Beam restriction refers to decreasing the size of the projected x-ray field to limit unnecessary radiation exposure and reduce scattered radiation. This improves image quality by increasing radiographic contrast. Common beam restricting devices include aperture diaphragms, cones, cylinders, and collimators. Collimators allow adjustable rectangular or square field sizes and include lights and templates to ensure accurate beam alignment. Proper collimation is important for patient safety and diagnostic image quality.

1. BEAM RESTRICTION
MUHAMMED ASLAM BS
BSC MIT

2. Beam restriction
• Beam restriction refers to decrease in the size of
projected radiation field from X-ray tube.
• Beam restricting devices & Radiographic Grids
are the tools used to limit the scatter radiation.
.

3. PURPOSES OF BEAM RESTRICTION:
• Limits patient exposure by decreasing the X
ray beam field size & hence protecting from
unnecessary exposure.

4. • Reduce the amount of scattered radiation
that is produced within the patient.
• Reduce the amount of scatter , the image
receptor is exposed to , thereby increasing the
radiographic contrast.

5. Primary Beam
• Unrestricted primary beam is cone shaped
projects a round field on the patient and
image receptor.

7. • If left unrestricted , it results in unnecessary
patient exposure.
• Limiting the field size of beam is achieved with
beam restricting device.
• They are placed just below the x-ray tube
housing to change the size & shape of primary
beam.

8. • Collimators are the most popular beam
restricting devices.
• Increasing the collimation implies decreasing
the field size & hence radiation dose to
patient.
• Decreasing the collimation means increasing
the field size.

10. Beam restriction & Scattered radiation
• Beam restricting devices reduce scattered
radiation
• This reduce amount of scatter the image
receptor is exposed
• Thus increasing the radiographic contrast

11. Collimation & Radiographic density
• Due to reduction in scattered radiation
produced , Collimation affects the number of
photons reaching the image receptor.
• This decreases the radiographic density
produced.
• Therefore exposure factors may be needed to
be increased when collimation is increased to
compensate for the loss of density.

12. • kVp value shouldn't be increased as it results
in decreased contrast
• To change only density of radiographic image ,
mAs should be changed.
• A significant collimation requires an increase
in as much as 30-50% of the mAs to
compensate for loss in density that occurs
because of collimation.

13. Beam restricting devices
• Made up of metal or a combination of metals
that readily absorb X-rays.
• They differ in sophistication & utility.

14. Types
Aperture Diaphragms
Cones & Cylinders
Collimators
Positive beam
limiting devices.

15. Aperture Diaphragms
• It is flat piece of lead diaphragm that has a
hole in it .
• They are placed directly below the X ray tube
window .
• They can be made by cutting the rubberized
Lead into size needed to create the diaphragm
& cutting the center to create the shape & size
of aperture

17. ADVANTAGES
• Simplest type of BRD
• Easy to use.
• The aperture’s size & shape can be changed.
• Home made or commercially made apertures
are available for the purpose of radiographic
unit.

18. DISADVANTAGES
• The aperture cannot be adjusted from the
designed size.
• Therefore the projected field size is not
adjustable.
• Because of aperture’s proximity to the
radiation source , a large area of unsharpness
surrounds the radiographic image called as
Penumbra.

19. Cones & Cylinders
• A Cone or Cylinder is essentially an aperture
diaphragm that has an extended flange
attached to it.
• The flange can very in length & can be shaped
as either a cone or cylinder.
• Though shaped differently , they have many of
the same attributes.

21. • The flange can also be made to telescope ,
thereby increasing its total length.

22. ADVANTAGES
• Easy to use
• They slide onto the tube , directly below the
window
• They limit unsharpness surrounding the
radiographic image more than the aperture
diaphragms , with Cylinders accomplishing the
task slightly better than Cones.

24. • Cones & Cylinders are almost made to
produce a circular field.
• Therefore they can be used to advantage for
particular radiographic procedures like
radiography of sinuses , mastoid & gallbladder.

25. DISADVANTAGES
• They are limited in terms of the sizes they are
available.
• They are not necessarily interchangeable among
tube housings.
• If the angle of the flange of cone is greater than
the angle of divergence of primary beam , the
base plate is the only metal actually restricting
the primary beam.
• Therefore Cylinders are generally more useful
than Cones.

26. COLLIMATORS
• A collimator has 2 or 3 sets of lead shutters.
• Located immediately below the tube window.
• Beam restriction achieved by the use of a
collimator is called Collimation.

28. Parts of a Collimator
• Sets of lead shutters
• Light source & mirror
• Plastic template with cross hair/lines on it.

29. • These shutters consists of longitudinal & lateral
leaves , each with its own control.
• The entrance shutters limit the X ray beam much
as the aperture diaphragm would.
• 1st set acts as an aperture & 2nd set acts to
deletes the penumbra produced by 1st.
• This makes the collimator adjustable in terms of
its ability to produce projected fields of varying
sizes

30. • Field shaped produced is always rectangular
or square unless a diaphragm or cone is slid in
below the collimator.
• They are equipped with a light source & a
mirror to project a light field onto the patient.
• The light is intended to accurately indicate
where the primary X-ray beam will be
projected during the exposure.

32. • A plastic template with cross hairs is affixed to
the bottom of collimator to indicate where the
center of the primary beam i.e. the central ray
will be directed.
• It helps in accurately centering the X ray field
to the patient as
the field is being
illuminted.

33. Drawbacks
• The mirror that reflects the light down
towards the patient or the light bulb itself
could be slightly out of position
• This can result in lack of accuracy of the light
bulb field.
• In such case the projected light field
inaccurately indicate where primary beam will
be projected.

34. • Present on the front of the collimator.
• In case of failure of light , it indicates the
projected field size based on the adjusted size
of collimator opening at a particular source to
image distance.
X Ray field measurement guide

35. Quality Control Check
- Collimator & Beam alignment test.
• Means of testing the accuracy of light field &
location of center of projected beam.
• Lack of congruency of X ray field & exposure field
, and misalignment of the light & Bucky tray ,
affect the quality of radiography.
• Collimator misalignment should be less than 2%
of source-to-image receptor distance used.
• The perpendicularity of central ray must be < or =
to 1 degree misaligned.

36. Automated Collimators
• Also known as Positive Beam-Limiting devices
• The device automatically limits the size &
shape of primary beam to the size & shape of
image receptor.
• The shutters are motor driven.

37. • The sensors in the buckey tray identify the size
& alignment of cassette and relay info to
collimators , which position the shutters to
exactly match the size of film being used.

38. Conclusion
• Beam restrictors are devices that regulate the
size & shape of X ray beam
• Three types- Aperture diaphragms , Cones &
Cylinders and Collimators.
• They are used to decrease the scattered
radiation and hence protection of patient
from unnecessary radiation and also a better
radiographic image quality .