Basic Interartions Of X-Rays With Matter

Question 1

What is the fate of an x-ray?

Answer 1

Absorption in the patient
Scatter
Transmission through patient*

Question 2

What does an x-ray interaction depend on?

Answer 2

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

Question 3

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

Answer 3

Greater % of the beam

Question 4

What do x-ray photons interact with?

Answer 4

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

Question 5

Most important ways x-ray photon interact with matter

Answer 5

Photoelectric effect
Compton scattering

Question 6

Photoelectric effect

Answer 6

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

Question 7

Photoelectric effect process

Answer 7

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

Question 8

What is the electron removed in the photoelectric effect called?

Answer 8

Photoelectron

Question 9

How is the atom stabilized during the photoelectron effect?

Answer 9

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

Question 10

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

Answer 10

characteristic radiation

Question 11

Compton scatter

Answer 11

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

Question 12

Results of compton scatter

Answer 12

Recoil electron and a scattered less energetic photon

Question 13

What does scatter radiation produce?

Answer 13

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

Question 14

Ways to reduce Compton scattering

Answer 14

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

Question 15

Collimators

Answer 15

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

Question 16

Advantages of collimators

Answer 16

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

Question 17

What are the purpose of grids

Answer 17

Absorbs scatter radiation and detracts from image quality

Question 18

Advantages of grids

Answer 18

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

Question 19

Disadvantages of grids

Answer 19

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

Question 20

Ionizing radiation: Particulate (alpha and beta particles)

Answer 20

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

Question 21

Ionizing radiation: electromagnetic radiation

Answer 21

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

Question 22

Alpha particles

Answer 22

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)

Question 23

Where do alpha particles come from?

Answer 23

Decay of the heaviest radioactive elements: uranium and radium

Question 24

Beta particles

Answer 24

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

Question 25

Where do beta particles come from?

Answer 25

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

Question 26

How can alpha and beta particles be stopped?

Answer 26

Alpha: sheet of paper
Beta: layer of clothing

Question 27

X-rays and gamma rays

Answer 27

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

Question 28

Where are gamma rays emitted and stopped?

Answer 28

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

Question 29

Where are x-rays emitted and stopped?

Answer 29

Emitted outside nucleus in electron cloud
Stopped by lead

Question 30

What produces ionizing radiation?

Answer 30

Radiographs
Fluoroscopy/ conventional angiography
CT
Nuclear medicine

Question 31

Suit up for radiation protection

Answer 31

Lead apron and gloves: 0.25- 1 mm lead

Question 32

Inverse square law

Answer 32

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

Question 33

ALARA

Answer 33

As low as reasonably achievable