Week 4 - Chapter 12

Question 1

Which types of interaction cause some degree of absorption within a patient?

Answer 1

All interactions - photoelectric, compton, coherent

Question 2

What is differential absorption?

Answer 2

The ratio between the absorption of one tissue and the adjacent tissue

Question 3

What is another name for differential absorption?

Answer 3

Subject contrast

Question 4

What type of contrast do bone and soft tissue provide?

Answer 4

High contrast because of how differently they attenuate the beam

Question 5

Where do more photoelectric and compton interactions occur?

Answer 5

In bone

Question 6

What is the result of the more interactions in the bone?

Answer 6

Higher attenuation factor

Question 7

How is subject contrast related to photoelectric/compton ratio?

Answer 7

It is directly proportional

Question 8

How is the attenuation factor calculated?

Answer 8

Photoelectric interaction value + Compton interaction value

Question 9

How is subject contrast ratio identified?

Answer 9

Higher Attenuation factor 1 / Lower Attenuation factor 2

Question 10

What would cause soft tissue to have more interactions?

Answer 10

Pathology

Question 11

How would the contrast ratio change when tissue pathology is present?

Answer 11

The contrast ratio would drop because the overall attenuation factor of soft tissue increases

Question 12

How does a smaller contrast ratio affect overall contrast?

Answer 12

The overall contrast would be reduced because the soft tissue would be lighter and look closer to the bone

Question 13

What three properties cause various subject contrast?

Answer 13

• thickness of tissue
• physical density of tissue
• average atomic number of the tissue

Question 14

How does atomic number affect attenuation?

Answer 14

Higher atomic number attenuates more x-rays

Question 15

What is tissue density?

Answer 15

The concentration of atoms or molecules within a tissue

Question 16

How are interactions affected by the number of atoms?

Answer 16

Photoelectric and compton interactions will double if the number of atoms double

Question 17

How are the density differences in the body classified?

Answer 17

They are so small that extreme differences in the density would be needed to get high subject contrast

Question 18

What are the three major categories based on tissue density?

Answer 18

Soft tissue, air in lungs and fat

Question 19

How does fat show up on an image?

Answer 19

Darker because it has less attenuation

Question 20

How does air show up on an image?

Answer 20

Very dark because there is very little attenuation

Question 21

Which type of xray is a good example of extreme differences in density?

Answer 21

A chest xray

Question 22

How does a chest xray demonstrate differences in density?

Answer 22

Air in the lungs and surrounding tissue will be highly contrasted, since tissue absorbed 1000x more radiation

Question 23

What does a high atomic number indicate?

Answer 23

An atom with more electrons in its shells

Question 24

How are atomic number and interactions related?

Answer 24

As atomic number increases, the likelihood of interactions increases exponentially

Question 25

What are contrast agents used for?

Answer 25

Introduced into cavities to provide increased subject contrast

Question 26

What is a common characteristic of contrast agents?

Answer 26

High atomic number

Question 27

What is the atomic number of barium?

Answer 27

56

Question 28

How do contrast agents affect the binding energy of the tissue?

Answer 28

It brings up the binding energy of the tissue closer to the x-ray energy which causes more photoelectric effect which causes brightness

Question 29

What impact does atomic number have on attenuation?

Answer 29

The impact is exponential, a small difference in atomic number yields a high contrast

Question 30

What is the atomic number of titanium?

Answer 30

Z# is 22

Question 31

What is the atomic number of water?

Answer 31

Average Z# 10

Question 32

How does scatter affect images?

Answer 32

Its bad for images and distributes a blanket of exposure across the IR

Question 33

How does scatter affect contrast?

Answer 33

Scatter reduces contrast by causing noise

Question 34

What is the opposite of attenuation?

Answer 34

Penetration

Question 35

What is penetration partially controlled by?

Answer 35

Changing the beam energy via kVp

Question 36

How are kVp, penetration and contrast related?

Answer 36

As kVp is increased, penetration is increased and contrast goes down

Question 37

How are contrast and gray scale related?

Answer 37

Low contrast = long gray scale
High contrast = short gray scale

Question 38

How is photoelectric effect related to kVP?

Answer 38

Photoelectric effect is inversely related to the cube of kVp
- As kVP increases probability of PE effect decreases

Question 39

How is scatter related to kVP?

Answer 39

As kVp increases scatter increases

Question 40

How does higher kVp affect the remnant beam?

Answer 40

Higher kVp increases radiation in the remnant beam which produces more scatter

Question 41

What factors affect scatter more than kVp?

Answer 41

Utilization of collimation and patient size

Question 42

What is spatial resolution?

Answer 42

Being able to see the object alone (sharpness or detail)

Question 43

What is contrast resolution?

Answer 43

Being able to tell the differences in the image in regards to color

Question 44

What is windowing?

Answer 44

The ability to make a longer scale of contrast shorter or shorter scale of contrast longer

Question 45

How does scatter show in images?

Answer 45

Make the images grayer overall

Question 46

What change will increase the proportion of photoelectric interactions occurring in a patient?

Answer 46

Introducing barium

Question 47

If the intensity of the x-ray beam is doubled, what effect will if have on the ratio between photoelectric interactions and Compton interactions?

Answer 47

Ratio will remain the same