1. Physical Characteristics of X- Ray Film & Film Processing
George David
Associate Professor
Medical College of Georgia
Department of Radiology

2. X-Ray Film Construction
Film base
Adhesive layer
attaches emulsion to base
Emulsion layer
Supercoating
.007”
.0005”
Supercoating
Adhesive
Layers
Film
Base
Emulsion
Layers

3. Film Base structural support for fragile emulsion low light absorption
no visible pattern
flexible, thick, & strong
processing
handling
viewbox insertion / removal abuse
dimensional stability
in processing
For archival
varying humidity
Film
Base

4. Film Base Materials early films used cellulose nitrate “safety” base
Flammable
“safety” base
cellulose triacetate used until 1960’s
polyester
.007 inches thick
Base color
Clear
Blue dye added
Requested by radiologists
reduces eye strain
Film
Base
.007”

5. Emulsion Most films use two emulsions Gelatin
each emulsion <=.5 mil thick
thicker emulsion = less light penetration
Gelatin
keeps silver halide grains dispersed / prevents clumping
allows penetration of processing solutions without compromising strength or permanence
made from cattle bones
Emulsion
Layers

6. Silver Halide
light sensitive
% silver bromide
1 - 10% silver iodide
increases sensitivity
small crystals (grains) precipitated and emulsified in gelatin
crystal has lattice structure
Ag+ / Br- / I-
silver nitrate added

7. Silver Halide precipitation determines crystal size & concentration
typical size: microns
1 grain averages million silver ions
chemical sensitization of crystal
sulfur-containing compound added to emulsion
silver sulfide formed
usually located on crystal surface
called sensitivity speck
traps electrons to begin formation of latent image centers

8. Light Image on Film
light photon allows escape of electron in bromine ion (Br -)
neutral bromine atoms leave crystal, go into emulsion gelatin
electron travels to, fixed in sensitivity speck
negative sensitivity speck attracts mobile silver (Ag+) ion forming silver atom Ag+ + electron Ag
repeated trapping of electrons results in growth of silver

9. Latent Image Centers one light photon produces one silver atom
silver atoms collect at sensitivity speck
no visible change in grain
visible amounts of silver deposited at latent image centers during processing
one or more latent image centers per grain
3 - 6 centers required for grain to be developable
centers may contain 100’s of silver atoms

10. Direct X-Ray Exposure of Film
photoelectric & Compton interactions in film
liberated electrons have long ranges
each electron reacts with many grains
electron’s strip other electrons from Br-
Bromine atoms & free electrons produced
electrons captured at sensitivity speck as before

11. Direct X-Ray Exposure Efficiency film as a dosimeter
most photon energy lost
much energy lost in gelatin
only % of photon energy produces silver
sensitivity varies with
kVp
processing
film as a dosimeter
20% accuracy
badge include filters of various thicknesses
allows estimate of x-ray spectrum

12. Supercoating Thin supercoating covers emulsion
protects from mechanical damage
makes film smooth & slick for use with processors
Supercoating

13. Processing Amplifies latent image by 100,000,000! forms visible silver
reduces silver ions into neutral black metallic silver atoms which remain on the film after processing Ag+ + electron Ag
processing initiated at latent image speck
grain either develops entirely or not at all

14. Processing Silver atoms at latent image center act as catalyst
Grains with no latent image also develop much more slowly
Developer time is fundamental in development
processing should stop when maximum difference between exposed & unexposed crystals

15. Processing Developing Solution
developing agent
hydroquinone
phenidone or metol
combination yields development rate greater than sum of each
alkali
adjusts pH
preservative (and oxidation preventative)
sodium sulfite
restrainers
antifoggants (reduces development of unexposed grains)

16. Developing Time Controlled by “90 second” processor Speed of transport
Film path in develop rack
System of rollers & chains which direct film through developer tank
“90 second” processor
90 seconds from film in to film out
Time in developer ~ 20 second
Time in fixer & wash tanks controlled by size of fixer & wash racks
Transport speed does not change because at any time films may be in any or all tanks

17. Developing Temperature Replenishment controlled to ~0.5 degrees
degrees for 90 second processor
100+ degrees for 60 second processor
Replenishment
automatic addition of fresh chemistry to replace chemistry depleted in development
even with replenishment, chemistry must be completely replaced periodically

18. Fixing Function composition
removes remaining silver halide / silver ions without damaging metallic silver
hardens gelatin
composition
cyanides (poisonous & not usually used)
thiosulfates
sodium or ammonium salt
hypo
buffers to maintain pH

19. Washing Removes fixer chemicals Fixing leaves milky appearance on film
unwashed film turns brown with age