Information limits of imaging through highly diffusive materials using spatiotemporal measurements of diffuse photons

Radford, Jack (2023) Information limits of imaging through highly diffusive materials using spatiotemporal measurements of diffuse photons. PhD thesis, University of Glasgow.

Abstract

Conventional medical imaging instruments are bulky, expensive, and use harmful ionising radiation. Combining ultrafast single-photon detectors and pulsed laser sources at optical wavelengths has the potential to offer inexpensive, safe, and potentially wearable alternatives. However, photons at optical wavelengths are strongly scattered by biological tissue, which corrupts direct imaging information about regions of absorbing interactions below the tissue surface. The work in this thesis studies the potential of measuring indirect imaging information by resolving diffuse photon measurements in space and time. The practical limits of imaging through highly diffusive material, e.g., biological tissue, is explored and validated with experimental measurements. The ill-posed problem of using the information in diffuse photon measurements to reconstruct images at the limits of the highly diffusive regime is tackled using probabilistic machine learning, demonstrating the potential of migrating diffuse optical imaging techniques beyond the currently accepted limits and underlining the importance of uncertainty quantification in reconstructions. The thesis is concluded with a challenging biomedical optics experiment to transmit photons diametrically through an adult human head. This problem was tackled experimentally and numerically using an anatomically accurate Monte Carlo simulation which uncovered key practical considerations when detecting photons at the extreme limits of the highly diffusive regime. Although the experimental measurements were inconclusive, comparisons with the numerical results were promising. More in-depth numerical simulations indicated that light could be guided in regions of low scattering and absorption to reach deep areas inside the head, and photons can, in principle, be transmitted through the entire diameter of the head. The collective evidence presented in this thesis reveals the potential of diffuse optical imaging to extend beyond the currently accepted limits to non-invasively image deep regions of the human body and brain using optical wavelengths.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QA Mathematics > QA75 Electronic computers. Computer science; Q Science > QC Physics; T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Funder's Name: Engineering and Physical Sciences Research Council (EPSRC), Engineering and Physical Sciences Research Council (EPSRC)
• Supervisor's Name: Faccio, Professor Daniele and Murray-Smith, Professor Roderick
• Date of Award: 2023
• Depositing User: Theses Team
• Unique ID: glathesis:2023-83762
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 10 Aug 2023 09:03
• Last Modified: 22 Aug 2023 12:52
• Thesis DOI: 10.5525/gla.thesis.83762
• URI: https://theses.gla.ac.uk/id/eprint/83762

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