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Ch 4
Photographic Properties
| Question | Answer |
|---|---|
| Photographic properties effect | Visbility, Density, Contrast |
| Geometric Properties Effect | Sharpness, Recorded Detail, Distortion |
| Radiographic Density | The overall blackness produced on the image after processing |
| Controlling factor of Density | mAs |
| Influencing factors of Density | kVp, Distance, Grids, Film-screen speed, collimation, anatomic part, anode heel effect, filtration, processing |
| mAs= | Quantity |
| kVp= | Quality |
| The Law of Reciprocity | mA x s = mAs (200mA @ .10s = 20 mAs) |
| The minimal change needed to correct density errors is determined by | multiplying or dividing mAs by 2. |
| When greater change in mAs is needed.. | multiply or divide by 4, 8, etc |
| ___ kVp ___ Quantity of radiation striking the IR and ___ density. | Increases, increases, increases |
| Increasing kVp by 15% will ___ density (math) | Double; __kVp x 1.15 = end kVp |
| Decreasing kVp by 15% will ___ density (math) | Cut in half; ___kVp x .85 = end kVp |
| To MAINTAIN density when kVp increases by 15% | Divide mAs by 2 kVp x 1.15 |
| To MAINTAIN density when kVp decreases by 15% | Multiply mAs by 2 kVp x .85 |
| To reduce patient dose ___ kVp ___ mAs | Increase; decrease |
| As SID increase, | the xray bream intensity is spread over a larger area, this decreases the overall intensity of the xray beam raching the IR |
| Inverse Square Law | I1/I2=SID2(squared)/SID1(squared) |
| Density Maintenance Formula | mAs1/mAs2=SID1(squared)/SID2(squared) |
| Increasing SID needs ___ mAs | More |
| Grids | Grids absorb the scatter radiation exiting the patient; Limiting the amount striking the IR and improves image quality; they also absorb some of the transmitted radiaion exiting the pt and reduce the amount of density produced on the radiograph |
| Grids are ___ for pt ___ for film | Bad; good The more efficient a grid absorbs scatter, the greater the increase in mAs is required |
| Grid Conversion Factor | mAs1/mAs2=GCF1/GCF2 |
| Grid Conversion FactorS | No grid 1 5:1 2 6:1 3 8:1 4 12:1 5 16:1 6 |
| Film Screen Speed | The greater the speed the greater the density; When the speed of the system changes; mAs should be changed |
| Film Screen Speed Formula | mAs1/mAs2=RS2/RS1 |
| Anatomic Part | Thickness of the anatomic part affects the amount of xray beam attenuation that occurs; thick-absorbs more (decreasing density) thin-absorbs less (increasing density) |
| Anatomic Part Conversion | For each 4-5cms of thickness, increase mAs x2 |
| The best for an anode heel effect is ____ SID and a ___ field size | Short, Large |
| Anode Heel Effect | The intensity along the longitudial axis of the primpart xray beam varies; this variance is called AHE AHE is a decrease in the primary beam intensity on the anode side of the tube |
| Tube Filtration Contributors | These variations are so slight that they would have very little effect on density |
| Compensating Filters Contributors | Produce uniform densities; mAs must be increased to maintain overall density |
| Film Processing Contributors | Variability in temp, chemisty and transporting can adversely affect density |
| Digital Imaging | Changes in mAs kVp SID will alter the I of radiation reaching the IR; The relationship b/t mAs and density is not the same for DR; Quality of image is adversly affected; Techs use more exposure then needed; The data can be altered to correct error in |
| Relationship to Density: mAs | Direct |
| Relationship to Density: kVp | Direct |
| Relationship to Density: SID | Inverse to the square of the SID |
| Relationship to Density: Grids | Inverse |
| Relationship to Density: Relative Speed | Direct |
| Relationship to Density: Collimation | Indirect |
| Relationship to Density: Bigger pt | Inverse |
| Relationship to Density: Generator output | Direct |
Created by:
rachelbeatty4
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