Cost reduction and quality preservation with digital scanner interfaces for optical coherence tomography

Optical coherence tomography (OCT) systems are traditionally decomposed into engine and scanner components with an expensive and noise-prone analog interface to communicate the scan pattern between the two. Although simple and convenient, analog signals are susceptible to interference and require expensive hardware to generate with appropriate precision for OCT.

To overcome these limitations, we implemented a digital interface for our OCT system using low-cost embedded microprocessors and custom PC software, exploiting recent trends toward digital servo drivers for optical scanning.

Our interface features USB interfacing with a PC for scan pattern download and position feedback upload, 50-kHz communication rate, external triggers with adjustable downsampling, and no external power requirements.

We quantitatively assessed the latency, noise characteristics, and imaging performance of our digital interface in comparison with a conventional analog system that is an order of magnitude more expensive. The signal analysis confirmed that the digital interface reliably transmitted the intended scan pattern to the galvanometer driver and significantly reduced noise in the position feedback signal. High-speed laser trajectory tracking during sparse raster scanning revealed that discrepancies in the analog feedback signal did not reflect actual galvanometer positioning errors; both interfaces achieved equivalent spatial accuracy. Resolution testing demonstrated that both interfaces produced comparable OCT image quality, with no discernible difference up to the system's resolution limit, whereas reconstruction based on digital interface position feedback outperformed other methods when demanding scan patterns, such as spiral scanning, were applied. To support reproducibility and system integration, we developed a custom printed circuit board (PCB), enabling a compact and robust configuration for future OCT deployments. A simplified version of the firmware is supported by our open-source library vortex.

Together, these results demonstrate quantitative and qualitative equivalence of the interfaces, despite an order of magnitude reduction in cost. We released open-source software, PCB schematics, design files, and a bill of materials so that the OCT community can benefit from these improvements and cost savings.