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55 Cards in this Set
- Front
- Back
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What are exposure technique factors? (Definition)
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Determines the basic characteristics of radiation of the patient and the image receptor.
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What do exposure technique factors include? (4 things)
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kVp, mAs, Distance, Imager characteristics (focal spot size and added filtration)
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What is kVp?
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The primary control of beam quality therefore beam penetrability.
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What does kVp control?
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Controls the scale of contrast on the film
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If you increase kVp, what happens to scatter?
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It increases
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What exposure technique factor has more effect then any other factor?
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kVp, because it not only affects beam quality, but also secondarily influences beam quantity
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If kvp increase, what happens to density?
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It increases
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What does mAs control?
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Density. It determines the number of xrays in the primary beam, therefore, principally controls radiation quantity.
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What is the inverse square law?
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The intensity of light is inversely proportional to the square of the distance of the object from the source.
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Formula for Inverse Square Law?
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(Intensity 1 / Intensity 2) / (Distance 2 / Distance 1)
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What is the mAs formula?
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mAs2 = mAs1 x (d2^2/d1^2)(GF/GF2)(SCSP1/SCSP2)
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How many sizes can the focal spot have?
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2
Small and Large |
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What are large focal spots used for?
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Trunk work, Chests, Abdomens
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What are small focal spots used for?
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Extremity work
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What does the focal spot size do?
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It ensures that a sufficient mAs can be produced to image the dense body part.
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What you see "mR" in a problem, what formula do you use?
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Inverse square law
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Why would you choose a large focal spot when imaging a large part?
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Large focal spots provide the shortest possible exposure time which minimizes patient motion blur.
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What is the difference between large and small focal spots?
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The difference is the capacity to produce xrays. More xrays can be produced with a large focal spot.
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What does focal spot control?
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It primarily controls detail and focal spot blur
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What does added filtration do?
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Removes low energy, long wavelength x-rays and lowers skin exposure and pt dose.
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What is the normal thickness of added filtration and what is it made out of?
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0.5mm Al
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How much added filtration does the variable-aperture collimator usually provide?
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1.0mm Al
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What is the thickness of the additional added filtration that the manufacturers add between the tube housing and the collimator?
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1.0mm Al
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What is the total amount of filtration required for an xray tube?
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2.5mm Al
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Above 70 kVp, what amount of filtration is used?
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2.5mm Al
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What are the Image Quality Factors? (4 things)
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Density
Contrast Detail Distortion |
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What do the image quality factors determine?
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The characteristics of the radiographic image.
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What is density?
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The overall blackness
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What is black and clear numerically equivalent to?
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Black is 3-4
Clear is less than 0.2 |
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What is the blackening on the film a result of?
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Development of the silver bromide crystals in the film emulsion.
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What is the optical density formula? *
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OD = log10 lo/lt
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A film that is too dark has high optical density resulting from?
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Overexposure
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A film that is too light has low optical density resulting from?
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Underexposure
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Density is controlled by what 2 things? *
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mAs and SID
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Increasing SID will do what to density?
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It will decrease density
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Increasing mAs will do what to density?
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Increase it
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If you want to see a slight increase in density, the mAs must be increased by how much?
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30%
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Density is secondarily controlled by what? *
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kVp
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A change in kVp affects what things?*
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Penetration, scatter, patient dose, and contrast.
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What is the 15% rule?
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To increase density using kVp, an increase in kVp by 15% would be equivalent to doubling mAs.
Increase kVp by 15% - 1/2 mAs Decrease kVp by 15% - 2 mAs |
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What is the easiest method to increase/decrease the density?
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Increase/Decrease mAs
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What is contrast?
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Difference in density on adjacent anatomic structures or the variation in density present on a radiograph.
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What is contrast the result of?
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Differences in attenuation of the xray beam as it passes through various tissues in the body.
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What is scale of contrast?
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The range of optical densities from the lightest to the blackest part of the radiograph.
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What is the scale of contrast for a high contrast radiograph?
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Short
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Saying for Low kVp?
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Low kVp, High Contrast, Short Scale, Narrow Latitude
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Saying for High kVp?
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High kVp, Low contrast, Long Scale, Wide Latitude
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How much change is required in kVp to visually affect the scale of contrast?
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At least a 4 kVp change.
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What is detail?
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It describes the sharpness of structures on a radiograph
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What is detail evaluated by?
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Sharpness of image detail
Visibility of image detail |
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Factors controlling sharpness of detail? (5 things)
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Focal spot size
SID OID Type if intensifying screen Presence of motion |
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To produce the best sharpness of image detail, one should use what 3 things? (Saying)
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Smallest focal spot size
Longest SID Smallest OID |
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Decreased screen speed does what to detail?
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Increases detail
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What is visibility of image detail?
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Describes the ability to see the detail on the radiograph.
Fog reduces the ability to see the image. |
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Any factor that affects density and contrast will also affect what?
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Visibility of the detail.
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