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Copyright © 2005 The Institute of Electronics, Information and Communication Engineers
Regular Section -- Papers -- Biological Engineering |
Eigen Image Recognition of Pulmonary Nodules from Thoracic CT Images by Use of Subspace Method
1 The authors are with Toyohashi University of Technology, Toyohashi-shi, 4418580 Japan. E-mail: Gentarou.Fukano{at}jp.yokogawa.com, 2 The author is with Yokogawa Electric Corporation, Musashi-no-shi, 1808750 Japan., 3 The author is with the University of Chicago, Chicago, IL, 60637, USA., 4 The author is with Kumamoto University, Kumamoto-shi, 8608555 Japan., 5 The authors are with National Institute of Radiological Sciences, Chiba-shi, 2638555 Japan.
We have proposed a recognition method for pulmonary nodules based on experimentally selected feature values (such as contrast, circularity, etc.) of pathologic candidate regions detected by our Variable N-Quoit (VNQ) filter. In this paper, we propose a new recognition method for pulmonary nodules by use of not experimentally selected feature values, but each CT value itself in a region of interest (ROI) as a feature value. The proposed method has 2 phases: learning and recognition. In the learning phase, first, the pathologic candidate regions are classified into several clusters based on a principal component score. This score is calculated from a set of CT values in the ROI that are regarded as a feature vector, and then eigen vectors and eigen values are calculated for each cluster by application of principal component analysis to the cluster. The eigen vectors (we call them "eigen-images") corresponding to the S-th largest eigen values are utilized as base vectors for subspaces of the clusters in a feature space. In the recognition phase, correlations are measured between the feature vector derived from testing data and the subspace which is spanned by the eigen-images. If the correlation with the nodule subspace is large, the pathologic candidate region is determined to be a nodule, otherwise, it is determined to be a normal organ. In the experiment, first, we decide on the optimal number of subspace dimensions. Then, we demonstrated the robustness of our algorithm by using simulated nodule images.
Key Words: pulmonary nodules, thoracic CT, computer aided diagnosis, automatic clustering, subspace method
Manuscript received July 28, 2004. Manuscript revised January 11, 2005.