Xray film & film processing

X Ray Film, Characteristics & Film Processing
Rakesh C A

Introduction
• X-ray films are the most important material
used to “decode” the information carried by
the attenuated x-ray beam, when they are
made to pass through the tissue
• They capture the invisible image into visible
form.

X-ray Film
• Main part of a X-ray film is a radiation-sensitive,
photographically active material
made in the form of emulsion quoted on the
supporting material called base.

Types of Films
• Basis of coating:
– Single Emulsion
– Double Emulsion
• Based on use of screens
– Non Screen type
– Screen type
• Single screen
• Double Screen
• Based on sensitivity
– Blue sensitive films
– Green sensitive films
– Panchromatic films

Some History
• Photography began before x-rays were discovered
• Certain silver compounds react to light making image
production possible
• These images could be made permanent by
treatment with certain chemicals
• This phenomenon was applied to x-ray procedures

More History
In 1812, silhouettes were recorded on glass plates
In 1819, the solvent action of sodium thiosulfate on
silver chloride was discovered
In 1839, the phenomenon of development was
discovered by Louis Daguerre
One year later, it was discovered that treating exposed
silver chloride paper with sodium chloride would
make the image permanent

Even More History
• By the time x-rays were discovered, photography was
already an art
• Photographic film with a nitrocellulose base was
already being marketed by George Eastman
• The first x-rays were recorded on glass plates
• These were coated with emulsion on one side only
• The exposure dose was quite high
• Glass plates were used up until WWI

And, Finally
• During WWI, nitrocelluose based film was found to
be a more feasible choice for recording x-rays
• This film was single-emulsion
• It was later discovered that double-emulsion
responded to x-rays faster
• The flaw with nitrocellulose-based film was its easy
flammability
• In 1924, cellulose triacetate replaced the
nitrocellulose based film
• In 1960, the first medical radiographic film using a
polyester base was introduced.

Base
• Supports the fragile photographic emulsion.

Film Base Requirements
• Clear with low light absorption - should not
produce visible pattern on the radiograph
• Strength, thickness and flexibility of the base
must allow for ease of developing
• Must have Dimensional Stability: Maintain size
and shape during processing, handling and
storage.
• Low flammability

Types of Bases
1. Glass Plates – Used in past, thin layer of emulsion on
one side.
2. Cellulose Nitrate – Used in 1914,
– inflammable – Caused fire accidents.
3. Cellulose Tri acetate – Adopted in 1924
– Non inflammable.
4. Polyester – Adopted in 1960.
– Better dimensional stability and colorless.
– Dimethyl terepthalate(DMT) and ethylene glycol are
brought together under low pressure and high
temperature to form molten polymer, stretched into
sheets.
• Eg. Cronex

Tinted blue film
• Triacetate and Polyester are clear and
colorless.
• Adopted in 1933, blue tint was added to the
x-ray film in an effort to produce a film that
was “easier” to look at.
• Causes less eye strain.
• Blue tint can be added to either to the base or
to the emulsion.
• All present x ray films are blue tinted.

Emulsion
• Photosensitive Layer of
the film.
• Key ingredients:
– Gelatin
– Silver Halide
• Thickness not more
than 0.5 mils ( 5-25
μm.)

Gelatin
• Produced from Cattle bones.
• Advantages:
-Keeps ‘Silver Halide grains’
• Well dispersed
• Prevents Clumping of grains
-Developing solutions can penetrate Gelatin rapidly
without damaging the structure and strength.
- Easily available in large and uniform quantity.

Silver Halide
• Light sensitive material in emulsion.
• Composition:
– 90-99% Silver Bromide
– 1-10% Silver Iodide - it increases sensitivity
• Silver Iodo-Bromide crystals are precipitated and
emulsified in Gelatin
• Precipitation reaction involves addition of Silver
Nitrate to Soluble Halide to form soluble silver
halide.
AgNO3 + KBr  AgBr + KnO3

• The Silver Iodo-Bromide crystals in the emulsion is
in the form of crystals suspended in gelatin.
• Crystals are formed by Ions of Ag+, Br-, I- arranged
in Cubic Lattice.

Crystal lattice
• Crystal is formed by Ag+
Br- and I-
• Crystal size will vary
from 1.0 to 1.5 microns
in diameter.
• Each cubic centimeter
of Emulsion contains
6.3 x 109 crystals.
• 1 grain averages 1 - 10
million silver ions

Silver Iodo Bromide Crystals
• An Imperfect Crystal
(perfect crystal has
almost no
photographic
sensitivity).
• Several types of
crystal defects
noted.

