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DISCLOSURES -
Honorarium – Research / Advisor, Expert Services and Conferences in Nuclear Cardiology
BMS, CVT, Astellas, Lantheus, PGx Health, International Atomic Energy Agency
Royalties – Publications in Nuclear Cardiology
Springer-Verlag-Nuclear Cardiology and Correlative Imaging: a teaching file, NY, 2004
Lippincott Williams & Wilkins, - Nuclear Medicine teaching File, 2009
João V. Vitola
Quanta Diagnostico Nuclear
Brazil
PET/CT vs SPECT
65 yo male
Atypical chest pain
No history of CAD/MI
HTN, hypercholesterolemia
Vitola and Delbeke: Nuclear Cardiology and Correlative Imaging, Springer 2004, NY, Chapter 3
Case
SAV – EXERCISE
SAV - REST
VLA – EXERCISE
VLA - REST
HLA – EXERCISE
HLA - REST
1- Does the ECG change represents a silent MI in the
past ?
2- Does he need any additional viability study ?
Myocardial Viability: 99mTc-perfusion agents
• Retention of MIBI and tetrofosmin depends on cell membrane integrity and mitochondrial function.
• 99mTc-perfusion agents do not redistribute and may underestimate viability compared to 201Tl or FDG
• Improvement for detection of viability with quantitative SPECT criteria and nitrate administration
Cuocolo A et al. J Nucl Med 1992;33:505-511. Soufer R et al. Am J Cardiol 1995;75:1214-1219. Altehoefer C et al. J Nucl Med 1994;35:569-574.
Conclusions • TMT was less sensitive than MPI for LCX
ischemia detection
• CAD and prior MI detected in a patient with no history
• MIBI was consistent with rest ECG, confirming the suspicion of a prior silent MI
• MIBI detected a large area of viable tissue at risk, not requiring any other test to decide management
• MIBI can be used as a viability agent, however underestimation of viable tissue may occur in some cases and further testing may be needed
Case
• 68 year-old woman with a history of silent inferior MI who presented with episodes of atrial fibrillation and ventricular tachycardia
• ECG:
– Q waves in II, III, AVF
• Coronary angiography:
– Occluded RCA with collaterals to the distal inferior wall from the left circulation
Rest only - 15 min Rest- 4h redistribution 201Tl
Membrane Integrity: Thallium-201
• Analog of potassium
– Myocardial extraction by active and passive transport
– High first pass uptake – 89%
– Myocardial localization: 4% injected dose
• Does redistribute according to perfusion
• Allows evaluation of perfusion and cell membrane integrity (a requirement for viability)
Vitola and Delbeke: Nuclear Cardiology and Correlative Imaging, Springer 2004, NY, Chapters 3 and 8
Membrane Integrity: 201Thallium SPECT Rest-4h redistribution - Semiquantitation
• Patterns of uptake in dysfunctional myocardium:
– Fixed defect: <50% of normal: transmural scar
– Fixed defect: 50-80% of normal: non-transmural scar
– Redistribution – Myocardium at risk - viable
Bax JJ et al. Eur J Nucl Med 1997;24:516-522.
Membrane Integrity: 201Thallium SPECT • Stress/Rest imaging
– 4-hour redistribution imaging:
• fixed defect frequently viable: 45% of fixed defects improve after revascularization.
– Resting imaging after reinjection of 201Tl improves viability assessment : 30-50% fixed defects at 4h redistribution show reversibility.
– 24-h redistribution imaging (in average additional 6%)
Kiat H et al. JACC 1988;12:1456-1463. Yang LD et al. JACC 1990;15:334-340. Dilsizian V et al. NEJM 1990;323:141-146.
Value of 24h imaging:
Small number of patients:
– Up to 30% of patients with fixed defects (rest-4 hrs) will show improved uptake at 24h
– But only 3% of patients with fixed defects of <50% uptake of normal
Membrane Integrity: 201Thallium SPECT
Wagdy HM et al. Nucl Med Commun 2002;23:629-637.
Matsunari I et al. J Nucl Med 1997;38:1073-1078.
