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.
brief description about CONTENTS Introduction Principles of panoramic imaging Image layer Panoramic machines Panoramic film Patient positioning Interpreting the panoramic imaging INDICATION Advantages Disadvantages Conclusion References
3. INTRODUCTION • Panoramic imaging also called pantomography is a technique for producing a single tomographic image of facial structures that includes both the maxillary and mandibular dental arches and their supporting structures . • This is a curvilinear variant of conventional tomography.
4. PRINCIPLES OF PANORAMIC IMAGE FORMATION • Patero and Numata - describe the principles of panoramic radiography • based on the principle of reciprocal movement of x-ray source and an image receptor around a central point or plane called the image layer, in which the OBJECT of image is located. • OBJECT in front or behind this image are not clearly captured because of their movement relative to the centre of rotation of the receptor and the x-ray source.
5. The film and x-ray tubehead move around the patient in opposite directions in panoramic radiography
6. ROTATION CENTER The pivotal point or axis around which the cassette carrier and tube head rotate is termed rotation center Three basic rotation center used in panoramic radiography Double centre rotation Triple centre rotation moving centre rotation The location and number of rotational centers INFLUENCE size and shape of focal trough
7. IMAGE LAYER • Also known as focal trough • It is a three dimensional curved zone where the structures lying within this layer are reasonably well defined on final panoramic image. • The structures seen on a panoramic image are primarily those located within image layer. • OBJECTSoutside the image layer are blurred magnified are reduced in size. Even distorted to the extent of not being recognizable. • This shape of image layer varies with the brand of equipment used.
8. FOCAL TROUGH
9. FACTORS AFFECTING SIZE OF IMAGE LAYER: Arc path Velocity of receptor and X-ray tube head Alignment of x-ray beam Collimator width The location of image layer change with extensive machine used so recalibration may be necessary if consistently suboptimal images are produced. As a position of object is moved within the image layer size and shape of image layer change.
10. PANORAMIC UNIT
11. A, Orthophos XG Plus extraoral x-ray machine. B, Orthoralix 8500 extraoral x-ray machine. C, Example of a digital panoramic system
12. PARTS OF PANORAMIC UNITS a. x-ray tube head b. head positioner: chin rest notched bite block forehead rest lateral head support c. exposure controls
13. X-RAY TUBE HEAD: • Similar to intraoral x-ray tube head • Each has a filament to produce electrons and a target to produce x-rays • Collimator is a lead plate with narrow vertical slit • Narrow x-ray beam emerges from collimator minimize patient exposure to radiation
1
IDEAL IMAGE CHARACTERISTICS
FACTORS RELATED TO THE RADIATION BEAM
FACTORS RELATED TO THE OBJECT
FACTORS RELATED TO THE TECHNIQUE
FACTORS RELATED TO RECORDING OF THE ROENTGEN IMAGE OF THE OBJECT
DARK/ LIGHT IMAGE IDEAL IMAGE
IDEAL QUALITY CRIETRIA
X-rays are used in medicine for medical analysis. Dentists use them to find complications, cavities and impacted teeth. Soft body tissue are transparent to the waves. Bones also block the rays.
brief description about CONTENTS Introduction Principles of panoramic imaging Image layer Panoramic machines Panoramic film Patient positioning Interpreting the panoramic imaging INDICATION Advantages Disadvantages Conclusion References
3. INTRODUCTION • Panoramic imaging also called pantomography is a technique for producing a single tomographic image of facial structures that includes both the maxillary and mandibular dental arches and their supporting structures . • This is a curvilinear variant of conventional tomography.
4. PRINCIPLES OF PANORAMIC IMAGE FORMATION • Patero and Numata - describe the principles of panoramic radiography • based on the principle of reciprocal movement of x-ray source and an image receptor around a central point or plane called the image layer, in which the OBJECT of image is located. • OBJECT in front or behind this image are not clearly captured because of their movement relative to the centre of rotation of the receptor and the x-ray source.
5. The film and x-ray tubehead move around the patient in opposite directions in panoramic radiography
6. ROTATION CENTER The pivotal point or axis around which the cassette carrier and tube head rotate is termed rotation center Three basic rotation center used in panoramic radiography Double centre rotation Triple centre rotation moving centre rotation The location and number of rotational centers INFLUENCE size and shape of focal trough
7. IMAGE LAYER • Also known as focal trough • It is a three dimensional curved zone where the structures lying within this layer are reasonably well defined on final panoramic image. • The structures seen on a panoramic image are primarily those located within image layer. • OBJECTSoutside the image layer are blurred magnified are reduced in size. Even distorted to the extent of not being recognizable. • This shape of image layer varies with the brand of equipment used.
8. FOCAL TROUGH
9. FACTORS AFFECTING SIZE OF IMAGE LAYER: Arc path Velocity of receptor and X-ray tube head Alignment of x-ray beam Collimator width The location of image layer change with extensive machine used so recalibration may be necessary if consistently suboptimal images are produced. As a position of object is moved within the image layer size and shape of image layer change.
10. PANORAMIC UNIT
11. A, Orthophos XG Plus extraoral x-ray machine. B, Orthoralix 8500 extraoral x-ray machine. C, Example of a digital panoramic system
12. PARTS OF PANORAMIC UNITS a. x-ray tube head b. head positioner: chin rest notched bite block forehead rest lateral head support c. exposure controls
13. X-RAY TUBE HEAD: • Similar to intraoral x-ray tube head • Each has a filament to produce electrons and a target to produce x-rays • Collimator is a lead plate with narrow vertical slit • Narrow x-ray beam emerges from collimator minimize patient exposure to radiation
1
IDEAL IMAGE CHARACTERISTICS
FACTORS RELATED TO THE RADIATION BEAM
FACTORS RELATED TO THE OBJECT
FACTORS RELATED TO THE TECHNIQUE
FACTORS RELATED TO RECORDING OF THE ROENTGEN IMAGE OF THE OBJECT
DARK/ LIGHT IMAGE IDEAL IMAGE
IDEAL QUALITY CRIETRIA
X-rays are used in medicine for medical analysis. Dentists use them to find complications, cavities and impacted teeth. Soft body tissue are transparent to the waves. Bones also block the rays.
IT REVIEWS Introduction and definition INTRODUCTION
BEAM-RESTRICTING DEVICES
ADVANTAGES AND DISADVANTAGES
TECHNIQUE
FILTERS
AND PHYSICS BEHIND IT AND LIGHT AND MIRROR ARRANGMENT CLEARLY EXPLAINED WELL.IT ALSO INCLUES THE FLITERS CLASSIFICATION AND COLLIMATORS CLASSIFICATION.
COLLIMATIORS ARE NOTHING BUT BEAM ALINERS
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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.
5.
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.
9. Fig. comparison of excess radiation area using cylindrical &
rectangular collimators.
10.
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.
