Henrique Fernandes1, Mario Forjaz Secca1,2, Alberto Leal3,4
1Cefitec, Physics Department, Universidade Nova de Lisboa, Monte de Caparica, Portugal; 2Ressonancia Magnetica - Caselas, Lisboa, Portugal; 3Dep. of Neurophysiology, Hospital Julio de Matos, Lisboa, Portugal; 4Dep. of Pediatric Neurology, Hospital Dona Estefania, Lisboa, Portugal
The simultaneous acquisition of EEG and fMRI has been used in focal epilepsy studies to correlate hemodynamic responses with interictal EEG spikes. However, HRFs vary across sessions, subjects, individuals and brain regions, and the use of one standard HRF contributes to false positives and negatives and a loss of information, decreasing the correlation of the processed fMRI data. Studying how HRFs affect statistical analysis we found that it is not possible to determine a gold standard HRF which would produce the most accurate BOLD statistical maps. This decision should be taken individually, since it varies across patients and affected regions.