Download Will PET replace single-photon emission computed tomography?

Will PET Replace Single Photon Emission
Computed Tomography?
T.H. Schindler, MD
Deputy Head Physician, Division of Cardiology,
University Hospitals of Geneva, Geneva, Switzerland
Disclosures
• None
CASE 1: N-13 Ammonia PET in a 58 Old
Asymptomatic Diabetic Patient
(Schindler TH et al, JACC Cardiovasc Imaging 2010)
Quantification of Myocardial Blood
Flow (MBF) by PET Imaging:
Technical and Methodological Aspects
Compartment Models for Tracers of
MBF Estimates in ml/g/min
Serially Acquired Images of a Bolus
Transit of N-13 Ammonia
2-Compartment Model for N-13
Ammonia
(Schelbert HR et al., Circulation 1981)
Arterial Radiotracer Input Function and
Myocardial Tissue Response
Through fitting of the time activity curves with the operational
equation formulated by the 2-compartment tracer kinetic model,
estimates of MBF in ml/g/min are obtained
Added Value of MFR in the Identification of
Flow-Limiting Lesions
Coronary
Angiography
Three vessel disease
LAD: 100% stenosis
LCX: 85% stenosis
RCA: 50% stenosis
(Schindler TH . JACC Cardiovasc Imaging 2010)
Coronary Angiography Unmasking
Multivessel Disease
LCx: >80%
50%
rMFR: 1.41
50%
LAD:100%
rMFR: 1.20
rMFR: 1.35
50%
Left Coronary Tree
Right Coronary Tree
Coronary Revascularization
1) Re-opening of the chronic LAD occlusion with
stent deployment?
2) PCI of LAD and LCx with stenting?
3) CABG of all three main territories ?
Stress-Induce Myocardial Ischemia, invasivelydetermined Coronary Flow Reserve (CVR) and
Fractional Flow Reserve (FFR)
(Kern MJ . Circulation 2000)
Added Diagnostic Value of MFR
 Stress-induced myocardial perfusion defect commonly
signifies the « culprit lesion » in multivessel CAD disease.
 Adding regional MFR may also unmask flow-limiting
downstream effects of lesions with intermediate severity
(>70% diameter stenosis).
 Keep in mind: Reductions of MFR are related to
increases in epicardial and microcirculatory resistance
and, thus, non-specific!
 In this case, however, adding regional MFR translated a
functional 1-vessel to a three vessel disease and the
patient was referred to CABG.
Coronary Vasodilator Capacity related to
Stenosis
(Uren MG et al. N Engl J Med 1994 )
(DiCarli MF et al. Circulation 1995)
Integration of PET Perfusion Imaging and MFR
(Schindler TH et al. JACC Cardiovasc Imaging 2010)
CASE 2
 62 year old type 2 diabetic patient.
 The patient was refered for N-13 ammonia PET/CT
stress-rest perfusion imaging as pre-operative risk
stratification (bioprothese for abdominal aneurysm).
 N-13 ammonia PET/CT perfusion imaging was
performed with dipyridamole-induced hyperemic flow
increases.
N-13 ammonia PET/CT Perfusion Images
Left Coronary Angiography and regional MFR
- LAD: 60-70% stenosis
- Marginal branch of the
LCx: 100%
-RCA: lesion <50% (not
shown)
PET-determined MBF
(ml/g/min)
rest stress MFR
LAD: 1.00 1.77 1.77
LCX: 1.07 1.32 1.23
RCA: 0.91 1.95 2.14
Clinical decision: PTCA and stent employment of the proximal LAD
stenosis in view of abnormally reduced MFR.
Interpretation
Stress-induced regional perfusion defect identifies « culprit lesion »
in multivessel CAD disease.
 Abnormally-reduced MFR in the LAD territory gave an argument for
PTCA and stent employment of the proximal LAD stenosis of
intermediate range.
 Conceptually, preventive medical care with statine and/or ACEInhibitors could have improved coronary microcirculatory
dysfunction leading to a normalization the MFR! This again could
have avoided the coronary intervention.
 Reductions of MFR are related to increases in epicardial and
microcirculatory resistance and, thus, non-specific!
Abnormal Epicardial Vasomotion
During CPT in a Smoker
Baseline
Cold Pressor Test
(Schindler TH, J Nucl Med 2004)
Diameter of LAD
PET Flow Measurements:
0.51 ml/min/g
0.61 ml/min/g
(Schindler TH, J Nucl Med 2004)
Prognostic Value of MFR to Sympathetic Stimulation with
Cold Pressor Testing in Cardiovascular Risk Individuals
1.0
Normal Endothelial
Function: MBF40%,
Event Free Survival
0.9
0.8
Mild to Moderate
Endothelial Dysfunction:
>0 MBF<40%
0.7
+
0.6
++++ + ++
Severe Endothelial
Dysfunction: MBF 0%
Log rank 7.42
p = 0.024
0.5
0.4
0
20
40
60
80
Follow-up (months)
(Schindler TH. J Am Coll Cardiol 2005)
Hyperemic MBF Increases to Adenosine Stimulation
(4 mg L-NAME / kg BW i.v.)
