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      Global, voxel, and cluster tests, by theory and permutation, for a difference between two groups of structural MR images of the brain.

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          Abstract

          We describe almost entirely automated procedures for estimation of global, voxel, and cluster-level statistics to test the null hypothesis of zero neuroanatomical difference between two groups of structural magnetic resonance imaging (MRI) data. Theoretical distributions under the null hypothesis are available for 1) global tissue class volumes; 2) standardized linear model [analysis of variance (ANOVA and ANCOVA)] coefficients estimated at each voxel; and 3) an area of spatially connected clusters generated by applying an arbitrary threshold to a two-dimensional (2-D) map of normal statistics at voxel level. We describe novel methods for economically ascertaining probability distributions under the null hypothesis, with fewer assumptions, by permutation of the observed data. Nominal Type I error control by permutation testing is generally excellent; whereas theoretical distributions may be over conservative. Permutation has the additional advantage that it can be used to test any statistic of interest, such as the sum of suprathreshold voxel statistics in a cluster (or cluster mass), regardless of its theoretical tractability under the null hypothesis. These issues are illustrated by application to MRI data acquired from 18 adolescents with hyperkinetic disorder and 16 control subjects matched for age and gender.

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          Author and article information

          Journal
          IEEE Trans Med Imaging
          IEEE transactions on medical imaging
          Institute of Electrical and Electronics Engineers (IEEE)
          0278-0062
          0278-0062
          Jan 1999
          : 18
          : 1
          Affiliations
          [1 ] Department of Biostatistics and Computing, Institute of Psychiatry, King's College, University of London, UK. e.bullmore@iop.kcl.ac.uk
          Article
          10.1109/42.750253
          10193695
          00057d65-96a1-4efd-bc6d-508341a36355
          History

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