Lecture 5 Flashcards
True or false:
A bad image can be fixed with post processing.
- False - a bad image cannot be fixed with post processing
When must ID be put on an image?
At the time of exposure - not acceptable to apply a label after the time of exposure (legal reasons)
What is the function of a casette?
Support:
- Intensifying screen
- X-ray film
- CR Digitial image plate
In DR no casette is used
What image defect is shown in the image below?
Poor film screen contact is shown in the image below
Breifly explain how intensifying screens work:
- Intensifying screen (IS) absorbs transmitted X-rays
- Luminscent crystals (phosphors) in the intensifying screen fluoresce visible light when irradiated
- Fluorescent light exposed the x-ray film (95% exposure = light, 5% is direct X-rays)
- Brightness of light is proportional to no. of X-rays and hence is an accurate reproduction of the image
How does the exposure required vary between fast and slow screen speed combinations?
Fast screen combinations require a lower exposure than slow screen combinations
What two screen properties normally affect screen speed?
- Large crystal size - greater absorption effeciency and greater screen speed
- Increased layer thickness = larger volume of light= greater absorption effeciency and increased screen speed
What is the name of the problem with the X-ray below? and state the two ways that this could happen and how they would be fixed:
Screen artefact:
- Object between intensifying screen + film - resolution = clean the screens
- Damaged or old phosphors - no longer fluoresce or produce light - resolution is to replace the screens
What does a higher slope on the image below indicate?
- Higher rate or steeper curve = higher contrast
- Lower rate or flatter curve = lower contrast
Breifly explain what the two measures below mean in practical terms:
- Exposure required for an optical density (OD) = 1
- Film latitude
- Lower OD required the faster the film is
- Film latitude is the margin of error - the range of exposures that will generate acceptable densities
Is it possible to have high contrast and a wide latitude?
No. They represent a trade-off so it is not possible.
How do artefacts appear as a result of hot humid moist conditions?
Appear as multiple small black dots
How do artefacts appear as a result of being stored upright and not flat?
- Stored flat = pressure artefacts, grey fog or increased film density in film centre
How do artefacts appear as a result of not being kept in a light tight box or hopper?
Black areas are seen down one side of the film
How do artefacts appear from not checking expiry dates?
Grey general fogging
Given the image below has:
- Low background film density
- Uneven background density
- Low image density
- Poor contrast and Poor detail
- Anatomic structure present
Provide two Ddx
- Underdeveloped or underexposed
What are two Ddx for the image below given that is has:
- High peripheral film density
- High background film density
- High image film density
- Poor contrast and poor detail
- Light fog
- Overexposure with excess peripheral scatter