Crystal Defects
• A Point defect consists
of a Silver Ion that has
moved out of its normal
position in crystal lattice
(Interstitial Ions).

Crystal Defects
• A dislocation is a line
imperfection in the
crystal.
• Cause a strain in the
wall structure.
• Iodine ion strains the
crystal in this way

Chemical sensitization
• Chemical sensitization of the crystals are
produced by adding allythiourea, a sulfur
containing compound to the emulsion , which
reacts with silver halide to form silver sulfide.

Sensitivity Speck
• This Silver Sulphide
is usually located
on surface of the
crystals and is
referred as
“sensitivity speck”.

Point defect in
cubic lattice.
Sensitivity
speck by Silver
sulfide
The sensitivity speck traps electron and form latent image.

The Latent Image
• Remnant radiation interacts with the silver halide
crystals
• Mainly by the photoelectric interaction
• The energy deposited into the film is in the same
pattern as the subject that was exposed to
radiation
• This invisible image is known as the latent image
• A latent image on photographic (radiographic)
film is an invisible image produced by the
exposure of the film to light (radiation).

The Manifest Image
• By chemically processing the latent image it is
made visible
• Certain chemicals permanently fixate the
image onto the film

Formation of Latent Image
• Metallic silver is black, so it is this metallic
silver that produces black areas on a
developed films.
• Exposure of silver-iodo-bromide grains to light
photons emitted by screen / direct x-ray
exposure initiates the formation of atomic
silver to form a visible pattern.

Gurney Mott hypothesis
This process repeats.

• Negative Bromine
Ions lose electron to
form bromine Atoms
leaves the crystal
and diffuses into
Gelatin.

Latent Image Formation: Gurney-Mott
 Light photon absorbed
by/ejects Br electron
 Electron trapped at
sensitivity speck
 Neg electron attracts
interstitial Ag+ ion
 Ag+ and e- combine to
form neutral (black) Ag
 If >6-10 Ag0
accumulate at speck, it
becomes a latent
image center: ie, it is
developable.

Direct X-Ray Exposure of Film
• Photoelectric & Compton interactions in film
(silver halide in the emulsion)
• Liberated electrons have long ranges
• These electrons strip other electrons from
Bromide ion
– Bromine atoms & free electrons produced
– Electrons captured at sensitivity speck as before

Direct X-Ray Exposure of Film
• Efficiency
– most photon energy lost
• much energy lost in gelatin
• only 3 - 10% of photon energy produces silver
– sensitivity varies with
• kVp (energy)
• processing
• Film as a dosimeter
– 20% accuracy
– badge include filters of various thicknesses
• allows estimate of x-ray spectrum

Adhesive Layer
• Firm attachment
between emulsion layer
and film base is
achieved .
• Guards integrity during
processing and fixing.

Super Coating
• Thin layer of Gelatin
• Protects the emulsion
from mechanical
damage
• Prevents scratches and
pressure marks.
• Makes the film smooth
and slick

Film Processing
• Series of events after the film is exposed to X-rays
• There is another stage in the manual processing known as rinsing
in between development and fixing.

Development
• It is the first stage in
processing of the
radiograph.
• Amplifies latent image
by 100,000,000!
• The primary purpose:
convert the invisible
latent image into
visible form.
• Processing initiated at
latent image speck

Chemistry Of Developer
• Development is a process of chemical reduction.
• The reduction is achieved by the developer donating
electrons to silver ions in the exposed silver bromide and
iodide grains converting them to atoms of metallic silver.
Ag+ + electron  Ag
• The mode of action of developer is not fully understood
but the existence of electric charge barriers around the
halide grains is thought to be involved.

Charge Barriers
• Both exposed and unexposed
silver bromide grains are
surrounded by a negative
charge barrier of bromide
ions created by the excess of
potassium bromide employed
in the synthesis of silver
bromide during the
manufacture of emulsion.
• The charge barrier protects
the silver bromide from
attack by electrons in the
developer solution.
UNEXPOSED GRAIN

Charge Barriers
EXPOSED GRAIN
• Exposed silver bromide grains
possess a weakness in the
charge barrier caused by the
presence of neutral silver
atoms, which have collected
at the sensitivity speck.
• This development center
enables electrons from the
developer to penetrate the
grain and reduce all its silver
ions to metallic silver.

