Chapter 11

Question 1

Primary factors of Exposure Technique

Answer 1

kVp - kilovoltage peak
mA - milliamperage
Time - seconds
mAs - milliamperage seconds

Question 2

What mA is used for small filament?

Answer 2

100mA

Question 3

Benefits of using small filament

Answer 3

Will use the small focal spot giving you sharpness and good spatial resolution

Question 4

What mA is used for large body parts?

Answer 4

300 mA

Question 5

What happens when large filament is used?

Answer 5

Will use large focal spot, giving you large penumbra, crappy spatial resolution - but good enough for large body part

Question 6

What type of relationship does mA and s have

Answer 6

Inverse Proportional Relationship

Numbers can be adjusted to come out with the same dose (Resiprocity Law)

Question 7

What kind of relationship is kVp and Receptor Expsoure (RE)

Answer 7

Direct - Increasing kVp will affect RE by making xrays stronger

Question 8

Relationship between kVp and scatter

Answer 8

Increasing kVp, increased scatter

Question 9

How do you get rid of scatter?

Answer 9

Grid

Question 10

How does scatter affect contrast?

Answer 10

Lowers contrast

Question 11

How does changing kVP affect xray transmission?

Answer 11

A higher kVP increases the number of xrays reaching the IR, therefore increasing transmission

Question 12

What is the Inverse Square Law?

Answer 12

Relationship between distance of the xray beam and intensity

Initial Intensity (final distance)^2
——————— = ————————
Final intensity (Initial distance)^2

If distance doubles, divide dose by 4
If distance halves, times the dose by 4

Question 13

What are the standards xray SIDs?

Answer 13

40 inch and 72 inch

Question 14

What is the Direct Square Law?

Answer 14

Used when you change SID in order to maintain an optimum exposure image

Relationship between mAs and distance

Initial mAs Intl Dis ^2
————— = —————-
Final mAs Fin Dis ^2

Question 15

What happens when SID increases/decreased (spatial resolution and magnification)?

Answer 15

Increases:
Spatial resoltuion increases and magnification decreases

Decreases:
Spatial resolution decreases and magnification increases

Question 16

How do you fix a noisy image?

Answer 16

mAs

Question 17

Grid conversion factors

Answer 17

No grid –> 1
5:1 –> 2
6:1 –> 3
8:1 –> 4
10:1 –> 5
12:1 –> 5
16:1 –> 6

Question 18

Grid conversion equation

Answer 18

New mAs New grid factor
————- = ———————–
Old mAs Old grid factor

Question 19

Where does mA come from?

Answer 19

Step down transformer

Question 20

What is attenuation?

Answer 20

Decrease in intensity as the photon passes through matter

Question 21

What is the gray blanket on an image?

Answer 21

Scatter

Question 22

What is the relationship between kVp and attenuation?

Answer 22

Inverse

Question 23

What happens if the grid is tilted more than 3 degrees from perp

Answer 23

Grid cutoff

Question 24

What does it mean if a problem has the IR speed?

Answer 24

No grid was used.

Question 25

What is a good magnification factor?

Answer 25

1.1 to 1.3

Question 26

What is the line focus prinicple?

Answer 26

The relationship between the actual focal spot on the anode surface and the effective focal spot. Decreasing the size of the anode angle, decreases the effective focal spot

Question 27

Magnification Factor Equation

Answer 27

SID/SOD

Question 28

Relationship between field size and collimation

Answer 28

Inverse A large field size - decrease collimation A smaller field size - increase collimation

Question 29

What are the effects of a large field size?

Answer 29

Increases the amont of tissue irradiated Increasing scatter Increasing the amount of radiation reaching the IR Lowering contrast

Question 30

What are the effects of using tube filtration?

Answer 30

Decreases x-ray quantity Filtration absorbs low-energy photons that do not contribute to the image. Reduces patient dose by removing these photons

Question 31

Relationship between mAs and part thickness

Answer 31

Thinner parts - need less mAs Thicker parts - need more mAs

Question 32

Guideline for thickness and mAs

Answer 32

For every change in part thickness of 4-5 cm, adjust the mAs by a factor of 2

Question 33

What exposure technique factors affect spatial resolution?

Answer 33

Focal Spot Size SID OID Central Ray Patient thickness Motion

Question 34

What exposure technique factors affect contrast?

Answer 34

kVp OID Grid use Collimation Tube filtration Patient thickness

Question 35

What exposure techniques affect RE?

Answer 35

kVp mAs Grid OID SID CR Angle Collimation Tube filtration Patient Thickness

Question 36

How does SID affect prenumbra?

Answer 36

The greater the SID, the less prenumbra