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Sensorimotor Cortex Localization: Comparison of Magnetoencephalography, Functional MR Imaging, and Intraoperative Cortical Mapping¹

¹ From the Functional Brain Imaging Unit, Helsinki Brain Research Center, Medical Imaging Center, University of Helsinki, Helsinki, Finland (A.K., H.J.A., E.S.); Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland (E.K., S.A., J.P.M., M.S.); BioMag Laboratory, Helsinki Brain Research Center, Engineering Centre (A.K., R.J.I.) and Department of Clinical Neurophysiology (E.K., J.H., T.K.), Helsinki University Central Hospital, Helsinki, Finland; Department of Neurosurgery, Kuopio University Hospital, Kuopio, Finland (J.E.J.); and Department of Radiology, Hyvinkää Hospital, Hospital District of Helsinki and Uusimaa, Hyvinkää, Finland (A.B.). From the 2000 RSNA Annual Meeting. Received May 10, 2005; revision requested July 8; revision received September 8; accepted October 14; final version accepted November 23. Supported by grants from the Finnish Radiological Society, Maire Taponen Foundation, Maud Kuistila Foundation, Finnish Cancer Organization, Helsinki University Central Hospital, Academy of Finland, Nordic Cancer Union, Sigrid Juselius Foundation, and Helsinki University Hospital Clinical Research Institute. Address correspondence to A.K., Radiology Department, Biomedicum Helsinki, PO Box 700, FI-00029 HUS, Helsinki, Finland (e-mail: antti.korvenoja{at}helsinki.fi).

View larger version (88K): [in this window] [in a new window] [Download PPT slide]   Figure 1: Somatosensory evoked magnetic fields after left median nerve stimulation in patient 12, who had parietal glioma (arrow, bottom left image). Top left: Individual response waveforms from two channels over the right sensorimotor cortex are shown; dashed vertical line marks the 20-msec component known to be generated in the postcentral wall of the central sulcus (Brodmann area 3b). Stimuli were applied at 0 msec. Top right: Corresponding isofield contour map (contour step, 20 fT) shows dipolar distribution of the magnetic field. Solid lines over helmet-shaped sensor array (white squares) represent magnetic field exiting the head; dashed lines represent magnetic field entering the head. Arrow depicts ECD fitted to the field distribution. Bottom: Dipole location is shown on transverse (left), coronal (middle), and sagittal (right) MR images in same patient. Position of dipole is illustrated by crosshairs and circled; line crossing shows dipole orientation. Dashed lines mark the central sulcus, as identified at intraoperative mapping.

View larger version (116K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Functional MR imaging activations and MEG dipole location in patient 10, who had parietal meningioma (arrows). Activations (orange) are shown with pseudocolor overlays on 3D surface reconstruction of contrast-enhanced 3D magnetization-prepared rapid gradient-echo image volume (bottom right) and on sagittal (top right), coronal (top left), and transverse (bottom left) image sections through primary sensorimotor cortex in right hemisphere. N20m dipole location is seen in postcentral gyrus (red dots). Both functional MR imaging and MEG correctly depicted the central sulcus in this patient. Activations are seen, in addition to in the primary sensorimotor cortex, in the frontal and posterior parietal cortices and in areas of the interhemispheric fissure walls. The meningioma has intense and homogeneous gadolinium enhancement. Central sulcus location, as verified at intraoperative mapping, is marked by dashed line.

View larger version (73K): [in this window] [in a new window] [Download PPT slide]   Figure 3: Activations and MEG dipole location (red areas) on functional MR images (pseudocolor maps) in patient 8, who had parietal glioma (arrows). Three-dimensional surface reconstruction of contrast-enhanced 3D magnetization-prepared rapid gradient-echo image volume (left) and four transverse image sections (right) through primary sensorimotor cortex are shown. Largest activation area was in postcentral sulcus and extended contiguously to central sulcus (dashed line). Area of peak statistical value (x, left image) also was in postcentral sulcus region. Other activations in precentral superior parietal gyrus and supplementary motor area are visible in left hemisphere. Central sulcus location, as verified at intraoperative mapping, is marked by dashed line.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 4: A, Part of 3D surface reconstruction of contrast-enhanced magnetization-prepared rapid gradient-echo MR image volume in patient 1 shows MEG dipole location (red dot) in postcentral gyrus and a cortical vein (open arrow) that can be identified also on the intraoperative view (B) of the brain surface in the same patient. This patient underwent repeat surgery of the residual tumor (Word Health Organization type 2 astrocytoma, solid black arrow in A–E) within the surgical cavity in left frontal lobe. The cortex was stimulated at labeled sites 1–4. Stimulation at sites 1 and 2 caused contraction of hand muscles; stimulation at sites 3 and 4 caused a motor response in mouth area. C, Brain surface at functional MR imaging activation during motor task and N20m dipole location at MEG (red areas in C and E). x marks location of peak value (area of highest z score) depicted on functional MR imaging statistical activation map. In left hemisphere, activation is also seen in supramarginal gyrus and in medial and inferior frontal gyri. D, E, Transverse cranial (D) and caudal (E) MR image sections through primary sensorimotor cortex show bulk of functional MR activation in postcentral sulcus region. In C–E, central sulcus location, as verified at intraoperative mapping, is marked by dashed line.