Chapter 12 Flashcards
(95 cards)
1
Q
The radiographic intensifying screen emits
A
visible light, which exposes the radiographic film placed between the two screens. Although, some x-rays reach the film emulsion, it is primarily light from the radiograpic intensifying screens that expose the radiographic film.
2
Q
Processing the invisible latent image
A
creates the visible image
3
Q
procesing
A
causes the silver ions in the silver halide crystal that have been exposes to light to be converted into microscopic grains of silver.
4
Q
film processing sequence
A
wetting, developing, rinsing, fixing, washing, and drying-is completed in 90 seconds in an automatic processor.
5
Q
penguin
A
Image forming x-rays are those that exit the patient and interact with the image receptor.
6
Q
exit x-ray beam
A
refers to the x-rays that remain as the useful beam exits the patient. It consist of x-rays scattered away from the image receptor and image forming x-rays.
7
Q
radiographic media
A
x-ray film fluoroscopic image intensifier television, or flat panel monitor laser imaging system solid state detectors
8
Q
the medium that converts the x-ray beam into a visible image is called
A
image receptor (IR) The classical IR is photographic film, although sokid state digital IRs are replacing film
9
Q
Radiographic film has two parts:
A
base and the emulsion
10
Q
double emulsion film
A
in most x-ray film, the emulsion is coated on both sides.
11
Q
Adhesive layer
A
between the emulsion and the base is a thin coating of material which ensures uniform adhesion of the emulsion to the base. This adhesive layer allows the emulsion and the base to maintain proper contact and integrity during use and processing.
12
Q
Base
A
is the foundation of radiographic film. its primary purpose is to provide a rigid structure onto which the emulsion can be coated. the base is flexible and fracture resistant to allow easy handling but is rigid enough to be snapped into a view box.
13
Q
penguin
A
the base of radiographic film is 150 to 300 um thick, semirigid, lucent, and made of polyester.
14
Q
dimensional stability
A
the base of radiographic film maintains its size and shape during use and processing so that it does not contribute to image distortion.
15
Q
lucency
A
the base is uniformed and is nearly transparent to light.
16
Q
film tinted blue
A
during manufacturing, dye is added to the base of most radiographic film to slightly tint the film blue. compared to untinted film, this coloring reduces eyestraing and fatigue, enhancing radiologists diagnostic efficiency and accuracy.
17
Q
Original film base
A
was a glass plate
18
Q
cellulose nitrate
A
replaced glass plates but was flawed because of its highly flammable state.
19
Q
cellulose triacetate
A
was referred to as “safety base” because it was not flammable. it was introduced in the mid 1920’s
20
Q
Polyester
A
was introduced in the 1960s. it took the place of cellulose triacetate as the film base of choice. it is more resistant to warping from age and is stronger than CT, permitting easier transport through automatic processors. its dimensional stability is superior. polyester bases are thinner than tracetate bases (175 um) but are just as strong.
21
Q
Emulsion
A
the heart of the radiograpphic film. it is the material with which x-rays or light photons from radiographic intensifying screens interact. it consists of a homogeneous mixture of gelatin and silver halide crystals. It is coated evenly with a layer that is 3 to 5 um thick. The gelatin is clear, so it transmits light, and is porous for processing chemicals to penetrate to the crystals of silver halide. Its principal function is to provide mechanical support for silver halide crystals by holding them uniformly dispersed in place.
22
Q
Radiographic emulsion
A
silver halide crystal is the active ingredient of the radiographic emulsion. In the typical emulsion, 98% of the silver halide is silver bromide; the remainder is usually silver iodide. The interaction of x-ray and light photons with high Z atoms ultimately results in the formation of a latent image on the radiograph.
23
Q
Silver halide crystals
A
Depending on the intended imaging application, silver halide crystals may have tabular, cubic, octahedral, polyhedral, or irregular shapes. Tabular grains are used in most radiographic films.
24
Q
tabular silver halide crystals
A
are flat and typically 0.1 um thick, with a triangular, hexagonal, or higher order polygonal cross section. The crystals are approximately 1 um in diameter.
The crystals are made by dissolving metallic silver (Ag) in nitric acid (HNO3) to form silver nitrate (AgNO3). Light sensitive silver bromide (AgBr) crystals are formed by mixing silver nitrate with potassium bromide (KBr)
25
Sensitivity center
The shape and lattice structure of silver halide crystals are not perfect, and some of the imperfections result in the imaging property of the crystals. the type of imperfection thought to be responsible is a chemical contaminant, usually silver sulfide, which is introduced by a chemical sensitization into the crystal lattice, usually at or near the surface. During exposure, phtotelectrons and silver ions are attracted to these sensitivity centers, where they are combine to form a latent image center of metallic silver.
differences in speed, contrast, and spatial resolution among various radiographic films are determined by the process by which silver halide crystals are manufactured and by the mixture of these crystals into the gelatin.
the number of sensitivity centers per crystal, the concentration of crystals in the emulsion, and the size and distribution of the crystals affect the performance characteristics of radiographic film.
