Wearable Electromagnetic Head Imaging System

Abstract

Strokes are among the leading causes of long-term disability and death worldwide. This emergency health dilemma requires a rapid and accurate medical diagnosis for prompt medicinal treatment to prevent permanent disability or the possibility of death. Currently, MRI and CT scan devices are used for stroke diagnosis, and they can provide accurate detection. However, they are relatively costly, not accessible in all hospitals, especially in rural areas.\xa0 Besides, these devices are bulky and mostly fixed, so cannot be transported by the first paramedic responders and consequently, cannot enable the early detection of stroke that would enable the patient to receive life-saving medication instantly. The aim of this thesis is to present the design and development of a wearable, wideband electromagnetic head imaging system for on-the-spot stroke diagnosis; one that is compatible, safe, lightweight, compact, and low-cost.This thesis makes several contributions to the current state of knowledge in the field of electromagnetic imaging. The first contribution includes the design and development of several flexible, low-profile, compact, and wideband on-body matched imaging antennas that operate at the lower microwave frequencies, with unidirectional near-field radiation and low SAR values.The second contribution is the design and development of multiple wearable wideband single-array electromagnetic head imaging systems as a proof-of-concept, utilizing the developed on-body matched imaging antennas. Subsequently, a fully integrated single-array wideband flexible custom-built electromagnetic cap for stroke detection is developed. The custom-built electromagnetic cap aims at overcoming the challenges of sizes, rigidities, and the complex structures of existing electromagnetic head imaging systems. The developed electromagnetic cap is experimentally validated with homogeneous head models, 3D realistic head phantoms, and several stroke-emulating targets. The imaging results using a polar sensitivity encoding (PSE) image processing algorithm demonstrate the merits and feasibility of the system for preclinical trials.The third contribution is the development of a new flexible, high-permittivity custom-made polymer-ceramic composite dielectric substrate, namely PDMS-Al2O3-C for on-body imaging antennas to attain higher efficiency and better match with the human head. The dielectric properties of the developed PDMS-Al2O3-C substrate can be tuned using different weight-ratio of fillers to suit various sensing antenna designs. Furthermore, an ultra-flexible, stretchy, and robust high-permittivity RTV-Al2O3 dielectric substrate is also developed from the mixture of the room-temperature-vulcanizing (RTV) silicone and aluminum oxide (Al2O3) powder. The advantages of developed dielectric substrates include the desirable dielectric properties that can improve the matching of the antennas with human head tissues, and the flexibility feature that allows the system to be configured and assembled in desired conformal shapes.To improve the coupling of the electromagnetic signal into the brain tissues, and to overcome the critical signal mismatch between the antenna array and skin of the head that can occur due to thick hairs or an air-gap in front of the antenna elements, different resilient purpose-built matching mediums are developed to cover the apertures of the antenna array with actual-mimicking dispersive dielectric properties close to those in head tissues. Unlike the existing matching mediums that mostly utilize liquids or semi-liquid materials and require complicated handling techniques to avoid leaking, the developed materials are highly flexible, durable and can be removed and replaced without affecting the antenna elements.The fifth contribution of this thesis includes the development of a double-array wideband flexible electromagnetic cap for stroke detection with the aim of achieving 3D and 2D multi-slice image reconstructions. The antenna array is configured as two semi-elliptical rings in the developed cap with a total of 24 elements to enable the generation of a 3D or 2D image of the brain. The detection capability of the system is then experimentally verified on the homogenous and 3D realistic head phantoms with multiple imaging scenarios and different types of stroke-emulating targets. The reconstructed 3D and 2D multi-slice images using the beamforming and polar sensitivity encoding (PSE) image processing algorithms indicate the applicability and potential of the proposed cap for future brain imaging.Finally, the developed compact, wideband, flexible, on-body matched antennas with comprehensive near-field and time-domain analysis have positively contributed to the fundamental specifications and requirements of efficient biomedical imaging antennas. On the other hand, the developed flexible polymer-ceramic substrate materials and matching medium materials in this thesis, contribute to the ongoing research in the field of electronic materials, which indicates the possibility of customizing the dielectric materials and their dielectric properties and mechanical features to meet not only the requirements of a wearable electromagnetic imaging system, but also other RF and microwave applications.