Radiology 6 Flashcards
What is this?
Barrier wrapped film (infection control): The plastic barrier protects the film from saliva and is torn open on completion of the x-ray and disposed of in the clinical waste leaving the clean film packet ready to handle.
Outer plastic wrapping purpose
- Keeps film dry - saliva free.
- Protects film from light damage - fogging.
- Indicates the correct orientation of the film in the mouth - while side towards X-ray tube.
Black paper function
Black paper function
- Protect film from light leakage.
- Stiffens & supports film. This is to prevent crimp/pressure marks on the film.
What’s happened to this?
Light has managed to leak into a film packet, you can see this by noticing the large over-exposed section.
What’s happened to this?
Light has managed to leak into a film packet, fogging just visible over the crowns.
What’s happened here?
Light has managed to leak into a film packet, fogging is visible down the left hand side of the film.
Function of the lead foil
- The shiny layer is lead foil.
- Lead foil is a mixture of lead and aluminium and readily absorbs back scatter.
- Powerful x-rays which have passed through the tooth and film will hit other structures such as the tongue, irradiating areas which are not required. These photons may then bounce back towards the film, ie back scatter, and would degrade the image if left unchecked. The lead foil prevents this by absorbing the scatter.
- The foil has a distinctive pattern embossed into it which will show up on the final image, if you happen to put the film in the patient’s mouth back to front!
What’s happened here?
The film is in the patient’s mouth back to front.
You should be able to make out the 4 rows of rectangles down the left hand side. This is the lead foil pattern.
Direct action film (final layer) function
The film is composed of a plastic polyester base layer, on either side an anti-glare tint, on either side of that you will find emulsion, which is then protected by a layer of gelatine.
B
Supercoat
C
Emulsion
D
Base
A
Adhesive layer
Emulsion
The emulsion is the layer that reacts with the x-rays to form the image. It is comprised of silver halide crystals, usually silver bromide, suspended in gelatin.
Function of the gelatin (2)
- It allows even distribution of the crystals and it also absorbs liquid easily which helps during processing.
- The adhesive layer sticks the emulsion to the base layer and the super coat helps protect the emulsion from physical damage.
Image formation: latent image
When an x-ray photon hits the silver halide crystal within the emulsion, it becomes sensitised and this is known as the latent image.
If you can imagine these black arrows are x-ray photons hitting a silver halide crystal. Some crystals are hit and sensitised by the photons and some are not. The sensitized crystals form the latent image.
So the latent image is the pattern produced within the emulsion by the sensitizing of silver bromide crystals, either by light or x-rays. It is not visible to the naked eye but can be made so during processing. The main reaction being the reduction of the silver bromide crystals to black metallic silver.
What is the speed of film?
The sensitivity of the film to x-rays, in other words how big an exposure is required to produce a certain degree of blackening on an image.
The sensitivity of the film is dependent on…
…the size of the crystals in the emulsion – the larger the crystals the faster the film speed and the lower the amount of x-rays required to produce an image.
However, the larger the crystals, the less detail you have on the film. It has a lower resolution.
Indirect action film is used for ____________
extra-oral radiography
If you were to use an indirect action film cassette, what would it typically be used for?
DPT’s, lateral Cephs and other head and neck radiography.
Indirect film is sensitive to _________ rather than __________
Indirect film is sensitive to light rather than x-rays.
What do the x-rays react with to produce light which then exposes the indirect film?
intensifying screens
What is being used here?
A DPT machine that uses an indirect film cassette to produce the image. However, there is not a lot of equipment left that still uses indirect action film.
Intensifying screen (composition)
Base layer: which can be plastic or polyester.
Reflective layer: which reflects all the light produced back towards the film.
Phosphor layer: which reacts with x-rays to produce the light, the light produced being in direct proportion to the energy in the x-ray photon.
Supercoat: which protects the phosphor layer from damage.
How can the use of intensifying screens be simultaneously advantageous and also disadvantageous?
Advantageous: a significant reduction in the radiation exposure as the screen in front absorbs and converts the low energy photons to light and the screen at the back absorbs the high energy photon and converts them to light, making the system extremely efficient.
Disadvantageous: one x-ray photon will produce several light photons, which in turn expose large areas of the film. This leads to a reduction in the fine detail seen on the film.
What should you NOT do when handling film?
Pressure sensitises the silver halide crystals so you must be careful not to bend it.
Never hold a film by one edge, the weight of it will make it bend, hold it by opposite corners and be careful not to scratch it with your nails.
What happened to this film?
It’s been bent.
How should you store film?
Not in too hot or cold or dry.
In the dark.
Away from radiation.
Stock rotation to prevent using old film.
How would you open this box and where would you then store it?
