2. Processing Cycle
The complete processing cycle comprises:
Manual Processing
Automatic Processing
•
•
•
•
•
•
•
•
•
Development
Rinse
Fixing
Washing &
Drying
Development
Fixing
Washing &
Drying
The object of the cycle is to produce a dry radiograph carrying a high quality
image which can be stored for a number of years without deterioration.
3. The formation of the latent image
• It is the first stage of photochemical process
• All information eventually seen in
radiograph is recorded as minute changes
in silver bromide crystal.
• These changes are so small that even
electron microscope reveal no difference
between an exposed and an unexposed
crystal.
• Only developer will show which is which.
4. The silver bromide crystals of
photographic emulsion consists
of positive silver and negative
bromide ions arranged in a
geometric pattern known as a
crystal.
Cubic crystal lattice: silver bromide
5. •
Diagram of one plane of a silver
halide crystal. The structure of a
silver halide crystal is simple
cubic, with alternating lattice
points occupied by either a
positively charged silver ion or a
negatively charged halide ion. In
a three-dimensional view, each
negatively charged halide ion has
six nearest neighbors along
orthogonal directions that are
positively charged silver ions.
Similarly, each positively charged silver ion has six nearest neighbors along
orthogonal directions that are negatively charged halide ions. The diagram also
illustrates the Frenkel defect, which consists of a silver ion vacancy and an
interstitial silver ion. Such defects are created by thermal excitation of a silver ion
from its lattice site into an interstitial position, and the equilibrium concentration of
such defects is a function of temperature
6. Diagram of one plane of a
.silver halide crystal
It is well known that exposure
of any substance to a source
containing the correct
wavelengths and energy
produces three effects;
1.Compton effect.
2.Photoelectric effect.
3.Pair production.
In the x-ray to the blue
range used to expose
conventional unsensitised
film the first two effects
occur in the silver halide
crystal (96% of the electrons
produced are from the
photoelectric effect .
7. • An electron-trap is a region
in the crystal of low energy
called a sensitivity speck is
produced during
manufacturing.
9. 1. The process starts with the absorption of a photon of light (hv). The
energy absorbed liberates an electron (e), which is hence called a
photoelectron.
2. The net result of this process is a photoelectron and a neutral
bromine atom or a photohole.
3. Both the photoelectron and photohobe can move through the silver
halide lattice by thermally activated transport processes.
4. The photoelectron is readily trapped at a sensitivity’ center in the
silver halide grain, making this center negatively charged.
5. A positively charged interstitial silver ion is then attracted to the now
negative by charged sensitivity center, where the photoelectron and
the interstitial silver ion combine to form a neutral silver atom.
6. This sensitivity center will now attract another photoelectron, and
the process repeats until this site is populated by at least four silver
atoms; this site forms a developable latent image center.
7. In an optimally exposed film, the number of silver atoms per latent
image center will range from four to about 30, with experiments
suggesting that the most common population is four or five .
11. 1. When silver bromide grain is exposed to light (or x-ray),
some of the bromine ions in the lattice emit electrons.
2. These electrons are able to travel through the crystal, and
their rapid movement carried them into what are known as
electron-traps existing in the crystals.
3. Not all silver ions in the crystal are held in the lattice
(interstitial- ions). Those that are able to travel are attracted
to the negatively charged electrons in sensitivity speck.
4. The negative charged on electrons neutralizes the
positive charge on the silver ions, and when this happens
silver atoms are formed.
5. The sequences repeats its and the sensitivity speck has a
number of atoms of silver ( Latent image).
6.This cycle of events takes place extremely quickly (10 ms)
12. Processing Chemistry Overview
• Developer – converts latent image into
manifest image
• Fixer – clear the film of unexposed,
undeveloped silver bromide crystals,
promotes archival quality
• Wash – rid the film of residual chemicals
13. Film Processing
The latent image is invisible because
only few silver ions have been
changed to metallic silver and deposited
at sensitivity centre.
