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# PRI Formulas Test 2

### PRI Mathematical Formulas

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