Importantly, this analysis notes that due to the dual-axis architecture, the depth of field (DOF) of the DA-OCT system is compromised, resulting in a 9-fold decrease in DOF compared to conventional OCT. Further, a detailed diffraction theory analysis suggests that the DA-OCT system offers similar scatter-free axial and lateral resolutions as a conventional co-axial OCT system. Monte Carlo simulations investigating the origin of improved depth performance for DA-OCT have predicted significant signal-to-background ratio (SBR) improvements at most depths. ![]() īuilding off these principles, dual-axis optical coherence tomography (DA-OCT) utilizes a distinct off-axis scanning approach to preferentially detect multiple forward scattered photons to image deep subsurface morphology. Novel imaging geometries which can collect multiply forward scattered photons have the ability to extend the depth penetration of an interferometric imaging system. While these low-order scattering events only introduce minor changes to the propagation trajectories of photons, thus preserving the essential structural tissue information they carry, conventional OCT is not capable of collecting these photons. ![]() Furthermore, the single-backscatter model provides an incomplete description of coherent beam propagation in tissue, and a significant portion of photons passing through the imaging layers only experience small-angle forward scattering. However, the ballistic signal attenuates exponentially, making deep tissue imaging extremely difficult. Conventional OCT imaging relies on detecting ballistic photons, or singly backscattered photons from a specific target layer, to provide near–diffraction-limited resolution. To address this problem, coherence imaging using a dual-axis architecture was introduced in the early 2010s. Unfortunately, most demonstrations of greater penetration depth have been restricted to tissues with high optical transparency, and penetration using the 1.3 µm wavelength band in highly scattering tissue remained in the 0.5-1.2 mm range. Shortly after, the utilization of 1.3 µm light sources led to a marked increase in imaging depth, slightly past 1 mm in biological tissue due to a reduction in scattering at longer wavelengths. Since its first demonstration in 1991, OCT has seen widespread application in the field of ophthalmology due to its micron-scale resolution and depth sectioning capability. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement 1. The results presented here suggest the potential use of DA-OCT in situations where a high degree of scattering limits depth penetration in OCT imaging. This improvement in penetration depth is quantified experimentally against conventional on-axis OCT using tissue phantoms and mouse skin. To overcome this limitation, our approach uses a tunable lens to coordinate focal plane selection with image acquisition to create an enhanced DOF for DA-OCT. Several unique aspects of DA-OCT are examined here, including the requirements for scattering properties to realize the improvement and the limited depth of focus (DOF) inherent to the technique. Here, we present a novel implementation of dual-axis optical coherence tomography (DA-OCT) that offers improved depth penetration in skin imaging at 1.3 µm compared to conventional OCT.
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