Robert Metzger, Ph.D. Roland Wong, Sc.M. Film Processing Robert Metzger, Ph.D. Roland Wong, Sc.M.

Film Emulsion Film consists of emulsion supported by a thick polyester base. Film emulsion consists of silver halide (95% Ag+Br- and 5% Ag+I-). The silver halide grains can be sensitized by radiation or light to hold a latent image. Silver halide grains are about 1 mm in diameter and contain between 106 and 107 silver atoms (109 grains per cm3).

Film Exposure – Latent Image Absorbed light photons liberate electrons in the emulsion, which combine with the positively charged silver ions to form a latent image of silver (Ag+ + e- → Ag). 3 to 5 silver atoms are needed to produce a latent image center. Few silver atoms along with Ag+ ions exist in the emulsion after exposure. A film that has been exposed but not yet developed is said to possess a latent image.

Development Development is a chemical process that converts the invisible latent image to a permanent image. During the development process, the latent image center catalyzes the reaction, which reduces the remaining silver ions in that silver halide crystal into a grain of metallic silver. A developed grain results in a speck of silver that appears black on the film. Darker areas of the film have a higher concentration of grains and lighter areas have fewer grains.

Development Each blackened grain contributes very slightly to the optical density of the film at that location. The unexposed grains with no latent image are washed out of the emulsion. Film speed, contrast, and base and fog levels are all affected by developer chemistry and temperature. Increasing the developer temperature or time increases the film contrast and density and also fog.

The Film Processor Developer tank temperature is typically 35°C (95°C) (31-35 range) Automatic replenishment of chemicals take place. Flooded replenishment for low film rates. Developer is circulated in a closed loop to equilibrate temperatures. c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 179.

The Film Processor Development The film is pushed into the entrance rollers, which direct the film into the developer tank. The developer solution wets the film The activator (sodium hydroxide) expands the emulsion to allow chemical access to halide crystals deep in the emulsion. Developing agents (hydroquinone / phenidone) reduce the ionic silver to free silver. They act as sources of electrons to initiate the reaction. Restrainers (KBr / KI) limits development to exposed halide crystals. Hardener (glutaraldehyde) controls the emulsion swelling. Time in the developer is typically 25 seconds at 92 degrees F for “Standard” cycle processing.

The Film Processor Development The developing agents (hydroquinone / phenidone) act on different areas of exposed halide concentrations. The hydroquinone acts more on the areas of film that have high concentrations of exposed silver halides. (The linear portion and shoulder portion of the H&d curve.) The phenidone acts more on the areas of film that have low concentrations of exposed silver halides. (The toe of the H&D curve.)

The Film Processor Development Preservative helps prevent the developer solution from oxidation with atmospheric oxygen. The released bromides and halides temper the chemical activity of the developer solution. A dynamic equilibrium is established to maintain a constant chemical activity of the developer solution. The solution is said to be aged. As the various agents in the solution are used, the developer solution is replenished by pumping in new solution. Fresh chemistry is artificially aged by the addition of “Starter” solution. Starter solution is added to replenishment solution for flooded replenishment.

The Film Processor Film is squeegeed of developer solution before it is passed on into the fixer tank. Fixing The fixer is acidic (acetic acid) which stops the development reactions. Fixing stabilizes the image against further sensitivity to light. Fixing removes unexposed silver halide atoms. Inadequate fixing can lead to milky residue in the film emulsion. Fixer is replenished by the same timing cycle. Fixer time: typically 21 seconds.

The Film Processor Film is squeegeed before being put into the wash tank. Washing The water bath simply washes residual chemicals out of the film emulsion Incomplete removal of the fixer causes the film to turn brown Drying A thermostatically regulated coil heats air blown from a powerful fan, and this warm air blows across both surfaces of the film The whole process will typically take 90 seconds (developer time, 25 seconds, fixer time, 21 seconds, washing & drying is 44 seconds)

Processor Artifacts Overdevelopment Concentration of developer too high Primarily affects the low OD part of the curve where silver halide crystals not exposed to light become developed c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 181.

Processor Artifacts Underdevelopment Concentration of developer too low or If the temperature of developer too low Reduction in OD at high exposure end Curve will appear flat and lack contrast c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 181.