Development
• Silver atoms at
latent image center
act as catalyst
• Grain either
develops entirely or
not at all

Constituents Of The Developer
• Replenisher solution:
– This consists of:
1. Solvent
2. Developing agents
3. Accelerator
4. Buffers
5. Restrainer
6. Preservative
7. Hardener
8. Sequestering agents

1. Solvent
Water is the solvent commonly used in replenisher
solution.
– This also controls developer activity by diluting its effects.
– It has a softening effect on the gelatin, thus allowing the
developing chemicals to penetrate the emulsion and act on the
silver halides.
– The presence of calcium salts in the water (hard water) may
form a chalky deposit or scum on the surface of the film.
– More serious would be contamination of the solvent with
dissolved metals like copper and iron. The presence of only a
fewer parts per million of copper could cause chemical fogging.
– In practice, such effects are extremely rare.

2. Developing Agents
• These are the reducing agents, which carry out the
primary function of supplying the electrons that
convert the exposed silver halide grains to silver.
• Characteristics:
1. Selectivity
2. High activity: Selectivity and activity tend to be
antagonistic properties.
An agent with high activity generally has low selectivity and vice versa.
3. Should be resistant to bromide ions in the solution.

• No single agent satisfies all these requirements
Modern X-ray developers use a combination of 2
developing agents phenidone and hydroquinone
known as PQ developer.
• Phenidone is a quick acting reducing agent capable of
developing all exposed silver halide grains. However,
its selectivity is low and if used alone would result in
high fog levels.
• Hydroquinone requires a strong alkaline medium for
its action. This is more selective than phenidone but
slower in onset of action. Once its action has begun
the development proceeds vigorously although lightly
exposed grains are not affected by hydroquinone.
– Hydroquinone and Phenidone – High Contrast
– Metol – High Speed/Low Contrast/Fine grain

Reaction
• Involves donation of Electron by developing agent to
form metallic Silver by Silver Ion (with inactivation of
developing agent and liberation of hydrogen ions )
Alkaline
Medium

• Advantages of PQ developers
1. Tolerant of increase in bromine ion concentration.
2. High selectivity and low chemical fog.
3. Adequate activity even in low concentrations.
4. Available in liquid concentrate form.
5. Fast acting
6. Adequate contrast
7. Super additive effect

3. Accelerators: PQ developers need alkaline
medium for their action (10 - 11.5 pH). Includes
Sodium Hydroxide, Sodium Carbonate and
Borates.
– This alkali is known as accelerator since its
effect is to accelerate the developing process.
4. Buffers: It has the effect of maintaining the pH
of a solution within close limits.
– Normally adequate buffering action is provided
by the carbonates used as accelerators and
sulphides used as preservatives. Thus no
additional buffers are necessary.

5. Anti-Foggants/Restrainers
• Decrease the formation of Fog (fog is the development
of the unexposed silver halide grains that do not
contain a latent image ).
• It also decrease the development of the latent image.
• Anti-foggants permit rapid development of exposed
grains at higher temp with minimized fog
development.
• The development process itself produces as a
byproduct potassium bromide which is a very effective
restrainer.
• So the developer replenisher need not include
potassium bromide among its constituents. However it
is usual to provide a powerful restrainer / antifoggant
such as benzotriazole.

6. Preservatives
• Sodium sulphite
• Oxidized products of developing agents form colored material that can stain the emulsion,
sodium sulphite forms colorless soluble products after combining with colored oxidized
products of developing agents (sulfonates).
• It acts as a preservative by preventing oxidation of hydroquinone by removing dissolved
oxygen in the solution and at the interface.
oxidation
Coloured product
(stain the emulsion)
Sodium Sulphite

7. Hardeners:
Powerful organic hardeners such as gluteraldehyde
which prevent the excessive swelling of gelatin in the
emulsion when it absorbs water during
development.
– If the emulsion is over hardened the speed with
which the developing agents penetrate the silver
halide grains is reduced.

8.Sequestering agents: Prevent precipitation
of insoluble mineral salts, which tend to
occur in hard water areas. Compounds
based on EDTA are used for this purpose.
9.Others: Bactericides and fungicides.

Rinsing
• Rinsed for about 30sec in running water.
• Will remove the developer diffused into
gelatin.
• Reduces the speed of development.

Replenishment
• During development Bromide Ions are released by the
reduction of silver ions to atoms and they pass into solution to
increase Br concentration, which limits the life of the
developing solution.
• The purpose is to maintain:
– developing agent conc.
– preservative conc.
– Bromide conc. and
– pH at constant level
(during the process of development the developing agents,
preservatives are consumed and H+, Br+ are increased )

Development reaction (high volume)
2AgBr + H2Q + Na2SO3

2Ag + HBr + HQSO3Na + NaBr
• Bromide and acid are formed (pH is lowered)
• Developer is consumed
• Replenisher formulas have a higher pH ,contains no
bromide.
• Rate of replenishment — 60ml of the developer is
replaced with replenisher for each 14 x 17 inch film.

