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Density & Contrast
| Question | Answer |
|---|---|
| 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
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