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Radiology12
Density
| Question | Answer |
|---|---|
| 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
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