Lecture No.5
Dr. Yousif Mohamed Yousif Abdallah
X-Ray Films
Types of
X-ray Films &
Sensitometry
What
Is X-ray Film?
X-ray film is a photographic receptor consisting of
photographically active or radiation sensitive emulsion
coated on a thin sheet like material, which is responsible
to record the physical impression of an object by which
we can get detail about the object.
3
Types of
X-ray Films &
Sensitometry





History
Early in Photography Certain silver compounds react to light
making image production possible
This phenomenon was applied to x-ray procedures
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.
4
Types of
X-ray Films &
Sensitometry


contd
During WWI, nitrocelluose based film was found to be a more
feasable 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 acetate replaced the nitrocellulose based film

Now a days safety base of polytetrapathalate resin is used
universally.
5
Types of
X-ray Films &
Sensitometry
Classification of the film
MEDICAL X-RAY FILM
double-coated
screen type
General
radiographic film
non-screen type
Dental film
Kidney
surgery film
Radiation
monitoring
film
single-coated
screen type
Mammographic
film
non-screen type
CRT film
Copying film
Laser film
Subtraction film
Drystar Flm
Dryview film
6
Types of
X-ray Films &
Sensitometry





Direct Exposure Film
Used without intensifying screens
Used mainly for extremities, previously for mammography
Requires 10 – 100 times more the exposure dose
The emulsion is thicker than screen film
Renders excellent detail
7
Types of
X-ray Films &
Sensitometry
Indirect Exposure Film

These films are used in conjunction with pairs of I.S. .

The latent image being produced mainly by light emission
from screen phosphors.

A wide range of different films are available both the bluesensitive and green - sensitive .

These types of films are sometimes referred to as contrast
amplifiers because their average gradient is >1
8
Types of
X-ray Films &
Sensitometry
Difference B/W Non Screen & Screen Film
CHARACTERISTICS
DIRECT EXPOSURE FILM
INDIRECT EXPOSURE FILM
Exposed with
Only by x-rays
Mainly by vissible light
Used
Without Screen
With screen
Emulsion layer
Thick
Thin
Image formation
In deep
superficialy
Processing time
more
less
Resolution
more
less
Characteristic curve
No apprent shoulder region
in useful density range
Shoulder region within useful
density range
Screen artifact
no
May possible
Exposure dose
more
less
Used in
Orbit and extremities
radiography. Also in
Industrial Radiography
General radiography
Types of
X-ray Films &
Sensitometry
Difference In B/W Photographic Film
And Radiographic Film
characteristic
Photographic film
Radiographic film
Mode of image capture
By reflected light
By penetrated/ transmitted
light
Emulsion layer
On one side
Either On one side or both
Speed
Slow
Fast
Grain size
Small
Large
Resolving power
1000 lines/mm
6-10 lines/mm
Irradiation by
Light only
Light as well as x-ray
Noncurl back layer
Always present
Absent in double coated
10
Types of
X-ray Films &
Sensitometry
Type Of Direct Exposure Film
A.
Dental Film
B.
Kidney Surgery Film
C.
Radiation Monitoring Film
D.
Industrial Film
11
Types of
X-ray Films &
Sensitometry
Dental Film

Periapical Dental Film:Used for single or group of Teeth

Occlusal Dental Fiim:Imaging mandibles or maxillae

Bitewing Dental film:Demonstrating the crown
12
Types of
X-ray Films &
Sensitometry


Kidney Surgery Film
This duplitized film non screen film is designed to enable to
radiographic exposure of kidney .
Each packet contains two films ,one with a fast emulsion,
the other slow.
10 CM
13 CM
FOR RENAL VESSELS
13
Types of
X-ray Films &
Sensitometry
Laser Film

A laser printer uses digital electronic signal from an imaging
device.

It is high-contrast single-emulsion film with extremely fine
grain, also known as IR film.

Laser film is a silver halide film sensitized red light
(Panchromatic) or laser light, e.g., HN Laser Film, IR Laser
Film.
14
Types of
X-ray Films &
Sensitometry
Films Used With Cathode Ray
Tube Or TV Monitor

These films are used with cathode ray tube camera and
multi-formatter.

The emulsions are orthochromatic of medium to high
contrast and made to match a wide variety of CRT
phosphor.

The film sizes commonly used are 8” x 10”, 11”x14” and
14”x17” .
15
contd...
Used in following modalities:
 Ultrasound
 Computerized tomography
 Magnetic resonance imaging
 Nuclear medicine
 Digital subtraction imaging
16
Types of
X-ray Films &
Sensitometry



Substraction film
A type of single emulsion film used with angiography
One type prepares a positive copy of the image
The other type enhances subject contrast and detail
Duplicating Film
 It is used to duplicate the pre-existing film.
 Duplicating film is a single emulsion film that is exposed
to ultraviolet light or Visible light through existing
radiograph to produce a copy.
17
Types of
X-ray Films &
Sensitometry



Polaroid Film
It is made up of positive and negative film sheets with a pod
of jellified processing chemistry.
Used particularly in ultrasound imaging.
The latent image is formed in the silver halide emulsion of
the negative sheet. And the positive image formed due to
migration of Ag ions from the negative sheet.
18
Types of
X-ray Films &
Sensitometry




