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Film Processing – Chapter 7Kalpana Kanal, Ph.D., DABR Lecturer, Diagnostic Physics Dept.. Kanal, Ph.D., DABR 2 Film Exposure – Film Emulsion ¬ Film consists of emulsion supported by a th

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Film Processing – Chapter 7

Kalpana Kanal, Ph.D., DABR Lecturer, Diagnostic Physics Dept of Radiology UWMC, HMC, SCCA

a copy of this lecture may be found at:

http://courses.washington.edu/radxphys/PhysicsCourse04-05.html

Kalpana M Kanal, Ph.D., DABR

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Film Exposure – 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 µm in diameter and contain between 106and 107silver atoms (109grains 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 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

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of the film at that location

emulsion

developer chemistry and temperature

contrast and density and also fog

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The Film Processor

temperature is typically 35°C (95°C) (31-35 range)

replenishment of chemicals take place

film volumes

c.f Bushberg, et al

The Essential Physics

of Medical Imaging,

2 nd ed., p 179.

The Film Processor

fixing solution

and remove unexposed silver halide atoms

light

c.f Bushberg, et al The Essential Physics of Medical

Imaging, 2 nd ed., p 180.

emulsion

fan, and this warm air blows across both surfaces of the film

seconds, fixer time, 21 seconds, washing & drying is 44 seconds)

The Film Processor

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Huda Ch4: Film Processor Question

¬ 1 The sensitive layer in an x-ray film contain an emulsion of gelatin and crystals of:

¬ (A) CaWO4

¬ (B) Silver bromide

¬ (D) Silver nitrate

¬ (E) CsI

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¬ 3 Increasing which temperature is most likely to result in

a high fog level?

¬ (B) Developer

¬ (C) Fixer

¬ (D) Dryer

¬ (E) Radiographic room

¬ 4 In film processing, the fixer is used to:

¬ (A) Modify the developer pH

¬ (B) Remove unexposed silver halide

¬ (C) Fix the silver to the emulsion

¬ (D) Remove the bromine

¬ (E) Reduce unexposed silver halide

Raphex 2002 Diagnostic Question

¬ D21 Failure to use adequate fixer for radiographic film processing will:

¬ A Decrease the film contrast gradient.

¬ B Decrease film speed.

¬ C Increase quantum mottle.

¬ D Increase silver reclamation.

¬ E Decrease archival storage.

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Processor Artifacts

developer too high

low OD part of the curve where silver halide crystals not exposed to light become developed

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Processor Artifacts

developer too low or

developer too low

high exposure end

and lack contrast

c.f Bushberg, et al The Essential Physics of Medical Imaging, 2 nd ed., p 181.

Other Artifacts

explanation of artifacts

Other Artifacts

incorrect or

mechanism that the film passes through after the wash tank is defective or

malfunctioning

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Other Artifacts

plus-density line perpendicular

to the direction of film travel that occurs near the trailing edge of the film

abrupt release of the back edge of the film as it passes through the developer-to-fixer crossover assembly

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Other Artifacts

clear areas of the film where emulsion has flecked off from the film base

rollers, non-uniform film transport, or a mismatch between the film emulsion and chemicals

Other Artifacts

apply too much or inconsistent pressure to the film in the developer or

crossover racks

Other Artifacts

against the guide shoes during transport

a series of evenly spaced lines parallel to the direction of film transport

caused by the guide shoes in the developer tank

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Other Artifacts

marks occur in the fixer-to-washer crossover

damage is present, the problem can be anywhere along the transport path

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Other Artifacts

fluid drips and occur at the trailing edge of a film

film surface not removed, as the film descends into the fixer the excess developer

“runs back” at the trailing edge of film

developer-to-fixer crossover assembly becomes oxidized and can cause this artifact

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

Other Artifacts

of lines perpendicular to the film transport direction that is caused

by binding of the roller assembly in the developer tank or

crossover assembly

show up black on the film

Other Considerations

process the film

achieved

temperature of the developer or both

38°C (100°F) for a 45-second process

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Other Considerations

the act of slowing down the film transport, typically increasing the transport time to 120 seconds

and reduces dose to the patient

unloading/loading film systems connected to a film processor

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Laser Cameras or Laser Imagers

Dry Processing

Ultrasound and digital radiography

less chemical waste

produce density on the film (adherographic)

adhesive layer, sandwiched between 2 polyester sheets

layer to the polyester film base

producing a positive and negative image

the readable film and the negative image is discarded

out of the system

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¬ D17 For a 90 second processor, a common developer temperature is 95°F For similar speed and contrast, a

45 second processor should be operated at:

¬ C 95°F with double the replenishment rate.

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¬ D18 Which will not produce film artifacts of increased optical density?

¬ A Static discharge from human handling of film.

¬ B Static discharge inside a daylight film handling processor.

¬ C Increased pressure from roughened or maladjusted developer rollers.

¬ D A light leak in the film cassette.

¬ E Dust particles on the intensifying screen.

Processor Quality Assurance

scrutinized by the Joint Commission on the Accreditation of Health Organizations (JCAHO) and regulatory bodies

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Quality Assurance Program

usually <0.2

near the mid-gray region of the stepped exposures

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QC Charts

c.f Bushberg, et al

The Essential Physics

of Medical Imaging,

2 nd ed., p 188.

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