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234 Cards in this Set
- Front
- Back
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Cassettes contain __________ ________ that hold the film tight to screen.
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INTENSIFYING SCREENS
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explain slow screens
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slow screen
slow exposure high detail BUT high patient dose (bad) *direct exposure film |
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explain fast screens
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fast screen
fast exposure less detail AND less patient dose (good) |
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Would you use a slow screen or a fast screen on an object?
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slow
DIRECT EXPOSURE film is old school |
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What is the difference between old school and modern era cassettes and screens?
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Old school: direct exposure, slow screen, slow exposure, high dosage, GREAT detail
*basically 2 pieces of cardboard to keep the light out, with your hand between them getting dosed to high heaven Modern: cassettes with intensifying screens (2), one for each emulsion (2) that sandwiches the polyester film. The cassette protects the film and screens. |
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Percentage of PHOTONS that contribute to film DARKENING
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1%
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Percentage of X-RAY BEAM that interacts with the screens
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30%
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Describe SCREENS
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*LOW patient exposure + LOW dose = LOW shielding requirements
*LOW motion artifacts (basically a high shutter speed for a sporting event, or taking an x-ray of a Parkinsonian patient) *LOW tube requirements *1 phosphor = thousands of visible light photons *are made from RARE EARTH METALS *the faster the screen, the less resolution (blurrier the image) |
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Workhorse of x-ray cassette
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INTENSIFYING SCREENS
take a little bit of x-ray (30%) and intensify it! |
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If you can see the HINGES on your x-ray, you did what?
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HINGES = put the cassette in BACKWARDS
Meaning: you put the high atomic # (lead) in front and it blocked the photons from penetrating completely. Underdeveloped. No light went in. Duh. 6 out of 15; Thank you for coming. |
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Why must the FRONT cover of the cassette have a LOW ATOMIC #?
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High atomic # needs to go behind the film or it will block the light from the x-ray going in.
Low # in front, high in back. |
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If you put the cassette in backwards, no light will penetrate and a FOG appearance will occur. Why?
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Because the high atomic # of the back screen blocks the photons. Back screen is made of lead.
*if you can see the hinges on the film, the cassette was in backwards |
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Purpose of high atomic # lead back cassette cover?
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Reduces BACKSCATTER
*in backscatter, photons don't reach screen and x-ray is undeveloped |
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Light
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LUMINESCENCE
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things that EMIT LIGHT
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[PHOSPHOR]
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DIFFERENCE between ~fluorescence~
and phosphorescence? |
~fluorescence~
While phosphor stimulated, gives off light. When stimulation stops, no more light (fluorescent lights, X-ray screens) phosphorescence: gives glow even after stimulation stops (watch dials, biolumenescence) |
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Why does an x-ray screen need to be ~fluorescent~ instead of phosphorescent?
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A phosphorescent screen would continue to glow, the phosphor giving off light and continuing the developing process.
A ~fluorescent~ light stops when the stimulation stops, ie, only when the phosphor is stimulated |
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What is the mechanism of luminescence?
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Electron goes from excited then bored (releases an outer shell e-)
"Outer shell e- excited to higher energy level. Returning to normal, it's accompanied by emission of visible light photon. Characteristic wavelength light is created based on material involved." |
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Some phosphorescence exists even in ~fluorescent~ materials. This is called __________.
Why is it bad in x-ray screens? |
AFTERGLOW
Continues to develop the film = overexposure (bad) |
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Describe bird's eye view of a cassette:
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From center, each is duplicated on other side except single sheet of polyester blue-tinted film:
1. polyester blue-tinted film 2. crossover layer 3. emulsion 4. protective layer 5. phosphor layer, studded with phosphor crystals that each have a sensitivity speck defect 6. reflective layer This is exactly repeated on other side of film. |
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What makes light in the cassette?
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SCREENS:
Phosphors + Fluorescence |
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We make phosphor screens out of
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rare earth metals
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Describe old school phosphor screens
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Made of calcium tungstenate = do not buy this kind.
CaWO4 bad. bad. bad. low efficiency. |
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Phosphor screen qualities
1. 2. 3. |
1. made of RARE EARTH metals
2. more REACTIVE 3. emit MORE LIGHT PER PHOTON (than bad ol' CaWO4 screens) |
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Phosphors emit light _________, in a wide 360* sphere.
What is added to a phosphor screen to keep from losing these photons? |
ISOTROPIC (every direction)
DYE is added to phosphor screens to keep from losing photons due to isotropic effect |
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Reflective layer qualities (one good, one bad)
1. 2. |
REFLECTIVE LAYER:
1. GOOD: reins in isotropic light/photons 2. BAD: decreases resolution/clarity |
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The _______ layer catches isotropic scattered photons from the phosphor layer's phosphor crystals. It pops them back to the phosphor layer.
How does the phosphor layer get these little suckers with the steep angles? |
REFLECTIVE LAYER
Phosphor layer has DYE to catch errant, steeply angled photons that bounced off reflective layer. THIS KEEPS YOUR ASS OUT OF YOUR HEAD on a film. |
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Keeps your ass out of your head on a film.