The Dry View Film
High quality silver based material coated.
The heat /laser light sensitive layer contains silver halide
/silver behnate crystal.
DRYVIEW Film also a type of laser film having highresolution,
It is infra red sensitive photothermographic film that needs
no wet film processor.
19
Types of
X-ray Films &
Sensitometry








The Drystar Film
Direct thermal printing Drystar dry imaging films are
designed to produce the highest diagnostic grayscale
hardcopies. These images can represent the same "look and
feel" as conventional x-ray film.
Blue base
Maximum optical density > 3.5
Daylight film loading (films are insensitive to light)
Shelf life: to be used min. 18 months from packaging date
Storage temperature: 5 - 25 °C
Relative humidity: 30 - 60%
Extended term storage: minimum 20 years
20
Types of
X-ray Films &
Sensitometry




TYPES OF DRYSTAR FILM
1.
CURIX FILM: the CURIX films are ideal for use in digitizers
where electrostatic charging is a problem.
Variable Range Hopping (VRH) is a unique Agfa-patented
anti-static feature used in the CURIX films
In VRH, a special electrically conducting polymer coating
remains on the film after processing. This polymer,
structured in clusters, is a fiber-like substance that allows
electrons to jump from one cluster to another under the
influence of an external electric field. As a consequence of
its anti-static characteristics, the film repels dirt and dust
and remains clean under the most adverse conditions
This technology simplifies the procedure of scanning the
film and guarantees images free of artifacts.
21
Types of
X-ray Films &
Sensitometry
contd…

2. DRYSTAR TS 2 :This films use Thermo-Sublimation.

A dry imaging technique that can be used in full
daylight.

Designed to provide brilliant, full-spectrum color
imaging with a minimum of effort

Thermo-Sublimation is a dual-component system
that uses heat to transfer colored dyes from a donor
sheet to an acceptor sheet. This state-of-the-art dry
color imaging solution produces higher Dmax and
contrast than any other thermal dye diffusion
printing systems
22
Types of
contd…
X-ray Films &
Sensitometry

CURIX Ultra UV
Technology.
film: uses exclusive UV Light Focus

Use with ultra Uv screen which have high-density Yttrium
Tantalate phosphor that emits Ultraviolet light.

Ultraviolet light reduces screen light diffusion by 90 percent
compared with conventional rare earth phosphors.

The resultant is formation of sharper image
23
Types of
X-ray Films &
Sensitometry
contd…

CURIX Ortho HT film :physical and chemical stability,
allowing film processing to take place at higher
temperatures.

All CURIX Ortho HT films are designed for processing in 45
seconds, enabling greater film volumes to be processed in a
shorter time.

This technology was made possible by the development of
techniques such as the Split Emulsion Layer technique and
an anti-static layer.

Used with CURIX intensifying screens & top coat of these
screen are based on Electron Beam Cured (E.B.C.) process.
24
Types of
X-ray Films &
Sensitometry
Cine film
Used with cardiac catheterization
Produced in 16 and 35mm sizes
Also used for radiography of the esophagus



Photoflourographic Film




This is the film used in cameras to take pictures of a
fluoroscopic screen (barium study).
It comes in rolls & is green or blue light sensitive.
It has emulsion on only one side.
It is used for mass screening as in the army.
25
Types of
X-ray Films &
Sensitometry
Mammographic Film
 3 emulsion layers allow the
contrast curve to be individually
steered for each portion of the
contrast curve
 Emulsion
Layer
1
provides
enhanced skin-line visualization
and controls OD > 3.8
 Emulsion Layer 2 maintains a steep
curve throughout the entire
diagnostic area
 Layer 2a controls OD <2.0
 Layer 2b controls OD >1.5
26
Types of
X-ray Films &
Sensitometry

Spectral Sensitivity
Spectral sensitivity is the
range of wavelength of the
electromagnetic
radiation
that the film will respond.

PEAK SENSITIVITY is the
range of wavelength in
which the film will exhibit
its highest response

CUT-OFF SENSITIVITY is
the range of wavelength
beyond which the film is no
longer sensitive.
Types of
X-ray Films &
Sensitometry

Types Of Film According To
Sensitivity
MONOCHROMATIC - blue sensitive films
Types of
X-ray Films &
Sensitometry

ORTHOCHROMATIC - green sensitive film
Contd…
Types of
X-ray Films &
Sensitometry

Contd…
PANCHROMATIC - sensitive to all colors of the visible
spectrum
Types of
X-ray Films &
Sensitometry
Layers Of Radiographic Film:

Base

Subbing layer

Emulsion layer

Supercoat
31
Types of
X-ray Films &
Sensitometry
Film Construction
Double –sided emulsion film
0.0004”
0.0005”
0.007”
0.008
TOTAL FILM THICKNESS =0.008 INCH
32
Types of
Contd…
X-ray Films &
Sensitometry
Single –sided emulsion film
0.0004”
0.0005”
0.007”
0.008
Anti –Halation /non curl backing
33
Types of
X-ray Films &
Sensitometry
Difference b/w Single Coated And
Double Coated X-ray Film
Characteristic
Single coated
Double coated
Emulsion layer
One side
Both side
Patient Radtation dose
More
Less
Noncurl back layer
Present
Absent
Radiographic detail
More
Less
Average gradient (G)
Very less
more
Parallax effect
No
yes
Contrast
Less
more
Types of
X-ray Films &
Sensitometry





