Nuclear CardiologyJohn 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.

Utilized for the assessment of functional categories as well as prognosis and risk.

Instrumentation

Scintillation (gamma) camera

Collimation (focusing Lens)

Computer (principal component)-processor

Spect Imaging

Single-photon emission computed tomography

Planar images obtained over 180 degree arc

Three planes- A) short axis B) Horizontal C) Vertical

Myocardial perfusion imaging

Allows RELATIVE distribution of myocardial blood flow

Absolute quantification is not feasible with spect

PET scanning is only absolute test

Myocardial perfusion imaging

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

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

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.

Radiopharmaceuticals

Thallium-201

Technetium-99

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.

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

Thallium-201

Images immediately after injection reflect the flow dependent initial distribution and thus regional myocardial blood flow-Ischemia

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

Myocardial Viability

Detection of living cells despite hypo-akinesis of ventricular contractility

Stunned myocardium

Hibernating myocardium

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

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.

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.

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.

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

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)