Marc Garbey

Contact-Free Measurement of Cardiac Pulse Based on the Analysis of Thermal Imagery

We have developed a novel method to measure human cardiac pulse at a distance. It is based on the information contained in the thermal signal emitted from major superficial vessels. This signal is acquired through a highly sensitive thermal imaging system. Temperature on the vessel is modulated by pulsative blood flow. To compute the frequency of modulation (pulse), we extract a line-based region along the vessel. Then, we apply fast Fourier transform (FFT) to individual points along this line of interest to capitalize on the pulses thermal propagation effect. Finally, we use an adaptive estimation function on the average FFT outcome to quantify the pulse. We have carried out experiments on a data set of 34 subjects and compared the pulse computed from our thermal signal analysis method to concomitant ground-truth measurements obtained through a standard contact sensor (piezo-electric transducer). The performance of the new method ranges from 88.52% to 90.33% depending on the clarity of the vessels thermal imprint. To the best of our knowledge, it is the first time that cardiac pulse has been measured several feet away from a subject with passive means.

Interacting with human physiology

We propose a novel system that incorporates physiological monitoring as part of the human-computer interface. The sensing element is a thermal camera that is employed as a computer peripheral. Through bioheat modeling of facial imagery almost the full range of vital signs can be extracted, including localize blood flow, cardiac pulse, and breath rate. This physiological information can then be used to draw inferences about a variety of health symptoms and psychological states. Our research aims to realize the notion of desktop health monitoring and create truly collaborative interactions in which humans and machines are both observing and responding.

Imaging the cardiovascular pulse

We have developed a novel method to measure human cardiac pulse at a distance. It is based on the information contained in the thermal signal emitted from major superficial vessels. This signal is acquired through a highly sensitive thermal imaging system. Temperature on the vessel is modulated by pulsative blood flow. To compute the frequency of modulation (pulse), we extract a line-based region along the vessel. Then, we apply Fast Fourier Transform (FFT) to individual points along this line of interest to capitalize on the pulse propagation effect. Finally, we use an adaptive estimation function on the average FFT outcome to quantify the pulse. We have tested the accuracy of our method on 5 subjects with highly successful results. The technology is expected to find applications among others in sustained physiological monitoring of cardiopulmonary diseases, sport training, sleep studies, and psychophysiology (polygraph).

Estimation of blood flow speed and vessel location from thermal video

In this paper we present a novel method for estimation of blood flow speed and vessel location from thermal video. The method is based on a bioheat transfer model that reflects the thermo-physiological processes in a skin region proximal to a major vessel. The model assumes the form of a partial differential equation (PDE) with boundary conditions. Initially, we test the soundness of our model by performing direct numerical simulation. Then, we solve the inverse problem both in steady and dynamic states on data provided by a thermal imaging system. Our method opens exciting possibilities in biometrics and biomedicine. Among others, it promises to revolutionize polygraph examinations by eliminating wiring and improving accuracy. It also establishes the feasibility of continuous 2D physiological monitoring of human patients in a contact-free manner.

Fault tolerant algorithms for heat transfer problems

With the emergence of new massively parallel systems in the high performance computing area allowing scientific simulations to run on thousands of processors, the mean time between failures of large machines is decreasing from several weeks to a few minutes. The ability of hardware and software components to handle these singular events called process failures is therefore getting increasingly important. In order for a scientific code to continue despite a process failure, the application must be able to retrieve the lost data items. The recovery procedure after failures might be fairly straightforward for elliptic and linear hyperbolic problems. However, the reversibility in time for parabolic problems appears to be the most challenging part because it is an ill-posed problem. This paper focuses on new fault-tolerant numerical schemes for the time integration of parabolic problems. The new algorithm allows the application to recover from process failures and to reconstruct numerically the lost data of the failed process(es) avoiding the expensive roll-back operation required in most checkpoint/restart schemes. As a fault tolerant communication library, we use the fault tolerant message passing interface developed by the Innovative Computing Laboratory at the University of Tennessee. Experimental results show promising performances. Indeed, the three-dimensional parabolic benchmark code is able to recover and to keep on running after failures, adding only a very small penalty to the overall time of execution.