Processing the film magnifies thus action
many millions of time.
Thus latent image is converted to visible
image.
14. The production of latent
image and the conversion
of the latent image into
manifest image follow
several steps.
A, radiation interaction
releases electrons.
B, these electrons
migrate to sensitivity center.
C, at the sensitivity center,
atomic silver is formed
by attracting an
interstitial silver ion.
D, this process is repeated
many times, resulting in
buildup of silver atoms.
E, the remaining silver halide
is converted to silver during
processing.
F, the resulting silver grain.
15. The nature of development
• Development is the first stage in processing cycle .
This is the production of a visible metallic silver
image from the latent one which exists in sensitive
material after exposure to light or x-radiation.
• Exposed silver halide grains + Development =
Metallic Silver (black color).
• Unexposed silver halide grains + Development =
remain largely unchanged (light color).
24. A developer is chemical solution that
converts the invisible (latent) image on
the a film into a visible one composed of
minute masses of metallic silver.
An alkali chemical solution
25. • Converts exposed silver bromide crystals
(latent image) to black metallic silver
(visible image).
26. Production Permanent image
• This involves the action of a chemical
agent to make the hidden image visible.
This stage is known as development, and
it is followed by further chemical
processes which fix the image and make
it into permanent record.
27. Developer Solution
(8 compounds)
1. Reducing Agent: reduce exposed silver
halide to black metallic silver
-Hydroquinone (Blacks)
-Metol or Elon
-Phenidone (Grays)
29. Activity of Reducing Agent
• High or low reduction potential.
Susceptibility to bromine ions concentration
released into solution.
• High or low selectivity ratio.
30. • The PH scale:
• The PH scale is used to express the degree of acidity
or alkalinity of a solution. Its based on measure of
concentration of positively charged hydrogen ions
in the a solution.
• In water the H2O molecule dissociates into H+ &
-OH-. In water these ions are equal in numbers, at
concentration of 10-7mol/l. addition of substances
result increase of H+ >10 -7. The solution said to b
acidic.When the added substances reduce to<107,the solution said to be alkaline.
31. •The logarithm of H+ concentration provides a
convenient figure on which to base a scale of
acidity and alkalinity.
•For gastric juice, for example: log10 (H +
concentration) =log10 10 -1.7 = -1.7 the pH of
gastric juice is then said to be 1.7.
•For blood plasma, log10 (H + concentration)
=log10 10-7.4 = -7.4 the pH of blood plasma is
then said to be 7.4.
32. pH scale
The pH scale. A
pH greater than 7
is alkali, less than
7 is acid. Note that
even unpolluted
rain water is acidic,
due to the effects
of dissolved
carbon dioxide.
33. The nature of development
• Development is the first stage in
processing cycle . This is the production
of a visible metallic silver image from the
latent one which exists in sensitive
material after exposure to light or xradiation.
34. Developing Agents
• Is a substance able to change silver halide
into metallic silver.
• Chemical reducing agents.
• Neutralize silver ions in silver bromide by
donating electrons to them.
• Has ability to differentiate between exposed
and unexposed grain of silver halide.
• Lack of this ability would make a reducing
agent totally unsuitable for use in a
developing solution.
37. Developer agents
Must exhibit certain characteristics:
1- Must be selective and distinguish effectively
between exposed and unexposed grains.
2- Must very active to allow complete
development in short time e.g 20-30 seconds,
giving a total processing tie of 11/2 –2
minutes (selectivity and activity tend to be
antagonistic properties).
3- Must be as resistant as possible to the
presence of bromide ions in solution.
38. The Action of the Developer
• Conversion of silver halide = metallic silver
• Developer ---- gives electrons to silver ions.
• Electrons + silver ions = silver atoms.
39. • By-products of developer:
• The developer becomes depleted of electrons; it
said to oxidized.
