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ABSTRACT: Optical Doppler Tomography (ODT) provides a novel method to measure the blood flow velocity in vessels with the diameter at
micrometer scale. Rats with cranial window are used as a model, and the changes in the blood flow velocity of cerebral arterioles
in sensory cortex are measured in real time with an established ODT system, under electrical stimulation and drug administration.
The results show significant differences in the blood flow velocity between experimental groups and control groups, demonstrating
the feasibility of ODT in the cerebral microcirculation study. Compared with the conventional Doppler ultrasound, ODT provides
much higher spatial resolution, and thus holds a promising future in the application of the cerebral microcirculation study,
especially in the observation of the blood flow velocity in micrometer scale vessels.
Science in China Series G Physics Mechanics and Astronomy 04/2012; 51(12):1883-1891. · 1.41 Impact Factor
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ABSTRACT: 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.
Journal of Biomedical Optics 04/2011; 16(4):046001. · 3.16 Impact Factor
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ABSTRACT: We propose a transit-time based method to ascertain the azimuth angle of a velocity vector by spectral-domain Doppler optical coherence tomography (DOCT), so that three-dimensional (3-D) velocity vector can be quantified. A custom-designed slit plate with predetermined slit orientation is placed into the sample beam to create three delay-encoded sub-beams of different beam shape for sample probing. Based on the transit-time analysis for Doppler bandwidth, the azimuth angle within 90 degrees range is evaluated by exploitation of the complex signals corresponding to three path length delays. 3-D velocity vector is quantified through further estimating of Doppler angle and flow velocity by combined Doppler shift and Doppler bandwidth measurements. The feasibility of the method is demonstrated by good agreement between the determined azimuth angles and the preset ones, and further confirmed by velocity vector measurement of flowing solution inside a capillary tube.
Optics Express 01/2010; 18(2):1261-70. · 3.59 Impact Factor
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ABSTRACT: A high speed spectral domain optical coherence tomography based on the spatial sinusoidal phase modulation for the elimination of complex-conjugate artifact is presented, where sinusoidal phase modulation of reference arm (M scan) and transverse scanning of sample arm (B scan) are performed simultaneously (sinusoidal B-M method). Herein, the linear phase modulation of the reference arm in conventional linear B-M method is modified to sinusoidal phase modulation. The proposed sinusoidal B-M method relaxes the requirements on the phase-shifting mechanical system and avoids sensitivity fall-off along the transverse direction in contrast to the linear B-M method. A criterion for the relation between transverse over-sampling factor and modulation frequency for optimal complex conjugate rejection is deduced and verified by experiments. Under this criterion, the complex spectral interferogram is reconstructed by harmonic analysis and digital synchronous demodulation. Double imaging depth range on fresh shrimp at A-scan rate of 10 kHz with complex conjugate rejection ratio up to 45 dB is achieved.
Optics Express 09/2009; 17(19):16820-33. · 3.59 Impact Factor
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ABSTRACT: We develop a high speed spectral domain optical coherence tomography (SD-OCT) system based on a custom-built spectrometer and non-uniform discrete Fourier transform (NDFT) to realize minimized depth dependent sensitivity fall-off. After precise spectral calibration of the spectrometer, NDFT of the acquired spectral data is adopted for image reconstruction. The spectrometer is able to measure a wavelength range of about 138 nm with a spectral resolution of 0.0674 nm at central wavelength of 835 nm, corresponding to an axial imaging range of 2.56 mm in air. Zemax simulations and sensitivity fall-off measurements under two alignment states of the spectrometer are given. Both theoretical simulations and experiments are done to study the depth dependent sensitivity of the developed system based on NDFT in contrast to those based on conventional discrete Fourier transform (DFT) with and without interpolation. In vivo imaging on human finger from volunteer is conducted at A-scan rate of 29 kHz and reconstruction is done based on different methods. The comparing results confirm that reconstruction method based on NDFT indeed improves sensitivity especially at large depth while maintaining the coherence-function-limited depth resolution.
Optics Express 08/2009; 17(14):12121-31. · 3.59 Impact Factor
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ABSTRACT: A deconvolution method for image enhancement suitable for spectral domain optical coherence tomography (SD-OCT) is proposed. The method includes Wiener filtering for spectral deconvolution and successive homomorphic filtering for spatial deconvolution, aiming to minimize blurring effect of axial point spread function (PSF) and its depth dependence. Tunable factor in Wiener filtering is optimized for tradeoff between compensation ratio and signal-to-noise ratio (SNR). In vivo OCT imaging of a fresh shrimp is done and image reconstructions are performed. Comparing results demonstrates the proposed method suppresses the coherent noises in OCT image while compensating sensitivity fall-off with increased averaged SNR and recovers structural information at deep depths. Contrast-to-noise ratio (CNR) and averaged SNR in the reconstructed image based on the proposed method in contrast to those without deconvolution are improved by 3.4 dB and 4.6 dB, respectively.Research highlights►Fall-off compensated axial point spread function. ► Combined Wiener filtering and homomorphic filering. ►Improved CNR and SNR in images of spectral domain OCT.
Optics Communications 284(12):3173-3180. · 1.49 Impact Factor
