Cassettes and films

1. Cassettes & Films in
Dark room
Presented by :
M.Naga Theja
Reg. No : 210153003
M.Sc. Radio Imaging Technology
1st semester

2. Table of content
❖ Cassette
➢ Introduction, Features, Construction, Fitting & Sizes, Types, Loading &
unloading, Care of cassette.
❖ X-Ray film
➢ Introduction, History, Layers, Types, Storage, Handling & Care
❖ Intensifying Screen
➢ Introduction, Layers, Spectral matching, Usage
❖ Tests for cassette

3. Cassette
1. A light proof rigid holder that supports screen and film.
Properties of cassette
1. Lightproof
2. No sharp edges
3. Strong enough to avoid damage from any external factors
4. Front should provide minimum attenuation, uniform
thickness, & no irregularities
5. Internal rear surface must provided with adjacent support
that minimize the risk of back scatter

4. Construction of cassette
1. Mainly consist of front & back hinged together at one end.
2. Cassette front should be of low atomic number so that it can let x-ray pass through and its
low atomic number also helps to reduce patient dose.
3. Cassette back is made up of high atomic number to minimize the back scatter or a lead foil is
at back side to reduce scatter radiation.
4. Pressure pads are arranged to have good contact to film & screen.
Cassette fitting
1. Hinges - stainless steel
2. Clips - metals or plastic
3. Pressure pads - plastic foam

5. Structure of a
X Ray
Cassette

6. Sizes of cassette
1. 6 x 8 inch
2. 8 x 10 inch
3. 10 x 12 inch
4. 12 x 15 inch
5. 11 x 14 inch
6. 14 x 14 inch
7. 14 x 17 inch

7. Types of cassette
1. Screen type cassette
Single screen Double screen
● Have single screen in front side of
film.
● Have 2 screens both in front and
back of film.
● Single emulsion film is used. ● Double emulsion film is used.
● Mostly used in mammography. ● Used in general radiography.

8. Curved cassette
1. Conventional cassette with double side intensifying screen.
2. Curved shape that provide good contact between screen &
film.
3. Used to attain images that can’t attained by flat cassette
such as intercondylar view & OPG (Orthopantomogram)
Grid cassette
1. Have a secondary radiation grid between cassette &
patient.
2. Used in conventional bucky system and mostly used in
bedside x rays in past.

9. Multisection cassette
1. Designed to hold 3-7 films with their respective intensifying screens & spacers of about 5 or
10 mm in thickness.
2. Film which are separated by 5mm spacers will produce images of body section of 5mm apart
and likewise with 10mm.
3. Most commonly used in tomography where we produce images in different height with one
exposure, images of different densities obtained.

10. Angiographic cassette
1. 30 sheets in film of 14 x 17 inch cassette inserted in equipment .
2. A button is present to open or close the sliding lid.
3. After the procedure the cassette is taken to processing in AOT equipment.

11. Vacuum cassette
1. Made up of flexible vinyl material.
2. It has the valve at one end
3. Inside this removable plastic folder contain a single
intensifying screen.
4. For use a single emulsion film is inserted inside the
folder
Photofluroscopic cassette
1. The cassette is used for recording the image coming
from output phosphor of an image intensifier tube.
2. Usually it is carried out on 70mm, 100mm or 105mm.

12. Loading & unloading of cassette
The life of intensifying screen & film also depend on loading and unloading of cassette also.
Loading
1. Under safelight, cassette is placed on bench &
opened from back.
2. The unexposed film tightly gripped at edge and
lowered gently in cassette wall.
3. The cassette is closed by bringing the back and
lock the edges.

13. Unloading of cassette
1. Under safelight, cassette is placed facing down and the lock og cassette is released.
2. Then the film is taken from the edge carefully but not the hands touch much region of film
except the edges that may cause any damage to latent image.
Care of cassette
1. Should handled gently.
2. Number of cassettes carried should be limited and hold between hands and body holding
fingers at the bottom edge.
3. If stored on edge if should be ensured that they are nearly vertical as possible.
4. Contact to fluids should be avoided.

