Introduction to Nuclear Cardiology II Principles of Instrumentation and Radiopharmacy Matthew M....
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Transcript of Introduction to Nuclear Cardiology II Principles of Instrumentation and Radiopharmacy Matthew M....
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.
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
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
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
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