PRI Mathematical Formulas
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| Calculating mAs | mAs = mA x second
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| Using 15% Rule: To increase density | Multiply the kVp by 1.15 (kVp * 1.15)
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| Using 15% Rule: To decrease density | Multiply the kVp by .85 (kVp * .85)
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| To maintain density: When increasing kVp by 15% | Divide the original mAs by 2 (mAs/2)
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| To maintain density: When decreasing kVp by 15% | Multiply the mAs by 2 (mAs * 2)
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| Density Maintenance Formula | mAs1/mAs2 = (SID1)^2/(SID2)^2
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| Adjusting mAs for Changes in Grid | mAs1/mAs2 = GCF1/GCF2
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| Grid Ratio: No grid | GCF:1
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| Grid Ratio: 5:1 | GCF: 2
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| Grid Ratio: 6:1 | GCF: 3
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| Grid Ratio: 8:1 | GCF: 4
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| Grid Ratio: 12:1 | GCF: 5
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| Grid Ratio: 16:1 | GCF: 6
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| Focal spot | the actual area of the target that is bombarded by electrons during x-ray productions
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| Do focal spot size only affect recorded detail | True
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| Resolution | the ability of the imaging system to resolve or distinguish between two adjacent structures
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| What is resolution expressed in | the unit of the pairs per millimeter(Lp/mm)
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| Distortion | misrepresentation of the size or shape of object being radiographed
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| Magnification | degree of image enlargement of the body tissues
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| Two factors that determine the amount of magnification | OID and SID
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| When is magnification greatest | with short SID and long OID
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| When is magnificationthe least | with long SID and short OID
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| Radiographic density | amount of overall blackness produced on the x-ray film
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| increasing mA (current) | increases amount electrons flowing
increases amount radiation (intensity)
increases density
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| increasing time | increases exposure
increases density
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| To make a visible change in density on an image requires what % change in mAs | at least 30%
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| kVp and density | direct relationship but not proportional throughout the range of kV
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| 15% Rule | changing the kVp by 15% will have the same effect on density as doubling the mAs or reducing the mAs by 50%
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| SID and density | increasing SID = decreased density
decreasing SID = increased density
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| Do distance have an effect on radiation quality | No effect
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| OID and density | increasing OID = decreased density
decreasing OID = increased density
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| large field size (decreasing collimation) | increases the amount of tissue irradiated
increases the amount of scatter radiation reaching the image receptor
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| small field size (increasing collimation) | reduces the amount of tissue irradiated
reduces the amount of scatter radiation reaching the image receptor
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| Grid and density relationship | increase in grid ratio = decrease in density
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| Grid and film speed relationship | increase in film speed = increase in density
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| milliamperage | control amount of radiation
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| focal spot size | determines recorded detail
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| large focal spot | have more exposure capacity
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| small focal spot | increases image detail
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| time | controls length of exposure
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| short exposure time | reduces patient motion
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| long exposure time | remove unwanted parts
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| mAs | control radiographic density
increase mAs = increases density
decrease mAs = decreases density
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| kVp | beam energy
controls scale of contrast
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| optimum or fixed kVp | amount of kVp that will penetrate the part no matter what size
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| distance | SID Source to image-detector distance
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| SID | reduce magnification
increase SID and decrease OID
increase magnification
decrease SID
increase OID
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| increase mA (milliampere) | increase mA(current)
increases amount electrons flowing
increases amount radiation (intensity)
increases density
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| increasing exposure time | increases exposure
increases density
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| mAs | does not influence radiation quality
control radiation quantity
increasing mAs = increases radiation
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| recorded detail | refers to the distinctness or sharpness of the structural lines that makeup the recorded images
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| focal spot size and recorded detail | as focal spot size increases, unsharpness increases and recorded detail decreases
as focal spot sizew decreases, unsharpness decreases and recorded detail increases
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| SID and recorded detail | increasing the SID decreases the amount of unsharpness and increases the amount of recorded detail
decreasing the SID increases the amount of unsharpness and decreases the recorded detail
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| OID and recorded detail | increasing the OID increases the amount of unsharpness and decreases the recorded
detail
decreasing the amount of OID decreases the amount of unsharpness and increases the recorded detail
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| recorded detail is affected by what five factos | focal spot size
SID
OID
intensifying screen
motion blur
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| The air gap must be how large in order to work | 6-10in
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| attenuation | reduction in the energy of the primary x-ray beam
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| contrast | the degree of difference between adjacent densities
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