Digital subtraction angiographic imaging of coronary flow reserve

Recent studies have demonstrated that subjective assessment of the severity of coronary artery stenoses results in poor interobserver concordance and poor correlation with physiologic significance as determined by Doppler measurements of coronary flow reserve. Use of the coronary flow reserve as an integrated measure of the effect of stenosis geometry has been emphasized within the context of quantitative cinemetric analysis. The comparison of two parametric digital subtraction angiographic flow images obtained before and after hyperemic intervention has led to calculation of flow reserve values that correlate well with electromagnetic flowmeter data in dogs. By means of a similar model relating blood flow and image variables, single flow ratio images have been formed. These parametric images provide a two-dimensional display of the ratio of hyperemic flow to baseline flow. Linear temporal interpolation of data from a sequence of cardiac phase-matched subtraction images is used to improve the resolution of the displayed flow ratios. Summation of flow variables measured within the perfusion bed was used to calculate a value for the overall coronary flow reserve and to characterize the significance of isolated lesions in an open-chest canine preparation. A linear regression calculation relating parametric image flow ratio values to electromagnetic flowmeter measurements resulted in a linear fit of y = .96x - 0.19 with a correlation coefficient of .90. The direct visual representation of flow ratio distribution provided by the parametric imaging method may aid in the interpretation of multiple complex lesions as well as of single lesions.