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The DYE in the phosphor layer catches steeply angled photons.
The photons that reflect directly back in a straight line are what makes a nice clean image. The reflective layer decreases resolution, but reins in the isotropic steeply angled photons. |
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How to get a slower screen...
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Slower screens take out MORE of the badly, steep-angled photons. This takes time and increases resolution but increases patient dose.
A faster screen allows a larger angle on badly angled protons before it removes them. ***Faster is blurrier because it removes fewer, but it is safer. |
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Slower screens remove badly angled photons at smaller angles so
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better image but higher patient dose. BAD.
removes more acutely angled photons that came off reflective layer, but takes so long that it exposes patient to too high a dose |
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Quality and Quantity of an x-ray are based on
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highest resolution with lowest patient dose.
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Recite the layers from film to front cassette: (7)
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1. polyester blue-tinted film (base)
2. crossover layer 3. emulsion 4. protective layer 5. phosphor layer containing phosphor crystals (w/ sulfur-based sensitivity speck) 6. reflective layer 7. cassette front with low atomic # |
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Where is the protective layer and what does it do? (2 fcns)
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Between emulsion and phosphor layer
*It stays in the cassette and protects the phosphor layer from mechanical wear and tear of film removal. *It decreases static electricity build-up. |
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Keeps phosphor layer from actually touching the film (polyester + crossover + emulsion layers)...
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Protective layer across the phosphor layer
*built-in obsolescence so the protective layer will wear out and you have to buy a new screen |
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SPEED of screen =
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INTENSIFICATION FACTOR
*par speed 100 |
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par speed 100
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INTENSIFICATION FACTOR meaning speed of screen
*par speed 100 |
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NOISE (3 causes)
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1. FAST SCREEN: decreased resolution > lose high quality because allow steep angled photons to go all over
2. HIGH kVp: more Compton scatter 3. LOW mAs: blurs so get QUANTUM model. Not enough photons hit the screen when mAs too low because mAs IS the # of photons! |
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QUANTUM MODEL
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grainy appearance of film because not enough photons hit film, ie, the mAs is set too low.
*mAs is the actual # of photons |
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a crisp picture would have high intensity, low noise and decreased _________
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resolution
Why use a fast screen then? Phosphors emit more light and dye removes fewer photons (allows larger angles) = LOW patient dose, LOW resolution, MORE noise |
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Faster screens have more noise, less ________
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resolution
They don't catch the steeply angled photons, but they are safer for pt. due to lower dose. |
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SPATIAL RESOLUTION
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how much detail can we see?
2-point discrimination |
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SLOW SCREEN
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LESS light from phosphors + BETTER dye to remove angled photons =
HIGH resolution, HIGH patient dose, LESS noise *not safe |
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speed of a screen
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INTENSIFICATION FACTOR
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how small of an object can be seen
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S-P-A-I-T-I-A-L RESOLUTION
*the measurement of everything! |
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Measurement of spatial resolution:
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LINE PAIRS per mm.
*What is the smallest line test I can read? *Larger crystals in the phosphor layer REDUCE spatial resolution. Larger means cheaper so less resolution. |
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S-P-A-T-I-A-L RESOLUTION (line pairs per mm.) is affected by:
1. 2. 3. 4. |
1. FOCAL SPOT SIZE (smaller, better)
2. EMULSION THICKNESS (more emulsion makes less resolution because chemicals never traverse entire emulsion to reach polyester film/base). Emulsion contains the phosphors that expose the film. 3. PHOSPHOR SIZE: the phosphors in the emulsion are more precise if SMALLER, as in d.p.i. or pixels per mm. making an tv screen better. Larger phosphor crystals mean fewer interactions, ie, less resolution. 4. Screen PHOSPHOR LAYER THICKNESS - larger phosphor crystals mean less resolution, less detail |
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Focal spot size, Emulsion thickness, Phosphor size, Screen phosphor layer thickness
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4 things which affect s-p-a-t-i-a-l resolution
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Which is faster, a spine or an extremity cassette and why?
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Spine! Organs, people! Resolution is lower but your liver doesn't go Chernobyl.
400 speed spine |
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Best FOCAL SPOT size?
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small - better resolution (fewer bad photons in the mix)
*the more phosphor crystals per mm, the lower the resolution |
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What determines the SPEED of the ENTIRE SYSTEM?
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FILM SPEED (100 par)
SCREEN SPEED (Fast screen) |
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All film is what speed?
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PAR SPEED 100 film
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Describe the overall speed qualities of the x-rays we take
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FAST SPEED (film @100 par, fast screen)
HIGH NOISE LOW RESOLUTION LOW PATIENT DOSE |
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Do we EVER change the speed of the film?
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no
no no no. It is ALWAYS 100 par. When reading the "system speed," say the speed of the cassette. Obese pt. spinal radiography recommendation: 100 speed film, 800 speed cassettes = 800 speed |
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General spinal radiography recommendation:
100 speed film, 400 speed cassettes = ? |
400 speed
*Never change film speed from 100 par, but read the cassette speed for the total system speed. |
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Screens wear out from ________
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MECHANICAL WEAR & TEAR, only.
