Prime Factors & X-Ray Interactions Ch 11

Front 1

what are the 3 prime factors?

Back 1

milliamplerage/seconds (mAs)

kilovoltage (kVp)

distance (d)

Front 2

what is controlled by the radiographer?

Back 2

mAs, kVp, d

Front 3

Define Quantity

Back 3

the number of x-ray photons in the useful beam

Front 4

Quantity can also be referred to as ...

Back 4

x-ray output, intensity, or exposure

Front 5

what is quantity measured in?

Back 5

roentgens (R)

Front 6

how is quantity affected?

Back 6

mAs, kVp, distance, and filtration

Front 7

Define quality

Back 7

a measurement of the penetrating ability of the x-ray beam

Front 8

Hard penetrating is also referred to as..

Back 8

hard x-ray

Front 9

low penetrating is also referred to as..

Back 9

soft x-ray

Front 10

What is quality affected by?

Back 10

kVp and filtration

Front 11

high energy = _____ penetration

Back 11

high

Front 12

quality is numerically represented by ...

Back 12

half-value layer (HVL)

Front 13

what is half-value layer

Back 13

how much material is needed to decrease the beams intensity to half the value

Front 14

what is the primary controller of quantity?

Back 14

mAs

Front 15

what is the primary controller of quality?

Back 15

kVp

Front 16

what is mA

Back 16

measurement of tube current ..

the number of electrons crossing from the cathode to the anode per second

Front 17

when there is an increase in mA .... =

Back 17

increased number of electrons that cross the tube and hit the target

Front 18

mA is __________ to the e- in the tube (tube current)

Back 18

directly proportional

Front 19

when mA doubles so does ...

Back 19

the number of e- able to cross the tube

Front 20

mA is the number of ...

Back 20

electrons per second

Front 21

True/False

changing the time of the exposure will change the number of electrons crossing from anode to cathode

Back 21

false

cathode to anode

Front 22

what is mAs

Back 22

the product of the number of electrons crossing the tube and the length of time the electrons are allowed to cross

Front 23

mAs is _________ to the quantity

Back 23

directly proportional

Front 24

Equation:

____ x _____ = mAs

Back 24

mA x s = mAs

Front 25

Problem:

100 mA x .05 s = 5 mAs

double the mA:

___ mA x ___ s = ____ mAs

double the sec:

____ mA x ____ s = ____ mAs

Back 25

double the mAs:

200 mA x .05 s = 10 mAs

100 mA x .1 s = 10 mAs

Front 26

what is the reciprocity law?

Back 26

the total exposure (mAs) will remain unchanged as long as the intensity (mA) and the duration (s) of the exposure remain unchanged

Front 27

Define radiographic density

Back 27

the degree of blackening of an x-ray film

Front 28

What is the primary controller of density?

Back 28

mAs

Front 29

mAs and density are ________________.

Back 29

directly proportional

Front 30

how do we numerically identify density for our images?

Back 30

S number

Front 31

Equations:

200 mA x .083 = _____

100 mA x 2/5 s = _____

75 mAs = 100 mA x _____ s

15 mAs = 300 mA x _____ s

60 mAs = 300 ms x ____ mA

Back 31

16.6 mAs

40 mAs

.75 seconds

.05 seconds

.2 mA

Front 32

Define kVp

Back 32

controls the speed and energy of the electrons crossing the tube

Front 33

kVp effects what?

Back 33

quality and quantity

Front 34

If kVp effects quality if there is an increase in energy of the electrons ....

Back 34

x-ray photons have greater energy therefore there is a greater penetrability

Front 35

If kVp effects quantity the then the greater energy of the electrons ...

Back 35

are able to interact more times, producing more photons

Front 36

How does increasing mAs increase the number of photons in the beam?

Back 36

increase in mAs = more electrons = more photons

Front 37

how does increasing kVp increase the number of photons in the beam

Back 37

higher kVp = more interactions = more photons

Front 38

kVp has a _____ relationship to quantity and quality

Back 38

direct

Front 39

True/False:

change in kVp will impact density

Back 39

true

Front 40

changes in kVp will impact density ... how?

Back 40

incrased quantity of phontons increased density

Front 41

a change in kVp impact the penetrability of the beam? what does this do to the image?

