S⁴R: Separated Self-Supervised Spectral Regression for Hyperspectral Histopathology Image Diagnosis

Hyperspectral images (HSIs) offer great potential for computational pathology. But, limited by the lack of adequate annotated data and the high spectral redundancy of HSIs, traditional supervised learning techniques are usually bottlenecked. To exploit the structural properties of HSIs and learn representations with good transferability, we propose Separated Self-Supervised Spectral Regression (S4R). Concretely, we find one spectral band can be represented by a linear combination of the remaining bands. Regressing the distribution of the linear coefficients learns the inherent properties of HSIs and pathological information about the tissue. Besides, reconstructing the missing band, especially the tissue boundaries makes the model learn pathology details that are critical to downstream tasks. Coupling these two pretext tasks makes the self-supervised model understand spectral structures of HSIs w.r.t. pathological semantics and spatial micro details. Furthermore, we design two brand-new architectures to avoid the interference of extraneous signal based on S4R: S4R-CLS and S4R-SEG for HSI classification and segmentation, respectively. Two downstream tasks are incorporated into a unified framework, which first encodes different bands from HSIs via a depthwise separable encoder, and then selectively aggregates band features to generate final predictions. In S4R-SEG, we propose to pick the best matching bands with the guidance of a classification paradigm. Extensive experiments show S4R performs much better than competitors on both tasks. Theoretical analysis and clinical discussion also indicate the great potential for further medical applications. The code and pre-trained checkpoints are available at https://github.com/DeepMed-Lab-ECNU/S4R.