Biomedical Engineering Reference
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alpha-band activity. The time courses of the three sources for the first trial are shown
in Fig.
7.2
a. The time courses had trial-to-trial time jitters. The time jitters for the
three time courses were generated using Gaussian random numbers with the same
standard deviation of 20 time points. These time courses were projected onto the
sensor space using the sensor lead field to obtain the signal magnetic recordings. The
simulated sensor recordings were computed by adding spontaneous MEG data to the
signal magnetic recordings. The signal-to-interference ratio was set to 0.5.
The voxel time courses were reconstructed using the vector-type narrow-band
the alpha frequency band. Reconstructed source power images on the plane
x
0cm
are shown in Fig.
7.3
a. The three sources are clearly resolved. Since the spherical
homogeneous conductor [
25
] was used for forward modeling, the vector adaptive
beamformer reconstructed two time courses corresponding to the two tangential
directions. We estimated a single representative time course at each voxel using
the method described in Sect.
7.2
, and computed voxel spectra. Coherence images
were then computed with respect to the seed voxel, which was set at the second
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Fig. 7.3
Results of imaging the alpha-band voxel coherence on the plane
x
0cm.
a
Results of
source reconstruction. The
asterisk
shows the location of the seed voxel.
b
Magnitude coherence
image.
c
Imaginary coherence image.
d
Corrected imaginary coherence image
=
