Transcript X rays

ORAL
RADIOLOGY
Radiation Physics
Ionization
 When the number of electrons in an atom is
equal to the number of protons in its nucleus
,the atom is electrically neutral.
 If such atom loses an electron ,the nucleus a
becomes positive ion & the free electron a
negative ion.
 This process of forming an ion pair is termed
ionization.
Ionization
 To ionize an atom requires sufficient energy
to overcome electrostatic force binding the
electrons to nucleus.
 The binding energy of an electron is related
to the atomic number of the atom & the
orbital type.
 Electron in in the inner orbitals are more tightly
bound than the more distant outer orbitals.
 Tightly bound electrons requires the energy of xrays or high energy particles to remove them,
whereas loosely bound electrons can be displaced
by ultraviolet radiation.
 However non ionizing radiation,
such as visible light, infrared,
& microwave radiation , &
radio waves do not have
sufficient energy to remove
bound electrons from their
orbitals.
Nature of Radiation
 Radiation is the transmission
of energy through space &
matter.
 Radiation occur in 2 forms:
I-particulate .
II-electromagnetic.
RADIOACTIVITY
 Small atoms have roughly equal numbers
of protons & neutrons.
 Larger atoms tend to have more neutrons
than protons. This makes them unstable &
they may brake up, releasing α or β or γ
rays. This process called radioacvtivity.
 PRTICULATE RADIATION
 Alpha particles α are helium nuclei consisting
of 2 protons & 2 neutrons. They result from
the radioactive decay of many large atomic
numbers like uranium, thorium, actinium, and
radium.
 Because of their double positive charge &
heavy mass , α particles densely ionize
matter through which they pass.
 These particles quickly give up their energy
& penetrate only a few micrometers of
body tissue (an ordinary sheet of paper
absorbs them).
 After stopping α particles acquire 2
electrons & become neutral helium atom.
 Beta particles β
 When a neutron in a radioactive nucleus decay, it
produces a proton, β particle. These β particles are
identical to electrons.
Feynman diagram
 High-speed β particles are not densely
ionizing : thus, they are able to penetrate
matter to a greater depth than α particles
can , up to a maximum of 1.5 cm in tissue.
 This deeper penetration occurs because β
particles are smaller & lighter & carry a
single negative charge.
 β particles are used in radiation therapy for
treatment of some skin cancers.
ELECTROMAGNETIC RADIATION
 Is the movement of energy through space
as a combination of electric & magnetic
fields.
 It is generated when the velocity of an
electrically charged particle is altered.
 Gamma ( γ ) rays , x rays , ultraviolet rays,
visible light, infrared radiations (heat),
microwaves, radio waves are all examples
of electromagnetic radiation.
ELECTROMAGNETIC SPECTRUM
 Gamma rays originate in the nuclei of radioactive
atoms. They typically have greater energy than do x
rays.
 X rays are produced extranuclearly from the
interaction of electrons with large atomic nuclei in
x ray machines.
 Quantum theory considers electromagnetic
radiation as a small bundles of energy called
photons. Each photon travels at the speed of light
& contains a specific amount of energy.
 The unite of photon energy is the electron volt
( eV ).
 High energy photons such as γ rays & x rays are
typically characterized by their energy ( electron
volts).
 Medium energy photons ( e.g., visible light &
ultraviolet waves ) characterized by their wave
length ( nanometers ).
 Low energy photons ( e.g., AM & FM radio waves )
characterized by their frequency (KHz & MHz)
X-RAY MACHINE
 The primary components of x-ray machine
are x-ray tube & its power supply.
Tube head
X-RAY TUBE
 An x-ray tube is composed of a cathode
& an anode situated within an evacuated
glass envelope or tube.
 Power supply is required to :1-heat the
cathode filament to generate electrons.
2-establish a high-voltage potential
between the anode & cathode to
accelerate the electrons toward the
anode.
Cathode
 Cathode consists of a filament & a
focusing cup.
 The filament lies in a focusing cup & it is
the source of electrons within x-ray tube
 The parabolic shape of the focusing cup
electrostatically focuses the electrons
into a narrow beam directed at a small
rectangular area on anode called focal
spot.
X-ray tube
X-ray tube
Anode
 The anode consists of tungsten
target embedded in a cupper
stem.
 The purpose of the target is to
convert the kinetic energy of
colliding electrons to x-ray
photons.
 The target material is made of tungsten,
an elements that has several
characteristics of an ideal target
material . It has :

