Test 3 Review Flashcards
film’s overall darkness
density
density is primarily controlled by
mAs. mA X s. increase either factor and increase density
50% mAs reciprocal rule
double the mAs to make film darker, cut in half to make lighter.
increased density
too dark
decreased density
too light
factors that affect density
patient size, SID/FFD, kVp, Screens, Developing, Filtration
patient size
the larger the patient, the more mAs needed due to the increase of tissue thickness
SID/FFD
an increase in distance results in a decrease in density (rule of 3)
kVp
increase in kVp results in increase in density (more scatter is produced)
how does scatter affect film
scatter shows up as shades of gray and each shade of gray contributes to the level of darkness, directly affecting the amount of darkness on a film
kVp 15% rule
increase kVp by 15% (or 10) increases film density. decreasing it decreases density
200 speed screen
crystals are smaller thus requiring more mAs to take them.
400 speed screen
crystals are larger. dont need as much mAs to take them
grids
used to clean up scatter by taking away levels of gray. must increase mAs.
developing
too much developer or too much time in developer = increased density.
filtration
used to even out radiographic density. used when xraying something that has two different densities to keep the thin part from burning up. if used incorrectly, it will reduce density on the think part and cause the thin part to burn out
contrast
varying shades of gray. controlled by kVp.
scatter
undesirable grays on the film making it non diagnostic
long scale
low contrast. very dull and gray. results in using too much kVp.
short scale
high contrast. very black and white film. result of using low kVp.
when do you use a grid
more than 10cm or 75kVp. the higher the grid ratio, the better it works. reduces radiographic density.
detail
How well represented the anatomy is radiographically. The crispness of the radiograph, the definition of the radiograph
SSD/FID
72” = best detail, the closer the tube 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.
factors affecting detail
SID/FFD, OFD, denity, long scale, increased developer, tube tilt
tube tilt
Wrong tube tilt results in loss of detail, or no tube tilt when one is required results in loss of detail.