• 61 yo man with exercise induced chest pain (typical angina)
• AMI 2 1/2 y ago, followed by CABG: LIMA to LAD and SVG to the LCX
• Last cath 6 mo ago: 99% native LAD, occluded LIMA, antero-apical akinesia
•Meds: Carvedilol, ACEI, nitrate, ASA, Statin and Aldactone
Referred for a SESTAMIBI study
•MPI: Bruce, 10 METS, ECG positive – new ST depression 1 mm, denied chest pain
Case
Stress/Rest MIBI • Hx of exercise induced chest pain + new ST depression 1 mm om TMT
Stress/Rest MIBI
•exercise induced chest pain, new ST depression
Next Step ?
Nitrate administration
Venodilation
Preload reduction
Decrease of LV volume and wall stress
Reduction of myocardial oxygen demand
Coronary blood flow redistribution towards ischemic
regions by reduction of LV end-diastolic pressure
Nitrate Myocardial Perfusion Imaging
0 5 10 15 20 25 30 50 70
SPECT imaging
Nitrateadministration
Tracerinjection
Resting conditions
Time (min)
MIBI with nitroglycerin (NTG)
Scar > Ischemia
MIBI without NTG
Ischemia > Scar
MIBI with NTG
STRESS
STRESS
REST
STRESS
REST
STRESS
REST
•exercise induced chest pain, new ST depression
Next Step : nitrate MIBI = good choice
REST
Rest without NTG Rest with NTG
STRESS STRESS
REST REST
Akinetic antero - apical region
Case
• 52 year-old man with CHF and global LV dysfunction on echocardiography
• Coronary angiography: severe 3-vessel CAD
• Nitrate: How does it work?
– Preload reduction, some dilatation of stenotic epicardial vessel and improvement of collateral circulation
• How to administer?
– 0.4-0.8 mg sublingually 5 -10 min before the radiopharmaceutical
• Can be used with 201Tl or 99mTc-perfusion agents
• Performance?
Myocardial Viability Resting and nitrate-enhanced SPECT
Bisi G et al. JACC 1994;24:1282-1289.
Batista JF et al. J Nucl Cardiol 1999;6:480-486.
Oudiz RJ et al. Am Heart J 1999;138:206-209.
FD
G
Viable Necrotic
Via
ble 75
(57%)
34
(26%)
3
(2%)
Necro
tic
19
(15%)
Baseline Tetrofosmin
Agreement: 94/131 (72%)
Kappa = 0.35
Nitrate Tetrofosmin
FD
G
Viable Necrotic
Via
ble 89
(68%)
20
(15%)
3
(2%)
Necro
tic
19
(15%)
Agreement: 109/131 (82%)
Kappa = 0.53
Cardiac Tomography After Nitrate Administration in Patients With
Ischemic LV Dysfunction: Relation to Metabolic Imaging by PET
He W, et al. J Nucl Cardiol 2003
Cardiac Tomography After Nitrate Administration in Patients
With Ischemic LV Dysfunction: Relation to Metabolic Imaging
by PET
He W, et al. J Nucl Cardiol 2003
Patient 1 Patient 2
69
8681
86
0
20
40
60
80
100
Sensitivity Specificity
He W, et al. J Nucl Cardiol 2003
Perc
ent
Baseline
Nitrate
Sensitivity and Specificity of Baseline and Nitrate Tetrofosmin
SPECT for Detecting Preserved Metabolic Activity in Patients With
Ischemic LV Dysfunction
p < 0.01 p = NS
Detection of Myocardial Viability by Radionuclide Imaging
Gold Standard: Recovery of LV Function
9086
81
91 92
54
6760
88
73
0
20
40
60
80
100
Tl-201 Red Tl-201 Rein Mibi Mibi-Nitrate FDG-PET
Bax et al. J Am Coll Cardiol 1997
%
Sensitivity Specificity
Stunning
Scar from prior MI
Hibernation
Subendocardium
20-30 % = akinesia
May have lots
of viable tissue
Chronic cases =
Mixed pattern
Lieberman AN et al, Circulation 1981;63:739-746
Contribution of the subendocardium to contractility
Akinetic anterior wall
Pooled Data from Studies Focusing on Prediction of Recovery of Function Post-revascularization
Technique #Studies/
patients
Sensitivity Specificity NPV PPV
FDG PET 20/598 93% 58% 86% 71%
201Tl 33/858 87% 55% 81% 64%
99mTc-tracers 20/488 81% 66% 77% 71%
Dobutamine
Echo/MRI
32/1090 81% 80% 85% 77%
Pooled data 105/3034 84% 69%
Bax JJ et al. Curr Probl Cardiol 2001;26:142-186
Why is nuclear less specific compared to echo for Fx improvement ?
