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From Invasive Neurosensing to Noninvasive Radiometric Core and Brain Monitoring

Tisdale, Katrina
http://orcid.org/0000-0001-5966-6913
http://rave.ohiolink.edu/etdc/view?acc_num=osu1649766173382556

Abstract Details

2022, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Brain-computer interfaces (BCIs) are supposed to revolutionize our ability to understand and treat brain injury, but to-date no system has fulfilled this promise. Ideally, BCIs should monitor with both high spatial and temporal resolution to identify the source of an issue. An implanted device should provide both, but current state-of-the-art technology comes with many issues. These issues include wires connecting the implant to external processing equipment, implanted heat-generating electronics causing damage to the surrounding tissues, and limited device lifetimes requiring multiple surgeries. Each limitation increases patient risk and limits the use of such devices to a laboratory setting. As such, noninvasive devices are an increasingly appealing monitoring modality. One such modality is microwave radiometry. However, prior radiometry work suffers from narrowband measurements, simplified modeling, and use of fully characterized phantoms, all equating to a system that is not useful in a real-world setting. Acknowledging the implant limitations, previous work in our group involved development of a wireless and fully passive neurosensor that operates without complex implanted electronics. However, even this device faces many challenges, such as characterizing the device in a realistic setting. To address this challenge, this dissertation reports a realistic in vitro testbed, leading to a better understanding of how the neurosensor operates and can be optimized. Nevertheless, the device still faces many issues including a wireless interface highly sensitive to misalignment and a large external setup, not to mention the immune system’s rejection of foreign implanted objects that all implants face. Even if the implanted device eventually proves feasible for real-world function, adoption would be limited to extreme cases. Hence, a noninvasive monitoring method is sought. In pursuit of noninvasive monitoring, this dissertation presents an intermediate step to develop a noninvasive temperature imaging system of the brain and involves one-dimensional temperature sensing. Noninvasive brain monitoring aside, an accurate noninvasive brain or core temperature sensor can improve surgical patient outcomes above current standards-of-care, which currently present a tradeoff between accuracy and invasiveness. This research seeks to overcome the challenges facing on-body radiometry to noninvasively sense the human core body temperature. We leverage bio-matched antennas (BMAs) previously developed in our group to enable broadband measurements and thermal and electromagnetic (EM) modeling of layered tissues for noninvasive and accurate core temperature monitoring to extract a temperature profile of the human head. We pursue thermal and EM modeling as well as feasibility experiments on simplified phantoms. For thermal modeling of the human head, we explore the use of Pennes’ bioheat equation and examine how population-representative thermal variables (e.g., thermal conductivity, heat capacity, density, etc.) gathered from literature affect the resulting temperature profile. These thermal models serve as an input for the EM model. The EM model determines the expected output measured by a radiometer. To demonstrate the feasibility of applying the thermal and coherent EM models, we present radiometer measurements using human tissue phantoms, along with pre-developed BMAs and a radiometer previously used for geophysical sensing. Minimal error between the calibrated experimental and model data sets suggests that a coherent EM model is sufficient to describe human head tissue thermal emissions. We additionally simulate experimental data from a six-layer human head and demonstrate temperature retrieval/measurement to within the clinically acceptable limit of 0.5°C when only layer thicknesses are known (i.e., all other thermal and EM parameters are unknown).
Asimina Kiourti (Advisor)
Joel Johnson (Committee Member)
Alexandra Bringer (Committee Member)
Darren Drewry (Committee Member)
Emre Ertin (Committee Member)
Electrical Engineering; Electromagnetics
Tissue radiometry; microwave thermography, BCI, electrochemical impedance spectroscopy

Recommended Citations

Citations

  • Tisdale, K. (2022). From Invasive Neurosensing to Noninvasive Radiometric Core and Brain Monitoring [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1649766173382556

    APA Style (7th edition)

  • Tisdale, Katrina. From Invasive Neurosensing to Noninvasive Radiometric Core and Brain Monitoring. 2022. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1649766173382556.

    MLA Style (8th edition)

  • Tisdale, Katrina. "From Invasive Neurosensing to Noninvasive Radiometric Core and Brain Monitoring." Doctoral dissertation, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu1649766173382556

    Chicago Manual of Style (17th edition)

osu1649766173382556
59
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This open access ETD is published by The Ohio State University and OhioLINK.