Effect of task-related extracerebral circulation.pdfVIP

Effect of task-related extracerebral circulation on diffuse optical tomography: experimental data and simulations on the forehead Tiina N?si,1,2,* Hanna M?ki,1,2 Petri Hiltunen,1 Juha Heiskala,3 Ilkka Nissil?,1,2 Kalle Kotilahti,1,2 and Risto J. Ilmoniemi1,2 1Department of Biomedical Engineering and Computational Science (BECS), Aalto University School of Science, P.O. Box 12200, FI-00076 AALTO, Espoo, Finland 2BioMag Laboratory, HUS Medical Imaging Center, Helsinki University Central Hospital, P.O. Box 340, FI-00029 HUS, Finland 3Department of Computer Science, University College London, Gower Street, London WC1E 6BT, United Kingdom *tiina.nasi@aalto.fi Abstract: The effect of task-related extracerebral circulatory changes on diffuse optical tomography (DOT) of brain activation was evaluated using experimental data from 14 healthy human subjects and computer simulations. Total hemoglobin responses to weekday-recitation, verbal- fluency, and hand-motor tasks were measured with a high-density optode grid placed on the forehead. The tasks caused varying levels of mental and physical stress, eliciting extracerebral circulatory changes that the reconstruction algorithm was unable to fully distinguish from cerebral hemodynamic changes, resulting in artifacts in the brain activation images. Crosstalk between intra- and extracranial layers was confirmed by the simulations. The extracerebral effects were attenuated by superficial signal regression and depended to some extent on the heart rate, thus allowing identification of hemodynamic changes related to brain activation during the verbal-fluency task. During the hand-motor task, the extracerebral component was stronger, making the separation less clear. DOT provides a tool for distinguishing extracerebral components from signals of cerebral origin. Especially in the case of strong task-related extracerebral circulatory changes, however, sophisticated reconstruction methods are needed to elimin