Biomedical Engineering Reference
In-Depth Information
Fig. 3.60.
Homonymous hemianopsia found by MEG
wed objective diagnosis of functional normality of the subject's visual sense
(Fig. 3.61).
Epilepsy Examination.
In some cases of focal epilepsy, medical doctors in-
troduce electrical cortical measurement, which is invasive examination, to
localize the foci before surgery. Noninvasive localization of foci has recently
been attempted with MEG. Figure 3.62 is an example of a 23-year-old male
with Lennox-Gastaut syndrome. A two-dipole pattern was observed on the
iso-contour map at the point of diffuse slow spike and wave discharges in the
EEG, and the equivalent current dipoles were estimated to originate in the
region of a cortical dysplasia lesion.
The results of the ECD estimation are as follows. All of the ECDs were
superimposed on to the area of the cortical dysplasia. The difference in the
gray levels of the rounded marker in Fig. 3.63 indicates the time sequence
of estimation. Cortical dysplasia bilaterally in the parietotemporal area was
found on MRI.
Measurement of Event-Related Field.
In addition to clinical applicati-
ons, the MEG system has been introduced into the field of brain and cogni-
tive science. One of the most frequently used methods with MEG in cognitive
science is the measurement of an event-related field. The MEG signals under
