Transcript Sources in diagnostic Rad. – Dental Radiology - gnssn

Radiation Sources in medicine
diagnostic Radiology
Dental Radiology
IAEA
International Atomic Energy Agency
Day 7 – Lecture 2(2)
Objective
• To become familiar with dental x-ray systems.
• To become familiar with specific radiation risks associated
with this equipment.
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Contents
• Description and characteristics of equipment for intra-oral
radiography.
• Description and characteristics of equipment for panoramic
radiography.
• Description and characteristics of equipment for
cephalometric radiography.
• Equipment malfunction affecting radiation protection.
• Minimum requirements for routine maintenance.
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Dental X-ray Equipment
• Dental radiography is one of the most common x-ray
examinations in the industrialized world.
• Although individual radiation doses and risks are low,
many extensive examinations are performed in younger
age groups.
• As for other radiological procedures, patient doses can
be significantly influenced by the equipment and
techniques used and the quality assurance measures in
place.
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Dental X-ray Equipment (cont)
Different types of equipment are used depending on the type of
image required. e.g.
•
x-ray equipment for intra-oral radiography uses small intraoral non-screen x-ray films for bitewing or periapical
radiography;
•
equipment for panoramic tomographic radiography uses a
narrow fan shaped x-ray beam (~5-10 mm wide and 150 mm
high) which rotates around different axes within the patient’s
head to provide a defined image of the plane of the dental
arch. Other unwanted structures are deliberately blurred
during this process.
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Dental X-ray Equipment (cont)
Intraoral x-ray
examination
FILM HOLDER AND
POSITIONING DEVICE
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Specific Requirements for Intraoral Equipment
• The operating tube voltage should be at least 60 kV peak.
• The filtration in the useful beam should be equivalent to at
least 1.5 mm Al at x-ray tube voltages up to 70 kV peak and
2.5 mm if greater than 70 kV peak.
• X-ray tube focus to skin distances of 200 mm or greater are
recommended.
• The diameter of the x-ray beam should not be greater than
60 mm at the outer end of the beam applicator.
• Rectangular collimation is recommended.
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Specific Requirements for Intraoral Equipment (cont)
• The fastest films consistent with the required clinical results
should be used.
• Whenever practicable, film holders incorporating beam
aiming devices should be used.
• On new equipment, manufacturers should provide a range
of x-ray outputs and exposure times so that different speed
image receptors (faster film and digital image receptors)
can be correctly exposed.
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Dental X-ray Equipment (cont)
Older “pointer cone” equipment. Open ended collimation (right)
should be used
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Specific Requirements for Panoramic Equipment
•
The rotation of the x-ray tube around the head that provides the
tomographic image of the entire dental arch must be precise
and reproducible.
•
Patient positioning devices should be simple, reliable and
accurate.
•
A fast intensifying screen / film combination (or comparable
speed image receptors) should be used.
•
All new equipment should incorporate a range of radiographic
exposures consistent with clinical requirements, the patient’s
build (i.e. adults, children) and the speed of the image receptor.
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Dental X-ray Equipment (cont)
Panoramic tomographic
x-ray equipment
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Dental X-ray Equipment (cont)
Panoramic tomographic
x-ray equipment patient positioning
devices
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Dental X-ray Equipment (cont)
For orthodontic analysis (the diagnosis and treatment of
dental disorders), two techniques are routinely employed:
• cephalometry, which provides
reproducible images of the skull,
dentition and facial profile including the
soft tissue;
• CT examinations
(dedicated dental Cone
Beam CT (CBCT)
scanner).
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Image development
Improper x-ray film development is a significant cause of
unnecessary patient exposure and reduced film quality.
140
120
Bitewing exposures
Sample size
651
Mean dose (mGy)
3.14
100
Number
This survey of
bitewing doses
indicates problems
with film development.
80
60
40
Doses should range
from 2.5 to 3.0 mGy
(without back scatter).
20
0
0
1
2
3
4
5
6
7
8
9
10
mGy (air kerma at skin entrance surface)
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Radiological Council, Western Australia 2000 Annual Report
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Malfunctions affecting radiation protection
Basically the same as for general x-ray system (see modules 2.1, 2.2
and 2.3) but the tests performed and the measuring instruments used
shall be adapted to the particular characteristics of the dental system
under investigation: e.g.
•
inaccuracy and inconsistency of the x-ray tube voltage and
radiation output;
•
inaccurate or defective timer;
•
misalignment between the x-ray beam and the image receptor;
•
unsatisfactory film storage conditions, image development and
viewing conditions.
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