Development of a computerized system for analyzing facial nerve paralysis -A method using the optical flow-

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We developed a computerized system to assess the degree of facial nerve paralysis. Our system calculates the optical flow throughout the facial area, using the gradient method.The results obtained with our system were both precise and reproducible. They were almost identical to those obtained using the matching method, and the inter-examiner variability was minimal. In addition, when expressed using the diseased-to-healthy side ratio of the optical flow, the results correlated well with the scores assigned to each facial movement using Yanagihara's grading scale. The optical flow index, which we defined using the results, is also highly correlated with the total scores on Yanagihara's grading scale.Another advantage of our system is that it permits flexible expression of the analysis results. For example, the optical flow for each small area within the facial region can be superimposed on the original picture of the patient. This enables intuitive understanding of the facial movements. Furthermore, the movement of each pixel in the facial region can be traced on a frame-to-frame basis. These two features are very useful for assessing associated movements.Our system initially ran only on Linux, but it now also works on Windows. We expect that our system will be used widely in daily clinical practice.