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Cerwin-Vega Subwoofers SL-36 USA made

film cassette

light-tight container which houses and protects the screens and film during transfer from darkroom to bucky tray and back to dark room

intensifying screens

rectangular, flat, shiny, white plates glued into the inside of both sides of a film cassette

intensifying screens holds the film tightly

between when the cassette door is closed

intensifying screesn function to

convert x-ray photon energy into visible light energy to intensify the film

(darkening effect of the x-ray beam)

50 x-ray photons can make

50 latent image centers on the film directly or make enough visible light to cause the formation of 1700 latent image centers with par speed screens

what is an advantage of x-ray intensifying screens

decrease heat damage to x-ray tube

intensifying screens used because

they decrease greatly the number of x-rays necessary to make an exposure (decrease patient dose) and decrease the tube loading (decrease mAs leads to decrease HU)

Michael Pupin first used

fluorescent screens with glass photographic plates in 1896

typical intensifying screen

base, reflecting coat, phospho layer, protective layer

what is the disadvantage of x-ray intensifying screens

decreases image sharpness and resolution

what function on x-ray intensifying screens

convert x-ray energy into light energy

light emission

luminescence

fluorescence

phosphorescence

luminescence

the emission of light from a substance following stimulation by chemicals, light, ionizing radiation

fluorescence

the instantaneous (within 10^-8 sec) emission of light from substances

in radiology, the emission of light from

special inorganic crystals (phosphors) after stimulation by x-rays

phosphorescence

the emission of light after stimulation is delayed beyond 10 ^ -8 sec

(undesirable in radiographic screens)

active ingredient in an intensifying screen

the phosphor layer, which contains the crystals that convert x-ray energy into light energy

calcium tungstate

first commercial phosphor
introduced around 1898 by Thomas Edisons group

rare earth screens

first manufactured in 1973

increased x-ray absorption and conversion efficiency

terbium-activated gadolinium oxysulfide

green emitter

thulium-activated lanthanum oxybromide

blue emitter

the radiologic health branch (RHB) recommends minimum system speed of

400

about what percentage of radiographic film density (darkness) is cause by direct x-ray to film exposure

less than 5% (insignificant)

what percentage of radiographic film density (darkness) is caused by x-ray to light screens to film exposure

greater than 95% (effectively all film darkening)

advantages of intensifying screens

patient ionizing radiation exposures utilizing modern rare earth screens are less than 1/100 the exposure the would be needed for direct x-ray to film exposure

advantages of intensifying screes

decrease tube loading (decrease mAs causes decrease HU)

disadvantage of intensifying screens

image resolution drops from 100 lines/mm to 10 lines/mm

loss of resolution cause (disadvantage of intensifying screens)

primarily by light diffusion within the phosphor crystal layer

within the same family of phosphor crystals image resolution (disadvantage of intensifying screens)

decreases as screen speed increases

phosphor crystal size (image quality with intensifying screes)

the larger the crystal size, the poorer the resultant image (increase light diffusion)

thickness of phosphor crystal layer

the thicker the phosphor layer, the poorer the resultant image (increases light diffusion)

presence of light-absorbing dyes placed in the phosphor layer (image quality with intensifying screes)

light-absorbing dyes increase image quality by decrease light diffusion

presence of TiO2 reflecting layers (image quality with intensifying screes)

reflecting layer decrease image quality by increase light diffusion

film screen contact (image quality with intensifying screes)

anything that interferes with tight film screen contact will decrease image quality (increases light diffusion)

T/F all images produced by intensifying screens have less sharpness and resolution than direct x-ray film exposure

T

which modifications/variables keep this image degradation to a minimum

small phosphor crystal size

thinnest screen phosphor layer

light absorbing dye in phosphor layer

no reflective layer between base and phosphor layer

use of single screen, single emulsion film systems

all modifications decrease

film/screen system speed

screen speed is inversely related to

image quality

screen speed is influenced by

type of phosphor (absorption/conversion ratio)

phosphor crystal size

thickness of phosphor layer

presence of reflecting layer

presence of light absorbing dye

kVp range (K-edge of phosphor)

what was the fisrt phosphors

barium platinocyanide was the first x-ray phosphor used

what is the x-ray absorbing ability of rare earth phosphors as compared to calcium

rare earth phosphors absorb about 50% more x-rays than an equal thickness of calcium tungstate at commonly-used kVps

(better k-edge/ave photon E match)

what is the x-ray to light conversion efficiency of rare earth phosphors compared to calcium tungstate

calcium tungstate 5%

rare earths 15-18%

how much better are rare earths than calcium tungstate when it comes to x-ray to light conversion efficiency