*never from radiation, etc. |
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How often to clean cassette screens?
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4-12x per year
Use ONLY screen cleaner: *decreases static and leaves protective layer intact *check contact points with mesh |
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Plain film for radiography is very similar to?
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35mm black and white photographic film
except...x-ray film has emulsion on BOTH sides of base/polyester |
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History of x-ray film
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GLASS >>cellulose NITRATE (highly flammable) >> cellulose TRINITRATE (gun cotton) >> cellulose TRIACETATE >>
POLYESTER!! shag me |
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Why POLYESTER film?
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RIGID (emulsion can hang on it)
FLEXIBLE, WATER RESISTANT DIMENSIONALLY STABLE - doesn't warp during processing TRANSPARENT - blue tint added to decrease eyestrain |
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Name the layers of film on one side, from base to cassette:
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Polyester film w/ blue tint
Crossover Layer Emulsion w/ silver halide Protective Layer Phosphor Layer studded w/ phosphor crystals (sulfur based defect called sensitivity speck) & dye Reflective Layer |
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Polyester Crossdressing Emus Protect Pho's dye-sensitive crystal Reflection
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Polyester film w/ blue tint
Crossover Layer Emulsion w/ silver halide Protective Layer Phosphor Layer studded w/ phosphor crystals (sulfur based defect called sensitivity speck) & dye Reflective Layer |
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Polyester Crossdressing Emus Protects Pho's dye-sensitive crystal Reflection
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Polyester film w/ blue tint
Crossover Layer Emulsion w/ silver halide Protective Layer Phosphor Layer studded w/ phosphor crystals (sulfur based defect called sensitivity speck) & dye Reflective Layer |
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EMULSION is made not from emus, but from?
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Argentinean cows (gelatin)
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SILVER HALIDE crystals in the cow emulsion are 98% _______ and 2% silver iodide.
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silver BROMIDE
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Explanation of photographic effect
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GURNEY-MOTT HYPOTHESIS
describes conversion of halide crystal into METALLIC SILVER how a LATENT IMAGE (black) is created |
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GURNEY-MOTT hypothesis
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explains photographic effect (creation of a latent image)
*really describes the CONVERSION OF HALIDE CRYSTAL INTO METALLIC SILVER, creating a black image |
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FRANKEL defect
remember: silver halide crystals are in the emulsion, whereas phosphor crystals are in the phosphor layer |
allows Ag+ and Br- to move within the silver halide crystal
*remember the ingredients are: silver bromide (majority) and silver iodide |
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How does the silver in silver halide get separated from the bromide and iodide?
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A photon slams into the sensitivity speck:
1. Photon is absorbed 2. PhotoELECTRON is produced PhotoELECTRON is captured by sensitivity speck. Because it is an ELECTRON, the effect is to turn the speck NEGATIVE. Negative charges repel each other and attract positive = Ag+ leaves Bromide and Iodide for the very negative sensitivity speck. Bromide and Iodide move to the far reaches of the silver halide to get away from the negative speck. When Ag+ migrates to the negative speck w/ the captured photoelectron, METALLIC SILVER is formed. This is what creates the LATENT IMAGE (black = metallic silver) Ag+ will be attracted to negative speck and CONVERTS to METALLIC silver (4-10 atoms) |
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LATENT IMAGE:
What passes through the emulsion turns __________. What is absorbed turns ________. |
passes through = black
absorbed = white (ie, bone) |
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The exposed and unexposed parts of film appear the same. This is called the latent image.
What will turn the entire crystal into metallic silver? |
PROCESSING
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Kind of film that gives the best detail but highest exposure
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DIRECT EXPOSURE film
* basically 2 pieces of cardboard * HIGH dose, VERY slow * bitewings at dentist |
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SCREEN FILM:
What creates the latent image, x-ray photons or light photons? |
LIGHT PHOTONS from the INTENSIFYING SCREENS inside the cassette creates the latent image.
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Never start with a ________ piece of film. NEVER!!!
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black
*if you start with black, it is a copy. You can't take an x-ray with copy film. |
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Copy film has a ________ emulsion.
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single
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Describe COPY FILM:
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SOLARIZED
*starts black (copy) >>> ends clear (white) |
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Describe SCREEN FILM:
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ORIGINAL
starts clear (polyester blue) >>> turns black (exposed) *always start with CLEAR |
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The speed of a film is its __________ to _______.
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SENSITIVITY to LIGHT = speed
how sensitive is the film to light? Really sensitive, then fast speed. 200 is most common but... WE USE 100 PAR SPEED (full speed) |
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full speed
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100 par speed
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How sensitive FILM is to light, or its SPEED, is determined by
1. N 2. S 3. T |
1. # of silver halide crystals (in emulsion, more crystals can capture more photons to make photoelectrons)
2. SIZE and SHAPE of crystals (larger means slower) 3. THICKNESS of emulsion (too thick and not all the mAs photons will get through the gelatin to the polyester itself) |
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N
S T |
Number of silver halide crystals
Size and shape of silver halide crystals Thickness of emulsion 3 factors that determine film SPEED |
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"covering power" refers to emulsion __________
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EMULSION EFFICIENCY
DOUBLE EMULSION: on both sides of polyester film cuts exposure time in half |
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film CONTRAST
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the differences between the blacks and whites of a film, including grey in middle
*the greyscale |
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LATITUDE regarding film contrast
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Latitude: the width of the H&D curve
(the RANGE of exposure techniques that result in archival x-ray image) Latitude is INVERSE to Contrast. Narrow latitude = High contrast Wide latitude = Low contrast |
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LATITUDE width starts with black and goes to white. Grays in middle.