- Opened by bursting one end of the cardboard and tearing open the sealed packet inside.
- The whole box should then be stored in the hopper or transferred into the cartridge if using a daylight processor. Daylight processors automatically remove the exposed film and pass it through into the chemical tanks.
- A fresh unexposed film is then placed back in the cassette and the cassette is then ejected from the processor ready to be used again.
Film processing
The reduction of the exposed silver bromide crystals to black metallic silver, and then making this image permanent.
Three methods of film processing
- Automatic processor
- Manual processor
- Instant processor
What is this and what are the black holes for?
automatic processor (holes are to stick your hands in where you then open the film packet)
You would place the film between 2 rollers which would then feed the film through the tanks and it would pop out developed from the slot on the top.
What is this and how does it work?
Manual processor: placing the film into the various tanks of chemicals until the image was ready, which meant you had to keep a close eye on the time the film spent in each tank.
What is this and how does it work?
Instant developing
Only tends to be done in disaster situations as it is not very reliable. The chemicals are contained in bubbles in the pouch which you burst and slide down around the film.
5 stages to developing an image
- Develop - make latent image visible
- Wash - stop development and remove the excess developer. This first wash only happens in manual processors.
- Fix - is where you make the image permanent.
- Wash - is where you stop the fix and remove the residual fixer.
- Dry - stops the image feeling sticky and prevents damage.
Components of automatic processor: A
Feed in rollers
Components of automatic processor: B
Developer rack
Components of automatic processor: C
Fixer rack
Components of automatic processor: D
Wash rack
Components of automatic processor: E
Dryer
Automatic processor components
- The film gets fed in at the LHS, through the rollers and down into the developer tank, up and over and down into the fixer tank, up and over into the wash tank, before the drying process hardens the film and it pops out fully developed at the top on the RHS.
- From the side it would look like this. Each tank would be full up to the level of the top rollers, and the journey through each tank takes the exact amount of time required to allow the chemical reactions to take place.
What process results in the latent image becoming visible to the naked eye?
Placing that film in a tank of developer allows the developing agents phendone and hydroquinone to act upon the sensitised silver halide crystals. This causes the chemical reduction of the silver bromide to silver plus bromide. The silver is in the form of black metallic silver, which gives the blackening you can see on the film.
Developer: Developing agents
Phenidone & hydroquinone
Developer: Activator
Calcium carbonate (controls the activity of the developing agents)
Developer: Restrainer
Potassium bromide (stops developer working on unexposed crystals)
Developer: Preservative
Sodium sulphite (slows down oxidation)
Developer: Solvent
Water
What is the action of the developing agents on the silver halide crystals dependent on?
- Time ( too long - dark, too short - light)
- Temperature (too hot - dark, too cold - light)
- Concentration (too strong - dark, too weak - light)
Fixing
The process by which the image is made permanent.
What happens during fixing?
The fixing agents change the unexposed silver halide crystals to a soluble compound so they can be washed away. Acid in the fixer maintains the pH and neutralises the developer.
Fixer: Clearing agent
Ammonium thiosulphate
Fixer: Acidifier
Acetic acid (maintains pH)
Fixer: Hardener
Aluminium chloride
Fixer: Preservative
Sodium sulphite
Fixer: solvent
water
What can happen if an image is over-fixed?
It will be completely removed from the film.
What can happen if a film is under-fixed?
The image will have a green/brown tinge and will not archive well.
What is the difference with washing for a manual compared with an automatic processor?
Manual will be washed between developing and fixing.
Automatic will be washed after fixing.
What is the effect of insufficient washing?
- Film will feel sticky and have a cloudy appearance
Why is it important the film is dry before handling?
Reduces the possibility of damage to emulsion.
Which processor is the best system to use?
Automatic processors
however manual processing if done well can be as good
When is instant processing particularly beneficial?
If you have to process images away from a power source, but the films do not archive well and should only be used in an emergency.
COSHH
Control of substances hazardous to health
Legislation meaning employers had a legal duty to ensure their staff were safe and risk free at work.
Health and safety at Work act 1974
Risk assessment
An exercise where you estimate the risks involved in carrying out a certain job or task, then come up with a system of work that will eliminate the risk, or if the risk cannot be eliminated personal protective equipment must be supplied.
What must all manufacturers of processing chemicals supply?
Material safety data sheets for all potentially hazardous substances. This will let you know how dangerous your developer and fixer are.
Darkroom disease
Referring to the symptoms experienced by darkroom technicians as a result of exposure to hazardous chemicals.
What is the recommended conditions when handling these chemicals?
Adequate ventilation (10 or more room volumes per hour)
PPE
How can we tell if a substance is hazardous?
Look at the packaging for indicative symbols.
