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 integrate d backscatter at end-diastole and end-systole, was dependent on the corresp onding time delay. We measured the cyclic variation in four myocardial segm ents of the parasternal short-axis view in 23 healthy subjects. The "appare nt" magnitude, actual magnitude, and time delay were compared for each segm ent. 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 poste rior wall. Segments exhibiting large time delays (> 1.0) resulted in a reve rsal in sign of the "apparent' magnitude of cyclic variation in one instanc e, and underestimated the true magnitude in both cases. Thus, estimates of the "apparent" magnitude of the cyclic variation are dependent on the assoc iated time delay, whereas a properly defined magnitude is not. (C) 1999 Wor ld Federation for Ultrasound in Medicine & Biology.