14. X Ray film
1. The x ray films are the image receptors device
that capture the x rays passing from the patient's
body and forms the latent image.
2. The x ray films mainly consist of 4 layers such as :
a. Base
b. Adhesive layer
c. Emulsion layer
d. Overcoat

15. History of film
1. First x ray image was developed on a glass plate coated
with emulsion on one side, the exposure dose was very
high.
2. In 1914, Cellulose Nitrate films are used to record the
image which is a single emulsion film and quite flexible.
3. Later the double emulsion films are quite response to
flame.
4. In 1924, cellulose triacetate are used for safety purpose
and during 1960’s polyester are used due to its stability.

16. Base
1. Gives strong rigid support to other layers and the base should be flexible, fracture free,
transparent, easy to handle without kinking with uniform lucency and transparent to light.
2. The base is initially made of cellulose nitrate and then cellulose triacetate is used, now
presently polyester is used due to its wrapping resistant, strong to high dimensional stability
and its thinner.
3. A blue dye is added so that it reduces the stress to eyes and helps in accurate diagnosis.
Adhesive layer
1. It’s a gelatine layer gives good attachment to base and emulsion layer.
2. Its uniformly distributed between emulsion and base.

17. Emulsion layer
1. It's coated over adhesive layer with silver halide crystals and a transparent gelatine layer
which gives support and holds the crystals properly.
2. These halide crystals are made up of silver bromide ( 98% ) and silver halide crystals ( 2% ).
3. The shape of crystals are may be of tubular, or any irregular shape.
4. The irregular shape provides insensitivity center for latent image formation.
5. When the film is exposed, photon react with Br ( photon + Br- ) and this may photoelectric or
compton effect.
6. The secondary electron migrates to sensatory center and get trapped.
7. The mobile silver atom are attracted the sensitivity center where the electron combign and
became metallic silver ( Ag+ + e- = Ag ) and the silver atoms gives the latent image.

19. Overcoating layer
1. Gelatine covered as overcoating layer which protects the film from scratching, pressure,
contamination & handly damage.
Relation between Grain size & Image density
Speed : Bigger the grain size, higher the speed of film.
Contrast : Affected by size distribution, improper distribution in film, lower the contrast.
Graininess : Grains are seen due to crystal size. Bigger the size, higher the graininess

20. Types of films
Based on their usage
Based on emulsion layer
Single emulsion film Double emulsion film
● Single emulsion layer present used
with single intensifying screen.
● Double emulsion layer present used
with intensifying screen on both sides.
● Due to single emulsion layer it require
adequate exposure.
● Due to double emulsion films it
requires less exposure.
● High resolution films generally used in
dental radiography & mammography.
● Generally used in general
radiography.

21. Based on intensifying screen
Screen type film Non-screen type film
● Used along with intensifying screen
hence it require less exposure.
● Used along without intensifying screen
so it requires adequate exposure.
● As exposure is low then time and
patient dose also reduced.
● Adequate factors kept no more than
enough to reduce patient dose.
● Emulsion layer is thin. ● Emulsion layer is thick.

22. Based on light sensitivity emulsion coating
1. The films base colour used should match the colour light emitted by the intensifying screen
to get the proper image & this property is called spectral matching.
2. Based on this the are 3 types of films such as
Film names Sensitivity to light Material used
Monochromatic film Blue light sensitivity Calcium tungstate
Orthochromatic film Green light sensitivity Gadolinium oxysulphate
Panochromatic film White & Black Cyanine derivative

23. Based on film speed
1. Film speed refer to sensitivity of film to given exposure.
2. Faster film require less radiation to produce image.
3. There are three speed of films.
a. Standard film
b. Fast speed film
c. Ultra fast speed film
4. Film latitude refers to the range of exposure factor that produces diagnostically useful
range of radiographic image.
5. Shape, size of crystals & thickness of emulsion also affects the speed of film.

24. Types of films based on their use
Mammographic film
1. Single coated film & intensifying screen
2. Slow speed
3. High contrast and sharpness of image
4. Currently green sensitive terbium eloped gadolinium oxysulphate screens are used.
Laser films
1. Used in CT, MRI and computed or digital radiography.
2. Digital electronic signal from the imaging system modulates a laser signal, laser beam writes
the image on the film.

