Monitoring tool usage in cataract surgery videos using boosted convolutional and recurrent neural networks
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With an estimated 19 million operations performed annually, cataract surgery is the most common surgical procedure. This paper investigates the automatic monitoring of tool usage during a cataract surgery, with potential applications in report generation, surgical training and real-time decision support. In this study, tool usage is monitored in videos recorded through the surgical microscope. Following state-of-the-art video analysis solutions, each frame of the video is analyzed by convolutional neural networks (CNNs) whose outputs are fed to recurrent neural networks (RNNs) in order to take temporal relationships between events into account. Novelty lies in the way those CNNs and RNNs are trained. Computational complexity prevents the end-to-end training of "CNN+RNN" systems. Therefore, CNNs are usually trained first, independently from the RNNs. This approach is clearly suboptimal for surgical tool analysis: many tools are very similar to one another, but they can generally be differentiated based on past events. CNNs should be trained to extract the most useful visual features in combination with the temporal context. A novel boosting strategy is proposed to achieve this goal: the CNN and RNN parts of the system are simultaneously enriched by progressively adding weak classifiers (either CNNs or RNNs) trained to improve the overall classification accuracy. Experiments were performed in a new dataset of 50 cataract surgery videos where the usage of 21 surgical tools was manually annotated. Very good classification performance are achieved in this dataset: tool usage could be labeled with an average area under the ROC curve of A_z = 0.9717 in offline mode (using past, present and future information) and A_z = 0.9696 in online mode (using past and present information only).
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