Vysakh Vasudevan

Bio: Vysakh Vasudevan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Engineering & Finite element method. The author has co-authored 2 publications.

Immediate subsurface skin blood flow monitoring using diffuse correlation spectroscopy: finite element simulations

Abstract: Diffuse correlation spectroscopy (DCS) is an evolving optical modality that provides a fast, non-invasive, portable alternative to costly medical diagnostics in quantifying the blood flow. DCS involves monitoring the temporal statistics of scattered light from the sample, upon illumination by a coherent source. The detected signal is related to RBC motion, and blood flow is derived combining a model for photon propagation through the target tissue with the experimental observations. Conventionally, blood flow index (BFI) is calculated for long source-detector separations (SDS), that quantifies the blood flow from deeper tissue layers. Reduced SDS is required in measuring perfusion for immediate tissue subsurface, which is important in monitoring related changes. Here, we investigate the application of short-range DCS for skin blood flow monitoring and demonstrate the capability in determining BFI from immediate subsurface. Bilayer skin tissue with embedded micro vessels was modelled using finite element methods (FEM). Time correlated light diffusion equation was solved for this tissue geometry, with a point source illumination and autocorrelation plots were generated. Our in-silico analysis illustrates the change in BFI for varying blood flow rate and capillary depth from the skin surface. The work performed here, after experimental validation, is expected to have the potential for non-invasive quantitative blood flow assessment and can aid in diagnosing related skin disorders.

Quantification of soft tissue parameters from spatially resolved diffuse reflectance finite element models.

Abstract: Spatially resolved diffuse reflectance spectroscopy (SRDRS) is a non-invasive optical technique that helps in clinical diagnosis of various tissue microcirculation and skin pigmentation disorders based on collected backscattered light from multi-layered tissue. The extraction of the optical properties from the reflectance spectrum using analytical solutions is laborious. Model-based light tissue interaction studies help in quantifying the optical properties. This work presents the use of finite element models of light tissue interaction for this purpose. A bilayer model mimicking human skin was considered and the diffused reflectance spectra at multiple detector points were generated using finite element modelling for varying melanin concentration, epidermal thickness, blood volume fraction, oxygen saturation and scattering components. The reflectance value based on varying optical parameters from multiple detection points lead to the generation of a look-up table (LUT), which is further used for finding the tissue parameters that contribute to the spatially resolved reflectance values. The tissue parameters estimated after inverse modelling showed a high degree of agreement with the expected tissue parameters for a test dataset different from the training dataset.

Spatially resolved diffuse optical correlation spectroscopy (SR-DOCS) for quantitative assessment of skin tissue perfusion matrix

Abstract: Assessment of skin tissue perfusion is vital for understanding the normal and the pathologic physiology of human body. Diffuse optical methods provide numerous pathways for assessing various static and dynamic perfusion markers such as variations in bulk tissue optical properties, depth dimensions of microvascular bed, rate and volume of blood flow and so on. There have been numerous studies on these aspects ending up with qualitative assessments on various parameters, where separate approaches are explored for individual parametric evaluation. With the introduction of precise optical tissue phantom models, integration of different static and dynamic perfusion markers are possible to facilitate quantitative assessment of such a perfusion matrix. In this work, we present the fabrication of a perfused tissue physical model that mimic skin tissue and subsequent estimation of perfusion matrix including optical properties, flow, and depth of the microvascular bed. Different layers of skin are spin coated onto micron-sized embedded channels, and the model was subjected to optical measurements, inducing different flow levels using a syringe pump. The parameters have been estimated using spatially resolved diffuse correlation optical spectral measurements, using a handheld fiber optic probe with a precise source to target distance sensing mechanism and associated signal processing algorithms. This work is aimed to provide a methodology for quantitative assessment of various perfusion parameters using a versatile physical model that provides flexibility in varying involved parameters accurately. The work performed here, after standardization is expected to have potential in developing non-invasive quantitative optical skin biopsy tools to augment the current histopathological studies.

Short-range diffuse correlation spectroscopic system for peripheral skin tissue blood flow assessment: in-vitro studies

Abstract: Assessment of blood perfusion from superficial layers would aid in monitoring the microcirculation and help diagnose numerous diseases involving altered microcirculation. Diffuse optical correlation spectroscopy looks at the correlation between temporal statistics of backscattered intensity from tissue surface upon illumination and has been a promising tool for tissue vascularity assessment. This work uses diffuse correlation spectroscopy operated in short source-to-detector separation to quantify microcirculation. Finite element models and simulations are validated with in-vitro skin flow models. The comparison returned a high correlation between the simulation and experimental models, proving short-range DCS's capability in assessing microcirculation.

Short-range diffuse correlation spectroscopic system for peripheral skin tissue blood flow assessment: in-vitro studies

Abstract: Assessment of blood perfusion from superficial layers would aid in monitoring the microcirculation and help diagnose numerous diseases involving altered microcirculation. Diffuse optical correlation spectroscopy looks at the correlation between temporal statistics of backscattered intensity from tissue surface upon illumination and has been a promising tool for tissue vascularity assessment. This work uses diffuse correlation spectroscopy operated in short source-to-detector separation to quantify microcirculation. Finite element models and simulations are validated with in-vitro skin flow models. The comparison returned a high correlation between the simulation and experimental models, proving short-range DCS's capability in assessing microcirculation.

Short-range diffuse correlation spectroscopic system for peripheral skin tissue blood flow assessment: in-vitro studies

Abstract: Assessment of blood perfusion from superficial layers would aid in monitoring the microcirculation and help diagnose numerous diseases involving altered microcirculation. Diffuse optical correlation spectroscopy looks at the correlation between temporal statistics of backscattered intensity from tissue surface upon illumination and has been a promising tool for tissue vascularity assessment. This work uses diffuse correlation spectroscopy operated in short source-to-detector separation to quantify microcirculation. Finite element models and simulations are validated with in-vitro skin flow models. The comparison returned a high correlation between the simulation and experimental models, proving short-range DCS's capability in assessing microcirculation.