A Pulsatile Optical Tissue Phantom for the Investigation of Light-Tissue Interaction in Reflectance Photoplethysmography

The aim of this study was to investigate the effect of emitter-detector separation distance and arterial depth in reflectance photoplethysmography (PPG), utilizing a homogenous pulsatile phantom that exhibits the broad optical absorbance and scattering properties of human tissue. The developed phantom comprised of embedded silicone arteries (outer diameter = 4 mm) that were arranged parallel to one another at nine increasing depths (3.2 mm to 24.4 mm). A pulsatile pump (Harvard Apparatus, MA, USA) circulated a blood imitating fluid through the vessels at the desired heart rate (60 bpm) and stroke volume (5 Lmin-1). The PPG sensor’s emitter and detector were isolated on a translation bridge to provide a computer-controlled separation distance between them. Recordings were taken at each vessel depth for emitter-detector separation distances from 2 mm to 8 mm in 0.1 mm steps. The optimum separation distance between the emitter and detector for vessels between depths of 3.2 mm and 10.5 mm was between 3.7 and 4.3 mm, suggesting that the maximum penetration of IR (930 nm) light in a homogenous pulsatile phantom is no greater than 10.5 mm

A wearable near-infrared diffuse optical system for monitoring in vivo breast tumor hemodynamics during chemotherapy infusions

Neoadjuvant chemotherapy (NAC) is increasingly being utilized to reduce tumor burden prior to surgery for breast cancer patients with stage II or higher disease. A pathologic complete response (pCR) to NAC has been correlated with longer 5-year survival and is generally considered as an absence of invasive cancer in the breast and axillary nodes at the time of surgery. Unfortunately, only about 10% of patients achieve pCR during NAC, and it may take months after the first infusion to determine response with methods that rely on anatomic information, such as palpation, mammography, ultrasound, and MRI. Functional imaging technologies such as Positron Emission Tomography, Magnetic Resonance Spectroscopy, and more recently, Diffuse Optical Spectroscopy, have shown promise for earlier predictions of therapy response. However, most of these techniques suffer from high expense, lack of portability, and safety issues related to the use of ionizing radiation or exogenous contrast agents. Furthermore, the repeated patient visits required by these techniques may hamper their clinical adoption for this purpose. This project aims to develop a new wearable diffuse optical device that can be used to investigate if very early timepoints during a patient’s first chemotherapy infusion are predictive of overall response (pCR versus non-pCR) to NAC. These timepoints correspond to an already scheduled patient visit and have so far been unexplored for their prognostic value. The development of this continuous-wave diffuse optical imaging device was conducted in three stages. First, a prototype rigid probe was designed and developed to test key optical and electrical components. Second, a high optode-density flexible probe was design and fabricated which can conform to the curved surface of the human breast. Finally, a control box with miniaturized electronics and high-speed electronics was designed and fabricated to complete a clinic-ready system. This system was then tested in both the laboratory setting and as part of a normal-volunteer clinical study in healthy subjects during a breath hold hemodynamic challenge.2019-10-22T00:00:00

Body sensor networks: smart monitoring solutions after reconstructive surgery

Advances in reconstructive surgery are providing treatment options in the face of major trauma and cancer. Body Sensor Networks (BSN) have the potential to offer smart solutions to a range of clinical challenges. The aim of this thesis was to review the current state of the art devices, then develop and apply bespoke technologies developed by the Hamlyn Centre BSN engineering team supported by the EPSRC ESPRIT programme to deliver post-operative monitoring options for patients undergoing reconstructive surgery. A wireless optical sensor was developed to provide a continuous monitoring solution for free tissue transplants (free flaps). By recording backscattered light from 2 different source wavelengths, we were able to estimate the oxygenation of the superficial microvasculature. In a custom-made upper limb pressure cuff model, forearm deoxygenation measured by our sensor and gold standard equipment showed strong correlations, with incremental reductions in response to increased cuff inflation durations. Such a device might allow early detection of flap failure, optimising the likelihood of flap salvage. An ear-worn activity recognition sensor was utilised to provide a platform capable of facilitating objective assessment of functional mobility. This work evolved from an initial feasibility study in a knee replacement cohort, to a larger clinical trial designed to establish a novel mobility score in patients recovering from open tibial fractures (OTF). The Hamlyn Mobility Score (HMS) assesses mobility over 3 activities of daily living: walking, stair climbing, and standing from a chair. Sensor-derived parameters including variation in both temporal and force aspects of gait were validated to measure differences in performance in line with fracture severity, which also matched questionnaire-based assessments. Monitoring the OTF cohort over 12 months with the HMS allowed functional recovery to be profiled in great detail. Further, a novel finding of continued improvements in walking quality after a plateau in walking quantity was demonstrated objectively. The methods described in this thesis provide an opportunity to revamp the recovery paradigm through continuous, objective patient monitoring along with self-directed, personalised rehabilitation strategies, which has the potential to improve both the quality and cost-effectiveness of reconstructive surgery services.Open Acces

Biomedical Photoacoustic Imaging and Sensing Using Affordable Resources

The overarching goal of this book is to provide a current picture of the latest developments in the capabilities of biomedical photoacoustic imaging and sensing in an affordable setting, such as advances in the technology involving light sources, and delivery, acoustic detection, and image reconstruction and processing algorithms. This book includes 14 chapters from globally prominent researchers , covering a comprehensive spectrum of photoacoustic imaging topics from technology developments and novel imaging methods to preclinical and clinical studies, predominantly in a cost-effective setting. Affordability is undoubtedly an important factor to be considered in the following years to help translate photoacoustic imaging to clinics around the globe. This first-ever book focused on biomedical photoacoustic imaging and sensing using affordable resources is thus timely, especially considering the fact that this technique is facing an exciting transition from benchtop to bedside. Given its scope, the book will appeal to scientists and engineers in academia and industry, as well as medical experts interested in the clinical applications of photoacoustic imaging