p < 0.001
3
Baseline
2.5
-21%
2
MBF
1.5
(ml/min/g)
L-NAME
endotheliumrelated
NS
smooth
muscle cell
relaxation to
adenosine
1
0.5
0
Rest MBF
Adenosine MBF
Measure of Integrated Coronary Circulatory Function
(Buus et al, Circulation 2001)
Epicardial Flow-Mediated Vasomotor Function
Baseline
Papaverin-induced
Hyperemic Flow
(Drexler H et al. Prog Cardiovasc Dis 1997)
Myocardial Perfusion, Flow Reserve and Prognosis
(Herzog B et al, J Am Coll Cardiol 2009)
Myocardial Perfusion, Flow Reserve and Prognosis
(Herzog B et al, J Am Coll Cardiol 2009)
Myocardial Flow Reserve by PET and Outcomes in
Ischemia
(Ziadi C. et al. J Am Coll Cardiol 2011)
Vasomotor Function, Medical Intervention and
Outcome
(Kitta J et al, J Am Coll Cardiol 2009)
Clinical Utility of Quantification of Myocardial
Blood Flow with PET
1.
Identification of subclinical CAD.
2.
Improved characterization of CAD burden.
3.
Identification of “balanced” reduction of MBF in all vascular territories.
4.
MFR as index of coronary vascular health with prognostic implications
5.
Image-guided and individualized cardiovascular therapy may be attained in
the near future.
(Schindler TH et al. JACC Img 2010)
Cardiac SPECT and PET Perfusion Imaging in a 43 yrs Old Obese
Women (BMI: 43kg/m2)
Non Attenuation Correction (AC) 99mTc-SPECT
99mTc- SPECT with AC
82Rubidium-PET
(Flotats A et al. Eur J Nucl Med Mol Imaging 2012)
Quality Distribution of SPECT and PET Studies
(Flotats A et al. Eur J Nucl Med Mol Imaging 2012)
Interpretive Confidence of SPECT and PET Studies
(Flotats A et al. Eur J Nucl Med Mol Imaging 2012)
Methodological Considerations
Spatial Resolution:
Contrast Resolution:
(First Pass extraction
fraction)
Energy Levels:
PET
SPECT
4-7mm
10-12mm
N-13 ammonia 80%
82-Rubidium  70%
511 keV
99mTc-labelled tracers  60%
140 keV
robust and precise
vague and inhomogen
Attenuation Correction:
(« photon attenuation free »)
Hot Spot Artifacts:
(liver or bowel uptake)
rare
frequent
High spatial and contrast resolution in concert with photon-attenuation free
images of PET versus SPECT leads to:
 Higher image quality associated with higher sensitivity and specifity for PET.
 Higher interpretative confidence and interreader agreement.
(Valenta et al. Eur J Nucl Med Mol Imaging 2012: editorial)
Dipyridamole stress and rest 82Rb PET/CT images in a 56
year old obese (BMI33kg/m2) patient
In obese individuals
and women:
Sensitivity: 95%
Specifity: 90%
Optimal attenuation correction with CT !
(Di Carli MF Circulation 2007)
Gated Rest-Stress 82-Rb Myocardial
Perfusion PET
Multivessel CAD
with stenoses > 70 %
Unmasked with
gated PET
Gated PET at “ Peak Stress“ !
(Dorbala S. J Nucl Med 2007)
Attenuation Correction with CT for SPECT
99mTc-SPECT/CT Attenuation Correction (AC)
Without AC
With AC
Stress
Rest
Stress
Rest
Stress
Rest
(University Hospitals of Geneva)
SPECT, CMR, and PET for Detecting CAD:
Diagnostic Accuracy (Meta-Analysis)
?
?
SPECT/CT
PET SPECT/CT ???
(attenuation correction by
CT and expert reading)
(Jaarsma C et al. JACC 2012)
SPECT/CT: Resolution Recovery Algorithm allows HalfTime Acquisition or Half-Dose Radiotracer Injection
1. SPECT/CT-Geneva :
-Sensitivity: 88%
-Specifity: 75%
2. Low Radiation
Exposure: 4-6 mSv !
-Environmental exposure 
3-4 mSv
-Heavy smokers /year
3 mSv
-Cath-Lab USA  8-12 mSv
Ultra-Fast SPECT Camera Designs
Schematic Detector Array
Cadmium Zinc Telluride
(CZT) Detector
5- to 10-fold increase in count sensitivity at no loss or even a
gain in resolution:
 acquiring a stress myocardial perfusion scan
injected with a standard dose in 2 minutes or less !
(Garcia EV J Nucl Cardiol 2012)
CZT Detector SPECT CT in the Assessment of
Flow-Limiting CAD Lesions
Stress
Rest
MPI polar plots demonstrating inferior
ischemia corresponding to angiographic
stenosis in the RCA.
(Fiechter M et al. Eur J Nucl Med Mol Imaging 2011 )
Will PET Replace Single Photon Emission
Computed Tomography?
Decision relevant aspects:
1. Availability of PET/CT scanners for cardiac
studies.
2. Patient volume.
3. Preference for bicycle stress test?
4. Reembursement for PET?
5. Clinical role of MFR quantification with PET?
6. Will flow quantification with SPECT/CT be feasible
in the near future?
The future will tell!
University Hospitals of Geneva,
Division of Cardiology
Thank You for your Attention !