Term
| What determines the K-shell absorption properties of the calcium tungstate screen? |
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Definition
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Term
| As the x-ray energy increases, the probability of absorption _________ rapidly until the x-ray energy is equal to the binding energy of the K-shell electron. |
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Definition
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Term
| What are the three parts of a "conventional imaging receptor"? |
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Definition
1. Cassette
2. Intensifying Screen
3. Radiographic Film |
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Term
| What are the 4 major layers of the intensifying screen? |
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Definition
1. Protective Coating
2. Phosphor
3. Reflective Layer
4. Base |
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Term
| What category of intensifying screen followed the traditional calcium tungstate screens? |
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Definition
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Term
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Definition
| When phosphor continues to emit light after stimulation |
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Term
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Definition
| Detective Quantum Efficiency |
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Term
| When the light sensitivity of the x-ray film is matched with the light emitting properties of the intensifying screen this is known as what? |
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Definition
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Term
| Any material that emits light in response to some outside stimulus is called what? |
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Definition
| luminescent (material) or a phosphor |
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Term
| What are two other names for afterglow? |
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Definition
1. Screen-lag
2. Phosphorescence |
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Term
| What are the 3 primary screen characteristics? |
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Definition
1. Screen Speed
2. Image Noise
3. Spatial Resolution |
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Term
| Screen speed is determined by what? |
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Definition
| How efficiently x-rays are converted into visible light |
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Term
| What are two big causes of image noise? |
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Definition
1. Fast Screens
2. High kVp |
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Term
| What type of resolution is determined by how small an object can be imaged? |
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Definition
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Term
| ________ __________ is the ability to image adjacent similar tissues. |
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Definition
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Term
| List 8 factors that can affect image contrast: |
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Definition
| 1. mAs 2. Anode Heel Effect 3. Distance 4. Filtration 5. Processing 6. Anatomical Part 7. Beam Restrictors 8. Grids |
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Term
| List 3 factors that contribute to increased scatter: |
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Definition
1. kVp
2. Increased field size
3. Increased patient thickness |
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Term
| What are the two types of x-rays responsible for the optical density and contrast of a radiographic image? |
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Definition
| 1. The x-rays that pass through the pt w/out interacting w/ the pt 2. The x-rays that are scattered within the pt through compton interaction |
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Term
| An x-ray that goes through the pt is called what? |
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Definition
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Term
| What types of devices are designed to control and minimize scatter radiation by limiting the x-ray field size to only the anatomy of interest? |
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Definition
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Term
| List the 3 major types of beam restricting devices: |
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Definition
1. Aperture Diaphragms
2. Cones or Cylinders
3. Variable Aperture Collimators |
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Term
| The __________ Rule: the size of the collimated x-ray field should be adjusted to the smallest reasonable size that will include the portion of the body to be imaged, and it should never be larger than the size of the film/IR. |
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Definition
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Term
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Definition
| Positive Beam-limiting (collimator) |
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Term
| What device is the only device to clean-up scatter that is between the patient and the IR? |
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Definition
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Term
| True or False: the grid's principle function is to improve image contrast by cleaning up scatter. |
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Definition
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Term
| Who invented the grid? When did he invent it? |
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Definition
| Gustav Bucky invented the grid in 1913 |
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Term
| What typical thickness of a body part should you start to consider the use of a grid? |
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Definition
| > 10 cm; typically anything as big or bigger than the knee on an average pt |
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Term
| What is the formula used to determine the % of x-rays absorbed by the grid? |
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Definition
| % x-ray absorption = (width of grid strip / width of grid strip + width of interspace) x 100 |
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Term
| What is the grid ratio formula? |
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Definition
| Grid Ratio = h/D (h = height of grid; D = width of interspace material) |
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Term
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Definition
| It is the # of grid strips (grid lines) per inch or centimeter |
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Term
| What is the interspace material typically made of in a grid? (Name 2) Which is the most common? |
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Definition
1. Plastic Fiber (most common)
2. Aluminum |
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Term
| What is the purpose of interspace material? |
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Definition
| To maintain precise separation between the delicate lead strips within the grid |
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Term
| ________ ___________ ______ (K): is the ratio of the contrast of a radiograph using a grid vs the contrast of the same radiograph without the grid. |
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Definition
| Contrast Improvement Factor (K) |
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Term
| What is the formula for the Contrast Improvement Factor (K)? |
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Definition
| K = contrast with grid / contrast without grid |
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Term
| When a grid is used, the radiographic technique must be increased to produce adequate OD. This is known by 2 names: |
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Definition
| 1. Bucky Factor 2. Grid Conversion Factor (GCF) |
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Term
| ___________ of a grid is the ratio of transmitted primary radiation through the grid to transmitted scatter radiation through the grid. |
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Definition
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Term
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Definition
1. Parallel
2. Crossed (Cross-hatched)
3. Focused
4. Moving |
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Term
| What are 4 common grid problems? |
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Definition
1. Off-level
2. Off-center
3. Off-focus
4. Upside-down |
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Term
| What technique is used as an alternative to using grids? Using this technique, the radiographer positions the pt so that a 10 - 15 cm gap is formed between the pt and the IR. This allows for scatter radiation to be deflected away from the IR and not detected. |
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Definition
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