1. Imaging on Film RVT: Chapter 5

2. Learning Objectives: Chapter 5
Identify cassettes, screens, and film, and understand how they work together to create an image
Understand latent image formation
Understand correct storage and care of film and cassettes

3. The Image Receptor
Device that receives the x-rays and produces an image
Receptor components in film-based imaging:
Cassette
Intensifying Screen
Film

4. The X-Ray Cassette
Hard, outer casing for a pair of intensifying screens and one sheet of film.
Must have the following properties:
Sturdy and unbendable
Protects the two other parts from damage
Must support the weight of your patient
Must latch closed securely
Film must not be exposed to light
Washable outer layer
Cleaning solutions, blood, fur, etc.
Radiolucent - permitting the passage of radiant energy, such as x-rays, with little attenuation, the representative areas appearing dark on the exposed film.
Radiopaque - Not allowing the passage of x-rays or other radiation
Different forms today include aluminum, polycarbonate, magnesium, and carbon fiber.

5. The X-Ray Cassette More properties: Radiolucent front
“Front” is placed nearest the patient
Lead lined back (facing away from the patient)
Absorbs scatter radiation

6. Inside The Cassette
Both sides lined with felt or foam pressure pads to ensure close contact of the film to the intensifying screens
Referred to as Film/Screen contact
Some companies also arch the back of the cassette to create even better contact
If inadequate, image
appears fuzzy

7. Poor Film/Screen Contact

8. Film Cassette

9. The Cassette Sizes vary Correspond to screen and film sizes.
Cost varies as well.
*Film is sold in specific sizes to match the cassette size

10. Lead Blocker Found in corner of cassette
Prevents irradiation of the part of the film necessary for identification.
Be careful not to have any important body part obscured

12. Cassette Maintenance Handle with care Cassettes should be kept clean
Common damage includes: dropping, bodily fluids
Cassettes should be kept clean
Use mild soap and water on a regular basis
Cassette storage:
Upright and away from radiation
Do not stack
Should always be loaded and ready to use
Avoid humidity & dust
Tip: Number the cassettes so repeat problems can be easily identified

13. Intensifying Screens Made of three layers:
Fluorescent sheets of plastic that convert x-ray radiation into visible light.
Found in between the cassette and the film
Made of three layers:
Base- plastic polymer that is very sturdy
Adhesive layer- holds emulsion layer onto base
Emulsion layer- contains phosphor crystals
Phosphors are what convert x-radiation to light
This is called ____________________.

14. Intensifying Screen: Emulsion Layer
Phosphors are elements that are efficient at capturing photons.
The intensity and color of this light are determined by the choice of phosphor
Calcium tungstate was original choice
Emit a blue light
______ _________ phosphors have been found to be much more efficient
Emit green light
Ex. Lanthinum oxybromide phosphor
Phosphor also determines the _________ at which the x-rays are converted to light

15. Intensifying Screen: Speed
Screens are rated by their speed
Rare earth phosphors convert much quicker than tungstate
This means less exposure time required!
Thick emulsion layers convert much quicker than thin emulsion layers
Fast screens reduce radiation exposure, but lose quality detail
Many manufactures, different screen ratings
Both types still available today

16. Intensifying Screens Why do we need these screens?
Film is more sensitive to light than to x-rays
Only _______ of exposure results from ionization of x-rays.
Where does the rest come from?
Screens reduce the amount of radiation required to produce a diagnostic radiograph
What factor determines the amount of x-rays produced?
What factor determines how long they are produced for?

17. Intensifying Screens: Safety First!
If we can decrease mAs …
Decreases radiation dose to patient/operator
Reduces the chance of motion on the radiograph

18. Intensifying Screens 2. Enhances contrast
Contrast between different parts of anatomy is required for an x-ray to be diagnostic
Large amount of x-rays produce more secondary and scatter radiation leading to ______ _____________ on the film.

19. Intensifying Screen: Color
Blue-emitting screens
Film must be made to react to blue light
This system is being phased out
Green-emitting screens
Kodak introduced in the 1980’s
Superior system
Must be aware of which screen is being used in order to match the film color!
*Note: green film can see both blue and green light

20. Intensifying Screen: Care
Ensure screen integrity is maintained during unloading of film
Let the film fall away naturally
Screen cleaners
Manufactured cleaners should be used annually
Always rinse with distilled water to remove any residue
Screens should be checked for scratches, bends and wear regularly
Can replace if needed

21. X-ray Film
Strong, yet flexible translucent material, made of a light & x-ray sensitive emulsion, coated in a protective gelatin.
Design:
Screen – Sensitive to wavelengths emitted from intensifying screens
Requires less exposure
Non-screen – Designed for direct exposure
Needs extra-long exposure times

22. X-ray Film: Layers
Film Base – bend w/o stretching; withstand changes in temp and humidity; polyester
Film Emulsion – Contains the photosensitive silver- based products, suspended in a gelatin layer
Produces the image
Super coat – Tough, protective coating of hard gelatin

23. X-ray Film: Emulsion
Gelatin provides support for photosensitive crystals
Provides an even suspension throughout
Contains mainly silver __________ crystals
Also silver iodide and silver chloride
This composition is termed silver halide
Double emulsion: emulsion layer on each side of the base
Quicker to react to light, less radiation required

24. Latent Image Formation
Latent- it’s there, but hasn’t been developed yet
Image formation begins when x-rays and light activate the silver crystals.
X-rays are sent from the __________.
Light is produced by the ___________ ______.
Silver halide particles move toward sensitivity specks to form the lattice network
Happens by electromagnetism

25. X-ray Film: Sensitivity Specks
Imperfections within the silver halide crystals
Requires aging (time in the warehouse)
Ratio of 3 Ag:1 speck required
*Without these, the silver would not “move” to form the lattice network

26. X-ray Film: Lattice Network
The arrangement of silver and sensitivity specks, that when developed will form the anatomical image
Easily disrupted
Pressure before exposure from improper __________.
After exposure from _________________ the cassette.
Leads to artifacts on film
Streaks will radiate from point of impact
Breaks down over time

27. Film responds to light emitted from the screens
X-ray film: Color
Film responds to light emitted from the screens
Blue-receiving film appears physically green
Green-receiving film appears violet
To have a visible identifier
Due to the antihalation dye
*Added to prevent reflection from one intensifying screen onto the opposite emulsion layer

28. X-ray Film: Storage Unopened film boxes should be stored on edge
Film is pressure sensitive
Open boxes must be stored in a light-tight designated film box
Must be protected from radiation
Must be protected from light
Film darkening:
Due to heat and aging
Check expiration dates!