Film Processing

1
Film Processing

• Robert Metzger, Ph.D.
• Roland Wong, Sc.M.

2
Film Emulsion

• Film consists of emulsion supported by a thick
  polyester base.
• Film emulsion consists of silver halide (95
  AgBr- and 5 AgI-).
• 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).

3
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.

4
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.

5
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.

6
The Film Processor

• Developer tank temperature is typically 35C
  (95C) (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.
7
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.

8
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 Hd curve.)
• The phenidone acts more on the areas of film
  that have low concentrations of exposed silver
  halides. (The toe of the HD curve.)

9
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.

10
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.

11
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)

12
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.
13
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.
14
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.
15
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.
16
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.
17
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.
18
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.
19
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.
20
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.
21
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.
22
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.
23
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.
24
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.
25
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.
26
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.
27
Artifacts

• Guide shoe marks

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 182.
28
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.
29
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.
30
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.
31
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 38C (100F) for a 45-second process.

32
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.
33
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.
34
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.

35
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

36
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

37
Sensitometry
c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 216.
38
Quality Assurance Program

• Base Fog
• OD measured anywhere on the film away from
  exposed steps, usually lt0.2.
• 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.

39
QC Chart
40
QC Chart