Co-integrating thermal and hemodynamic imaging for physiological monitoring

Photoplethysmographic imaging (PPGI) has gained popularity fornon-intrusive cardiovascular monitoring. However, certain symptoms(e.g., fever) may not be easily detectable using cardiovascularbiomarkers. Here, we investigate the co-integration of PPGIand thermal imaging to create a non-contact, widefield, multimodalphysiological monitoring system. To achieve strong PPGI performance,high-power infrared LED stability was investigated by evaluatingtwo LED driver boards. Results show that the multimodalimaging system was able to acquire spatially consistent hemodynamicpulsatility and heat distributions in a case study. This multimodalsystem may lead to improved systemic disease detectionand monitoring

Widefield Computational Biophotonic Imaging for Spatiotemporal Cardiovascular Hemodynamic Monitoring

Cardiovascular disease is the leading cause of mortality, resulting in 17.3 million deaths per year globally. Although cardiovascular disease accounts for approximately 30% of deaths in the United States, many deleterious events can be mitigated or prevented if detected and treated early. Indeed, early intervention and healthier behaviour adoption can reduce the relative risk of first heart attacks by up to 80% compared to those who do not adopt new healthy behaviours. Cardiovascular monitoring is a vital component of disease detection, mitigation, and treatment. The cardiovascular system is an incredibly dynamic system that constantly adapts to internal and external stimuli. Monitoring cardiovascular function and response is vital for disease detection and monitoring. Biophotonic technologies provide unique solutions for cardiovascular assessment and monitoring in naturalistic and clinical settings. These technologies leverage the properties of light as it enters and interacts with the tissue, providing safe and rapid sensing that can be performed in many different environments. Light entering into human tissue undergoes a complex series of absorption and scattering events according to both the illumination and tissue properties. The field of quantitative biomedical optics seeks to quantify physiological processes by analysing the remitted light characteristics relative to the controlled illumination source. Drawing inspiration from contact-based biophotonic sensing technologies such as pulse oximetry and near infrared spectroscopy, we explored the feasibility of widefield hemodynamic assessment using computational biophotonic imaging. Specifically, we investigated the hypothesis that computational biophotonic imaging can assess spatial and temporal properties of pulsatile blood flow across large tissue regions. This thesis presents the design, development, and evaluation of a novel photoplethysmographic imaging system for assessing spatial and temporal hemodynamics in major pulsatile vasculature through the sensing and processing of subtle light intensity fluctuations arising from local changes in blood volume. This system co-integrates methods from biomedical optics, electronic control, and biomedical image and signal processing to enable non-contact widefield hemodynamic assessment over large tissue regions. A biophotonic optical model was developed to quantitatively assess transient blood volume changes in a manner that does not require a priori information about the tissue's absorption and scattering characteristics. A novel automatic blood pulse waveform extraction method was developed to encourage passive monitoring. This spectral-spatial pixel fusion method uses physiological hemodynamic priors to guide a probabilistic framework for learning pixel weights across the scene. Pixels are combined according to their signal weight, resulting in a single waveform. Widefield hemodynamic imaging was assessed in three biomedical applications using the aforementioned developed system. First, spatial vascular distribution was investigated across a sample with highly varying demographics for assessing common pulsatile vascular pathways. Second, non-contact biophotonic assessment of the jugular venous pulse waveform was assessed, demonstrating clinically important information about cardiac contractility function in a manner which is currently assessed through invasive catheterization. Lastly, non-contact biophotonic assessment of cardiac arrhythmia was demonstrated, leveraging the system's ability to extract strong hemodynamic signals for assessing subtle fluctuations in the waveform. This research demonstrates that this novel approach for computational biophotonic hemodynamic imaging offers new cardiovascular monitoring and assessment techniques, which can enable new scientific discoveries and clinical detection related to cardiovascular function

Remote Assessment of the Cardiovascular Function Using Camera-Based Photoplethysmography

Camera-based photoplethysmography (cbPPG) is a novel measurement technique that allows the continuous monitoring of vital signs by using common video cameras. In the last decade, the technology has attracted a lot of attention as it is easy to set up, operates remotely, and offers new diagnostic opportunities. Despite the growing interest, cbPPG is not completely established yet and is still primarily the object of research. There are a variety of reasons for this lack of development including that reliable and autonomous hardware setups are missing, that robust processing algorithms are needed, that application fields are still limited, and that it is not completely understood which physiological factors impact the captured signal. In this thesis, these issues will be addressed. A new and innovative measuring system for cbPPG was developed. In the course of three large studies conducted in clinical and non-clinical environments, the system’s great flexibility, autonomy, user-friendliness, and integrability could be successfully proven. Furthermore, it was investigated what value optical polarization filtration adds to cbPPG. The results show that a perpendicular filter setting can significantly enhance the signal quality. In addition, the performed analyses were used to draw conclusions about the origin of cbPPG signals: Blood volume changes are most likely the defining element for the signal's modulation. Besides the hardware-related topics, the software topic was addressed. A new method for the selection of regions of interest (ROIs) in cbPPG videos was developed. Choosing valid ROIs is one of the most important steps in the processing chain of cbPPG software. The new method has the advantage of being fully automated, more independent, and universally applicable. Moreover, it suppresses ballistocardiographic artifacts by utilizing a level-set-based approach. The suitability of the ROI selection method was demonstrated on a large and challenging data set. In the last part of the work, a potentially new application field for cbPPG was explored. It was investigated how cbPPG can be used to assess autonomic reactions of the nervous system at the cutaneous vasculature. The results show that changes in the vasomotor tone, i.e. vasodilation and vasoconstriction, reflect in the pulsation strength of cbPPG signals. These characteristics also shed more light on the origin problem. Similar to the polarization analyses, they support the classic blood volume theory. In conclusion, this thesis tackles relevant issues regarding the application of cbPPG. The proposed solutions pave the way for cbPPG to become an established and widely accepted technology

