This document discusses collimation and filtration in dental x-rays. It explains that collimators are used to restrict the size of the x-ray beam in order to minimize radiation exposure and scattered radiation. There are different types of collimators including diaphragm, round, rectangular, and slit collimators. Filtration is also discussed, which involves removing low-energy photons from the beam to reduce unnecessary radiation exposure while maintaining diagnostic image quality. Common filtration materials mentioned are aluminum, copper, tin, and lead. The effects of proper collimation and filtration are to harden the beam and reduce radiation dose to patients.

1. Presented by:- POOJA KUMARI Under Guidance Of:-
Dr. Leela Krishna Prasad
Dr. Prachi Anand
Dr. Abhishek Dubey

2. Collimation
 A collimator is a metallic barrier with an aperture in the
middle used to restrict the size of the x-ray beam & the
volume of tissue irradiated.
 Dental x-ray beams are usually collimated to a circle 2 ¾
inches (7 cm) in diameter at the patient’s face.
 In intraoral machines there are fixed collimators & in
extraoral machines there are adjustable collimators.

3. Continued….
 Collimation decreases the risk of radiation, minimises
scattered radiation & decreases the fog, with a sharper
image & better contrast.
Typesof collimators:-
1. Diaphragm collimator
2. Round / cylindrical collimator
3. Rectangular collimator
4. Slit collimator

4. Diaphragm collimator
 It consists of a thick plate of radiopaque material
(usually lead) with an aperture or an opening in it.
 The device is usually placed over the port in x-ray
head through which the x-ray beam emerges.
 The aperture may be of different size & shape as
per the requirement.

6. Round / cylindrical collimator
 A round collimator is a thick plate of radiopaque
material with a circular opening centered over the port
in the x-ray head through which the x-ray beam
emerges.
 These are built into open-ended aiming cylinders.

7. Rectangular collimators
 Rectangular collimators further limit the size of the beam to just larger than
the x-ray film, further reducing patient exposure.
 Some types of film holding instruments also provide rectangular collimation
of the x-ray beam.
 Since a rectangular collimator decreases the radiation dose by up to fivefold
as compared with a circular one, radiographic equipment should provide
rectangular collimation for exposure of periapical & bitewing radiographs.

8. Slit collimators
 Slit collimator is used in OPG machines.

9. Fig. comparison of excess radiation area using cylindrical &
rectangular collimators.

11. Filtration
 This involves removal of unwanted radiation whilst leaving the wanted radiation
undiminished.
• Radiation emitted by an x-ray tube is made up of photons of much different energy.
• The maximum photon energy depends only upon the kilovoltage used to generate
the radiation.
• And the minimum energy depends upon the nature & thickness of the material of
the wall of the x-ray tube.
• Because of their different energies, the photons have different penetrating powers.
• When the beam of radiation is incident upon the patient, the bulk of the low energy
photons is absorbed in the superficial layers, which produce unwanted effects.
• Thus, these low energy radiations must be removed by a process called filtration.

12. Filtration of a beam is accomplished by:-
 Inherentfiltration:- The primary beam of radiation passes through the glass wall of the
tube, a layer of oil & the aperture window.
As it passes through these components of the tube, a certain amount of filtration takes
place, which is called inherent filtration.

13.  Additionalfiltration:- Additional materials are placed in the path of the primary
beam to aid in further filtration.
 Totalfiltration is the sum of inherent filtration plus the added filtration. (I.F+
A.F)

14. Requirements of filter material
 It should be able to discriminate against the lower energy photons.
 The material should not have an absorption ‘edge’ at an energy close to the energies
of the photons that are desired to be used.
 The thickness of the material must not be too small because in such cases, due to
irregularities in thickness, the beam thus produced would be non-uniform.

15. Materials used for filtration
 The materials used may vary depending upon whether the beam is of high or low
energy & therefore depending upon the generating voltage used.
 The generally accepted x-ray range for the materials used is:-
• 30-120 kV Aluminium (most commonly used)
• 100-250 kV Copper (with appropriate backing)
• 200-600 kV Tin (with appropriate backing)
• 600-2 mV Lead (with appropriate backing)

16. Effects of filtration
 It removes unwanted radiations & hardens the beam, thus increasing the
penetrating power.
 Reduces unnecessary less penetrating radiation to the patient, which has no
diagnostic value.
Profile Wedge Filter:-
 It is an absorbing device which consists of a vertical bar that is wedge shaped
anteroposteriorly.
 The thin edge of the filter is positioned posteriorly over the bone area of the patient
to absorb less x-rays, while the thick edge is positioned in the soft tissue region.
 The wedge is usually made up of aluminium & can be located in the cassette, in the
x-ray beam between the patient & the x-ray source.

17. Wedge filter:-
 These are used with mega-voltage radiations & in radiotherapy when it is desirable
to treat from one side of the patient only, though it is necessary to use more than
one beam.
 The material used for wedge filters is relatively unimportant, local convenience &
availability of material are often the deciding factors, rather than physical
properties.
 Aluminium, copper, brass or lead are often used, the denser materials have an
advantage as they give thinner filters than aluminium.

18. References :-
 Oral Radiology -White N Pharoah…
 Freny