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PRI Formulas Test 2
PRI Mathematical Formulas
| Question | Answer |
|---|---|
| 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 |
| milliamperage | control amount of radiation |
| 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 |
| mAs | does not influence radiation quality control radiation quantity increasing mAs = increases radiation |
| recorded detail | refers to the distinctness or sharpness of the structural lines that makeup the recorded images |
| 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 |
| 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 |
| 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 |
| recorded detail is affected by what five factos | focal spot size SID OID intensifying screen motion blur |
| The air gap must be how large in order to work | 6-10in |
| attenuation | reduction in the energy of the primary x-ray beam |
| contrast | the degree of difference between adjacent densities |
Created by:
dawn2000
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