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Principles of Nuclear Principles of Nuclear MedicineMedicine

-- --

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THE ATOMTHE ATOM

Th e nucleus h as protons andTh e nucleus h as protons andneutrons.neutrons.

Protons are positively ch argedProtons are positively ch argedparticles.particles.Neurons are particles with out ch arge.Neurons are particles with out ch arge.Electrons orbit th e nucleus inElectrons orbit th e nucleus inprecisely defined sh ells and subprecisely defined sh ells and sub--sh ells.sh ells.

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A tom anatomy A tom anatomy

Electron Proton Neutron

Nucleons

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The AtomThe Atom

Th e symbol X is given to any atom.Th e symbol X is given to any atom. A is th e atomic mass number w h ich is A is th e atomic mass number w h ich is

th e total number of protons and neutrons.th e total number of protons and neutrons.Z is th e atomic number wh ich is th eZ is th e atomic number wh ich is th enumber of protons. A tomic number definesnumber of protons. A tomic number definesth e atom.th e atom.

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Atomic ShorthandAtomic Shorthand

II131131535353 Protons + 78 Neutrons = 131 Nucleons53 Protons + 78 Neutrons = 131 Nucleons

X X A A

ZZ

Atomic Mass Atomic Mass

Atomic Number Atomic Number

ElementElement

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Nuclea r F am ilies and Nuclea r F am ilies and Nomencla tu r eNomencla tu r e

CC1212

66CC

1313

66CC

1414

66

Same number ofSame number of PProtons = Isotorotons = Isoto p p eses

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R adioactive I otopesR adioactive Isotopes

S ome isotopes are stable (nonS ome isotopes are stable (non- -radioactive).radioactive).

S ome isotopes are unstable (radioactive).S ome isotopes are unstable (radioactive).

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UN STAB ILITY AND D ECAYUN STAB ILITY AND D ECAY

U nstable isotope seeks greater stability byU nstable isotope seeks greater stability bysome kind of radiation (decay).some kind of radiation (decay).

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IsotopesIsotopes

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Ha lf Ha lf--L if eLif eTh e time required for h alf of th eTh e time required for h alf of th eradioactive isotope to undergo decay isradioactive isotope to undergo decay iscalled th e h alf called th e h alf--life.life.A fter 4 h alf A fter 4 h alf--life's, th e residual activitylife's, th e residual activitywould be 6.2 5% of original activity, wh ich would be 6.2 5% of original activity, wh ich means t h ere is no significant activity left.means t h ere is no significant activity left.

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T ypes of radiationT ypes of radiation

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D ecay o f R adioactiveD ecay o f R adioactive

Isotopes (e lectron emission)Isotopes (e lectron emission)

R

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Sing le Step R adioactiveSing le Step R adioactiveD ecayD ecay

II

131131

5353 Xe Xe

131131

5454(stable)(stable)

(unstable)(unstable)

.

R

F

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D ecay o f R adioactive IsotopesD ecay o f R adioactive Isotopes

(photon emission)(photon emission)

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PhotonsPhotons

Ph oton is electromagnetic wave.Ph oton is electromagnetic wave.It is part of electromagnetic spectrum.It is part of electromagnetic spectrum.Ph otons are used in imaging inPh otons are used in imaging inradiology (conventional radiograph yradiology (conventional radiograph yand CT scanning) and in nuclear and CT scanning) and in nuclear medicine.medicine.

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1010 33 1010 22 1010 11 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

R adio/TVR adio/TV In f raredIn f rared

Visib leVisib le

U VU V XX--raysrays

GammaGamma

Wave length (m)Wave length (m)

4, 000 A4, 000 A7, 000 A7, 000 A

E lectromagnetic SpectrumE lectromagnetic Spectrum

requency (Hz)requency (Hz)1010 55 1010 66 1010 77 1010 88 1010 99 1010 1010 1010 1111 1010 1212 1010 1313 1010 1 41 4 1010 1 51 5 1010 1 61 6 1010 1 71 7 1010 1 81 8 1010 1 91 9 1010 2020

Vi sual

Imaging

MRI X-ray

Imaging

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E lectromagneticE lectromagnetic r radiationadiation

GAMMA

VISIBLE X-R AYS COSMIC

INFR ARED U LTR AVIOL ET

MICR OVAV ES

TV,R ADIO

Decreasingw

ave lengthIncreasing f requency

Increasing photon energy

IONIZINGR ADIATO N

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XX--R ay and Gamma R ayR ay and Gamma R ay

XX--ray is emitted from outside th e nucleusray is emitted from outside th e nucleus(electron sh ells).(electron sh ells).Gamma ray is a p h oton emitted form someGamma ray is a p h oton emitted form someisotopes in th e process of t h eir decay.isotopes in th e process of t h eir decay.

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XX--rays andrays andgammagamma

raysrays

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Ionizing RadiationIonizing RadiationRadiation causes ionization of atoms andRadiation causes ionization of atoms andmolecules.molecules.Ionization is th e underlying mech anism for Ionization is th e underlying mech anism for most radiation detectors and also ismost radiation detectors and also isresponsible for most radiobiologicalresponsible for most radiobiologicaleffects.effects.

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Bio logica l E ff ect o f R adiationBio logica l E ff ect o f R adiation

W h y sh ould we protect ourselves fromW h y sh ould we protect ourselves fromradiation?radiation?

