Biomedical Engineering Reference
In-Depth Information
the PFA algorithm successfully removes the interference, even though the number
of factors for the signal and interference components are significantly overspecified.
We next performed a source reconstruction experiment. We computed the
interference-removed covariance matrix
R
in Eq. (
5.133
), and used it with the adap-
tive beamformer algorithm. The results are shown in Fig.
5.5
.InFig.
5.5
a, the results
of source reconstruction, obtained using the signal-only data (data before adding
the interferences), are shown. The results of source reconstruction obtained with the
interference-added data are shown in Fig.
5.5
b. We can observe a certain amount of
distortion in Fig.
5.5
b. The results of reconstruction using
R
are shown in Fig.
5.5
c.
The distortion is significantly reduced, demonstrating the effectiveness of the PFA
algorithm.
Finally, a source reconstruction experiment using the Saketini algorithm was per-
formed. Simulated MEG data was generated in which the signal-to-noise ratio (SNR)
was set equal to two. We computed the power map using tr
(
ʦ
−
1
with the number of
factors
L
set to 20. The results are shown in Fig.
5.6
. The reconstructed source power
map on the plane of
x
)
=
0 is shown in Fig.
5.6
a. The reconstructed time courses
(a)
(b)
12
12
11
11
10
10
9
9
8
8
7
7
6
6
5
5
4
2
0
2
4
4
2
0
2
4
y (cm)
y (cm)
(c)
12
11
10
9
8
7
6
5
4
2
0
2
4
y (cm)
Fig. 5.5
Results of source reconstruction experiments using the interference-removed covariance
matrix
R
in Eq. (
5.133
). The adaptive beamformer algorithm was used for source reconstruction,
and the reconstructed source distribution at
x
0cmisshown.
a
The results obtained with a sample
covariance matrix computed from signal-only simulated recordings.
b
The results obtained with
a sample covariance matrix computed from the interference-added sensor data.
c
The results of
the interference-removal experiment, obtained with
R
in Eq. (
5.133
). The
(
y
,
z
)
coordinates of the
three sources were set to
(
−
2
.
0
,
10
.
2
)
cm, (2.5, 10.2) cm, and (1.0, 7.2) cm in this experiment
=
