Dynamic Light Scattering aproach in blood flow imaging

Laser speckle is a random interference pattern arising from interaction of the coherent light with rough scattering surface and/or with turbid randomly inhomogeneous media. Changes in local dynamics in observed media (moving of scattering particles) leads to fluctuations of speckle pattern and, thus,results in its blurring on captured frame due to the finite camera exposure time. The higher movement in observed object the more blurred speckle pattern will be captured by camera. This blurring consequently decreases the speckle contrast value, which, in fact, allows the quantification of the flow rate.

Our research group aims at investigation of the applicability boundaries of the LSCI in the case when the ergodicity condition is not fulfilled, as well as at estimating optimal parameters for conducting measurements with live objects.

Selected results

Hemodynamic patterns assessment in postmortem mice brains

We employ Laser Speckle Contrast Imaging (LSCI) to visualize cerebral blood flow in mice during and after cardiac arrest. Through analysis of LSCI images, we observed changes in blood flow across the brain surface for several hours postmortem. Fast Fourier Transform (FFT) analysis revealed the decay of blood flow and microcirculation following death. The Continuous Wavelet Transform (CWT) identified possible patterns of cerebral hemodynamic synchronization. Additionally, non-negative matrix factorization (NMF) with four components was used to segment LSCI images, uncovering structural subcomponent changes over time. This combined approach utilizing LSCI, FFT, CWT, and NMF provides a comprehensive tool for investigating cerebral blood flow dynamics, metaphorically capturing the experience of ‘the end of the tunnel.’ Our results indicate initial postmortem hemodynamic activity in the olfactory bulbs, followed by shifts in blood microflow between the somatosensory and visual cortical regions through the superior sagittal sinus. This methodology offers new opportunities for exploring these phenomena, potentially linking neuroscientific findings with the mysteries of consciousness and perception at the end of life.

Coefficient of speckle dynamics

Based on a simple phenomenological approach, we introduced a coefficient of speckle dynamics to quantitatively assess the ratio of the dynamic part of a scattering medium to the static one. The introduced coefficient allows one to distinguish real changes in motion from the mere appearance of static components in the field of view.

Analysis of spatial and temporal speckle contrasts, the values of the coefficient of speckle dynamics, along with the results of Monte-Carlo simulation of the sampling volume, revealed that the presence of a relatively thin, up to 30% of entire volume, static layer does not introduce considerable changes into the results of measurements by the method of laser speckle-contrast imaging. The exposure time of the camera, along with the number of frames used for image processing, can be varied and chosen individually for each experiment. The developed algorithms of spatial and temporal processing of images obtained by the method of laser speckle-contrast imaging were tested in the experiments on transcranial visualization of the cerebral blood flow of a mouse.

Combined use of speckle contrast and fluorescent intravital microscopy

Utilizing a combined use of speckle contrast and fluorescent intravital microscopy , we present a simple and robust method to overcome the limitations mentioned above for the speckle contrast approach. The proposed technique provides more relevant, abundant, and valuable information regarding perfusion rate ration between different types of vessels that makes this method highly useful for in vivo brain surgical operations.

Media appearance:

(ENG) https://www.sott.net/article/424346-Handwriting-as-detector-Scientists

(ENG) https://phys.org/news/2019-12-scientists-lasers-mental-states.html

Selected references

  1. Sdobnov, A., Tsytsarev, V., Piavchenko, G., Bykov, A., & Meglinski, I. (2024). Beyond life: Exploring hemodynamic patterns in postmortem mice brains. Journal of Biophotonics, e202400017. DOI: 10.1002/jbio.202400017.
  2. Sdobnov, A., Piavchenko, G., Bykov, A., & Meglinski, I. (2024). Advances in dynamic light scattering imaging of blood flow. Laser & Photonics Reviews, 18(2), 2300494. DOI: 10.1002/lpor.202300494.
  3. Piavchenko, G., Kozlov, I., Dremin, V., Stavtsev, D., Seryogina, E., Kandurova, K., ... & Meglinski, I. (2021). Impairments of cerebral blood flow microcirculation in rats brought on by cardiac cessation and respiratory arrest. Journal of Biophotonics, e202100216. DOI: 10.1002/jbio.202100216.
  4. Kalchenko, V., Sdobnov, A., Meglinski, I., Kuznetsov, Y., Molodij, G., & Harmelin, A. (2019). A robust method for adjustment of laser speckle contrast imaging during transcranial mouse brain visualization. Photonics, 6(3), 80. DOI:10.3390/photonics6030080.
  5. Kalchenko, V., Meglinski, I., Sdobnov, A., Kuznetsov, Y., & Harmelin, A. (2019). Combined laser speckle imaging and fluorescent intravital microscopy for monitoring acute vascular permeability reaction. J Biomed Opt, 24(6), 060501. DOI: 10.1117/1.JBO.24.6.060501.
  6. Sdobnov, A., Bykov, A., Molodij, G., Kalchenko, V., Jarvinen, T., Popov, A., Kprdas, K. & Meglinski, I. (2018). Speckle dynamics under ergodicity breaking. J Phys D: Appl Phys, 51(15), 155401. DOI: 10.1088/1361-6463/aab404.