3-4 times better

since rare earth phosphors absorb 50% more x-rays than calcium tungstate, and convert 3-4 times as much absorbed x-ray energy into light energy, which type of phosphor is faster (more film density per mAs)

rare earth

considering the film-darkening effect of various speeds of intensifying screens, how much faster is an 800 speed rare earth film/screen system than a 200 speed high plus calcium tungstate film/screen system

4 times

calcium tungstate phosphor emits a continuous spectrum with maximum intensity in the

blue purple region of the EM spectrum

regular halide film is maximally sensitive to

light in the UV and purple blue regions

what is well matched to calcium tungstate phosphor

halide

rare earth phosphors emit a non-continuous (line) spectrum that comes in 2 types

blue light emitting

green light emitting

green light emitting is used with

gadolinium

an example of a green light emitter is

Kodak Lanex

what happens if green emitting screens are used with standard halide (blue-purple sensitive) film

spike of useful green light emitted will not be seen by regular halide film

primary light emission will be wasted

adequate film exposure will not take place

film/screen system becomes slow

patient receives excessive radiation

the solution is special

orthocrhomatic film which is sensitive to green light

T/F

orthochromatic film must be used with any green-emitting system

T/F rare earth screens & film must be carefully matched to ensure compatibility

T

T/F Panchromatic film is not used in radiography

T

regular halide film is not sensitive to (darkroom safe light)

red or green light

what kind of safelight can be safely used with halide film

amber

what film is sensitive to some of the shorter wavelengths emitted by the amber safelight (yellow green) and will be fogged

orthocrhomatic

what safelight can safely be used with green sensitive film

true red safelight

whats the proper safelight color to use with gadolinium based RE screens

red

advantages of screens over non-screen technique

shorter exposure times causes less motion sharpness

smaller focal spots used leading to increase image quality

longer FFDs lead to increase image quality & decrease patient dose

extend x-ray tube life

decrease mAs causes decrease HU

reduce patient/operator exposure to ionizing radiation

screens inherently increase image contrast

advantages of rare earth over calcium tungstate screens

decreased tube loading

reduced patient/operator radiation dose

decreased tube loading (advantages or rare earth over calcium tungstate screens)

shorter exposure times causes less motion unsharpness

smaller focal spots can be used leading to increase image quality

longer FFDs lead to increase image quality & decrease patient dose

extend x-ray tube life

reduced patient/operator radiation dose (advantages or rare earth over calcium tungstate screens)

75% reduction w/ 800 speed rare earth system compared to 200 speed tungstate system

T/F magnification radiography benefits from smaller focal spot sizes

T

disadvantages of rare earth over calcium tungstate screens

cost

mottle

so much speed (light) is produced by so few x-ray photons that mottle (graininess) becomes

a significant problem which degrades image quality

T/F dont use film/screen system speeds greater than 800 (mottle)

T

mottle is a

signal to noise ratio problem

mottle results from

statistical fluctuation in the number of x-ray photons absorbed by the intensifying screens to form the light image recorded on film

if x-ray photons are not evenly distributed in the x-ray beam they

clump randomly producing a pattern on the film

mottle background noise consists of a

random clumping pattern that is only visible on sharp films taken with very few x-ray photons

the fewer the number of photons the

worse the noise

increasing the number of photons

fills in the spaces

covers the clumping pattern

if the film/screen system is so fast that very few x-ray photons (lower mAs) are being used to create the image then the bacground clumping patter/graininess/mottle becomes

prominent and the image (signal) becomes weak and loses clarity

excessive mottle/graininess causes

an unacceptable degradation in image clarity at film/screen system speeds above 800

excessive mottle can only be corrected by using

more x-rays (mAs) which can only be accomplished by switching to a slower film/screen system

gradient/split screens one end is

slower than the other

gradient/split screens can be an

abrupt change (split) or gradual (gradient)

gradient split screens are used primarily in

full spine radiography to compensate for tissue thickness differences in the patient

gradient/split screens slower portion of the screen is placed

over the thinner portion of the patient

gradient/split screens allows the thin portion of the patient to receive

excessive radiation dose but not overexpose the film

gradient/split screens are to be

discouraged, and should be replaced by single-speed screens and compensating filters

film and screens should make tight

contact throughout every part of the film

film screen contact gaps between the screens and films increases

light diffusion which degrades the image

Z screen is

large mesh, Cu, brass or Zn galvanized steel

high Z screen is x-rayed with

an air-gap using the film/screen system in question

processed image is carefully

scrutinized for areas of poor image clarity

(should be uniformly sharp)

T/F never snap shut the door of any cassette unless it is completely dry and loaded with film

T

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