Development of apparatus and software for myocardial contrast echocardiography

We can now perform myocardial contrast echocardiography (MCE) at bed-side with intravenous injection of Levovist. High mechanical index and triggered image are essential techniques to obtain myocardial contrast enhancement. Several imaging modalities, including harmonic-B, harmonic power Doppler, pulse inversion, ultraharmonic and 1.5 harmonic, are used to detect harmonic signals originating from microbubbles. MCE provides a noble technique for the diagnosis of myocardial infarction and ischemia as an area of hypo-enhancement or contrast defect. At present, however, there are several drawbacks with MCE that make the evaluation of MCE images difficult. Contrast enhancement is heterogeneous among myocardial segments in normal subjects and thus contrast defect does not necessarily imply any abnormality. This is because contrast enhancement is influenced by several factors, including concentration of microbubbles, acoustic power and so on. To resolve these problems, we have developed a new calibration method of MCE image. We hypothesized that we can reduce heterogeneity of contrast intensity and can estimate myocardial blood volume (MBV) by calibrating myocardial contrast amplitude (CA) to CA of the adjacent left ventricular (LV) cavity. Since CA is proportional to bubble concentration, we can estimate MBV by taking the ratio of myocardial CA to CA of the adjacent LV cavity. In normal segment, a mean of 14.5 dB reduction in myocardial CA from CA of 100% blood LV cavity, implies about 4 ml blood/100 g LV mass. In the infarct segments, there was a - 21 dB reduction from the LV cavity, implying < 1 ml blood/100 g LV mass, and this was significantly lower than in normal segments. By making a color-coded map of calibrated myocardial CA, we can estimate spatial distribution of irreversibly damaged myocardium as a area of calibrated CA < - 18 dB. This new calibration method provides a simple and noninvasive estimate of MBV in the clinical setting. Measuring MBV provided useful estimates of myocardial viability in patients with myocardial infarction relatively independent of heterogeneity of acoustic fields.