Laser Speckle Contrast Imaging: Theory, Instrumentation and Applications

Abstract

Laser Speckle Contrast Imaging (LSCI) is a wide field of view, non scanning optical technique for observing blood flow. Speckles are produced when coherent light scattered back from biological tissue is diffracted through the limiting aperture of focusing optics. Mobile scatterers cause the speckle pattern to blur; a model can be constructed by inversely relating the degree of blur, termed speckle contrast to the scatterer speed. In tissue, red blood cells are the main source of moving scatterers. Therefore, blood flow acts as a virtual contrast agent, outlining blood vessels. The spatial resolution (~10 μm) and temporal resolution (10 ms to 10 s) of LSCI can be tailored to the application. Restricted by the penetration depth of light, LSCI can only visualize superficial blood flow. Additionally, due to its non scanning nature, LSCI is unable to provide depth resolved images. The simple setup and non-dependence on exogenous contrast agents have made LSCI a popular tool for studying vascular structure and blood flow dynamics. We discuss the theory and practice of LSCI and critically analyze its merit in major areas of application such as retinal imaging, imaging of skin perfusion as well as imaging of neurophysiology.

Accessing to arteriovenous blood flow dynamics response using combined laser speckle contrast imaging and skin optical clearing

“…It was also demonstrated that LSCI would has an optimal contrast-to-noise ratio (CNR) and a low noise when the exposure time of the CCD camera T is set to 5 ms [57]. Under the widely-used assumption of a random Lorentzian velocity distribution, the speckle contrast C spec can be simplified as follows [54,58,59]:…”

“…The simplest approach after ignoring many inessential factors leads to a characteristic velocity c υ defined as follows [54,59]:…”

Optimization of camera exposure durations for multi-exposure speckle imaging of the microcirculation

“…Beginning with the optimal 6 exposure set (T Set6 ), the deviations resulting from the removal of an exposure are calculated for each animal. The exposure removal having the least impact on the calculated correlation times versus the full exposure set is identified, which in this iteration is the T Set6 [5] = 25 msec exposure. Conversely, the greatest impact results from removal of the first exposure (T Set6 [1] = 0.05 msec) with average deviations over 50%, and then followed more distally by the third (T Set6 [3] = 0.75 msec, %Δ ~16%) and last (T Set6 [6] = 80 msec, %Δ ~15%) exposures.…”

“…The 6 exposure subset is also statistically comparable to the metrics obtained with its progenitor subset of 7. T Set7 [1] 7.9 ± 11 1.09 2.1 T Set7 [2] 4.2 ± 3.5 1.05 2.0 T Set7 [3] 11 ± 19 1.10 0.6 T Set7 [4] 20 ± 21 1.14 7.0 T Set7 [5] 12 ± 11 1.13 7.0 T Set7 [6] 7.4 ± 11 0.60 18 T Set7 [7] 15 ± 15 0.23 28 T Set7 3.7 ± 2.9 1.03 0.06…”

“…Although initially developed for retinal imaging, LSCI has become predominantly used for neurovascular applications from small animals to humans [1][2][3][4][5]. Given technical and inversemodeling improvements the technique has increased its quantitative accuracy in observing functional hemodynamics beyond just qualitative angiography.…”