Biomedical Engineering Reference
In-Depth Information
Fig. 3.57.
An example of the MEG response and estimated equivalent current
dipole of a normal subject, a right-handed 35-year-old male, with electrical sti-
mulation on his right-hand thumb. The time chart (
upper left
) shows the signals
measured with 160 channel sensors. The iso-field contour map is displayed in the
upper right in reference to the positions of the sensors (
dots
). The ECD is displayed
as a white dot superimposed on the MRI image (
lower three diagrams
). The graphs
in the lower left, lower center, and lower right are transversal, sagittal, and coronal
views. The
white lines
stretching from the
white dots
show the direction and the
amplitude of the estimated ECD
responsible lesion. Electroencephalography failed to find homonymous hemi-
anopsia, because the right and left visual areas are close to each other. The
whole visual field of the right eye was stimulated. The right occipital region
responded. MEG measurement shows that the left occipital region did not
respond, as the patient claims (Fig. 3.60).
MEG is also useful when medical doctors would like to diagnose children
who are too young to have objective communication. A five-year-old female
with left occipital brain neoplasms was examined with MEG. Upon measu-
ring visual evoked fields resulting from flash stimulation to the left eye, the
right and left occipital regions responded. Since the subject was too young
to fix her eyes, visual field examination was impossible. Visual evoked po-
tential measurement can hardly help to find hemianopsia, because the right
and left visual areas are close to each other. Magnetoencephalograms allo-
