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94 Cards in this Set
- Front
- Back
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What are 3 functions of the radiographic cassette?
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1. provide close, tight contact between film & intensifying screen
2. provide a light proof container for film 3. protect screen & film from physical damage |
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Describe the construction of a radiographic cassette
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Plastic or aluminum front (doesn't block xrays)w/ lead patch for the photoimprinter label, metallic back lined w/ lead to prevent scatter, front & back hinged together.
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Are radiographic cassettes very sturdy?
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No, they are easily damaged if dropped or stepped on.
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Where are the intensifying screens? Purpose?
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They line the front and back of the cassette. They emit light when exposed to radiation and thus decrease the amount of radiation needed to expose the film.
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What are intensifying screen made of?
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Plastic sheet coated w/ phosphor material (crystals that emit light)suspended in a binding material.
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What determines a screen speed?
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The size of the phosphor crystal.
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High speed screens - made of what and what quality of image produced?
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Made w/ lg crystals that produce more light thus less radiation needed.
Produces an image w/ poor resolution and more graininess |
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Slow speed screens - made of what and what quality of image is produced?
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Made of small crystals that produce less light, thus more radiation is needed. Produces a better quality image w/ better resolution and less graniness
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What are 3 different types of intensifying screens?
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Rare earth, Hi-plus, Ultra detail
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Describe a rare earth screen - speed, crystals, features
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High speed screen w/ large crystals made of rare earth elements. Cost is high from separating the elements from their source. These are an attempt to combine high speed w/ good resolution.
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What is Quantum Mottle? What causes it?
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A mottling that can be seen on the film when using rare earth screen and vy low exposures. This is due to the extreme sensitivity of the rare earth phosphors.
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What type of screen is used in most clinics?
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Hi-Plus screens
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Describe a Hi-Plus screen
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Medium speed and medium crystals made of calcium tungstate. Avg. resolution - used for general x-rays
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Describe an Ultra Detail screen
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Slow speed w/ small crystals. Excellent resolution - often used in orthopedics.
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Describe screen care
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1. Clean at least monthly - keep log of when cleaned
2. Use commercial screen cleaner or mild soap & water 3. Check screen adhesion to cassette |
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Describe the construction of film
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Silver halide crystals suspended in gelatin on both sides of a plastic acetate base that is covered w/ a protective coating
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What is a latent image?
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Imagine on film before processing
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How is a latent image produced?
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X-rays hit screen crystals which produce light. The light from the screen causes a change in the silver halide on the film which produces the image.
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How is a latent image made visible?
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Processing
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Name two types of film
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Screen & non screen
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Which type of film is more sensitive to visible light?
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Screen film
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Which type of film is more sensitive to x-ray radiation?
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Non-screen film
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Which type of film produces higher detail?
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Non-screen
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Which type of film is common for dental and orthopedic use?
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Non-screen
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Name three film speeds
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Fast, medium, and slow
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Fast speed film is also called what?
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Ultraspeed
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Describe fast speed film - crystals, exposure, and detail produced.
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lg crystals, needs less exposure and produces an image w/ less detail
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Describe medium speed film - crystals, exposure needed, and detail produced.
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Medium crystals, needs medium exposure, produces and image w/ moderate detail
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Other names for med speed film?
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Par film & standard film
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What is the most common speed of film?
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Medium
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Slow speed film is also called what?
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High Detail Film
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Describe slow speed film - crystals, exposure, and detail
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Smaller crystals need more exposure but produce greater detail
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4 important things re: film care
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1. Store vertically
2. Keep in cool are a w/ low humidity 3. Avoid chemicals and vapors 4. Check expiration date |
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What are grids made of?
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Thin lead strips and spacers
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What do grids do?
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Absorb x-rays that are not parallel to the primary beam.
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What is a grid ratio?
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height of lead strip and distance between - 12:1 grid is 12mm tall w/ 1mm spacing between
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The higher the grid ratio, the more _____ the grid
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efficient
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The higher the grid ratio, the more primary beam that is also absobed so you need to _______ the exposure to compensate.
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increase
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Name three types of grids.
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Parallel, focused, crisscross
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Describe a parallel grid
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lead strips are perpendicular to the table and going in a single direction
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Describe a focused grid
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The lead strips are perpendicular to the natural divergence of the primary beam, slightly angled in relation to the table.
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Describe a crisscross grid
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2 parallel grids superimposed on eachother producing a cross-hatch pattern
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What is grid cut off?
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Absorption of part of the primary beam due to the improper use of the grid
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4 causes of grid cut off
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1. focus grid upside down
2. primary beam not centered over a focus grid 3. either type of grid not parallel to tube 4. focus grid used w/ incorrect SID |
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How is a stationary grid used and what does it show?
