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Nuclear Cardiology

Nuclear Cardiology. John N. Hamaty D.O. Second year student module. Nuclear cardiology has been an active clinical discipline for more than two decades. Indirect measure of coronary perfusion to the myocardium.

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Nuclear Cardiology

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  1. Nuclear Cardiology John N. Hamaty D.O. Second year student module

  2. Nuclear cardiology has been an active clinical discipline for more than two decades. Indirect measure of coronary perfusion to the myocardium. Utilized for the assessment of functional categories as well as prognosis and risk.

  3. Instrumentation • Scintillation (gamma) camera • Collimation (focusing Lens) • Computer (principal component)-processor

  4. Spect Imaging • Single-photon emission computed tomography • Planar images obtained over 180 degree arc • Three planes- • A) short axis • B) Horizontal • C) Vertical

  5. Myocardial perfusion imaging • Allows RELATIVE distribution of myocardial blood flow • Absolute quantification is not feasible with spect • PET scanning is only absolute test

  6. Myocardial perfusion imaging • Most important clinical application of myocardial perfusion imaging is in conjunction with stress testing for evaluation of ischemic heart disease

  7. Stress testing • Objective is to “stress” the heart via treadmill or pharmacologic testing • Alterations in heart rate, O2 consumption and blood pressure effect uptake of the nuclear agent. • Goal heart rate is 85% of predicted based on age (220-age) then 85% is target. • Sensitivity/Specificity is 85% with nuclear/echo augmentation

  8. Myocardial perfusion imaging • Demonstrated that findings on stress images reflect the hemodynamic and functional significance of coronary artery stenosis and thus provide important prognostic information.

  9. Radiopharmaceuticals Thallium-201 Technetium-99

  10. Thallium-201 • Cyclotron produced • Doses of 3-4 mCi • Initial myocardial accumulation is proportional to myocardial blood flow. • Continuous exchange of Tl takes place across the cell membrane.

  11. Thallium-201 • Energy requiring (Na-K-Atp-ase) • Cell re-accumulation of Tl gives effective half-life in heart of 7.5 hours. • Unique property because it allows early and late imaging after injection

  12. Thallium-201 • Images immediately after injection reflect the flow dependent initial distribution and thus regional myocardial blood flow-Ischemia

  13. Thallium-201 • Images taken after a delay of 2-24 hours reflect the distribution of the potassium pool and hence allow for detection of Myocardial Viability

  14. Myocardial Viability • Detection of living cells despite hypo-akinesis of ventricular contractility • Stunned myocardium • Hibernating myocardium

  15. Technetium-99 • Emmits Gamma rays at 140 kev • Half-life is 6 hours • Slow body clearance • 30 mCi • Initial distribution is similar to Tl and is proportional to regional blood blow

  16. Technetium-99M • Difference is tech extraction from the heart is greater (65%) and redistribution is much less than Tl. • Because the intracellular retention is relatively fixed over time, no significant redistribution occurs.

  17. Technetium-99M • Since no significant redistribution occurs, the myocardial blood flow at the time of injection is “frozen” over time and imaging can occur hours later.

  18. Technetium-99M • This also allows for assessment of wall motion and ejection fraction. Since image is “fixed” for a period of time, we can look at systolic and diastolic function. Allows greater sensitivity in detection of infarcted and ischemic myocardium.

  19. Gated spect imaging • This has increased the sensitivity and specificity of interpretation due to detection of breast/diaphram artifact. • Chamber size and right ventricular function can also be assessed

  20. Dual isotope imaging • Utilizing an “Hybrid” of imaging proticals, two injections of rest thallium and stress tecnetium • Greater patient throughput • Allows for viability testing • Comparing apples and oranges(two different agents)

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