Use of four-dimensional analysis of power Doppler perfusion indices to demonstrate cardiac cycle pulsatility in fetoplacental flow.

The aim of this study is to quantify fetoplacental cardiac cycle variation in virtual organ computer-aided analysis (VOCAL) power Doppler (PD) indices by novel application of spatio-temporal imaging correlation (STIC). We recruited 25 healthy women (20-34 weeks gestation) with uncomplicated, viable singleton pregnancies with anterior placentae. Three four-dimensional (4-D) STIC PD datasets of the fetoplacental circulation were obtained above the placental cord insertion. The vascularization index (VI), flow index (FI) and vascularization-flow index (VFI) were calculated offline using a standardized spherical sonobiopsy technique for all frames of the cardiac cycle. Clear maximum (systole) and minimum (diastole) values with progressive fluctuation were seen in the majority of datasets (VI 66/75 [88%]; FI 58/75 [77%]; VFI 68/75 [91%]). Variation from mean was: VI ± 3.33% (0.34%-9.69%); VFI ± 3.46% (0.27%-10.02%); FI ± 0.74% (0.14%-1.60%). All indices were significantly higher in systole than diastole (p < 0.001). Mean systolic:diastolic ratios were: VI 1.07 (SD 0.06), FI 1.01 (SD 0.01) and VFI 1.07 (SD 0.06). Intraclass correlation coefficients (ICCs) for the frames ascribed to systole and diastole and to the mean value across the cardiac cycle of the indices (95% confidence interval [CI]) were: systole VI 0.91 (0.83-0.96), FI 0.85 (0.72-0.92), VFI 0.92 (0.85-0.96); diastole VI 0.91 (0.84-0.96), FI 0.84 (0.71-0.92), VFI 0.92 (0.86-0.96); mean VI 0.91 (0.84-0.96), FI 0.84 (0.72-0.92), VFI 0.92 (0.86-0.96). There is clear cardiac cycle variation in VOCAL indices of fetoplacental blood flow, establishing the need to control for phase of the cardiac cycle, and raising the possibility of future 4-D evaluation of vascular flow change or impedance.