Radiographic film is manufactured in total darkness. From the moment the emulsion ingredients are brought together until final packaging, no light is present.
26
screen film
the most commonly used film
26
screen film
is the type of film that is used with radiographic intensifying screens.
several characteristics must be considered when one is selecting screen film: contrast, speed, spectral matching, anticrossover or antihalation dyes, and requirement for a safelight.
26
screen film
| contrast
most manufacturers offer screen film with multiple contrast levels. the contrast IR is inversely proportional to its exposure latitude, that is, the range of exposure technique that produce an acceptable image. Usually the manufacturer identifies the contrast of these films as medium, high, or higher. the difference depends on the size and distribution of the silver halide crystals. a high contrast emulsion contains smaller silver halide grains with a relatively uniform grain size. low contrast films, contain larger grains that have a wider range of sizes.
26
screen film
| speed
speed is the sensitivity of the screen film combination to x-rays and light.
for direct exposure film, speed is principally a function of the concentration and the total number of silver halide crystals. for screen film, silver halide grain size, shape, and concentration are the principal determinants of film speed.
to optimize speed, screen films are usually double emulsion, that is, an emulsion is layered on either side of the base. this double layering is attributable primarily to the efficiency conferred by the use of two screens to expose the film from both sides. this produces twice the speed that could be attained with a single emulsion film even if the single emulsion were made twice as thick.
compared with earlier technology, current emulsions contain less silver yet produce the same optical density per unit exposure. this more efficient use of silver in the emulsion is called the covering power of the emulsion.
26
screen film
| crossover
most emulsions contain tabular grains, which are flat silver halide crystals, and provide a large surface area to volume ratio. the result is improved covering power an significantly lower crossover.
when light is emitted by a radiographic intensifying screen, it not only exposes the adjacent emulsion, it can also expose the emulsion on the other side of the base.
when light crosses over the base, it causes increased blurring of the image.
tabular grain emulsions reduce crossover because the covering power is increased, which relates not only to light absorption from the screen (which is increased) but also to light transmitted through the emulsion to cause crossover (which is reduced).
The addition of a absorbing dye in a crossover control layer reduces crossover to near zero. the crossover control layer has three critical characteristics 1) it absorbs most of the crossover light, 2) it does not diffuse into the emulsion but remains as a separate layer, and 3) it is completely removed during processing.
26
screen film
| spectral matching
the most important consideration in the selection of modern screen film is its spectral absorption characteristics.
26
penguin
crossover is the exposure of an emulsion caused by light from opposite radiographic intensifying screen.
26
penguin
large grain emulsions are more sensitive than small grain emulsions.
26
penguins
rare earth screens are made with rare earth elements--those with atomic numbers of 57 to 71.
26
penguin
the fog level for unprocessed film is approximately 2 uGy (0.2 mR)
26
genguin
the latent image is the invisible change that is induced in the silver halide crystal.
26
penguin
an ion is an atom that has too many or too few electrons and therefore has electric charge
26
penguin
the result is the same whether the interaction involves visible light from a radiographic intensifying screen or direct exposure by x-rays.
26
penguin
the radiographic intensifying screen amplifies the effect of image forming x-rays that reach the screen film cassette
26
penguin
the phosphor converts the x-ray beam into light
26
spectral response
radiologic technologists must be particularly careful to use a film whose sensitivity to various colors of light is properly matched to the spectrum of light emitted by the screen
27
penguin
isotropic emission refers to radiation emitted with equal intensity in all directions
28
penguin
higher conversion efficiency results in increased noise.
29
penguin
generally, condition that increase the IF reduce spatial resolution
30
penguin
in mammography, the screen is positioned in contact with the emulsion on the side of the film away from the x-ray source to reduce screen blur and improve spatial resolution.
31
penguin
screen film compatibility is essential; use only those films for which the screens are designed.
32
penguin
rare earth radiographic intensifying screens have the principal advantage of speed.
33
penguin
the combination of improved CE and higher DQE results in the ins.creased speed of rare earth radiographic intensifying screen
34
penguin
developing is the stage of processing during which the latent image is converted to a visible image.
35
penguin
fixing the silver halide that was not exposed to radiation is the process of clearing it from the emulsion and hardening the emulsion to preserve the image.
36
penguin
synergism occurs when action of two agents working together is greater than the sum of the action of each agent working independently
37
penguin
lack of sufficient glutaraldehyde may be the biggest cause of problems with anatomic processing.
