Role of nuclear medicine

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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

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  • The ischemic cascade is a series of temporal events that occurs after the experimental occlusion of a coronary artery, or clinically, the production of myocardial ischemia.
    By definition, flow disparities are the first physiological changes noted. Abnormalities in ventricular function, first diastolic, then systolic, are noted shortly after the onset of ischemia. This is followed by the development of electrocardiographic (ECG) changes and usually by the onset of angina pectoris.
    Noninvasive testing using exercise ECG relies on late findings within the ischemic cascade. Stress echocardiography depends on the production of ischemia-induced wall motion abnormalities. Flow disparities on stress perfusion imaging are noted early in the ischemic cascade.
    The numbers 1 to 5 correspond to those on the next slide.
    [Adapted from Sigwart U, et al. In: Silent Myocardial Ischemia. W Rutishauser, H Roskamm, eds. Springer-Verlag, Berlin, 1984:29-36.]
  • The gated portion of the SPECT study allows both the visual and quantitative assessment of left ventricular function. These measures include left ventricular ejection fraction and end-diastolic and end-systolic volumes. In addition, this modality achieves excellent visualization of both the endocardial and epicardial surfaces, allowing for the evaluation of left ventricular wall motion and wall thickening.
    In this scan, the top row represents 3 short axis images (apical, mid, and basal short-axis slices) and the bottom row represents the mid horizontal and vertical long-axis slices.
  • Role of nuclear medicine

    1. 1. Role of Nuclear medicine in Cardiology Lokendra Yadav
    2. 2. 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
    3. 3. Detection of Ischemia Noninvasive Testing: Critical Concepts • Differences between testing options • Diagnostic accuracy and pretest likelihood of disease • Posttest risk assessment
    4. 4. Radionuclide ventriculography  99m Tc- RBC blood pool study (ERNA)  Acqusition protocol : Gated  Processing - Automatic - Semiautomatic -Manual  Indications : Monitoring LVEF low LVEF Doxorubicin toxicity Stem cell therapy
    5. 5. 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
    6. 6. 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
    7. 7. 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
    8. 8. 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
    9. 9. 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
    10. 10. ECG Patterns Indicative of Myocardial Ischaemia ECG Patterns Not Indicative of Myocardial Ischaemia
    11. 11. 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
    12. 12. Myocardial Perfusion Imaging Exercise Stress  Treadmill  Bicycle ergometer Pharmacologic Stress  dipyridamole  Adenosine  Dobutamine  Isotopes  Thallium 201  Technesium 99m  Sestamibi MIBI (Cardiolyte)  Tetrofosmin (Myoview)  PET  Rubidium 82 (flow agent)  FDG (viability)
    13. 13. Scanning
    14. 14. Myocardial Perfusion Gated SPECT Scan
    15. 15. Computer-rendered, 3-D Image of Left Ventricular Surfaces
    16. 16. Coronary Territories
    17. 17. High Risk Indicators Myocardial Perfusion Imaging Increased pulmonary thallium uptake indicating low CO or elevated LVEDP  Ischaemic LV dilatation (TID)  Multiple perfusion defects  Large perfusion defects
    18. 18. 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
    19. 19. NR - 14-7-2011 - Stress - Rest MPS - Slices
    20. 20. NR - 14-7-2011 - Stress - Rest MPS - Polar Plot
    21. 21. NR - 14-7-2011 - Stress - Rest MPS - Scores
    22. 22. NR - 14-7-2011 - Stress - Rest MPS - Viability
    23. 23. NR - 14-7-2011 - Stress - Rest MPS - Summary
    24. 24. PD - 27-7-2011 - Rest MPS Rest Myocardial perfusion imaging was done 1 hour following iv injection of 24 mCi of Tc-99m MIBI
    25. 25. PD - 27-7-2011 - Rest MPS - Slices
    26. 26. PD - 27-7-2011 - Rest MPS - Polar Plot
    27. 27. PD - 27-7-2011 - Rest MPS - Viability
    28. 28. PD - 27-7-2011 - Rest MPS - LVEF
    29. 29. PD - 27-7-2011 - Rest MPS - Myocardial mass
    30. 30. 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
    31. 31. 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
    32. 32. 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
    33. 33. 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)
    34. 34. 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
    35. 35. Present Status  CMS Reimbursment Fee Schedule Changes State a 20% Increase in Cardiac PET and a 36% Decrease in SPECT  Clinical Indications : Low risk CAD Intermediate risk CAD LBBB Women Obese Diabetes  Research : Endothelial function and Plaque bilology
    36. 36. 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
    37. 37. 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.
    38. 38. 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
    39. 39. Diagnostic Accuracy of PET MPI for CAD Author Year Agent No.of Patient Sensitivit y Specificit y 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
    40. 40. Comparison of PET and SPECT MPI for detection of CAD in same patient Author et al Year Tracer Accurac y (% ) Sensitivi ty Specifici ty 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
    41. 41. Coronary calcium score
    42. 42. 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
    43. 43. Calcium score,Perfusion and Viabilty
    44. 44. 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
    45. 45. 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
    46. 46. Thank you

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