Reproducibility of regional placental vascularity/perfusion measurement using 3D power Doppler

Abstract

Objectives: To assess reproducibility and regional variability of placental perfusion measurement using three-dimensional (3D) power Doppler VOCAL() (Virtual Organ Computer-aided AnaLysis).

Methods: Twenty pregnant women at 26-34 weeks' gestation with normally grown, biophysically normal, singleton pregnancies with anterior placentae had placental power Doppler mapping data stored digitally from each of the four placental quadrants. Each was imaged by two investigators, with two datasets stored per investigator per quadrant. 5760 data values from the 320 datasets were evaluated by the same two investigators. Power Doppler imaging of the placental cord insertion was performed to generate a value for standardization as 'fractional moving blood volume' if appropriate. The vascularization index (VI), flow index (FI) and vascularization flow index (VFI) were calculated from spherical regions-of-interest to assess reproducibility within and between quadrants and between investigators for both acquisition and analysis.

Results: We found extensive variability for all readings. For repeated measurements within the same dataset the intra-analyzer intraclass correlation coefficient (ICC) range was: 0.24-0.57 for VI, 0.33-0.78 for FI and 0.12-0.48 for VFI. The corresponding interanalyzer ICC range was: 0.38-0.92 for VI, 0.40-0.85 for FI and 0.10-0.92 for VFI. The intra-acquirer variability (paired t-test) mean differences range was: - 3.91 to 4.71 for VI, - 2.68 to 3.31 for FI and - 2.23 to 2.78 for VFI; the corresponding interacquirer variability (paired t-test) range was: - 1.92 to 5.18 for VI, - 3.06 to 2.04 for FI and - 1.69 to 2.60 for VFI. The regional variability range (coefficient of variation) was: 6.28-126.34% for VI, 2.26-49.01% for FI and 6.09-151.55% for VFI. For all analyzed data, FI showed least variability and cord values for VI were consistently 100% (mean VFI, 98.4 and 98.8 between observers).

Conclusions: There is insufficient evidence to support the meaning, reliability or reproducibility of VOCAL (VI, FI or VFI) as a tool to quantify placental perfusion, despite its use in multiple publications and journal submissions. There is poor reproducibility at the most fundamental level. Further investigation into the reproducibility of placental perfusion and quantification using VOCAL is required before development and application as a clinically useful tool.