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Fluorescent vs. radioactive microsphere measurement of regional myocardial blood flow
G L Chien1, C G Anselone, R F Davis
1Department of Anesthesiology, Oregon Health Sciences University, Portland 97201, USA.
Objectives:
This study compared simultaneous regional myocardial blood flow (RMBF) measurements using fluorescent microspheres (FM) and radiolabeled microspheres (RM). The utility of an internal standard during processing was also examined.
Methods:
Paired FM and RM were injected into the left atrium of 9 anaesthetised rabbits. RMBF was altered by use of either regional ischaemia or (-)-N6-(2-phenylisopropyl)-adenosine. Radioactivity of blood reference and tissue samples was quantitated using standard methods. Samples were then digested with potassium hydroxide and microspheres recovered by vacuum filtration, with an additional label of FM as the internal standard. FM labels were extracted using Carbitol acetate and quantitated using fluorescence spectroscopy. Agreement between the fluorescent and radioactive methods was assessed using both orthogonal regression and difference-against-mean analyses.
Results:
Using recovery-uncorrected data, the slope of the orthogonal regression of RM and FM-determined RMBF was not statistically different from 1, but the intercept was statistically different from 0 [-0.03(0.01), P = 0.005] and the mean RMBF by each method differed from one another [1.24(0.08) vs. 1.17(0.08) ml.min-1.g-1, P = 0.0002]. The mean +/- 2 s.d. of the differences of RMBF (RM minus FM) was +0.07 +/- 0.30 ml.min-1.g-1. Although recovery of FM from tissue averaged 97.6(1.2)%, use of the internal standard to correct for losses substantially improved the agreement between RM and FM-determined RMBF: the orthogonal regression slope was not statistically different from 1, the intercept was not statistically different from 0, and the means of the flows were not different. The mean +/- 2 s.d. of the differences of RMBF was -0.01 +/- 0.22 ml.min-1.g-1. The internal standard also improved RMBF estimates from samples with simulated large spillage during processing.
Conclusion:
Fluorescent microspheres are an equivalent alternative to radiolabeled microspheres for the estimation of RMBF. Although the overall recovery of microspheres using this technique was high, use of an internal standard is recommended for correction of random losses.
Insights
Fluorescent microspheres (FM) provide an equivalent alternative to radiolabeled microspheres (RM) for measuring regional myocardial blood flow (RMBF). Using an internal standard during processing significantly improves the accuracy of FM-based RMBF measurements.
Area of Science:
- Cardiovascular Physiology
- Biomedical Imaging
- Methodological Validation
Background:
- Accurate measurement of regional myocardial blood flow (RMBF) is crucial for diagnosing and managing cardiovascular diseases.
- Radiolabeled microspheres (RM) are a common method for RMBF assessment, but fluorescent microspheres (FM) offer potential advantages.
- Evaluating the comparability and reliability of FM against RM is essential for clinical adoption.
Purpose of the Study:
- To compare the accuracy of simultaneous regional myocardial blood flow (RMBF) measurements using fluorescent microspheres (FM) and radiolabeled microspheres (RM).
- To assess the utility of incorporating an internal standard during the processing of FM samples.
- To determine if FM can serve as a reliable alternative to RM for RMBF quantification.
Main Methods:
- Paired injections of FM and RM into the left atrium of anesthetized rabbits.
- Induction of altered RMBF using regional ischemia or pharmacological agents.
- Quantification of radioactivity and fluorescence in blood and tissue samples.
- Recovery of microspheres from digested tissue samples, with FM used as an internal standard.
- Analysis of agreement between FM and RM methods using orthogonal regression and difference-against-mean analyses.
Main Results:
- Without correction, FM and RM methods showed statistically different intercepts and mean RMBF values, indicating systematic differences.
- The mean difference between uncorrected RM and FM RMBF was +0.07 +/- 0.30 ml/min/g.
- Use of an internal standard to correct for FM recovery (average 97.6%) significantly improved agreement between methods.
- Corrected FM measurements resulted in no statistically significant differences in slope, intercept, or mean RMBF compared to RM.
- The mean difference between corrected RM and FM RMBF was -0.01 +/- 0.22 ml/min/g.
Conclusions:
- Fluorescent microspheres (FM) are a validated and equivalent alternative to radiolabeled microspheres (RM) for estimating regional myocardial blood flow (RMBF).
- While overall FM recovery is high, employing an internal standard is strongly recommended to correct for potential random losses during sample processing.
- This methodological refinement enhances the precision and reliability of FM-based RMBF measurements.