Abstract
Speckle contrast imaging enables rapid mapping of relative blood flow distributions using camera detection of back-scattered laser light. However, speckle derived flow measures deviate from direct measurements of erythrocyte speeds by 47 ± 15% (n = 13 mice) in vessels of various calibers. Alternatively, deviations with estimates of volumetric flux are on average 91 ± 43%. We highlight and attempt to alleviate this discrepancy by accounting for the effects of multiple dynamic scattering with speckle imaging of microfluidic channels of varying sizes and then with red blood cell (RBC) tracking correlated speckle imaging of vascular flows in the cerebral cortex. By revisiting the governing dynamic light scattering models, we test the ability to predict the degree of multiple dynamic scattering across vessels in order to correct for the observed discrepancies between relative RBC speeds and multi-exposure speckle imaging estimates of inverse correlation times. The analysis reveals that traditional speckle contrast imagery of vascular flows is neither a measure of volumetric flux nor particle speed, but rather the product of speed and vessel diameter. The corrected speckle estimates of the relative RBC speeds have an average 10 ± 3% deviation in vivo with those obtained from RBC tracking.
Highlights
Laser speckle contrast imaging (LSCI) utilizes widefield laser illumination and camera acquisition, achieving millisecond order temporal resolution and spatial resolution on the order of tens of microns for full-field imaging of specimen motion, such as blood flows
Speckle visibility expressions have relied on the assumption that inverse correlation times are an estimate of particle speed
As speckle imaging is reliant on dynamic light scatting, we examine the scattering variations encountered within the disparately sized channels through photon migratory modeling
Summary
Laser speckle contrast imaging (LSCI) utilizes widefield laser illumination and camera acquisition, achieving millisecond order temporal resolution and spatial resolution on the order of tens of microns for full-field imaging of specimen motion, such as blood flows. LSCI has been predominantly adopted for imaging cerebral blood flow (CBF) dynamics in small animals [1,2,3] and clinically during intra-operative neurosurgery [4,5,6]. Dynamic scattering of coherent light introduces temporal fluctuations in the observed speckles, which manifests as a blurring of the speckle pattern imaged over a fixed exposure duration [8]. The degree of blurring can be quantified by computing the local spatial contrast: K (T ) = σ s (T ) I , defined as the standard deviation over the mean pixel intensities within a small spatial window in the image taken over the camera exposure duration, T. From dynamic light scattering (DLS) theory, this speckle correlation time has been posed to be inversely proportional to the speed of the scatterers [12] and weighted by the number of dynamic scattering events in the multiple scattering limit [13,14]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
