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Paper   IPM / Cognitive / 7867
School of Cognitive Sciences
  Title:   ROC-based determination of number of clusters for fMRI activation detection
1.  H. Jahanian
2.  H. Soltanian Zadeh
3.  G.A. Hossein Zadeh
4.  M.R. Siadat
  Status:   In Proceedings
  Proceeding: SPIE, Bellingham, WA, 2004
  Vol.:  5370
  Year:  2004
  Supported by:  IPM
Fuzzy C-means (FCM), in spite of its potent advantages in exploratory analyze of functional magnetic resonance imaging (fMRI), suffers from limitations such as a priori determination of number of clusters, unknown statistical significance for the results, and instability of the results when it is applied on raw fMRI time series. Choosing different number of clusters, or thresholding the membership degree at different levels, lead to considerably different activation maps. However, research work for finding a standard index to determine the number of clusters has not yet succeeded. Using randomization, we developed a method to control false positive rate in FCM, which gives a meaningful statistical significance to the results. Making use of this novel method and an ROC-based cluster validity measure, we determined the optimal number of clusters. In this study, we applied the FCM on a feature space that takes the variability of hemodynamic response function into account (HRF-based feature space). The proposed method found the accurate number of clusters in simulated fMRI data. In addition, the proposed method generated excellent results for experimental fMRI data and showed a good reproducibility for determining the number of clusters. Keywords: fMRI, fuzzy clustering, statistical test, randomization, cluster validity, Receiver Operating Characteristics (ROC) curve.

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