Chapter 11

Question 1

define 15% rule

Answer 1

• The 15% rule states that changing the kVp by 15% has the same effect as doubling the mAs or reducing the mAs by 50%
• Maintaining or adjusting exposure to the IR can be accomplished with kVp

Question 2

define body habitus

Answer 2

the general form or build of the body, including size

Question 3

what are the 4 different types of body habitus

Answer 3

• sthenic
• hyposthenic
• hypersthenic
• asthenic

Question 4

define sthenic

Question 5

define hyposthenic

Question 6

define hypersthenic

Question 7

define asthenic

Question 8

define direct square law

Answer 8

provides a mathematical calculation for adjusting the mAs when changing the SID.

Question 9

define exposure maintenance formula

Answer 9

provides a mathematical calculation for adjusting the mAs when changing the SID.

Question 10

define inverse square law

Answer 10

• states that the intensity of the x-ray beam is inversely proportional to the square of the distance from the source
• The relationship between distance and x-ray beam intensity

Question 11

define magnification factor (MF)

Answer 11

• indicates how much size distortion or magnification is demonstrated on a radiographic image.
• MF = SID / SOD

Question 12

define object to image receptor distance (OID)

Answer 12

• When distance is created between the object radiographed and the IR
• decreased beam intensity may result

Question 13

define source to image receptor distance (SID)

Answer 13

• The distance between the source of the radiation and the IR
• affects the amount of radiation reaching the patient
• the intensity of the radiation varies at different distances

Question 14

define source to object distance (SOD)

Answer 14

• the distance from the x-ray source (focal spot) to the object being imaged
• SOD = SID - OID

Question 15

what are the 3 primary exposure factors?

Answer 15

• mA
• seconds
• kVp

Question 16

does mAs control quality or quantity?

Answer 16

• quantity
• controls the number of electrons boiled off the filament

Question 17

does mAs and exposure value have a direct or indirect relationship?

Answer 17

direct

Question 18

What happens to the exposure value when mAs is increased?

Answer 18

• exposure increases

Question 19

what happens when the exposure value when mAs is decreased?

Answer 19

• exposure decreases

Question 20

true or false: In order to get a certain mAs, the milliamperage or time can be adjusted to get the same byproduct

Answer 20

true
- when we look for a mAs of 20, different methods can be applied:
100 mA x 0.2s = 20 mAs
200 mA x 0.1s = 20 mAs

Question 21

what type of relationship does milliamperage and exposure time have?

Answer 21

• indirect
• when adjusting mAs and time, they have an indirect relationship in order to get a specific mAs
• 50 mA x 200ms (0.2s) = 10 mAs
• 200 mA x 50ms (0.05s) = 10 mAs
• the variables depend on the type of examination being done and the type of tissue density (pediatrics, elders, etc.)

Question 22

Can mAs control brightness level when using digital IR?

Answer 22

• no
• need to make sure your exposure is correct in order for the Image to be diagnostic

Question 23

How is the brightness level affected when thr mAs is too low?

Answer 23

• image is bright, but there’s an increased on quantum noise

Question 24

How is the brightness level affected when the mAs is too high?

Answer 24

• exposes the patient with too much radiation

Question 25

define kVp

Answer 25

- affects the exposure to the IR because it alters the amount and penetrating ability of the x-ray beam - more kVp increases kinetic energy

Question 26

true or false: Increasing or decreasing the kVp changes the amount of radiation exposure to the IR and the subject contrast produced within the image.

Answer 26

true

Question 27

Can kVp control brightness level when using digital IR?

Answer 27

-no - has the same affect as mAs

Question 28

what controls image brightness?

Answer 28

- computer processing

Question 29

What is the formula to increase kVp by 15%?

Answer 29

- multiply kVp by 1.15 - divide mAs by 2

Question 30

what is the formula to decrease kVp by 15%?

Answer 30

- multiply kVp by 0.85 - multiply the mAs by 2

Question 31

what is a disadvantage of high kVp?

Answer 31

- increase of scatter - higher chances of photoelectric - possible lower contrast (due to scatter)

Question 32

what is a desired technique when doing examinations?

Answer 32

- a high kVp and a law mAs - helps reduce patient dose

Question 33

name the secondary factors

Answer 33

- focal spot size - SID - OID

Question 34

define focal spot size

Answer 34

- affects the sharpness of the beam - small filament = increased spatial resolution (lower mA setting) - large filament = decreased spatial resolution (higher mA setting)

Question 35

what focal spot size is desirable?

Answer 35

- large focal spot - spreads out heat better

Question 36

true or false: Modern radiographic x-ray generators are equipped with safety circuits that prevent an exposure from being made if that exposure exceeds the tube-loading capacity for the focal spot size selected.

Answer 36

true

Question 37

whats the formula for inverse square law?

Answer 37

- I1/I2 = D2^2/D1^2

Question 38

true or false: Increasing the SID requires that the mAs be increased to maintain exposure to the IR, and decreasing the SID requires a decrease in the mAs to maintain exposure to the IR.

Answer 38

true

Question 39

what are the standard SID distances?

Answer 39

40, 48, 72 inches

Question 40

what other components does SID effect?

Answer 40

- image distortion (magnification) - spatial resolution

Question 41

true or false: As SID increases, size distortion (magnification) decreases and spatial resolution increases; as SID decreases, size distortion (magnification) increases and spatial resolution decreases.

Answer 41

True

Question 42

what does it mean when the MF is greater than 1?

Answer 42

there is a percentage of magnification