Radiographic Film Base
Initially X-RAY were taken on glass plates.
In 1918 cellulose nitrate bases film replaced glass,but
discarded because of highly inflammable .
In 1920 cellulose tricetate or safety base was introduced.
Polyester base replaced cellulose tricetate in the 1960”s,
Now a days POLYETHYLENE TEREPHTHLATE RESIN are
used.
.007”
Film
Base
35
Types of
X-ray Films &
Sensitometry






Character Of Good Base Material.
structural support for fragile emulsion
low light absorption
flexible, thick, & strong
• processing
• handling
• viewbox insertion / removal abuse
dimensional stability
• in processing
• For archival
varying humidity
NON -FLAMMABLE
36
Types of
X-ray Films &
Sensitometry
Function Of Base

Provide support for emulsion layer.

To transmit light.
37
Types of
X-ray Films &
Sensitometry





Subbing Layer (Adhesive Layer)
Also called adhesive layer or Substratum layer.
Made of mixture of gelatin solution and solvent of film
base.
It keeps emulsion layer and base adhered to each other
during coating stage and processing.
When dye is added, it counteracts cross over effect.
Provides uniform surface over which the emulsion can be
coated uniformly.
38
Types of
X-ray Films &
Sensitometry




Emulsion Layer
Emulsion is the heart of radiographic film .
The X-RAY or Light from I.S. interact with the emulsion and
transfer information to the film.
It consists of a very homogeneous mixture of gelatin and
silver crystal.
In typical emulsion 90 to 99% is AgBr and about 1 to 10% AgI .
NOTE:
• The presence of AgI produce an emulsion of much
sensitivity than a pure AgBr emulsion.
• It also contains traces of sulfur(ALLYLTHIOUREA).
Emulsion
Layers
39
contd…



Silver halide in a emulsion is in the form of small crystals.
Silver halide crystals may be tabular,globular,polyhedral,or
irregular in shape.
Crystal size might vary from 1.0 –1.5 microns in dimeter
with about 6.3 x 1010 grains per centimeter of emulsion.
40
Types of
X-ray Films &
Sensitometry


Grain Technology
Globular Grain:spherical in shape and has a bigger
volume.Use for blue sensitive film.
Tabular Grain:Has a table –top like structure that provides
bigger surface but smaller volume.
41
Types of
X-ray Films &
Sensitometry



Advantages Of Tabular Grain
Increased RESOLUTION due to reduction in cross- over.
Reduction in silver coating weight.
Suitable for 45 s processing.
42
Types of
X-ray Films &
Sensitometry
Grain Size And Distribution
GRAIN SIZE and DISTRIBUTION affects the following:



SPEED: The bigger the average grain size, the higher the
speed of the film.
CONTRAST:
Affected by size distribution. The more
available in the film, the lower the contrast.
GRAININESS: Graininess is the apparent clumping of the
crystal as seen on the radiograph. The bigger the crystal,the
higher the graininess o f the film.
43
Types of
X-ray Films &
Sensitometry


Binder
A binder is an ingredient used to bind together two or more
other materials in mixtures.
There are two types of binders which we can use:
1. Collodion
2. Gelatin
44
Types of
X-ray Films &
Sensitometry





contd
Collodion is a flammable, syrupy solution of pyroxylin in
ether and alcohol.
In 1851, the Englishman Frederick Scott Archer discovered
that collodion could be used as an alternative to egg white
(albumen) on glass plates
This also reduced the exposure time when making the
image
This became known as the 'wet plate collodion' or 'wet
collodion' method.
Collodion was also grainless and colorless, and allowed for
one of the first high quality duplication processes, also
known as negatives.
45
Types of
X-ray Films &
Sensitometry
Gelatin

Gelatin is used as the suspending medium and binding
agent for the silver halide particles.

It comes collagen fiber in which primary source are the
cartilage, skin and the protein matrix (ossein) of bone of
animals.
46
Types of
X-ray Films &
Sensitometry








Why We Use Gelatin As Binder?
It is a medium in which SILVER NITRATE and SODIUM
BROMIDE can react and the resulting AgBr get finely and
evenly dispersed and remain suspended.
In warm state it can be easily spread on the film base.
On cooling, it sets firmly on the base as gel.
It is flexible and does not crack easily on bending.
It is optically transparent .
Gelatin does not react chemically with the silver halide .
It is porous so the processing chemicals can penetrate to
the silver halide crystals.
Some of the constituents in gelatin enhances the activity of
Silver bromide and some act as antifoggant.
47
contd…

It is the great advantage of the gelatin in which it can set
its intermolecular space a/c to the condition of the
environment, While processing, gelatin swells up in contact
with water, allows processing chemicals to enter the layer
and react with the grains of emulsion, & On drying it
regains its former state.