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Radiation Effects at th e Molecular Radiation Effects at th e Molecular LevelLevel -- Direct A ctionDirect A ction

Direct molecular Direct molecular absorption of absorption of

energyenergyDN A mostDN A mostsusceptiblesusceptible

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DN ADN A llesions andesions and c chromosomehromosomeaaberrationsberrations

DN A S NGLE

STR AND BRE AK

DN A DOUBLE

STR AND BRE AK

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Indirect A ctionIndirect A ction--Radiolysis of W ater Radiolysis of W ater

IonizationIonization D issociationD issociation

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F ree Radical Biological DamageF ree Radical Biological Damage

Cause damage toCause damage to(DN A/ RN A ) wh ich (DN A/ RN A ) wh ich become nonbecome non--functionalfunctional

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S omatic EffectsS omatic EffectsA cute or early (deterministic) A cute or early (deterministic)

with in dayswith in daysdose dependentdose dependent

S een in accidents and nuclear warsS een in accidents and nuclear warsA ffects acutely bone marrow, G I tract and A ffects acutely bone marrow, G I tract andskin and less neurological system.skin and less neurological system.

Latent or delayed (stoc h astic).Latent or delayed (stoc h astic).

not seen for yearsnot seen for yearscancer, cataract, s h ortened life spancancer, cataract, s h ortened life span

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Principals of Radiation ProtectionPrincipals of Radiation Protection

T imeT imeDistanceDistanceS h ieldingS h ielding

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T IMET IMETh e total radiation exposure to anTh e total radiation exposure to anindividual is directly proportional to th eindividual is directly proportional to th e

timeh

e is exposed to th

e source.timeh

e is exposed to th

e source.Th erefore, it is wise to spend no moreTh erefore, it is wise to spend no moretime th an necessary near t h e source of time th an necessary near t h e source of

radiation.radiation.

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DIS T A NCEDIS T A NCETh e intensity of radiation from a sourceTh e intensity of radiation from a sourcevaries inversely with th e square of t h evaries inversely with th e square of t h e

distance.distance.Th erefore, radiation workers s h ouldTh erefore, radiation workers s h ouldmaximize th e distance betweenmaximize th e distance betweenth emselves and t h e radiation source.th emselves and t h e radiation source.

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S h ieldingS h ieldingLead is most commonly used to s h ield ph otonsLead is most commonly used to s h ield ph otonsin diagnostic imaging.in diagnostic imaging.

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56 0 mGy/h

1 mGy/h

2 mm lead

Via l Shie lds

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N uc lear Medicine ImagingN uc lear Medicine Imaging

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Technetium 99 m (TcTechnetium 99 m (Tc 99 m)99 m)It is th e main isotope used in nuclear It is th e main isotope used in nuclear medicine imaging. It is used in more t h anmedicine imaging. It is used in more t h an7070--80% of cases.80% of cases.It emits gamma ray only.It emits gamma ray only.Its h alf life is 6h ours.Its h alf life is 6h ours.It can easily label different kind of It can easily label different kind of ph armaceuticals.ph armaceuticals.It is always given intravenously.It is always given intravenously.

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R adiopharmaceutica lsR adiopharmaceutica lsPh armaceuticals are c h emical compoundsPh armaceuticals are c h emical compoundsth at h ave p h armacokinetics but do notth at h ave p h armacokinetics but do noth ave p h armacological effects.h ave p h armacological effects.Th ey are usually labeled with T c99m.Th ey are usually labeled with T c99m.F or eac h organ th ere is certainF or eac h organ th ere is certainradioph armaceuticalsradioph armaceuticals

In general, nuclear medicine images t h eIn general, nuclear medicine images t h efunction (ph ysiology), not th e anatomy asfunction (ph ysiology), not th e anatomy asin conventional radiology.in conventional radiology.

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Ph armaceuticalPh armaceutical

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Different Ph rmaceuticalsDifferent Ph rmaceuticals

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RadioRadio--labeling of Glucose with labeling of Glucose with radioactive F lourineradioactive F lourine--1 81 8

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The Gamma CameraThe Gamma Camera

It is a device th at uses gamma rays toIt is a device th at uses gamma rays tomake an image of radiop h armaceuticalmake an image of radiop h armaceuticaldistribution and uptake in patients.distribution and uptake in patients.Its crystal h as a c h emical propriety th at if itIts crystal h as a c h emical propriety th at if itis h it by a ph oton it will scintillate.is h it by a ph oton it will scintillate.

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Nuclear Imag ing Nuclear Imag ing

Not enough to detect just radioactive levelsNot enough to detect just radioactive levelsor concentrationsor concentrations

Need device to map th

e radioactiveNeed device to map th

e radioactivedistributiondistributionExternal Rad iat ion Detector

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Gamma cameraGamma camera --cont..cont..

S cintillation means ligh t production.S cintillation means ligh t production.yy Th e ligh t is converted into electricalTh e ligh t is converted into electrical

current wh

ich

th

en is stored in th

ecurrent wh

ich

th

en is stored in th

ecomputer as a dot.computer as a dot.

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S cintillation of Gamma CameraS cintillation of Gamma Camera

Crystal

Gamma Ray

Light

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G amma Camera Crystal (B)G amma Camera Crystal (B)

NaINaI(T l)(T l)1/ 41/ 4 -- 1/21/2 **** th ickth ick 3/8 most popular 3/8 most popular 1 01 0-- 21 in diameter 21 in diameter rectangular popular rectangular popular

S ensitive toS ensitive tomoisture andmoisture andtemperaturetemperature

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G amma CameraG amma Camera

S taticS taticImageImage

DyamicDyamicAcquisitionAcquisition

ImagesImages

MobileMobileCameraCamera

S tationary DualS tationary DualHead CameraHead Camera

S tationary S ingleS tationary S ingleHead CameraHead Camera

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Gamma CameraGamma Camera