Transcript Introduction to Nucl..

Introduction to Nuclear Cardiology II
Principles of Instrumentation and Radiopharmacy
Matthew M. Schumaecker, MD, FACC
Carilion Clinic / VTSOM
Assistant Professor of Medicine
Objectives
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Become familiar with the terminology used in nuclear
imaging
Become familiar with the concepts underlying nuclear
perfusion imaging
Become familiar with 99mTc and 201Tl as
radiopharmaceuticals
Preliminary exposure to instrumentation, image
acquisition and processing
Tutorial: how to read a scan
Become familiar with prognostic data associated with
nuclear imaging
Corollary concepts
Principles of nuclear physics
 Principles of risk stratification
 Principles of stress testing
 Principles of radiation safety
 PET imaging
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MPI - The Basic Process
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Radioisotope is injected into patient.
Radioisotope is taken up into certain cells.
Radioisotope decays emitting gamma-photons
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Gamma photons are detected by NaI/CZT
crystal.
Gamma photons are transformed into visible
photons by NaI/CZT crystal.
Visible photons are turned into electrons by a
photomultiplier tube.
Electrons convert to digital signal.
MPI - The Basic Process
Slide from E. Lindsay Tauxe ASNC, 7/2007
Compton Scatter and Collimators
A lot of Compton
Scatter
Collimators minimize
compton scatter
201Thallium
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– Physical Properties
Produced offisite by a cyclotron
Physical t1/2 = 73 hours
 Biological t1/2 = 10 days
 Principal photon energies = 68-80 kEV
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Prolonged half life limits total dose to 24mCi
201Thallium
Monovalent Cation
 Some uptake via active transport
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K+
K+
Tl+
Rb+
ATPase
Na+
Tl+
201Thallium
- Redistribution
Around 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.
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201Thallium
Advantages
 Widely used
 Less expensive than
technetium
 High myocardial
extraction fraction
 Good linearity of
uptake vs. flow
Disadvantages
 Long half-life limits
maximal dose to 4.5
mCi
 Substantial portion
of photons scatter
 Low-energy photons
are easily attenuated
99mTechnetium
Also emits photons by gamma-decay
 T1/2 is 6 hours
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◦ This allows much higher dosing
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Higher photo peak (~140 kEV)
◦ This causes less photon scatter and attenuation
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Three 99mTc agents are approved:
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Sestamibi (Cardiolite)
Tetrofosmin (Myoview)
Teboroxime (Cardiotec) – not currently available
Sestamibi
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Lipophilic monovalent cation
Na/K/ATPase pump not used
Exact mechanism of myocardial uptake is unclear
Appears 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.
Sestamibi
Non-linearity of uptake vs. coronary flow
Slide from Dr. Gary Heller ASNC, 7/2007
Sestamibi
Advantages
 Higher 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
Disadvantages
 Non-linear extraction
 60% first-pass extraction
 Lack of redistribution –
need 2 injections; limited
viability information
 Excretion in
hepatobiliary system
Tetrofosmin
Lipophilic, cationic diphosphine
compound
 Similar uptake mechanism as Sestamibi
 Quick clearance from the liver
 Slow clearance from the heart
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Sestambi vs Tetrofosmin
Soman et. al
Sestambi vs Tetrofosmin
Soman et. al
REVIEW
Stress Modality: Dobutamine
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Beta agonist
Simulates exercise by positive chronotropy
and inotropy.
Can be difficult to achieve 85% MPHR with
dobutamine alone
May need to augment chronotrophic
response with atropine up to 1 mg.
Can cause SAM and LVOT obstruction in
patients with significant septal hypertrophy.
REVIEW
Stress Modality:Vasodilator
Slide by Dr. Robert Hendel. ASNC 7/07
REVIEW
Stress Modality:Vasodilator
Slide by Dr. Robert Hendel. ASNC 7/07
REVIEW
Stress Modality: Adenosine
Causes coronary arteriolar vasodilation
 Extremely short half life
 Given in a four or six minute infusion
 Tracer is injected halfway through the
protocol
 Can cause flushing, diaphoresis,
chest pain. Usually resolves within
minutes after infusion
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Stress Modality: Dipyridamole
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Trade Name: Persantine
Acts by blocking the cellular uptake of
adenosine
Four to ten times less expensive than adenosine
Comparable to adenosine with respect to
sensitivity; specificity may be lower
Much longer half life so adverse reactions tend
to be more severe
Segmental Scoring
0 = Normal
1 = Slight reduction of uptake
2 = Moderate reduction of uptake
3 = Severe reduction of uptake
4 = Absent uptake
Segmental Scoring
Most outcome data uses old 20-segment
model
0-4 Normal
 4-8 Mildly abnormal
 9-13 Moderately abnormal
 >13 Severely abnormal
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In 17-segment model >11 is severely abnormal
SPECT - Prognostic Value
Slide from Dr. Robert Hendel ASNC, 7/2007
SPECT - Prognostic Value
Slide from Dr. Robert Hendel ASNC, 7/2007
Gated Images - Prognostic Value
Slide from Dr. Robert Hendel ASNC, 7/2007
SPECT vs. Direct Cath - Outcomes
Slide from Dr. Robert Hendel ASNC, 7/2007
SPECT vs. Direct Cath - Outcomes
Slide from Dr. Donna Polk ASNC, 7/2007
Attenuation Correction
Slide from Dr. Robert Hendel ASNC, 7/2007
Attenuation Correction
Slide from Dr. Robert Hendel ASNC, 7/2007
Attenuation Correction
Slide from Dr. Robert Hendel ASNC, 7/2007
Special Considerations
Slide from E. Lindsay Tauxe ASNC, 7/2007
Cardiac SPECT - Conclusions
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Excellent prognostic information
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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
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Safe and cost-effective gatekeeper to the cath lab