
Q

Short scale of contrast means what?

A

High contrast radiographs - all black and white.

47
Q

How does sound transmit energy?

A

By alternating between low pressure (rarefaction) and high pressure (compression)

48
Q

What is the difference between light/radio waves and sound?

A

Sound needs a medium to travel through

49
Q

The velocity of sound is based off of what?

A

The physical density (mass per volume) and stiffness of the medium

Velocity = Freq (MHz) X Wavelength (mm)

50
Q

What is the average velocity of sound?

A

1.54mm/us or 1540 m/s

51
Q

What is acoustic impedance and what is the equation?

A

Acoustic impedance = Velocity x Tissue density

52
Q

What is the equation for % reflected in US?

A

% reflected = (z2 - z1)/ (z2+z1) x 100

z = acoustic impedance

z2 is the acoustic impedance of the second tissue

z1 = first tissue.

53
Q

What is the angle of incidence?

A

The angle at which the sound wave encounters a medium.

Over 3º off of perpendicular and the sound will likely not reach the transducer.

54
Q

What are the three ways sound is attenuated?

A
  1. Absorption - heat - dominant coomponent in soft tissue
  2. Reflection
  3. Scatter

Thrall (19 decks)

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