![]() Scale: 200 µm.ĭoppler OCT is capable of quantitative volumetric measurement of axial blood flow speed by detecting the Doppler frequency shift of backscattered light from a moving particle (e.g., a flowing RBC). Capillaries are more readily resolved with the 10X objective. (B) Obtained with a 10X objective (0.28 NA). (A) Obtained with a 5X objective (0.14 NA). ![]() For more information about OCTA please refer to Zhang A, 2015, J Biomed Opt, and Wang RK, 2007, Opt Express.įig 1. MIPs of OCTA images of cerebral vasculature spanning a depth of ~500 µm from brain surface. With the 10X objective in our OCT system, the capillary bed from a depth of 0 to 1,000 µm could be imaged with an isotropic 3D resolution of 3.5 µm. ![]() flowing RBCs), and will thus appear as bright areas in the OCT angiogram image. In contrast, dynamic tissue, such as a blood vessel, will experience a large difference between repeated B-scans due to particle movement (e.g. There will be no difference for repeated voxels when static tissue is imaged. Briefly, while conventional structural OCT imaging typically acquires one B-scan for each Y position, the decorrelation-based method repeats two B-scans and then analyzes the differences in the image intensity and phase between the two repeated B-scans. OCTA images are constructed by a decorrelation-based method described in. These techniques include OCT angiography (OCTA) for cerebral vasculature visualization, Doppler OCT (D-OCT) for measuring the axial speed of red blood cells in both large vessels and capillaries, Dynamic Light Scattering-Optical Coherence Tomography (DLSOCT) for absolute blood flow speed detection and the measurement of diffusive motion, and intrinsic contrast OCT (iOCT) for neuron cell body and myelinated axon imaging. In the Neurophotonics Center, we have been developing and are using various OCT imaging techniques based on S/FD-OCT for studying cerebral physiology and pathophysiology. Relative to other widely used optical imaging technologies for functional brain imaging such as two/multi photon microscopy and confocal fluorescence microscopy, OCT possesses several advantages including, 1) it only takes a few seconds to a minute for a volumetric imaging with OCT compared to tens of minutes to a few hours using two photon microscopy 2) OCT is capable of imaging at depths of greater than 1 mm in brain tissue 3) since the axial resolution depends on the coherence length OCT can maintain high axial resolution with low NA objectives, allowing it image a large field of view while maintaining axial resolution 4) OCT detects backscattered signal from intrinsic scattering avoiding the concern of cumulative dye toxicity in fluorescent imaging and 5) direct access to the interference fringes provided by S/FD-OCT provides a wide range of novel functional application, such as SD-OCT for absorption measurements and Doppler OCT for flow velocity measurements. Compared to time domain OCT (TD-OCT), Spectral/Fourier domain OCT (S/FD-OCT) offers significantly improved volumetric imaging speed and sensitivity. Analogous to ultrasound imaging, OCT provides depth-resolved cross-sectional image at micrometer spatial resolution with the use of low coherence interferometry. Utilizing the advantages of non-invasive, fast volumetric imaging at micron-scale resolution with intrinsic contrast agents, Optical Coherence Tomography (OCT) has been one of the most powerful optical imaging modalities in the last two decades and has been widely used in ophthalmology, cardiology, dermatology, gastroenterology, and neurology.
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