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

Mikael Rosbacke, Tony Lindeberg and Per E. Roland

Technical report ISRN KTH NA/P--99/14--SE. Department of Numerical Analysis and Computing Science, KTH (Royal Institute of Technology), S-100 44 Stockholm, Sweden, December 1999.

Journal of Medical Image Analysis, vol. 5, Issue 2, pp. 89--110, 2001.

Abstract

A dominant approach to brain mapping is to define functional regions in the brain by analyzing images of brain activation obtained from positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). This paper presents an evaluation of using one such tool, called the scale-space primal sketch, for brain activation analysis. A comparison is made concerning two possible definitions of the scale-space significance measure, where local contrast is measured either relative to a local or global reference level.

Experiments on real brain data show that the global approach with absolute base level gives a higher significance to small blobs superimposed on larger scale structures, than a local approach with relative base level, whereas the significance of isolated blobs largely remains unaffected. The global approach also has a higher degree of correspondence to a traditional statistical method.

Relative to previously reported works, the following two technical improvements are also presented: (i) A post-processing tool is introduced for merging multiple blob responses to similar image structures. This simplifies automated analysis from the scale-space primal sketch. (ii) A new approach is introduced for scale-space normalization of the significance measure, by collecting reference statistics of residual noise images obtained from the general linear model.

Keywords: brain activation, brain mapping, functional region, scale-space, primal sketch, blob detection, multi-scale representation, computer vision

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Background and related material: (Previous work on brain activation analysis using the scale-space primal sketch) (General reference on the scale-space primal sketch) (Monograph on scale-space theory)