Engineering Development and Signal Processing Advancements in OCT Angiography: From Custom System Integration to Temporal Domain Denoising

Abstract

Optical Coherence Tomography Angiography (OCTA) positions itself as a highly effective, non-invasive technique that provides depth-resolved visualization of vascular structure and function. With a continuously emerging need to transition from static angiography to functional, time-resolved imaging, researchers have identified interconnected challenges. This thesis fundamentally explores two of these challenges: speckle noise and processing latency. Typically, spatial filters used to suppress speckle and denoise images are computationally expensive and act as temporal low-pass filters, destroying the dynamic physiological signals they intend to isolate. This thesis presents the design, implementation, and in vivo validation of a streaming-compatible swept-source OCTA (SS-OCTA) architecture relying on a hardware/software co-design to overcome these limitations. Rather than relying on isolated downstream algorithms, the system described in this research establishes a validated quality baseline starting at the hardware level. The custom 1060 nm MEMS-VCSEL SS-OCT platform developed in this thesis, leverages an adaptive software flyback filter to assess fast-axis position derivatives, actively isolating and discarding corrupted scans prior to contrast processing. Building upon this stationary signal foundation, the thesis introduces Temporal Subband Decomposition and Amplification (TSDA). TSDA operates as a dual-rate infinite impulse response (IIR) filter along the per-pixel temporal axis, decomposing the signal into structural, flow, and high frequency speckle bands. This continuous formulation reduces computational complexity to O(1), bypassing the buffering requirements of discrete Fourier methods and aiming to isolate physiologically driven flow from coherent noise. The integrated hardware/software stack was validated against a microfluidic phantom and an in vivo 14-day-old chorioallantoic membrane (CAM) preparation. An ablation study reported here confirms the TSDA architecture achieves a processing latency within the 10 ms budget. Furthermore, the complete pipeline delivered a Peak Signal-to-Noise Ratio (PSNR) of 27.8 dB against a multi-frame average reference, while yielding statistically significant improvements in Vessel Contrast-to-Noise Ratio (VCNR). By replacing spatial averaging with targeted temporal band isolation, the integrated platform extracts OCTA contrast while preserving the temporal flow signal within the filter passband.