It is believed that gelatin reduces the tendency of reversal
of reaction of Silver bromide after exposure
48
Types of
X-ray Films &
Sensitometry
Making Of The Film Emulsion
The light sensitive layer of a film is termed the Emulsion. The
preparation of emulsion is carried out in four stages:
 Emulsification
 Ripening
 Washing
 Digestion
49
Types of
X-ray Films &
Sensitometry



Emulsification
Aqueous solution of Silver nitrate and Potassium bromide is
mixed with warm solution of gelatin.
AgNO3 + KBr
AgBr + KNO3
Insoluble Silver bromide (AgBr) remains suspended in
viscous gelatin.
More rapid process of mixing results small grain size, that
results narrow grain size distribution hence there is low
graininess & better resolution.
Note:
More bromide is used to increase the negative charge
barrier that helps in development process.
50
Types of
X-ray Films &
Sensitometry
Ripening
Emulsion is placed in certain temperature and more gelatin
is mixed. Size of the grains and their even distribution is
determined at this stage

Slow mixing with long ripening
at high temp.
=> Fast emulsion (with large grains)

Rapid mixing with short ripening at low temp.
=> Slow emulsion (with fine grains)

Slow
mixing
with
NH3
at
low
=> Fast emulsion (with large grains)
temp.
51
Types of
X-ray Films &
Sensitometry
Washing

After ripening, emulsion is chilled to form thick gel.

This gel is shredded.

It is washed with water that remove KNO3 and excess KBr by
diffusion process.
52
Types of
X-ray Films &
Sensitometry
Digestion

Shredded and washed emulsion is re-heated to further
increase its sensitivity.

Re-heating also make the emulsion liquid and suitable to
spread on the film base.
53
Types of
X-ray Films &
Sensitometry
Supercoat (overcoat)
Protective layer of gelatin



Provides sturdiness to unexposed radiographic film.
Antistatic
Reduces damage from scratches, pressure,
contamination during storage, handling and processing.
Supercoating
54
or
Types of
X-ray Films &
Sensitometry






Few Additives
Preservative – Phenol as bacteriocide
Silver iodide – To extend sensitivity towards blue range.
Some dyes may extend Colour sensitivity further
Glycerin to make the emulsion pliable
Saponin – To make the emulsion receptive to the processing
chemicals
Alcohol – To prevent frothing during coating
55
Types of
X-ray Films &
Sensitometry
Coating The Film

Different layers of film are coated on the base material with
rollers and squeezers.

The film lengths are then passed over chilled rollers so that
liquefied gelatinous layers settle and harden.

Then The film lengths are hung like festoons in an air
conditioned room to dry.

Mechanical cutters cut The film lengths in sheets of
desirable sizes.
56
Types of
X-ray Films &
Sensitometry


Anti- Halation Layer
Halation : it is a phenomenon characterized by formation of
a diffuse image or halo around the proper image.
This occurs mainly in the single sided film.
57
Types of
X-ray Films &
Sensitometry


Methods To Prevent Halation
Adding a dye to base
Adding a dye to non-curling layer.
58
Types of
X-ray Films &
Sensitometry
Non-curling Layer

Preferred for single sided emulsion film.

This layer is not removed during development.
59
Types of
X-ray Films &
Sensitometry
Adding A Dye To Base

These dyes cannot be removed during development.

Dye introduced in the base is carefully controlled because it
increase the density and may interrupt the transparency of
the film.

Note-dye used in this should be complementary to the
exposing light. e.g.,red dye is used for greeen sensitive
film,yellow dye is used for blue sensitive film .
60
Types of
X-ray Films &
Sensitometry
Cross Over Effect

It is a type of halation which occurs when film is used with
intensifying screen.

Occurs only with double emulsion films and two screens.

Light from one screen expands in the form of a cone as it
passes through the screen and emulsion where a slightly
enlarged, less sharp image is formed.
61
Types of
X-ray Films &
Sensitometry




contd
Special dyes incorporated in the emulsion
Colored subbing layer is used.
Addition of magenta dye also reduces cross over effect.
62
Types of
X-ray Films &
Sensitometry
Irradiation

It is the sideway scattering of light within the crystal of
emulsion.

This contributes to unsharpness (blurring) of image.
63
Types of
X-ray Films &
Sensitometry
How Film Records An Image
There are three steps
 formation of subject contrast (Optical image)
 Recording of latent image
 Conversion of latent image into permanent image
(processing)
64
Types of
X-ray Films &
Sensitometry



The Latent Image
The latent image is the invisible change in the silver halide
crystals.
The interaction between the photons and the silver halide
crystals produces the latent image or manifest image on
the emulsion layer.
This interaction is sometimes referred to as the
photographic effect.
65
Types of
X-ray Films &
Sensitometry
Formation Of Subject Contrast

Subject contrast:-the variation in intensity of x-ray beam
after passing the absorber.

Subject contrast depends upon atomic No., density,
thickness of absorber and the energy of the x-ray beam.

Different intensity of beam react differently with the
photographic material of the film.
66
Types of
X-ray Films &
Sensitometry
Sensitivity Speck

The shape and lattice structure of silver halide are not
perfect.

