Cortical surface harmonic motion during open cranial neurosurgery is well observed in image-guided neurosurgery.
Recently, we quantified cortical surface deformation noninvasively with synchronized blood pressure pulsation (BPP)
from a sequence of stereo image pairs using optical flow motion tracking. With three subjects, we found the average
cortical surface displacement can reach more than 1 mm and in-plane principal strains of up to 7% relative to the first
image pair. In addition, the temporal changes in deformation and strain were in concert with BPP and patient respiration
. However, because deformation was essentially computed relative to an arbitrary reference, comparing cortical
surface deformation at different times was not possible. In this study, we extend the technique developed earlier by
establishing a more reliable reference profile of the cortical surface for each sequence of stereo image acquisitions.
Specifically, fast Fourier transform (FFT) was applied to the dynamic cortical surface deformation, and the fundamental
frequencies corresponding to patient respiration and BPP were identified, which were used to determine the number of
image acquisitions for use in averaging cortical surface images. This technique is important because it potentially allows
in vivo characterization of soft tissue biomechanical properties using intraoperative stereovision and motion tracking.