Biomedical Engineering Reference
In-Depth Information
Pixel noise was removed with a smoothing filter of window
size 27
m.
Next, the ratio of the post-stimulus over pre-stimulus scans
was calculated for all the grating stimuli and the control condition
as follows:
×
21
μ
R
pos
s
(
x
,
z
,
t
)
Prescans
R
Pre
γ
s
(
x
,
z
,
t
)
=
(6.2)
(
x
,
z
,
t
)
s
Here R
s
is the reflectivity at position (
x
,
z
) at time
t
.“post”
and “pre” indicate post-stimulus and pre-stimulus scans. The
division operation removes the unchanging common variation
and extracts only changes due to visual stimulation. Next, the
ratio was averaged for all the scans obtained for each stimulus
<γ
s
(
x
,
z
)
>
. Finally, the differential OCT signal
<γ
diff
(
x
,
z
)
>
was calculated as,
<γ
diff
(
x
,
z
)
>
=
<γ
grating
(
x
,
z
)
>
−
<γ
control
(
x
,
z
)
>
. (6. 3)
With the above equation, by subtracting the differential OCT
signal of the control, we could remove noise fluctuations such as
respiration artifacts that were locked to the recording but not to
the grating stimulus . We have restricted this discussion mainly
to the results obtained by calculating the difference between
<γ
s
(x,z)
that were obtained for two orthogonal gratings. The spa-
tial map has been smoothed with a moving average filter roughly
100
>
×
115
μ
m.
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