Statistical parametric mapping: Difference between revisions

Revision as of 15:51, 17 November 2010

Revision as of 18:01, 16 January 2011

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A study will usually scan a subject several times. To account for the motion of the head between scans, the images will usually be adjusted so each of the voxels in the images corresponds (approximately) to the same site in the brain. This is referred to as ''realignment'' or ''motion correction'', see [[image realignment]].

Functional neuroimaging studies usually involve several participants, who will have slightly differently shaped brains. All are likely to have the same gross anatomy, but there will be minor differences in overall brain size, individual variation in topography of the [[gyri]] and [[Sulcus (anatomyneuroanatomy)|sulci]] of the [[cerebral cortex]], and morphological differences in deep structures such as the [[corpus callosum]]. To aid comparisons, the 3D image of each brain is transformed so that superficial structures line up, a process known as ''[[spatial normalization]]''. Such normalization typically involves not only translation and rotation, but also scaling and nonlinear warping of the brain surface to match a standard template. Standard brain maps such as the [[Talairach]]-Tournoux or templates from the [[Montréal Neurological Institute]] (MNI) are often used to allow researchers from across the world to compare their results.

Images are often smoothed (similar to the 'blur' effect used in some image-editing software) by which voxels are averaged with their neighbours, typically using a [[Gaussian]] filter or by [[wavelet]] transformation, to make the data less noisy.