It causes some imperfection which results in imaging
property of crystals.

So the sensivity specks is that low energy centre of the
crystal which acts as rest house for the 1º electron and
development centre for the 2º electron.
67
Types of
X-ray Films &
Sensitometry
contd
For the formation of sensitivity specks impurity, usually a
Silver-gold Sulfide is introduced by chemical sensitization
at or near the surface.
68
Types of
X-ray Films &
Sensitometry
contd

The image forming x-rays deposit energy by photoelectric
interaction with atoms of silver halide crystals.

Formation of latent image is given by Gurney-Mott theory
69
SILVER HALIDE CRYSTAL
-
+
SENSITIVITY SPECK
1. Photon Absorption
INTERSTITIAL Ag ION
+
2. Electron Trapping
6. Ag Ion Migration
+
-
-
5. Electron Trapping
3. Ag Ion Migration
+
-
4. Photon Absorption
Types of
X-ray Films &
Sensitometry







Producing the Latent Image
Radiation interaction releases electrons.
Electrons migrate to the sensitivity center.
At the sensitivity center, atomic silver is formed by
attracting an interstitial silver ion.
The process is repeated many times resulting in the build up
of silver atoms.
The remaining silver halide is converted to silver during
processing.
The resulting silver grain is formed.
Silver halide that is not irradiated remain inactive. The
irradiated and non-irradiated silver halide produces the
latent image.
71
Types of
X-ray Films &
Sensitometry
Conversion Of Latent Image Into
Visible Image
This step is also known as
processing. There are 4
step in this processing:
1. Development
2. Fixing
3. Washing
4. Drying
72
Types of
X-ray Films &
Sensitometry






Characteristics To Be Considered
While Selecting Film:
Contrast
Speed
Crossover
Spectral matching
Bulk of purchase
Time of purchase
73
Types of
X-ray Films &
Sensitometry
Care And Protection Of Film
Films should be protected from
 Physical damage
 Light
 High temperature
 High relative humidity
 Harmful gases and fumes
 X-rays and radioactive source
 Fire and theft
74
Types of
X-ray Films &
Sensitometry
Resolving Power Of Films

Ability of a photographic emulsion to record fine details

It is expressed as the number of line pairs per millimeter
which can be distinguished in the image as separate entities

Factors affecting the resolution of an image are – Grain size,
Processing, Diffusion of light inside the emulsion layer and
Modular transfer function
75
Types of
X-ray Films &
Sensitometry
Line Pairs Per Millimeter

A black and a white line make a line pair

A test pattern of slits cut on a metal plate with gradual
fineness is exposed, processed and evaluated under
magnification.

Radiographic emulsions show 8 – 20 LP/mm

Photographic Fast emulsions show 40 – 50 LP/mm
• Medium emulsions show 70 – 100 LP/mm
• Slow emulsions show over 1000 LP/mm
76
Types of
X-ray Films &
Sensitometry
Storage Of Film
STORAGE AREAS : The hospital or x-ray department


The dark room

The imaging room
77
Types of
X-ray Films &
Sensitometry
Handling And Storage Of
Radiographic Film
X-ray film is a sensitive radiation detector and it must be
handled in an area free of radiation.
 Film storage must be shielded.
 The darkroom adjacent to the x-ray room must be
shielded.
 If film use is low more shielding may be required.
78
Types of
X-ray Films &
Sensitometry






Handling And Storage Of
Radiographic Film
Improper handling of the film will result in poor image
quality due to artifacts.
Avoid bending, creasing or otherwise rough handling the
film. Avoid sharp objects contacting the film.
Hands must be clean and dry.
Avoid hand creams, lotions or water free hand cleaners.
Static electricity or a dirty processor can cause artifacts.
Artifacts must be avoided.
79
Types of
X-ray Films &
Sensitometry



Handling And Storage Of
Radiographic Film
Heat and Humidity must be controlled. Film is sensitive to
heat and humidity from the time it is manufactured until
the time it is viewed.
Heat and humidity causes fog or a loss of contrast. Film
should be stored at 20º C (68º F).
Humidity should be between 40% and 60%.
80
Types of
X-ray Films &
Sensitometry




Handling And Storage Of
Radiographic Film
Light will expose the film. Film must be handled and stored
in dark.
If low level diffuse light exposes the film, fog is increased.
Luminous watches, cell phone and darkroom light leaks
should be avoided.
Bright light causes gross exposure.
81
Types of
X-ray Films &
Sensitometry
Handling And Storage Of
Radiographic Film
Shelf life. All film is supplied in boxes with an expiration
date.
 Most film is supplied in boxes of 100 sheets.
 The oldest film in stock should always be used first.
Rotation is important.
 Expired will loose speed and contrast and have increased
fog.

82
83
Types of
X-ray Films &
Sensitometry
Sensitometry

It is the science in which we Study the response of
Photographic materials towards various exposure.

In other words , it is the measurement of sensitivity of that
material.

