Inspect quantitative signals in placental histopathology: Computer-assisted multiple functional tissues identification through multi-model fusion and distillation framework

Pathological analysis of placenta is currently a valuable tool for gaining insights into pregnancy outcomes. In placental histopathology, multiple functional tissues can be inspected as potential signals reflecting the transfer functionality between fetal and maternal circulations. However, the identification of multiple functional tissues is challenging due to (1) severe heterogeneity in texture, size and shape, (2) distribution across different scales and (3) the need for comprehensive assessment at the whole slide image (WSI) level. To solve aforementioned problems, we establish a brand new dataset and propose a computer-aided segmentation framework through multi-model fusion and distillation to identify multiple functional tissues in placental histopathologic images, including villi, capillaries, fibrin deposits and trophoblast aggregations. Specifically, we propose a two-stage Multi-model Fusion and Distillation (MMFD) framework. Considering the multi-scale distribution and heterogeneity of multiple functional tissues, we enhance the visual representation in the first stage by fusing feature from multiple models to boost the effectiveness of the network. However, the multi-model fusion stage contributes to extra parameters and a significant computational burden, which is impractical for recognizing gigapixels of WSIs within clinical practice. In the second stage, we propose straightforward plug-in feature distillation method that transfers knowledge from the large fused model to a compact student model. In self-collected placental dataset, our proposed MMFD framework demonstrates an improvement of 4.3% in mean Intersection over Union (mIoU) while achieving an approximate 50% increase in inference speed and utilizing only 10% of parameters and computational resources, compared to the parameter-efficient fine-tuned Segment Anything Model (SAM) baseline. Visualization of segmentation results across entire WSIs on unseen cases demonstrates the generalizability of our proposed MMFD framework. Besides, experimental results on a public dataset further prove the effectiveness of MMFD framework on other tasks. Our work can present a fundamental method to expedite quantitative analysis of placental histopathology.