The Subject (Patient) and Radiobiology

Question 1

What are the different shades of gray on a film the result of?

Answer 1

differing amounts of photons making it through the patient (differential absorption)

Question 2

What happens to the photons that don’t make it?

Answer 2

they are attenuated

attenuation = any interaction that removes a photon from the primary beam

Question 3

What is the term for any interaction that removes a photon from the primary beam?

Answer 3

attenuation

Question 4

What is transmission the opposite of?

Answer 4

attenuation

Question 5

What is the term for an x-ray that passes through the patient?

Answer 5

transmission

Question 6

What impact will an increase kVp have on transmission?

Answer 6

it will increase transmission

Question 7

What are the two types of Attenuation of our focus?

Answer 7

Compton Scatter

Photoelectric Effect

Question 8

What is the most common interaction of attenuation?

Answer 8

Compton Scatter

~90%

Question 9

Where is the photon hitting the atom in Compton Scatter? And what happens?

Answer 9

hits OUTER shell electron –> electron is ejected–> photon deflected–> photon loses energy

Question 10

Does Compton Scatter or Photoelectric Effect ionize the atom? Is this good or bad?

Answer 10

BOTH ionizes atom

it is BAD

Question 11

Which type of attenuation deflects (scatters) the photon?

Answer 11

Compton Scatter

scatter = BAD; we want to reduce is as much as possible

Question 12

What does the angle of deflection occurring during Compton Scatter depend on?

Answer 12

the energy lost to electron

Question 13

What does a larger angle tell us about the energy lost during Compton Scatter?

Answer 13

larger angle = more energy lost

Question 14

At what angle does the electron deflect between for Compton Scatter? Greater than what angle is it considered “backscatter”?

Answer 14

0 to 180 degrees

greater than 90 called backscatter

Question 15

Of the attenuated interactions, what percentage does the Photoelectric Effect make up?

Answer 15

~10%

Question 16

Where does the photon hit during the Photoelectric Effect? What then happens?

Answer 16

hits INNER shell electron –> electron ejected–> photon disappears–> outer shell electrons fill “hole” –> gives off radiation

Question 17

What type of Attenuated interaction is the photon absorbed?

Answer 17

Photoelectric Effect

Question 18

During the Photoelectric Effect, what must the energy be of the photon in order to eject the electron?

Answer 18

greater than the binding energy of the inner shell electron

Question 19

What other interaction does the Photoelectric Effect should similar to?

Answer 19

Characteristic X-rays w/in the tube–> the only difference is the in the tube it is electron hitting electron

Question 20

Out of the Photoelectric Effect and the Compton Scatter, which one deflects and which one absorbs?

Answer 20

Photoelectric = absorbs

Compton Scatter = deflects

Question 21

When we increase the kVp, how is the percent of Photoelectric and Compton interactions change?

Answer 21

increase kVp will:

• decrease percent of Photoelectric interaction
• increase percent of Compton scatter

Question 22

Which type of Attenuation is it when the photon does not reach the film? What does this give our film?

Answer 22

Photoelectric Effect

CONTRAST

Question 23

Which type of Attenuation is it when the photon reaches the film? How does this impact contrast?

Answer 23

Compton Scatter

creates fog–> decreases film contrast and adds shades of gray

Question 24

What effect will more Transmission have on the absorption, shade, and density?

Answer 24

less absorption

darker shade

higher film density

Question 25

What effect does less Transmission have on absorption, shade, and density?

Answer 25

more absorption lighter shade lower film density

Question 26

What four things does Scatter production depend on?

Answer 26

1. density 2. kVp 3. atomic number of material 4. amount of tissue imaged

Question 27

Out of the four things that produce Scatter, which two can be controlled? 1. density 2. kVp 3. atomic number of material 4. amount of tissue imaged

Answer 27

kVp and amount of tissue imaged (collimation)

Question 28

What are the three ways that we can reduce the amount of tissue imaged to reduce scatter?

Answer 28

1. collimate in (increase collimation) 2. Recumbent-- have the patient lay down --> flattens out tissue due to gravity 3. use a grid

Question 29

What is a grid for x-ray taking? What does it do?

Answer 29

a thin plate in front of Bucky/image receptor it is innumerable amount of thin strops of lead that STOP scatter from reaching the film