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High atomic number (74).
High melting point .
High thermal conductivity.
Low vapor pressure at working temperatures
of x-ray tube .
 More than 99% of the kinetic energy of the
electrons converted to heat & only 1% of
this energy converted to x-ray.
 A target made of high atomic number
material is most efficient in producing x-rays.
 Because heat is generated at the anode,
there is a requirement for a target of a high
melting point is clear.
X-ray tube
Focal spot
 Is the area on target to which the focusing
cup directs the electrons & from which x-rays
are produced.
 The sharpness of a radiographic image
increases as the size of focal spot decreases .
 The target is inclined about 20 degrees to the
central ray of the x-ray beam, this causes the
effective focal spot to approximately 1 x 1
mm.
POWER SUPPLY
The primary function of power supply :
1-provide a low voltage current to heat
the x-ray tube filament.
2-generate a high potential difference
between the anode & cathode.
Tube current
 Is the follow of electrons through the tube, from
the cathode filament, across the tube to the
anode & then back to the filament.
 The mA setting on the filament current control
actually refers to the tube current, typically 10
mA, which is measured by the milliammeter .
 The tube current is dependant on the tube
voltage : as the voltage increases between the
anode & cathode , so does the current flow.
Tube voltage
 A high voltage is required between the anode
& cathode to give electrons sufficient energy to
produce x-ray.
 The actual voltage is adjusted with the
autotransformer.
 The best tube voltage is as high as 60 to 100
kVp to boost the peak energy of electrons &
provides them sufficient energy to produce xray.
 By using the kilovolt peak ( kVp ) selector,
the operator adjusts the autotransformer
& converts the primary voltage from input
source into desired secondary voltage.
Timer
 A timer is built into the high voltage
circuit to control the duration of x-ray
exposure.
 The electronic timer controls the length
of time that high voltage is applied to
the tube & therefore the during which
the tube current flows & x-rays are
produced.
CHAPTER 2
RADIOBIOLOGY
Radiobiology : is the study of the
effects of ionizing radiation on living
systems.
Radiation Causes Ionizations of:
ATOMS
which may affect
MOLECULES
which may affect
CELLS
which may affect
TISSUES
which may affect
ORGANS
which may affect
THE WHOLE BODY
 The initial interaction between ionizing radiation
and matter occurs at the level of the electron
within the first 10-13 second after exposure.
 These changes result in modification of biologic
molecules within the ensuing seconds to hours.
 In turn, the molecular changes may lead to
alterations in cells and organisms that persist for
hours, decades, and possibly even generations.
 These changes may result in injury or death.
 Radiation Chemistry
 Radiation acts on living systems
through direct and indirect effects.
 When the energy of a photon or
secondary electron ionizes biologic
macromolecules, the effect is termed
direct effect.
 Alternatively, a photon may be absorbed by
water in an organism, ionizing some of its
water molecules.
 The resulting ions form free radicals
(radiolysis of water) that in turn interacts and
produce changes in biologic molecules.
 Because intermediate changes involving water
molecules are required to alter the biologic
molecules, this series of events is termed
indirect effect.
 DIRECT EFFECT
 If radiation interacts with the atoms of the
DNA molecule, or some other cellular
component critical to the survival of the cell, it
is referred to as a direct effect.

Such an interaction may affect the ability of
the cell to reproduce and, thus, survive.
 If enough atoms are affected such that the
chromosomes do not replicate properly, or if
there is significant alteration in the information
carried by the DNA molecule,
 then the cell may be destroyed by “direct”
interference with its life-sustaining system.
 Approximately
one third of the biologic
effects of x-ray exposure result from direct
effects.
 However, direct effects are the most common
outcome for particulate radiation such as
neutrons and α particles.
 INDIRECT EFFECTS
 If a cell is exposed to radiation, the probability of the
radiation interacting with the DNA molecule is very
small since these critical components make up such a
small part of the cell.

