Feasibility of Specular Reflection Imaging for Extraction of Neck Vessel Pressure Waveforms

Abstract

Cardiovascular disease (CVD) is a leading cause of death worldwide and was responsible for 31% of all deaths in 2015. Changes in fluid pressures within the vessels of the circulatory system reflect the mechanical function of the heart. The jugular venous (JV) pulse waveform is an important clinical sign for assessing cardiac function. However, technology able to aid evaluation and interpretation are currently lacking. The goal of the current study was to develop a remote monitoring tool that aid clinicians in robust measurements of JV pulse waveforms. To address this need, we have developed a novel imaging modality, Specular Reflection Vascular Imaging (SRVI). The technology uses specular reflection for visualization of skin displacements caused by pressure pulsations in blood vessels. SRVI has been tested on 10 healthy volunteers. 10-seconds videos of the neck illuminated with a diffuse light source were captured at 250 fps. SRVI was able to identify and discriminate skin displacements caused by carotid artery and jugular vein pulsations to extract both carotid artery and jugular vein waveforms, making them easier to be visualized and interpreted. The method provided a 6-fold improvement in signal strength over a comparator remote PPG dataset. The current pilot study is a proof-of-concept demonstration of the potential of Specular Reflection Vascular Imaging for extraction of JV pulse waveforms.

Remote Photoplethysmography with a High-Speed Camera Reveals Temporal and Amplitude Differences between Glabrous and Non-Glabrous Skin

“…The temporal lag analysis was also applied to the red channel and green channel within the glabrous skin and the red channel and green channel within the non-glabrous skin, with a minimal coherence of 0.33 acting as the requirement for temporal inclusion. Next, the ratio of the amplitudes of the glabrous signal compared with the non-glabrous signal was calculated per each color channel using the envelope methodology previously described in [ 18 ], with values greater than 1 indicating a higher amplitude in glabrous. The signal processing methodology described here was applied to all acquired signals.…”

Towards Development of Specular Reflection Vascular Imaging

“…However, the diffuse reflection contribution is minimized through the SRVI methodology, which promotes the specular reflection through the use of the smoothening agent, targeted diffuse light source, and dimmed ambient lighting. Experimentally, the amplitude of SRVI was approximately 6-fold greater than a comparator rPPG dataset, demonstrating that the SRVI signal is dominated by specular reflection, with minimal contribution from diffuse reflection [38]. However, given the steps that must be taken to enhance specular reflection to the appropriate level, the SRVI acquisition process must be managed carefully, with the light source intensity and the exposure time of the camera selected accordingly to avoid saturation and overexposure.…”

“…The major limitation of the current work is the lack of understanding of SRVI subject variability since we have analyzed a single subject as a case study. Our immediate goal is to present a validation of the methodology on a large set of volunteers [38].…”

Remote physiological monitoring of neck blood vessels

“…In particular, several things occur when light interacts with the skin surface. A small portion of the incident light undergoes specular reflection, bouncing off the surface at the same angle 14 . Another fraction of light enters the tissue, where it gets absorbed and scattered 14 .…”

“…A small portion of the incident light undergoes specular reflection, bouncing off the surface at the same angle 14 . Another fraction of light enters the tissue, where it gets absorbed and scattered 14 . The diffuse reflection, characterized by absorption and scattering coefficients, is influenced by factors such as average hemoglobin concentration, hemoglobin oxygen saturation, incident light angle, average fat and water content, and the wavelength of light 12,15,16 .…”