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Anatomically Constrained Neural Networks (ACNN): Application to Cardiac Image Enhancement and Segmentation (1705.08302v4)

Published 22 May 2017 in cs.CV

Abstract: Incorporation of prior knowledge about organ shape and location is key to improve performance of image analysis approaches. In particular, priors can be useful in cases where images are corrupted and contain artefacts due to limitations in image acquisition. The highly constrained nature of anatomical objects can be well captured with learning based techniques. However, in most recent and promising techniques such as CNN based segmentation it is not obvious how to incorporate such prior knowledge. State-of-the-art methods operate as pixel-wise classifiers where the training objectives do not incorporate the structure and inter-dependencies of the output. To overcome this limitation, we propose a generic training strategy that incorporates anatomical prior knowledge into CNNs through a new regularisation model, which is trained end-to-end. The new framework encourages models to follow the global anatomical properties of the underlying anatomy (e.g. shape, label structure) via learned non-linear representations of the shape. We show that the proposed approach can be easily adapted to different analysis tasks (e.g. image enhancement, segmentation) and improve the prediction accuracy of the state-of-the-art models. The applicability of our approach is shown on multi-modal cardiac datasets and public benchmarks. Additionally, we demonstrate how the learned deep models of 3D shapes can be interpreted and used as biomarkers for classification of cardiac pathologies.

Citations (629)

Summary

  • The paper introduces ACNN, a framework that integrates anatomical constraints into CNNs to significantly improve cardiac image segmentation and enhancement.
  • It employs a novel training strategy using autoencoder-based regularization to enforce global anatomical consistency beyond local pixel predictions.
  • Experimental evaluation on cardiac MR datasets demonstrates improved accuracy and robustness in both segmentation and super-resolution tasks.

Anatomically Constrained Neural Networks (ACNN): Application to Cardiac Image Enhancement and Segmentation

The paper presents a novel methodology for incorporating anatomical prior knowledge into convolutional neural networks (CNNs), specifically targeting applications in cardiac image enhancement and segmentation. Recognizing the inherent limitations of pixel-wise classifiers that ignore structural output dependencies, the authors introduce Anatomically Constrained Neural Networks (ACNN), which integrate a regularization model that captures global anatomical properties. This regularization is achieved through a deep-learning framework that learns non-linear representations of anatomical shapes, enhancing the prediction accuracy and robustness of state-of-the-art models.

Key Contributions and Methodology

The core contribution of this research lies in leveraging anatomical priors through a training strategy that enforces the CNNs to align with predefined anatomical constraints such as shape and label structures. The approach is generalizable across different image analysis tasks, including image segmentation and enhancement. The primary framework, referred to as ACNN, consists of a regularization model that synergizes with standard CNN architectures through an autoencoder (AE) or a T-L network model.

Segmentation and Super-Resolution

In segmentation, conventional methods often employ localized loss functions, lacking global coherence. The paper proposes substituting or augmenting such losses with a global training objective, ensuring model predictions adhere to learned anatomical representations. ACNN-Seg aims to resolve the inaccuracies inherent in low-quality, artifact-prone images.

For super-resolution (SR), the ACNN-SR model adopts similar principles by embedding learned shape representations into the reconstruction process, addressing the ill-posed nature of SR tasks. The T-L network model contributes by generating low-dimensional shape codes directly from intensity images, allowing the synthesized high-resolution images to maintain anatomical plausibility.

Experimental Evaluation

The research evaluates ACNN on several data sets, including multi-modal cardiac data sets and public benchmarks. In cardiac MR imaging, ACNN-Seg demonstrates substantial improvements over baseline models in accurately delineating anatomical structures under conditions of slice misalignment or motion artifacts. The proposed ACNN-SR method excels in producing high-quality MR images, computationally outperforming conventional SR-CNN models due to reduced reliance on high-dimensional feature spaces.

Additionally, the learned latent representations, interpreted as shape codes, provide an innovative pathway for pathology classification, furnishing insights into anatomical variations indicative of specific cardiac conditions such as cardiomyopathies.

Implications and Future Work

The implications of this research extend both theoretically and practically. Theoretically, it suggests a promising direction for integrating domain-specific knowledge into deep learning models, potentially enriching the interpretability and generalization of neural networks in medical imaging. Practically, ACNN offers pathways to improve diagnostic and analytical accuracy in clinical settings, especially where high-resolution data is unavailable or impractical.

Future developments could involve expanding this framework to other anatomical structures and medical imaging modalities. Furthermore, exploring variations of the T-L architecture, potentially incorporating generative models, could enhance the flexibility and applicability of the anatomically constrained approaches.

In summary, this paper offers a substantial advancement in the integration of anatomical constraints into CNNs, marking a significant step forward in the capability of automated medical image analysis to deliver reliable and anatomically coherent outputs.