Transcript Basic Concept in Radiologic Physics

Basic Concept in Radiologic Physics
IONIZATION PROCESS
REMOVAL OF AN ELECTRON FROM AN
ATOM
Ionization
SOURCES OF IONIZING RADIATION
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COSMIC
TERRESTRIAL
INTERNAL
MEDICAL X-RAYS
NUCLEAR MEDICINE
CONSUMER PRODUCTS
NUCLEAR POWER---INDUSTRIAL
NATURAL ENVIRONMENTAL
RADIATION
• COSMIC
• TERRESTRIAL
• INTERNAL
MAN MADE IONIZING RADIATION
SOURCES
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MEDICAL X-RAYS
NUCLEAR MEDICINE
CONSUMER PRODUCTS
NUCLEAR POWER---INDUSTRIAL
THE CONTRIBUTION OF VARIOUS SOURCES TO
THE AVERAGE US POPULATION RADIATION DOSE
Cosmic Radiation
The earth’s atmosphere is
bombarded by high-energy
particles from our galaxy
(primary cosmic radiation). In
the upper atmospheric layers,
these particles react with air
molecules. As a result of
nuclear reactions, a great
number of secondary particles
(secondary cosmic radiation) is
formed. Some of these
secondary particles decay
again, are absorbed in the
atmosphere or possibly
penetrate into the earth.
Terrestrial Radiation – Radon is the Largest
Source
RADON MOVEMENT
RADON INTERNAL EXPOSURE
RADON EXTERNAL EXPOSURE
RADON EMITS ALPHA PARTICLE
Internal Radiation
In addition to the cosmic and terrestrial sources,
all people also have radioactive potassium-40,
carbon-14, lead-210, and other isotopes inside
their bodies from birth. The variation in dose
from one person to another is not as great as
the variation in dose from cosmic and terrestrial
sources.
Man-made radiation sources that result in
an exposure to members of the public:
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Tobacco
Televisions
Medical X-rays
Smoke detectors
Lantern mantles
Nuclear medicine
Building materials
Nuclear power plants
By far, the most significant source of man-made radiation exposure to the public is from
medical procedures, such as diagnostic X-rays, nuclear medicine, and radiation therapy.
Some of the major isotopes would be I-131, Tc-99m, Co-60, Ir-192, Cs-137, and others.
In addition, members of the public are exposed to radiation from consumer products, such
as tobacco (thorium), building materials, combustible fuels (gas, coal, etc.), ophthalmic glass,
televisions, luminous watches and dials (tritium), airport X-ray systems, smoke detectors
(americium), road construction materials, electron tubes, fluorescent lamp starters, lantern
mantles (thorium), etc.
Of lesser magnitude, members of the public are exposed to radiation from the nuclear fuel
cycle, which includes the entire sequence from mining and milling of uranium to the actual
production of power at a nuclear plant. This would be uranium and its daughter products.
The final sources of exposure to the public would be shipment of radioactive materials and
residual fallout from nuclear weapons testing and accidents, such as Chernobyl.
Debate still persists as to who was the first to discover
X-rays. Was it the Ukrainian scientist Jan Puluj (Ivan
Puliui) or a German physicist Wilhelm Conrad
Roentgen, the 1901 Nobel Prize winner?
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The lives of both physicists are connected with Strasbourg
University. In the 1890s both Messrs. Roentgen and Puliui
worked in the same department under the guidance of
Prof. Kundt, and Mr. Roentgen made a point of attending
lectures given by Mr. Puliui. While at Strasbourg, Mr.
Puliui commenced his experiments with X-rays, and Mr.
Roentgen was soon to become fascinated by these
phenomena.
Puluj tube
Phosphorescent tube acc. to Puluj, 1870.
Through his experiments into the nature of "cold light," Mr. Puliui
invented an X-ray emitting device as early as 1881. The tubes of
this invention became known as the "Pului lamp" and were massproduced for a period. Mr. Puliui personally presented one of them
to Mr. Roentgen. And it was Mr. Puliui, not Mr. Roentgen, who first
demonstrated an X-ray photograph of a 13-year-old boy's broken
arm and an X-ray photograph of his daughter's hand with a pin
lying under it. A couple of years later, Mr. Roentgen was to publicly
repeat the same experiments, but in doing so did not once credit
Mr. Puliui's role in this discovery.