The width or range of latitude determines the level of _________. |
CONTRAST
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Describe the Hurter & Driffield Curve (H&D Curve)
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Begin at zero/WHITE/clear/UNDERexposured = TOE
Then draw a gently sloping upward curve, the latitude = SLOPE that plateaus out at finish/BLACK/OVERexposed = SHOULDER *The width or range of this latitude H&D curve determines the contrast. A narrow, quick ascension means high contrast. A wide, slow rise means low contrast. |
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High contrast, narrow latitude film would have _______, _________ crystals.
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small, uniform
(think of a diamond with a lot of faces vs. a cube. Diamond will have higher contrast and narrow latitude) |
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Low contrast has lots of ______, and larger, non-uniform crystals.
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greys
(wide latitude, low contrast, greys) |
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FOG
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Blurry image created by:
Light Pressure Heat |
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TOE is created by
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FOG + Base (polyester film itself)
Toe is the CHARACTERISTIC CURVE = it is the THRESHOLD needed for exposing the film |
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H&D curve describes film ________ and the inherent film ________.
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reactivity, contrast
*the two qualities of film described by the H&D curve (latitude with toe, slope and shoulder) |
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CROSSOVER control layer
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PREVENTS LIGHT FROM traveling through BOTH EMULSIONS
*this would result in a sort of ghost or mirror image. *Crossover layer is removed during processing |
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Stops light from going through the second emulsion and printing the x-ray picture twice/overlap that would make the image blurry.
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CROSSOVER control layer
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A film has sensitivity to 2 colors:
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RED & GREEN spectral sensitivity
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Green spectral sensitivity film is termed ____________
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ORTHOCHROMATIC
*think Ortho, the weed killer and green |
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Blue spectral sensitivity film is termed ___________.
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blue.
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If you stick blue spectrum sensitive film in a green screen cassette or vice versa, what happens?
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You have just OVERDOSED the patient with 4x the normal level of radiation.
*SPECTRAL MISMATCH - you suck. |
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SAFE LIGHTS are ______.
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RED
If you need a safelight, buy red. They come in amber, too, but buy red. It works for both orthochromatic (green) and blue spectrum sensitive film. |
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max wattage of Red safe light and placement distance
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15 watts, 5' away
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GBX-2
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red safe light
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Why store film upright?
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FOG!
Lay it flat and it crushes one of the emulsion layers due to weight of the other. FOG (heat, light, pressure) |
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Toe =
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FOG + base/film
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Why buy only the amount of film you need?
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it expires
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Why can't you use fluorescent light as a safe light?
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it has an AFTERGLOW that would keep developing the film. Bad.
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3 things that affect spatial resolution
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1. FOCAL SPOT SIZE
2. EMULSION THICKNESS (more makes less spatial res.) 3. PHOSPHOR SIZE (larger crystals, less resolution) |
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Chemical PROCESSING converts the ________ image to a ________ image.
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LATENT >> VISIBLE
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'WET READ'
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should not be done anymore - old HAND TANKS
when someone takes the wet film out of the developer tank and holds it up to view was done when film took a hour to develop means PRONTO now |
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Created the 1st automatic processor with rollers in 1956
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KODAK
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How did KODAK improve the processing speed from 60min to 90sec. in 1965?
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the RAISED the temperature
*current industry standard is 60-90sec. |
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AUTOMATIC film processing cut down on time of __________.
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FIXING
from manual 15 min. to automatic 22 sec |
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Why must you wait until a film is FIXED in order to view it?
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So light does NOT continue to develop the film
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DEVELOPER converts?
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ionic Ag+ >>>>> METALLIC Ag+
Ionic is Ab+Br- where metallic is Ag+ only |
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If your film comes out wet, what is the problem?
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DEVELOPER
wet film = developer problem |
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What is the OPTIMAL color for developer?
What is the WORST color for developer? |
Optimal color = apple juice
Worst color = Starbucks French roast |
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Developer converts exposed _____________ (dark grey) into metallic silver (polished black).
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silver halide >>>>> metallic silver
grey to black latent to visible |
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Developer is a _________ agent; it donates contributes electrons.
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REDUCING
ionic silver halide >> metallic silver grey >> black latent >> visible |
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Light as photons >> intensifying screens >> sensitivity speck >> makes negative >> Frankel defect lets Br- migrate to edges and Ag+ glom to speck.
Then what happens? |
Sensitivity speck ELECTRONS in phosphor crystal bind 4-10 silver halide Ag+ and converts/REDUCES them to 4-10 METALLIC Ag+.
