Image processing & quality assurance

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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

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