this ppt describes about filtration and collimation

1. FILTRATION AND COLLIMATION

2. FILTRATION
 an x-ray beam consists of a spectrum of x-ray photons of
different energies, only photons with sufficient energy to
penetrate through anatomic structures and reach the
image receptor (usually film) are useful for diagnostic
radiology.
 Those that are of low energy (long wavelength) contribute
to patient exposure (and risk) but do not have enough
energy to reach the film

3.  Design: The filter is made up an aluminum disc.
 It selectively allows the passage of high-energy X-ray
photons and prevents the low energy X-ray photons
from leaving the X-ray tube.
 The aluminum disk is about 0.1 mm in thickness.
 Types of filtration
 1. Inherent
 2. Added
 3. Total.

4. 1.Inherent filtration :As the name suggests it is the filtration
offered by the design of the X-ray tube
Inherent filtration
• Takes place when the
primary beam passes
through the glass window of
the X-ray tube, the insulating
oil and the tube head seal.
• In the dental X-ray machines
the inherent filtration is
approximately equivalent to
0.5 to 1 mm of aluminum.
Added filtration
• Refers to the placement of
aluminum disks in the path
of the X-ray beam between
the collimator and the tube
head seal
• In the dental X-ray tube
head. Aluminum disks may
be added in 0.5 mm
increments

5. COLLIMATION
 A collimator is a metallic barrier with an aperture in the
middle used
 to reduce the size of the x-ray beam and thereby the volume
of irradiated tissue
 Dental x-ray beams are usually collimated to a circle 2 3/4
inches (7 cm) in diameter
 It is a lead plate with a central hole that fits directly over the
opening of the metal housing where the X-rays exit

7. FUNCTIONS OF THE COLLIMATOR
1.Reduces patient exposure by constricting the size of the
X-ray beam to the site that has to be exposed.
2. Prevents scattered radiation from reaching the film,
that add to film fog and thereby degrading the
diagnostic quality of the radiographic image

8. Types of collimators
1. Rectangular collimators
2. Diaphragm collimators
3. Tubular collimators

9.  Rectangular collimators further limit the size of the
beam to just larger than the x-ray film, thereby
further reducing patient exposure

11. THANK YOU…