Rad Physics Review Flashcards
Density
film’s overall darkness
primarily controlled by mAs
increased density = too dark
decreased density = too light
What is ‘overall darkness’ called?
Density
What controls Density?
mAs
What is the 50% mAs reciprocal rule?
double mAs to make film darker, cut mAs in half to make film lighter
Increased Density makes film
too dark / darker
Decreased Density makes film
too light / lighter
Factors Affecting Film Density
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.
Patient Size:
Density
the larger the patient the more mAs is needed due to the increase in tissue thickness
SID/FFD:
Density
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:
Density
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:
Density
increase kVp by 10 increases film density, decrease kVp by 10 decreases film density
200 speed screens
Density
crystals are smaller thus requiring more mAs to make them fluoresce.
400 speed screens
Density
crystals are larger so not as much mAs is needed to make them fluoresce.
Grids:
Density
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:
Density
too much developer = increased density, too much time in developer = increased density
Filtration:
Density
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.
Contrast
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
Scatter
undesirable grays on the film making it non diagnostic
Film appearance descriptors associated with kVp
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.
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.
Changing scale of a film while maintaining density / Density Maintenance Rule:
Long Scale to Short Scale
decrease kVp and increase mAs
Changing scale of a film while maintaining density / Density Maintenance Rule:
Short Scale to Long Scale
increase kVp and decrease mAs
Grids
used to clean up scatter
When are grids required?
When tissue thickness is 11cm or greater
Is mAs alteration required to maintain density?
Yes
Higher grid ratio the more scatter is cleaned up
Thus reducing radiographic density
Detail
how well represented the anatomy is radiographically. The crispness of the radiograph, the definition of the radiograph
Factors Affecting Detail
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
SID/FFD:
Detail
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:
Detail
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:
Detail
Increased density decreases detail (film will be too dark, anatomy not seen)
Long Scale:
Detail
too gray anatomy, not well demonstrated
Increased Developer:
Detail
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:
Detail
wrong tube tilt results in loss of detail, or no tube tilt when one is required results in loss of detail
Focal Spot:
Detail
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:
Detail
slow screen speed give more detail but also requires more mAs thus resulting in more radiation to the patient
