Brain mapping of median nerve somatosensory evoked potentials with combined99mTc-ECD single-photon emission tomography and magnetic resonance imaging

Single-photon emission tomography (SPET) was performed during electrical median nerve stimulation and used to detect focal neuronal activation in the somatosensory pathways. Intravenously administered technetium-99m ethyl cysteinate dimer (ECD) was used as a blood flow tracer to obtain baseline and activated images in each of three subjects. After image registration, baseline images were compared voxel by voxel with the activation images. In addition, the mean summation of the activated-state images of the subjects was compared with the mean summation of the baseline-state images of ten normal subjects. Discrete brain regions occupying 0.9%–1.6% of total brain volume showed an increase in signal from 33.6% to 35.0%. For further anatomical localization of regional increases in signal, the MRI scan of each subject was registered and superimposed on the activated-state SPET image. This method may be used to localize lesions in various disorders of the central nervous system.