Unit 1

Question 1

What is AEC? (the acronym AND what it is used for)

Answer 1

“Automatic Exposure Control”
A system used to consistently control amount of radiation reaching the IR by terminating the length of exposure

Question 2

[with AEC] How does changing KVP affect: density

Answer 2

No appreciable effect

Question 3

[with AEC] How does increasing KVP affect: exposure time

Answer 3

Higher kVP will decrease the exposure time to reach predetermined amount of exposure

Question 4

[with AEC] How does increasing KVP affect: radiation exposure to patient/dose

Answer 4

Higher kVp will decrease exposure to patient as there will be a decreased exposure time

Question 5

[with AEC] How does increasing mA affect: time of exposure

Answer 5

Increasing mA decreases exposure time

Question 6

[with AEC] How does decreasing mA affect: time of exposure

Answer 6

Decreasing mA increases exposure time

Question 7

[with AEC] How does changing mA affect: density

Answer 7

Density remains the same. With AEC the machine will continue running until the optimal amount radiation has hit the IR

Question 8

What is essential when using AEC?

Answer 8

-Selecting the appropriate bucky
-Selecting the appropriate detector(s)
-Centering anatomy over the detector(s)

Question 9

What 2 things might cause improper receptor exposure despite centering/selecting AEC options correctly?

Answer 9

• The patient has anatomic or pathologic variants (ex. using AEC on a patient with a prosthesis)
  -Inappropriate collimation (excessive will result in long exposure times, insufficient will result in very short exposures)

Question 10

How do you adjust exposure when using AEC?

Answer 10

Density controls (ex. -2, -1, +1, +2). Usually in 25% increments

Ex. Selecting +2 will increase the predetermined exposure level needed to terminate the time by 50%

Question 11

What is differential absorption?

Answer 11

Anatomic tissues absorb and transmit x-rays differently based on their composition (atomic number and tissue density)

Question 12

What is attenuation?

Answer 12

Primary beam loses some of its energy (number of photons) as it interacts with anatomic tissue

Question 13

What is the photoelectric effect?

Answer 13

Complete absorption of incoming photons (ex. x-rays ionizing an atom)

Question 14

What is the Compton effect?

Answer 14

When an incoming photon loses some but not all of its energy, then changes direction

Question 15

How does tissue thickness affect beam attenuation?

Answer 15

Thin patient transmits more radiation than thick

Thick patient absorbs more radiation than thin

Question 16

How does type of tissue affect beam attenuation? (High or low atomic #?)

Answer 16

Tissues of higher atomic numbers increase beam attenuation

Question 17

Which tissue type absorbs the most radiation: bone, fat, or air?

Answer 17

Bone

Question 18

How does tissue density affect beam attenuation?

Answer 18

Increasing the compactness of atomic particles/tissue density, will increase beam attenuation

Question 19

How does x-ray beam quality affect beam attenuation?

Answer 19

Higher kVp will decrease beam attenuation

Question 20

What is exit radiation composed of?

Answer 20

Transmitted and scattered radiation

Question 21

What is exit radiation also known as?

Answer 21

Remnant radiation

Question 22

What is radiographic quality determined by?

Answer 22

How the image accurately represents anatomic area of interest

Question 23

What determines the visibility of anatomic structures?

Answer 23

Brightness and contrast

Question 24

What determines accuracy of structural lines?

Answer 24

Spatial resolution and distortion

Question 25

What is subject contrast the result of?

Answer 25

Absorption characteristics of anatomic tissue radiographed and the quality of the x-ray beam

Question 26

Would this produce high contrast or low contrast: Great differences in radiation absorption between tissues that vary greatly

Answer 26

Higher contrast

Question 27

Would this produce high contrast or low contrast: Fewer differences in radiation absorption between tissues that are more similarly composed

Answer 27

Lower contrast

Question 28

What is gray scale?

Answer 28

The number of different shades of gray that can be stored and displayed in a digital image

Question 29

What is scale of contrast?

Answer 29

Range of densities visible on film

Question 30

Describe the brightness of this image

Answer 30

Excessive brightness

Question 31

Describe the brightness of this image

Answer 31

Insufficient brightness

Question 32

What refers to the smallest object that can be detected in a digital image?

Answer 32

Spatial resolution

Question 33

What is radiographic misrepresentation of shape/size of an atomic part?

Answer 33

Distortion

Question 34

What causes size distortion?

Answer 34

SID and OID

Question 35

What causes shape distortion?

Answer 35

Misalignment of central ray, anatomical part, or IR

Question 36

What is unwanted exposure to the IR resulting in fog?

Answer 36

Scatter

Question 37

What phenomenon can scatter be caused by

Answer 37

Compton interactions

Question 38

Is scatter helpful? (It's exposure after all...)

Answer 38

No! Provides no useful diagnostic information. Just exposure to the patient

Question 39

How does scatter affect image contrast?

Answer 39

Scatter/fog will decrease image contrast

Question 40

What is quantum noise visible as?

Answer 40

Brightness/density fluctuations

Question 41

What does quantum noise depend on? What aspect of technique?

