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228 terms

Image processing & quality assurance

STUDY
PLAY
Boxes of film stored in too warm an area may be subject to
film fog
X-ray film emulsion is sensitive
requires proper handling and storage. It should be stored in a cool (40° to 60°F), dry (40% to 60% humidity) place. Exposure to excessive temperatures or humidity can lead to film fog and loss of contrast. Static marks are a result of low humidity.
Exposed silver halide crystals are changed to black metallic silver by the
reducers
As the film emulsion is exposed to light or x-rays
latent image formation takes place. The exposed silver halide crystals are reduced to black metallic silver in the developer solution. Automatic processor developer agents are hydroquinone and phenidone. The preservative—sodium sulfite—helps prevent oxidation. The activator provides the necessary alkalinity for the developer solution, and hardener is added to the developer in automatic processing to keep emulsion swelling to a minimum.
Which of the following is performed to check the correctness of the developing parameters?
Sensitometry
Sensitometry is
a method of quality control for daily monitoring of the automatic film processor
A densitometer is
a device used to read optical density
crossover rollers should be cleaned
daily to prevent the buildup of crystallized solution on the rollers.
A warm-up procedure is
performed on an x-ray tube for safe operation after prolonged disuse.
A film emerging from the automatic processor exhibits excessive density. This may be attributable to which of the following?
1. Developer temperature too high
2. Chemical fog
Excessive radiographic density may be a result of
overdevelopment
Overdevelopment may be due to
excessive developer temperature, resulting in chemical fog. Excessive density can also be a result of overreplenishment as a result of faulty microswitches or of feeding film into the processor "the long way" rather than "the wide way."
Image receptors/cassettes frequently have a lead foil layer behind the rear screen that functions to
absorb backscatter
Many cassettes/image receptors have a thin lead foil layer behind the rear screen to
absorb backscattered radiation that is energetic enough to exit the rear screen, strike the metal back, and bounce back to fog the image. When this happens, the image receptor's metal hinges or straps may be imaged in high-kVp radiography. The lead foil absorbs the backscatter before it can fog the film.
Which of the following are methods used for silver reclamation?
1. Metallic replacement method
2. Electrolytic method
About half the silver in a film emulsion remains to form the image. The other half is removed from the film during
the fixing process
fixer solution has a high
silver content
Silver is a
toxic metal and cannot simply be disposed of into the public sewer system. As silver is also a precious metal, it becomes financially wise to recycle the silver removed from x-ray film
The three most commonly used silver recovery systems are
the electrolytic, metallic replacement, and chemical precipitation methods
In electrolytic units
an electric current is passed through the fixer solution. Silver ions are attracted to, and become plated onto, the negative electrode of the unit. The plated silver is periodically scraped from the cathode and accurately measured so that the hospital can be appropriately reimbursed. The electrolytic method is a practical recovery system for moderate- and high-use processors
The metallic replacement (or displacement) method of silver recovery
uses a steel mesh/steel wool type of cartridge that traps silver as fixer is run through it. This system is useful for low-volume processors and is often also used as a backup to the electrolytic unit.
Chemical precipitation
adds chemicals that release electrons into the fixer solution. This causes the metallic silver to precipitate out, fall to the bottom of the tank, and form a recoverable sludge. This method is used principally by commercial silver dealers.
Film base is currently made of which of the following materials?
Polyester
Film base functions to
support the silver halide emulsion
Today's film base is made of
tough, nonflammable polyester. Cellulose nitrate was used in the past, but it was highly flammable. Cellulose acetate, also used in the past, was not flammable, but it was not as durable as polyester. The earliest supports for emulsion were plates of glass (hence the term flat plate).
Which of the following can result from improper film storage or darkroom conditions?
1. Safelight fog
2. Background radiation fog
If the safelight bulb is of a higher wattage than it should be, the safelight filter is incorrect for the film type, or the filter is cracked,
film fog can occur
If film is not stored in a radiation-safe area,
it can be fogged by background radiation.
