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Density & Contrast

QuestionAnswer
What is Density? The overall blackness of an entire image.
What is Radiographic Density? The amount of overall blackness produced on the image after processing.
Controlling factors for Density. Ma & Time (mAs)
Influencing Factors for Density kVp Distance (SID) Grids Film Screen Speed Collimation Anatomic Part Anode Heel Effect Reciprocity Law Generator Output Filtration Film Processing
For there to be an "Optical" change in density, how much must you increase or decrease mAs? 30%
How does kVp influence density? Increase kVp, increase penetration = increase in density
To maintain density, if you increase kVp what must you do to your mAs? If you decrease kVp what must you do to you mAs? Decrease mAs, increase mAs
What is the 15% rule? Increase kVp by 15% decrease mAs by 50% Decrease kVp by 15% increase mAs by double
How does SID effect density? Increase SID, decrease penetration = decrease density Decrease SID, increase penetration = increase density
What is the Inverse Square Law? The relationship between beam INTENSITY (measured in mR) and distance. I1 (D2)2 I2 (D1)2
What is the Density Maintenance Formula? Maintaining density when the SID is altered. mAs1 = (SID1)2 mAs2 (SID2)2
How does OID influence density? increase in OID = decrease in quantity = decrease in density decrease in OID = increase in quantity = increase in density
How do grids influence density? increase grid = decrease in quantity = decrease in density decrease grid = increase in quantity = increase in density
Grid Conversion Formula mAs1 = GCF1 mAs2 GCF2 No grid = 1 5:1 grid = 2 6:1 grid = 3 8:1 grid = 4 (portable) 10:1 12:1 grid = 5 (bucky) 16:1 grid = 6
How does film screen speed influence density? increase in screen speed = increased density
What is the Film Screen Speed Formula? mAs1 = SS2 mAs2 SS1
How does anatomic part influence density? increased part = decrease quantity = decreased density decreased part = increased quantity = increased density **the thicker the part the more the part absorbs the xrays**
Which side of the tube are the xrays more intense? Cathode or Anode? Cathode
How does the Anode Heel Effect influence density? Decrease in beam intensity on anode side. To truly see the anode heel effect open collimators to 14x17
What is he Reciprocity Law? mA and time are inversely proportional when trying to main mA/film density Example: 400mA x .05s = 20mAs 200mA x .10s = 20mAs 300mA x 1/15s = 20mAs ** mainly used to control MOTION! **
How does generator output influenced density? Optimum exposure depends on the type of generator. More efficient generator require smaller technique settings. Increased frequency = increased density Increased frequency = mAs
How does tube filtration influence density? Increase filtration = decrease in density Increase filtration = increased mAs
2 types of filtration Added filtration and inherent filtration (makes up total filtration)
What is the purpose of filtration? Clean up scatter and harden the beam
What is inherent filtration? Filtration in the tube. Glass envelope, oil, metal tube housing.
What is added filtration? Filters added by technologist
What are compensating filters used for? To compensate for part thickness
How does film processing influence density? Increased temperature = increased density Increased time = increased density Increased temperature = increased density
Define Contrast The degree of difference between two adjacent densities
What is high contrast? Short scale, more black and white, few shades of gray
What is low contrast? Large number of densities and few differences among them. More grays, long scale.
What is film contrast? A result of inherent properties manufactured into a type of film and how it is radiographed.
What is subject contrast? Result of the combination of the absorption characteristics of the anatomic tissue radiographed and the level of kVp used
What are the controlling factors of contrast? kVp (the ONLY controlling factor for contrast)
What are the influencing factors of contrast? Grids, collimation, OID, anatomic part, contrast media, and processing
How does kVp control contrast? Controls the quality/penetrating power of the X-ray beam
How does kVp effect contract? Increase kVp, increase scatter, increase fog = decrease contrast, low contrast, long scale, lots of grays
How do grids influence contrast? Increase grid, decrease scatter, decrease fog = increase contrast, high contrast, short scale! more black and white
How does collimation influence contrast? Increase collimation (smaller field size), decrease scatter, decrease fog = increased contrast, high contrast, short scale, more black and white
How does OID influence contrast? Increased OID, decrease scatter, decrease fog = increased contrast, high contrast! short scale! more black and white
What is airgap? An OID of 6" or more that acts as a grid
How does the anatomic part influence contrast? Increase part size, increased kVp, increased scatter, increased fog = decreased contrast, low contrast! long scale! more shade of gray
How does tube filtration influence contrast? Increased filtration, decreased scatter in tube, increased beam hardness, increased penetration, increased scatter in body, increased fog = decrease in contrast, short scale, low contrast, more shades of gray
How does filtration influence contrast? Increase filtration, decrease in low energy X-rays, increase in beam intensity, increase scatter in body = decrease in contrast, low contrast, long scale, more grays
What does contrast media do? Adds density to anatomic structures that have low subject contrast
What is positive contrast? Materials with higher atomic number Ex: Barium and Iodine Produces LESS radiographic density than adjacent tissue on film ****APPEARS WHITE ON FILM****
What is negative contrast? Materials with lower atomic numbers Ex: air Produces MORE density than adjacent tissue in film **** APPEARS BLACK ON FILM****
How dies procession influence contrast? Increase OR decrease in time, temp, or chemicals = decrease contrast Either all shades of blacks OR all shades of white
How to change technique for fiberglass or plaster cast Fiberglass= increase mAs by at least 1 step Wet Plaster= 3x's mAs Dry Plaster= 2x's mAs
What are the 4 types of body habitus? Sthenic Hyposthenic Hypersthenic Asthenic
What do you do to your kVp when a patient has an additive disease? Increase
What do you do to your kVp when a patient has a subtractive disease? Decrease
Created by: Aborys88