ORAL & MAXILLOFACIAL
RADIOLOGY
DENTAL RADIATION
PHYSICS
DR.MOHAMMED R. SHAMIAH
MSC. ORAL & MAXILLOFACIAL SURGERY
INTRODUCTION
• X-rays and their ability to
penetrate human tissues were
discovered by Roentgen in
1895.
• He found shadow of his bone
on fluorescent screen.
• He called them X-rays
because their nature was then
unknown. Dr.Mohammed R. Shamiah 2
• They are in fact a form of high-energy
electromagnetic radiation and are part of
the electromagnetic spectrum, which also
includes low energy radiowaves, television
and visible light.
Dr.Mohammed R. Shamiah 3
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ATOMIC STRUCTURE
- Atoms are the basic building blocks
of matter.
- They consist of minute particles –
the so-called fundamental or
elementary particles – held
together by electric and nuclear
forces.
- They consist of a central dense
nucleus made up of nuclear
particles – protons and neutrons –
surrounded by electrons in specific
orbits or shells Dr.Mohammed R. Shamiah 6
DEFINITIONS
● Atomic number (Z) – The number of protons in the
nucleus of an atom
● Neutron number (N) – The number of neutrons in the
nucleus of an atom
● Atomic mass number (A) – Sum of the number of
protons and number of neutrons in an atom (A = Z + N)
● Isotopes – Atoms with the same atomic number (Z)
but with different atomic mass numbers (A) and hence
different numbers of neutrons (N)
● Radioisotopes – Isotopes with unstable nuclei which
undergo radioactive disintegration.
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X-RAY PRODUCTION
X-ray are produced in the machine.
X-ray interact with the patient.
Image is recorded in the x-ray plate.
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X-RAY PRODUCTION
X-rays are produced inside
machines called X-ray
generating equipment.
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THE X-RAY TUBE
• The X-ray generating part is referred to as the
tubehead , within which is a small evacuated glass
envelope called the X-ray tube.
• X-rays are produced inside the X-ray tube when
energetic (high-speed) electrons bombard the target
and are suddenly brought to rest.
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MAIN FEATURES AND REQUIREMENTS OF
AN X-RAY TUBE
● The cathode (negative) consists of a heated filament
of tungsten that provides the source of electrons.
● The anode (positive) consists of a tungsten target set
into the angled face of a large copper block to allow
efficient removal of heat.
● A focusing device aims the stream of electrons at
the focal spot on the target.
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● A high-voltage (kilovoltage, kV) connected between
the cathode and anode accelerates the electrons from
the negative filament to the positive target. This is
sometimes referred to as kVp or kilovoltage peak.
● A current (milliamperage, mA) flows from the cathode
to the anode. This is a measure of the quantity of electrons
being accelerated.
● A surrounding lead casing absorbs unwanted X-rays as a
radiation protection measure since X-rays are emitted in
all directions.
● Surrounding oil facilitates the R.removal
Dr.Mohammed Shamiah of heat. 14
PRACTICAL CONSIDERATIONS
The production of X-rays can be summarized as
the following sequence of events:
1. The filament is electrically heated and a cloud of
electrons is produced around the filament.
2. The high-voltage (potential difference) across the
tube accelerates the electrons at very high speed
towards the anode.
3. The focusing device aims the electron stream at the
focal spot on the target.
4. The electrons bombard the target and are brought
suddenly to rest.
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5. The energy lost by the electrons is transferred into
either heat (about 99%) or X-rays (about 1%).
6. The heat produced is removed and dissipated by
the copper block and the surrounding oil.
7. The X-rays are emitted in all directions from the
target. Those emitted through the small window in
the lead casing constitute the beam used for
diagnostic purposes.
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SUMMARY OF THE MAIN PROPERTIES
AND CHARACTERISTICS OF X-RAYS
● X-rays are wave packets of energy of electromagnetic
radiation that originate at the atomic level.
● Each wave packet is equivalent to a quantum of energy
and is called a photon.
● An X-ray beam is made up of millions of photons of
different energies.
● The diagnostic X-ray beam can vary in its intensity and in
its quality:
– Intensity = the number or quantity of X-ray photons in the
beam
– Quality = the energy carried by the X-ray photons which
is a measure of their penetrating power.
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● The factors that can affect the intensity and/or the
quality of the beam include:
– Size of the tube voltage (kV)
– Size of the tube current (mA)
– Distance from the target (d)
– Time = length of exposure (t)
– Filtration.
– Target material.
– Tube voltage waveform.
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INTERACTION OF X-RAYS WITH
MATTER
When X-rays strike matter, such as a patient’s tissues,
the photons have four possible fates, it may be:
● Completely scattered with no loss of energy.
● Absorbed with total loss of energy.
● Scattered with some absorption and loss of energy.
● Transmitted unchanged.
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DEFINITION OF TERMS USED IN X-RAY
INTERACTIONS
● Scattering – change in direction of a photon with or
without a loss of energy.
● Absorption – deposition of energy, i.e. removal of
energy from the beam.
● Attenuation – reduction in the intensity of the main X-
ray beam caused by absorption and scattering.
Attenuation = Absorption + Scattering
● Ionization – removal of an electron from a neutral
atom producing a negative ion (the electron) and a
positive ion (the remaining atom).
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DEFINITION OF TERMS USED IN X-RAY
INTERACTIONS
Primary radiation (Primary or useful beam):
- refers to the penetrating x-ray beam that is produced
at the target of the anode and that exits the
tubehead.
Secondary radiation :
- Refers to x-radiation that is created when the primary
beam interacts with matter. (Includes the soft tissues of
the head, the bones of the skull, and the teeth)
- Secondary radiation is less penetrating than primary
radiation.
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Scatter radiation:
- Is a form of secondary radiation and is the result of an x-
ray that has been deflected from its path by the
interaction with matter.
- Scatter radiation is deflected in all directions by the
patient’s tissues and travels to all parts of the patient’s
body and to all areas of the dental operatory.
- Scatter radiation is detrimental to both the patient and
the radiographer.
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PROPERTIES OF X-RAYS
• Appearance: X-rays are invisible and cannot be detected
by any of the senses.
• Mass: X-rays have no mass or weight.
• Charge: X-rays have no charge.
• Speed: X-rays travel at the speed of light. (3 × 108 ms)
• Wavelength: X-rays travel in waves and have short
wavelengths with a high frequency.
• Path of travel: X-rays travel in straight lines and can be
deflected, or scattered.
• Focusing capability: X-rays cannot be focused to a point
and always diverge from a point.
• Penetrating power: X-rays can penetrate liquids, solids and
gases. (According to the composition of
theDr.Mohammed
substance).
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• Absorption: X-rays are absorbed by matter;
(depends on the atomic structure of matter and the
wavelength of the x-ray).
• Ionization capability: X-rays interact with materials they
penetrate and cause ionization.
• Fluorescence capability: X-rays can cause certain
substances to fluoresce or emit radiation in longer
wavelengths (e.g., visible light and ultraviolet light).
• Effect on film: X-rays can produce an image on
photographic film.
• Effect on living tissues: X-rays cause biologic changes
in living cells. (ionization )
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- Wavelength (λ) is the distance between 2 crests or
bottoms of 2 successive waves.
- Frequency (ν) is the number of cycles or waves
emitted/sec.
- Wavelength x Frequency = Speed of wave
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•Thank you
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