Screen lag
caused by aged or defective intensifying screens
Conditions contributing to poor radiographic film archival quality include
1. fixer retention.
2. insufficient developer replenishment.
3. poor storage conditions.
The archival quality of a film refers to
its ability to retain its image for a long period of time
Many states have laws governing
how long a patient's medical records, including films, must be retained. Very importantly, they must be retained in their original condition.
Archival quality is poor if
radiographic films begin to show evidence of stain after being stored for only a short time.
the most common cause of stain, and hence of poor archival quality, is
retained fixer within the emulsion
Fixer may be retained as a result of
poor washing or because there was insufficient hardener (underreplenishment) in the developer, thus permitting fixer to be retained by the swollen emulsion
A test for quantity of retained fixer in film emulsion is often included as part of
a quality control program
Stain may also be caused by
poor storage conditions
Storage in a hot, humid place will cause
even the smallest amount of retained fixer to react with silver, causing stain
A film emulsion having wide latitude is likely to exhibit
low contrast
Every film emulsion has a characteristic curve representative of
that film's speed, contrast, and latitude
A gentle curve (as opposed to a steep curve) usually indicates
a film with slow speed, low contrast, and more latitude
What information, located on each box of film, is important to note and has a direct relationship to image quality?
Expiration date
Every box of film comes with
the expiration date noted
Film used after its expiration date will usually suffer
a loss of speed and contrast and will exhibit fog
Film should be ordered
in quantities that will ensure that it is used before it becomes outdated, and it should be rotated in storage so that the oldest is used first.
The purpose of the automatic processor's circulation system is to
agitate, mix, and filter solutions
The automatic film processor has
a number of component systems
The circulation system functions to
agitate, mix, and filter solutions.
The transport system
moves film from solution to solution between rollers, changing the direction of the film around critical turns
The temperature control system functions to
monitor and control solution temperature.
The replenishment system serves to
monitor the solution and replace it as needed.
The term latitude describes
1. an emulsion's ability to record a range of densities.
2. the degree of error tolerated with given exposure factors.
The term latitude may refer to either
film emulsion latitude or exposure latitude
Exposure latitude refers to
the margin of error inherent in a particular group of exposure factors
Selection of high-kVp and low-mAs factors will allow
greater exposure latitude than low-kVp and high-mAs factors
Film emulsion latitude is
chemically built into the film emulsion and refers to the emulsion's ability to record a long range of densities from black to white (long-scale contrast)
Base-plus fog is a result of
1. blue-tinted film base.
2. chemical development.
3. the manufacturing process.
Every film emulsion has a particular
base-plus fog, which should not exceed 0.2.
base density is a result of
the manufacturing process (environmental radiation) and the blue tint added to the base to reduce glare
The remaining fog density is a result of
the chemical development process, when exposed silver bromide grains are converted to black metallic silver
A characteristic curve is representative of
a film emulsion's response to light or x-rays.
A slow film emulsion (one with greater latitude and lower contrast) responds
more gradually than does a fast film
In general, the more gentle or gradual the slope of a particular film's characteristic curve,
the slower the film is, the longer the scale of contrast it will produce, the more latitude it possesses, and the more exposure that is required to produce a particular density
Which of the following can be used to determine the sensitivity of a particular film emulsion?
Sensitometric curve
The characteristic (sensitometric) curve is used to show
the relationship between the exposure given the film and the resulting film density
It can therefore be used to evaluate
a particular film emulsion's response (speed, sensitivity) by determining how long it takes to record a particular density
A dose-response curve is used in radiation protection and illustrates
the quantity of dose required to produce a particular effect
The reciprocity law states
a particular mAs, regardless of the combination of milliamperage and time, should produce the same degree of blackening
The inverse square law illustrates
the relationship between distance and radiation intensity.
