可解释深度学习在光谱和医学影像分析中的应用

Explainable Deep Learning in Spectral and Medical Image Analysis

深度学习是一种基于神经网络的建模方法,通过不同功能感知层的构建获得优化模型,提取大量数据的内在规律,实现端到端的建模。数据规模的增长和计算能力的提高促进了深度学习在光谱及医学影像分析中的应用,但深度学习模型可解释性的不足是阻碍其应用的关键因素。为克服深度学习可解释性的不足,研究者提出并发展了可解释性方法。根据解释原理的不同,可解释性方法划分为可视化方法、模型蒸馏及可解释模型,其中可视化方法及模型蒸馏属于外部解释算法,在不改变模型结构的前提下解释模型,而可解释模型旨在使模型结构可解释。本文从算法角度介绍了深度学习及三类可解释性方法的原理,综述了近三年深度学习及可解释性方法在光谱及医学影像分析中的应用。多数研究聚焦于可解释性方法的建立,通过外部算法揭示模型的预测机制并解释模型,但构建可解释模型方面的研究相对较少。此外,采用大量标记数据训练模型是目前的主流研究方式,但给数据的采集带来了巨大的负担。基于小规模数据的训练策略、增强模型可解释性的方法及可解释模型的构建仍是未来的发展趋势。

Deep learning is a modeling method based on neural network, which is constructed of multiple different functional perception layers and optimized by learning the inherent regularity of a large amount of data to achieve end-to-end modeling. The growth of data and the improvement of computing power promoted the applications of deep learning in spectral and medical image analysis. The lack of interpretability of the constructed models, however, constitutes an obstacle to their further development and applications. To overcome this obstacle of deep learning, various interpretability methods are proposed. According to different principles of explanation, interpretability methods are divided into three categories: visualization methods, model distillation, and interpretable models. Visualization methods and model distillation belong to external algorithms, which interpret a model without changing its structure, while interpretable models aim to make the model structure interpretable. In this review, the principles of deep learning and three interpretability methods are introduced from the perspective of algorithms. Moreover, the applications of the interpretability methods in spectral and medical image analysis in the past three years are summarized. In most studies, external algorithms were developed to make the models explainable, and these methods were found to be able to provide reasonable explanation for the abilities of the deep learning models. However, few studies attempt to construct interpretable algorithms within networks. Furthermore, most studies try to train the model through collecting large amounts of labeled data, which leads to huge costs in both labor and expenses. Therefore, training strategies with small data sets, approaches to enhance the interpretability of models, and the construction of interpretable deep learning architectures are still required in future work.