This paper reports recent advances in spectral domain Doppler optical coherence tomography (SD-DOCT) in our group.
A high speed SD-DOCT system is developed and applied to animal study and microchip evaluation. Further
improvements concerning SD-DOCT are presented, those including higher-order cross-correlation for phase retrieval,
transit-time analysis for velocity quantification, and orthogonal dispersive SD-OCT for depth extension.
A high speed swept source optical coherence tomography (SS-OCT) system capable of full-range imaging is presented. Wave-number carrier frequency is introduced into the spectral interference signal by a transmissive dispersive optical delay line (TDODL). High carrier frequency in the spectral interference signal corresponding to an equivalent distance-shift is exploited to obtain full-range OCT imaging. Theoretical development is conducted with the instantaneous coherence function introduced for a complete description of a spectral interference signal. Performance advantage of the TDODL-based method over the conventional approach where only one side (positive or negative path length difference) is used for imaging to avoid overlaying mirror artifacts is confirmed by the measured envelopes of spectral interference signal. Feasibility of the proposed method for full-range imaging is validated in a custom-built SS-OCT system by in vivo imaging of a biological sample.
A portable choroidal laser Doppler flowmeter (LDF) with enhanced sensitivity based on a scattering plate is developed. The portable LDF is weighted 2 kg operated at center wavelength of 780 nm, leading to a better penetration into the eye fundus in contrast to the previous LDF operated at center wavelength of 670 nm. Enhancement of number of detected photons that undergo Doppler scattering and improved measured speed of choroidal blood flow are achieved with the use of a scattering plate positioned in front of the eye. The mechanism of detection and sensitivity enhancement is theoretically analyzed. Evaluation of system performance is done by in vivo measurements on ten volunteers. The results demonstrate that an increased percentage of backscattering light at high Doppler shift frequency is collected due to utilization of the scattering plate. However, this kind of light detection influences spatial resolution of the system and decreases the total signal measured. The proposed method for detection and sensitivity enhancement might be useful in a case where the perception of very slight alternation of blood flow is pursued and the spatial resolution is not as critical as that in a choroidal vascular bed.
Doppler optical coherence tomography (DOCT) provides a novel method to measure blood flow velocity in vessels with diameter at micrometer scale. In this study, a developed spectral domain DOCT system is applied to monitor cerebral blood flow velocity changes in a rat. An animal model with a cranial window is used, and by application of a drug, light, and electric stimulations, changes in blood flow velocity of the pial artery in sensory cortex are measured in real time. The results show significant differences in blood flow velocity before and after drug administration or light and electric stimulations, demonstrating the feasibility of DOCT in cerebral microcirculation study. Given its noninvasive nature, high spatial resolution, high velocity sensitivity, and high imaging speed, DOCT shows great promise in brain research by imaging blood flow changes at micrometer scale vessels, which helps to understand the pathogenesis of cerebral diseases and neurodegenerative diseases.
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