Unopened boxes of radiographic film should be stored away from radiation and
in the vertical position
If film boxes are stacked upon one another
the sensitive emulsion can be affected by pressure from the boxes above
Pressure marks are
produced and result in loss of contrast in that area of the radiographic image
When retrieving x-ray film from storage, the oldest should be used
first
The term spectral matching refers to the fact that film sensitivity must be matched with the
proper color screen fluorescence
Some intensifying screens emit
a blue and others a green fluorescent light; Film emulsions are manufactured to be sensitive to one of these colors, this is called spectral matching
If the film emulsion and intensifying screens are incorrectly matched
speed will be reduced.
The sensitometric curve may be used to
1. identify automatic processing problems.
2. determine film sensitivity.
The sensitometric, or characteristic, curve is used to illustrate
the relationship between the exposure, given the film and the resulting film density
The sensitometric, or characteristic, curve can be used to predict
a particular film emulsion's response (speed, sensitivity) by determining how long it takes to record a particular density
The sensitometric curve is used in sensitometry to monitor
automatic processing efficiency and consistency; A film is given a series of predetermined exposures and processed. The resulting densities are plotted, and the resulting curve is compared with a known correct curve. Any deviation between the two may indicate processing difficulties.
The sensitrometric curve illustrates
the effects of exposure and processing on radiographic film emulsion; it is unrelated to screen speed.
Which apparatus is needed for the construction of a sensitometric curve?
1. Penetrometer
2. Densitometer
to construct a sensitometric curve
First, a penetrometer (aluminum step wedge) is used to expose a film. Once the film is processed, a densitometer is needed to read the resulting densities. Log relative exposure is charted along the x (horizontal) axis; an increase in log relative exposure of 0.3 results from doubling the exposure. Optical density is plotted on the y (vertical) axis and represents the amount of light transmitted through a film compared to the amount of light striking the film (expressed as a logarithm).
The squeegee assembly in an automatic processor
1. functions to remove excess solution from films.
2. is located near the crossover rollers.
An exposed radiographic film contains
an invisible (latent) image
Only through processing can this image be converted to a
permanent, visible (manifest) image
As the film exits the developer section
it passes through the crossover assembly, and before it enters the fixer section, it passes through the squeegee assembly
The squeegee assembly rollers function to
remove excess developer solution from the emulsion before the film enters the fixer. This process helps maintain fixer strength/activity.
The rate of travel through the processor is determined by
the transport mechanism, that is, the speed of the rollers as established at time of manufacture.
Which of the following developing agents has the biggest impact on the shoulder of the characteristic curve?
Hydroquinone
The characteristic curve is shaped by
the combined actions of the developer reducing agents.
The reducing agents are
hydroquinone, which works slowly to build up blacks in the film areas of greater exposure, and phenidone, which quickly produces the gray tones in areas of lesser exposure.
With respect to sensitometry, hydroquinone controls
the shoulder (Dmax) of the characteristic curve, and phenidone controls the toe (Dmin) area.
Factors that contribute to film fog include
1. the age of the film.
2. excessive exposure to safelight.
3. processor chemistry.
Film age is an important consideration when determining
the causes of film fog
Outdated film will exhibit
loss of contrast in the form of fog and loss of speed.
A safelight is "safe" only
for practical periods of time required for the necessary handling of film. Films that are left out on the darkroom counter can be fogged by excessive exposure to the safelight.
Film emulsion is much more sensitive to safelight fog
after exposure
The high temperatures required for automatic processors' rapid processing are a source of
film fog
Daily QA ensures that fog levels do not exceed
the upper limit of 0.2 density.
Chemical fog may be attributed to
1. excessive developer temperature.
2. oxidized developer.
3. excessive replenishment.
If developer temperature is too high
some of the less-exposed or unexposed silver halide crystals may be reduced, thus creating chemical fog
If the developer solution has become oxidized from exposure to air
chemical fog also results.
If developer replenishment is excessive
too much new solution is replacing the deteriorated developer, and chemical fog is again the result.
The conversion of the invisible latent image into a visible manifest image takes place in the
developer
The invisible silver halide image is composed of
exposed silver grains. These are "reduced" to a visible black metallic silver image in the developer solution.
