Fourier-domain mode-locked (FDML) laser sources allow OCT imaging systems with sweep rates reaching 1.6 MHz. However, physical limitations of conventional scanning systems require consideration. Resonant scanners fix imaging frequency, whereas galvanometer scanner (GS) systems require either raster scanning with large flyback that reduce usable data, or bi-directional scans that require many repeated scans. To overcome these limitations, we employed an effective 1.6 MHz stepped bi-directional scanning protocol, allowing 2 BM-scan OCT-angiography (OCTA) imaging using high-speed FDML. We present the ideal acquisition protocol and processing algorithm for optimum OCTA quality, with results demonstrating high vasculature contrast at 1.6 MHz scan rates.
Contrast for imaging the retinal microvasculature and the retinal pigment epithelium (RPE) is essential for pre-clinical studies of vision-robbing diseases. By integrating polarization diversity detection (PDD) with OCT angiography (OCTA), we have developed a novel quantitative multi-contrast OCT for imaging pigment in the RPE as well as flow in the retinal capillaries. An adaptive filter was developed for degree of polarization uniformity (DOPU) processing to provide improved measurements of melanin region thickness in tilted retina. The retinas of three mouse strains were imaged in vivo, with results demonstrating potential for simultaneous mapping of vasculature and melanin distribution in the RPE.
In this study we describe our novel Multi-Scale and multi-Mode Sensorless Adaptive Optics OCT system (MSM-SAO-OCT). Our system expands upon our previously reported work by introducing a zoomable collimator, phase calibration interferometer, and polarization diversity detection module. By using a zoomable collimator into the system setup, we allow an adjustable probing beam diameter without the need to change the optical setup, permitting imaging with both low and high lateral resolution (18 µm – 6 µm) at various Fields of View (FOV) within diffraction limited resolution. By employing SAO optimization algorithm, different morphological structures and microvasculature in a retina were clearly visualized after wavefront aberration correction with dual deformable optical elements – Variable Focus Lens (VFL) for defocus and a Multi-Actuator Adaptive Lens (MAL) for two astigmatisms. For retinal vasculature imaging, MSM-SAO-OCT system generates flow-specific contrast as measuring amplitude of complex variance from the multiple OCT B-scans from the same transverse location after stabilizing OCT signals in a phase using a static interference signal from phase calibration interferometer. In addition, the use of polarization diversity detection allows to create Degree Of Polarization Uniformity (DOPU) contrast using for visualization of the Retinal Pigment Epithelium (RPE) with its inherent tissue characteristic (polarization scrambling). In order to demonstrate functionality and clinical utility of the MSM-SAO-OCT system, in vivo human retinal imaging was performed on research subjects, and imaging results are presented and discussed.
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