Crystal EJECTS 4-10 Br- ions. |
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Describe DEVELOPER:
1. 2. 3. |
Developer:
1. REDUCING AGENTS = HYDROQUINONE blacks & PHENIDONE/METOL greys 2. ACTIVATOR makes gel swell (controls pH) 3. HARDENER = GLUTERALDEHYDE keeps gel from overswelling |
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What is wrong if your film is coming out undeveloped and why?
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Underdeveloped if gels swells too much - chemicals do NOT have time to make it all the way through emulsion to polyester film.
GLUTERALDEHYDE problem *Can lead to processor BREAKAGE |
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2 options as to why film is undeveloped?
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UNDEREXPOSED = mAs
or UNDERDEVELOPED = gluteraldehyde *look at ID stamper: ~ if dark/jet black, then underexposed, change mAs ~if light grey, then udderly undeveloped, gluteraldehyde worn out so change developer |
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light grey ID stamp when film is too light
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UNDERDEVELOPED
worn out gluteraldehyde in developer so change it. remember: gluteraldehyde keeps gel from swelling too much and making trip too far for chemicals to reach polyester film. If it is worn out, the FILM SWELLS, chemicals don't reach and film is considered UNDER-DEVELOPED, ergo too light. |
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if ID stamp is black when film is too light
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turn up the mAs
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Out of these 3 developer factors, which one can we adjust?
1. Time 2. Temperature 3. Concentration |
CONCENTRATION:
determined by color want apple juice, not Starbucks change the developer and stop underdeveloping your film |
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If you leave your developer just sitting for a long time, it will ______. You should always check it for color.
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oxidize
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FIXER fixes the
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image to the film.
* needed for archival quality |
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CLEARING agent
Removes unexposed SILVER halide from the phosphor crystal |
FIXER
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White/CLEAR areas on a fixed film are the areas that were not exposed, and black/FIXED areas were exposed. Explain how we get the contrast when we used FIXER...
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exposed is black/fixed while white/clear is unexposed...
White/CLEAR as in bone is where the photons were absorbed and could not get through to the phosphor layer's crystals. If you shoot a man against a wall, the bullets he absorbs do not get through to the wall. The ones that do leave an outline of him in black. Those got through because there was nothing there to block them. That area is black, or exposed - the area/outline around him which is FIXED and went from ionic silver halide (Ag+Br-) to metallic silver Ag+. His outline is black, exposed, fixed. Where he was standing remains clear because we took the body away that was full of bullets (photons), removed the unexposed silver halide crystals, washed it clean. That's the white/clear where he was standing. We basically have him in relief. |
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Will crumble the film
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Retention of FIXER. Need to wash. Something is wrong.
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What is FIXER made of?
How must it be treated? |
AMMONIUM THIOSULFATE
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ammonium thiosulfate
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FIXER
used to wash away unexposed silver halide (dissolves it) this makes HAZARDOUS MATERIAL so you can NEVER flush fixer down the drain. |
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When I say 'DRAINS,' you say?
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FIXER
do not flush fixer down the drain ammonium thiosulfate & acetic acid (vinegar) |
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The HARDENER in FIXER is _____
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ALUM
Tweety feeds Sylvester alum to pucker or FIX his lips shut! |
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FIXER RETENTION
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occurs if WASHED IMPROPERLY
Loss of archival quality GEL PEELS OFF |
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Excessive ________ can bake your film so don't.
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drying
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4 FIXER contents:
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FIXING AGENT (ammonium thiosulfate)
HARDENER (alum) SOLVENT (water) ACTIVATOR (acetic acid/vinegar) |
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ammonium thiosulfate
alum acetic acid water |
FIXER
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YELLOW FILM means
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fixer RETENTION from not washing enough
makes it smell like pee (ammonium) Wears off emulsion/peels gel |
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If I say YELLOW film, you say
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FIXER RETENTION
*from not washing thoroughly |
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If your film comes out wet (tacky), what to do?
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Check gluteraldehyde (hardener) & CHANGE REPLENISHER
or SHORTEN CLEANING SCHEDULE |
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Temperature in processor tank
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95-98*
Never use mercury thermometer. Never. |
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How should you cover your developer tank?
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With a FLOATING LID
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Regarding processor, if wet film, change the ___________
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REPLENISHER (gluteraldehyde is shot/hardener is not stopping emulsion gel from overswelling)
or... Change your CLEANING SCHEDULE |
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If your film gets caught in processor, what's the problem?
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Gluteraldehyde is shot and is allowing the gel emulsion to overswell. Change/replenish.
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how much ambient/flash light (strength of flash = penetration)
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kVp
Strength of flash - penetration |
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how long you leave the shutter open. The longer it's open, the more photons will get through and the stronger in number they will be.
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mAs
More photons - greater # - longer you leave it open. Underexposed means you didn't leave it open long enough and not enough photons got through. |
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What passes through the emulsion turns BLACK.
What is absorbed by the body turns WHITE. This is called _________. |
LATENCY
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Say you want to HARDEN your beam. What does this mean?