The fixer solution functions to
remove unexposed silver halide crystals from the film.
If the quantity of black metallic silver on a particular radiograph is such that it allows 1% of the illuminator light to pass through the film, that film has a density of
2.0
According to the equation
Density=log10(incident light intensity/transmitted light intensity)
If 10% of the illuminator's light passes through the film, that film has a density of 1. If 1% of the light passes through the film, that film has a density of 2.
When green-sensitive rare earth screens are properly matched with the correct film, what type of safelight should be used in the darkroom?
GBX
The GBX is a
red filter that is safe with green-sensitive film emulsion.
The amber-colored Wratten 6B filter is safe only for
blue-sensitive film
Although using no safelight is possible, it is not
a practical way to function
The clearing agent is found in the
fixer
The function of the fixer (hypo) is to
clear the film of unexposed, undeveloped silver bromide crystals
This process serves to
protect the film from further exposure
The fixing or clearing agent is
ammonium thiosulfate
The developer functions to
convert the latent (invisible) image into the manifest (visible) silver image by reducing the exposed silver bromide crystals to black metallic silver.
Which of the following can cause poor screen-film contact?
1. Damaged image receptor frame
2. Foreign body in image receptor
3. Warped image receptor front
Perfect contact between the intensifying screens and the film is essential to
maintain image sharpness
Any separation between them allows
diffusion of fluorescent light and subsequent blurriness and loss of detail
Screen-film contact can be diminished if
the image receptor frame is damaged and misshapen, if the front is warped, or if there is a foreign body between the screens, elevating them.
Guide shoes are found at
crossover and turnaround assemblies and function to direct the film around corners as it changes direction
If a guide shoe becomes misaligned, it will
scratch the emulsion and leave the characteristic guide shoe marks running in the direction of film travel,
Pi lines appear as
plus-density lines running perpendicular to the direction of film travel; they are sometimes seen in new processors or after a complete maintenance/overhaul.
Hesitation marks are
plus-density lines occurring as a result of pauses, or hesitations, in a faulty roller transport system.
The developer temperature in a 90-second automatic processor is usually about
90° to 95°F
The advantages of automatic processors are
quick, efficient operation and consistent results.
Quick operation is attained with
increased solution temperatures
Excessively high developer temperature can cause
chemical fog.
A wire mesh test is performed to diagnose screen
contact
A wire mesh supported between two rigid pieces of clear plastic is used to evaluate
screen-film contact
A screen lag test is performed by
radiographing a phantom using an empty cassette-image receptor, then loading it with film and leaving for it a few minutes. If, after processing, there is any indication of an image, there is most probably screen lag.
Film emulsion consists of
silver halide crystals suspended in gelatin.
Sodium sulfite is a
film-processing preservative
potassium bromide is
a developer restrainer
Potassium and chrome alum are
emulsion hardeners used in fixer solution.
X-ray film emulsion is most sensitive to safelight fog
after exposure.
X-ray film emulsion becomes more sensitive to safelight fog following exposure to
fluorescent light from intensifying screens
Care must be taken not to leave exposed film on the darkroom workbench for any length of time, as
its sensitivity to safelight fog is now greatly heightened.
Which of the following will result if developer replenishment is inadequate?
Images with excessively low contrast
As films are developed, the developer solution becomes weaker and
oxidation products are produced in the solution
If sufficient replenishment of new developer solution does not take place
the activity of the older solution decreases, and chemical fog is produced. Films lack contrast and have a flat, gray appearance.
The microswitch for controlling the amount of replenishment used in an automatic processor is located at the
entrance roller
The length of the film (the shorter dimension) activates the
microswitch, and replenisher is added according to the length of the film; a 10 x 12-inch film will receive less replenisher than will a 14 x 17-inch film.
Quality control in mammography includes
scrupulous testing of virtually all component parts of the mammographic imaging system
It includes
processor checks, screen maintenance, accurate and consistent viewing conditions, and evaluation of phantom images, to name a few
A mammographic phantom contains
Mylar fibers, simulated masses, and specks of simulated calcifications.
