Investigating Polarisation-Sensitive Optical Coherence Tomography as a Measure of Biomarkers in Systemic Sclerosis

Abstract

Polarisation-sensitive optical coherence tomography (PS-OCT) is an enhancement of OCT, utilising circularly-polarised light for structural analysis. Polarised light imaging is an established assessment method for biological tissues and PS-OCT has been used in clinical assessment across a wide range of medical specialities since its inception. Systemic sclerosis is a debilitating rheumatic auto-immune disease in which connective tissues experience fibrosis (scarring) and lesions. Collagen, which is known to be birefringent, is a key component in these changes. This thesis reports on three clinical studies that were undertaken to investigate physical metrics by statistical assessment. These were focused on: the correlation of structural measurements, retardation as a biomarker, system reliability, and the feasibility of 3D lesion assessment. The first study's primary aim was the assessment of retardation as a biomarker comparing a cohort of healthy controls and patients. The second study's main objective was to validate PS-OCT's structural depth measurements by comparison to a gold standard, high-frequency ultrasound (HFUS). The third study aimed to assess the feasibility of imaging lesions in 3D. Ulcers and pitting in patients were scanned with polarisation sensitivity. Study one found an indicative relation between tissue retardation and grouped modified Rodnan skin score, the gold standard for skin thickness assessment. In the second study validation of epidermal thickness measurements with HFUS was not possible due to low reliability of ultrasound measurements (HFUS Intra/Inter-Class Correlations (ICCs) between 0.1-0.6). The PS-OCT system was able to achieve a penetration depth in skin of up to 800 µm. In study three, 3D imaging was performed on two pitting lesions, tissue adjacent to pitting, and five ulcerations. Surface and subsurface structure, and retardation, were clearly visible establishing the usefulness of this technique for longitudinal response to treatment studies.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mark Dickinson (Supervisor) & Andrea Murray (Supervisor)