Research for Undergraduate Students

1. Improving Photoplethysmography (PPG) in Optical Wearables Using Time-of-Flight Diffuse Reflectance

Obesity can cause hypertension (elevated blood pressure) and is often linked to cardiovascular diseases (CVD) because elevated blood pressure (BP) is a major risk for CVD . Research into cuff-less and continuous BP devices based on optical photoplethysmography (PPG) is rapidly expanding with the U.S. Food and Drug Administration (FDA) approval of commercial wearable devices for BP monitoring. As the prevalence of optical wearables grows, it is important to understand the effects of obese physiology (skin layered thickness, skin tone and vascular density) and device parameters (optical wavelengths and source-detector geometry) on the accuracy of PPG measurements. Currently, optical PPG relies on the measurement of steady state diffuse reflection. However, such technique produces poor sensitivity for photon from deep dermal where capillary vessel are found.

This research project uses time-resolved Monte Carlo simulations to improve optical PPG. Overall, the tasks include but not limited: (1) understanding skin anatomy dynamics with obese progression, (2) understanding the interaction between light and biological tissues and familiarizing with the theories of light propagation in turbid media including diffusion theory and Monte Carlo, (3) designing simulated parameters by thoroughly evaluating available references to study the mentioned effects on PPG, and (4) analyzing the results of the simulations and making preliminary conclusions

Ajmal, T. Boonya-Ananta, A. J. Rodriguez, V. N. Du Le, and J. C. Ramella-Roman “A Monte Carlo Analysis of Optical Heart Rate sensors in Commercial Wearables: The Effect of Skin Tone and Obesity on Photoplethysmography (PPG) Signal” Biomedical Optics Express 12(12), (2021). https://doi.org/10.1364/BOE.439893
T. Boonya-Ananta, A. J Rodriguez, A. Ajmal, V. N. Du Le, Anders K Hansen, Joshua D Hutcheson, Jessica C Ramella-Roman "Synthetic Photoplethysmography (PPG) of the radial artery through parallelized Monte Carlo and its correlation to Body Mass Index (BMI) " Scientific Reports 11, 2570 (2021). https://doi.org/10.1038/s41598-021-82124-4

2. Mueller Matrix Polarimetry Microscope (MMPM) for Visualization of Collagen Structure

Collagen accounts for 30% of the human body’s protein, providing structure, support or strength to the skin, muscles, bones and connective tissues. The crosslinking between the collagen fibers determines the strength and mechanical activity of the tissues. Subsequently, how collagen fibers are arranged can have a significant impact on the normal function of these tissues. For example, the weakening in collagen crosslinking in the cervix can lead to preterm birth labor or that in the cornea can lead to changes in corneal shape and a degradation of the optical properties of the cornea (keratoconus).

In the translational biophysics laboratory (TBL) at UAH, the student will have the opportunities to learn the principal of polarized light interaction with biological tissues, and apply this knowledge into building a simple lab-based Mueller Matrix Polarimetry Microscope to quantify the orientation of collagen-rich tissue including mice cervix and cornea. Subsequently, students will also learn the principal of Mueller matrix imaging and familiarize with image decomposition using MATLAB-based algorithm. Overall, the student will gain the knowledge of optical polarization, light-tissue interaction, optical alignment and principal of microscopy as well as MATLAB image processing and data acquisition.

V. N. Du Le*, I. Saytashev, S. Saha, P. F. Lopez, M. Laughrey, and J. C. Ramella-Roman, "Depth-resolved Mueller matrix polarimetry microscopy of the rat cornea," Biomedical Optics Express 11, 5982-5994 (2020). https://doi.org/10.1364/BOE.402201
C. Roa, V. N. Du Le*, M. Mahendroo, J. C. Ramella-Roman, "Auto-detection of cervical collagen and elastin in Mueller matrix polarimetry microscopic images using K-NN and Semantic Segmentation classification " Biomedical Optics Express 12(4), (2021). https://doi.org/10.1364/BOE.420079

3.Fabrication and Characterization of Optical Phantoms for Biophotonics Application

Optical phantoms are test objects that simulate the optical characteristics of tissues, and are commonly used to mimic light distributions in living tissue. Depending on the target simulated tissues, the materials and components of the phantoms can vary. These phantoms can be in liquid, gel or solid form. The latter is commonly produced with 3-D Printer. Optical Phantoms are primarily used for calibration of bio-optical devices to ensure the functionality, safety and accuracy of these devices. Such phantoms are often required by the Food and Drug Administration for 510(k) premarket application of bio-optical devices.

In the translational biophysics laboratory (TBL) at UAH, the student will be fabricating liquid and gel-based phantoms using standard components such as India ink and synthetic hemoglobin to simulate absorption of human skin and blood, and Intralipid and microsphere to simulate optical scattering of human cells. The students will have the opportunities to use the spectrophotometer integrating sphere and invert adding-doubling algorithm to measure these phantoms optical properties. The students will gain knowledge of beer-lambert's law, optical measurement of total reflection and transmission, light-tissue interaction theories, working with spectrophotometer, and acquire basic skills of chemistry and of data processing in MATLAB.

V. N. Du Le*, M. Manser, S. Gurm, B. Wagner, J. Hayward and Q. Fang, “Calibration of Spectral Imaging Devices with Oxygenation-Controlled Phantoms: Introducing a Simple Gel-based Hemoglobin Model”, Frontiers in Physics 7 (2019). https://doi.org/10.3389/fphy.2019.00192
J. Wang, J. Coburn, C. Liang, N. Woolsey, Du Le, J. Ramella-Roman, Y. Chen, and J. Pfefer "Characterization and application of 3D-printed phantoms for biophotonic imaging", Proc. SPIE 8719, Smart Biomedical and Physiological Sensor Technology X, 87190Y (31 May 2013); https://doi.org/10.1117/12.2018285
V. N. Du Le, Z. Nie, J. E. Hayward, T. J. Farrell, and Q. Fang “Measurements of extrinsic fluorescence in Intralipid and polystyrene microspheres”, Biomedical Optics Express 5 (8):2726-2735 (2014). https://doi.org/10.1364/BOE.5.002726

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