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Ch 4

Photographic Properties

QuestionAnswer
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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