Introduction to Nuclear Introduction to Nuclear Cardiology IICardiology IIPrinciples of Instrumentation and Principles of Instrumentation and RadiopharmacyRadiopharmacy

Matthew M. Schumaecker, MD, FACCCarilion Clinic / VTSOMAssistant Professor of Medicine

ObjectivesObjectivesBecome familiar with the terminology used

in nuclear imagingBecome familiar with the concepts

underlying nuclear perfusion imagingBecome familiar with 99mTc and 201Tl as

radiopharmaceuticalsPreliminary exposure to instrumentation,

image acquisition and processingTutorial: how to read a scanBecome familiar with prognostic data

associated with nuclear imaging

Corollary conceptsCorollary conceptsPrinciples of nuclear physicsPrinciples of risk stratificationPrinciples of stress testingPrinciples of radiation safetyPET imaging

MPI - The Basic ProcessMPI - The Basic Process1. Radioisotope is injected into patient.2. Radioisotope is taken up into certain

cells.3. Radioisotope decays emitting gamma-

photons .4. Gamma photons are detected by

NaI/CZT crystal.5. Gamma photons are transformed into

visible photons by NaI/CZT crystal.6. Visible photons are turned into electrons

by a photomultiplier tube.7. Electrons convert to digital signal.

MPI - The Basic ProcessMPI - The Basic Process

Slide from E. Lindsay Tauxe ASNC, 7/2007

Compton Scatter and Compton Scatter and CollimatorsCollimators

Collimators minimize compton scatter

A lot of Compton Scatter

201201Thallium – Physical Thallium – Physical PropertiesPropertiesProduced offisite by a cyclotron

Physical t1/2 = 73 hoursBiological t1/2 = 10 daysPrincipal photon energies = 68-80

kEV

Prolonged half life limits total dose to 2-4mCi

201201ThalliumThalliumMonovalent CationSome uptake via active transport

ATPase

Na+

K+

Tl+

Rb+

K+

Tl+

201201Thallium - RedistributionThallium - RedistributionAround 4% of the dose is rapidly

taken up by the myocardium – this demonstrates coronary flow.

After initial extraction, there is continuous exchange of thallium between myocyte and intracellular compartment – this demonstrates viability.

201201ThalliumThallium

AdvantagesWidely usedLess expensive

than technetiumHigh myocardial

extraction fraction

Good linearity of uptake vs. flow

DisadvantagesLong half-life

limits maximal dose to 4.5 mCi

Substantial portion of photons scatter

Low-energy photons are easily attenuated

99m99mTechnetiumTechnetiumAlso emits photons by gamma-decayT1/2 is 6 hours

◦ This allows much higher dosingHigher photo peak (~140 kEV)

◦ This causes less photon scatter and attenuation

Three 99mTc agents are approved:1.Sestamibi (Cardiolite)

2.Tetrofosmin (Myoview)

3.Teboroxime (Cardiotec) – not currently available

SestamibiSestamibiLipophilic monovalent cationNa/K/ATPase pump not usedExact mechanism of myocardial uptake

is unclearAppears to be passive across the

plasma membrane and mitochondrial membrane

Becomes sequestered in the mitochondria because of the negative membrane potential

Therefore only minimal, if any, redistribution occurs with sestamibi.

SestamibiSestamibi

Non-linearity of uptake vs. coronary flow

Slide from Dr. Gary Heller ASNC, 7/2007

SestamibiSestamibi

AdvantagesHigher dose can be

given because of short half life

Lack of redistribution – can obtain multiple images over several hours

Can obtain perfusion imaging and gating in one study

DisadvantagesNon-linear extraction60% first-pass

extractionLack of redistribution

– need 2 injections; limited viability information

Excretion in hepatobiliary system

TetrofosminTetrofosminLipophilic, cationic diphosphine

compoundSimilar uptake mechanism as

SestamibiQuick clearance from the liverSlow clearance from the heart

Sestambi vs TetrofosminSestambi vs TetrofosminSoman et. alSoman et. al

Sestambi vs TetrofosminSestambi vs TetrofosminSoman et. alSoman et. al

REVIEWREVIEWStress Modality: DobutamineStress Modality: DobutamineBeta agonistSimulates exercise by positive

chronotropy and inotropy.Can be difficult to achieve 85%

MPHR with dobutamine aloneMay need to augment

chronotrophic response with atropine up to 1 mg.

Can cause SAM and LVOT obstruction in patients with significant septal hypertrophy.

REVIEWREVIEWStress Modality: VasodilatorStress Modality: Vasodilator

Slide by Dr. Robert Hendel. ASNC 7/07

REVIEWREVIEWStress Modality: VasodilatorStress Modality: Vasodilator

Slide by Dr. Robert Hendel. ASNC 7/07

REVIEWREVIEWStress Modality: AdenosineStress Modality: AdenosineCauses coronary arteriolar vasodilationExtremely short half lifeGiven in a four or six minute infusionTracer is injected halfway through the

protocolCan cause flushing, diaphoresis,

chest pain. Usually resolves within minutes after infusion

Stress Modality: Stress Modality: DipyridamoleDipyridamoleTrade Name: PersantineActs by blocking the cellular uptake of

adenosineFour to ten times less expensive than

adenosineComparable to adenosine with respect

to sensitivity; specificity may be lowerMuch longer half life so adverse

reactions tend to be more severe

0 = Normal1 = Slight reduction of uptake2 = Moderate reduction of uptake3 = Severe reduction of uptake4 = Absent uptake

Segmental Scoring

Segmental ScoringSegmental ScoringMost outcome data uses old 20-

segment model

0-4 Normal4-8 Mildly abnormal9-13 Moderately abnormal>13 Severely abnormal

In 17-segment model >11 is severely abnormal

SPECT - Prognostic ValueSPECT - Prognostic Value

Slide from Dr. Robert Hendel ASNC, 7/2007

SPECT - Prognostic ValueSPECT - Prognostic Value

Slide from Dr. Robert Hendel ASNC, 7/2007

Gated Images - Prognostic Gated Images - Prognostic ValueValue

Slide from Dr. Robert Hendel ASNC, 7/2007

SPECT vs. Direct Cath - SPECT vs. Direct Cath - OutcomesOutcomes

Slide from Dr. Robert Hendel ASNC, 7/2007

SPECT vs. Direct Cath - SPECT vs. Direct Cath - OutcomesOutcomes

Slide from Dr. Donna Polk ASNC, 7/2007

Attenuation CorrectionAttenuation Correction

Slide from Dr. Robert Hendel ASNC, 7/2007

Attenuation CorrectionAttenuation Correction

Slide from Dr. Robert Hendel ASNC, 7/2007

Attenuation CorrectionAttenuation Correction

Slide from Dr. Robert Hendel ASNC, 7/2007

Special ConsiderationsSpecial Considerations

Slide from E. Lindsay Tauxe ASNC, 7/2007

Cardiac SPECT - Cardiac SPECT - ConclusionsConclusions

Excellent prognostic information◦ Can tell likelihood of angiographically significant

CAD and◦ Likelihood of a cardiac event◦ Negative study is very powerful◦ LV function data

Excellent diagnostic accuracy◦ With all tracers and stress modalities◦ Additive benefit of supine/prone◦ Additive benefit of attenuation correction

Safe and cost-effective gatekeeper to the cath lab