gms | German Medical Science

Functional Magnetic Resonance Imaging (fMRI) represents an accepted diagnostic modality of neuroscience. The use of fMRI in a clinical environment is rapidly expanding, especially since more scientific groups are seeking a clinical application. Functional MRI-analysis for perioperative evaluation depends on an applicable, repeatable, practical and fail-proof paradigm. The presently-applied paradigms for fMRI-activation and identification of the central region are based on motor tasks requiring a compliant patient and may not be obtainable from hemiparetic or even anesthetized patients. The aim of this study is to develop and evaluate the feasibility of a “passive” paradigm for activation-analysis of the somatosensory cortex under anesthesia.

A defined peripheral electrical stimulus to the median and tibial nerves (3 Hz, motor threshold) was applied as block-designed stimulation paradigm in four anesthetized patients, suffering from different cerebral pathological entities. Two specially custom-designed mass-protected coaxial leads were utilized, which took into consideration the technical difficulties and the application of an electrical current in the fMRI-environment. During stimulation T2*-weighted EPI sequences were acquired. Data cross correlation analysis followed using statistical parametric mapping (SPM) where activation is considered valid for correlation coefficients higher than 0.55. The examined patients were anesthetized using propofol and fentanyl.

After realignment, spatial normalization and spatial smoothing, the statistical analysis revealed a significant activation of the contralateral primary sensorimotor cortex in all patients examined.

This method seems to be a feasible way of obtaining functional information about the sensorimotor cortex and its localization in anesthetized patients. Ongoing studies have already evaluated the feasibility of this method in an intraoperative context.