Oxidation Reaction (low volume)
H2Q + Na2SO3 + O2

HQSO3Na + NaOH + Na2SO4
• pH is raised
• No bromide is produced.
• Replenisher formulas have a lower pH ,contains
bromide and high sulfite conc. to retard oxidation.
• Rate of replenishment — 90ml of the developer is
replaced with replenisher for each14 x 17 inch film
(rate is higher to increase the developer turn over
rate).

Factors affecting development:
1. Constitution of developing solution
2. Developer temperature
3. Development time
1. Constitution of developing solution:For a
particular level of exposure image density depends
both on the emulsion characteristics and on the
developer activity. The developer activity is
influenced by
1. Choice of developing agents and their relative
proportions.
2. Concentration of developing agents in solution.
3. pH of the developer solution.
4. Concentration of restrainer and antifoggant.

3. Development time
2. Developer Temperature: Developer activity increases
with temperature as many other chemical reactions.
High temperature development: A range of 38-420C is
used which enables 90 seconds or even faster cycle times to
be operated.
Low temperature development: Operated at around
300C and can still produce very rapid results.
Some developers are extremely versatile and can be used
over a range of temperature requiring different processor
cycle times (ex. a 7 minutes cycle at 200C, a 90 seconds
cycle at 300C).
Medium temperature development:
Between 33-370C.

Effects on the image of increased
temperature:
• Slightly raised temperature
causes
– increased image density for
the same exposure (thus
increased film speed).
– Slightly increased chemical
fog.
– Increased image contrast.
• More severe raise in
temperature leads to
– gross increase in density.
– Un-acceptable increase in
chemical fog.
– Reduction in contrast.

Effects on the image of decreased
temperature:
• If the temperature raise
is left uncorrected, the
developer becomes
exhausted resulting in
– low density and
– low contrast.
• A more severe fall in
temperature leads to
– gross overall reduction
of density and
– loss of contrast.

3. Development time
3. Development time:
– Defined as the time between the entry of a specified part of
the film into the developing solution and exit from the
developing solution of the same part of the film.
• Factors determining development time:
(a) Developer activity
(b) Type of emulsion: Developer solution takes
longer time to penetrate a thick emulsion than a
thin one. Non-screen films require longer time.
(c) Agitation of the developer solution: This is not a
problem in automatic processors because of constant
motion of the solution caused by the roller mechanism

FIXING
• It has 4 major functions:
1. To stop further development
• Making it acidic
2. To clear the image
• by removing the remaining silver halide from emulsion
3. To fix the image
• no longer sensitive to light
4. To complete the process of hardening of
the film emulsion

Constituents of the fixing solution:
1. Solvent
2. Fixing agent
3. Acid
4. Hardener
5. Buffer
6. Preservative
7. Anti-sludging agent

2. Fixing Agent
• 2 agents:
– Cyanides
• Poisonous
• Not generally used.
– Thiosulfates - Sodium and Ammonium Salt (more
active) – called Hypo.
AgBr + sod. Thiosulfate

Ag thiosulfate complex + NaBr
(water soluble)

3. Acid:
– Prevents dichoric fog by inhibiting developing agents.
– Provides a suitable environment for the hardening agents in
the fixer.
– Acetic acid is used usually at a pH of 4-4.5.
4. Hardener:
– Reduces drying time and prevents physical damage.
– Aluminium chloride and aluminium sulfate (or Chromium
compounds) are used commonly.
5. Buffer:
– Prevents sulphurization.
– Neutralizes the developer
– Optimizes hardener activity
– Sodium acetate is commonly used in conjunction with acetic
acid

6. Preservative:
– Retards decomposition of thiosulphates
– Sodium sulphate is commonly used
7. Antisludging agent:
– Boric acid is commonly used and this prevents sludging of
insoluble aluminium compounds in the hardener.

Washing
 Film must be washed well with water after developing
and fixing.
 Removes all thiosulfite complexes.
 Tap water is a satisfactory washing medium. In a 90
seconds cycle about 15 seconds is allowed for the
washing stage, while in manual processing a minimum
of 10 minutes is advised.
 Incomplete wash causes retained hypo to react with
silver to form silver sulfide acquiring brown colour.
Hypo + Silver

Silver Sulfide(brown) + Sodium sulfite

DRYING
• All the surface water and most
of that retained in the emulsion
should be removed.
• The drying medium is dry air of
low humidity, which accelerates
the evaporation process and
reduces drying time.
• Heated air can retain more
moisture than cold air and is
therefore a more effective
drying medium. However, the
excessive use of heat may
damage the film emulsion.
• Air temperatures between 40-
650C are commonly used.

