[An approach of in vivo measurement for ultrasonic myocardial tissue characterization].

The purpose of this study is to characterize regional myocardial alternations of reflected ultrasound throughout a cardiac cycle in normal and ischemic myocardium. Integrated ultrasonic backscatter (2-5 MHz) gated R wave of ECG was measured at the base, middle and apex in 4 dogs, and the apex before and after ischemia in other 4 dogs. Quantitative ultrasonic backscatter (IB) was reflected to a steel reflector. At the apex and middle, where a cyclic pattern of IB was discernible, maximum values were recorded near end diastole and minimum near end systole. The amplitude of the variation of IB throughout a cardiac cycle for each region increase progressively from base to middle to apex. Time-averaged IB over a cardiac cycle (averaged IB) was similar for each area of the heart (base = -50.6 +/- 0.5 dB (mean +/- SE), middle -49.4 +/- 0.5 dB, apex -49.7 +/- 0.6 dB. p = NS for comparison of any two regions). After occluding left anterior descending coronary artery for 30 minutes, the variation of IB was markedly blunted and averaged IB increased significantly (-47.5 +/- 0.5 dB. p less than 0.01 compared with preocclusion (-50.8 +/- 0.5 dB]. These results suggested that IB and averaged IB may permit assessment of intrinsic geometrical changes throughout a cardiac cycle (contractile properties) and histological changes respectively.