Holographic tissue dynamics spectroscopy

Abstract

Tissue dynamics spectroscopy uses digital holography as a coherence gate to extract depth-resolved quasi-elastic dynamic light scattering from inside multicellular tumor spheroids. The temporal speckle contrast provides endogenous dynamical images of proliferating and hypoxic or necrotic tissues. Fluctuation spectroscopy similar to diffusing wave spectroscopy is performed on the dynamic speckle to generate tissue-response spectrograms that track time-resolved changes in intracellular motility in response to environmental perturbations. The spectrograms consist of several frequency bands that range from 0.005 to 5 Hz. The fluctuation spectral density and temporal autocorrelations show the signature of constrained anomalous diffusion, but with large fluctuation amplitudes caused by active processes far from equilibrium. Differences in the tissue-response spectrograms between the proliferating outer shell and the hypoxic inner core differentiate normal from starved conditions. The differential spectrograms provide an initial library of tissue-response signatures to environmental conditions of temperature, osmolarity, pH, and serum growth factors.

Quantitative Imaging of Cerebral Blood Flow Velocity and Intracellular Motility using Dynamic Light Scattering–Optical Coherence Tomography

“…The evidence supporting this conclusion can be summarized by: (i) their positions highly correspond to neuronal cell bodies; (ii) they distribute over the space surrounding the nuclei; (iii) their sizes are close to the typical size of neuronal cell bodies (E5 mm in radius); (iv) the motion of particles are not stochastic but highly fit with the model of diffusive movements (R 2 40.998); and (v) the diffusion coefficient of the spots agrees with those of the motion of intracellular organelles measured in vitro. 4,7,21 In addition, the decrease in neuronal IM observed during ischemic stroke ( Figure 7C) suggests that the measured IM may correspond to metabolism-related active motions rather than free diffusion of particles in the cytoplasm. If it corresponded to the latter, IM would likely have increased during occlusion, because ischemic stroke generally results in cell swelling and intracellular-free diffusion increases when the cell volume is enlarged.…”

“…Further, this motion can be described by an effective diffusion coefficient similar to our result. 4,7 Therefore, the active motion of intracellular organelles may dominantly contribute to the measured neuronal IM and its decrease during ischemic stroke. Cellular nuclei also exhibit motions, a part of which can result in an effective diffusion coefficient on the order of 1 mm 2 /second.…”

“…If it corresponded to the latter, IM would likely have increased during occlusion, because ischemic stroke generally results in cell swelling and intracellular-free diffusion increases when the cell volume is enlarged. 7,21 Some movements of macromolecules (o20 nm in diameter) in the cytoplasm can result in an effective diffusion coefficient on the order of 1 mm 2 /second. 21 However, such small macromolecules would not significantly contribute to the OCT signal as discussed above (Supplementary Fig.…”

“…In addition, the diffusion coefficient of the spots agrees with those of the motion of intracellular organelles measured in vitro. 4,7,21 Therefore, the green spots likely represent the diffusion-like movements of intracellular organelles of neurons. Interpretation of this result will be further discussed later.…”

“…This intracellular motility (IM) has been shown to exhibit diffusion-like dynamics by using either fluorescence label-based methods [1][2] or label-free methods based on dynamic light scattering (DLS) analysis. [3][4][5][6][7] However, IM has not been imaged in the cerebral cortex of a living animal, probably because the dynamics are obscured by the larger contribution from cerebral blood flow (CBF). In this paper, we describe a novel method for label-free in vivo imaging of both IM and CBF.…”