• Reaction with atmospheric oxygen, causing
aerial oxidation of developer.
• Thus the supply of reducing agent in developer
is gradually exhausted.
• pH fall due to formation of hydrotropic acid as
combination of positive hydrogen ions and
bromide ions release by developed silver halide
grain.
• If not corrected, these chemical changes will
cause the developer to become progressively
less effective.
41. Unexposed crystal protected from attack by electrons
because of the presence of a complete negative barrier
around the crystal. Exposed crystal has break in the
barrier, due to presence of neutral silver atoms at
sensitivity speck,constitutes a development center which
enables electrons from developer to penetrate the crystal
and reduce it completely to silver.
42. Underdevelopment results in a dull radiograph
overdevelopment produced too dark
radiograph. Proper development in maximum contrast.
43. Superadditivity effect obtained with a PQ or MQ
developer. The effect obtained from the phenidonehydroquinone mixture is far greater than the simple
arithmetic sum of their separate effect.
44. اذا قل التظهير هذا يعني وجود هلوجينات معرضة لم
تنمي )تظهر( لم تصبح سوداء والعكس.
45. PQ compared with MQ
1.
2.
3.
4.
High contrast than MQ
High speed than MQ
Low auto oxidation than MQ
The activity not dependent on Brconcentration
5. Temperature dependent
6. Liquids concentration
7. Less likely to cause dermatitis
8. Cause less stain (color) than MQ
9. Long shelf life time
46. Phenidone (P) characteristics
High speed
Low selectivity
low contrast
Liquids concentration
5. Only 10-15% compared with Q give
similar activity( more active)
47. Metol (M) characteristics
slow speed
High selectivity
High contrast
Ability to auto oxidation by O2
The activity not dependent on tem- and
PH .
Metol (M) characteristics =
Hydroquinone (Q) characteristics
48. Development time
• The time for reducing all exposed Ag Br
only ,do not cause changes in unexposed
one.
49. Factors determining development time; the
development time required to produce
optimum image quality is determined by :
Developer activity.
Type of film.
Agitation of developer solution.
50.
51. Factors affecting development
The production of optical density and
radiographic contrast can be used as a
measure of the efficacy of development. The
following factors influence the quantity and
quality of development;
1. Constitution of developing solution.
2. Developer temperature.
3. Development time.
53. Most chemical activity is temperature-dependent, and
photographic development is no exception. In general,
developer activity increases with temperature.
temperature control therefore essential to development.
15º C
16º C
18º C
20º C
22º C
24º C
26º C
28º C
7 min
6 min
5 min
4 min
3 min
2 min
1 min
30 sec
54. Replenishment;
Adding of fresh developer to the used developer (exhausted)
to maintain activity and volume .
Without replenishment the activity of a developing solution
inevitably falls and image quality suffers.
Activity of developer can only be maintained if the lost
chemicals are replaced by adding developer replenished at the
correct rate
55. Maintenance of developer volume
Carry over
1.Developer solution which has been
absorbed in the emulsion.
2.Developer solution adhering to the surface
of the film.
Evaporation a small amount of solution
volume will be loss due evaporation.
56. Factors affecting developer replenishment rate
• Area of processed film. (35x43 cm film uses more developer
than 18x24 cm).
• Type of emulsion. (direct exposure film consumes more
developer agent than a screen –type).
• Type of image. (radiograph for the which the has been collimated,
uses less developing agent than a similar radiograph with collimation)
• Aerial oxidation. ( the rate of aerial oxidation
and thus the
need for replenishment are reduced if the area of the surface od
developer solution exposed to the air can be minimized).
57. Developer Solution
2. Activator: (Accelerators)
an alkali,
PH
softens gelatin, maintains alkaline pH
(increase pH)
-Sodium Carbonate
•
sodium carbonate NaCo3& NaoH
•
soften and swells film emulsion
58. Development
• The stage convert invisible latent image into visible image
• Development is a process of chemical reduction oxidized.
