Training a deep convolutional neural network (CNN) from scratch is difficult because it requires a large amount of labeled training data and a great deal of expertise to ensure proper convergence. A promising alternative is to fine-tune a CNN that has been pre-trained using, for instance, a large set of labeled natural images. However, the substantial differences between natural and medical images may advise against such knowledge transfer. In this paper, we seek to answer the following central question in the context of medical image analysis: \emph{Can the use of pre-trained deep CNNs with sufficient fine-tuning eliminate the need for training a deep CNN from scratch?} To address this question, we considered 4 distinct medical imaging applications in 3 specialties (radiology, cardiology, and gastroenterology) involving classification, detection, and segmentation from 3 different imaging modalities, and investigated how the performance of deep CNNs trained from scratch compared with the pre-trained CNNs fine-tuned in a layer-wise manner. Our experiments consistently demonstrated that (1) the use of a pre-trained CNN with adequate fine-tuning outperformed or, in the worst case, performed as well as a CNN trained from scratch; (2) fine-tuned CNNs were more robust to the size of training sets than CNNs trained from scratch; (3) neither shallow tuning nor deep tuning was the optimal choice for a particular application; and (4) our layer-wise fine-tuning scheme could offer a practical way to reach the best performance for the application at hand based on the amount of available data.

本研究旨在解答在医学图像分析的背景下，如何才能让使用具有足够精细调整过的预训练深度CNN能够消除从头开始使用CNN进行训练的需求这一核心问题。在考虑了医学成像应用中的分类，检测和分割等方面时，我们的实验结果一致表明：1）使用经过足够精细调整的预训练CNN显著优于或者和从头开始训练的CNN一样好；2）相比于从头开始训练的CNN，精细调整的CNN更加稳健；3）浅调整和深度调整都不是特定应用的最佳选择；4）我们的逐层精细调整方案可以根据可用数据量为手头的应用程序提供达到最佳性能的实用方法。

卷积神经网络用于医学图像分析：完全训练还是微调？