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rtec
week 7 - image quality
| Question | Answer |
|---|---|
| What are the two photographic image qualities | Density & Contrast |
| What is density | Overall darkening of an image |
| What happens when the density is high | Dark image |
| What happens when the density is low | Bright image |
| A lot of photons means | High density |
| A low amount of photons mean | Low density |
| Anatomic Density | How thick a patient is |
| What happens when a patient is thicker | High anatomic density; photons stop |
| Optical Density | Seeing with our eyes an image |
| What happens to optical density when you have high anatomic density | Low optical density |
| What kind of relationship does anatomic and optical density have | Inverse relationship |
| What needs to be done in order to penetrate a thicker patient | Increase kVp and mAs |
| What needs to be done to get double density | mAs increased or doubled or kVp increased by 15% |
| Is density directly proportional to mAs | Yes |
| What is the controlling factor for density | mAs |
| How many influencing factors does density have | 6 |
| What are the influencing factors for density | kVp, SID, Beam Filtration, Beam Restriction, Body Thickness, Grids |
| Relationship between kVp and density | Not directly proportional but direct |
| Increasing kVp | Increases density (increasing x ray photons) |
| What does 15% mean | Double density |
| Relationship between SID and density | Inverse relationship |
| Decreasing SID (D) | Increases density |
| Relationship between beam filtration and density | Inverse relationship |
| Increasing filtration (D) | Decreases density |
| Relationship between beam restriction and density | Inverse relationship |
| Increasing beam restriction (D) | Decreases density |
| Relationship between body thickness and density | Inverse relationship |
| Increasing body thickness (D) | Decreases density |
| What is a disadvantage being a thick patient | Increased exposure |
| Relationship between grids and density | Direct relationship |
| Reducing grids (D) | Reduces density |
| What is contrast | Difference between dark and light areas |
| A slow transition has | A lot of grays in an area |
| Can scatter create lower contrast | Yes |
| Is viewing high or low contrast subjective | Yes |
| How do you know when an image is high in contrast | More black to white - fewer/no grays |
| How do you know when an image is low in contrast | Foggier, grayed our |
| To differentiate body structures, what contrast is needed | High contrast |
| What is high contrast also known as | Short-scale contrast |
| What is a short-scale contrast known from | kVp chart; narrow latitude and fewer grays |
| What is a step wedge | Metal piece, "mini staircase" |
| High kVp determines | Long time to go from black to white |
| Low kVp determines | A lot of white and a couple steps to completely dark |
| Mid-range kVp determines | Bunch of darks, some grays, then to white |
| What is Photoelectric Effect | Photons approaching a patient and completely absorbing it |
| Do the photons ever reach the IR when in Photoelectric Effect | No |
| What is Photoelectric Effect responsible for | White areas on an image |
| How are dark areas created | When there is no interaction |
| What is the controlling factor for contrast | kVp |
| How many influencing factors does contrast have | 5 |
| What are the influencing factors to contrast | Subject contrast, Beam Filtration, Beam Restriction, Grids, and SID (if needed) |
| Low kVp means | High contrast |
| High kVp means | Low contrast |
| High penetrability means | More photons; more fog |
| Increasing subject contrast means | High contrast and vice versa (optical contrast) |
| What is another name for subject contrast | Differential Absorption |
| Can muscle and fat be differentiated | No, because the photons attenuate the same way - appearing similar |
| Can bone and fat be differentiated | Yes, because bone is more dense; high subject contrast |
| Increasing beam filtration (C) | Decreases contrast |
| Increasing beam restriction (C) | Increases contrast - less scatter; higher contrast |
| Increasing grids (C) | Increases contrast - removes scatter and vice versa |
| What is the formula for Inverse Square Law | I1/I2 = (D2)^2/(D1)^2 |
| What does the I stand for in the formula | Intensity |
| What does the D stand for in the formula | Distance |
| Relationship between differential absorption and contrast | Direct relationship |
| Relationship between beam filtration and contrast | Inverse relationship |
| Relationship between beam restriction and contrast | Direct relationship |
| Relationship between grids and contrast | Direct relationship |
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