38
penguin
archival quality refers to the permanence of the radiographic: the image does not deteriorate with age but remains in its original state.
39
penguin
silver sulfide stain is the most common cause of poor archival quality
40
penguin
the shorter dimension of the film should always be against the side rail, so the proper replenishment rate is maintained.
41
penguin
cleaning the tanks and the transport system should be a part of the routine maintenance of any processor.
42
penguin
most processing faults leading to damp film are because of depletion of glutaraldehyde, the hardener in the developer.
43
penguin
a finished radiograph that is damp easily picks up dust particles that could result in artifacts.
44
Calcium tungstate screens
which emit blue violet light, have been largely replaced with rare Earth screens, which are faster. Now many rare Earth phosphors emit ultraviolet, blue, green, and red. All silver halide films respond to violet and blue light but not to green, yellow, or red unless they are spectrally sensitized with dyes.
If green emitting screens are used, they should be matched with a film that is sensitive not only to blue light but also to green light. Such film is orthochromatic and is called green-sensitive film. This is distinct from panchromatic film, which is used in photography and is sensitive to the entire visible light spectrum. proper spectral matching results in selection of the correct screen film combination.
45
reciprocity law
One would expect that the total exposure of a film would not depend on the time taken to expose it. That is the definition of the reciprocity law.
exposure = intensity * time= constant optical density
the reciprocity law is true for film exposed directly to x-rays. Industrial radiographers do not have to compensate for this effect. The reciprocity law fails when film is exposed to light from radiographic intensifying screens.
Very long or very short exposure times produce a lower OD than that predicted by the reciprocity law.
Reciprocity law failure is important when exposure times are long (as in mammography) or short (as in interventional radiography). the result of long or short exposures is reduced speed.
46
safelights
the use of radiographic film requires certain precautions in the darkroom. Mose safelights are incandescent lamps with a color filter; safelights provide enough light to iluminate the darkroom while ensuring that the film remains unexposed.
proper dark room illumination depends not only on the color of the filter but also on the wattage of the bulb and the distance between the lamp and the work surface. A 15w bulb should be no closer than 1.5 m (5ft) from the work surface.
With blue-sensitive film, an amber filter is used. the amber filter transmits light that has wavelengths longer than approximately 550 nm, which is above the spectral response of blue-sensitive film.
the use of an amber filter would fog green sensitive film; therefore, a red filter, which transmits only light above approximately 600nm, must be used in this case. A red filter is suitable for both green and blue sensitive film.
47
Direct exposure film
The use of radiographic intensifying screens with film allows reduced technique and therefore reduced patient radiation dose. however, the image is more blurred than it would be after exposure without screens.
Most extremity examinations now use fine-grain, high-detail screens and double emulsion film as the IR. The emulsion of a direct exposure film is thicker than that of screen film, and it contains higher concentrations of silver halide crystals to improve direct x-ray interactions.
48
mammography film
was originally performed with an industrial grade, double emulsion, direct exposure film.
the radiation doses associated with such a technique were much too high; so specialty films were developed
mammography film is single emulsion film that is designed to be exposed with a single radiographic intensifying screen. all currently available mammography screen film systems use greide screens emitting terbium-doped gadolinium oxysulfide screens with green sensitive film.
49
halation
the surface of the base opposite the screen is coated with a special light absorbing dye to reduce reflection of screen light, which is transmitted through the emulsion and base. the absorbing dye is an antihalation coating. such an antihalation coating is used on all single emulsion screen film, not just mammography film. the coating is removed during processing for better viewing.
50
heat and humidity (film)
radiographic film is sensitive to the effects of elevated temperature and humidity, especially for long periods. heat increases the fog of a radiograph and therefore reduces contrast. Radiographic film should be stored at temperatures lower than 68 degrees f.
51
light
radiographic film must be stored and handled in the dark. any light at all can expose the emulsion before processing. if low level, diffuse light exposes the film, fog is increased. if bright light exposes or partially exposes the film, a gross, obvious artifacts are produced.
control of light is ensured by a well sealed darkroom and a light-proof storage bin for film that ha been opened bud.t not clinically expose.
52
radiation
ionizing radiation, other than the useful beam, creates an image artifact by increasing fog and reducing contrast. film fog is dull, uniform OD that appears if the film has been inadvertently exposed to light, x-rays, heat, or humidity.
Darkrooms are lined with lead.
53
formation of the latent image
immediately after exposure, no image can be observed on the film. an invisible image is present. with proper chemical processing, the latent image becomes a visible image.
the formation of the latent image, sometimes is called photographic effect.
