Flow and flow reserve by parametric imaging

Summary

9 mongrel dogs were instrumented with electromagnetic flow probes (EMF) to measure coronary blood flow through the left anterior descending (LAD) and left circumflex (LCX) coronary arteries at rest and after maximal, adenosine induced coronary vasodilation. Relative coronary blood flow was determined by parametric imaging using digital subtraction angiography (DSA). Transmural myocardial perfusion of the LAD and LCX beds was determined with tracer-labeled microspheres. Coronary flow reserve (CFR, maximal coronary blood flow divided by resting blood flow) was calculated under control conditions and after constriction of the proximal LAD or LCX by a screw occluder. Coronary blood flow showed a good correlation between EMF and microspheres (correlation coefficient r= 0.87, p< 0.001) with a standard error of estimate (SEE) of 0.78 ml/gm/min. CFR also showed a good correlation between EMF and microspheres (r= 0.82, p< 0.001) with an SEE of 0.93. There was a moderate correlation between EMF and DSA (r= 0.68, p< 0.001) with a SEE of 1.35 (=40% of the mean CFR). The correlation coefficient between microspheres and DSA was 0.54 (p< 0.01) with an SEE of 1.46 (=39% of the mean CFR). Thus determination of CFR by parametric imaging is associated with large variations that are greater than variations also inherent in the two reference techniques. This low precision is probably due to the superposition of different cardiac structures in the two-dimensional display of a three-dimensional perfusion zone, potentially in-homogeneous contrast distribution, poor temporal resolution of the onceper-cycle imaging, inadequate displacement of blood by contrast material, and perturbations of flow caused by contrast material.