Laser speckle imaging of flowing blood: A numerical study

Abstract

Laser speckle imaging (LSI) can be used to study dynamic processes in turbid media, such as blood flow. However, it is presently still challenging to obtain meaningful quantitative information from speckle, mainly because speckle is the interferometric summation of multiply scattered light. Consequently, speckle represents a convolution of the local dynamics of the medium. In this paper, we present a computational model for simulating the LSI process, which we aim to use for improving our understanding of the underlying physics. Thereby reliable methods for extracting meaningful information from speckle can be developed. To validate our code, we apply it to a case study resembling blood flow: a cylindrical fluid flow geometry seeded with small spherical particles and modulated with a heartbeat signal. From the simulated speckle pattern, we successfully retrieve the main frequency modes of the original heartbeat signal. By comparing Poiseuille flow to plug flow, we show that speckle boiling causes a small amount of uniform spectral noise. Our results indicate that our computational model is capable of simulating LSI and will therefore be useful in future studies for further developing LSI as a quantitative imaging tool.

The dependence of speckle contrast on velocity: a numerical study

“…The figure nicely shows that K ≈ 1 at zero velocity, which is the expected value for fully-developed static speckle [27]. Actually, K is slightly (∼1.2%) less than unity [24], but this is not substantial when compared to the uncertainties of discretization and of the random particle instantiations.…”

“…Thus strictly speaking our model is only applicable to sufficiently dilute flow, but it may be expected that the results on dynamic speckle imaging are more widely applicable nonetheless. More details about our code and the assumptions may be found in our previous paper [24].…”

“…The data points in the figure are the resulting mean speckle contrasts, and the error bars show the resulting standard deviations. Additional errors are not incorporated into these error bars, such as due to spatial and temporal discretization (which are ∼2% each [24]). The figure nicely shows that K ≈ 1 at zero velocity, which is the expected value for fully-developed static speckle [27].…”

Experimental study of speckle patterns generated by low-coherence semiconductor laser light

“…12 Different approaches for extracting meaningful information from speckle patterns have been proposed. [13][14][15] In addition, the intensity distribution, the speckle spot size, and speckle correlations provide information of the spectral properties of the source that generates the light. 16 High-precision spectrometers have been demonstrated, where wavelength-dependent speckle patterns are detected and, after calibration, used to recover the spectrum of the light.…”

“…For example, speckle has been used for remote vibration analysis and the remote recovery of audio signals 12 . Different approaches for extracting meaningful infor-arXiv:2006.02719v1 [physics.optics] 4 Jun 2020 mation from speckle patterns have been proposed [13][14][15] .…”