2. X-RAY BEAM RESTRICTORS
• An x-ray beam restrictor is a device that is attached to
the opening in the x-ray tube housing to regulate the size
and shape of an x-ray beam.
• Basically,there are three types of beam restrictor
devices;
1.Aperature diaphragm
2.Cones and cylinders
3.Collimators
3. Aperature diaphragm
• Simplest type of X-ray beam restrictor attached to the x-
ray tube head.
• It is basicalllly lead or lead lined metal diaphagm with a
hole in the center,the size and shape of the hole determine
the size and shape of the x-ray beam.
• Principal advantage- simplicity, but produces large
penumbra.
• Lead closed to focal spot.
• Fixed image receptor size ,Constant SID.
• The width of the penbra can be reduced by positioning
the appratur diaphragm as far away from the x-ray
target as possible .
• Usually possible by attaching the diaphragm to the end
of a cone
4.
5. Cones and cylinder
❖Are the modification of aperture
diaphragm.
❖In both an extend metal structure
restricts the useful beam to the required
size.
❖Most commonly used type is cylinder.
❖Difficulty with using cone is
alignment.(cone cutting).
❖The flated shape of the cone would
seem to be ideal geometric
configuration for an x-ray
beamrestrictor but flared of cone is
greater the flared of x-ray beam.
7. Collimators
◆Collimators adjust the size and shape of the x-ray field
emerging from the tube port.
◆Collimators assembly typically attached to the tube
housing at the tube port with swivel joint.
◆It has two advantage's over other types:
◆Has two sets of shutters i.e longittudinal and trnsverse.
◆Sets may actually have two pairs of shutters operating
together.
◆The shutters functions as to adjustable Aprature
diaphragm
✓ provide adjustable rectangular field.
✓ Light beam indicate x-ray field.
10. ◆X-ray fields is illuminated by light beam from the bulb in
the collimator,which is deflected by a mirror mounted in
the path of the X ray beam at an angle of 45°.
◆The target of the X ray tube and bulb should be exactly
the same distance from the center of the mirror.
◆Have back up system for identifying field size in case the
bulb should burn out. Indicated by a calibrated scale on
the front of the collimator.
◆ Today,positive beam limiting (automatic collimator) are
used,which are same as other collimators except that
their shutters are motor driven.
11. ◆When casstes is loaded in to the Bucky sensor in the tray
sense the cassette size and alignment. Which relay
information to the collimator toanupulates the x ray field
size.
12. ◆Senses the film size , orientation
&SID.
◆ Limits x-ray field to size of the
film.But it doesn't insure tube
&bucket are aligned.
◆PBL must be accurate to with in 2%
of the SID
◆Light field and x-ray field aligned so
that the sum of the
misalignment,along either the
length or width of the field,with in
2%of the SID.
13. Testing X-ray Beam and Light beam
◆The alignment of the x-ray beam and light beam
should be checked periodically.
◆Equipment;
◆Make an exposurey to mark the position of the X-ray
field on the film(40 in.,3.3mAS, 40kVp).
◆ Then, enlarge the field size to 12×12in. and expose the
film again as same exposure.
● 4L shaped wires
● X-RAY film with cassette
● Small lead letter R
15. Functions Of Restrictors
◆Collimators and others x-ray beam restrictors two basic
functions.
○ Decrease off focus radiation.
○ Smaller the x-ray field ,smaller the volume of the
patient that is irradiated.
○ Patient protection is principal reason for using
collimator.
✓ Patient protection
✓ Decrease scatter radiation
16. Transmitted photon
Field size (cm²)
Figure; Transmitted radiation for various sizes of x-ray field
Transmittedphoton(Arbitrary
Units)