Coded Hemodynamic Imaging of the Jugular Vein and Ultrasound Imaging of the Optic Nerve Sheath Diameter during Manipulations of Intracranial Pressure by Head-Down Tilt

Background: Spaceflight associated neuro-ocular syndrome (SANS) is a condition in which worsening vision occurs while in microgravity. It has been hypothesized that SANS is caused by an increase in intracranial pressure (ICP) due to the cephalad fluid shift that occurs in microgravity, however, due to the invasive nature of ICP measurements, ICP cannot safely be measured in microgravity. Non-invasive estimates of ICP (nICP) act as surrogates for ICP, but few methods of nICP are validated and all currently involve an operator and contact with the skin. Indicators of cerebral venous congestion, such as internal jugular vein cross-sectional area (IJV CSA) and central venous pressure (CVP), have not been utilized to reflect changes in nICP to date, despite the association between IJV CSA, CVP and ICP. Coded Hemodynamic Imaging (CHI) is a novel, non-contact camera device which uses infrared light to “see” blood volume in the superficial vasculature and to track changes in the jugular venous pulse. By leveraging CHI’s ability to detect cardiovascular biomarkers of IJV hemodynamics, it was hypothesized that changes in jugular venous absorption (JVA) as measured by CHI would be associated with changes in nICP during head-down tilt (HDT), a common surrogate for microgravity. Objective: (1) To determine the ability of JVA, determined by CHI, to track changes in IJV CSA, CVP, and nICP during a severe cephalad fluid shift induced by 12° HDT and 30° HDT. (2) To determine the effect of a severe cephalad fluid shift on cerebral venous outflow (IJV CSA and IJV blood flow), and how those changes are associated with nICP. Methods: Eleven healthy young adults (5 female, 26±6 years, 166±10 cm, 64±11 kg) underwent ophthalmic ultrasound, IJV ultrasound and CHI imaging after 5-minutes in supine (baseline), and every 5-minutes up to 20-minutes in 12° HDT, 30° HDT and again in supine (recovery). Transcranial Doppler (TCD) continuously measured the velocity of the middle cerebral artery and 5 participants had CVP continuously monitored by a catheter in a right antecubital vein. Repeated measures correlation as well as individual regression were used to test the association between JVA and nICP as measured by nICP-TCD and optic nerve sheath diameter (ONSD). Linear mixed models were used to determine how IJV CSA, IJV blood flow, nICP-TCD and ONSD changed with HDT and over time. Repeated measures correlation was used to test the associations between IJV CSA, IJV blood flow, nICP-TCD, and ONSD. Results: JVA and IJV CSA had a moderate positive association (rrm=0.51, pmean=0.57, rmedian=0.78), as did JVA and CVP (rrm=0.48, pmean=0.45, rmedian=0.67, n=4). JVA and nICP-TCD had a weak positive association (rrm=0.28, p=0.003; rmean=0.24, rmedian=0.31) as did JVA and ONSD (rrm=0.17, p=0.078; rmean=0.09, rmedian=0.17). HDT had a significant main effect on IJV CSA (p<0.001), nICP-TCD (p<0.001), and ONSD (p<0.05) but not on IJV blood flow (p=0.70). Time had no significant main effect on any variable. IJV CSA and nICP-TCD significantly increased at 30° HDT compared to baseline (p<0.001) but did not result in a significant change in IJV blood flow or ONSD. Conclusions: JVA, determined by CHI, was moderately associated with both IJV CSA and CVP, suggesting that CHI-derived-JVA can track changes in cardiovascular biomarkers during a severe cephalad shift. However, JVA had a weak association with nICP, suggesting that CHI-derived-JVA does not provide the same information as nICP. Due to the limitations of nICP, future studies should determine the association between JVA and invasive ICP to better determine the ability of CHI to be an nICP surrogate. Lastly, while IJV CSA and nICP-TCD significantly increased with 30° HDT, IJV blood flow remained the same, suggesting that the relationship between IJV hemodynamics, cerebral venous congestion and nICP during a cephalad fluid shift is more complex than what these measures can capture alone. Future work should focus on identifying abnormal IJV flow patterns with severe cephalad fluid shift, and how these patterns impact nICP

Optical Methods in Sensing and Imaging for Medical and Biological Applications

The recent advances in optical sources and detectors have opened up new opportunities for sensing and imaging techniques which can be successfully used in biomedical and healthcare applications. This book, entitled ‘Optical Methods in Sensing and Imaging for Medical and Biological Applications’, focuses on various aspects of the research and development related to these areas. The book will be a valuable source of information presenting the recent advances in optical methods and novel techniques, as well as their applications in the fields of biomedicine and healthcare, to anyone interested in this subject