The photographic material of film reacts differentially with
differentially attenuated x-ray beam
84
Types of
X-ray Films &
Sensitometry
Radiographic Density

All radiographs have some Transparent, some Opaque
and some Not-so-opaque areas, which make the pattern
we call an Image

Density refers level of blackness

If we take a small area of that image, it’ll show three
characteristics
•
Transmission
•
Opacity
•
Density
85
Types of
X-ray Films &
Sensitometry
Transmission
Transmission is how much of the light gets through the film.
Transmission ratio = Tr. light / Inc. light
= L t / Li
This ratio usually expressed as Percentage Transmission ratio
% Transmission ratio = (Lt / Li) x 100
Example:
If 100 lux of light is falling on one side of the film, but only
25 lux gets through, then the transmission is 0.25.
A perfectly opaque area of an image has 0 transmission ratio and 0 % transmission
86
Types of
X-ray Films &
Sensitometry
Opacity

It is ability to stop the light by a certain part of an image.

It is reciprocal of Transmission
Opacity = Li / Lt

The previous example shows
Opacity = 100 / 10 = 10
As incident light is always greater than Transmitted
light, Opacity is always greater than 1
The blackest part of image has an OPACITY approaching 10000
87
Types of
X-ray Films &
Sensitometry






Optical Density
This is the common Logarithm of
Opacity
Density = Log10 Li / Lt
If we continue with the same example
Density = Log10 100/10 = 1
Useful density range in Radiography is
between 0.25 – 2.5
Density range commonly found in C X
R is
0.3 – 1.5 (in the abdominal area)
to 2.5 – 3.0 (in the lung field)
Measured by densitometer .
Density on film depends upon mAs that
represents amount of Ag-atom on the
film
88
Types of
X-ray Films &
Sensitometry
Optical Density: examples
T
OD
Comment
1.0000
0
Perfectly clear (does not exist)
0.7760
0.11
Unexposed film (base + fog)
0.1000
1
Medium gray
0.0100
2
Dark
0.0010
3
Very dark; requires hot lamp
0.00025
3.6
Maximum OD used in medical radiography
89
Types of
Contd…
X-ray Films &
Sensitometry
To relate the number of sensitized grains to the optical
density D the absorption of the light in the film material of thickness
t can be described as:
Using this relation the optical density can be calculated to:
This relation is known as Nuttings Law !
Where as g=sensetised grains per unit
area
δ=cross section area of silver
speck where the grain is being
sensetised
G= no. of total grains per unit area
Maximum optical density for an area on the film is obtained when all
grains are sensitized:
g=G
E.G.- Typically for X –RAY material the optical density Dmax ≈3, for a
typical diameter of 2.5 µm for the developed grain,the number of grains
per area correspondsto:
90
Types of
X-ray Films &
Sensitometry
Why We Take Log
We use density in log form for 3 purpose
 There is large difference in no. on a small scale is not
possible because opacity varies from 10-1000 & by the
use of log we can compress this into 1-3only.
 The physiological response of the eye to difference in
light intensity is logarithmic.
 Addition & superimposition of density is logarithmic.
We take log of relative exposure because.
 It allows very wide range of exposure variation on small
scale.
 Analysis of curve becomes easier .
91
Types of
X-ray Films &
Sensitometry




The Characteristic Curve
The characteristic curve is a graph which illustrates the way
in which a film or film – screen system responds to different
levels of exposure.
The characteristic curve a valuable tool for describing the
sensitometric behavior of a recording.
The characteristic curve is a plot of DENSITY(D) against LOG
RELATIVE EXPOSURE (LOG E).
The curve is sometimes known as a D log E curve and also
called Hurter and Driffield curve.
92
Types of
X-ray Films &
Sensitometry



Relative Exposure
Relative exposure plotted on the X-axis of the C.C. is not
exact as given on the film it is relative to some unit
exposure.
e.g. suppose we use 48kvp with 2.0 mAs in first step and in
the second step we use 48kvp and 4.0mAs and we assume
first as unit exposure than second is relatively double than
previous
An increase in the log relative exposure with 0.3 always
represents doubling the relative exposure that result
double of density.
93
Types of
X-ray Films &
Sensitometry
How Is A Characteristic Curve
Produced
There are three basic stage involved:
1.
Exposing and processing the film.
2.
Measuring the densities produced.
3.
Plotting the curve.
94
Types of
X-ray Films &
Sensitometry







Tools Needed For Making The C.C
Densitometer
Sensitometer
Step wedge
X-ray film
x-ray equipment
Processing unit
Graph paper
95
Types of
X-ray Films &
Sensitometry
Exposing And Processing The Film
TO generate a CHARACTERISTIC CURVE we need to irradiate
the film or film screen system with a series of exposures .
 The exposure series can be achieved in one of two ways:
1. TIME –SCALE SENSITOMETRY
2. INTENSITY –SCALE SENSITOMETRY

96
Types of
X-ray Films &
Sensitometry
Varying Exp (Mas).

A series of exposures are made on an X ray film using a
wedge factor

If 2 is considered as the wedge factor and the first exposure
is X mAs, then the second exposure’ll be 2 X mAs, third
exposure’ll be 2x(2 X mAs)= 4 X mAs and so on
97
Types of
X-ray Films &
Sensitometry
Varying Exp Time
To get same result as the previous one we make the first exposure
(X mAs) through a slit or hole of a lead mask, then shift the
spot and make two exposures, and go on exposing spots
doubling it every time. Thus we get spots exposed by factors X mAs,2 X mAs, 4 X mAs etc
98
Types of
X-ray Films &
Sensitometry
Using Step Wedge

It is a simple device resembling a flight of stairs. It is actually
a filter with gradually varying filtration. The variation is
governed by a constant wedge factor

In diagnostic range Aluminium Step wedge is used but
plastic and steel are common in softer or harder range

When a single exposure is given through this device, we get
a film strip with varying densities
99
Types of
X-ray Films &
Sensitometry
Measuring The Densities Produced.