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Moving the Bremstrahlung peak to the right...
i.e., start with 10-50. That's 40 photons total and you could only use 20 because it has to be over 30+ range. INCREASE the kVP. Now the beam is between 30-100 and you can use anything over 30+ so you can use ALL of the beam = HARDENING means MORE USABLE PHOTONS |
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Only ___% from ___% of the photons are usable.
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30% of the light from 1% of the photons
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What do you add after you harden the beam by increasing kVp (moving Bremstrahlung peak to the right)?
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high frequency electrons via FULL WAVE RECTIFICATION
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__________ is what we want in the TUBE (along with characteristic, but who cares about them!).
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BREMSTRAHLUNG is what we want in the tube...
PHOTOELECTRIC is what we want in the patient (film is a photoelectric representation of what happened in the patient) |
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Your film is too light:
ID stamp is black. Developer is okay. What is wrong? How to fix? |
The film is underexposed.
What to do? Increase the mAs by 30% and lower the kVp by 5%. Use the 5% rule. |
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In a chest film, use a high ____ to GREY THINGS OUT so you can see all the different tissues.
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kVp
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The setting which is determined by the THICKNESS of the body part you measured with the calipers.
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mAs
(mass determines mAs) |
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On the chart, the actual body part determines the ____.
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USE A FIXED kVp CHART!
ie, so 'spine' is 80-90 kVp |
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Your film is grainy. Fix it.
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30% change in mAs - need to turn mAs up, which will also mean a 5% downturn in kVp.
Grainy = QUANTUM MODEL |
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Contrast is _________ + _____.
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Contrast is LATITUDE + kVp
High contrast is stark Low contrast is greyed out |
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Toe is _____ + ____/_____
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Toe is FOG + base/film
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4 things that kVp affects: (COQ2)
1. 2. 3. 4. |
kVp affects COQ2:
1. Quality 2. Quantity 3. Contrast 4. Optical Density |
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A 5% change in kVp is NOT going to affect the optical density but will affect the ________ because it changes mAs by 30%. In order to affect the optical density, you must change the kVp by at least ___%.
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contrast
15% |
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In order to affect the OPTICAL DENSITY, you must change kVp by at least ____%.
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15%
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Image detail is the same thing as ____________
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spatial resolution:
how much detail can we see? 2-point discrimination RESOLUTION involves image detail in line pairs per mm + patient movement (so..stabilize the patient!) |
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How many breaths before shooting film?
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2 - shoot on patient's second deep breath (hold)
because now their lungs are saturated with O2 and they aren't likely to cough |
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What kind of films use the longest exposure
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thoracic and lumbar = lumbar take the longest exposure
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describe patient prep before shooting film
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patient holds bucky
leans against if possible eyes open 2nd deep breath |
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the SHADOW of the object
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UMBRA = SHADOW
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FUZZY MARGINS outside the actual shadow of the object
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penumbra - around the umbra
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How to fix the penumbra, or reduce the fuzziness, distortion?
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Move object (patient) closer to bucky = reduce OID
Move tube (light source) as far away as possible = increase SID/FFD) |
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Low OID, high ____
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SID
Low OID (move patient towards bucky) + high SID (move light source/tube as far back as possible) will reduce magnification and fuzziness (PENUMBRA). |
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# 1 reason for a minimal diagnostic series of at least 2 x-rays?
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DISTORTION
(due to distorted perspective from body part thickness or patient position) ie, foreshadowing, foreshortening, elongation |
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The ______ effect is always faster than the photoelectric effect.
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COMPTON is always faster than photoelectric.
Try to stay behind the crossing of the two curves (Compton rising, photoelectric falling) and your film should turn out okay |
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Reasons to decrease the OID (put the patient as close as possible to the bucky) ?
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Magnification (image size huge and fuzzy because object itself is bigger)
& Focal Spot Blur (FSB is same term as penumbra) due to weaker beam on anode side (HEEL EFFECT) Fix all with decrease in distance between object/patient and image by moving patient closer to bucky |
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Distortion
(major reason you take @ least 2 views ) misrepresentation of object shape and size due to: |
Distortion is due to:
1. Object thickness = increases penumbra/FSB 2. Object position = must be dead on in the beam or will elongate/magnify or foreshorten 3. Object shape = if not dead on, the light cast may look like something else entirely (funhouse mirror effect) |
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Why can you fix the anode heel effect on the FSB by shortening the distance between the object/patient and the image?
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Because the penumbra 'cone' of fuzziness is shortening, too, as you move the patient closer to the bucky. This remaining penumbra is tiny and is called the FOCAL SPOT BLUR.
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Recite the overall concepts of quality
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move the patient as close to the bucky as possible (low OID)
move the tube/light source as far away as possible (high SID/FFD) Use high kVp to balance dose with contrast Use fixed kVp charts so you get consistent quality Short exposure time decreases blur from patient movement |
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Compton scatter
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don't go there
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Optimally, only x-rays that don't interact with the patient would hit the film (TRANSMITTED) but what happens instead?
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COMPTON SCATTER
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Name for absorbed x-rays?
