Detection and estimation of liquid flow through a pipe in a tissue-like object with ultrasound-assisted diffuse correlation spectroscopy

Abstract

Using coherent light interrogating a turbid object perturbed by a focused ultrasound (US) beam, we demonstrate localized measurement of dynamics in the focal region, termed the region-of-interest (ROI), from the decay of the modulation in intensity autocorrelation of light. When the ROI contains a pipe flow, the decay is shown to be sensitive to the average flow velocity from which the mean-squared displacement (MSD) of the scattering centers in the flow can be estimated. While the MSD estimated is seen to be an order of magnitude higher than that obtainable through the usual diffusing wave spectroscopy (DWS) without the US, it is seen to be more accurate as verified by the volume flow estimated from it. It is further observed that, whereas the MSD from the localized measurement grows with time as τ(α) with α≈1.65, without using the US, α is seen to be much less. Moreover, with the local measurement, this super-diffusive nature of the pipe flow is seen to persist longer, i.e., over a wider range of initial τ, than with the unassisted DWS. The reason for the super-diffusivity of flow, i.e., α<2, in the ROI is the presence of a fluctuating (thermodynamically nonequilibrium) component in the dynamics induced by the US forcing. Beyond this initial range, both methods measure MSDs that rise linearly with time, indicating that ballistic and near-ballistic photons hardly capture anything beyond the background Brownian motion.

Calibration of diffuse correlation spectroscopy blood flow index with venous-occlusion diffuse optical spectroscopy in skeletal muscle

“…DCS is a noninvasive optical method that quantitatively measures tissue BF using speckle correlation techniques. 39,40,[42][43][44][45][46] Herein, aspects of this technique relevant to our study are highlighted; for additional details, the reader should consult comprehensive reviews and papers. 7,[36][37][38][39][40] DCS measures the temporal intensity fluctuations of coherent near-infrared (NIR) light that has multiply scattered from moving red blood cells in tissue.…”

“…41 DCS is a simple noninvasive technique that derives flow information from measurements of the temporal intensity fluctuations of multiply scattered light. 39,40,[42][43][44][45][46] The DCS BFI has been validated against a plethora of gold-standard techniques; 7,[47][48][49][50][51][52] in these studies, the BFI and especially its variation were demonstrated to be approximately proportional to true BF in a range of subjects and tissue types. However, clinical interpretation of the DCS BFI is complicated by its unusual units of [cm 2 ∕s].…”

Diffuse Correlation Spectroscopy at Short Source-Detector Separations: Simulations, Experiments and Theoretical Modeling

“…∆r 2 (τ) is a correlation-time (τ) dependent term and represents the ensemble-averaged, mean-squared displacement of moving scatterers in time τ. k 0 is the wave-vector associated with the laser source and S(r) describes the spatial geometry of the source to be modeled [15]. Two models are commonly used for ∆r 2 (τ) : the Brownian flow model (where ∆r 2 (τ) = 6D B τ) with Brownian flow coefficient D B ; the random flow model (where ∆r 2 (τ) = V 2 τ 2 ) where V is the average volumetric flow-speed of the scattering particles [5,15,16,[18][19][20].…”

Imaging blood flow inside highly scattering media using ultrasound modulated optical tomography

“…Recently, the use of ultrasonically modulated light has been suggested for sensing the flow of scattering particles. Chandran et al [24] demonstrated that the temporal fluctuations in the reflected light intensity can be linked to the flow speed of the moving particles in the US focus. Tsalach et al [25] proposed the use of ultrasonic modulation of light for depth selective flow measurements.…”

“…Finally, we demonstrate a sim-ple flow imaging method that relies on comparing UOT images taken with a short and a long integration time of the CCD. In comparison with work of Chandran et al and Tsalach et al [24,25] on sensing flow of scattering particle using UOT using a single, fast photodetectors, we employ a parallel detection scheme with a CCD camera. Our method relates to these studies as LASCA relates to laser Doppler flowmetry [26].…”