Laser Speckle Imaging to Monitor Microvascular Blood Flow: A Review

Abstract

Laser speckle is a complex interference phenomenon that can easily be understood, in concept, but is difficult to predict mathematically, because it is a stochastic process. The use of laser speckle to produce images, which can carry many types of information, is called laser speckle imaging (LSI). The biomedical applications of LSI started in 1981 and, since then, many scientists have improved the laser speckle theory and developed different imaging techniques. During this process, some inconsistencies have been propagated up to now. These inconsistencies should be clarified in order to avoid errors in future works. This review presents a review of the laser speckle theory used in biomedical applications. Moreover, we also make a review of the practical concepts that are useful in the construction of laser speckle imagers. This study is not only an exposition of the concepts that can be found in the literature but also a critical analysis of the investigations presented so far. Concepts like scatterers velocity distribution, effect of static scatterers, optimal speckle size, light penetration angle, and contrast computation algorithms are discussed in detail.

Engenharia na Medicina

“…Muitos destes trabalhos já resultaram em dispositivos e metodologias já em aplicação ou patenteadas e em processo de futura comercialização, tais como "uma técnica indolor de diagnóstico para o cancro da mama", 21 e "um sistema de monitorização da corrente sanguínea", 22 e o "Métrica Vertebral" que efetua a análise biomecânica da coluna vertebral através de um equipamento inovador (patenteado nacional e internacionalmente). 23 Na área da saúde, tais como nas restantes áreas de intervenção humana, a realidade ultrapassa sempre a ficção e as previsões, pelo que se afigura um espetacular mundo novo.…”

Roadmap on optical sensors

“…It can be a simple and powerful method for 2D mapping of flow or vibration. However, the spatial and temporal resolutions are relatively poor in comparison with other laser-based sensing techniques, and absolute velocity estimation or deep assessment beyond a few hundred μ m remains an issue [63]. Further improvements in both theoretical models and measurement techniques are strongly in demand.…”

Gaussian sliding window for robust processing laser speckle contrast images

“…Nowadays, the laser speckle contrast analysis (LASCA) is one of the most applicable tools for studying problems related to blood microcirculation and perfusion in living tissues . Such popularity may be explained by several method features, that include a relatively simple technical (optical) implementation, easy assessment of the relative velocity of scattering particles (most often—red blood cells), and the possibility to distinguish between their ordered motion and random walk.…”

“…Thus, although such spatio‐temporal combination of LASCA methods is accepted now for specific research needs, the data processing methods related to spatial, temporal, and spatio‐temporal processing are still considered separately, as different ones, see for example a table in Basak et al, where the comparison is given with a special attention to distortions, which each of them produces in the restored image.…”

“…Nowadays, the laser speckle contrast analysis (LASCA) is one of the most applicable tools for studying problems related to blood microcirculation and perfusion in living tissues. [1][2][3][4] Such popularity may be explained by several method features, that include a relatively simple technical (optical) implementation, easy assessment of the relative velocity of scattering particles (most often-red blood cells), and the possibility to distinguish between their ordered motion and random walk. However, the simplicity of a technical implementation has a dark side in the requirement of more or less sophisticated data processing algorithms since the raw data are highly stochastic and noisy by the essence of this experimental method.…”