However, each cell, just as is the case for the human
body, is mostly water(about 70% by weight).
 Therefore, there is a much higher probability of
radiation interacting with the water that makes up
most of the cell’s volume.
 About two thirds of radiation-induced biologic
damage results from indirect effects.
 When radiation interacts with water, it may
break the bonds that hold the water molecule
together, producing fragments such as hydrogen
(H) and hydroxyls (OH).
 These fragments may recombine or may interact
with other fragments or ions to form
compounds, such as water, which would not
harm the cell.
 However, they could combine to form toxic
substances, such as hydrogen peroxide (H2O2),
which can contribute to the destruction of the
cell.
 CHANGES IN DEOXYRIBONUCLEIC ACID
 Damage to a cell ’ s deoxyribonucleic acid (DNA) is the
primary cause of (1) radiation-induced cell death, (2)
heritable (genetic) mutations, and (3) cancer formation
(carcinogenesis).
 Radiation produces a number of different types of
alterations in DNA, including the following:
1-Breakage of one or both DNA strands
2-Cross-linking of DNA strands within the helix to other
DNA strands or to proteins
3-Change or loss of a base
4- Disruption of hydrogen bonds between DNA strands
Radiosensitivity of various cells
Not all living cells are equally sensitive to radiation.
Those cells which are actively reproducing are
more sensitive than those which are not.
This is because dividing cells require correct DNA
information in order for the cell’s offspring to
survive.
 A direct interaction of radiation with an active cell
could result in the death or mutation of the cell,
As a result, living cells can be classified according to
their rate of reproduction, which also indicates
their relative sensitivity to radiation.
This means that different cell systems have different
sensitivities.
 Lymphocytes (white blood cells) and cells which
produce blood are constantly regenerating, and
are, therefore, the most sensitive.
 Reproductive and gastrointestinal cells are not
regenerating as quickly and are less sensitive.
 The nerve and muscle cells are the slowest to
regenerate and are the least sensitive cells.
Cellular effects of radiation
 Cells, like the human body, have a tremendous
ability to repair damage.
 As a result, not all radiation effects are
irreversible.

In many instances, the cells are able to
completely repair any damage and function
normally.
 If the damage is severe enough, the affected cell
dies.
 In some instances, the cell is damaged but is still
able to reproduce.
 The daughter cells, however, may be lacking in
some critical life-sustaining component, and they
die.
The other possible result of radiation exposure is
that the cell is affected in such a way that it does
not die but is simply mutated.
The mutated cell reproduces and thus remains the
mutation. This could be the beginning of a
malignant tumor
Cellular effects of radiation
Radiosensitivity of organs
 The sensitivity of the various organs of the human
body correlate with the relative sensitivity of the cells
from which they are composed.
 For example, since the blood forming cells were
one of the most sensitive cells due to their rapid
regeneration rate, the blood forming organs are
one of the most sensitive organs to radiation.
 Muscle and nerve cells were relatively insensitive
to radiation, and therefore, so are the muscles and
the brain.
 RADIATION EFFECTS ON EMBRYOS AND
FETUSES
 Embryos and fetuse are considerably more
radiosensitive than adults because most
embryonic cells are relatively undifferentiated
and rapidly mitotic.
 Exposures in the range of 2 to 3 Gy during the
first few days after conception are thought to
cause undetectable death of the embryo.
 .
 The cells in the embryo are dividing rapidly
and are highly sensitive to radiation.
 Lethality is common and many of these
embryos fail to implant in the uterine wall.
 The first 15 weeks includes the period of
organogenesis when the major organ systems
form
 The most common abnormalities among the
Japanese children exposed early in gestation
were: Reduced growth that persists through life and
reduced head circumference (microcephaly),
often associated with mental retardation.
 Other abnormalities included small birth size,
cataracts, genital and skeletal malformations,
and microphthalmia.
 The period of maximal sensitivity of the brain is 8 to
15 weeks after conception.
 The frequency of severe mental retardation after
exposure to 1 Gy during this period is about 43%.
 These effects are believed to have a threshold of
about 0.1 to 0.2 Gy.
 This threshold dose is 400 to 800 times higher than
the exposure from a dental examination (0.25 mGy
from a full-mouth examination when a leaded apron
is used).
 CARCINOGENESIS
 Radiation causes cancer by modifying DNA. The most
likely mechanism is radiation-induced gene mutation.
 Most investigators think that radiation acts as an
initiator, that is, it induces a change in the cell so that
it no longer undergoes terminal differentiation.
 Evidence also exists that radiation acts as a promoter,
stimulating cells to multiply.
 Finally, it may also convert premalignant cells into
malignant ones, for instance, conversion of protooncogenes to oncogenes.
Balanced diet

Imagine that, every time you breath, free radicals are formed. This
process of oxidation is similar to what you see when metal rusts or
an apple slice turns brown from exposure to air. Once again, your
body can defend against normal levels of free radicals, but if you
exercise intensely, live in a polluted area, or have a stressful life, as
most of you and your students do, then supplementing your diet
with antioxidants may be of great value.

A well balanced diet with plenty of fruits and vegetables is
important and will help, but alone it’s just not enough. Factory
processing, additives and pesticides all work to destroy antioxidants
within our foods and nutrient depleted soils no longer provide us
with the nutrient rich foods that our grandparents enjoyed.

The following list of antioxidants play an important role in free
radical protection, especially for the active athlete: Vitamin C,
Vitamin E, Vitamin A, selenium, coenzyme Q10 and glutathione.

Eating a well balanced diet and a taking strong MultiVitamin/Mineral/Antioxidant Supplement each day should be
considered for adequate antioxidant protection and to promote
optimum performance and long-term health