Detecting Outlying Subjects in High-Dimensional Neuroimaging Datasets with Regularized Minimum Covariance Determinant
Medical imaging datasets used in clinical studies or basic research often comprise highly variable multi-subject data. Statistically-controlled inclusion of a subject in a group study, i.e. deciding whether its images should be considered as samples from a given population or whether they should be rejected as outlier data, is a challenging issue. While the informal approaches often used do not provide any statistical assessment that a given dataset is indeed an outlier, traditional statistical procedures are not well-suited to the noisy, high-dimensional, settings encountered in medical imaging, e.g. with functional brain images. In this work, we modify the classical Minimum Covariance Determinant approach by adding a regularization term, that ensures that the estimation is well-posed in high-dimensional settings and in the presence of many outliers. We show on simulated and real data that outliers can be detected satisfactorily, even in situations where the number of dimensions of the data exceeds the number of observations.
KeywordsOutlier detection Minimum Covariance Determinant regularization robust estimation neuroimaging fMRI
- 1.Aljabar, P., Wolz, R., Srinivasan, L., Counsell, S., Boardman, J.P., Murgasova, M., Doria, V., Rutherford, M.A., Edwards, A.D., Hajnal, J.V., Rueckert, D.: Combining morphological information in a manifold learning framework: application to neonatal MRI. Med. Image Comput. Comput. Assist. Interv. 13, 1 (2010)Google Scholar
- 3.Gerber, S., Tasdizen, T., Joshi, S., Whitaker, R.: On the manifold structure of the space of brain images. Med. Image Comput. Comput. Assist. Interv. 12, 305 (2009)Google Scholar
- 5.Kherif, F., Flandin, G., Ciuciu, P., Benali, H., Simon, O., Poline, J.B.: Model based spatial and temporal similarity measures between series of functional magnetic resonance images. Med. Image Comput. Comput. Assist. Interv., 509 (2002)Google Scholar