Qureshi U et al. Circulation 1997;95:626-635
Subendocardium MI may lead to akinesia
Akinetic segments may have lots of viable tissue detected by Nuclear
Scar may prevent improvement of function and detection by echo
Conclusions
• MIBI can be used as a viability agent, however underestimation of viable tissue may occur and further testing may be needed in special cases
• Nitrates are easy and safe to use and increase the sensitivity of rest MIBI to detect viable tissue
• There are data in the literature supporting the use of Nitrate MPI with similar accuracy to other protocols including thallium and FDG (LV Fx dependent)
• Akinetic areas may be present after a subendocardium MI
• Viability studies may show large quantities of viable tissue at risk in akinetic areas
PET CT
Integrated PET-CT Imaging
System
PET
CT
PET - CT
Hybrid Technology - PET/CT Widespread due to oncology
Availability may push for more cardiac utilization
Cardiac PET/CT
PET/CT
Viability
Systolic/
Diastolic
function
First
Pass
Image
Fusion
CAC
Perfusion
COMPLETE STATE OF THE ART EVALUATION IN 30 MINUTES ANATOMY, PERFUSION AND FUNCTION
Differences SPECT vs. PET Radiotracers
Characteristic SPECT PET
Radiotracer Generator Generator/Cyclotron
Energy 80-140 KeV 511KeV
Resolution 20 mm FWHM 10 mm FWHM
Attenuation More Less
Half-life 6 hrs-72 hrs 1.5 to 13 min
Radiation Greater Less
Study duration 3-4 hrs 35-45 min
Stress Exercise > pharm
Pharm > exercise
Estimated radiation dose to patients: PET vs. SPECT
Adapted from: Gerber et al.
Circulation, Feb 2009; 119: 1056 -
1065.
Einstein et al Circulation.
2007;116:1290-1305
Senthamizhchelvan J. Nucl. Med.
2011 52: 485-491
Stabin, Health Physics: December
2010 - Volume 99 - Issue 6 - pp 811-
813
SPECT
• Flow heterogeneity to see the defect
• Homogenous decrease: • Three vessel disease, Left main
• Microvascular disease
Beanlands et al. J Am Coll Cardiol 2009 54: 157-159
PET - Myocardial blood flow absolute quantification: Clinical applications
Diagnosis
Multivascular disease (Diffuse disease)
Microvascular disease
Evaluation of endothelial function
Patient’s treatment follow-up
Myocardial Viability
Advantages of Cardiac PET
• High image resolution
– Spatial, contrast and temporal
• Superior efficiency
– Time
– Radiation
• Superior ability to delineate extent of CAD
– Quantitative imaging capabilities
– Peak stress LVEF
– Hybrid PET/CT applications
Variable Soft Tissue Attenuation: SPECT
Stress
Rest
Stress
Rest
Stress
Rest
Variable Soft Tissue Attenuation on SPECT:
Normal 82 Rb PET
Stress
Rest
Stress
Rest
Stress
Rest
Stress
Rest
Limited Rest SPECT
Rb-82 Rest-Stress PET
Stress
Rest
Stress
Rest
Stress
Rest
Stress
Rest
Equivocal Tc 99m SPECT
5’6”, 190 lbs, F
Stress Tc 99m
Rest Tc 99m
Mildly Abnormal 82Rb PET
Stress Rb-82
Rest Rb-82
Overall Diagnostic Accuracy
PET vs. SPECT
0
20
40
60
80
100
120
Sensitivity Specificity Accuracy
%
SPECT
PET
P<0.05
P<0.05
Bateman et al, J Nucl Cardiol; 2006:
Jan
86%
100%
ACC/ASNC Radionuclide guidelines
SPECT: Sensitivity 89%, Specificity:75%
• FDG is taken up by viable myocardial regions
even when flow is significantly reduced.
• Effectively differentiates nontransmural MI
from hibernating condition.
• Soft tissue attenuation correction is routinely
performed.
PET FDG for Viability Assessment
Advantages over SPECT
>50% uptake
Post-revascularization
Wall motion recovery
Not likely
Nontransmural MI Nontransmural MI
+
Hibernating myocardium
Post-revascularization
Wall motion recovery
likely
• PET FDG is the preferred imaging method for
assessment of myocardial viability.
• If SPECT is done first, PET should be
considered in those with non- or partially
reversible defects.
PET vs. SPECT for Viability Assessment