Image Processing Reference
In-Depth Information
16
Exploratory Data
Analysis Methods
in Functional MRI
Nicola Vanello and Luigi Landini
CONTENTS
16.1 Introduction............................................................................................506
16.2 Multivariate Approaches ........................................................................506
16.3 Data Clustering Approaches ..................................................................508
16.3.1 Similarity .................................................................................509
16.3.2 Clustering Techniques .............................................................510
16.3.2.1 Hierarchical Methods.............................................510
16.3.2.2 Hard Partitioning Methods ....................................512
16.3.2.3 Fuzzy Clustering ....................................................513
16.3.2.4 Artificial Neural Networks ....................................515
16.4 PCA........................................................................................................516
16.4.1 Spatial and Temporal PCA .....................................................517
16.4.1.1 Preprocessing of fMRI Data before PCA .............520
16.4.2 Interpretation of the PCA Decomposition..............................520
16.5 ICA.........................................................................................................522
16.5.1 Spatial and Temporal ICA ......................................................523
16.5.2 Methods for ICA .....................................................................524
16.5.2.1 Historical Background ...........................................524
16.5.2.2 Nonlinear Decorrelation ........................................525
16.5.2.3 Information Maximization and Maximum
Likelihood Approaches..........................................527
16.5.2.4 Non-Gaussianity and Negentropy..........................529
16.5.2.5 Ambiguities in the ICA Model..............................530
16.5.3 Preprocessing ..........................................................................530
16.5.4 Model Validation .....................................................................532
16.5.5 Interpretation of the Results ...................................................533
16.5.5.1 Thresholding the Maps ..........................................533
16.5.5.2 Task-Related Activations .......................................533
16.5.6 Simulation and Algorithm Comparison..................................535
References .........................................................................................................535
505
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