Breaking the accessibility barrier: the development of low-cost dual-modal ophthalmic imaging and remote vital sign monitoring technologies

Yang, Xingyu (2023) Breaking the accessibility barrier: the development of low-cost dual-modal ophthalmic imaging and remote vital sign monitoring technologies. PhD thesis, University of Liverpool.

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Abstract

Accessibility for medical care is a constant topic of one of the global challenges that humanity is facing. Despite the importance, patient care access is not a reality for many patients around the globe, especially in developing countries. Searching for solutions at the technological level remains an invaluable research field for years to come. Ophthalmic imaging is an ever-evolving field of research. Although in developed countries, fundus examinations are in a matured state, challenges of accessibility are commonly seen in developing countries. A gap exists between the conventional colour fundus photography (CFP) and scanning laser ophthalmoscopy (SLO), as the trade-offs among cost, field of view (FOV), colour, and image contrast remain significant. This thesis reports a novel low-cost scanning-based fundus camera that produces higher contrast and larger FOV (60°) than CFP. The proposed technique takes the advantage of using a white light source and line confocal gating to achieve a quasi-line-field imaging scheme. The novel camera is at a similar cost to the conventional CFP while producing images that are fit for retinal screening without the need for manual montaging and operation from skilled personals. Moreover, the scanning component allows the possible integration with other imaging techniques, including optical coherence tomography (OCT). OCT has been extensively developed and implemented in ophthalmic imaging for more than a decade. However, due to the high-cost of the technology, OCT has not yet been formalised as a tool for screening programmes. Therefore, developing a low-cost OCT that can be integrated as part of the retinal screening process will significantly improve accessibility. In this study, the cost of OCT is reduced mainly by using a customised light source and area-array cameras. Three low-cost configurations were thoroughly investigated and the experimental results were evaluated. Eventually, a single-point OCT is chosen to be coupled with our above-mentioned fundus imaging device with a common scanner and ocular lens, leading to much reduced complexity and cost of the device. The design of the combination, to the best of the author’s knowledge, has not been reported in publications. The developed system was proven feasible in clinical setting as a result of a clinical study conducted in Xiamen, China, where more than 50 patients participated in the programme. The accessibility barrier in ophthalmic imaging can be significantly lowered as this technology allows the deployment of imaging devices in secondary care, especially in communities with a limited budget for screening. Telemedicine, or telehealth in general, is the delivery and facilitation of health and health-related services including medical care, provider, and patient. Reliable and contactless measurements of vital signs, such as respiration and heart rate, are still unmet needs in clinical and home settings. Millimetre wave (mm-wave) radar and video-based technologies are promising, but currently, the signal processing-based vital sign extraction methods are prone to body motion disruptions or illumination variations in the surrounding environment. Here we propose an image segmentation-based method to extract vital signs from the recorded video and mm-wave radar signals. The proposed method analyses time-frequency spectrograms obtained from Short-Time Fourier Transform rather than individual time-domain signals. This leads to much-improved robustness and accuracy of the heart rate and respiration rate extraction over existing methods. The experiments were conducted under pre- and post-exercise conditions and were repeated on multiple individuals. The results are evaluated by using four metrics against the gold standard contact-based measurements. Significant improvements were observed in terms of precision, accuracy, and stability. The performance was reflected by achieving an averaged Pearson correlation coefficient (PCC) of 93.8% on multiple subjects. The estimation method developed here will help address the needs for the increasingly popular remote cardiovascular sensing and diagnosing posed by Covid‐19. Additionally, this work was carried out in response to lab closure during Covid-19 period. The author believes the technologies developed in this study can lower the barrier to health care accessibly for the general population. The Covid-19 outbreak had an adverse impact on the ophthalmic aiming sector of healthcare, given that the focus has been on treating affected patients and curbing the pandemic spread. Therefore, patients affected by other diseases remain largely untreated. Lowering or breaking the barriers for accessibility will help the healthcare industry to face this upcoming challenge and it will be an increasingly demanded field of research in the future.

Item Type:	Thesis (PhD)
Divisions:	Faculty of Science and Engineering > School of Electrical Engineering, Electronics and Computer Science
Depositing User:	Symplectic Admin
Date Deposited:	24 Aug 2023 15:13
Last Modified:	24 Aug 2023 15:14
DOI:	10.17638/03171210
Supervisors:	Shen, Yaochun Zheng, Yalin
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3171210