Total process of developing in schematic representation

4 Steps of Processing
• Developing – formation of the image
• Fixing – stopping of development,
permanent fixing of image on film
• Washing – removal of residual fixer
• Drying – warm air blowing over film

Systems of the Automatic Processor
1. The Film Feed Section
2. Transport System
3. Temperature Control
System
4. Recirculation System
5. Replenishment System
6. Dryer System
7. Electrical System

1. The Film Feed Section
• As a film is fed to the processor,
so the cycle of events listed
below is initiated:
1. Drive motor energized (to turn
the rollers).
2. Safelight above feed tray
extinguished.
3. Developer and fixer replenisher
pumped into tanks.
4. Drier heater energized.
5. Wash water flow rate boosted.
6. Film signal delay timer activated
(audible signal which will sound
1-3s after the trailing edge of
the film has passed the entry
rollers, to let the operator know
that the next film can be fed to
the processor).

2. The Film Transport Section
• A system of rollers that
moves the film through the
developer, fixer, washing and
drying sections of the
processor.
• Also acts as a squeegee
action to remove excess
chemicals from the film.

Make up of the Transport System
1. Entrance roller or detector roller
2. Vertical or Deep racks (transport racks)
3. Crossover assembly
4. Squeegee assembly

1. Entrance Roller Or Detector Roller
• Entrance rollers grab film
and draw it into developer
• Entrance rollers separate
slightly, film passes
between rollers activating
microswitch controlling
replenishment of chemicals
• When film is completely in
developer tank, bell ring or
light flicks on – safe to turn
on light

2. Vertical or Deep racks (transport racks)
• Moves film into and
through solutions and
dryer
• Uses a turn around
assembly at the
bottom of the tank to
turn film direction
upward.

3. Crossover Assembly
• Moves film from
developer to fixer
tank and from the
fixer to the wash tank
• Forces solutions from
film back into the
tank it is coming
from.

4. Squeegee Assembly
• Moves the film from
the wash tank to the
dryer
• Squeegee action
removes excess water
from the film.

Transport System (Rollers)
Entrance
Deep
Racks
Turnaround
Crossover
Squeegee
Dryer

Water System
• 2 functions:
– Washing the film
– Temperature control

Washing
• Removes the last traces of
processing chemicals and
prevents fading or
discoloration.
• This enables long term
storage capability

3. Temperature Control System
• Maintains
developer, fixer &
dryer temperature
Processing Temperatures
Developer 35° C
Fixer 35 ° C
Wash 32-35 ° C
Dryer 57 ° C

4. Circulation or Recirculation or
Filtration System
• Agitates developer solution
• Removes reaction particles by the use of a filtration
system
• Helps stabilize developer temperature.
– Agitation and circulation
– Agitation keeps solutions in contact with a heater element
in the bottom of the tank and prevents layering of
chemicals
– Maintains developer temperature
– Heating element is controlled by a thermostat

Recirculation System
• Controlled by recirculation pumps that agitate solutions
to keep them mixed to maintain constant temperature
• Circulation of water required to wash residual fixer (12
litres per minute)

5. Replenishment System
• Fixer & developer levels drop as films
processed
• System replaces lost chemicals
• Microswitch of entrance rollers starts
replenishment pump – stops when film exits
entrance rollers

Replenishment System
• Typical replenishment rates: 60-70 mls of developer, and 100-110
ml of fixer for every 14 inches of x-ray film (per 35 x 43cm
crosswise film)

Types of Replenishment
• Volume Replenishment
– A volume of chemicals are replaced for each film
that is processed.
• Flood Replenishment
– Periodically replenishes chemicals regardless of
the number of films processed.

6. Dryer System
• Dries the film before its removal for viewing
• If not dry, difficult to hang on viewing box
• Consists of blower, ventilation ducts, vented
dryer tubes & exhaust system
• Blower draws in air from room and passes it
over heating coils
• Heated air enters ventilation ducts & dryer
tubes & then blows over film
• Moist warm air vented

Processing Rates
• Amount of time it
takes a film to go
through processor –
ranges from 45-210
seconds
• Film manufacturers
determine
temperatures and
replenishment rates
Processing Times
Developer 20-25secs
Fixer 20
Wash 20
Dryer 25-30
Travel Time 10
Total Time 90 sec

Daylight Automatic Processors
• Enable film to be
processed without need
for darkroom
• Special cassettes
• Increase in department
efficiency, no need for
special darkroom staff
• Disadvantages
– Cost
– Mechanical breakdowns

