Fourier phase analysis can be used to objectively analyze real-time myocardial contrast echocardiograms

Real-time myocardial contrast echocardiography (MCE) is increasingly used to assess myocardial perfusion. However, objective methods for evaluating MCE are not yet widely available. We sought to validate the ability of Fourier analysis applied to MCE to assess serial changes in microvascular perfusion during coronary occlusion and reperfusion.

Six pigs underwent 45 min of left anterior descending coronary artery (LAD) occlusion followed by 120 min of reperfusion. Real time MCE was performed at baseline, during coronary occlusion, and at 5, 30, 60 and 120 min of reperfusion. Signal intensities from replenishment curves were fitted to an exponential function to obtain plateau SI (A) and the rate of SI rise (b). MCE images were mathematically transformed using a first-harmonic Fourier algorithm displaying the sequence of myocardial intensity changes as phase angles in parametric images. The phase angle difference (PD) of posterior vs. anterior region was calculated as an index of myocardial opacification heterogeneity and compared to MCE index of myocardial blood flow A x b.

After initial hyperemia, a progressive reduction in flow was observed during reperfusion. During LAD occlusion signal intensities were significantly reduced in anterior regions (A x b = 0.02+/-0.01) compared to baseline (1.2+/-0.34, p < 0.01) defining risk areas and approached higher levels postrecanalization (A x b = 1.48+/-0.6) but gradually decreased during 120 min of reperfusion (A = 0.51+/-0.3, p < 0.01). Similarly, profiles of phase angles in LAD perfusion territorities were consistently modified during reperfusion. The mean PD at baseline was 18 degrees+/-15 degrees. PD decreased during coronary occlusion to -108 degrees+/-38 degrees, increased to 29 degrees+/-19 degrees postrecanalization but decreased to -61 degrees+/-35 degrees after 120 min of reperfusion. PD significantly correlated with A (r = 0.8, p < 0.0001) and b (r = 0.73, p < 0.0001).

The progressive reduction in post-ischemic microvascular perfusion was accurately detected by real-time MCE. Fourier phase imaging is feasible to quantify dynamics of myocardial opacification in a simple and objective format and is a promising approach for the interpretation of contrast echocardiograms.