Imaging Blood Flow Dynamics Using Laser Speckle: A Technological Overview
Fundamentals of Laser Speckle Contrast Imaging (LSCI)
Information pertaining to pulsatile blood flow dynamics within the XyCAM’s or VasoVUE’s field of view is obtained via Laser Speckle Contrast Imaging (LSCI). LSCI, a key tool in visualizing pulsatile blood flow, relies on the formation of interference patterns (called speckle patterns) in the image when any tissue is illuminated with coherent light such as a laser. Any motion in the field of view, particularly pulsatile blood flow dynamics, causes a blurring effect in the speckle pattern of the captured image over the camera’s exposure time. The rate of blood motion at any location can thus be estimated by analyzing the extent of blurring at that location, which can be achieved by computing the contrast in the captured intensity values vis-à-vis the location’s neighborhood. Thus intensity values in the captured sequence of images are processed to obtain blood flow velocity indices (BFVi) that are often depicted in pseudo-color for effective visualization. LSCI is implemented at a rapid rate to provide high resolution blood flow data.
OCT-A vs LSCI: Visualizing Perfused Vessels versus Visualizing Blood Flow Dynamics
It is different. LSCI provides complementary dynamic blood flow information.
Fundus imaging, optical coherence tomography (OCT), and scanning laser ophthalmoscopy (SLO) obtain structural and anatomical data.
Angiography adds crucial perfusion status information to structural data, for more clinical insights. Via dye injection, fluorescein angiography and ICG angiography enable high resolution visualization of perfused vessels, areas of non-perfusion, and leakage.
OCT angiography (OCT-A) helps noninvasively:
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Visualize perfusion status in the posterior segment,
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Quantify the density of perfused vasculature, and
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Determine unperfused or avascular areas.
Laser speckle contrast imaging (LSCI) technology complements clinical imaging modalities with a direct visualization of pulsatile blood flow dynamics with high spatial and temporal resolution.
It is possible to analyze the blood flow time sequence from specific vessels and regions for dynamic metrics such as dip and peak blood flow velocity index, fractional time-to-rise, volumetric skew, and pulsatile index that characterize ocular blood flow dynamics using pulsatile blood flow measurements.
