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Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 Film Exposure – Film Emulsion Film Processing – Chapter ¬ Kalpana Kanal, Ph.D., DABR Lecturer, Diagnostic Physics Dept of Radiology UWMC, HMC, SCCA 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 ¬ a copy of this lecture may be found at: http://courses.washington.edu/radxphys/PhysicsCourse04http://courses.washington.edu/radxphys/PhysicsCourse04-05.html Silver halide grains are about µm in diameter and contain between 106 and 107 silver atoms (109 grains per cm3) Kalpana M Kanal, Ph.D., DABR Film Exposure – Development Film Exposure – Latent Image ¬ Absorbed light photons liberate electrons in the emulsion, which combine with the positively charged silver ions to form a latent Ag) image of silver (Ag+ + e¬ ¬ ¬ to 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 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR ¬ Development is a chemical process that converts the invisible latent latent image to a permanent image ¬ During the development process, the latent image center catalyzes catalyzes the reaction, which reduces the remaining silver ions in that silver silver halide crystal into a grain of metallic silver ¬ A developed grain results in a speck of silver that appears black black on the film ¬ Darker areas of the film have a higher concentration of grains and lighter areas have fewer grains Kalpana M Kanal, Ph.D., DABR Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 The Film Processor Film Exposure – Development ¬ Each blackened grain contributes very slightly to the optical density 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 by developer chemistry and temperature ¬ Increasing the developer temperature or time increases the film contrast and density and also fog ¬ Developer tank temperature is typically 35° 35°C (95° (95°C) (31(31-35 range) ¬ Automatic replenishment of chemicals take place ¬ Flood mode with low film volumes c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 179 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR The Film Processor The Film Processor ¬ The film is washed to remove all developer before proceeding to the fixing solution ¬ The fixing solution contains acetic acid to inhibit further development development and remove unexposed silver halide atoms ¬ Fixing makes the image stable and prevents any further effects by by light ¬ Inadequate fixation can result in a milky appearance to the film ¬ 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 powerful fan, and this warm air blows across both surfaces of the film ¬ The whole process will typically take 90 seconds (developer time, time, 25 seconds, fixer time, 21 seconds, washing & drying is 44 seconds) c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 180 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 Huda Ch4: Film Processor Question Huda Ch4: Film Processor Question ¬ The sensitive layer in an xx-ray film contain an emulsion of gelatin and crystals of: ¬ Increasing which temperature is most likely to result in a high fog level? ¬ (A) CaWO4 (B) Silver bromide (C) LaOBr (D) Silver nitrate (E) CsI ¬ (A) Anode (B) Developer (C) Fixer (D) Dryer (E) Radiographic room ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Huda Ch4: Film Processor Question ¬ 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 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 ¬ ¬ ¬ ¬ Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 10 11 Kalpana M Kanal, Ph.D., DABR 12 Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 Processor Artifacts ¬ 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 13 Other Artifacts ¬ See slides 1616-23 for explanation of artifacts ¬ Water spots Slap line PickPick-off Wet pressure marks Shoe marks Runback Chatter ¬ ¬ ¬ ¬ ¬ ¬ Kalpana M Kanal, Ph.D., DABR ¬ Curve will appear flat and lack contrast Kalpana M Kanal, Ph.D., DABR 14 Other Artifacts ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 182 Kalpana M Kanal, Ph.D., DABR Underdevelopment ¬ Concentration of developer too low or ¬ If the temperature of developer too low ¬ Reduction in OD at high exposure end c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 181 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 181 Kalpana M Kanal, Ph.D., DABR ¬ Water spots occur if ¬ replenishment rates are incorrect or ¬ the squeegee mechanism that the film passes through after the wash tank is defective or ¬ if the dryer is malfunctioning c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 182 15 Kalpana M Kanal, Ph.D., DABR 16 Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 Other Artifacts ¬ A slap line is a plusplusdensity 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 developerdeveloper-toto-fixer crossover assembly Other Artifacts c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 182 Kalpana M Kanal, Ph.D., DABR ¬ PickPick-off artifacts are small, clear areas of the film where emulsion has flecked off from the film base ¬ Can be caused by rough rollers, nonnon-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 17 Kalpana M Kanal, Ph.D., DABR 18 Other Artifacts Other Artifacts ¬ ¬ Wet pressure marks occur ¬ When the pinch rollers apply too much or inconsistent pressure to the film in the developer or ¬ in the developerdeveloper-toto-fixer crossover racks c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 182 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 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 ¬ PlusPlus-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 19 Kalpana M Kanal, Ph.D., DABR 20 Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 Other Artifacts Other Artifacts ¬ ¬ Shoe marks result ¬ MinusMinus-density shoe marks occur in the fixerfixertoto-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 Kalpana M Kanal, Ph.D., DABR 21 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 182 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Other 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 developerdeveloper-toto-fixer crossover assembly becomes oxidized and can cause this artifact 22 Other Considerations 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 developerdeveloper-toto-fixer crossover assembly ¬ Static discharge will show up black on the film Rapid processing ¬ Standard film process in radiology requires 90 seconds to process the film ¬ In some areas like ER, a 4545-sec processor time can be achieved ¬ Concentration of developer is increased or by increasing the temperature of the developer or both ¬ Typically, the processor temperature is increased to about 38° 38°C (100° (100°F) for a 4545-second process c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 182 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 23 Kalpana M Kanal, Ph.D., DABR 24 Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 Laser Cameras or Laser Imagers 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 Kalpana M Kanal, Ph.D., DABR c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 185 Kalpana M Kanal, Ph.D., DABR 25 ¬ Used for producing images from digital modalities such as MRI, CT, 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 systems Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 26 Dry Processing – Details Dry Processing ¬ Typically used to produce films from CT and MRI Use digital images as the source Light in the laser beam exposes the film 27 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 laserlaser-sensitive adhesive layer, sandwiched between polyester sheets ¬ The imaging layer is a matrix of carbon particles and polymer ¬ Laser energy focused at the laserlaser-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, 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 pops out of the system Kalpana M Kanal, Ph.D., DABR 28 Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 Raphex 2000 Diagnostic Question ¬ D17 D17 For a 90 second processor, a common developer temperature is 95° 95°F For similar speed and contrast, a 45 second processor should be operated at: ¬ A 93° 93°F B 95° 95°F C 95° 95°F with double the replenishment rate D 99° 99°F E 190° 190°F ¬ ¬ ¬ ¬ Raphex 2000 Diagnostic Question ¬ D18 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 ¬ ¬ ¬ ¬ Kalpana M Kanal, Ph.D., DABR 29 Kalpana M Kanal, Ph.D., DABR 30 Processor Quality Assurance ¬ Quality control of film processors is a standard of practice that that is scrutinized by the Joint Commission on the Accreditation of Health Health Organizations (JCAHO) and regulatory bodies ¬ A sensitometer and densitometer are needed c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 216 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 31 Kalpana M Kanal, Ph.D., DABR 32 Film Processing – Chapter Diagnostic Radiology Imaging Physics Course 30 September 2004 Quality Assurance Program ¬ ¬ ¬ QC Charts Base + Fog ¬ OD measured anywhere on the film away from exposed steps, usually