Wilhelm Conrad Röntgen. While working with a Crookes tube, a plate of
Barium Platino-Cyanide (fluorescent crystals) on a table six feet away in his
workroom glowed when he activated the tube. Even after covering the tube
with black cardboard it kept glowing. He concluded that a new type of ray
emitted from the tube, passed through the covering, and casted shadows of
solid objects. The rays passes through most substances, including the soft
tissues of the body, but left the bones and most metals visible. One of his
earliest photographic plate from his experiments was a film of his wife,
Bertha's hand with a ring, was produced on Friday, November 8, 1895
On New Kind of Rays
The news of Roentgen’s discovery spread quickly
throughout the world. Scientists everywhere could
duplicate his experiment because the cathode tube was
very well known during this period. In early 1896, X-rays
were being utilized clinically in the United States for such
things as bone fractures and gun shot wounds.
Internal structures of the body could be
made visible without the necessity of
surgery.
Roentgen discovered x-rays while experimenting with the Crookes tube. Crookes tube
had almost a complete vaccum inside, in addition. It had a positive electrode (anode)
which served as a target for electrons and the negative one (cathode) which served as
a source of electrons. Unlike Coolidge tube it had a cold cathode. When high potential
difference (kVp) was created between a cathode and anode, electrons rushed from a
cathode and smashed in the anode. Upon collision with an anode or target they lost
their kinetic energy. As a result of it, their loss of kinetic energy was transformed into
the electromagnetic energy: x-rays and heat. An x-ray production process is a very
inefficient process, in the midium range kVp (70 -80) kinetic energy of electrons is
converted to more than 99% of heat and less than 1% of x-rays. In 1913 Dr. Coolidge
invented an x-ray tube with a hot cathode. In that tube cathode was heated to liberate
electrons necessary for the trip towards anode. This liberation process of electrons is
called thermionic emission. The figure in the next slide demonstrates the x-ray
production process in the Coolidge tube
X-rays characteristics
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Highly penetrating, invisible rays
Electrically neutral
Travel in straight lines.
Travel with the speed of light in vaccum:
300, 000 km/sec or 186, 400 miles/sec.
• Ionize matter by removing orbital electrons
• Induce fluorescense in some substances. Fluorescent screen
glow after being stricken with photons.
• Can't be focused by lenses nor by collimators.
light
X-rays
http://www.spineuniverse.com/videos/x-rays/
kVp - kilovolt peak: Thousands of volts of electric
potential applied accross cathode and anode. In a
diagnostic radiology this potential ranges from 50 -150
kVp ( excluding mammography.) Anode is highly positively
charged electrode and attracts the electrons. The higher
the kVp, the faster the electrons travel from cathode to
anode, as a result, the electromagnetic photons have
higher energy. Consequently, kVp controls the energy (
quality) of an x-ray beam, not the speed of photons.
Speed of photons is constant.
Low kVp
High kVp
mA
mA - milliamperage: Number of
electrons traveling from cathode to
anode. mA describes x-ray tube current.
Low mA
High mA
CONVENTIONAL RADIOGRAPHY
PRODUCES STATIC IMAGES
FLUOROSCOPE WAS INVENTED BY
THOMAS EDISON
Fluoroscopy is an imaging technique commonly used by
physicians to obtain real-time moving images of the internal
structures of a patient through the use of a fluoroscope. In its
simplest form, a fluoroscope consists of an x-ray source and
fluorescent screen between which a patient is placed.
However, modern fluoroscopes couple the screen to an x-ray
image intensifier and CCD video camera allowing the images
to be recorded and played on a monitor.
FIRST X-RAY FATILITY IN THE US
CLARENCE DALLY
OTHER INVENTIONS IN
RADIOGRAPHY
•INTENSIFYING SCREENS
•COLLIMATION
•FILTRATION
•DOUBLE EMULSION FILM
X-rays are highly penetrative rays that can ionize
matter by removing electrons from the atoms. Are they
harmful? Yes, they are. Nevertheless, radiography is
considered a safe profession? Despite the fact that xrays are harmful radiography is considered a safe
profession. In order to understand this we must explain
principles of the ALARA concept
"ALARA" is an acronym for "As Low As Reasonably
Achievable". ALARA is a basic radiation protection
concept or philosophy. It is an application of the "Linear
No Threshold Hypothesis," which assumes that there is
no "safe" dose of radiation. Under this assumption, the
probability for harmful biological effects increases with
increased radiation dose, no matter how small.
Therefore, it is important to keep radiation doses to
affected populations (for example, radiation workers,
minors, visitors, students, members of the general
public, etc.) as low as is reasonably achievable.
ALARA
• Time
• Distance
• Shielding
Shielding