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RAD 121

Unit 4 PP

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