Screen Film Radiography

Screen Film Radiography
Muhammad Arif Afridi
Lecturer In Medical Imaging
Email: drarifafridi@gmail.com
MUHAMMAD ARIF AFRIDI | LECTURER IN MEDICAL IMAGING | DRARIFAFRIDI@GMAIL.COM 1

Objective
1. Screen Film Radiography Cassettes Standard sizes:
2. Construction of radiographic film
3. Formation of the latent image
4. Construction of radiographic intensifying screen
5. Luminescence and its relationship to phosphorescence
and fluorescence.
6. Quantum efficiency and Conversion efficiency and
Receptor speed and image noise
7. Automatic film processor

Screen Film Radiography Cassettes
Standard sizes:
1. 35 x 43 cm (14“ x 17“)
2. 35 x 35 cm (14“ x 14“)
3. 24 x 30 cm (10“ x 12“)
4. 18 x 24 cm (8“ x 10“)
5. 15 x 30 cm (6“ x 12“)

Short Introduction
Image forming x-rays exit the patient and expose the radiographic intensifying screen placed in
the protective radiographic cassette.
The radiographic intensifying screen emits visible light, which exposes the radiographic film
placed between the two screens.
Although some x-rays reach the film emulsion, it is primarily light from the radiographic
intensifying screens that expose the radiographic film.
Processing the invisible latent image creates the visible image.
4MUHAMMAD ARIF AFRIDI | LECTURER IN MEDICAL IMAGING | DRARIFAFRIDI@GMAIL.COM

Continue…
Processing causes the silver ions in the silver halide crystal that have been exposes to light to be
converted into microscopic grains of silver.
The film processing sequence–wetting, developing, rinsing, fixing, washing, and drying–is
completed in 90 seconds in an automatic processor.
This class covers the information required for an understanding of the radiographic screen-film
receptor and the production of the visible image.

x-ray beam
emerges
from the x-
ray tube
Uniform
destruction
in space
After
interaction
with patient
Varies
according to
the density
of tissue
X-ray passed
from the
body
Exit xray
beam is
know as
useful beam
Image Forming X-rays

Image Forming X-rays: Theory
•The primary purpose of radiographic imaging is to transfer information.
•The x-ray beam that emerges from the x-ray tube is nearly uniformly distributed in space.
•After interaction with the patient, the beam of image-forming x-rays is varies in intensity
according to the characteristics of the tissue through which it has passed.
•Image-forming x-rays are those that exit the patient and interact with the image receptor.

X-ray Film Act as a Medium
X-ray film is one such medium.
Other media include the fluoroscopic image intensifier, the television or flat panel monitor.
The medium that converts the x-ray beam into a visible image is called the image receptor (IR).
The classical IR is photographic film, although solid-state digital IRs are replacing film.

Radiographic Film
Radiographic film has two parts:
1. Base
2. Emulsion

Cross Section of Radiographic Film
X-ray film, the emulsion is coated on both sides;
therefore, it is called double emulsion film.
adhesive layer is between the emulsion and the base.
Adhesive layer allows the emulsion and the base to
maintain proper contact and integrity during use and
processing.
The emulsion is enclosed by a protective covering of
gelatin called the overcoat.
This overcoat protects the emulsion from scratches,
pressure, and contamination during handling,
processing, and storage.
The thickness of radiographic film is approximately
150 to 300 μm.

Base
The base is the foundation of radiographic film. Its primary purpose is to provide a rigid structure.
Conventional photographic film has a much thinner base than radiographic film and therefore is not
as rigid.
The base of radiographic film is 150 to 300 μm thick, semirigid, lucent, and made of polyester.
The base of radiographic film maintains its size and shape during use and processing so that it does
not contribute to image distortion. This property of the base is known as dimensional stability.

A substitute material, cellulose nitrate, soon became the standard base.
It was flammable. Improper storage and handling of some x-ray film files resulted in severe
hospital fires during the 1920s and early 1930s.
In the early 1960s, a polyester (≈175 μm) base was introduced, has taken the place of cellulose
triacetate as the film base of choice.

Emulsion
The emulsion is the heart of the radiographic film.
It is the material with which x-rays or light photons from radiographic intensifying screens
interact.
The emulsion consists of a homogeneous mixture of gelatin and silver halide crystals.
It is coated evenly with a layer that is 3 to 5 μm thick.
The gelatin is similar to that used in salads and desserts but is of much higher quality.
Its principal function is to provide mechanical support for silver halide crystals by holding them
uniformly dispersed in place.

HANDLING AND STORAGE OF FILM
Radiographic film is a sensitive radiation detector and must be handled accordingly.
Improper handling and storage result in poor radiographs with artifacts that interfere with
diagnosis.
Heat and Humidity
Radiographic film is sensitive to the effects of elevated temperature and humidity, especially for
long periods.
Heat increases the fog of a radiograph and therefore reduces contrast.
Radiographic film should be stored at temperatures lower than approximately 20°C (68°F).

Light
Radiographic film must be stored and handled in the dark.
Any light at all can expose the emulsion before processing.
Radiation:
Ionizing radiation, other than the useful beam, creates an image artifact by increasing fog and
reducing contrast.
Film fog is the dull, uniform OD that appears if the film has been inadvertently exposed to light,
x-rays, heat, or humidity.

FORMATION OF THE LATENT IMAGE
The image-forming x-rays exiting the patient
Incident on the radiographic intensifying screen-film
Deposit visible light energy in the emulsion primarily by interaction with atoms of the silver
halide crystal.
Immediately after exposure, no image can be observed on the film.
An invisible image is present, however, and is called a latent image.
With proper chemical processing, the latent image becomes a visible image, sometimes called
the photographic effect.
The latent image is the invisible change that is induced in the silver halide crystal.

Silver Halide Crystal
The silver, bromine, and iodine atoms are fixed in the crystal lattice in ion form.
Silver is a positive ion, and bromide and iodide are negative ions.
When a silver halide crystal is formed, each silver atom releases an outer-shell electron, which
becomes attached to a halide atom (either bromine or iodine).

Thank you!

Screen Film Radiography

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