Artifacts See slides 16-23 for explanation of artifacts Water spots Slap line Pick-off Wet pressure marks Shoe marks Runback Chatter c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Shadow images: typically caused by dust between the film and the screen. Appearance is that of small, clear areas of the film. Seen only on single emulsion films. Artifact that occurs most often. c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Shadow images: typically caused by dust between the film and the screen. Appearance is that of small, clear areas of the film. Seen only on single emulsion films. Artifact that occurs most often. c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Pick-off artifacts are small, clear areas of the film where emulsion has flecked off from the film base. Can be confused with dust artifact. Can be caused by rough rollers, non-uniform film transport, or a mismatch between the film emulsion and chemicals c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Pick-off artifacts are small, clear areas of the film where emulsion has flecked off from the film base. Often confused with dust artifact. Can be caused by rough rollers, non-uniform film transport, or a mismatch between the film emulsion and chemicals. c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Wet pressure marks occur When the pinch rollers apply too much or inconsistent pressure to the film in the developer or in the developer-to-fixer crossover racks c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Wet pressure marks occur When the pinch rollers apply too much or inconsistent pressure to the film in the developer or in the developer-to-fixer crossover racks c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Chatter is a periodic set of lines perpendicular to the film transport direction that is caused by binding of the roller assembly in the developer tank or in the developer-to-fixer crossover assembly Static discharge will show up black on the film c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Chatter is a periodic set of lines perpendicular to the film transport direction that is caused by binding of the roller assembly in the developer tank or in the developer-to-fixer crossover assembly Static discharge will show up black on the film c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts A slap line is a plus-density line perpendicular to the direction of film travel that occurs near the trailing edge of the film This is caused by the abrupt release of the back edge of the film as it passes through the developer-to-fixer crossover assembly c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts A slap line is a plus-density line perpendicular to the direction of film travel that occurs near the trailing edge of the film This is caused by the abrupt release of the back edge of the film as it passes through the developer-to-fixer crossover assembly c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Guide shoe marks result When the film rubs against the guide shoes during transport The artifact manifests as a series of evenly spaced lines parallel to the direction of film transport Plus-density shoe marks caused by the guide shoes in the developer tank c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Guide shoe marks result Minus-density shoe marks occur in the fixer-to-washer crossover If emulsion surface damage is present, the problem can be anywhere along the transport path c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Guide shoe marks c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Runback artifacts look like fluid drips and occur at the trailing edge of a film when developer from the film surface not removed, as the film descends into the fixer the excess developer “runs back” at the trailing edge of film Developer on the developer-to-fixer crossover assembly becomes oxidized and can cause this artifact c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Runback artifacts when developer from the film surface not removed, as the film descends into the fixer the excess developer “runs back” at the trailing edge of film c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Artifacts Flame artifact looks like a gas flame when the film is oriented with the direction of travel horizontal. when developer is re-circulated through the fixer and wash tanks, it picks up heat and is more chemically active. When the solution is squirted back into the developer tank, onto the film, then the more active solution will develop the film more, differentially. c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 182.

Other Considerations Rapid processing Standard film process in radiology requires 90 seconds to process the film. In some areas like ER, a 45-sec processor time can be achieved. Activity of developer solution increased by increasing concentration of solution or by increasing the solution temperature or both. Typically, the processor temperature is increased to about 38°C (100°F) for a 45-second process.

Other Considerations Extended or push processing is the act of slowing down the film transport, typically increasing the transport time to 120 seconds. Increases the speed of the film and reduces dose to the patient. Was used in mammography . Daylight processors Automatic unloading/loading film systems connected to a film processor c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 183.

Laser Cameras & Imagers Typically used to produce films from CT and MRI. Use digital images as the source. Light in the laser beam exposes the film. c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 185.

Dry Processing Used for producing images from digital modalities such as MRI, CT, Ultrasound and digital radiography. No plumbing required, no chemical vats which produce fumes and less chemical waste. Cost per sheet of film is higher compared to wet processing systems.

Dry Processing One dry system makes use of carbon instead of silver grains to produce density on the film (adherographic) Raw film consists of a imaging layer and a laser-sensitive adhesive layer, sandwiched between 2 polyester sheets The imaging layer is a matrix of carbon particles and polymer Laser energy focused at the laser-sensitive adhesive layer Thermal sensitization by laser causes adhesion of the carbon layer to the polyester film base After laser exposure, the two outer polyester layers are separated, producing a positive and negative image The positive image is coated with a protective layer and becomes the readable film and the negative image is discarded All these steps performed in a laser camera and finished film pops out of the system

Processor Quality Control Quality control of film processors is required for mammography per MQSA and is a standard of practice that is scrutinized by the Joint Commission on the Accreditation of Health Organizations (JCAHO) and regulatory bodies A sensitometer and densitometer are needed

Sensitometry c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 216.

Quality Assurance Program Base + Fog OD measured anywhere on the film away from exposed steps, usually <0.2. Affected by film storage, developer temperature, chemistry. Mid-density (Speed) Step corresponding to an OD of about 1.0 + base + fog. Density Difference (Contrast) Contrast index is the difference in OD between two of the steps near the mid-gray region of the stepped exposures.

QC Chart

QC Chart