The American College of Radiology accreditation criteria state that
a minimum of 10 objects (4 fibers, 3 specks, and 3 masses) must be visualized on test images
Changes in any part(s) of the imaging system (film, screens, image receptors, x-ray equipment, filtration, or viewbox) can result in
unsuccessful results.
The cause of films coming from the automatic processor still damp can be
insufficient hardening action
If the fixer fails to harden the gelatin emulsion sufficiently,
water will remain within the still-swollen emulsion. The dryer mechanism will be unable to completely rid the emulsion of wash water, and the film will emerge from the processor damp and tacky.
excessive hardening action may produce
brittle radiographs.
Unbalanced processing temperatures can result in
blistering of the emulsion
Developer underreplenishment results in
"light" images and can be the cause of transport problems as a result of insufficient hardener.
Which of the following is (are) tested as part of a QA program?
1. Beam alignment
2. Reproducibility
3. Linearity
Beam alignment must be accurate to
within 2% of the SID
Reproducibility means
that repeated exposures at a given technique must provide consistent intensity.
Linearity means that
a given mAs, using different mA stations with appropriate exposure time adjustments, will provide consistent intensity.
What is the purpose of the thin layer of lead that is often located behind the rear intensifying screen in a image receptor?
To prevent scattered radiation fog
The purpose of the thin layer of lead that is often located behind the rear intensifying screen in a cassette is to
absorb x-rays that penetrate the screens, strike the rear of the cassette, and bounce back toward the film emulsion, resulting in scattered radiation fog. The thin layer of lead absorbs these x-ray photons and thus improves the radiographic image.
The darkroom should be constructed and equipped so as to avoid
1. external light leaks.
2. film bin light leaks.
3. safelight fog.
The darkroom must be constructed in such a way as to be free from
any white-light leaks
Safelight bulbs must be
of the correct wattage, and the filter should be appropriate for the type of film used
An unexposed and processed film will have a density of about
0.1
Film that is unexposed and has been processed will not be
completely clear.
The blue-tinted base contributes
a small measure of density
A small but measurable amount of exposure from background radiation can also be present, and processing itself produces a small amount of
density from chemical fog.
Together, this is expressed as
base-plus fog and should never exceed a density of 0.2.
The rate of chemical replenishment in automatic processing is based on
amount of film processed
The rate of chemical replenishment in automatic processing is based on
the amount (length) of film processed.
Typically, a 14 x 17 film will require
60-70 mL of developer replenisher and 100-110 mL of fixer replenisher.
Processor transport speed is
constant
Solution temperature and agitation are unrelated to
replenishment
Cassette front material can be made of which of the following?
1. Carbon fiber
2. Magnesium
The cassette-image receptor front material must not
attenuate the remnant beam, yet must be sturdy enough to withstand daily use
Bakelite has long been used as the material for tabletops and image receptor fronts, but it has now largely been replaced by
magnesium and carbon fiber
The relationship between the intensity of light striking a film and the intensity of light transmitted through the film is an expression of?
Radiographic density
The greater the quantity of black metallic silver deposited on a film, the greater the
radiographic density.
The greater the degree of radiographic density (degree of blackening), the less the
quantity of illuminator light transmitted through the film
the relationship between the amount of illuminator light striking the film and the amount of light transmitted through the film is an expression of
radiographic density
The function(s) of the fixer in film processing is (are) to
1. remove the unexposed silver bromide crystals.
2. harden the emulsion.
Developing agents change the exposed silver bromide crystals to
black metallic silver, producing a manifest image
The fixer solution
removes the unexposed silver bromide crystals from the emulsion and hardens the gelatin emulsion, thus ensuring permanence of the radiograph
Which of the following is the correct order of radiographic film processing?
Developer, fixer, wash, dry
During automatic processing (see the figure below), radiographic film is first immersed in the
developer solution, which functions to reduce the exposed silver bromide crystals in the film emulsion to black metallic silver (which constitutes the image).