The optical density of each exposed step on the film test
must be measured using a densitometer.

The values should be tabulated alongside the corresponding
values of relative exposure.
100
Types of
X-ray Films &
Sensitometry
Plotting The Curve
101
Types of
X-ray Films &
Sensitometry
Features Of The Characteristic
Curve
There are 3 parts of C.C.
The region to the left of the TOE
1. basic density
2. basic fog
3. Threshold exposure
Region b/w toe and shoulder
1. Contrast
2. Speed and sensitivity
3. Gradient
4. Film
and
Exposure
Latitude
Region to the right of the shoulder
1. Solarisation or Reversal
of film
2. Max density
102
Types of
X-ray Films &
Sensitometry
The region to the left of the
toe :
This is sometimes referred of underexposure.
1.BASIC DENSITY-:due to the absorption of light as it is transmitted
through the polyster film base.
2 FOG-: it is the density recorded on the film without exposure.It has
several cause
 storage fog
 chemical fog
 safelight fog
 Age veil

Note that density of base plus fog is often referred to as
GROSS FOG or BASIC FOG.
GROSS FOG(<.2) = fog +density
103
Contd…..



NET DENSITY: Gross density-Gross fog
THRESHOLD EXPOSURE:- it is minimum exposure required
that can produce any amount of net density on the film.
Subphrenic region of the chest radiograph is lies in this level
of density.
104
Types of
X-ray Films &
Sensitometry
Region B/W Toe And Shoulder

This is often called the straight-line part of the curve.

There are two major part of this
1: CONTRAST
2: LATITUDE
105
Types of
X-ray Films &
Sensitometry





Contrast
The exposure variation that constitutes subject contrast
generate differences in image therefore produce contrast
in the radiographic image.
STEEPER THE CURVE HIGHER THE CONTRAST.
So the maximum contrast shown by the straight line part
of the curve.
We can calculate this by plotting slope on any point of C.C.
Generally it calculated at the point of INFLECTION where
the slope is maximum.
Actually in the C.C. no any exact straight line part and the
point of inflection refers the point from where the C.C.
changes its curve from convexity to concavity.
106
Types of
X-ray Films &
Sensitometry
Contd…
107
Types of
X-ray Films &
Sensitometry
Film Gamma
The maximum slope of the characteristic curve of an X ray
film.
The film gamma is a measure of the maximum change of film
density for a certain change of exposure.
This corresponds to the part of the characteristic curve with
the steepest slope,
i.e. at the point where the maximum derivative is
found
108
Types of
X-ray Films &
Sensitometry
Contd…
109
Types of
X-ray Films &
Sensitometry
Average Gradient

The slope of a straight line joining the useful density
range(0.2 -2.5)on C.C.

Average gradient depends upon film and the intensifying
screen system not upon subject, or on KVp selected so
that it is different from contrast.

It is calculated by straight line slope that meets the lower
density and the upper density range.
Useful density range
Average gradient=
Film latitude
110
Types of
Contd…
X-ray Films &
Sensitometry
Average gradientY=
Db-Da
LogEb-Log Ea
tanØ= useful density ange= 0.94
1.43
film latitude
Ø
111
Types of
X-ray Films &
Sensitometry
Latitude

Latitude refers to the range of log relative exposure that
will produce density within the accepted range for
diagnostic radiology. Also express the tolerance of the
system to extreme condition of exposure.

LATITUDE studies in two parts .
• film latitude
• Exposure latitude
FILM LATITUDE:-this represent the difference b/w the
upper and lower limits of relative exposure, which produce
useful density range.

Film latitude =Log Eb –Log Ea
112
Types of
Contd…
X-ray Films &
Sensitometry

Useful density range
=
1.75
Average gradient
1.75
Film latitude= Average gradient Average gradient




EXPOSURE LATITUDE:-this represent the tolerance of the film
or film screen system to error in selection of exposure
factor(e.g.-kvp, mAs, time, FFD)
EXPOSURE LATITUDE=film latitude- log exposure range
If the film latitude and exposure latitude approach each other
in magnitude than the selection of exposure factors by
radiographers demands great accuracy and the exposure
latitude is poor.
USEFUL DENSITY RANGE:-it is the range of exposure within
which the image gets formed.
113
Types of
X-ray Films &
Sensitometry