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It is placed between film and patient on top of cassette. Film shows grid lines when processed
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Where is the Potter-Bucky diaphragm that hold the grids?
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Inside the table
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What is grid factor?
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Fact that a portion of the primary beam is absorbed by any grid.
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How do you compensate for grid factor?
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Double the MAS and adding a grid factor value to the KVP
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What is the process of turning a latent image into the visible image on the film called?
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Film processing
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It is estimated that 90% of poor quality radiographs can be contributed to what?
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Poor processing
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What are the 5 general steps in film processing?
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develop, rinse, fix, wash, dry
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4 darkroom essentials
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1. Keep clean
2. Keep organized & uncluttered 3. Light-proof 4. Well ventilated |
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A darkroom should be organized into what two distinct areas?
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Wet side & dry side
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What is a safelight?
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A 15 watt red light used to produce enough light to work efficiently w/o fogging the film
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How far away should you keep the safelight from the film?
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at least 4 feet
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What does the developing step of processing do?
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reduces the exposed silver halide crystals to black metallic crystals
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What does the rinse step of film processing do?
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removes the developer and reduces the carry over of the developer into the fix
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What does the fix step of film processing do?
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Removes the unexposed silver halide crystals
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What does the wash step of film processing do?
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removes the fixing agent
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4 advantages of automatic film processing
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1. faster
2. fewer artifacts 3. more consistent 4. less expertise required |
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2 disadvantages of automatic film processing
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1. higher initial cost
2. periodic maintenance needed |
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________ can be added to the developer and fixer to return them to their original strengths
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Replenishers
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Why is silver recovery used?
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to allow *legal* disposal of corrosive processing chemicals
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What are 3 *legal* methods of film identification?
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1. lead letters placed on film at time of exposure
2. lead labeling tape 3. photo imprinter in darkroom - it is after exposure but before processing |
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In order to be legal, film identification must be _____ & _____
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permanent & unalterable
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5 things that should be on the film id?
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name of hospital, date, name/id of patient, owner's name, x-ray view or orientation
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Legally, how long must x-rays be kept?
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Minimum of 7 years
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Radiographic quality is based on what three things?
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1. Density
2. Contrast 3. Definition |
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What is film density?
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degree of blackness on x-ray
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What is film contrast?
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visible difference between two densities
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What is definition?
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Ability to differentiate body parts from eachother
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A diagnostic radiograph will have sufficient amounts of what 4 characteristics?
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density, definition, contrast, and penetration
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What is radiographic penetration?
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provides internal detail, not just tissue silhouettes
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What three factors influence x-ray penetration?
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wavelength, subject composition, and tissue thickness
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Re: film density - many blacks = ____ density
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high
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Re: film density - many whites - ____ density
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low
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Film density is controlled directly by ____
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MAs
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Radiolucent shows as black on film which means that _____ of the radiation being produced is hitting the film
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most
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Radiopaque shows as white on film which means that _____ of the radiation being produced is hitting the film
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less/least
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What are 4 variables that can affect film density
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KVP, SID, processing, film brand
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The greater the tissue density, the ____ the film density.
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lesser (more dense tissues show as white on film)
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What are 5 patient densities of concern in radiology?
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gas, fat, water, bone, and metal
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Radiographic contrast is mostly controlled by what?
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KVP
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Describe high contrast. What is is also called? Used mostly in what field?
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Abrupt changes of density tomes from black to white - few grays. Also called "short scale contrast" and is used mostly in orthopedics
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What is low contrast? Also called? Used for what?
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Gradual changes of density tones from black to white - many shades of gray. Also called "long scale contrast", is is used primarily for soft tissues.
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Re: film contrast, describe wide latitude film
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Needs large changes in exposure to change visible density - is less sensitive to radiation changes.
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Re: film contrast, describe short latitude film
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Needs only minor changes in exposure to show density change - is more sensitive to radiation changes.
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Three thing that definition or image sharpness is affected by
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motion, geometric unsharpness, material unsharpness
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What is radiographic distortion?
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size or shape of image distorted
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What is radiographic magnification and what is it caused by?
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Object appears larger than it is - caused by image not being as close to film as possible
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What is radiographic elongation and what is it caused by?
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The object appears longer than it is - caused by the tub not being perpendicular to the object
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What is radiographic foreshortening and what is it caused by?
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Object appears shorter than it is w/ the elevated portion magnified - caused by the object not being parallel to the film.
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What two questions should be asked when critiquing the quality of a radiograph?
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1. Is the film too light or too dark?
2. Is the density suitable? |
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What are some other things that should be looked at when critiquing a radiograph?
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Positioning, collimation, proper directional label, and is the film labeled?
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