Open AccessStatistical flattening of MEG beamformer images
Author(s) -
Barnes Gareth R.,
Hillebrand Arjan
Publication year - 2003
Publication title -
human brain mapping
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.005
H-Index - 191
eISSN - 1097-0193
pISSN - 1065-9471
DOI - 10.1002/hbm.10072
Subject(s) - smoothness , voxel , flattening , residual , parametric statistics , algorithm , nonparametric statistics , mathematics , artificial intelligence , computer science , statistical parametric mapping , pattern recognition (psychology) , statistics , physics , mathematical analysis , astronomy , medicine , magnetic resonance imaging , radiology
We propose a method of correction for multiple comparisons in MEG beamformer based Statistical Parametric Maps (SPMs). We introduce a modification to the minimum‐variance beamformer, in which beamformer weights and SPMs of source‐power change are computed in distinct steps. This approach allows the calculation of image smoothness based on the computed weights alone. In the first instance we estimate image smoothness by looking at local spatial correlations in residual images generated using random data; we then go on to show how the smoothness of the SPM can be obtained analytically by measuring the correlations between the adjacent weight vectors. In simulations we show that the smoothness of the SPM is highly inhomogeneous and depends on the source strength. We show that, for the minimum variance beamformer, knowledge of image smoothness is sufficient to allow for correction of the multiple comparison problem. Per‐voxel threshold estimates, based on the voxels extent (or cluster size) in flattened space, provide accurate corrected false positive error rates for these highly inhomogeneously smooth images. Hum. Brain Mapping 18:1–12, 2003. © 2002 Wiley‐Liss, Inc.