Automatic Film Processing: Benefits
• Compact size
• Faster
• Density and contrast is constant
• Time and temperature controlled
• Produces dry radiograph immediately

Automatic Film Processing: Disadvantages
• Artifacts caused by rollers.
• Expensive and requires maintenance.
• Manual processing required as a back up in
case of break down

Maintenance
To maintain quality, attention needed in 3 areas:
1. Quality control
2. Processor cleanliness
3. Basic operation

LOCATION
• Centrally located
• Serviced by hatches
from the adjacent
imaging room
• Away from damp or hot
areas
• Accessible in terms of
power and water
supply
• Adjoining viewing room

SIZE
• Minimum floor area of 10 sq meter
• Ceiling height of 2.5 - 3 meter
• Size may be reduced depending upon the
department needs

RADIATION PROTECTION
• Walls adjacent to the radiographic room
should be shielded with correct thickness of
the lead all the way to the ceiling
• In the interests of both darkroom staff and
film material alike
• 1.6 mm lead is mostly used

FLOORS
• Non-porous flooring
• Non-slip flooring
• Chemical resistant
• Stain proof
• Durable & easy to
maintain
• Light coloured (low-light
working conditions)
• Asphalt tiles
• Porcelain tiles
• Clay tiles
• Plastic tiles may be used
in the dry dark-rooms

WALLS/CEILING
• Light in colour to reflect as much light as
possible onto the working surface
• Easy to wipe or clean
• Covered with chemical resistant materials
• Special paints, varnish, ceramic or plastic wall

VENTILATION AND HEATING
• Satisfactory working conditions for the staff
• Good film handling and storage conditions
• Efficient automatic processor performance
• Relative humidity is maintained at around 40-60 %
• Room temperature maintained between 18-20 degree
celsius
• A minimum of 10 air changes per hour
• All of these conditions can be achieved by using a good
air-conditioning system
• Alternatively, fairly satisfactory ventilation can be
achieved by using an extractor fan sited higher than
and diagonally opposite a second fan, the latter being
so placed as to obtain fresh and filtered air from
outside.

TYPE OF ENTRANCE
• SINGLE DOOR SYSTEM
• DOUBLE DOOR SYSTEM
• MAZE TYPE ENTRANCE
• LABYRINTH
• ROTATING DOOR SYSTEM

Fire Safety
• Ideally, all darkrooms should be provided with
an alternative exit, which should be indicated
clearly and left unobstructed at all times

DARK ROOM ILLUMINATION
• WHITE LIGHTING
• SAFELIGHTING

WHITE LIGHTING
• For inspection & maintenance of cassettes &
screens
• Cleaning of work surfaces
• Servicing of equipment
• Sited close to the ceiling
• Moderate in intensity
– (60w tungsten, 30w fluorescent )
• Preferably centrally placed
• More than one switch preferable
• Identification of respective switches is important

SAFE LIGHTING
• DIRECT SAFE LIGHTING:
• Light from safe lamp
directly falls onto the
work surface
– Eg. Beehive safelamp
• Minimum distance of
1.2 m from the working
surface
• Best for loading &
unloading areas

INDIRECT SAFE LIGHTING
• Directs the light towards the ceiling which
reflects light back into the room
• Is intended to provide general illumination of
the dark room
• Suspended atleast 2.1 m above floor level

Safe lamp for both direct & indirect illumination

SAFE LIGHT FILTERS
• Sheet of gelatin dyed to
the appropriate colour
and sandwiched between
two sheets of glass for
protection
• Used in conjunction with
a 25 W lamp
• Extremes of heat and
temperature deteriorates
the filter gelatin
• Should be cleaned
periodically

How Does A Safelight Work?
• When white light is passed
through coloured filters,
certain wavelengths (or
colours) are absorbed by
the filters, whilst those
wavelengths, which
correspond to the colour of
the filters will be
transmitted.
• Making the correct
selection of safelight filter
(matching the filter to the
film), means choosing a
filter, which will transmit a
colour to which the film is
relatively unresponsive,
whilst stopping all light to
which the film is most
sensitive.

Spectrum Transmission Graph:
• Manufacturers produce graphs for their safelights
called spectral transmission or filter transmission
graphs.
• Their purpose is to indicate that part of the visible
spectrum, which will be transmitted by the filter, and
so aid the radiographer in matching the appropriate
filter to the type of film in use.
• Panchromatic film presents special problems, since it
will have colour sensitivity extending as far as the red
end of the spectrum.
• It is thus advisable to process such film in complete
darkness.

