Role of Nuclear medicine in Cardiology

Lokendra Yadav

Radionuclide studies in cardiology

CAD – leading cause of death

Cardiac SPECT – steady growth in last two decades & played an important role in clinical mangement

Radionuclide ventriculography (MUGA)

First pass studies

PET/CT

Detection of IschemiaNoninvasive Testing: Critical Concepts

• Differences between testing options

• Diagnostic accuracy and pretest likelihood of disease

• Posttest risk assessment

Radionuclide ventriculography

99m Tc- RBC blood pool study (ERNA) Acqusition protocol : Gated Processing - Automatic

- Semiautomatic -Manual

Indications : Monitoring LVEF

low LVEFDoxorubicin toxicityStem cell therapy

Indications for Stress Testing Objective confirmation of ischaemia Assessing extent of ischaemia Documenting exercise capacity Functional assessment of known CAD Determining risk and prognosis Determining need for angiography

High risk cut points

Assessing response to treatment

Contraindications for stress testing Acute myocardial infarction (within two days) Unstable angina pectoris Uncontrolled arrhythmias causing symptoms of

hemodynamic compromise Symptomatic severe aortic stenosis Uncontrolled symptomatic heart failure Active endocarditis or acute myocarditis or

pericarditis Acute aortic dissection Acute pulmonary or systemic embolism Acute noncardiac disorders that may affect

exercise performance or may be aggravated by exercise

Stress Testing Options

Exercise stress alone (usually Bruce protocol) Exercise stress with nuclear myocardial perfusion

imaging (MPI) Pharmacologic stress nuclear myocardial perfusion

imaging (MPI) Exercise stress echo Pharmacologic stress echo

Sensitivity and Specificity of Non-invasive Tests for the Diagnosis of CAD*Diagnostic Test

Sensitivity

% (range)

Specificity% (range)

# Studies # Patients

TMT 68 77 132 24,027

Planar MPI 79

(70-94)

73

(43-97)

6 510

SPECT 88

(73-98)

77

(53-96)

8 628

Stress echo 76

(40-100)

88

(80-95)

10 1174

* NEJM Vol. 344, No. 24 June 14, 2001

Exercise stress testing

Treadmill or bicycle ergometer

Protocols vary - symptom limited

Bruce most popular 8 stages Incline and speed

increment every 3 minutes

Target 85-100% maximum age predicted HR

Achieve at least 6 METS for diagnostic accuracy

ECG Patterns Indicative of Myocardial Ischaemia

ECG Patterns Not Indicative of Myocardial Ischaemia

Indications for Myocardial Perfusion Imaging (Exercise or Pharmacologic Stress) Suspected false +ve

or-ve TMT Resting ST changes LBBB,RBBB,LVH,

digitalis,pre-excitation or pacemaker

Women with +ve TMT and low or intermediate probability CAD

Inability to exercise

Prognosis of known CAD Detecting post PTCA or

CABG ischaemia Assessing myocardial

viability Risk evaluation in non-

cardiac surgery patients Assessment functional

significance of documented coronary stenosis

Myocardial Perfusion ImagingExercise Stress Treadmill Bicycle ergometerPharmacologic

Stress dipyridamole Adenosine Dobutamine

Isotopes Thallium 201 Technesium 99m

Sestamibi MIBI (Cardiolyte)

Tetrofosmin (Myoview)

PET Rubidium 82 (flow

agent) FDG (viability)

Scanning

Myocardial Perfusion Gated SPECT Scan

Computer-rendered, 3-D Image of Left Ventricular Surfaces

Coronary Territories

High Risk IndicatorsMyocardial Perfusion Imaging Increased pulmonary thallium uptake indicating low CO

or elevated LVEDP

Ischaemic LV dilatation (TID)

Multiple perfusion defects

Large perfusion defects

NR - 14-7-2011 - Stress-Rest MPS

Stress- Rest Myocardial perfusion imaging

Stress- Adenosine 140 mcg/kg/min for 4 minutes. Injection of 10 mCi of Tc99m labelled MIBI at 2 minutes.

ECG Gated SPECT-CT after approx 45 minutes.

Nitrate augmented Rest myocardial perfusion - 5 mg sublingual nitrate - followed by 30 mCi of Tc99m MIBI, 2 hours after stress

ECG Gated SPECT-CT after 1 hour

NR - 14-7-2011 - Stress - Rest MPS - Slices

NR - 14-7-2011 - Stress - Rest MPS - Polar Plot

NR - 14-7-2011 - Stress - Rest MPS - Scores

NR - 14-7-2011 - Stress - Rest MPS - Viability

NR - 14-7-2011 - Stress - Rest MPS - Summary

PD - 27-7-2011 - Rest MPS

Rest Myocardial perfusion imaging was done 1 hour following iv injection of 24 mCi of Tc-99m MIBI

PD - 27-7-2011 - Rest MPS - Slices

PD - 27-7-2011 - Rest MPS - Polar Plot

PD - 27-7-2011 - Rest MPS - Viability

PD - 27-7-2011 - Rest MPS - LVEF

PD - 27-7-2011 - Rest MPS - Myocardial mass

Limitations of cardiac SPECT

Decreased sensitivity and specificity in single vessel CAD ( 60 – 76% )

Diffuse disease in all three vessels (Balanced ischemia)

Diffuse disease without segmental stenosis(Vulnerable for plaque rupture and coronary events)

Early disease identification Artifacts – Non uniform attenuation Relative low efficiency of Gamma camera Longer acquisition protocols

Characteristics of SPECT vs. PET.