•A good developer is highly selectivity act on exposed grains
•A poor developer is low selectivity act on exposed grains
59. Developer Solution
3. Hardener: prevents damage to the film
from over swelling of gelatin in automatic
processors.
-Gluteraldehyde
•
Hardener Glutaraldehyde)
•
prevent swelling;
60. Developer Solution
4. Preservative: Antioxidant that prevents
oxidation of developer
-Sodium Sulfite
• (antioxidant; sodium sulphite)
•
Slow oxidation of the reducing agent by
room air
61. Developer Solution
5. Restrainer: prevents chemical fog in new
developer
-Potassium Bromide
6. Solvent: dissolves & ionizes the developer
chemicals
-Water
62. Developer Solution
5. Restrainer: prevents chemical fog in new
developer
-Potassium Bromide
•
(potassium bromide KBr , potassium
iodide).
•
Reduce the action of the reducing
agents
63. Developer Solution
6. Solvent: dissolves & ionizes the developer
chemicals
-Water
• Solvent (water)
•
Medium in which chemicals are
dissolved
64. •
Developer Solution
• 7 Buffers
• maintaining the pH;carbonates
{accelerators, and sulphite acting as
preservative}.
• 8.Sequestering agents (prevent
precipitation of insoluble mineral salts
EDTA (Ethylene-diamine-tetra-acetic –
acid}).
65. Rinsing : Stop bath or water rinse
Between developing and fixing stages to avoid
carry of the developer to fixer and this cause:
1. Dichotic fog ( Pink greenish color if view
reflective light and yellow brown when viewe by
transmitted light.)
2. Increase fixer alkalinity.
3. Require about 30 sec
66. Rinsing stage
•
Manually by
1. Static water
2. Continually renewed water
More effect water + acid to stop developer
action.
67. • Different between silver halide and metallic
silver
1. Silver halide can be converted into soluble
compound by action of chemicals known as
fixing agent
Metallic silver Ag un affected and remains in
soluble.
2. Metallic silver is opaque to light the black
parts of radiographic image are formed from
metallic silver.
3. Silver halides are sensitive to light, metallic
silver is not
69. Ag Br + Na2 S2 O3
Argento thiosulphate complexes
Ag S2 O3 (NH4 ) or Ag S2 O3 Na2
(white Solvent ( milky appearance
70. Clearing time
• The clearing time” is defined as the time for the
milky appearance of film that receiving fixation,
to just disappear, leaving the expected transparent
image.
• The clearing times and fixing times for the two
common agent used are:
• Ammonium thiosulphate;
Fixing time = 1.3 x clearing time, clearing time = 8-10 sec
(approx.).
• Sodium thiosulphate;
Fixing time = 2 x clearing time, clearing time = 4-5 min.
71. Fixation
• Fixing agent;
It has four majors functions:
1. To stop any further development.
2. To clear the image by removing the remaining
silver halide from the emulsion.
3. To fix the image.
4. To complete the process of hardening the
emulsion.
72. Fixer Solution
2. Hardener (Tanning) Agent: shrinks,
hardens, preserves emulsion
-Aluminum Salt
Aluminum chloride Shrink and hardens
emulsion
73. Fixer Solution
3. Activator: neutralizes developer, maintains
acidic pH (decrease pH)
-Acetic Acid
• Acidifier
Acetic acid provides acid medium in which
fixing agent operates
stop the action of the alkaline developer
solution on contact.
74. Fixer Solution
• 4.Buffer (acetic acid + sodium sulphate
or potasium
sulphate)
Is a solution whose acidity or alkalinity
is practically unchanged by dilution
and which resists a change in pH on
adition of acid or alkali.
