Two-dimensional ultrasonic tissue characterization: backscatter power, endocardial wall motion, and their phase...

To understand the possible differences in reflected ultrasonic energy from normal, ischemic, and infarcted myocardium, we studied 20 open-chest dogs with a commercially available two-dimensional ultrasonic scanner. Echocardiographic radiofrequency images of anterior myocardium were obtained serially during complete coronary occlusion for 2 hr (n = 15) or 5 hr (n = 10), or after temporary coronary clamping for 15 min with release for 1 hr (n = 5). We investigated two variables: the cyclic backscatter power and the phase difference among endocardial wall motion (EWM), cyclic backscatter power (BSP), and left ventricular pressure (LVP). The cyclic BSP decreased from a control (nonischemic) level of 5.1 +/- 0.8 to 2.3 +/- 0.7 dB during ischemia (up to 30 min after coronary ligation). The phase difference between the EWM and BSP progressed from a control (nonischemic) value of 38 +/- 20 to 115 +/- 23 degrees during ischemia. For the infarction period (2 to 5 hr after coronary ligation), the cyclic BSP progressively returned toward baseline control levels to 4.0 +/- 1.2 dB, but the phase had increased further to 170 +/- 28 degrees. The reperfusion study showed a similar decrease in cyclic BSP and an increase in phase after arterial clamping and both returned to near-normal nonischemic values upon arterial release. Simultaneous LVP recordings were performed to assess the phase contribution of endocardial dyskinesis to the total phase difference measurement. At 5 hr the dyskinesis had contributed 46% to the total phase difference, while the backscatter power contributed 54%. However, the EWM contribution occurred immediately while BSP contribution changed progressively during the 5 hr study period.(ABSTRACT TRUNCATED AT 250 WORDS)