Microscope-mounted intraoperative optical coherence tomography with actively tunable focus and optical path length (Conference Presentation)

We present a method for an intraoperative microscope-mounted Fourier-domain optical coherence tomography (FD-OCT) system to maintain high image contrast while dynamic adjusting focal planes. Because two imaging system with different imaging depth are integrated into one system, active control of OCT imaging conditions is indispensible for functioning high quality imaging modality. For the purpose of active adjustment of the focal plane, an electrically focus tunable lens (FTL) was used in the sample arm of the OCT system. Because the OCT image contrast at a depth is given by roll-off characteristics of the FD-OCT that is a function of difference in OPL between the sample and reference arm, we should compensate the difference in the OPL to enhance image contrast. We proposed the use of a piezoelectric actuator (PZT) attached to a reflection optic to actively control the OPL in the reference arm. With active controlling the FTL and PZT simultaneously, we can optimize and keep the OCT image contrast while maintaining image depth positions. From a surface position in the OCT image, the focal length variations with the FTL are calculated and the focal length of the FTL is tuned to match on the sample surface. Contrast optimization with the PZT is performed with compensating the optical path length difference from the additional focal length of the FTL. We integrated the OCT to a conventional surgical microscope and demonstrate feasible observation of OCT image with high contrast at constant imaging depth under the change of focal plane of the microscope.