Attenuation Process

Question 1

What type of interaction of energy (high, medium, low) with electrons is used in diagnostic x-ray?

Answer 1

Medium energy

Question 2

Define attenuation:

Answer 2

Any process that has a reduciton in radiation intensity

Question 3

What is the shape of the graph when depicting attenuation

Answer 3

Semilogarithmic

Question 4

Describe the interaction happening during the photoelectric effect:

Answer 4

1. Photon ionizes atom and a K shell electron in the body is ejected
2. All of the energy is absorbed-none left over from photon
3. The outershell electron drops down to vacancy and secondary charecteristic radiation (photoelectron) is produced

Question 5

What are the end products of the photoelectric effect?

Answer 5

1. Ion pair (free radical of the atom)
2. Photoelectron, which can cause new ionizations
3. Secondary charectoristic radiation (ussualy K shell)

Question 6

When is there no probability that the photoelectric effect will take place?

Answer 6

If the energy of the photon is just below the BE of the atom

Or reallyyyyy high

Question 7

When is there the greatest probability that the photo will occur?

Answer 7

Greatest probability if the photon E is just above the BE

Question 8

What is the relationship between the photoelectric effect density, E, ect.?

Answer 8

PE—> density, Z^3
————
E^3

Question 9

What happens when secondary charecteristic radiation is produced?

Answer 9

Will have lower E and will get absorbed by outer shell e-

Question 10

What is the effect on the image from the photoelectric effect?

Answer 10

1. No scattter radiation produced
2. Magnifies subject contrast
3. Shows difference in both Z and density

Question 11

How do you see greater attenuation with the photoelectric effect?

Answer 11

Lower kVp closer to the binding E of what you want to see absorbed

Question 12

What is the effect on the patient from the photoelectric effect?

Answer 12

1. Is a high dose interaction
2. All of the energy of the photon is absorbed by the body

Question 13

What are the other names for coherent scatter?

Answer 13

1. Thomson scatter
2. Rayleigh scatter
3. Unmodified scatter
4. Classical scatter

Question 14

Descibe the interactions that occurs during coherent scatter:

Answer 14

1. The photon strikes the whole atom and excites the entire thing
2. Once it calms down, all of energy is released
3. All of the E released adds up to the energy of a photon which is the same as the photon that hit it and will have the same wavelength

Question 15

What type of interaction occurs with coherent scatter?

Answer 15

Low energy interaction

Question 16

It what circumstance is it more likely that coherent scatter will occur?

Answer 16

Increased probability with high atomic number, and low energy photons

Doesnt happen often in radiography

Question 17

What is the relationship between coherent scatter and E, denstiy, ect.?

Answer 17

Coherent scatter—>Z^2/E

Question 18

What is the effect on the patient dose with coherent scatter?

Answer 18

No affect on dose because it doesnt damage the tissue

Question 19

What is another name for compton scatter?

Answer 19

Modified scatter

Question 20

Describe the interaction that occurs during compton scatter:

Answer 20

1. Photon ionizes atom (ussually outershell)
2. During ionization, it creates a compton e-
3. The photon gives random amount of kE to compton e-
4. The x ray photon changes direction and has less energy due to how much it gave up

Question 21

What is the angle of change in direction dependant upon in compton scatter? How much initial energy does it retain?

Answer 21

-Angle of change depends on how much energy was lost
-It retains 2/3 of initial energy and can interact with other tissues in the body

Question 22

What are the end products of compton scatter?

Answer 22

1. Ion pair (positive atom)-free radical
2. Compton e-
3. . Scattered photon with a longer wavelength

Question 23

What is the relationship between Compton scatter and E, density, ect.?

Answer 23

Compton scatter–> (density)/E

Question 24

When is compton scatter most likely to occur?

Answer 24

Occurs most when photon E is much higher than the binding energy of the atom

Question 25

With higher kVp's do we get more scatter?

Answer 25

At high kVp's, theres less scatter OCCURING, but SCATTERED PHOTONS have more energy so they can go out of the body and reach the IR

Question 26

What is the effect on the image from compton scatter?

Answer 26

1. Degrades image qualilty 2. Reduces contrast 3. Creates noise

Question 27

What are ways we can decrease compton scatter?

Answer 27

1. Grids 2. Collimation 3. Compression

Question 28

What is the effect on the patient from compton scatter?

Answer 28

1. Limited dose to patient -minimal photon energy loss 2. Compton electron -Further ionizations and absorption 3. Staff safety hazard-becuse high Es scatter can reach others in room

Question 29

Read over the interaction during pair production:

Answer 29

1. Photon comes in and interacts with the nucleus 2. **The electric field interacts with the photons and takes the E, and converts it into mass** 3. Pair of subatomic particles (e- and positron) is created and they fly off 4. Two photons are created by the positron called inialtion radiation

Question 30

When is pair production used in radiography?

Answer 30

Used in pet scans

Question 31

What energy does pair production require?

Answer 31

Greater than 1.02 MeV | If it was higher than this, E would split between 2 inialation radiation

Question 31

Read happens in photodisintigration

Answer 31

1. A photon interacts with the nucleus and excites it 2. It ejects nuclear fragments 3. It is how universe creates heavy metals (ei;supernova)

Question 31

What is the minimum amount of energy required for photodisintigration?

Answer 31

Greater than 10 MeV