Unit 6 (AEC & Film Processing)
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What is a somewhat outdated term for AEC in practice?
Modern equipment uses ____________ rather than __________ when it comes to AEC.
- ionization chambers
- photocells "cells"
Using the AEC eliminates the need for the radiographer to select:
- time (and therefore mAs)
- helps prevent repeats
When using AEC, the technologist selects:
- kVp (to control contrast)
- Detectors activated (to control density)
When it comes to the Ionization Chambers for AEC, _________ is crucial.
The ionization chambers are located:
in front of the IR, but behind the grid
Name some examples of xrays that are taken using the center cell:
- lateral chest
- (most extremeties)
Name some examples of xrays that are taken using the outer cells:
- chest (PA)
- bilateral hip
- weight-bearing knee
Name an example of an xray that is taken using all three cells:
Plastic inserts for collimators are only accurate at:
the intended SID
What two things does the operational amplifier do?
- receives and averages the signal from each chamber
- terminates exposure once intensity is achieved
Name three aspects of the overhead BE film when all three detectors are selected:
- barium located over one of the chambers
- penetration occurring only at other two sensors
- resulting image slightly overexposed
Name three aspects of the overhead BE film when only one detector is activated:
- barium located over the detector
- little penetration occurring
- resulting image greatly overexposed
What allows you to adjust the intensity of the beam and vary the length of exposure time?
Density controls (-2, -1, 0, +1, +2) make changes in relative exposure in what increments?
What should not be used to compensate for changes in part thickness when it comes to AEC?
- density controls (AEC does this automatically)
- but you DO manually change the kVp
As the thickness of the part increases, what is a guide to follow on how much to increase the kVp?
for every 1cm of increased part thickness, increase the kVp by 2
On exposure technique charts, what is specified?
- Ionization chamber configurations
- (rather than time selections)
With the AEC the mA and kVp are set. What does it adjust in order to get an adequate technique?
What does APR stand for?
Anatomically Programmed Radiography
What is the most common cause of an increased repeat rate when using AEC?
poor positioning skills
When do subject density and contrast problems occur, and three examples?
- whenever an unexpected density is present
- whenever an expected density is absent
- fluid in lungs
What will collimation within an activated chamber result in?
an overexposed image
What can inadequate collimation result in?
a light image
Name two timing problems:
- minimum response time
- back-up time
Back-up time will terminate after ____% of the expected time.
Federal law requires automatic termination at:
600mAs when working above 50kVp
Computerized technique charts that use AEC capabilities:
APR (anatomically programmed radiography)
What always provides a repeatable exposure?
- manual technique
- AEC leaves you guessing
Care must be used when an activated sensor is not completely covered by tissue and is:
not advised for use by inexperienced radiographers
What is the purpose of film processing?
to accumulate enough black metallic silver at sensitivity specks to yield a visible image
What are the four film processing steps?
When you develop a latent image, it becomes a ________ _________.
What are the six parts of the developing step of film processing?
- Reducing agents (primary agent)
What provides free electrons to the silver ions in the sensitivity speck?
What charge does the sensitivity speck have before the reducing agents add free electrons to it? and after?
- before: neutral
- after: negative (again)
What takes place as you use reducing agents?
Name the two reducing agents used in film developer and how they work (speed, curve, contrast):
- Phenidone: fast, horizontal curve, low contrast
- Hydroquinone: slow, vertical curve, high contrast
How do the two reducing agents work together?
Phenidone (P developer) and Hydroquinone (Q developer) work synergistically to change the overall contrast.
What color does developer become as it becomes oxidized?
first deep amber, then BROWN, and finally rust red
What is the activator for the film developer?
Why is an activator, like sodium carbonate, added to developer?
- to maintain an alkaline pH
- swells gelatin making it easier to penetrate (helps reducing agents get to the silver halides)
What's an important aspect to remember when working with/around a film developer activator like sodium carbonate?
It makes the developer solution very caustic, so rubber gloves and aprons should be worn and spills neutralized with fixer or diluted with water.
What is the restrainer used in the film developer?
What does the restrainer in film developer, like potassium bromide, do(2)?
- provides a "distraction" to overactive reducers (SLOWS them down)
- prevents the developer from acting on unexposed silver halide crystals
What is the job of the preservative in the developer?
decreases the oxidation process
What is the most common preservative used in film developer?
What can be done to aid the developer's preservative in reducing air exposure (oxidation)?
careful tank design
What is the hardener used in the developer?
What does the developer's hardener, Glutaraldehyde, do (3)?
- controls swelling of gelatin (re-hardens it)
- prevents abrasions during processing
- maintains uniform film thickness
What happens when there's not enough hardener (glutaraldehyde) in the developer (5)?
- gelatin can stick to rollers
- can cause processor jams
- can leave artifacts on film
- can present moist, sticky films even after being dried
- can show pi-lines on film (3.14 distance apart)
What happens when there's too much hardener (glutaraldehyde) in the developer (3)?
- emulsion hardens too soon
- prevents chemical interactions from happening
- traps moisture in gelatin
What size filter should be used for the solvent (water) in the developer?
5-10 micrometer filter
What is the solvent used in film developer?
Why should the developer solvent (water) be treated in tropical areas?
for bacteria and fungi
How much fixer can be present in the developer tank to stop the action of the reducers?
