Information Technology Reference
In-Depth Information
20.3.2 Statistical Method for Pairwise Comparison of
STL
MAX
One of the statistical measures of similarity between two different channels was
introduced via T-index. It quantifies the statistical mean difference between two
EEG channels with respect to their dynamics such as STLmax. As shown in [33],
although the critical electrode sites involved in transition into the seizure state vary
from patient to patient, the conditions for an impending seizure can be characterized
by the fall in the average T-index for pairs of critical electrodes, signifying that on
average, all critical electrode sites exhibit convergence in STLmax values, as shown
in Fig. 20.3.
Fig. 20.3: T-index curve that quantifies the spatiotemporal pattern of five STLmax
curves over a 140-min time window that includes a seizure.
Mathematically, the value of the T-index statistic at time
t
for the STLmax values
between a pair of electrode sites
i
and
j
in a moving window
W
t
with
n
points of
STLmax is given by the following formula:
√
η
|
ij
μ
ˆ
(
t
)
|
T
ij
=
,
(20.3)
ˆ
ij
σ
(
t
)
ij
and
ˆ
ij
(
where
ˆ
, respectively, denote the sample mean and the sample stan-
dard deviation of the differences STL
i
MAX
−
μ
σ
t
)
STL
j
MAX
in the values of STLmax for
channels
i
and
j
estimated successively at times
t
,
t
+
1
, ··· ,
t
+(
n
−
1
)
.