A least square extrapolation method for improving solution accuracy of PDE computations

Richardson extrapolation (RE) is based on a very simple and elegant mathematical idea that has been successful in several areas of numerical analysis such as quadrature or time integration of ODEs. In theory, RE can be used also on PDE approximations when the convergence order of a discrete solution is clearly known. But in practice, the order of a numerical method often depends on space location and is not accurately satisfied on different levels of grids used in the extrapolation formula. We propose in this paper a more robust and numerically efficient method based on the idea of finding automatically the order of a method as the solution of a least square minimization problem on the residual. We introduce a two-level and three-level least square extrapolation method that works on nonmatching embedded grid solutions via spline interpolation. Our least square extrapolation method is a post-processing of data produced by existing PDE codes, that is easy to implement and can be a better tool than RE for code verification. It can be also used to make a cascade of computation more numerically efficient. We can establish a consistent linear combination of coarser grid solutions to produce a better approximation of the PDE solution at a much lower cost than direct computation on a finer grid. To illustrate the performance of the method, examples including two-dimensional turning point problem with sharp transition layer and the Navier-Stokes flow inside a lid-driven cavity are adopted.

A parallel solver for unsteady incompressible 3D Navier—Stokes equations

Abstract We describe some algorithms and software components that allow us to solve on parallel computers classical test cases for unsteady incompressible 3D Navier–Stokes equations. Our main focus is the design of robust and efficient parallel solvers for systems with singularly perturbed convection–reaction–diffusion and Laplace operators, which are important constituents of the Navier–Stokes solvers. The performance of the solvers on two parallel computers is examined.

A Parallel Schwarz Method for a Convection-Diffusion Problem

This paper describes a parallel convection-diffusion solver which may be used as part of a Navier--Stokes solver for three-dimensional channel flow at moderately large Reynolds numbers [S. Turek, Efficient Solvers for Incompessible Flow Problems: An Algorithmic Approach in View of Computational Aspects, Springer-Verlag, 1999]. The solver uses a multiplicative Schwarz domain decomposition with overlapping subdomains to solve singularly perturbed convection-diffusion equations where convection is dominant. Upwind finite differences are used for the spatial discretization. The algorithm uses special features of the singularly perturbed convection-diffusion operator. The error due to a local perturbation of the boundary conditions decays extremely fast, in the upwind as well as the crosswind direction, so the overlap in the domain decomposition can be kept to a minimum. The algorithm parallelizes well and is particularly suited for applications in three dimensions. Results of two- and three-dimensional numerical experiments are presented.

Harvesting the thermal cardiac pulse signal

In the present paper, we propose a new pulse measurement methodology based on thermal imaging (contact-free). The method capitalizes both on the thermal undulation produced by the traveling pulse as well as the periodic expansion of the compliant vessel wall. The paper reports experiments on 34 subjects, where it compares the performance of the new pulse measurement method to the one we reported previously. The measurements were ground-truthed through a piezo-electric sensor. Statistical analysis reveals that the new imaging methodology is more accurate and robust than the previous one. Its performance becomes nearly perfect, when the vessel is not obstructed by a thick fat deposit.

A dynamical system that describes vein graft adaptation and failure.

Adaptation of vein bypass grafts to the mechanical stresses imposed by the arterial circulation is thought to be the primary determinant for lesion development, yet an understanding of how the various forces dictate local wall remodeling is lacking. We develop a dynamical system that summarizes the complex interplay between the mechanical environment and cell/matrix kinetics, ultimately dictating changes in the vein graft architecture. Based on a systematic mapping of the parameter space, three general remodeling response patterns are observed: (1) shear stabilized intimal thickening, (2) tension induced wall thinning and lumen expansion, and (3) tension stabilized wall thickening. Notable is our observation that the integration of multiple feedback mechanisms leads to a variety of non-linear responses that would be unanticipated by an analysis of each system component independently. This dynamic analysis supports the clinical observation that the majority of vein grafts proceed along an adaptive trajectory, where grafts dilate and mildly thicken in response to the increased tension and shear, but a small portion of the grafts demonstrate a maladaptive phenotype, where progressive inward remodeling and accentuated wall thickening lead to graft failure.