Answer 41

Dependent on photons (when there are too FEW x-ray photons). Happens with insufficient mAs

Question 42

What is an unwanted image on radiograph that may obscure anatomic information?

Answer 42

Artifact

Question 43

As SID increases, what should you do to technique? What about if SID decreases?

Answer 43

An increase in SID requires an increase in technique A decrease in SID requires a decrease in technique

Question 44

What formula is used to maintain exposure while changing SID?

Answer 44

Direct square law/"old mAs/new mAs"

Question 45

What is the rule for tube angulation and SID changes?

Answer 45

For every 5 degree angle, decrease SID by 1"

Question 46

How does technique change as you implement a tube angle?

Answer 46

Technique INCREASES

Question 47

How do you adjust technique for: Dry plaster cast

Answer 47

Double mAs OR Add 10 kVp

Question 48

How do you adjust technique for: Wet plaster cast

Answer 48

Double mAs AND Increase kVp 10%

Question 49

How do you adjust technique for: Dry fiberglass cast

Answer 49

No change in technique!

Question 50

How do you adjust technique for: Wet fiberglass cast

Answer 50

[No adjustment to mAs] Increase kVp by 5%

Question 51

What is the purpose of beam limiting devices (BLD)?

Answer 51

Limit the size of the field This reduces the amount of scatter radiation produced (makes a better picture) AND reduces PT exposure

Question 52

In general, how should technique change when you increase collimation?

Answer 52

Increase technique

Question 53

In general, how should technique change when you decrease collimation?

Answer 53

Decrease technique

Question 54

When changing technique for collimation, do you change mAs or kVp, or both?

Answer 54

You will alter one or the other- not both. Increasing kVp instead of mAs will result in less patient dose

Question 55

When increasing collimation from 14"x17" to 10"x12", how do you adjust mAs?

Answer 55

Increase mAs 40%

Question 56

When increasing collimation from 14"x17" to 10"x12", how do you adjust kVp?

Answer 56

Increase kVp +5

Question 57

When increasing collimation from 14"x17" to 8"x10", how do you adjust mAs?

Answer 57

Increase mAs 60%

Question 58

When increasing collimation from 14"x17" to 8"x10", how do you adjust kVp?

Answer 58

Increase kVp +10

Question 59

When decreasing collimation from 10"x12" to 14"x17", how do you adjust mAs?

Answer 59

Decrease mAs 40%

Question 60

When decreasing collimation from 10"x12" to 14"x17", how do you adjust kVp?

Answer 60

Decrease kVp -5

Question 61

When decreasing collimation from 8"x10" to 14"x17", how do you adjust mAs?

Answer 61

Decrease mAs 60%

Question 62

When decreasing collimation from 8"x10" to 14"x17", how do you adjust kVp?

Answer 62

Decrease kVp -10

Question 63

What is magnification factor (MF)?

Answer 63

The amount of size distortion or magnification demonstrated on a radiograph

Question 64

How do you determine Magnification Factor?

Answer 64

Question 65

What is the equation for determining true object size?

Answer 65

Image size/MF

Question 66

What is the equation for finding the object % of magnification?

Answer 66

Obj % mag = (image size-true size)/true size ×100

Question 67

What is the photographic effect formula?

Answer 67

Question 68

What is the ratio for seconds and milliseconds?

Answer 68

1 s/1000 ms

Question 69

As the primary beam attenuates, where does this energy go?

Answer 69

Photons are absorbed, scattered, and transmitted

Question 70

What is the photoelectric effect (PE)?

Answer 70

Complete absorption of the incoming photon. The x-ray ionizes the atom. A low-energy secondary x-ray photon is created.

Question 71

What is the probability of the photoelectric effect dependent on?

Answer 71

The energy of the incoming x-ray photon and the tissue's atomic number

Question 72

In what situations might the Compton effect occur?

Answer 72

It can occur within all diagnostic x-ray energies and is only dependent on the energy of the incoming photon, NOT the tissue's atomic number

Question 73

Does kVp reduce the number of Compton interactions?

Answer 73

No. Higher kVp reduces the number of interactions OVERALL, but the number of Compton interactions INCREASES in comparison to the number of PE interactions

Question 74

What is coherent (classical) scattering?

Answer 74

The incoming photon interacts with the atom, causing it to become excited. The x-ray does not lose energy, but it changes direction

Question 75

What happens to photons in the PE?

Answer 75

An incoming photon has sufficient energy to eject an inner-shell electron and be completely absorbed

Question 76

What fills the vacancy from the ejected inner-shell electron in the PE?

Answer 76

An electron from an outer-shell

Question 77

What is created in PE due to the difference in the electron's binding energies?

Answer 77

A secondary photon is created

Question 78

What does the probability of the PE depend on?

Answer 78

The energy of the incoming x-ray photon and the composition of the anatomic tissue

Question 79

What's the general rate of beam attenuation based on tissue thickness?

Answer 79

Every 4-5 cm/1.6-2" of tissue thickness, the beam is reduced by 50%