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RAD 121
Unit 4 PP
| Question | Answer |
|---|---|
| Why is compression used for mammography? | It reduces tissue thickness and scatter radiation. p179/Orth |
| When scatter radiation occurs, how does it affect radiographic contrast? | It creates more shades of gray. |
| What factors indicate the need for use of a grid? | Body part thickness > 10 cm; kVp settings higher than 70kVp (60 per book) p179/Orth |
| When is higher kVp useful during exams? | When using contrast media, body parts with higher proportions of soft tissue. Also, when you reduce the mAs, you reduce the patient dose of radiation. |
| What type of scale does higher kVp produce? | long scale which increases the amount of useful information in the final image. |
| what are the relationships between scatter, receptor exposure and contrast? | Increase scatter, increase receptor exposure, decrease contrast |
| What causes fog? | Scatter radiation, light, chemicals... |
| What is scatter - fog? | supplemental receptor exposure that doesn't contribute useful information on the radiograph |
| Define density in the DR age. | Density referred to film blackening (film screen). Density is the equivalent of brightness. (more density of photons) INCREASED photon density on a monitor means DECREASED brightness on the monitor. (Consider dark areas (lung field) in the image.) |
| Decreased brightness refers to scatter or transmission? | transmission - more photons made it through to the IR |
| Decreased density refers to what brightness? | Increased brightness - think lighter areas of the final image. |
| Increased brightness refers to attenuation/absorption or transmission? | Attenuation and absorption - fewer photons made it through to the IR |
| Which type of scatter produces unwanted "density" on the image? How does it affect the image? | Compton scatter; Unwanted density degrades or decreases the visibility of the anatomic structures seen in the image. |
| What is the most effective method of reducing scatter? Why? | Beam restriction is the MOST effective method of reducing scatter; less matter / less scatter reducing amount of tissue exposed reduces the amount of scatter produced in the part |
| what are the three basic non adjustable types of beam limiting devices? | Aperture diaphragm; cone/cylinder; Collimator |
| Describe the aperture diaphragm. | Very simple beam-restricting device. It's a flat piece of lead with a square or circle in middle. The opening is "aperture". It cannot be adjusted from designated size. It created the necessary field size (8x10, 10x12, etc) No collimator box. |
| Describe the cone and cylinder. | An aperture with an extension flange attached to it. It is lead. If 2 pieces, allowed for telescoping ability. The cylinder is straight and the cone flares out. Most used currently for paranasal sinuses. |
| Does the radiographic cone absorb radiation? | it does, but its shape allows for unwanted radiation to continue to patient. |
| What is the other name for automatic collimators? | PBL - Positive Beam Limiting device |
| Why is PBL preferred? | Helps reduce scatter, reduce patient dose, improves image visibility. |
| What is the atomic number for Lead and what is it's chemical symbol? | 82; Pb |
| What is the purpose of beam limitation? | A) reduces patient dose B) Decreases receptor exposure (collimator absorbs photons) C) Improved visibility of detail (less matter, less scatter) need to adjust technique for extreme changes in collimation |
Created by:
Larobbins
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