Viewing rate and reference ranges for papillary muscle areas of the foetal heart using four-dimensional ultrasound in the rendering mode

Objective To assess the viewing rate and determine reference ranges ​​for the papillary muscle areas in the foetal atrio-ventricular valves using four-dimensional (4D) ultrasound and spatio-temporal image correlation (STIC) in the rendering mode. Methods This cross-sectional prospective study included 310 4D STIC volume data sets of normal foetuses between 18w0d and 34w0d of gestation. The papillary muscles were antero-lateral (MPAL) and postero-medial (MPPM) to the mitral valve and antero-superior (MPAS), inferior (MPI) and septal (MPS) to the tricuspid valve. Polynomial regressions were built to determine the reference ranges, and adjustments were made using the determination coefficient (R2). To assess inter-observer reproducibility, the intra-class correlation coefficient (ICC) was used. Results Identification of the papillary muscles was possible in 89.3% patients. The best-fit regression equations between papillary muscle areas and gestational age were second degree. The inter-observer reproducibility was good (ICC: 0.98 to MPAS, 0.97 to MPI, 0.98 to MPS, 0.98 to MPAL, and 0.97 to MPPM). Conclusions Identification of the papillary muscles of the foetal valves was possible in the most of the 4D STIC volume data sets, enabling the determination of reference ranges using the rendering mode. The reference ranges for the papillary muscle areas were determined.