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Principles of Nuclear
Medicine
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THE ATOM
The nucleus has protons and
neutrons.
Protons are positively chargedparticles.
Neurons are particles without charge.
Electrons orbit the nucleus in
precisely defined shells and sub-
shells.
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Atomic StructureAtomic Structure
Atom is smallest partAtom is smallest partof element thatof element thatretains chemicalretains chemicalproperties of thatproperties of that
elementelement Atoms are neutralAtoms are neutral
(no charge),(no charge),
but are divisible intobut are divisible intosmaller elementarysmaller elementaryor fundamentalor fundamental
particlesparticles
Not to scaleNot to scale
NucleusNucleus
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Atom anatomy
ElectronProton Neutron
Nucleons
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The Atom
The symbol X is given to any atom.
A is the atomic mass number which is
the total number of protons and neutrons.
Z is the atomic number which is the
number of protons. Atomic number defines
the atom.
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Atomic ShorthandAtomic Shorthand
II131131535353 Protons + 78 Neutrons = 131 Nucleons53 Protons + 78 Neutrons = 131 Nucleons
XXAA
ZZ
Atomic MassAtomic Mass
Atomic NumberAtomic Number
ElementElement
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ISOTOPES
If proton number Z changes, the atom
will change (different element).
If neutron number change, the element will
be the same, but we will have isotopes.
By definition; all isotopes of a given
element have the same number of protons
and differ only in the number of neutrons.
Example: 53I123, 53I125, 53I131.
N l F ili d
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Nuclear Families anduc ear am es an
NomenclatureNomenclature
CC1212
66CC
1313
66CC
1414
66
Same number ofSame number of PProtons = Isotorotons = Isotoppeses
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Radioactive Isotopes
Some isotopes are stable (non-
radioactive).
Some isotopes are unstable (radioactive).
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UNSTABILITY AND DECAY
Unstable isotope seeks greater stability by
some kind of radiation (decay).
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Isotopes
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Half-Life
The time required for half of the
radioactive isotope to undergo decay is
called the half-life.
After 4 half-life's, the residual activity
would be 6.25% of original activity, which
means there is no significant activity left.
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Types of Radiation
Particulate:
Emission of beta particles (electrons)
The isotope is converted into different element.
Photonic (electromagnetic) : gamma ray
and x-ray
Emission of photons (gamma ray or x-ray)
The isotope does not change.
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Types of radiation
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Decay of Radioactive
Isotopes (electron emission)
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Single Step RadioactiveSingle Step Radioactive
DecayDecay
II131131
5353
XeXe131131
5454(stable)(stable)
(unstable)(unstable)
.
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Decay of Radioactive Isotopes
(photon emission)
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Photons
Photon is electromagnetic wave.
It is part of electromagnetic spectrum.
Photons are used in imaging inradiology (conventional radiography
and CT scanning) and in nuclear
medicine.
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101033 101022 101011 1010--11 1010--22 1010--33 1010--44 1010--22 1010--33 1010--44 1010--55 1010--66 1010--77 1010--88 1010--99 1010--1010
Radio/TVRadio/TV InfraredInfrared
VisibleVisible
UVUV XX--raysrays
GammaGamma
Wavelength (m)Wavelength (m)
4,000A4,000A7,000A7,000A
Electromagnetic SpectrumElectromagnetic Spectrum
Frequency (Hz)Frequency (Hz)
101055 101066 101077 101088 101099 1010101010101111 10101212 1010131310101414 10101515 10101616 1010171710101818 1010191910102020
Visual
Imaging
MRIX-ray
Imaging
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Electromagnetic radiation
GAMMA
VISIBLE X-RAYS COSMIC
INFRARED ULTRAVIOLET
MICROVAVES
TV,
RADIO Decreasing wave length
Increasing frequency
Increasingphoton energy
IONIZING
RADIATON
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X-Ray and Gamma Ray
X-ray is emitted from outside the nucleus
(electron shells).
Gamma ray is a photon emitted form some
isotopes in the process of their decay.
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XX--rays andrays and
gammagammaraysrays
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Ionizing Radiation
Radiation causes ionization of atoms andmolecules.
Ionization is the underlying mechanism for
most radiation detectors and also isresponsible for most radiobiologicaleffects.
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Biological Effect of Radiation
Why should we protect ourselves from
radiation?
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Radiation Effects at the Molecular
Level - Direct Action
Direct molecular
absorption of
energy
DNA most
susceptible
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DNA lesions and chromosome
aberrations
DNA SNGLE
STRAND BREAK
DNA DOUBLE
STRAND BREAK
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Indirect Action-Radiolysis of Water
IonizationDissociation
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Free Radical Biological Damage
Cause damage to(DNA/RNA) which
become non-
functional
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Somatic Effects
Acute or early (deterministic) within days
dose dependent
Seen in accidents and nuclear wars
Affects acutely bone marrow, GI tract andskin and less neurological system.
Latent or delayed (stochastic).
not seen for years
cancer, cataract, shortened life span
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Principals of Radiation Protection
Time
Distance
Shielding
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TIME
The total radiation exposure to anindividual is directly proportional to the
time he is exposed to the source.
Therefore, it is wise to spend no moretime than necessary near the source of
radiation.
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DISTANCE
The intensity of radiation from a sourcevaries inversely with the square of the
distance.
Therefore, radiation workers shouldmaximize the distance between
themselves and the radiation source.
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Shielding
Lead is most commonly used to shield photonsin diagnostic imaging.
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560 mGy/h
1 mGy/h
2 mm lead
Vial Shields
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Nuclear Medicine Imaging
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Technetium 99m (Tc 99m)
It is the main isotope used in nuclear
medicine imaging. It is used in more than
70-80% of cases.
It emits gamma ray only.
Its half life is 6 hours.
It can easily label different kind of
pharmaceuticals.
It is always given intravenously.
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Radiopharmaceuticals
Pharmaceuticals are chemical compoundsthat have pharmacokinetics but do nothave pharmacological effects.
They are usually labeled with Tc99m. For each organ there is certain
radiopharmaceuticals
In general, nuclear medicine images thefunction (physiology), not the anatomy asin conventional radiology.
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Pharmaceutical
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Different Phrmaceuticals
R di l b li f Gl ith
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Radio-labeling of Glucose with
radioactive Flourine-18
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The Gamma Camera
It is a device that uses gamma rays to
make an image of radiopharmaceutical
distribution and uptake in patients.
Its crystal has a chemical propriety that if it
is hit by a photon it will scintillate.
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Nuclear ImagingNuclear Imaging
Not enough to detect just radioactive levelsNot enough to detect just radioactive levels
or concentrationsor concentrations
Need device to map the radioactiveNeed device to map the radioactive
distributiondistribution
External Radiation Detector
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Gamma camera-cont..
Scintillation means light production.
The light is converted into electrical
current which then is stored in the
computer as a dot.
S i till ti f G C
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Scintillation of Gamma Camera
Crystal
Gamma Ray
Light
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Gamma Camera Crystal (B)Gamma Camera Crystal (B)
NaINaI(Tl)(Tl)
1/41/4 -- 1/21/2**** thickthick
3/8 most popular3/8 most popular
1010-- 21 in diameter21 in diameter rectangular popularrectangular popular
Sensitive toSensitive tomoisture andmoisture and
temperaturetemperature
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Gamma CameraGamma Camera
StaticStaticImageImage
DyamicDyamicAcquisitionAcquisition
ImagesImages
MobileMobile
CameraCameraStationary DualStationary DualHead CameraHead Camera
Stationary SingleStationary SingleHead CameraHead Camera
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Gamma Camera