Dependence of 'apparent' magnitude on the time delay of cyclic variation of myocardial backscatter

The goal of this study was to determine if the 'apparent' magnitude of the cyclic variation, defined as the difference between the values of integrated backscatter at end-diastole and end-systole, was dependent on the corresponding time delay. We measured the cyclic variation in four myocardial segments of the parasternal short-axis view in 23 healthy subjects. The 'apparent' magnitude, actual magnitude, and time delay were compared for each segment. Measured time delays were: 2.22 ± 0.71 (lateral wall); 1.65 ± 0.66 (inferior septum); and approximately 1.0 for the anterior septum and posterior wall. Segments exhibiting large time delays (> 1.0) resulted in a reversal in sign of the apparent magnitude of cyclic variation in one instance, and underestimated the true magnitude in both cases. Thus, estimates of the 'apparent' magnitude of the cyclic variation are dependent on the associated time delay, whereas a properly defined magnitude is not.