Myocardial blood flow as measured by fractional uptake of rubidium-84 and microspheres

Area of Science:

• Cardiovascular physiology
• Nuclear cardiology
• Myocardial perfusion imaging

Background:

• Accurate measurement of myocardial blood flow (MBF) is crucial for diagnosing and managing ischemic heart disease.
• Rubidium-84 (Rb-84) fractional uptake is a potential method for MBF assessment, but its reliability under various physiological conditions needs validation.
• Microspheres are considered a gold standard for MBF measurement but are invasive and not suitable for clinical use.

Purpose of the Study:

• To compare the accuracy of Rb-84 fractional uptake with microsphere-based methods for measuring total and regional MBF.
• To evaluate the reliability of Rb-84 uptake in the presence of myocardial ischemia and pharmacologic interventions.
• To assess the impact of varying flow rates on the accuracy of the Rb-84 fractional uptake method.

Main Methods:

• Open-chested dogs (n=47) underwent simultaneous measurements of MBF using Rb-84 fractional uptake and differently labeled microspheres (Cerium-141 or Chromium-51).
• Measurements were performed under control conditions, following left anterior descending coronary artery ligation, and after administration of isoproterenol and dipyridamole.
• Regional MBF was assessed in the left ventricle, posterior wall (reference area), and anterior wall (ischemic area).

Main Results:

• No significant differences were observed between Rb-84 fractional uptake and microsphere methods for total and regional MBF measurements.
• The accuracy of Rb-84 uptake remained consistent across control, ischemic, and drug-intervention states.
• Estimates of ischemic area size were comparable between the two methods.

Conclusions:

• Fractional uptake of Rb-84 is a reliable and accurate method for quantifying myocardial blood flow, even in the setting of ischemia and pharmacologic manipulation.
• The method's validity is maintained across a range of flow rates, suggesting that variations in extraction ratio do not significantly impact results.
• Rb-84 fractional uptake offers a dependable alternative for assessing myocardial perfusion, particularly in research settings involving ischemia and drug studies.