1. introduction chest imaging (2010)

7/29/2019 1. Introduction Chest imaging (2010)

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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

1. introduction chest imaging (2010)

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