Rad Physics Review

Question 1

Density

Answer 1

film’s overall darkness
primarily controlled by mAs
increased density = too dark
decreased density = too light

Question 2

What is ‘overall darkness’ called?

Answer 2

Density

Question 3

What controls Density?

Answer 3

mAs

Question 4

What is the 50% mAs reciprocal rule?

Answer 4

double mAs to make film darker, cut mAs in half to make film lighter

Question 5

Increased Density makes film

Answer 5

too dark / darker

Question 6

Decreased Density makes film

Answer 6

too light / lighter

Question 7

Factors Affecting Film Density

Answer 7

Patient Size: the larger the patient the more mAs is needed due to the increase in tissue thickness

SID/FFD: an increase in distance results in a decrease in density (rule of 3)

40” to 72” need to multiply mAs by 3

72” to 40” need to divide mAs by 3

kVp: an increase in kVp results in an increase in density (because when increasing kVp more scatter is produced which shows up on a radiograph as shades of gray and each shade of gray contributes to a level of darkness thus directly effecting the amount of darkness on a film (density)

kVp 15% rule or Rule of 10: increase kVp by 10 increases film density, decrease kVp by 10 decreases film density

Screens: 200 speed screens - crystals are smaller thus requiring more mAs to make them fluoresce. 400 speed screens - crystals are larger so not as much mAs is needed to make them fluoresce.

Grids: used to clean up scatter. When using a grid the mAs needs to be increased because the grid takes away levels of scatter (grays) thus taking away some color which results in taking away darkness so more mAs is needed to compensate. (Increasing the kVp will only increase scatter production which is what we are trying to get rid of.)

Developing: too much developer = increased density, too much time in developer = increased density

Filtration: used to even out radiographic density. When xraying a part that has two different thicknesses a filter is used cover the thin part to keep it from burning out. If used incorrectly it will reduce radiographic density on that thick part and cause the thin part to burn out.

Question 8

Patient Size:

Density

Answer 8

the larger the patient the more mAs is needed due to the increase in tissue thickness

Question 9

SID/FFD:

Density

Answer 9

an increase in distance results in a decrease in density (rule of 3)

40” to 72” need to multiply mAs by 3

72” to 40” need to divide mAs by 3

Question 10

kVp:

Density

Answer 10

an increase in kVp results in an increase in density (because when increasing kVp more scatter is produced which shows up on a radiograph as shades of gray and each shade of gray contributes to a level of darkness thus directly effecting the amount of darkness on a film (density)

Question 11

kVp 15% rule or Rule of 10:

Density

Answer 11

increase kVp by 10 increases film density, decrease kVp by 10 decreases film density

Question 12

200 speed screens

Density

Answer 12

crystals are smaller thus requiring more mAs to make them fluoresce.

Question 13

400 speed screens

Density

Answer 13

crystals are larger so not as much mAs is needed to make them fluoresce.

Question 14

Grids:

Density

Answer 14

used to clean up scatter. When using a grid the mAs needs to be increased because the grid takes away levels of scatter (grays) thus taking away some color which results in taking away darkness so more mAs is needed to compensate. (Increasing the kVp will only increase scatter production which is what we are trying to get rid of.)

Question 15

Developing:

Density

Answer 15

too much developer = increased density, too much time in developer = increased density

Question 16

Filtration:

Density

Answer 16

used to even out radiographic density. When xraying a part that has two different thicknesses a filter is used cover the thin part to keep it from burning out. If used incorrectly it will reduce radiographic density on that thick part and cause the thin part to burn out.

Question 17

Contrast

Answer 17

the varying shades of gray on a radiograph
primarily controlled by kVp
kVp is the power in the X-ray bundle, brings anatomy to the film, and causes scatter (thicker tissue causes scatter as well)
Scatter = undesirable grays on the film making it non diagnostic

Question 18

Scatter

Answer 18

undesirable grays on the film making it non diagnostic

Question 19

Film appearance descriptors associated with kVp

Answer 19

Long Scale / Low Contrast: a very dull gray film, this is a result of using high kVp (high kVp = lots of scatter production) Low contrast means low difference in color on the film it’s one big blob of gray

Short Scale / High Contrast: a very black and white film, this is a result of using low kVp (the low kVp gets absorbed thus causing the white on the film) High Contrast means high difference in color there is a big difference between black and white.

Question 20

Long Scale / Low Contrast:

Answer 20

a very dull gray film, this is a result of using high kVp (high kVp = lots of scatter production) Low contrast means low difference in color on the film it’s one big blob of gray

Question 21

Short Scale / High Contrast:

Answer 21

a very black and white film, this is a result of using low kVp (the low kVp gets absorbed thus causing the white on the film) High Contrast means high difference in color there is a big difference between black and white.

Question 22

Changing scale of a film while maintaining density / Density Maintenance Rule:
Long Scale to Short Scale

Answer 22

decrease kVp and increase mAs

Question 23

Changing scale of a film while maintaining density / Density Maintenance Rule:
Short Scale to Long Scale

Answer 23

increase kVp and decrease mAs

Question 24

Grids

Answer 24

used to clean up scatter

Question 25

When are grids required?

Answer 25

When tissue thickness is 11cm or greater

Question 26

Is mAs alteration required to maintain density?

Answer 26

Yes

Question 27

Higher grid ratio the more scatter is cleaned up

Answer 27

Thus reducing radiographic density

Question 28

Detail

Answer 28

how well represented the anatomy is radiographically. The crispness of the radiograph, the definition of the radiograph

Question 29

Factors Affecting Detail

Answer 29

SID/FFD: 72” is the best detail, the closer the tube is to the object there will be an increase in magnification thus the image will not be well-defined

OFD: if the part is not as close to the film as possible there will be magnification and that destroys detail. The part is not truly demonstrated.

Density: Increased density decreases detail (film will be too dark, anatomy not seen)

Long Scale: too gray anatomy, not well demonstrated

Increased Developer: decreased detail because there will be an increase in density thus the film will be too dark and anatomy will not be visible

Tube Tilt: wrong tube tilt results in loss of detail, or no tube tilt when one is required results in loss of detail

Focal Spot: located on the anode there is a large focal spot and a small focal spot. Routinely, the large focal spot is used to take X-rays. The small focal spot is used for better detail imaging like that of the odontoid.

Screen Speed: slow screen speed give more detail but also requires more mAs thus resulting in more radiation to the patient

Question 30

SID/FFD:

Detail

Answer 30

72” is the best detail, the closer the tube is to the object there will be an increase in magnification thus the image will not be well-defined

Question 31

OFD:

Detail

Answer 31

if the part is not as close to the film as possible there will be magnification and that destroys detail. The part is not truly demonstrated.

Question 32

Density:

Detail

Answer 32

Increased density decreases detail (film will be too dark, anatomy not seen)

Question 33

Long Scale:

Detail

Answer 33

too gray anatomy, not well demonstrated

Question 34

Increased Developer:

Detail

Answer 34

decreased detail because there will be an increase in density thus the film will be too dark and anatomy will not be visible

Question 35

Tube Tilt:

Detail

Answer 35

wrong tube tilt results in loss of detail, or no tube tilt when one is required results in loss of detail

Question 36

Focal Spot:

Detail

Answer 36

located on the anode there is a large focal spot and a small focal spot. Routinely, the large focal spot is used to take X-rays. The small focal spot is used for better detail imaging like that of the odontoid.

Question 37

Screen Speed:

Detail

Answer 37

slow screen speed give more detail but also requires more mAs thus resulting in more radiation to the patient