Biomedical Engineering Reference
In-Depth Information
6. Reliability of
the Signal as a
Measure of
Localization of
Neural Activity
As the correlation of OISI maps with neural activity is already
well established
(3, 4, 41)
, a comparison of fOCT with OISI is
a reasonable validation approach. We compared the intensity
variation of an OISI map across the scanned line (
Fig. 6.8
) with
the integrated profile of fOCT. In order to calculate the inte-
grated profile, all the pixels across the
z
-direction were summed
to obtain a profile that varies only across
x
; then the differential
OCT at each
x
was calculated.
Figure 6.9D
shows the result
of such a comparison with the red line indicating the integrated
result and green line indicating the OIS intensity variation. A
clear and remarkable agreement between the profiles can be
seen. This indicates that fOCT signal is indeed correlated with
OISI and thus correlated with the neural activity. Experiments
were done in 5 cats and showed a good correlation between
the integrated fOCT signal and the intensity profiles obtained
from intrinsic maps. Correlation coefficients vary in the range of
0.3-0.9.
Table 6.1
gives the results of correlation coefficients
obtained from a cat from different scan positions. However, a
general caveat is that there are many differences between OISI
and fOCT, including illumination and detection geometries,
wavelengths used and the origin of the signals. In fOCT, as
near-infrared wavelength is used, oxy- and deoxy-hemoglobin
have almost the same absorption coefficients and hence the
absorption changes are minimal. The main source of the signal is
thought to be scattering changes. Nevertheless, the OISI results
corresponded very well with the integrated profiles of fOCT.
Table 6.1
The correlation coefficients between the profiles obtained
by the OISI intensity profile and the corresponding
depth-integrated fOCT intensity profile obtained from 6
different scan positions of a single cat
Correlation for 0-90
◦
Correlation for 45-135
◦
Scan position index
Position 1
0.58
0.65
Position 2
0.32
0.29
Position 3
0.24
0.39
Position 4
0.89
0.77
Position 5
0.407
0.539
Position 6
0.566
0.559
