Evaluation of using absolute versus relative base level when analyzing brain activation images using the scale-space primal sketch

A dominant approach to brain mapping is to define functional regions in the brain by analyzing images of brain activation obtained from positron emiss ion tomography (PET) and functional magnetic resonance imaging (fMRI). This paper presents an evaluation of using one such tool, called the scale-spac e primal sketch, for brain activation analysis. A comparison is made concer ning two possible definitions of a significance measure of blob structures in scale-space, where local contrast is measured either relative to a local or global reference level. Experiments on real brain data show that (i) th e global approach with absolute base level has a higher degree of correspon dence to a traditional statistical method than a local approach with relati ve base level, and that (ii) the global approach with absolute base level g ives a higher significance to small blobs that are superimposed on larger s cale structures, whereas the significance of isolated blobs largely remains unaffected. Relative to previously reported works, the following two techn ical improvements are also presented. (i) A post-processing tool is introdu ced for merging blobs that are multiple responses to image structures. This simplifies automated analysis from the scale-space primal sketch. (ii) A n ew approach is introduced for scale-space normalization of the significance measure, by collecting reference statistics of residual noise images obtai ned from the general Linear model. (C) 2001 Elsevier Science B.V. All right s reserved.