Source: https://www.osapublishing.org/boe/abstract.cfm?uri=boe-5-9-3217
Timestamp: 2019-04-22 00:54:44+00:00

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Optical coherence Doppler tomography (ODT) is a promising neurotechnique that permits 3D imaging of the cerebral blood flow (CBF) network; however, quantitative CBF velocity (CBFv) imaging remains challenging. Here we present a simple phase summation method to enhance slow capillary flow detection sensitivity without sacrificing dynamic range for fast flow and vessel tracking to improve angle correction for absolute CBFv quantification. Flow phantom validation indicated that the CBFv quantification accuracy increased from 15% to 91% and the coefficient of variation (CV) decreased 9.3-fold; in vivo mouse brain validation showed that CV decreased 4.4-/10.8- fold for venular/arteriolar flows. ODT was able to identify cocaine-elicited microischemia and quantify CBFv disruption in branch vessels and capillaries that otherwise would have not been possible.
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Fig. 1 A schematic of spectral-domain μOCT system for simultaneous 3D μODT and μOCA imaging. CM: collimator, D: dispersion compensator; FPC: fiber polarization controller, L1, L2, L3: achromatic lenses, G: servo mirrors. BS: beam splitter.
Fig. 2 A sketch of new image acquisition and processing GUI to enable instantaneous display of 3D ODT of the quantitative CBFv network. a) Diagram of multi-threading structure with 6 sub-threads running separately with inter-thread data synchronization. b) Screen capture of GUI control panel during scanning CBFv network in vivo.
Fig. 3 Numerical method for vessel tracking and least-squares fitted angle correction. Vessel skeleton (b) was generated by centroid tracking of the raw data (a). 2D (c) and 3D (d) curve fitting was applied to smoothen raw vessel skeleton extracted by centroid tracking technique, i.e., blue dots in (d). As result of two-step fitting, a vessel skeleton f(x,y,z) was obtained in (e). (f): Doppler angle |cosθz(x,y,z)| was calculated by Eq. (9) and further smoothened by Fourier curve (red line) to avoid extreme case when cosθz = 0.
Fig. 4 Comparison of time partition between data acquisition thread and phase reconstruction threads.
Fig. 5 Phantom flow study (1% intralipid, ϕ280µm tubing) to demonstrate that phase summation method enhances the sensitivity for slow flow detection and increases the dynamic range for fast flow detection. All images are projected onto same phase scale [0, π] for comparison.
Fig. 6 Results of flow phantom study (1% intralipid, ϕ280µm tubing) to show that angle correction using gradient vessel tracking dramatically ~9.3-fold reduces the error in flow rate quantification.
Fig. 7 3D ODT image of quantitative CBFv network on a mouse somatosensory motor cortex (1.9 × 1.5 × 1mm3). Left panel: 3D CBFv image without angle correction; Right panel: comparison of flow rate correction for a vein and an artery.
Fig. 8 3D OCA images (upper panels) and 3D ODT images (lower panels) of the somatosensory motor cortex (2 × 1.5 × 1mm3) from a control mouse (left) and a chronic cocaine treated mouse (right), showing significant decreases in the entire CBFv network. Dashed circles show examples of vasoconstriction.
Fig. 9 Ratio image to quickly track the ROIs, e.g., vessels with drastic flow decrease after repeated cocaine administration (2.5mg/kg/ea, iv). a) baseline CBFv image, b) currently updating CBFv image, c) ratio image of (b)/(a) to identify flow disruptions, d) statistical analysis of CBFv decrease. White dashed lines: ROIs with diminishing flows.

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