Color-coded functional imaging of myocardial perfusion by contrast echocardiography

The arrival time into the myocardium of an echo contrast agent injected upstream in the coronary circulation is inversely related to coronary blood flow (CBF). Aims of this study were (1) to develop a densitometric computerized method for measuring the time to peak increment rate in contrast intensity (TTP) from a series of echo images, (2) to display the anatomic distribution of such measurements as a 'functional' or 'parametric' image, and (3) to test the ability of this method in detecting regional myocardial underperfusion. In seven anesthetized open-chest dogs, 10 mL of the contrast agent SHU-454 were bolus-injected into the aortic root during short axis two-dimensional echo. Injections were performed both at the baseline and after having generated a coronary stenosis limiting resting CBF of the circumflex coronary artery, measured by an electromagnetic flow meter. To identify the perfusion territory of the circumflex coronary artery, injections were also performed after coronary occlusion. End-diastolic echo images were digitized off-line into a 256 x 256 pixel matrix with 256 gray levels per pixel, and the endocardial and epicardial edges of the first image were digitized to build a myocardial mask. Images were spatially filtered (3 x 3 low-pass filter) and temorally filtered (mobile mean). Then, each image was digitally subtraced from the following one. From the sequence of processed images, an algorithm generated a functional image containing in each pixel the corresponding value of TTP. The values of TTP in the anteroseptal (normally perfused) and posterolateral (normal or underperfused) walls were measured, and the delay of posterior v anterior wall was calculated. In baseline images, a short delay in TTP of the posterior v anterior wall was present (0.1 ± 0.2 seconds, P = .05). During circimflex underperfusion, the posterolateral wall showed a further delay of TTP (1.0 ± .7 seconds, P<.05). TTP images were also displayed according to a color code. In baseline images, the ventricular myocardium showed a rather uniform red color; during circumflex underperfusion, the posterolateral wall showed a yellow color. Thus, a functional imaging of myocardial perfusion by contrast echo has been developed, which identifies the presence of regional myocardial underperfusion.