Basic Interartions Of X-Rays With Matter Flashcards

1
Q

What is the fate of an x-ray?

A

Absorption in the patient
Scatter
Transmission through patient*

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2
Q

What does an x-ray interaction depend on?

A

Atomic number of the element (Ca in bones, H20 in cells)
Energy of x-ray (weak rays absorbed by tissue)

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3
Q

Higher atomic number materials attenuate (reduction in force) a ____________ than low atomic number materials

A

Greater % of the beam

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4
Q

What do x-ray photons interact with?

A

Orbital electrons (diagnostic energy range interactions ALWAYS) or nucleus of atoms

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5
Q

Most important ways x-ray photon interact with matter

A

Photoelectric effect
Compton scattering

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6
Q

Photoelectric effect

A

When a photon interacts with an inner shell electron in the atom and removes it from the shell

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7
Q

Photoelectric effect process

A

X-ray photon strikes an electron in the inner (K) shell —> incident photon must have enough energy to remove electrons in shell —> photoelectron removed —> incident photon absorbed

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8
Q

What is the electron removed in the photoelectric effect called?

A

Photoelectron

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9
Q

How is the atom stabilized during the photoelectron effect?

A

An electron from the outer shell drops into the inner shell and continues from shell to shell until the atom is stabilized

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10
Q

The energy lost by outer shell electrons filling the vacancies is emitted as____________

A

characteristic radiation

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11
Q

Compton scatter

A

Incident photon with high energy strikes a free outer shell electron —> ejects it from orbit —> photon deflected by electron and travels in a new direction as scatter

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12
Q

Results of compton scatter

A

Recoil electron and a scattered less energetic photon

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13
Q

What does scatter radiation produce?

A

Fog: produces an overall density to the image —> reduction in radio graphic contrast

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14
Q

Ways to reduce Compton scattering

A

Collimation to a small field size
Use high energy beam (kVp)
Use grids
Decrease size of patient thickness (no control)

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15
Q

Collimators

A

X-ray beam restrictors that include the center of the beam for a smaller field of view and less scatter
Adjustment horizontal and vertical shutters

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16
Q

Advantages of collimators

A

Improve image quality by reducing scatter
Less exposure to patient and personnel by limiting area exposed to radiation

17
Q

What are the purpose of grids

A

Absorbs scatter radiation and detracts from image quality

18
Q

Advantages of grids

A

Improves image detail by removing x-rays traveling at angles (not carrying representative information)

19
Q

Disadvantages of grids

A

Some useful rays are absorbed
Requires increase in mAs to accomplish adequate film exposure
Increased patient radiation exposure

20
Q

Ionizing radiation: Particulate (alpha and beta particles)

A

Emitted from nuclei
Short range of travel through matter due to mass and charge

21
Q

Ionizing radiation: electromagnetic radiation

A

X-rays (emitted from orbital shell)
Gamma rays (emitted from nucleus)

22
Q

Alpha particles

A

Positively charged, made of 2 proteins and 2 neutrons from atoms nucleus
Energetic, heavy and use up energy over short distances (can’t travel far from atom)

23
Q

Where do alpha particles come from?

A

Decay of the heaviest radioactive elements: uranium and radium

24
Q

Beta particles

A

Small, fast moving, negative charge and emitted from atoms nucleus during radioactive decay
More penetrating, less damaging to living tissue and DNA

25
Q

Where do beta particles come from?

A

Emitted by unstable atoms: hydrogen 3 (tritium), carbon 14 (strontium 90)

26
Q

How can alpha and beta particles be stopped?

A

Alpha: sheet of paper
Beta: layer of clothing

27
Q

X-rays and gamma rays

A

Photons
Travel @ the speed of light and unlimited travel in matter

28
Q

Where are gamma rays emitted and stopped?

A

Emitted from nucleus (shortest wavelength of EM radiation)
Stopped by several feet of concrete

29
Q

Where are x-rays emitted and stopped?

A

Emitted outside nucleus in electron cloud
Stopped by lead

30
Q

What produces ionizing radiation?

A

Radiographs
Fluoroscopy/ conventional angiography
CT
Nuclear medicine

31
Q

Suit up for radiation protection

A

Lead apron and gloves: 0.25- 1 mm lead

32
Q

Inverse square law

A

Intensity of rays change inversely with the square of the distance
Intensity decreases with distance from the source

33
Q

ALARA

A

As low as reasonably achievable