Lalit Keshav Mestha

Toward Ubiquitous Blood Pressure Monitoring via Pulse Transit Time: Theory and Practice

Ubiquitous blood pressure (BP) monitoring is needed to improve hypertension detection and control and is becoming feasible due to recent technological advances such as in wearable sensing. Pulse transit time (PTT) represents a well-known potential approach for ubiquitous BP monitoring. The goal of this review is to facilitate the achievement of reliable ubiquitous BP monitoring via PTT. We explain the conventional BP measurement methods and their limitations; present models to summarize the theory of the PTT-BP relationship; outline the approach while pinpointing the key challenges; overview the previous work toward putting the theory to practice; make suggestions for best practice and future research; and discuss realistic expectations for the approach.

Towards continuous monitoring of pulse rate in neonatal intensive care unit with a webcam.

We describe a novel method to monitor pulse rate (PR) on a continuous basis of patients in a neonatal intensive care unit (NICU) using videos taken from a high definition (HD) webcam. We describe algorithms that determine PR from videoplethysmographic (VPG) signals extracted from multiple regions of interest (ROI) simultaneously available within the field of view of the camera where cardiac signal is registered. We detect motion from video images and compensate for motion artifacts from each ROI. Preliminary clinical results are presented on 8 neonates each with 30 minutes of uninterrupted video. Comparisons to hospital equipment indicate that the proposed technology can meet medical industry standards and give improved patient comfort and ease of use for practitioners when instrumented with proper hardware.

Practical algorithm for the inversion of an experimental input-output color map for color correction

We introduce the iteratively clustered interpolation algorithm to compute a structured printer inverse look-up table from irregularly sampled experimental color data. The algorithm is based on a gradient optimization method, with initial points generated through an iterative technique. Experimental results with a digital color printer are provided to illustrate the algorithm.

Non contact monitoring of respiratory function via depth sensing

Monitoring respiratory events is of clinical importance in the early detection of potentially fatal conditions. Current technologies involve contact sensors the individual must wear constantly. Such a requirement can lead to patient discomfort, and consequently may fail due to a variety of reasons including refusal to wear the monitoring device. Elderly patients and neo-natal infants are even more likely to suffer from the adverse effects of continued monitoring. Unobtrusive, non-contact, remote-sensing-based methods are increasingly needed for monitoring patient respiratory function at homes, which can in turn help to establish patterns over time. We propose to use active-stereo-based depth sensing system for forced flow-volume loop measurements and for semi-automatic and automatic assessment of abnormal breathing patterns.

A method to detect cardiac arrhythmias with a webcam

We describe a novel method to detect the presence of atrial fibrillation (A-Fib) by video recording of the face of a patient. The signal processing algorithm extracts A-Fib episodes by processing time-series signals generated by video images in a remote sensing environment. The process removes the non-stationary components of the green component of the RGB signal. Beat-to-beat pulse points are detected using an adaptive threshold technique; the successive thresholds are based on variations detected in previous magnitudes of the pulse peaks. The existence of cardiac arrhythmia is determined by quantifying the variability of the peak-to-peak intervals. We report preliminary results of our on-going study on six subjects undergoing electro-cardioversion for persistent A-Fib.

Control of Color Imaging Systems: Analysis and Design

Preface Acknowledgments An Overview of Digital Printing Systems Introduction Printing and Publishing System Digital Front End Digital Print Engine (Electrophotographic) Evolution of Controls Technology for Digital Printers-Color Controls View Prepress-Based Processing DFE-Based Processing Print Engine-Based Processing References Fundamentals of Digital Image Processing Introduction Digital Image Formation and Systems Optical and Modulation Transfer Functions Image Sampling and Quantization Image Transform Image Filtering Image Resizing Image Enhancement Image Restoration Image Halftoning Problems References Mathematical Foundations Introduction General Continuous-Time System Description Laplace Transform General Linear Discrete-Time Systems z-Transform Discrete-Time Fourier Transform Two-Dimensional z-Transform Two-Dimensional Discrete-Space Fourier Transform Eigenvalues and Eigenvectors Singular Value Decomposition Matrix Polynomials and Functions of Square Matrices Fundamentals of Matrix Calculus Problems References State-Variable Representation Introduction Concept of States State-Space Representation of Continuous-Time Systems State-Space Representation of General Continuous LTI Systems Solution of LTI Continuous-Time State Equations State-Space Representation of Discrete-Time Systems State-Space Representation of Discrete-Time LTI Systems Solution of LTI Discrete-Time State Equations Controllability of LTI Systems Observability of LTI Systems Problems References Closed-Loop System Analysis and Design Introduction State Feedback LQR Design State Estimators (Observers) Design Combined State Estimation and Control Problems References Interpolation of Multidimensional Functions Introduction Interpolation of Uniformly Spaced Lookup Tables Nonuniformly Spaced Lookup Tables Lookup Table Inverse Compression of Lookup Tables Smoothing Algorithm for Multidimensional Functions Problems References Three-Dimensional Control of Color Management Systems Introduction Image Path Architecture Profiling-A Complex System Problem Characterization of Color Systems GCR Selection and Inversion Gamut-Mapping Methods Evaluation of Profiles An Example Showing How to Build Multidimensional LUT Problems References One-Dimensional, Two-Dimensional, and Spot-Color Management and Control Methods Introduction Principles of Color Management One-Dimensional Gray-Balance Calibration Two-Dimensional Calibration One-Dimensional and Two-Dimensional Printer Calibration Using Printer Models One-Dimensional and Two-Dimensional Printer Calibration with State-Feedback Methods Spot-Color Control Problems References Internal Process Controls Introduction Process Control Models-A General Control View Time Hierarchical Process Control Loops Level 1 Electrostatic Control System State Space to Transfer Function Conversions Level 2 Developability Controller Steady-State Error Design of the Gain Matrix Level 3 Control Loops Dead Beat Response TC Control Loop Process Controls Under Limited Actuation Optimal Controls for Selective States Optimal Measurements Problems References Printing System Models Introduction Process Models Modulation Transfer Functions Tone Reproduction Curve Image Simulation with Fusing and Color Models Virtual Printer Color Gamut Virtual Printer Model Tuning to an Experimental Printer Problems References Appendices (A-C) Index