Speed
The speed system is defined as the reciprocal of the
exposure in roentgens required to produce an density of 1.0.
Nearer the C.C. with the density axis speeder the film or film
screen system.
Where
G = average gradient
A is a mathematical constant of straight-line
intersection point with the horizontal axis.
114
Types of
Contd…
X-ray Films &
Sensitometry
Film A is faster than film B because the
C.C. film A is closer to the density axis
A2
A1
115
Types of
X-ray Films &
Sensitometry
•
•
Maximum density :-As the film or film-screen system is subjected to
greater and greater exposure,a point is reached where all of the silver
halide grains in the film emulsion are reduced during development.
Further increase in exposure cannot then in any increase in density.
Thus .the film achieves a maximum level of density known as Dmax.
Dmax
Density

Region To The Right Of The Shoulder
Log relative exposure
116
Types of
X-ray Films &
Sensitometry
Contd…
• Numerical value of Dmax depends on two major factors:
• 1-Silver coating weight-greater the amount of halide per
unit area of film ,the higher is Dmax.A non screen direct –
exposure film has a higher value of Dmax than screen –
type film.
• 2-Processing conditions-changes in developer activity
,perhaps due to temp variations or exhaustion of
developing agents can lead to achieve the optimum value
oe D max.
117
Types of
Contd…
X-ray Films &
Sensitometry

Solarisation/reversal of the film :-as we increase the exposure density
increase up to Dmax. Beyond that exposure the film starts to respond
in the opposite way to normal, producing a reduction in image
density as a result of increase in exposure.
Reversal or region
of solarization

Use of reversal properties is being seen in duplicating the film .

Historically photographic film were exposed to bright sunlight in
order to trigger image reversal such films are solarized.
118
Types of
X-ray Films &
Sensitometry





Uses Of Ch. Curve
Comparison of films – Contrast, Speed, Latitude
Comparison of Intensifying screens
Comparison of Developers
Determining the performance of developer over a period
Determining the fog level of a film stock.
119
Types of
X-ray Films &
Sensitometry

Ouality control of x-ray - film
The radiograph is the its self a important QA tool so that
that the quality of the x-ray film should be assured, so that
we can evaluate our equipment and performance of an
technologist. Quality control programme includes the
folllowing ………..
 Safe
storage and handling of the x-ray film
 Reject
film analysis
120
Types of
X-ray Films &
Sensitometry
FILM STORAGE
• Film packs must be placed in vertical position
(date wise) & not horizontally to prevent static
marks caused by discharge energy of static
electricity due to pressure.
121
Types of
X-ray Films &
Sensitometry


Reject film analysis
The analysis of rejected images is a basic component
of the quality assurance program
Those images judged to be of inadequate quality are
categorized according to cause of reject, which may
be related to the competence of the technical
personnel, to equipment problems or specific
difficulties associated with the examination, or some
combination of these elements
 Due to exposure 38.6
 Due to patient movement 2.3%
 Due to wrong techniques 2.1 %
 Due to processing 27.4
122
Types of
Artifact On Film
X-ray Films &
Sensitometry
Quality of the equipment and the performance of the
radiological technologist is assured by the quality of the
radiograph & the quality of the radiograph assured by there
should no any artifact on the radiograph so the study of film
artifact is neccessory.
What is film artifact ?
 Any irregularity on an image that is not caused by the proper shadowing of
tissue by the primary
 An undesirable optical density on radiograph
How Are They Produced?
Due to fault in following
procedure



Exposure
Processing
Handling & Storage
123
Types of
X-ray Films &
Sensitometry

Film artifact
Due to Handling & Storage
 Radiation and Light fog
 Rough Handling- kink marks
 Static
 Hypo retention
 Kinks
 Scratches
Static=results due to Electron buildup on emulsion In dry &Low
humidity, these are,
crown
tree
smuldge
Before or After processing
 Kink marks
 Scratches
 Fingerprints
124
Types of
Radiographic Artifacts
X-ray Films &
Sensitometry
CONTD
STATIC
HYPORETENTION
FINGER
WATER
MARKS
STAIN
23: Organizing a QA in Diagnostic Radiology
125
Types of
X-ray Films &
Sensitometry

Standards of acceptable image quality
Prior to the initiation of a quality control program,
standards of acceptable image quality should be
established.

Ideally these standards should be objective, for
example “acceptability limits for parameters that
characterize image quality”, but they may be
subjective for example “the opinions of
professional personnel” in cases where adequate
objective standards cannot be defined.
126
Types of
X-ray Films &
Sensitometry




Conclusion
X -ray film is a type of receptor which is widely used in
radiology & it is very important component of whole imaging
procedure in radio diagnosis deptt.
A good practice to handling & storage of x-ray film reduces
unwanted density on film & artifacts on film , hence increases
good diagnostic detail.
Like other diagnostic tool it also needed good QA & QC.
Intellectual knowledge of sensitometery also makes the
technologist work perfect.
No doubt, the emerging technology of receptor makes film
less examination & easier as well as reduces waiting time but
there is significant importance of x-ray film due to high
spatial resolution of conventional radiograph as well as less
economic.
127
REFERENCES
Radiographic Equipments
By Chesney
Christensen’s
Physics For Diagnostic Radiology
www.xray2000.uk
www.radiologyinfo.com
128
THANKS