1. Intensifying Screens
Kyle Thornton
DMI 50B

2. History Of Intensifying Screens
First developed by Thomas Edison
Calcium tungstate was used as the phosphor
Converted x-rays to ultraviolet-blue light
First screens were flawed in design
Screen design was perfected in the 1920’s

3. What Is An Intensifying Screen?
Part of the radiographic cassette
Screens contain phosphors that emit visible light when struck with x-ray photons
Depending on the phosphor used, the screen will emit light in the blue or green spectrum
Usage of screens result in lowered patient doses

4. Screen Construction Protective coating Phosphor layer Reflective layer
Layer closest to film
about micrometers thick
Phosphor layer
Active layer
emits light
Reflective layer
25 micrometers thick
Intercepts light and redirects it to film
Base
Provides support
Farthest from film

5. Screen Construction

6. Cassette Construction

7. Luminescence The emission of visible light Two types of visible light
Fluorescence
Emitted only during stimulation of phosphors
Phosphorescence
Continues to emit light after stimulation
Afterglow or screen lag
A flaw with early screens

8. Intensifying Screen Characteristics
X-ray absorption
Screen conversion efficiency
Image noise
Spatial resolution
Image blur
Screen speed

9. Intensification Factor
Compares patient dosage with screens to without screens
A reduction in dose is expected
Technical factors must be modified to accommodate changes in screen speed

10. Screen speed Also depends on speed of film used
Assigned speeds - 100, 200, 400, 800, and 1000
Screen speed depends on:
Number of x-rays interacting with phosphor layer
Conversion of x-ray energy to visible light
This is interrelated with phosphor distribution and size

11. Manufacturer’s Design Of Intensifying Screens
Phosphor composition
Rare earth elements are most efficient
Phosphor thickness
The number of x-rays converted to light increases with phosphor thickness
Reflective layer
Increases conversion efficiency but adds to image blur
Dye
Controls spread of light
Improves spatial resolution
Crystal size
Larger phosphors produce more light
Concentration of phosphor crystals
Higher crystal concentration results in higher conversion efficiency

12. Penumbra

13. X-Ray Absorption
The percent absorption of x-rays in the phosphor layer of intensifying screens

14. Conversion Efficiency
The efficiency of converting x-ray to visible light
Increase in conversion efficiency will make a screen brighter and affects image receptor speed

15. Conversion Efficiency

16. Image Noise Deterioration of the image Affected by Quantum mottle
mAs - or number of x-rays used
limited absorption efficiency
randomness of conversion
Quantum mottle
Noisy appearance of an image
More apparent in fluoroscopy
Raising mAs tends to overcome Q.M.

17. Spatial Resolution/Image Blur
Measured in line pairs/mm
Direct exposure film has highest lp/mm
The slower the speed, the more lp/mm

18. Resolution Test Tool

19. Compatibility Film must match the screen
Each screen exposes the emulsion that it is nearest

20. Advantages Of Screen Film
Increased
Adjustment of radiographic contrast
Spatial resolution w/small focal spots
Ability for magnification radiography
Flexibility of kVp selection
X-ray tube life
Decreased
Patient dose
Occupational exposure
Heat production
Exposure time
Tube mA
Focal spot size

21. Elements Used Rare earth Gadolinium - Green Lanthanum - Blue
Yttrium - Blue
Very high conversion efficiency %

22. Screen Variations Asymmetric cassettes Advantages in: Chest Pediatric
Portable radiography

23. Care Of Intensifying Screens
Handle with care
Must be cleaned periodically
Special cleaning fluid must be used
Must be tested for screen-film contact
Wire mesh test

24. Wire-Mesh Test Results