Using optical coherence tomography angiography, we measured blood flow from the vessels in the lateral wall in the mouse cochlea directly through bone in mice with and without sympathetic neuronal function. We present in vivo imaging of blood flow and mechanical vibration in mice subjected to 30 min of loud sound. Loud sound caused blood flow reduction. In mice with superior cervical ganglion ablation, the loud sound-induced reduction in blood flow was partially ameliorated. These results demonstrate that sympathetic innervation likely plays a role in the pathological decrease in blood flow observed in the lateral wall vessels in response to loud sound.
Cutaneous wound healing consists of multiple overlapping phases starting with blood coagulation following incision of blood vessels. We utilized label-free optical coherence tomography and optical microangiography (OMAG) to noninvasively monitor healing process and dynamics of microcirculation system in a mouse ear pinna wound model. Mouse ear pinna is composed of two layers of skin separated by a layer of cartilage and because its total thickness is around 500 μm, it can be utilized as an ideal model for optical imaging techniques. These skin layers are identical to human skin structure except for sweat ducts and glands. Microcirculatory system responds to the wound injury by recruiting collateral vessels to supply blood flow to hypoxic region. During the inflammatory phase, lymphatic vessels play an important role in the immune response of the tissue and clearing waste from interstitial fluid. In the final phase of wound healing, tissue maturation, and remodeling, the wound area is fully closed while blood vessels mature to support the tissue cells. We show that using OMAG technology allows noninvasive and label-free monitoring and imaging each phase of wound healing that can be used to replace invasive tissue sample histology and immunochemistry technologies.
We use rodent parietal cortex as a model system and utilize a synchronized dual wavelength laser speckle imaging (SDW-LSCI) technique to explore the hemodynamic response of infarct and penumbra to a brain injury (middle cerebral artery occlusion (MCAO) model). The SDW-LSCI system is able to take snapshots rapidly (maximum 500 Hz) over the entire brain surface, providing key information about the hemodynamic response, in terms of which it may be used to elucidate evolution of penumbra region from onsite to 90 min of MCAO. Changes in flow are quantified as to the flow experiencing physical occlusions of the MCA normalized to that of baseline. Furthermore, the system is capable of providing information as to the changes of the concentration of oxygenated, (HbO) deoxygenated (Hb), and total hemoglobin (HbT) in the cortex based on the spectral characteristics of HbO and Hb. We observe that the oxygenation variations in the four regions are detectable and distinct. Combining the useful information, four regions of interest (ROI), infarct, penumbra, reduced flow and contralateral portions in the brain upon ischemic injury may be differentiated. Implications of our results are discussed with respect to current understanding of the mechanisms underlying MCAO. We anticipate that SDW-LSCI holds promise for rapid and large field of view localization of ischemic injury.
Ability to non-invasively monitor and quantify of blood flow, blood vessel morphology, oxygenation and tissue morphology is important for improved diagnosis, treatment and management of various neurovascular disorders, e.g., stroke. Currently, no imaging technique is available that can satisfactorily extract these parameters from in vivo microcirculatory tissue beds, with large field of view and sufficient resolution at defined depth without any harm to the tissue. In order for more effective therapeutics, we need to determine the area of brain that is damaged but not yet dead after focal ischemia. Here we develop an integrated multi-functional imaging system, in which SDW-LSCI (synchronized dual wavelength laser speckle imaging) is used as a guiding tool for OMAG (optical microangiography) to investigate the fine detail of tissue hemodynamics, such as vessel flow, profile, and flow direction. We determine the utility of the integrated system for serial monitoring afore mentioned parameters in experimental stroke, middle cerebral artery occlusion (MCAO) in mice. For 90 min MCAO, onsite and 24 hours following reperfusion, we use SDW-LSCI to determine distinct flow and oxygenation variations for differentiation of the infarction, peri-infarct, reduced flow and contralateral regions. The blood volumes are quantifiable and distinct in afore mentioned regions. We also demonstrate the behaviors of flow and flow direction in the arterials connected to MCA play important role in the time course of MCAO. These achievements may improve our understanding of vascular involvement under pathologic and physiological conditions, and ultimately facilitate clinical diagnosis, monitoring and therapeutic interventions of neurovascular diseases, such as ischemic stroke.
