Mask-R2CNN: a distance-field regression version of Mask-RCNN for fetal-head delineation in ultrasound images

Background and objectives Fetal head-circumference (HC) measurement from ultrasound (US) images provides useful hints for assessing fetal growth. Such measurement is performed manually during the actual clinical practice, posing issues relevant to intra- and inter-clinician variability. This work presents a fully automatic, deep-learning-based approach to HC delineation, which we named Mask-(RCNN)-C-2. It advances our previous work in the field and performs HC distance-field regression in an end-to-end fashion, without requiring a priori HC localization nor any postprocessing for outlier removal.Methods Mask-(RCNN)-C-2 follows the Mask-RCNN architecture, with a backbone inspired by feature-pyramid networks, a region-proposal network and the ROI align. The Mask-RCNN segmentation head is here modified to regress the HC distance field.Results Mask-(RCNN)-C-2 was tested on the HC18 Challenge dataset, which consists of 999 training and 335 testing images. With a comprehensive ablation study, we showed that Mask-(RCNN)-C-2 achieved a mean absolute difference of 1.95 nun (standard deviation = +/- 1.92 mm), outperforming other approaches in the literature.Conclusions With this work, we proposed an end-to-end model for HC distance-field regression. With our experimental results, we showed that Mask-(RCNN)-C-2 may be an effective support for clinicians for assessing fetal growth.