Speckle-scale focusing in the diffusive regime with time reversal of variance-encoded light (TROVE)

Focusing of light in the diffusive regime inside scattering media has long been considered impossible. Recently, this limitation has been overcome with time reversal of ultrasound-encoded light (TRUE), but the resolution of this approach is fundamentally limited by the large number of optical modes within the ultrasound focus. Here, we introduce a new approach, time reversal of variance-encoded light (TROVE), which demixes these spatial modes by variance encoding to break the resolution barrier imposed by the ultrasound. By encoding individual spatial modes inside the scattering sample with unique variances, we effectively uncouple the system resolution from the size of the ultrasound focus. This enables us to demonstrate optical focusing and imaging with diffuse light at an unprecedented, speckle-scale lateral resolution of ~5 µm

Evaluating the Viscoelastic Properties of Tissue from Laser Speckle Fluctuations

Most pathological conditions such as atherosclerosis, cancer, neurodegenerative, and orthopedic disorders are accompanied with alterations in tissue viscoelasticity. Laser Speckle Rheology (LSR) is a novel optical technology that provides the invaluable potential for mechanical assessment of tissue in situ. In LSR, the specimen is illuminated with coherent light and the time constant of speckle fluctuations, τ, is measured using a high speed camera. Prior work indicates that τ is closely correlated with tissue microstructure and composition. Here, we investigate the relationship between LSR measurements of τ and sample mechanical properties defined by the viscoelastic modulus, G*. Phantoms and tissue samples over a broad range of viscoelastic properties are evaluated using LSR and conventional mechanical testing. Results demonstrate a strong correlation between τ and |G*| for both phantom (r = 0.79, p <0.0001) and tissue (r = 0.88, p<0.0001) specimens, establishing the unique capability of LSR in characterizing tissue viscoelasticity

Mapping Mechanical Properties of the Tumor Microenvironment by Laser Speckle Rheological Microscopy

Altered mechanical properties of the tumor matrix have emerged as both the cause and consequence of breast carcinogenesis. Increased tumor stiffness has traditionally provided a viable metric to screen for malignancies via palpation or imaging. Previous studies have demonstrated that the micro-scale mechanical properties of the cell substrate influence tumor proliferation and invasive migration in vitro. Nevertheless, the association of the mechanical microenvironment with clinical hallmarks of aggressiveness in human breast tumors, including histopathological subtype, grade, receptor expression status, and lymph node involvement is poorly understood. This is largely due to the lack of tools for mapping tumor viscoelastic properties in clinical specimens with high spatial resolution over a large field-of-view (FoV). Here we introduce laser Speckle rHEologicAl micRoscopy (SHEAR) that for the first time enables mapping the magnitude viscoelastic or shear modulus, ∣G*(x,y,ω)∣, over a range of frequencies (ω=1-250 rad/s) in excised tumors within minutes with a spatial resolution of ~50 μm, over multiple cm(2) FoV. Application of SHEAR in a cohort of 251 breast cancer specimens from 148 patients demonstrated that ∣G*(x,y,ω)∣ (ω=2π rad/s) closely corresponds with histological features of the tumor, and that the spatial gradient of the shear modulus, ∣∇∣G*(x,y,ω)∥, is elevated at the tumor invasive front. Multivariate analyses established that the metrics, (∣G*∣) and (∣∇∣G* ∥), measured by SHEAR are associated with prognosis. These findings implicate the viscoelastic properties of the tumor microenvironment in breast cancer prognosis and likely pave the path for identifying new modifiable targets for treatment. SIGNIFICANCE: Laser speckle rheological microscopy establishes the links between microscale heterogeneities of viscoelasticity and histopathological subtype, tumor grade, receptor expression, as well as lymph node status in breast carcinoma

Real-time intraoperative monitoring of blood coagulability via coherence-gated light scattering

When characterizing dynamic processes, ergodicity - that is, the equivalence of time averages and of averages over a system\u27s possible microstates - is often invoked. Yet many complex social, economic and material systems are such that practical observations cannot survey the entire ensemble of microstates. In the case of non-ergodic fluids, their slow structural dynamics makes such an approach prohibitive. Blood is a prominent example of a non-ergodic, complex fluid for which today\u27s standards for coagulation tests in vivo are chemically induced offline assays. Here, we show that heterodyne amplification - that is, amplification of a signal by frequency conversion - combined with suitable control of spatiotemporal coherence permits measurements of non-stationary dynamics in non-ergodic, complex media. By taking advantage of this approach, we developed an optical-fibre-based tool that can be directly incorporated into standard vascular-access devices for real-time monitoring of blood coagulability in the operating room