Objective, quantitative assessment of burn scars with optical coherence tomography

    Research output: ThesisDoctoral Thesis

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    Abstract

    Skin scarring arises from a wide range of traumatic injuries and can lead to significant physical discomfort, such as pain, itching and reduced mobility, and psychological problems for patients. There is a large body of work on treatment methods for preventing scarring, and improving the healing of scars. However, the outcomes of these methods vary greatly among patients. The understanding of scar responses to treatment is limited partially by the lack of robust scar assessment techniques. The aim of the research reported in this thesis is to develop an objective, quantitative scar assessment method to advance our understanding of scar characteristics and responses to treatment, using a high-resolution, non-invasive, three-dimensional optical imaging technique, called optical coherence tomography (OCT).

    Scars, especially pathological scars, commonly show the abnormalities of an over proliferation of blood vessels and excess collagen growth. The research presented in this thesis first focuses on the development of OCT for clinical assessment of the scar vasculature. A method based on OCT speckle decorrelation was developed to image and automatically quantify the diameter and area density of the cutaneous microvasculature in scars. This method was applied to burn scar patients and prolific larger blood vessels were observed in the pathological hypertrophic scars as compared to normal skin. The feasibility of this method for longitudinal assessment was investigated by tracking the wound healing process in injured human skin. The injured skin showed an elevated level of vasculature at the beginning and a decrease to normal levels at the end of the healing process. The vasculature assessment method reported in this thesis provides not only an objective assessment of the scar vasculature, but also the basis for removing (masking) the effects of vasculature in the following assessment of scar collagen.

    The second part of the work is on the development of OCT for clinical assessment of the collagen network in scars by using OCT to measure their optical properties using two separate approaches. The first approach quantifies the optical attenuation coefficient by fitting the corrected OCT A-scans to a single-scattering model. The second approach calculates the optical birefringence of scar tissue by measuring the rate of change of phase retardation with depth in polarisation-sensitive OCT scans. The vascular masking technique was incorporated into both approaches to remove the artefacts caused by the vasculature. The measured optical properties in both instances were visualised as en face parametric images, showing lower attenuation coefficient and higher birefringence values for scars than for normal skin.

    Finally, scar assessment with OCT was investigated for two different clinical applications. The first study applied OCT assessment of vasculature to the longitudinal monitoring of burn scars following fractional laser treatment. The scar tissue showed different responses to the treatment according to the scar type: decreased and increased degree of vasculature following treatment, respectively, in immature and mature scars. The second study investigated the feasibility of OCT for delineating scar boundaries by using another OCT-based method, optical palpation, to measure the stiffness at the surface of scar tissue. Case studies demonstrated the ability of OCT optical palpation to provide contrast between scar tissue and the surrounding normal skin.

    The OCT scar assessment methods presented in this thesis provide a comprehensive measurement framework for both vasculature and collagen assessment in burn scars, and establish a basis for future clinical application of objective, quantitative OCT-based methods in scar assessment.

    Original languageEnglish
    QualificationDoctor of Philosophy
    Supervisors/Advisors
    • McLaughlin, Robert, Supervisor
    • Sampson, David, Supervisor
    Publication statusUnpublished - Nov 2015

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