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What is density? The overall darkening or blackness of a radiograph.
What is the numerical values associated with optical density? Logarithms are used to demonstrate a wide range of values with small numbers (scale of 1-4)
OD can range from areas that are completely black where no light is transmitted (____) to almost clear (____) where nearly all light is transmitted. black= a numerical value of 4 clear= a numerical value of 0
Diagnostically, what is the useful range of densities? Between .5 and 2.5
What is the useful range of base + fog? Typically, .1 to .3
A radiograph that is too dark has _____ optical density and is considered to be ______ or _______. *Too much *overexposed *over penetrated
A radiograph that doesn't have enough optical density is ______, and is considered to be ____ or _____. *Too light *underexposed *under penetrated
What is the characteristic curve also known as? *H&D (Hunter & Driffield) curve *Sensitometric *D log E curve
What is the characteristic curve used for? To measure exposure to a film and the percent of light transmitted through the processed radiograph
The relationship between radiation exposure and optical density is termed ______. Sensitometry
Constructing a characteristic curve reqires: *Sensitometer (optical step wedge) *Penetometer (aluminum step wedge) * Densitometer
What is a densitometer? A device that has a light source focused through a pinhole. It measures the amount of light transmitted through each step of the radiographic image
What is a Penetrometer? A device that measures optical density.
What are the three major portions of a characteristic curve? *toe *straight-line portion *shoulder
What kind of density occurs at the toe end of the characteristic curve? Low densitites (light) = poor contrast/detail
What kind of density occurs at the shoulder end of the characteristic curve? High densities (dark) = poor contrast/detail
What happens in the straight-line portion of the characteristic curve? Maximum contrast = optimum quality
True or False. The characteristic curve is also useful in identifying image receptor contrast. True
The steeper the straight-line portion of the curve, the ____ the contrast of the image receptor. Higher
Does the characteristic curve identify latitude? yes
A high contrast image receptor (one with a steeper curve) has the _____ latitude, while the low contrast image receptor has the _____ latitude. *Narrowest *Widest
True or False. Latitude and contrast are inversely proportional. True
What are two factors that have a large impact on controlling density? mAs and SID
SID is generally fixed at certain measurements; most often 40" and 72". However, as the SID is made shorter or less, the density on a given image ______. Increases
What is the major controlling factor of density if SID is fixed? mAs
True or False. If a radiograph is too dark or too light, mAs would be the primary factor to change because it does not adversely affect other qualities. True. mAs is NOT a primary controlling factor in the other 3 radiographic qualities; only density.
How much must mAs be changed in order to see a visible change in optical density? 30%
The general rule for adjusting mAs to see a visible change in optical density is to_____. Either double the mAs or half it
True or False. Changes in mAs are directly proportional to changes in optical denstiy. True.
When mAs increases, what happens to optical density? It increases proportionally.
Should kVp be used to change optical density? No, because changing kVp affects other things such as penetration, scatter, and contrast.
If kVp were used to influence density, what rule would you apply? The 15% rule, which says changing the kVp by 15% will be equivalent to either doubling or halving the mAs.
True of False. In cases of low or high kVp ranges, the amount of kVp necessary to produce the desired change may be greater or less than 15%. Which law is this associated with? True. Failure of the law of reciprocity.
Density produced on a radiograph will be ____ ___ to the square of the distance. Inversely proportional
If all factors remain the same, the longer SID, the ____ optical density that will be present on the image. Why? *less, because the intensity of the beam is spread over a larger area.
How do grids affect optical density? The higher the grid ratio, more exposure factors must be utilized in order to maintain density.
How does filtration affect optical density? If filtration is added above the required minimum, an increase in exposure factors is required to maintain density. If exposure factors are not adjusted, an increase in filtration will result in a decrease in density.
How does beam restriction affect optical density? If you increase the collimation (which decreases the field size) equals a decrease in density.
Where is density the greatest if you use the anode heel effect? the cathode end of the tube
As mAs increases, what happens to density? It increases.
As kVp increases, density ____. Increases
If you increase your SID, you ____ your density. Decrease
If you use a higher grid ratio, what happens to density? Decreases
As filtration increases, density ___. Decreases
As film-screen speed increases, density ___. Increases
If you increase your beam restriction, the density does what? Decreases
If your patient factors (size, pathology) increase, density ____. Decreases
Created by: danielle89