Transient Thermal Response of Blood Vessels during Laser Irradiation Monitored by Laser Speckle Contrast Imaging

Abstract

Real-time monitoring of blood flow and thrombosis formation induced by laser irradiation is critical to reveal the thermal-damage mechanism and successfully implement vascular-dermatology laser surgery. Laser speckle contrast imaging (LSCI) is a non-invasive technique to visualize perfusion in various tissues. However, the ability of the LSCI to monitor the transient thermal response of blood vessels, especially thrombus formation during laser irradiation, requires further research. In this paper, an LSCI system was constructed and a 632 nm He-Ne laser was employed to illuminate a Sprague Dawley rat dorsal skin chamber model irradiated by a 1064 nm Nd: YAG therapy laser. The anisotropic diffusion filtering (ADF) technique is implemented after temporal LSCI (tLSCI) processing to improve the SNR and temporal resolution. The speckle flow index is used to characterize the blood-flow velocity to reduce the computational cost. The combination of the tLSCI and ADF increases the temporal resolution by five times and the SNR by 17.2 times and 16.14 times, without and with laser therapy, respectively. The laser-induced thrombus formation and vascular damage during laser surgery can be visualized without any exogenous labels, which provides a powerful tool for thrombus monitoring during laser surgery.

Non-invasive laser speckle imaging of extra-embryonic blood vessels in intact few-days-old avian eggs

“…3 for more details. To reduce the speckle noise after tLSCI reconstruction, we used an anisotropic diffusion filter (ADF), which can preserve image details while enabling image smoothing 27,28 . We also found that the application of ADF denoising enhanced the temporal resolution of the imaging, achieving imaging of the blood vessels with as few as N = 3 speckle frames, see additional results in Supplementary Fig.…”

“…tLSCI is resistant to static scattering because α t will not change when adding a static term to . To reduce the dot-like speckle noise after tLSCI reconstruction, we used an anisotropic diffusion filter (ADF) 27,28 , which works in an iterative way by: where n is the number of filtering iterations, λ = 1/4 represents the diffusion rate. d and ∇ K t are the diffusion coefficient and the contrast gradient in the direction of four neighboring pixels (up, down, left, right).…”

“…To address these challenges, we have implemented an improved LSCI system that is capable of imaging the blood vessel network of few-days-old chicken eggs using temporal Fourier filtering and additional speckle noise reduction techniques 27,28 . Our results showed a significant improvement for imaging the chicken egg blood vessel network than previously reported 26 .…”