SPECTRAL TRANSMISSION GRAPH
MONOCHROMATIC FILM ORTHOCHROMATIC FILM

How Safe Is Safe Lighting?
• No safe lighting is completely safe; all films will
become significantly fogged if exposed to safelights
for long enough.
• This is because safelight filters are not perfect
absorbers of the undesirable wavelengths and, in
truth, all films have some sensitivity to all
wavelengths.
• Thus, the intensity of illumination and the film-handling
time must be kept to a minimum if
significant fogging is not to occur.

Effect Of Excessive Safe Light Exposure
Two principal features
occur when film is
exposed to safelights
for too long:
1. An increase in gross fog;
2. An overall loss of
contrast.

DARK ROOM EQUIPMENTS
• Automatic processor
• Manual process unit
• Processing chemicals
• Hangers for suspending film
• Cassette
• Film storage hopper
• Loading bench
• Cupboards

Hangers used for suspending films during processing

FILM HOPPER FOR THE STORAGE OF UNEXPOSED FILMS

Layout of a typical dark room : ample storage & work surfaces

HEALTH AND SAFETY IN THE
PROCESSING AREA
• ELECTRICAL SAFETY
• GENERAL SAFETY
• CHEMICAL SAFETY

ELECTRICAL SAFETTY
• All electrical equipments to be sited well away
from sinks & manual processing units
• Adequate earthing of all electrical appliances
• No trailing cables from appliances
• Pull-cord switching for lights

GENERAL SAFETY MEASURES
• The maximum level of safe lighting consistent
with film sensitivity
• Adequate ventilation
• Second exits for fire safety

CHEMICAL HAZARDS
• Processing chemicals contain many toxic substances
and must always be handled with care.
• Staff should always be aware of the harmful effects
of exposure to the chemistry its fumes through
inhalation, ingestion or skin contact.
• All staff involved with the handling of film chemistry
should be regularly advised to read product labels
and mixing instructions before handling solutions.
• Safety glasses, facemask, rubber gloves and plastic
apron should be available within the processing area
for each procedure.

Control of substances hazardous to
health (COSHH) Regulations 1988
Make it clear that employers have a
responsibility, in so far as is reasonably
practicable, to prevent or adequately control
exposure to fumes and chemicals using
measures other than the personal protective
equipment.

Photographic Characteristics of X-Ray Film

Photographic Density
• Film’s response to incident radiation
• Tissue absorption
Film
Absorption
Variations
Photographic
Density
Variations

Tissue Absorption Dependencies
• Patient
– composition
– thickness
• Beam
– energy spectrum
• kVp
• phase
• filtration
Film
Absorption
Variations
Photographic
Density
Variations

PHOTOGRAHIC OR OPTICAL DENSITY
Measure of film blackness or opacity

• Opacity is doubled by an
increase in density of 0.3
• Useful densities range:
0.3 - 2.0
 50% down to 1% of
light transmitted

Definitions
 Opacity
 ability of film to block light = Io/It
 Transmittance
 ability of film to transmit light=It/Io
 Higher density value
means
 darker film
 less light transmitted

Base + Fog
Unexposed film has optical density > 0
(min = 0.12)
 Base
 The plastic material absorbs small amount of light
 blue dye
 OD ~ 0.07
 Fog
 development of unexposed silver halide grains
 OD ~ 0.05

Why Logarithms?
1. Easily represent large
dynamic ranges
– factors of 10
2. Represent physiologic
response of eye to
differences in light
intensity
3. Densities can be
added
Input Logarithm
100,000
10,000
1,000
100
10
1
5
4
3
2
1
0
Using logarithms the difference
between 10,000 and 100,000 is
the same as the difference
between 10 and 100

Why Logarithms?
1. Easily represent large
dynamic ranges
– factors of 10
2. Represent physiologic
response of eye to
differences in light
intensity
3. Densities can be
added
O.D.=0.3
O.D.=0.5
+ O.D. = 0.8

Plot derived by giving a film a series of exposures, developing the film, and plotting the
resulting density against the known exposure.