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PHOTOELECTRIC (yes!) - these are the ones that get stuck in the bones.
Transmitted x-rays go through to film. Compton scatter x-rays bounce every which way and cause LOSS of CONTRAST |
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What percentage of incident x-rays actually reach the film?
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1%
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x-rays that cause LOSS of CONTRAST
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COMPTON SCATTER
*once you get stuck in Compton, you can't see the forest for the trees - there ain't no contrast to your life, yo. |
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The higher the kVP...
The bigger the field size... The thicker the patient... The less contrast you get because you can't get outta ________. |
Compton
You want to get outta Compton? Focus (narrow your field size) Let some more light in (increase the mAs # within a safe dose and lower the kVp to increase the contrast inside a big object/patient.) |
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When you increase the kVp and lower the mAs, Compton scatter goes down a little. Why should you decrease the kVp and up the mAs, even though it increases patient dose a bit?
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Because as you increase kVp, Compton goes down a little but the useful PHOTOELECTRIC DECREASES A LOT! Therefore, there is a higher percentage of Compton interactions.
Use the LOWEST KVP to yield enough contrast but HIGH ENOUGH TO DECREASE THE mAs (dose). 5% rule - increase kVp by 5% and mAs drops by 30%. |
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Why reduce the field size?
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Smaller amt of tissue irradiated means less Compton scatter.
NARROW YOUR FOCUS - collimate tightly down to a small focal spot and GET THE HELL OUTTA COMPTON. |
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On an obese person, collimate to the tightest possible field. Why?
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to reduce Compton scatter
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Fat people are harder to x-ray because there is more Compton scatter. What to do?
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Corset them or ask them to lie down so fat spreads to sides.
Don't be shy - women do it with their breasts all the time! |
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There are 3 kinds of BEAM RESTRICTORS.
Which one do we use? |
VARIABLE APERTURE COLLIMATOR
VAC! |
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least effect beam restrictor
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aperature diaphragm
old school like photography |
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second least effective beam restrictor
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cones/cylinders
Dentists use these for bitewings. Crazy high dose. This isn't high school geometry. No shapes, please. |
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Beam restrictor we use.
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VARIABLE APERATURE COLLIMATOR
2 sets of SHUTTERS (one for focus, one to control radiation) Collimate as tightly as possible |
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film at 40" = 2% of SID is
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0.8" as your beam restriction
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3 types of filtration
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inherent
added collimator mirror |
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light field restriction for variable aperature collimator
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+/- 2% of SID so light field for
film @ 40" ? 40 x 0.2 = 0.8" SID (the 2% of 40") your light field will be 0.8" for a film 40" away |
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Place the central beam
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right over the middle of the object being shot, collimate the +/- 2% radiation field of the total distance and do it!
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Collimator mirror contributes ___ Aluminum equivalent to filtration.
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~1 mm. Al for collimator mirror
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INHERENT FILTRATION in the tube / INHERENT _________ of the body (ie, forefoot vs. ankle)
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CONTRAST
inherent filtration in tube divided by inherent contrast of body part |
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PITA
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Pain In The Ass
federal mandate for boards: you radiation must be within your film size |
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Creates a straight pathway for photons
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GRIDS polarize radiation
*cleans 80-90% of scattered radiation - eliminates those pesky heavily angled photons that fast screens let go by |
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Describe a GRID
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radiopaque LEAD strips
+ radiolucent ALUMINUM interspaces |
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High ratio grid
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reduced scatter and quality image but HIGH PATIENT DOSE.
high ratio of lead to aluminum is bad for patients |
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How to determine a good grid ratio?
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Ratio is the height of grid (Bucky)
divided by Interspace width (Aluminum interspaces) height/interspaces 10:1 is a good ratio of height to interspaces |
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Grid frequency
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the number of strips per inch
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Contrast IMPROVEMENT factor
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GRIDS increase contrast because they decrease scatter (fuzzy stuff)
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Grid FREQUENCY is the same as Grid _________.
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RATIO
Frequency/Ratio is the height of the bucky versus the number of interspaces. h/i |
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h/i there!
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height of bucky/interspace #
is grid ratio/frequency. good is 10:1 110 lines per inch on analog sys is good h/i |
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You can see grid lines...
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you are about to be thrown shackled into the lake by Dr. Warshel because you are using a low frequency grid and he hates low frequency anything.
However, you can get rid of these lines because a true Bucky will move the grid for you. Less dose for patient with low frequency grid. The Bucky that Bucky invented will move itself and blur the grid lines. |
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Upright film holder vs. Bucky
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Bucky bucks (moves) so blurs your grid lines.
Upright pianos don't move. |
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GRIDS decrease contrast (have a contrast improvement factor) by decreasing scatter. Contrast is _______ by using a GRID.
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doubled!
Don't use a grid when shooting extremities - don't need it. More important for big parts that have higher mAs needs (higher patient doses). |
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The Bucky IS the _____.
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GRID
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Bucky factor is same as Grid factor.
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It's how much you have to increase the dose to compensate for putting a grid in place.
