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deoxygenated hemoglobin). OISI provides 2D, depth-integrated
activation maps of brain activity by imaging the optical reec-
tivity of the brain onto a CCD camera and calculating the ratio
of post-stimulus scans over pre-stimulus images for each indi-
vidual trial (identical to the OCT calculations). OISI provides an
image of the change in total hemoglobin concentration, which is
proportional to total blood volume if the hematocrit is assumed
constant.
Figure 14.7 shows the co-registered OISI and OCT images
in the region of functional activation. e functional sig-
nal was computed as a ratio of