Differential functional benefits of ultra highfield MR systems within the language network.
Bottom Line: Improvement is expected from ultra highfield systems but studies on possible benefits for cognitive networks are lacking.During data acquisition and analysis we made particular efforts to minimize effects not related to static magnetic field strength differences.We conclude that functional UHF benefits are evident, however these depend crucially on the brain region investigated and the ability to control local artifacts.
Affiliation: Study Group Clinical fMRI, Department of Neurology, Medical University of Vienna, Austria; High Field MR Center, Medical University of Vienna, Austria; Department of Neurology, Medical University of Vienna, Austria.Show MeSH
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Mentions: To allow inferences about benefits for individual subjects and minimize postprocessing related confounds (Beisteiner et al., 2010) all functional analyses were performed on non-transformed (non-normalized) individual data (Fig.┬á1). The analysis was focused on left hemispheric essential areas of the language network (Broca's and Wernicke's areas) as the most relevant with regard to a possible functional signal improvement. In addition, these areas provide an important dichotomy concerning their susceptibility to artifacts: Wernicke lies in the posterior superior temporal gyrus, a relatively magnetically homogeneous region while Broca, in the inferior frontal cortex, is subject to much higher susceptibility-related field gradients. Broca and Wernicke activation clusters were defined for every patient by a clinical fMRI expert (RB) on the basis of the individual SPM t-maps and the existing functional medical reports. This was done for both field strengths. Afterwards the voxels with the highest t-values in each Broca and Wernicke cluster were identified. These peak voxels served as the center for patient-specific spherical regions of interest (ROI), which had a radius of 5┬ámm. To avoid the inclusion of non-brain areas (e.g. scalp, skull) ROIs were defined on the skull-stripped mean EPI volume (BET2 with a subject specific fractional intensity threshold, Jenkinson et al., 2002). Spherical ROIs were cropped at the brain border if necessary. Further analysis was limited to these ROIs.
Affiliation: Study Group Clinical fMRI, Department of Neurology, Medical University of Vienna, Austria; High Field MR Center, Medical University of Vienna, Austria; Department of Neurology, Medical University of Vienna, Austria.