Blind Source Separation by Nuclear Norm Minimization and Local Recoverability Analysis

We propose a new blind source separation (BSS) algorithm that is effective when Hankel matrices constructed from individual source signals are near low-rank and satisfy a certain near-orthogonality condition. Source separation is achieved by finding a nonsingular reverse-mixing operation that minimizes nuclear norms of Hankel matrices constructed from estimated source signals. The new formulation results in a non-convex optimization problem involving a reverse-mixing matrix. Preliminary analysis of local recoverability of source signals as well as few numerical simulations are presented in this letter.

Estimation of Respiratory Pattern From Video Using Selective Ensemble Aggregation

Noncontact estimation of respiratory pattern (RP) and respiratory rate (RR) has multiple applications. Existing methods for RP and RR measurement fall into one of the three categories—1) estimation through nasal air flow measurement, 2) estimation from video-based remote photoplethysmography, and 2) estimation by measurement of motion induced by respiration using motion detectors. However, these methods require specialized sensors, are computationally expensive, and/or critically depend on selection of a region of interest (ROI) for processing. In this paper, a general framework is described for estimating a periodic signal driving noisy linear time-invariant (LTI) channels connected in parallel with unknown dynamics. The method is then applied to derive a computationally inexpensive method for estimating RP using two-dimensional cameras that does not critically depend on ROI. Specifically, RP is estimated by imaging changes in the reflected light caused by respiration-induced motion. Each spatial location in the field of view of the camera is modeled as a noise-corrupted LTI measurement channel with unknown system dynamics, driven by a single generating respiratory signal. Estimation of RP is cast as a blind deconvolution problem and is solved through a method comprising subspace projection and statistical aggregation. Experiments are carried out on 31 healthy human subjects by generating multiple RPs and comparing the proposed estimates with simultaneously acquired ground truth from an impedance pneumograph device. The proposed estimator agrees well with the ground truth in terms of correlation measures, despite variability in clothing pattern, camera angle, and ROI.

Method for classifying cardiac arrhythmias using photoplethysmography

Advances in mobile computing and miniature devices have contributed to the accelerated development of wearable technologies for clinical applications. The new trend of wearable technologies has fostered a growth of interest for sensors that can be easily integrated into wearable devices. In particular, photoplethysmography (PPG) is especially suitable for wearable sensing, as it is low-cost, noninvasive, and does not require wet electrodes like the electrocardiogram. Photoplethysmograph signals contain rich information about the blood pulsating variation which is strongly related to the electrical activities of the heart. Therefore, in this paper we hypothesize that the ambulatory PPG monitoring could be employed for arrhythmia detection and classification. This paper presents a method for classifying ventricular premature contraction (VPC) and ventricular tachycardia (VT) from normal sinus rhythm (NSR) and supraventricular premature contraction (SVPC) recorded in patients going through ablation therapy for arrhythmia. Although occasional VPCs are benign, the increase in the frequency of VPC events may lead to VT, which in turn,could evolve into ventricular fibrillation and sudden cardiac death. Therefore the accurate measurement of VPC frequency and early detection of VT events becomes essential for patients with cardiac disease.

Evaluation of efficacy of thermographic breast imaging in breast cancer: A pilot study

BACKGROUND Thermographic imaging is a non-invasive and radiation free imaging modality that measures the infrared radiation released by the body. Recently, there is a renewed interest regarding the scope of thermal imaging for breast cancer. OBJECTIVE To evaluate the efficacy of thermographic breast imaging in detecting breast cancer. METHODS A Prospective observational study was carried out from January 2014 to December 2014 at Kasturba Hospital, Manipal, India. Patients in whom breast cancer was confirmed on FNAC or biopsy, were included in the study and further evaluated with thermographic imaging of the breast. RESULTS 65 patients with FNAC or biopsy proven breast carcinoma were included in the study. Using thermographic imaging, malignancy was accurately detected in 60 patients (92.31%). Mammography was able to detect malignancy in 62 out of the 65 patients (95.38%). Thermography was able to detect malignancy in all 3 cases in which conventional mammography missed it. CONCLUSION Thermography may have a role in detection of breast cancer. However, it is too early to recommend thermographic imaging as a standard imaging modality for breast cancer. Larger studies are required to evaluate the usefulness of thermography in diagnosis and/or screening of breast cancer.