Frequency-domain diffuse optical spectroscopy for cardiovascular and respiratory applications

Frequency Domain Diffuse Optical Spectroscopy (FD-DOS) is an emerging optical technique that uses near infrared light to probe the hemodynamics of biological tissue. Compared to more common Continuous Wave (CW) methods, FD-DOS uses light that is temporally modulated on the order of MHz to quantify the absorption and scattering of tissue. FD-DOS can also be used to obtain absolute concentration of tissue chromophores such as oxy- and deoxy-hemoglobin, which allow for quantitative measurements of tissue hemodynamics. This dissertation focuses on the evolution of our lab’s custom digital FD-DOS as a platform for taking optical measurement of biological tissue for respiratory and cardiovascular applications. Several important instrumentation improvements will be reviewed that have enhanced the performance of the system while making it more portable and clinic ready. Two translational applications will be described in detail: 1) the use of high-speed FD-DOS for the non-invasive extraction of venous oxygen saturation (SvO2) and 2) the use of FD-DOS to monitor the hemodynamics of the sternocleidomastoid (SCM) muscle towards the non-invasive monitoring of patients on mechanical ventilation. The custom FD-DOS system parameters were adjusted for each application, with a focus on high speed to extract the cardiac signal for the SvO2 project, and a focus on high SNR to measure the highly absorbing SCM. Measurements on healthy volunteers and rabbits were used to assess the feasibility of using FD-DOS for these applications. Finally, preliminary work was conducted to characterize a miniature FD-DOS source and detector with the goal of moving towards a wearable version of FD-DOS.2022-05-15T00:00:00

Noninvasive Blood Flow and Oxygenation Measurements in Diseased Tissue

The research presented in this dissertation focused on the application of optical imaging techniques to establish blood flow and oxygen saturation as effective biomarkers for two disease cases, Autism Spectrum Disorder (ASD) and Huntington’s Disease (HD). The BTBR mouse model of ASD was utilized to validate measurements of cerebral blood flow and oxygenation as biomarkers for autism. The R6/2 mouse model of juvenile HD was utilized to validate measurements of skeletal muscle blood flow following tetanic muscle contractions induced by electrical nerve stimulation. Next, a noncontact, camera-based system to measure blood flow and oxygen saturation maps was implemented to improve upon the previous HD mouse results by providing spatial heterogeneity in a wild-type mouse model. Finally, translational research was performed to validate a research design conducting concurrent grip strength force and skeletal muscle blood flow and oxygenation measurements in a healthy human population that will be used to establish HD biomarkers in humans in future clinical applications

Sources of inaccuracy in photoplethysmography for continuous cardiovascular monitoring

Photoplethysmography (PPG) is a low-cost, noninvasive optical technique that uses change in light transmission with changes in blood volume within tissue to provide information for cardiovascular health and fitness. As remote health and wearable medical devices become more prevalent, PPG devices are being developed as part of wearable systems to monitor parameters such as heart rate (HR) that do not require complex analysis of the PPG waveform. However, complex analyses of the PPG waveform yield valuable clinical information, such as: blood pressure, respiratory information, sympathetic nervous system activity, and heart rate variability. Systems aiming to derive such complex parameters do not always account for realistic sources of noise, as testing is performed within controlled parameter spaces. A wearable monitoring tool to be used beyond fitness and heart rate must account for noise sources originating from individual patient variations (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to the skin). Here, we present a comprehensive review of the literature that aims to summarize these noise sources for future PPG device development for use in health monitoring

Development of a smartphone-based optical device to measure hemoglobin concentration changes for remote monitoring of wounds

Telemedicine (TM) can revolutionize the impact of diabetic wound care management, along with tools for remote patient monitoring (RPM). There are no low-cost mobile RPM devices for TM technology to provide comprehensive (visual and physiological) clinical assessments. Here, a novel low-cost smartphone-based optical imaging device has been developed to provide physiological measurements of tissues in terms of hemoglobin concentration maps. The device (SmartPhone Oxygenation Tool—SPOT) constitutes an add-on optical module, a smartphone, and a custom app to automate data acquisition while syncing a multi-wavelength near-infrared light-emitting diode (LED) light source (690, 810, 830 nm). The optimal imaging conditions of the SPOT device were determined from signal-to-noise maps. A standard vascular occlusion test was performed in three control subjects to observe changes in hemoglobin concentration maps between rest, occlusion, and release time points on the dorsal of the hand. Hemoglobin concentration maps were compared with and without applying an image de-noising algorithm, single value decomposition. Statistical analysis demonstrated that the hemoglobin concentrations changed significantly across the three-time stamps. Ongoing efforts are in imaging diabetic foot ulcers using the SPOT device to assess its potential as a smart health device for physiological monitoring of wounds remotely

Best practices for fNIRS publications

The application of functional near-infrared spectroscopy (fNIRS) in the neurosciences has been expanding over the last 40 years. Today, it is addressing a wide range of applications within different populations and utilizes a great variety of experimental paradigms. With the rapid growth and the diversification of research methods, some inconsistencies are appearing in the way in which methods are presented, which can make the interpretation and replication of studies unnecessarily challenging. The Society for Functional Near-Infrared Spectroscopy has thus been motivated to organize a representative (but not exhaustive) group of leaders in the field to build a consensus on the best practices for describing the methods utilized in fNIRS studies. Our paper has been designed to provide guidelines to help enhance the reliability, repeatability, and traceability of reported fNIRS studies and encourage best practices throughout the community. A checklist is provided to guide authors in the preparation of their manuscripts and to assist reviewers when evaluating fNIRS papers