Back 41

changes in contrast

Front 42

kVp is the primary controller of ..

Back 42

contrast

Front 43

Increasing the kVp will increase penetrability of the beam .. therefore creates an image with ...

Back 43

higher contrast

Front 44

a high contrast image is ..

Back 44

more black and white

Front 45

a low contrast image is ..

Back 45

more shades of gray

Front 46

Because adjusting kVp will change both quantity and quality .. what guide was developed to maintain exposure?

Back 46

15% rule

Front 47

If we increase kVp by 15% .. what will it cause with the exposure?

Back 47

double.

Front 48

if we decrease the kVp by 15% .. what will happen to the exposure?

Back 48

half

Front 49

Problem:

a pelvis x-ray is produced at 25 mAs and 70 kVp. what kVp would you need to double the exposure?

Back 49

15% increase in kVp .......

80.5 kVp

25 mAs

Front 50

Decrease kVp =

Back 50

decrease in density .. less dense .. more white

Front 51

increase in kVp by 15% corresponds with a ____ in mAs by _____.

Back 51

decrease in mAs by 1/2

Front 52

Problem:

an acceptable radiograph of the knee is produced using 10 mA at 60 Kvp. if the kVp is increase dby 15% to 69 kVp, what mAs would be needed to maintain the exposure?

Back 52

Half of 10 mAs ...

5 mAs

Front 53

which number should you adjust since mAs and kVp adjust density/IR exposure?

Back 53

mAs ...

mAs is hte primary controller of density/IR exposure.

Front 54

Define distance

Back 54

intensity of the x-ray photons vary greatly as distance is changed

Front 55

Increase in distance = _____ in intensity

Back 55

decrease

Front 56

intensity is expressed/measured in ...

Back 56

roentgen (R)

Front 57

how is intensity measured (tool)

Back 57

dosimeter

Front 58

Distance has a ______ relationship with exposure

Back 58

inverse

increase distance will decrease exposure

Front 59

What is the inverse square law?

Back 59

the intensity of radiation at a given distance from the source in inversely proportional to the square distance law

spine chest, tube wont get 72 inches. adjust technical factors for distance we can get

Front 60

what is the equation for the inverse square law

Back 60

Intensity 1 Distance 2 (squared)

___________ = _____________________

Intensity 2 Distance 1 (squared)

or

I1D1^2 = I2D2^2

Front 61

When we double the distance .... ____ area to cover ... equal to _____ the intensity

Back 61

4x the area 1/4 the intensity

Front 62

Double the distance = ____ the intensity

Back 62

1/4

Front 63

Half the distance = ____ the intensity

Back 63

4x

Front 64

Equation:

An exposure of 240 mR is recorded at a distance of 20 inches. assuming the same technical factors are used, what would the exposure be at 40 inches?

What equation is used?

Back 64

I1/I2=D2^2/D1^2

240 40^2

____ = ______

I2 20^2

I2 = 60 mR

Front 65

Increase distance = _____ in intensity = _____ in exposure

Back 65

decrease

decrease

Front 66

Define Expsoure maintenance formula.

What is it also called

Back 66

a practical application if the inverse square law in determining adjustment to mAs.

Also called direct square law

Front 67

What is the Exposure maintenance formula?

Back 67

mAs1 D1^2

______ = ______

mAs2 D2^2

Front 68

More distance = more or less mAs?

Back 68

more

Front 69

Equation:

an acceptable radiograph is taken using 25 mAs at 80 kVp with 40 inches SID. A repeat is needed at 56 inches. what should the new technical factors be?

What equation is used?

Back 69

mAs 1 D1^2

______ = ______

mAs 2 D2^2

25 mAs 40^2

________ = _______

x 56^2

x = 49 mAs

80 kVp

Front 70

if you are going to adjust kVp for an exam that is over-exposed would you decrease or increase by 15%

Back 70

decrease

Front 71

if you are going to adjust kVp for an exam that is under-exposed would you decrease or increase by 15%

Back 71

increase

Front 72

if you are going to adjust mAs for an exam that is under-exposed. would you half or double the mAs?

Back 72

double mAs

Front 73

if you are going to adjest mAs for an exam that is over-exposed. would you half or double the mAs?

Back 73

half mAs