BRAIN MAPPING OF MEDIAN NERVE SOMATOSENSORY-EVOKED POTENTIALS WITH COMBINED TC-99M-ECD SINGLE-PHOTON EMISSION TOMOGRAPHY AND MAGNETIC-RESONANCE-IMAGING

Single-photon emission tomography (SPET) was performed during electric al median nerve stimulation and used to detect focal neuronal activati on in the somatosensory pathways. Intravenously administered technetiu m-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 activate d-state images of the subjects was compared with the mean summation of the baseline-state images of ten normal subjects. Discrete brain regi ons occupying 0.9%-1.6% of total brain volume showed an increase in si gnal from 33.6% to 35.0%. For further anatomical localization of regio nal increases in signal, the MRI scan of each subject was registered a nd superimposed on the activated-state SPET image. This method may be used to localize lesions in various disorders of the central nervous s ystem.