Sensitometric Curve
• Other Names:
– Characteristic Curve
– H & D Curve (after
inventors Hurter & Driffield)
• Properties:
– Base + fog
– Dmax
– Speed
– Contrast
– Latitude

Characteristic Curve
 Linear portion in mid
densities
 Flatter portions at
bottom & top
 change in exposure
results in little density
change
 Shoulder
 flat portion of curve near
top
 high exposure & density
 Toe
 flat portion of curve near
bottom
 low exposure & density

Characteristic Curve
• “Straight Line” region
– density approximately
proportional to log
relative exposure

Radiographic Contrast
• Density difference
between image areas
• Depends upon
– Subject contrast
– Film contrast
Density
Difference
Subject
Contrast
Film
Contrast

Subject Contrast Dependency
• Thickness
• Density
• Atomic differences
• Energy spectrum (kvp)
• Contrast material
• Scatter radiation

Film Contrast Dependancy
1. Characteristic curve of the film
2. Film density
3. Screen or direct x-ray exposure
4. Film processing

 Film Gamma
 maximum slope of
characteristic curve
D2 - D1
Gamma = --------------------
log E2 - log E1
 Slope shows change in film
density for given change in
exposure
 Ranges from 2.0 – 3.5

• Average gradient
– slope between points
with densities at ends of
useful range
– usually between 0.25
and 2.0

Average Gradient
>1: exaggerates subject
contrast
typical for x-ray film
=1: no change in subject
contrast
<1: decreases subject
contrast

2. Contrast vs. Density
 Subject contrast depends on density
 Slope of H & D curve changes with density
log relative exposure
Optical
Density
H & D Curve
Slope of H & D

3. Direct (non-screen) X-Ray Exposure
• Requires Much Higher Exposure (30mR Vs 1mR)
• Lower Contrast
• More Scatter Sensitivity (X Ray Film Is More Sensitive To Lower
Kvp X Rays, The Scatter Radiation)
– Rare Earth Screens Less Responsive To Lower Energies Of
Scattered Radiation
• Direct X Ray Exposure Will Produce Lower Average
Gradient.
• Average Gradient Is Maximum When The Film Is
Exposed With Intensifying Screens.

4. Film Processing
• Longer time or higher temperature (up to a
point)
– increases average gradient (increase contrast)
– increases film speed (increases density)
– increases fog (decreases contrast)
• Follow manufacturer’s recommendations to
optimize processing parameters

Speed
Definition of speed
– reciprocal of exposure (in roentgens) required to
produce density of 1.0 above base + fog
1.0
Optical
Density
B + F

Speed & Contrast on the curve
• Contrast controls slope of characteristic curve
Optical
Density
Optical
Density
Lower
Contrast
Higher
Contrast

Speed & Contrast on the curve
• Speed controls left-right location of
characteristic curve
Optical
Density
Optical
Density
X
X
Slower
Speed
Faster
Speed

Latitude
• Definition
– The range of log relative exposure (mAs)
producing density within acceptable range
(usually 0.25 to 2.0)
Optical
Density
log rel. exp.
2.0
.25
Latitude

Latitude
• Inversely related to
contrast
– high contrast = low latitude
– low contrast = high latitude
• Significance
– Variation from optimal technique
less critical
– higher range of subject contrasts
imaged on single film (such as chest)

Double-Emulsion Film: Advantages
• Physical advantage
– Emulsion shrinks when it dries
– Having two emulsions minimizes curling
• Photographic advantage
– Faster system
• Two screens used
• DE film – 2x contrast
• Increase density  Increase speed
• Each emulsion optimally captures light produced by
“its” screen
double emulsion film screens

Double-Emulsion Film
• Why use 2 thin emulsions rather than 1 thicker one?
– Light photons are easily absorbed by the emulsion, however, only the
outer layer of the emulsion is affected by light from intensifying screens.
– Light produced closer to emulsion
• less light spread
X-Ray X-Ray

Crossover Exposure or
Print Through Exposure
• Light from one screen exposes opposite emulsion
Top
Screen
Bottom
Screen
Top
Emulsion
Bottom
Emulsion
Film
X-Ray

Crossover
• caused by incomplete
absorption of light by
adjacent emulsion
• poorer resolution
– light travels further, spreads more
• can account for up to
40% of total exposure
X-Ray

Crossover Reduction
• Increase the light absorption in
the silver halide grains of the
film emulsion –
– use light-absorbing dye on
film base
• can reduce crossover exposure
~ 13%
• also reduces system speed by
up to 40%
X-Ray

Crossover Reduction by Increasing
Light Absorption
• Match screen light emission to
silver halide natural sensitivity
1. Yttrium tantalate phosphor
intensifying screens
2. Adding a dye, matched to light
emission of the screen, to the
emulsion
– reduces crossover without decreasing
speed
• use flat film grains
– present larger surface to incoming light
– Large surface-area-to-volume ratio
absorb more light photons
• Kodak “T-Mat” film
• cuts crossover ~ X2

Transparency vs Print
Why are radiographs viewed as transparencies
rather than prints?
– The density of a print is related to the amount of
light reflected or absorbed by the paper
– maximum print density between 1.3 & 2.0
– maximum usable transparency density up to 3.0
– transparencies offer greater density range

Xray film & film processing

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