Next, the film goes directly into the
fixer, which functions to remove the unexposed silver bromide crystals from the emulsion.
The film is then transported to the
wash tank, where chemicals are removed from the film
and then into the
dryer section, where it is dried before leaving the processor.
The clearing agent is found in the
fixer
The function of the fixer (hypo) is to
clear the film of unexposed, undeveloped silver bromide crystals
This process serves to
protect the film from further exposure.
The fixing or clearing agent is
ammonium thiosulfate
The developer functions to
convert the latent (invisible) image into the manifest (visible) silver image by reducing the exposed silver bromide crystals to black metallic silver.
The reducing agents are
hydroquinone, which works slowly to build up blacks in the film areas of greater exposure, and phenidone, which quickly produces the gray tones in areas of lesser exposure
When an automatic processor is started up at the beginning of the day, or restarted after an extended standby period, the technologist should process an
unexposed, undeveloped 14 x 17 inches film
After the processor has been turned off overnight, or after it has been on standby for an extended period of time,
artifacts can be produced on the first few films processed
"Delay streaks"
can be produced and are usually caused by a buildup of oxidized developer on the crossover rack as a result of inadequate ventilation.
A "cleanup" film or two
should first be processed to rid the rollers of any accumulated foreign particles, such as lint, oxidized developer, and gelatin.
It is important that the cleanup film be
unprocessed film to avoid contamination of the developer with any retained fixer on the film or redepositing of any foreign particles on the rollers.
Which of the following can affect the amount of developer replenisher delivered per film in an automatic processor?
Film size
The film processor is automated, and replenishment quantities are
preset
A microswitch is activated as
a film enters the processor at the entrance rollers.
Replenisher is added according to
the length of the x-ray film—for as long as the detector senses the presence of film
Once the back end of the film passes the entrance roller sensor, replenishment
stops
When films are fed into the processor the "long way," too much
replenishment occurs, and the image can exhibit excessive density
Hardener is added to the developer solution of automatic processors to
1. keep emulsion swelling to a minimum.
2. decrease the possibility of a processor jam-up.
The distance between transport rollers in an automatic processor is
extremely critical and allows for exact film thickness with minimum emulsion swelling
If the emulsion is allowed to swell excessively
(as a result of excessive temperature or inadequate replenishment), the emulsion will stick to the rollers and cause a processor jam-up.
Glutaraldehyde is
a hardener that is added to the developer to keep the emulsion swelling to a minimum.
Unexposed silver halide crystals are removed in the
fixer solution
The steeper the straight-line portion of a characteristic curve for a particular film, the
higher the film contrast.
The steepness of the characteristic curve is representative of
image contrast
The steeper the curve, the greater the
density differences and the higher the contrast
The speed of the film is determined by the curve's
position on the log relative scale
When comparing two or more characteristic curves, the faster film lies
farthest to the left.
The faster the film speed, the less the
exposure latitude
If the developer temperature in the automatic processor is higher than normal, what will be the effect on the finished radiograph?
1. Loss of contrast
2. Increased density
Higher than normal developing temperatures cause
overdevelopment of the less exposed silver halide crystals, producing chemical fog. The resulting radiograph will appear very gray, exhibiting loss of contrast and increased density
Wet, tacky films are usually the result of
lower-than-normal dryer temperature or fixer underreplenishment.
The device used to give a film a predetermined exposure in order to test its response to processing is called the
sensitometer
The film is then processed, and the densities are read using a
densitometer
A step wedge is used to
evaluate the effect of kVp on contrast
spinning top test is used to check
timer accuracy
A quality assurance program serves to
1. keep patient dose to a minimum.
2. keep radiographic quality consistent.
3. ensure equipment efficiency.
A quality assurance program includes
regular overseeing of all components of the imaging system: equipment calibration, film and cassettes, processor, x-ray equipment, and so on.
With regular maintenance, testing, and repairs, equipment should operate
efficiently and consistently
In turn, radiographic quality will be consistent and repeat exposures will be minimized, thereby reducing
patient exposure