25. Dental films
1. Non screen,thick emulsion & low speed film
is used.
2. Three types and sizes such as
a. Peri-apical : 31mm x 41mm ( for single or group of
teeth )
b. Occlusal : 57mm x 76mm ( maxillary and mandible )
c. Bite-wing : Similar to periapical, but positioned
vertically behind upper and lower teeth
Peri-apical
Occlusal
Bite-wing

26. Storage of films
1. Stored at low temperature of 10 - 20 °C and at low humid temperature.
2. Kept vertically without any pressure on film.
3. Away from radiation area and heat source.
Handling of films
1. Film loading & unloading on a clean dark under a proper safe light.
2. Handled safely with dry hands without wet or any chemical strains in hands.
3. Used before expiry period.
4. Wet films should never touch.

27. Intensifying screen
1. Generally it requires high amount of exposure to produce
an image.
2. Hence intensifying screens are used that convert one x
ray photon into thousands of light photons and expose
the film.
3. So not much exposure required and patient dose also
reduced.
4. The intensifying layer consist of 4 layers.
i. Base
ii. Reflective layer
iii. Phosphor
iv. Protective layer

28. Principle of intensifying screen
1. Intensifying screen works on principle of Luminescence in which the radiation exposed to
antom of a matter, the energy is converted to visible light.
2. There are 2 types in luminescence such as
a. Fluorescence : gives of light out simultaneously.
b. Phosphorescence : gives light after exposure ( afterglow )
Properties
1. Radioparent (Penetrable by x-rays or other forms of radiation).and chemically inert
2. Tough, flexible & not colour with age
3. Uniformly homogeneous phosphor layer

29. Base
1. Polyester base is used of 1mm thickness, polyester is used due to its moist frees nature,
strong, chemically inert and flexible.
2. It basically gives support to other 3 layers.
Reflective layer
1. Made up of white substance such as titanium dioxide ( TiO2 ) or manganese dioxide with
thickness of 25 μm.
2. This layer reflects light towards the phosphor and make the light emission isotropic, thus
this layer increases the efficiency of intensifying screen by doubling the number of light
photon.

30. Phosphor layer
1. Thickness of this layer is 50-300 μm.
2. Commonly used phosphor are calcium tungstate ( CaWO4 ), Zinc cadmium sulphide
cesium, Cesium iodide.
3. High atomic number, not affected by heat, humidity and environment factor.
4. Rare earth phosphor such as Gadolinium oxysulphide, Lanthanum oxysulphide, lanthanum
oxybromide, yttrium tantalate ( YTaO4 ) are used as their absorption and conversion is
high.
5. The spectral emission of rare earth material is discredited and centered at 540nm, hence
green sensitive film is used as phosphor.
6. The phosphor layer reduces the patient dose by multiplying the x ray photon to multiple
light photons.

31. Protective layer
1. Thickness of 10-20 μm and transparent to light.
2. Reduce the damage to film from handling.
3. Reduce static electricity.
4. Provide a surface cleaning.

32. Speeds of Intensifying Screens.
1. Fast screens - thick layer, and relatively large crystals used, maximum speed is
attained but with some sacrifice in definition.
2. Slow screens or high definition screens - a thin layer and relatively small crystals
are used; detail is the best, but speed is slow necessitating a higher dose of
ionizing radiation.
3. Medium screens - medium thick layer of medium sized crystals in order to provide comprise
between speed and definition.
There are three types of intensifying screens:
a) Standard - slow screens ( calcium tungstate )
b) Rare earth - fast screens ( gadolinium or lanthanum )
c) Combination

33. Wire mesh test

34. Light leak test
1. Take an unexposed cassette in and divide the cassette surface into 4 areas.
2. Then a glowing bulb is shown around the all the sides of the cassette each side
atleast of 10mins it should be exposed.
3. Then the cassette is processed, there should be no development of film if there is
any development in film then it means the cassette is having light leakage.