Anatomical mapping of functional activation in stereotactic coordinate space

Abstract

Numerous applications have been reported for the stereotactic mapping of focal changes in cerebral blood flow during sensory and cognitive activation as measured with positron emission tomography (PET) subtraction images. Since these images lack significant anatomical information, analysis of these kinds of data has been restricted to an automated search for peaks in the PET subtraction dataset and localization of the peak coordinates within a standardized stereotactic atlas. This method is designed to identify isolated foci with dimensions smaller than the image resolution. Details of activation patterns that may extend over finite distances, following the underlying anatomical structures, will not be apparent. We describe the combined mapping into stereotactic coordinate space of magnetic resonance imaging (MRI) and PET information from each of a set of subjects such that the major features of the activation pattern, particularly extended tracts of increased blood flow, can be immediately assessed within their true anatomical context as opposed to that presumed using a standard atlas alone. Near areas of high anatomical variability, e.g., central sulcus, or of sharp curvature, e.g., frontal and temporal poles, this information can be essential to the localization of a focus to the correct gyrus or for the rejection of extracerebral peaks. It also allows for the removal from further analysis of data from cognitively-normal subjects with abnormal anatomy such as enlarged ventricles. In patients with neuropathology, e.g., Alzheimer's disease, arteriovenous malformation, stroke, or neoplasm, the use of correlated MRI is mandatory for correct localization of functional activation.