Transcript Generation of X-Rays

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
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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).
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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
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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
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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
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
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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Guide shoe marks result
 Minus-density shoe
marks occur in the fixerto-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
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Guide shoe marks
c.f. Bushberg, et al. The Essential Physics of Medical
Imaging, 2nd ed., p. 182.
Artifacts

c.f. Bushberg, et al. The Essential Physics of Medical
Imaging, 2nd ed., p. 182.
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
Artifacts
c.f. Bushberg, et al. The Essential Physics of Medical
Imaging, 2nd ed., p. 182.

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
Artifacts

c.f. Bushberg, et al. The Essential Physics of Medical
Imaging, 2nd ed., p. 182.
Flame artifact looks like a
gas flame when the film is
oriented with the direction of
travel horizontal.
 when developer is recirculated 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.
Other Considerations
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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
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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
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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
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Used for producing images from digital modalities such as
MRI, CT, Ultrasound and digital radiography.
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No plumbing required, no chemical vats which produce
fumes and less chemical waste.
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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
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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
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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