Download Chapter 7 Intensifying Screens and Cassettes

Answers to revision questions
Chapter 10 : Intensifying screens and cassettes
1. Describe the function of an intensifying screen.
An intensifying screen converts the energy from x-rays into light which is used
to expose the x-ray film and form a latent image. This requires a lower x-ray
exposure reducing the dose to the patient.
2. How does a phosphor grain convert x-rays into light?
The process is known as luminescence and involves the movement of
electrons in the phosphor grains when they are exposed to radiation. This
movement results in the emission of light.
3. Name the three speeds of screen and when each may be used.
Screen
Speed
Uses
High
Slow
Fine detail, needs higher exposure so should be
Resolution
used where lower exposure factors are
acceptable
Regular
Medium
Fast
Fast
General radiography
Produce a darker radiographic image for given
exposure factors when compared to regular or
high resolution screens
Ideal for use where movement may be a
problem
4. What are the two main types of phosphor used in an intensifying
screen?
Calcium tungstate and rare earth.
5. Give two factors that can alter the speed of a screen.
The speed of screen can be altered by the phosphor grain size, the thickness
of the intensifying layer the presence or absence of a reflective layer and the
amount of crossover that may occur from screen to film.
6. Why is film screen contact so essential?
Without good contact of the film and screen divergence of the light will occur
between the screen and the film resulting in a blurred image.
7. How would you clean a screen?
Screens should be cleaned regularly to remove any dust or other foreign
material from their surfaces. This can be done easily using a mild liquid
detergent or a proprietary screen cleaner.

A soft cloth, but not cotton wool (as it leaves tiny fibres) should be
moistened with the detergent and wiped gently over the screen

The screen should never become wet and spillage to the back of the
screen must be avoided.

The screen should then be wiped clean using a fresh dry cloth of piece
of gauze.

The cassette should then be left standing upright and slightly open to
allow it to dry.

It is a good idea to record when this is done.
8. Describe the layers within an x-ray cassette.
Cassette Front
The front of the cassette is a uniform thickness. The front is usually made
from plastic or carbon fibre. This provides stiffness whilst still being
lightweight.
Cassette Back
The back is usually of a similar material to the front and is lined with lead foil
to protect the film from backscatter. The back is usually curved to ensure
good film screen contact. The back may also contain a foam pressure pad
under the intensifying screen to increase film screen contact further.
7. Why are the insides of a cassette black?
To prevent reflection of light within the cassette.
8. Give three main points to consider when caring for a cassette.

Use them gently.

Do not drop them.

Carry a few at a time.

Cassettes can be damaged if they are stored at an angle so they
should be as near to vertical as possible.

If the cassette is used under a patient, the use of a cassette tunnel
should be considered to prevent unnecessary pressure being applied
to the cassette.

Try to avoid getting the cassettes wet. If this is unavoidable, cover the
cassette in a waterproof covering (carrier bag is adequate!)

Number all cassettes and keep a record of their first use, any damage
that occurs and any maintenance that is carried out.