The "volumetric" pulsatility index as evaluated by spatiotemporal imaging correlation (STIC): a preliminary description of a novel technique, its application to the endometrium and an evaluation of its reproducibility

We propose new volumetric indices derived from three-dimensional (3-D) power Doppler (PD) using spatiotemporal imaging correlation (STIC) to overcome the influence of machine settings and attenuation. In this study, we describe these indices and evaluate their interobserver reliability: two static-3-D and two STIC PD datasets were acquired from 60 women and two observers (blinded analysis) evaluated vascularization index (VI), the flow index (FI) and the vascularization flow index (VFI) of standardized spherical samples of endometrium. Three new indices were determined based on maximum, minimum and mean values (vPI, vRI_max-min, vS/D_max-min) and two indices from frames subjectively defined as systole and diastole (vRI_sys-dia, vS/D_sys-dia). Highest intraclass coefficient correlations (ICCs) were obtained from vPI derived from VI or VFI (0.77-0.76), followed by vRI_max-min (0.72-0.72) and vS/D_max-min (0.52-0.49). ICCs from indices based on subjectively systole and diastole or FI were consistently lower (<0.40). We conclude that the subjective choice of systolic and diastolic frames only lacks reliability but indices based on complete evaluation may reliably be used.