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Lista articulos de trabajo

1. R. Baumgartner, L. Ryner, W. Richter, R. Summers, M. Jarmasz, R. Somorjai*, Comparison of two exploratory data analysis methods for fMRI: fuzzy clustering vs. principal component analysis. Magnetic Resonance Imaging 18 (2000) 89–94.

Abstract

Exploratory data-driven methods such as Fuzzy clustering analysis (FCA) and Principal component analysis (PCA) may be considered as hypothesis-generating procedures that are complementary to the hypothesis-led statistical inferential methods in functional magnetic resonance imaging (fMRI). Here, a comparison between FCA and PCA is presented in a systematic fMRI study, with MR data acquired under the null condition, i.e., no activation, with different noise contributions and simulated, varying “activation.” The contrast-to-noise (CNR) ratio ranged between 1–10. We found that if fMRI data are corrupted by scanner noise only, FCA and PCA show comparable performance. In the presence of other sources of signal variation (e.g., physiological noise), FCA outperforms PCA in the entire CNR range of interest in fMRI, particularly for low CNR values. The comparison method that we introduced may be used to assess other exploratory approaches such as independent component analysis or neural network-based techniques.

2. R. Baumgartner, PhD, R. Somorjai, PhD,* R. Summers, MSc, W. Richter, PhD, L. Ryner, PhD, and M. Jarmasz, PhD, Resampling as a Cluster Validation Technique in fMRI. JOURNAL OF MAGNETIC RESONANCE IMAGING 11:228–231 (2000).

Abstract

Exploratory, data-driven analysis approaches such as cluster analysis, principal component analysis, independent component analysis, or neural network-based techniques are complementary to hypothesis-led methods. They may be considered as hypothesis generating methods. The representative time courses they produce may be viewed as alternative hypotheses to the null hypothesis, ie, “no activation.” We present here a resampling technique to validate the results of exploratory fuzzy clustering analysis. In this case an alternative hypothesis is represented by a cluster centroid. For both simulated and in vivo functional magnetic resonance imaging data, we show that by permutation-based resampling, statistical significance may be computed for each voxel belonging to a cluster of interest without parametric distributional assumptions.