JBHI Journal 2025 Journal Article
ERSR: An Ellipse-constrained pseudo-label refinement and symmetric regularization framework for semi-supervised fetal head segmentation in ultrasound images
- Linkuan Zhou
- Zhexin Chen
- Yufei Shen
- Junlin Xu
- Ping Xuan
- Yixin Zhu
- Yuqi Fang
- Cong Cong
Automated segmentation of the fetal head in ultrasound images is critical for prenatal monitoring. How-ever, achieving robust segmentation remains challenging due to the poor quality of ultrasound images and the lack of annotated data. Semi-supervised methods alleviate the lack of annotated data but struggle with the unique characteristics of fetal head ultrasound images, making it challenging to generate reliable pseudo-labels and enforce effective consistency regularization constraints. To address this issue, we propose a novel semi-supervised framework, ERSR, for fetal head ultrasound segmentation. Our framework consists of the dual-scoring adaptive filtering strategy, the ellipse-constrained pseudo-label refinement, and the symmetry-based multiple consistency regularization. The dual-scoring adaptive filtering strategy uses boundary consistency and contour regularity criteria to evaluate and filter teacher outputs. The ellipse-constrained pseudo-label refinement refines these filtered outputs by fitting leastsquares ellipses, which strengthens pixels near the center of the fitted ellipse and suppresses noise simultaneously. The symmetry-based multiple consistency regularization enforces multi-level consistency across perturbed images, symmetric regions, and between original predictions and pseudo-labels, enabling the model to capture robust and stable shape representations. Our method achieves stateof-the-art performance on two benchmarks. On the HC18 dataset, it reaches Dice scores of 92. 05% and 95. 36% with 10% and 20% labeled data, respectively. On the PSFH dataset, the scores are 91. 68% and 93. 70% under the same settings.