Developments of High-speed Near-infrared Fourier domain Mode-locking Optical Coherence Tomography for Clinical Applications

Optical coherence tomography (OCT) has gained significant attention in both medical and non-medical fields due to its non-invasive, real-time, three-dimensional, in-vivo, and multi-functional imaging capabilities. In dermatology, OCT enables the visualisation of tissue microstructure, vasculature, and collagen distribution, making it highly effective for diagnosing and monitoring conditions such as skin cancers and inflammatory diseases. However, the slow scan rates of commercial systems limit the acquisition speed of functional information.
This thesis addresses that challenge through the development of a high-speed near-infrared Fourier-domain mode-locked (FDML) OCT system tailored for clinical dermatological applications. Chapter 2 presents the system, which achieves an ultrahigh A-scan rate of 1.67 MHz, with axial and lateral resolutions of ~13 µm and ~25 µm respectively, sensitivity of ~100 dB, and imaging depth of ~4.8 mm in air. Real-time imaging and data acquisition are enabled through custom software, and the system’s capability is demonstrated through in-vivo imaging of various skin sites.
Chapter 3 demonstrates rapid measurement of skin biomarkers, including epidermal thickness and vascular morphology, using custom automated segmentation and OCT angiography algorithms. Chapter 4 presents the first application of variable interscan time analysis (VISTA) for quantifying cutaneous blood flow using an FDML OCT system. A novel auto-fitting method is also introduced into the VISTA framework, improving the accuracy of decorrelation coefficient estimation.
Chapter 5 proposes a novel algorithm for skin topographical matching to enable precise re-scanning of treated sites. This is the first OCT-based approach that automatically estimates matching scores to support longitudinal skin monitoring. Additionally, this FDML OCT system is combined with an in-house designed colposcopic scanning probe to aid in its alignment and characterisation.
Finally, Chapter 6 summarises the system's development and discusses its potential applications and future extensions. This high-speed FDML OCT system demonstrates readiness for translation into dermatological clinics.