We propose a novel optical microrheology technique that assesses tissue viscoelasticity by tracking the stochastic motion of optical vortices in speckles from turbid tissues. We validate the optical vortex tracking microrheology by illustrating the universal inverse relation between vortex displacements and the viscoelastic modulus. Moreover, we notice the phase angle of the viscoelastic sample is directly related to the vortices subdiffusion exponent. We also observe that the subdiffusion of optical vortices exhibits diverse characteristics for homogeneous and inhomogeneous samples. We believe the optical vortex tracking microrheology may find wide applications in different clinical scenarios like localizing tumors and fabricating biomaterials.
We present a single-shot laser speckle optical micro-rheology technique that measures tissue viscoelasticity from a single elongated speckle image, avoiding the need for high-speed cameras used in traditional optical micro-rheology. By calculating the intensity autocorrelation between rows of a rolling shutter speckle image with different inter-row delays, we can extract the decorrelation time of dynamic speckles, which directly related to the viscoelastic modulus of multiple scattering samples. Our method extends the range of measured viscoelastic modulus in optical micro-rheology by capturing speckle images with equivalent frame rates over 100,000 frame per second. This enables precise viscoelasticity assessments of diverse biological tissues and tissue phantoms.
We proposed a new approach to evaluate tissue rheological properties by assessing the stochastic motion of optical vortices in the pseudo-phase representation of laser speckles. By studying the vortex MSD and VAF, we observed the anomalous diffusion of optical vortices and evaluated the viscoelastic modulus of different gel phantoms and tissue samples with diverse mechanical and optical properties. We established the direct relationship which connects the microscopic motion of the optical vortices to the macroscopic viscoelastic response of the multiple scattering viscoelastic media. We can imagine amounts of biomedical applications including blood coagulability monitoring, atherosclerotic plaque characterization, and tumor localization.
The whole dynamic process of blood coagulation can be characterized by tracking the MSD of optical vortices with our previous coagulation measurement system. To develop a portable prototype of the coagulation detection system, we use an embedded system for whole blood laser speckle image acquisition, and apply deep learning methods for the temporal and spatial interpolation of the acquired images and the fast localization of optical vortex. The prototype implementation with a compact optical design and experimental validation provide a feasible idea and method for the miniaturization of blood coagulation devices.
KEYWORDS: Laser tissue interaction, Speckle, Tissues, Photomedicine, Arteries, In vivo imaging, Endoscopes, Tissue optics, Elastography, Current controlled current source
A number of disease conditions including coronary atherosclerosis, peripheral artery disease and gastro-intestinal malignancies are associated with alterations in tissue mechanical properties. Laser speckle rheology (LSR) has been demonstrated to provide important information on tissue mechanical properties by analyzing the time scale of temporal speckle intensity fluctuations, which serves as an index of tissue viscoelasticity. In order to measure the mechanical properties of luminal organs in vivo, LSR must be conducted via a miniature endoscope or catheter. Here we demonstrate the capability of an omni-directional LSR catheter to quantify tissue mechanical properties over the entire luminal circumference without the need for rotational motion. Retracting the catheter using a motor-drive assembly enables the reconstruction of cylindrical maps of tissue mechanical properties. The performance of the LSR catheter is tested using a luminal phantom with mechanical moduli that vary in both circumferential and longitudinal directions. 2D cylindrical maps of phantom viscoelastic properties are reconstructed over four quadrants of the coronary circumference simultaneously during catheter pullback. The reconstructed cylindrical maps of the decorrelation time constants easily distinguish the different gel components of the phantom with different viscoelastic moduli. The average values of decorrelation times calculated for each gel component of the phantom show a strong correspondence with the viscoelastic moduli measured via standard mechanical rheometry. These results highlight the capability for cylindrical mapping of tissue viscoelastic properties using LSR in luminal organs using a miniature catheter, thus opening the opportunity for improved diagnosis of several disease conditions.
Acute myocardial infarction is frequently caused by the rupture of coronary plaques with severely compromised viscoelastic properties. We have developed a new optical technology termed intravascular laser speckle imaging (ILSI) that evaluates plaque viscoelastic properties, by measuring the time scale (time constant, τ) of temporally evolving laser speckle fluctuations. To enable coronary evaluation in vivo, an optical ILSI catheter has been developed that accomplishes omni-directional illumination and viewing of the entire coronary circumference without the need for mechanical rotation. Here, we describe the capability of ILSI for evaluating human coronary atherosclerosis in cadaveric hearts. ILSI was conducted in conjunction with optical coherence tomography (OCT) imaging in five human cadaveric hearts. The left coronary artery (LCA), left anterior descending (LAD), left circumflex artery (LCx), and right coronary artery (RCA) segments were resected and secured on custom-developed coronary holders to enable accurate co-registration between ILSI, OCT, and histopathology. Speckle time constants, τ, calculated from each ILSI section were compared with lipid and collagen content measured from quantitative Histopathological analysis of the corresponding Oil Red O and Picrosirius Red stained sections. Because the presence of low viscosity lipid elicits rapid speckle fluctuations, we observed an inverse correlation between τ measured by ILSI and lipid content (R= -0.64, p< 0.05). In contrast, the higher viscoelastic modulus of fibrous regions resulted in a positive correlation between τ and collagen content (R= 0.54, p< 0.05). These results demonstrate the feasibility of conducting ILSI evaluation of arterial mechanical properties using a miniaturized omni-directional catheter.
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