75. Fixer Solution
5. Preservative: prevents oxidation, prolongs
solution life
-Sodium Sulfite
6. Sequestering agent; to remove aluminum
ions
- Boric acid
7. Solvent: dissolves other ingredients
-Water
76. Factors control fixation rate
1. Agitation
2. fixer Agent type
3. Temperature
4. Solution concentration.
77. Wash
• Rid the film of residual chemicals
• Residual chemicals on the film will discolor
radiograph over time.
• Cold water processors are less efficient in
removing chemicals – Warm water
processors much better.
• Agitation during wash process is essential
78. Washing
• Water is as washing solution.
• Function of washing is to remove from the emulsion of the
film fixer and silver complex salts.
• Silver complex deteriorates with time to form silver sulphide
which produces an overall yellow/brown fog.
• Residual thiosulphate if not completely removed it
decomposes to produce acid which attacks the silver image
and converts it to silver sulphide. This result in
yellow/brown staining and image fade.
• The level of fixer residual in the film determines the archival
performance.
79. Factors affecting wash rate
1.
2.
3.
4.
5.
6.
7.
•
Steepness of concentration gradient.
Rate of water flow.
Degree of agitation.
Temperature.
Degree of hardening.
Time in wash tank.
pH of wash water.
81. Drying
Is to remove all of the surface water from the film’s
emulsion.
Factors affecting drying time
the time required to dry a radiograph adequately by evaporation
depends on two major factors;
(1) The wetness of the emulsion (volume of water retained in the
emulsion). It depends on hardness of emulsion and emulsion
thickness.
(2) The drying conditions. The medium is air, the speed with which
it can evaporate moisture from the emulsion depends on: air
humidity, air temperature and circulation.
82.
83. Manual Processing
MQ
Whichever way they are produced, processing chemicals must be mixed and
handled according to manufacture’s published instructions. This includes careful
control of cleanliness of receptacles, contamination, temperture, and volume of
chemical and water used .
84. Automatic Processing
PQ
Whichever way they are produced, processing chemicals must be mixed and handled according to
manufacture’s published instructions. This includes careful control of cleanliness of receptacles,
contamination, temperture, and volume of chemical and water used .
85.
86.
87.
88. Manual processing
• Before the introduction of automatic film
processing films were processed manually.
• The film was first immersed in tank
containing developer
• Immersed in a stop bath.
• Fixer solution.
• Water for washing.
• Hung to drip dry.
89. Processing Sequence
• Developing
Developing is the stage during
which latent image is converted to a manifest
image.
• Rinsing stop bath
• Fixing
Is the stage of processing during which unexposed
silver halide dissolved & removed from the
emulsion.
• Washing
Is the stage during which any remaining
chemicals are removed from the film
90.
91.
92.
93.
94.
95.
96. Processing Equipment Materials
Film hanger and film tanks made from material
• Do not cause change by action of processing
solutions
• with low cost
97. Processing tank
Two types of tanks
1) Vertically (deep tank)
2) Horizontally (shallow tank)
Manual processing tanks. The tank labeled A, is developer
B, is the rinse and wash tank and C is fixer tank
98. Water jacket to control processing chemical temperature and keep site clean
99. Film hanger
1. Channel hangers
2. Tension hangers
3. Dental hanger
4. Hanger bar sand clips
A clip hanger (left) versus a channel film hanger
Made from steel resistant to solutions reaction
101. 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
102. 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
103. 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)
104. Developing Time
• Controlled by
– 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
105. •
Developing
Temperature
controlled to ~0.5 degrees
90 - 95 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
106. Fixing
• Function
– 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
107. Washing
• Removes fixer chemicals
• Fixing leaves milky appearance on
film
– unwashed film turns brown with age
108. CONCLUSIONS
• Understanding the basic physics and chemistry’
involved in the photographic process and the various
steps involved in recording and interpreting a
radiographic image is an important prerequisite to
producing consistently’ good diagnostic image
quality.
• Because the technologist is ultimately responsible for
the production quality image that he or she makes, it
is appropriate that student radiographers are provided
with the information needed to achieve such an
understanding.