SPECT PET Availability Wide Limited Atten. correction Less accurate

Accurate Spatial resolution 12-15 mm 5-7 mm Protocol 2 days <1 hour Radiation >10 mSv <10 mSv Images Qualitative Quantitative

Hybrid with CT Yes Yes

Rationale for PET/CT MPS

To decrease invasive coronary angiography unless necessary i.e if therapeutic

Highly sensitive and specific Absolute Quantification of myocardial

blood flow Assesment of coronary flow reserve Blood flow,myocardial cell integrity,Wall

motion and LVEF Calcium score & Luminal narrowing

Imaging Protocol

Patient preparation and stress testing - Dypiridamole & adenosine Imaging 82 Rb varies with PET scanner

crystal Reconstruction of images

Perfusion: filtered back projection

Gated wall motion : iterative 2 D Vs 3 D & 4 D PET LVEF PET Vs planar gated blood pool ( r = 0.81) PET Vs MIBI SPECT ( r = 0.91)

Current status of Cardiac PET

Extensive infrastructure Improved PET scanners with LSO

crystal Availability of PET-CT Rubidium –82 PET perfusion tracer

-Generator produced

- Reimbursible since 1995 in USA

- Already clinically useful in tertiary care and community hospitals

Present Status

CMS Reimbursment Fee Schedule Changes State a 20% Increase in Cardiac PET and a 36% Decrease in SPECT

Clinical Indications : Low risk CADIntermediate risk CADLBBBWomenObeseDiabetes

Research : Endothelial function and Plaque bilology

Cardiac PET Perfusion Tracers

Agent Physical half life

Extraction Production

13N NH3 10 min 80 % Cyclotron

82 Rb 75 sec 50-60% Generator

15 O H2O 2 min Diffusible Cyclotron

Rb – 82 Production

Cation like Tl-201 and Potassium analogue Uptake reflects function of blood flow and

myocardial cell integrity Generator produced from Sr-82 Replaced every 4 weeks Decays by positron emission with short half

life (75 sec) Eluted with 25-50 ml normal saline by

controlled elution pump and connected with IV tubing to patient

Fully replenished every 10 min and 90% of max. activity can be available after 5 min.

Imaging Protocol for Rb 82 PET imaging With a LSO PET-CT Scanner

Procedure Time

Positioning (Scout) 1 min

CT transmission scan 1 min

Rest gated imaging 8 min

Rest perfusion imaging 8 min

Pharmacological stress 7 min

CT transmission scan 1 min

Stress imaging 8 min

Total duration 34 min

Diagnostic Accuracy of PET MPI for CAD

Author Year Agent No.of Patient

Sensitivity

Specificity

Gould et al

1986 NH3,Rb 82

50 95 100

Demer 1989 Rb 82 193 94 95

Go et al 1990 Rb 82 202 93 78

Schelbert 1982 NH 3 45 97 100

Yonekura 1987 NH 3 49 93 100

Williams 1989 Rb 82 146 98 93

Stewart 1991 Rb 82 81 84 88

Tamaki 1988 NH 3 25 95 95

Average 791 93 92

Comparison of PET and SPECT MPI for detection of CAD in same patient

Author

et al

Year Tracer Accuracy (% )

Sensitivity

Specificity

Go

n=132

1990 Rb 82

Tl-201

92

78

95

79

82

76

Stewart

n = 81

1991 Rb 82

Tl 201

85

78

87

87

82

52

Tamaki

n=51

1988 NH 3

Tl 201

98

98

98

96

100

100

Total

n=264

PET

SPECT

91

81

93

85

82

67

Coronary calcium score

Clinical applications of PET/CT MPS

Diagnosis of coronary artery disease Assesment of blood flow : Prognosis

(Yosinaga K et al JACC 2006 :48;Sept.1029-30)

Noninvasive coronary angiography (CTA)High false positivity- 25 %Poor assesment of lumen – 18-24%

Early detection of CAD in asymptomatic patients

Identifying plaques by molecular markers Assesment of heart failure

Calcium score,Perfusion and Viabilty

Radiation dose from PET/CT

Study Effective radiation dose (mSv)

PET F-18 FDG (370 MBq) 7.0 N-13 NH3 rest/stress (2×550 MBq) 2.2 Rb-82 rest/stress (2×740 MBq) 3.6 H2O-15 rest/stress (2×740 MBq) 1.4 Transmission Ge-68 rod sources 0.08–0.13

MSCT Calcium scoring 0.7–6.2 CT angiography 3.7–13.0 CT based PET attenuation correction 0.23–

5.66

Utility of PET/CT in CAD

Excellent noninvasive imaging procedure

Extent & severity of perfusion abnormality

Extent of tissue viability Risk stratify each patient prior to

clinical decision making Attractive translational research tool in

combination with molecular probes i.e Cell therapy or Gene therapy

Thank you