If the action of the reducers in the developer is stopped by fixer being present, what is the result?
gray, low contrast films
When cleaning the processor, what order should things be done in?
- first, fixer tank should be filled
- second, developer tank should be cleaned
What can be done to help avoid contamination of the developer?
splash guards can be used
To avoid contamination of the developer, what step should be taken when shutting down the processor?
The lid should be opened to prevent fixer condensation from dripping into the developer tank.
What is the goal of the fixing step of film processing?
removing undeveloped silver halides from the film
What are the five parts of the fixing step of film processing?
- Clearing agent (primary agent)
What is the clearing agent used in the fixer?
ammonium thiosulfate (the active ingredient)
What is the job of the clearing agent (ammonium thiosulfate) in the fixer?
It bonds with unexposed silver halides, becoming ammonium thiosilversulfate
How will the film appear if not properly cleared by the clearing agent in the fixer?
What is the typical clearing time of the clearing agent in the fixer?
What is the activator in the fixer?
What is the purpose of the activator (acetic acid) in the fixer (3)?
- maintains an acidic pH
- enhances the function of the clearing agents
- neutralizes developer solution (STOPS reducers)
What is the preservative used in the fixer?
What is the purpose of the preservative (sodium sulfite) used in the fixer?
removes the silver from the ammonium thiosilversulfate, allowing the ammonium thiosulfate to continue to remove silver halides
What is the hardener used in the fixer?
aluminum chloride, chromium alum, or potassium alum
What is the purpose of the hardener used in the fixer?
maintains film thickness (same as the hardener in the developer)
What is the solvent used in the fixer?
filtered and treated water
What happens eventually to the fixer solution?
it becomes silver saturated (with silver ions), making the clearing time longer
Depletion due to silver saturation of the fixer solution can be prevented/remedied by:
- Replenishment Systems
- Silver Recovery Systems
What is the purpose of the washing step of film processing?
to remove as much of the chemistry as possible (from the developer and fixer steps)
What should the temperature of the developer, fixer, washing, and dryer solutions be?
- developer: 90ish°F (32ish°C)
- fixer: 90ish°F (32ish°C)
- washing: 5°F (3°C) lower than 1st two
- dryer: 120-150°F (43-65°C)
What will happen if the washing water is too cool?
the emulsion will reticulate, leaving a crackled appearance on the film
If the fixer is not washed from the film, what will the result be?
film will appear yellow/dingy and will brown with age
What does proper washing of the film require?
agitation and enough time
What is the wash tank prone to, and what step should be taken because of it?
- prone to algae and bacteria growth
- tank should be drained when the processor is shut down
What is the purpose of the drying step of film processing?
hardens the emulsion and seals the supercoat by forcing hot air over both sides of the film through slotted tubes (as film goes through through several squeegee crossover rollers to remove excess water)
After the processing, films should be stored at what temperature and humidity?
What is the length of time that film is kept in storage?
- depends on state law and the institution
- usually 5-7 years
- minor and legal cases indefinitely
- mammograms always kept
What three parts make up the transport system of the film processor?
- the transport racks
- crossover networks
- drive system
What makes up the transport racks?
- three series of rollers that provide constant tension to move the film through each tank:
- master roller (the "sun")
- planetary rollers (rotate around the "sun")
- guide shoes (metal guides on the bottom of each side)
What can result from misaligned guide shoes?
they can scratch the film
How do you feed the film into the processor?
always straight along the short axis (the shortest dimension is fed into the processor first)
What powers the drive system of the film processor?
a single motor
What determines the length of time for processing and what is an average processing time (the entire process)?
- determined by the speed of the motor
- 90 seconds
What are the two types of Replenishment?
- Volume replenishment
- Flood replenishment
What must be added to fresh developer chemistry?
starter solution: acetic acid and potassium bromide
Describe "seasoning" the processor:
- an adequate mixing of developer chemistry is necessary
- this requires running the processor for 15-20 minutes prior to processing films
What are the replenishment rates?
- 4-5 ml of developer/inch of film
- 6-8 ml of fixer/inch of film
Name two entities that govern/regulate processor solution safety:
What does the circulation system do?
- stabilizes temperature
- agitates and mixes chemistry
- filters solutions
What is the job of the Temperature Control System?
- it maintains all three solutions at compatible temperatures
- (developer and fixer 90ish°, washing 5° cooler, dryer 120-150°)
What is the most common darkroom safelight and some of its aspects (4)?
- Kodak GBX filter
- dark red
- low intensity: 7-15 watts (long wavelengths)
- 4 feet from work area
- direct illumination usually possible
What safelight for the darkroom is safe for films sensitive to blue/violet light and emits orange-brown light (amber filter)?
Kodak Wratten Series 6B
What safelight for the darkroom has a high initial cost but is long lasting?
LED (Light Emitting Diode)
What can result from too many safelights?
too much light intensity, causing fogging (density too dark)
Name 4 types of darkroom entrances:
- single door
- double interlocking doors
- revolving door
- light-proof maze
What makes up the pass boxes of the darkroom?
exposed and unexposed compartments
What should the humidification ratio of the darkroom be?
Name some Silver Recovery Systems (6):
- Metallic replacement
- chemical precipitation
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