MOTIVATION: Intracellular organelle networks (IONs) such as the endoplasmic reticulum (ER) network and the mitochondrial (MITO) network serve crucial physiological functions. The morphology of these networks plays a critical role in mediating their functions. Accurate image segmentation is required for analyzing the morphology and topology of these networks for applications such as molecular mechanism analysis and drug target screening. So far, however, progress has been hindered by their structural complexity and density. RESULTS: In this study, we first establish a rigorous performance baseline for accurate segmentation of these organelle networks from fluorescence microscopy images by optimizing a baseline U-Net model. We then develop the multi-resolution encoder (MRE) and the hierarchical fusion loss (Lhf) based on two inductive components, namely low-level features and topological self-similarity, to assist the model in better adapting to the task of segmenting IONs. Empowered by MRE and Lhf, both U-Net and Pyramid Vision Transformer (PVT) outperform competing state-of-the-art models such as U-Net++, HR-Net, nnU-Net, and TransUNet on custom datasets of the ER network and the MITO network, as well as on public datasets of another biological network, the retinal blood vessel network. In addition, integrating MRE and Lhf with models such as HR-Net and TransUNet also enhances their segmentation performance. These experimental results confirm the generalization capability and potential of our approach. Furthermore, accurate segmentation of the ER network enables analysis that provides novel insights into its dynamic morphological and topological properties. AVAILABILITY AND IMPLEMENTATION: Code and data are openly accessible at https://github.com/cbmi-group/MRE.

The scarcity of annotated data, particularly for rare diseases, limits the variability of training data and the range of detectable lesions, presenting a significant challenge for supervised anomaly detection in medical imaging. To solve this problem, we propose a novel unsupervised method for medical image anomaly detection: Attention-Augmented Differentiable top-k Feature Adaptation (ADFA). The method utilizes Wide-ResNet50-2 (WR50) network pre-trained on ImageNet to extract initial feature representations. To reduce the channel dimensionality while preserving relevant channel information, we employ an attention-augmented patch descriptor on the extracted features. We then apply differentiable top-k feature adaptation to train the patch descriptor, mapping the extracted feature representations to a new vector space, enabling effective detection of anomalies. Experiments show that ADFA outperforms state-of-the-art (SOTA) methods on multiple challenging medical image datasets, confirming its effectiveness in medical anomaly detection.

In this study we propose an explicit formulation of the learning behavior of deep neural networks (DNNs) trained with noisy labels in image classification. Specifically, we show theoretically and experimentally that the training process can be divided into two phases: a learning phase in which the outputs of DNNs converge to a hidden noisy label distribution; and a memorization phase in which DNNs start to overfit until the output for each sample converges to its corresponding noisy label. This two-phase formulation enables us to resolve a common pitfall of existing methods for robust training against noisy labels based on the small-loss assumption, namely clean samples have smaller losses than noisy samples in the early training phase. We show that these methods fail when the noise transition matrix is not column diagonally maximal and that this pitfall can be fixed by a simple modification of the small-loss assumption.

How deep neural networks (DNNs) learn from noisy labels has been studied extensively in image classification but much less in image segmentation. So far, our understanding of the learning behavior of DNNs trained by noisy segmentation labels remains limited. In this study, we address this deficiency in both binary segmentation of biological microscopy images and multi-class segmentation of natural images. We generate extremely noisy labels by randomly sampling a small fraction (e.g., 10%) or flipping a large fraction (e.g., 90%) of the ground truth labels. When trained with these noisy labels, DNNs provide largely the same segmentation performance as trained by the original ground truth. This indicates that DNNs learn structures hidden in labels rather than pixel-level labels per se in their supervised training for semantic segmentation. We refer to these hidden structures in labels as meta-structures. When DNNs are trained by labels with different perturbations to the meta-structure, we find consistent degradation in their segmentation performance. In contrast, incorporation of meta-structure information substantially improves performance of an unsupervised segmentation model developed for binary semantic segmentation. We define meta-structures mathematically as spatial density distributions and show both theoretically and experimentally how this formulation explains key observed learning behavior of DNNs.

To identify and localize macromolecules of interest in crowded intracellular environment, the low signal-to-noise ratio and missing imaging wedge of cryo-electron tomography (cryo-ET) data pose substantial technical challenges. Currently, mainstream approaches of 3D particle picking in cryo-ET either follow the ‘segment-then-cluster’ strategy, or extract potential structural regions as sub-tomograms and then perform classification. Different from these two-step methods, we solve the problem using a one-step instance segmentation approach, termed 3D-SOLOv2. Specifically, the category and mask of each 3D particle are predicted according to the particle’s location and size. To solve the lack of real masks for 3D particles in cryo-ET, a Gaussian-shaped mask is proposed to approximate real masks. When tested on simulated datasets of SHREC2020 challenge, our model achieves the fastest inference speed and the state-of-the-art performance for both localization and classification tasks. When tested on real cryo-ET dataset of EMPIAR-10045, our model also achieves better performance than other methods.