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.
Optical Doppler Tomography (ODT) is a high-resolved and non-invasive biomedical imaging technique, which can
obtain tissue structure and blood flow velocity at the same time. A novel phase-resolved ODT method to measure 3-D
velocity vector is presented. After inserting the designed narrowband phase plate between the collimator and focusing
lens of the sample arm, three independent path length delays are formed. By calculating the Doppler shift and the
Doppler bandwidth corresponding to three delays, 3-D velocity vector distribution of the solution inside the glass
capillary is obtained. Experiments of polystyrene solution flowing at different velocity are conducted, demonstrating the
feasibility of the proposed method for 3-D velocity vector measurement.
Endoscopic optical coherence tomography (OCT) allowing high-resolution imaging of internal tissue is attractive for
medical imaging. Fibre, fibre bundle or GRIN lens rod acting as endoscopic probe is placed in the sample arm of a
Michelson interferometer in current endoscopic OCT systems, this arrangement has to be carefully configured to avoid
dispersion and polarization fading. In this study, a common path OCT system with outside path length compensation is
presented. The system based on Fizeau configuration requires a Michelson interferometer to compensate the optical path
difference between the reference and signal light in the Fizeau sensing interferometer. Experiments of path length
compensation and vibration are conducted, and the results demonstrate that this outside compensation method is feasible
and the system is immune to the vibration which occurs at the Fizeau sensing interferometer. This OCT imaging
approach is very suitable for endoscopic imaging and detailed endoscopic OCT system is also presented. Several
samples were imaged to demonstrate the performance of the proposed OCT system.
Optical Doppler tomography (ODT) combines Doppler principle with Optical coherence tomography (OCT) to image
both the structure and the flow velocity of moving particles in highly scattering biological tissues. The flow velocity can
be determined by measurement of the Doppler shift of the interference fringe frequency with a short-time Fourier
transform (STFT) or a Hilbert transform. For STFT ODT, velocity resolution varies inversely with the Fourier transform
window size at each pixel, while spatial resolution is proportional to the window size. Consequently, velocity resolution
and spatial resolution are coupled. For phase-resolved ODT with Hilbert transform, high velocity resolution can be
achieved while maintaining a high spatial resolution. However, the maximum determinable Doppler shift is limited by
axial-line scanning speed. As a result, STFT ODT and phase-resolved ODT are applicable to measurement of high speed
and low speed velocity, respectively. We use these two methods in the established ODT system. An in vitro model using
a small circular glass tubule with flowing solution of polystyrene beads inside and an in vivo model of rat's cerebral
arterioles are investigated, demonstrating the advantage and disadvantage of STFT ODT and phase-resolved ODT.
Spectroscopic optical coherence tomography (OCT), a functional extension of conventional structural OCT is developed
based on previous fiber-based OCT system. Spectral information is obtained by carrying out Fourier transformation of
the detected OCT signal without recurring to hardware. The developed system is applied to film reflectivity
measurement and spectroscopic imaging of a finger from a human volunteer. The feasibility for spectroscopic
extension of the developed system is confirmed by comparison curves of film reflectivity measured by the developed
system with that obtained from a commercial spectrometer.
Axial resolution is a key factor in optical coherence tomography (OCT). Biomedical applications will benefit from
improved resolution and quality that ultrahigh resolution OCT can provide. Existing approaches to improve axial
resolution of OCT mostly depend on new broadband light sources, which are always costly and inconvenient in
instrumentation. In this paper we adopt an alternative method to enhance the axial resolution of OCT by combining
coherence gate with optical superresolution. A three-zone phase pupil filter is designed and inserted into the sample
arm of OCT. The depth responses measured demonstrate that an improvement of more than 15% in axial resolution is
achieved in the proposed OCT system.
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