Higher grid ratio (height of grid/ width of Aluminum interspaces)= higher bucky factor (correction for optical density) When you use a higher kVp, you get more Compton scatter and fewer photoelectric effects. Narrow your focus, increase your mAs by 30%, this will reduce your kVp, but the Bucky factor will reduce patient dose, decrease scatter and correct optical density. This slide is kind of bullshit because the grid performance notes aren't clear and I have a huge test in the morning that is a 6 hour class instead of this 2 hour credit but I'm typing crap about bucky factors instead of Ewing's sarcoma. |
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3 types of grids
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Parallel (leads to cut off)
Crossed (extremely high dose) Focused (YES!) |
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Focused grids do what?
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FAN like a beam - this is why your Bucky is set to 40" or 72" because you use a FOCUSED GRID that FANS perfectly from 40" or 72" away. No cutoffs or divergent beams.
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GRIDS decrease contrast (have a contrast improvement factor) by decreasing scatter. Contrast is _______ by using a GRID.
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doubled!
Don't use a grid when shooting extremities - don't need it. More important for big parts that have higher mAs needs (higher patient doses). |
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The Bucky IS the _____.
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GRID
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Bucky factor is same as Grid factor.
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It's how much you have to increase the dose to compensate for putting a grid in place.
Higher grid ratio (height of grid/ width of Aluminum interspaces)= higher bucky factor (correction for optical density) When you use a higher kVp, you get more Compton scatter and fewer photoelectric effects. Narrow your focus, increase your mAs by 30%, this will reduce your kVp, but the Bucky factor will reduce patient dose, decrease scatter and correct optical density. This slide is kind of bullshit because the grid performance notes aren't clear and I have a huge test in the morning that is a 6 hour class instead of this 2 hour credit but I'm typing crap about bucky factors instead of Ewing's sarcoma. |
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3 types of grids
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Parallel (leads to cut off)
Crossed (extremely high dose) Focused (YES!) |
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Focused grids do what?
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FAN like a beam - this is why your Bucky is set to 40" or 72" because you use a FOCUSED GRID that FANS perfectly from 40" or 72" away. No cutoffs or divergent beams.
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I can't believe I'm getting up at 4am to study musculoskeletal pathophys and am still typing these cards for radiology physics.
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chiro school is sucking this tri.
just sayin' |
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Exposure artifacts
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CLOTHING OR JEWELRY
Patient INSTRUCTIONS WRONG ( didn't use 2nd breath) Patient POSITIONING WRONG DOUBLE EXPOSURES FILM + SCREEN CONTACT (protective layer worn out) GRID misalignment (upside down, off center, off level, off focus) |
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Processing artifacts
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Crossover marks (run with film direction - gunked up brushes)
Pi lines (parallel to insertion, exactly 3.124 apart) Dichroic (2 color) staining from chemical fog (gluteraldehyde shot -fixer problem) Wet pressure sensitization (dirty rollers produced pressure fog) Milky, greasy, brittle emulsion |
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Handling and storage artifacts
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STATIC low humidity looks like lightning
ROUGH handling leaves pressure or kink or thumnail marks FOG darkroom, safelight, hydrocollator, cell phone, fridge Film SAFE OPENED duh Cassette EDGE LEAKS |
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A higher grid ratio (h/i) would increase patient dose because?
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you are taking out the bad scatter from only 1% of usable photons and you need a minimum of 1% usable photons!
Less grid ratio is less scatter removed but LOWER patient dose. Use a 10:1 |
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What is inside a cassette of digital system?
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IMAGING PLATE
Instead of film |
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PSP
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photostimulable phosphor in imaging plate of digital cassette
half fluoresce immediately, half stay metastable |
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Less tech time
Fewer retakes Higher image quality Higher patient satisfaction More throughput Long term savings |
Benefits of digital
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You must make offsite ______ with digital records.
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backups
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Cons of digital
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expensive set up
dose creep (higher with digital) (~20%) due to tendency to leave film on high dose settings even though should reduce dose by up to 50%! |
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Which has better resolution, digital or plain film?
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plain film
*because you cannot resolve any items smaller than a pixel |
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Contrast is not controlled by ____ on digital.
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kVp
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Equivalent of LATITUDE on digital
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WINDOWING
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Why is mAs so high on digital?
|
less quantum mottle
better signal to noise ratio balances quality w/ dose ALARA! |
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Your eye can see 30 shades of grey, while a computer screen can see 256. CT can see 4000 Hounsfield units, CD/CR can see 10,000.
What's the point? |
Great greyscale...But what's the point if your monitor can still only see 256? So you can reduce the window width (greyscale) to get better contrast.
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Changes the center point of the 256 shades of grey displayed on the window...
|
window LEVEL moves it left or right, lighter or darker
Moving window LEVEL allows DIFFERENTIATION of tissues |
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DICOM
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Digital Imaging and Communication in Medicine
software for dif. systems |
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PACS
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the computer server
PICTURE ARCHIVING & COMMUNICATION SYSTEM database! |
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PACS is the _______
DICOM is the _________ |
PACS = database
DICOM = compatability software |
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What is the minimum megapixel proposed for the Display
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2MP
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