Development of the SQUID-CT for Functional Brain Mapping Based on a Helmet-Shaped Whole Head Magnetoencephalography System

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In this study, we have designed a new magnetoencephalography (MEG) system as an advanced clinical diagnostic tool, as follows : First, visual and gustatory stimurators were designed so as not to produce magnetic noise. Second, stimulation and measurement parameters were carefully selected in order to minimize total measurement time of evoked magnetic fields for patients. Third, multimodal evoked responses were analyzed and compared between normal subjects and patients with intracranial structural lesions.Results are summarized as follows. For somatosensory stimuli, corresponding primary sensory cortices were indentified for not only major nerve stimuli in upper and lower extremities but also for single digit stimuli and for dorsal penile nerve stimuli. There found fine correspondence between functional localization and gyral anatomy in primary sensory cortex. For auditory stimuli, various types of interhemispheric asymmetries were revealed for both middle and late components of the evoked fields. Delayd latency of the major peaks were found in cases of temporal lobe tumors. Primary visual cortices on both hemispheres were localized using full visual-field stimuli and a two-dipole model. Patients with homonymous hemianopsia and bitemporal hemianopsia presented corresponding magnetic field patterns respectively. Gustatory evoked magnetic fields were measured in normal subjects. Abnormal slow wave of magnetic fields were also investigated in cases with ischemic lesion.These results promise further utility of MEG as clinical diagnostic tools as well as new rsearch tools of non-invasive human brain function. Development of clinical MEG system and other applications of superconducting physics will be accelerated.