title: Assessing the significance of focal activations using their spatial extent.
abstract: Current approaches to detecting significantly activated regions of cerebral tissue use statistical parametric maps, which are thresholded to render the probability of one or more activated regions of one voxel, or larger, suitably small (e. g., 0.05). We present an approximate analysis giving the probability that one or more activated regions of a specified volume, or larger, could have occurred by chance. These results mean that detecting significant activations no longer depends on a fixed (and high) threshold, but can be effected at any (lower) threshold, in terms of the spatial extent of the activated region. The substantial improvement in sensitivity that ensues is illustrated using a power analysis and a simulated phantom activation study. © 1994 Wiley-Liss, Inc.
authors.affiliation: MRC Cyclotron Unit, Hammersmith Hospital, London W12 OHS, United Kingdom.
authors.forename: K J
authors.initials: KJ
authors.lastname: Friston
authors.forename: K J
authors.initials: KJ
authors.lastname: Worsley
authors.forename: R S
authors.initials: RS
authors.lastname: Frackowiak
authors.forename: J C
authors.initials: JC
authors.lastname: Mazziotta
authors.forename: A C
authors.initials: AC
authors.lastname: Evans
keywords: activation; excursion set; functional imaging; gaussian fields; statistical parametric mapping; thresholds