54
silver halide crystal
the silver, bromine, and iodine atoms are fixed in the crystal lattice in ion form. silver is a positive ion, and bromide and iodide are negative ions. when a silver halide crystal is formed, each silver atom releases and outer shell electron, which becomes attached to a halide atom (either bromine or iodine).
the silver atom is missing an electron and therefore is a positively charged ion, identified as Ag. the bromine and iodine atoms each have one extra electron and therefore are negatively charged ions.
55
photon interaction with silver halide
when light photons from the radiographic intensifying screen interact with film, it is the interaction with the silver and halide atoms that forms the latent image. the interaction releases electrons in the crystal.
56
Radiographic intensifying screen construction
most radiographs are made with the film in contact with a radiographic intensifying screen because the use of film alone requires a high patient radiation dose. a radiographic intensifying screen is a device that converts the energy of the xray beam into visible light. this visible light then interacts with the radiographic film, forming the latent image.
on the other hand, use of a radiographic intensifying screen lowers the patient dose considerably; on the other hand, the image is slightly blurred.
the film used is called double-emulsion film because it has an emulsion coating on both sides of the base.
57
protective coating
the layer of the radiographic intensifying screen closest to the radiographic film is the protective coating. it is 10 to 20 um thick and is applied to the face of the screen to make the screen resistant to the abrasion and damage caused by handling. this layer also helps to eliminate the buildup of static electricity and provides a surface for routine cleaning without disturbing the active phosphor. the protective layer is transparent to light.
58
phospher
The active layer of the radiographic intensifying screen is the phosphor. the phosphor emits light during stimulation by x-rays. phosphor layers vary in thickness from 50 to 300 um, depending on the type of screen. the active substance of most phosphors before about 1980 was crystalline callcium tunganum, and state embedded in a polymer matrix. the rare earth elements gadolinium, lanthanum, and yttrium are the phosphor material in newer faster screens.
59
thomas a edison
developed calcium tungstate
60
luminescent material/phosphor
any material that emits light in response to some outside stimulation
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emitted visible light
luminescence
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luminescence
involves outer shell electrons
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fluorescence
if visible light is emitted only while the phosphor is stimulated
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phosphorescence
if the phosphor continues to emit light after stimulation
65
radiologic technologists are concerned with three primary characteristics of radiogrphic intensifying screens.
screen speed, image noise, and spatial resolution
66
intensification factor (IF)
because screens are used to reduce patient dose, one characteristic is the magnitude of dose reduction, it is the measure of the speed of the screen and is a measure of the speed of the screen.
67
screen speed
is a relative number that describes how efficiently x-rays are converted into light.
68
properties of radiographic intensifying screens that are not controlled by the radiologic technologists
1) phosphor composition--rare earth phosphors efficiently convert x-rays into usable light.
2) phosphor thickness--the thicker the phosphor layer, the higher is the detective quantum efficiency. high speed screens have thick phosphor layers; fine detailed screens have thin phosphor layers.
3) reflective layer--the presence of a reflective layer increases screen speed but also increases image blur.
4) dye-light absorbing dyes are added to some phosphors to control the spread of light. these dyeighs improved spatial resolution but reduce speed.
5) crystal size--larger individual phosphor crystals produce more light per x-ray interaction. the crystals of detail screens are approximately half the size of the crystals of high speed screens
5) concentration of phosphor crystals--higher crystal concentration results in higher screen speed.
69
Several conditions that affect radiographic intensifying that are controlled by the radiologic technologist
10 Radiation quality--as x-ray tube potential is increased, the IF also increases
image processing--only the superficial layers of the emulsion are affected when radiographic film is exposed to light. however, the emulsion is affected uniformly throughout when the film is exposed to x-rays.
temperature---radiographic intensifying screens emit more light per x-ray interaction at low temperatures than at high temperatures. Consequently, the IF is lower at a higher temperatures.
70
image noise
appears on a radiograph as a speckled background. it occurs most often when fast screens and high kVP techniques are used. noise reduces image contrast.
71
detective quantum efficiency (DQE)
the percentage of x-rays absorbed by the screen is higher
72
conversion efficiency (CE)
the amount of light emitted for each x-ray absorbed also is higher
73
quantum mottle
a principal component of image noise
74
image detail or visibility of detail
these terms are used when describing image quality
75
spatial resolution
refers how small an object can be imaged
76
contrast resolution
refers to the ability to image similar tissues, such as the liver and pancreas or gray matter or white matter.
77
spatial resolution
in screen film radiography is limited principally by effective focal spot size
78
rare Earth screens
except for barium and zinc based phosphors, the other new phosphors are identified as rare Earth. therefore, all of these screens have come to be known as rare earth screens
79
Earth Screens
are principally gadolinium, lanthanum, and yttrium
80
higher x-ray absorption
when diagnostic x-rays interact with a calcium tungstate screen, approximately 30% of the x-rays are absorbed. this mechanism of absorption is almost entirely the photoelectric affect.