Visualization and measurement of retinal blood flow (RBF) is important to the diagnosis and management of different eye diseases, including diabetic retinopathy. Optical microangiography (OMAG) is developed for generating 3D dynamic microcirculation image and later refined into ultra-high sensitive OMAG (UHS-OMAG) for true capillary vessels imaging. Here, we present the application of OMAG imaging technique for visualization of depth-resolved vascular network within retina and choroid as well as measurement of total retinal blood flow in mice. A fast speed spectral domain OCT imaging system at 820nm with a line scan rate of 140 kHz was developed to image mouse posterior eye. By applying UHS-OMAG scanning protocol and processing algorithm, we achieved true capillary level imaging of retina and choroid vasculature in mouse eye. The vascular pattern within different retinal layers and choroid was presented. An en face Doppler OCT approach [1] without knowing Doppler angle was adopted for the measurement of total retinal blood flow. The axial blood flow velocity is measured in an en face plane by raster scanning and the flow is calculated by integrating over the vessel area of the central retinal artery.
Skipping various numbers of A-lines is effective to obtain multi-range velocimetry using Doppler optical coherence
tomography (DOCT). High correlation between A-lines is a fundamental prerequisite for DOCT processing. Therefore,
high oversampling is normally necessary, especially when skipping A-lines. That requires quite a long time of imaging,
which might not be acceptable on some occasions. Step-scanning protocol, which captures repeated A-scans, has been
employed for multi-range DOCT previously. We develop it by waiting for the scanner to stabilize, but not capturing
continuously. In this way the cross-correlation of step scanning maintains almost constant for all the captured A-lines,
and is higher than that of conventional linear scanning with similar imaging time. Due to the limited numbers of A-lines
at each lateral position, we choose previously proposed high-pass filter in ultrahigh sensitive optical microangiography
(OMAG) to enhance flow sensitivity. Doppler processing is implemented after the filter, both of which utilize A-line
skipping to achieve variable velocity ranges. The obtained Doppler signal in blood flow is encircled by much noise in
non-flow area. This is because that the static components are rejected by the filter, leaving random phase noise. The
phase variance, which is a flow indicator, is employed to generate a binary mask to extract the Doppler signal out of
noise. The technique is demonstrated in bi-directional cross-section and maximum projection en face images of middle
cerebral artery (MCA) occluded mouse model. The vasculature responses from artery down to capillary during baseline,
occlusion and reperfusion are illustrated. In some arteries that branch from MCA the flow is reversed but not simply
reduced or vanished.
Reduced cochlear blood flow (CoBF) is a main contributor to hearing loss. Studying CoBF has remained a challenge due to the lack of available tools. Doppler optical microangiography (DOMAG), a method to quantify single-vessel absolute blood flow, and laser Doppler flowmetry (LDF), a method for measuring the relative blood flow within a large volume of tissue, were used for determining the changes in CoBF due to systemic hypoxia in mice. DOMAG determined the change in blood flow in the apical turn (AT) with single-vessel resolution, while LDF averaged the change in the blood flow within a large volume of the cochlea (hemisphere with ∼1 to 1.5 mm radius). Hypoxia was induced by decreasing the concentration of oxygen-inspired gas, so that the oxygen saturation was reduced from >95% to ∼80% . DOMAG determined that during hypoxia the blood flow in two areas of the AT near and far from the helicotrema were increased and decreased, respectively. The LDF detected a decrease in blood flow within a larger volume of the cochlea (several turns averaged together). Therefore, the use of DOMAG as a tool for studying cochlear blood flow due to its ability to determine absolute flow values with single-vessel resolution was proposed.
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