Real Time and Full-range Complex Fourier Domain Optical Coherence Tomography

Numerical analysis of one-shot full-range FD-OCT system based on orthogonally polarized light

We report a new yet simple method to achieve full-range complex Fourier-domain optical coherence tomography (OCT) for in vivo imaging. The method utilizes a scanner that is dedicated for lateral scanning in the system to introduce a constant carrier frequency into the OCT spectral interferograms during the scanning. This is achieved by simply offsetting the sampling beam spot away from the pivot point of the scanning mirror. We demonstrate the method experimentally for in vivo full-range imaging of the anterior segment of a human eye. The method is free from complex conjugate mirror image and self-cross-correlation image artifacts.

Agreement between Fourier-domain and swept-source optical coherence tomography used for optic nerve head measurements

To describe key developments of optical biometry and optical coherence tomography (OCT) for ophthalmic applications made by one of the pioneering research groups. Partial coherence interferometry (PCI) as the basic ranging technology for modern optical biometry and for OCT was introduced for biomedical applications in the 1980s. Later, Fourier domain (FD) OCT was introduced and demonstrated to provide superior sensitivity as compared to time domain OCT. Further developments comprised ultrahigh-resolution OCT and deep-penetration OCT at wavelengths of approximately 1050 nm. Important functional extensions comprise Doppler OCT/OCT angiography, polarization-sensitive OCT, and adaptive optics OCT. High-precision PCI biometry has found extensive applications in cataract surgery and in research on intraocular lens design. Optical coherence tomography, especially in the second-generation variant of FD OCT, is now indispensable for ocular diagnostics in general and for retinal diagnostics in particular; 1050 nm OCT shows improved penetration into deeper layers like the choroid. The contributions of the Vienna research group helped to establish PCI biometry and FD OCT as the gold standards in their respective fields.

We present a full-range Fourier-domain optical coherence tomography (OCT) system that is capable of acquiring two-dimensional images of living tissue in a single shot. By using line illumination of the sample in combination with a two-dimensional imaging spectrometer, 1040 depth scans are performed simultaneously on a sub-millisecond timescale. Furthermore, we demonstrate an easy and flexible real-time single-shot technique for full-range (complex-conjugate cancelled) OCT imaging that is compatible with both two-dimensional as well as ultrahigh-resolution OCT. By implementing a dispersion imbalance between reference and sample arms of the interferometer, we eliminate the complex-conjugate signal through numerical dispersion compensation, effectively increasing the useful depth range by a factor of two. The system allows us to record 6.7 x 3.2 mm images at 5 microm depth resolution in 0.2 ms. Data postprocessing requires only 4 s. We demonstrate the capability of our system by imaging the anterior chamber of a mouse eye in vitro, as well as human skin in vivo.

Transmission optical coherence tomography (tOCT) is gaining interest for imaging biological samples; however, so far, quantitative phase information has not been directly obtained. This study introduces SOPHAST-OCT, an approach for integrated 2D phase recovery in Off-Axis Full-Field Swept-Source tOCT. It uses phase-shifting to leverage OCT’s inherent phase changes between recorded interferograms. SOPHAST-OCT demonstrates promising phase agreement with the simulated ground truth phase. This approach represents a first step toward quantitative imaging in tOCT. Full Text: PDF References Y. Park, C. Depeursinge, G. Popescu, "Quantitative phase imaging in biomedicine", Nature Photon 12, 578 (2018). CrossRef K. Alm, H. Cirenajwis, L. Gisselsson, A.G. Wingren, B. Janicke, A. Mölder, et al., in Holography, Research and Technologies (IntechOpen, 2011). CrossRef W. Drexler, J. Fujimoto, editors , Optical Coherence Tomography: Technology and Applications, 2nd ed. (Springer Cham, 2015). CrossRef W. Krauze, P. Ossowski, M. Nowakowski, M. Szkulmowski, M. Kujawińska, "Enhanced QPI functionality by combining OCT and ODT methods", Quantitative Phase Imaging VII, 11653, 19 (2021). CrossRef B.C. Wilson, S.L. Jacques, "Optical reflectance and transmittance of tissues: principles and applications", IEEE J. Quantum Electron. 26, 2186 (1990). CrossRef J. van der Horst, A.K. Trull, J. Kalkman, "Deep-tissue label-free quantitative optical tomography", Optica 7, 1682 (2020). CrossRef P. Hosseini, Y. Sung, Y. Choi, N. Lue, Z. Yaqoob, P. So, "Scanning color optical tomography (SCOT)", Opt. Expr. 23, 19752 (2015). CrossRef P. de Groot, "Phase Shifting Interferometry" in Optical Measurement of Surface Topography, edited by R. Leach (Springer, Berlin, Heidelberg, 2011). CrossRef M. Wojtkowski, A. Kowalczyk, R. Leitgeb, A.F. Fercher, "Full range complex spectral optical coherence tomography technique in eye imaging", Opt. Lett. 27, 1415 (2002). CrossRef Q. Zhang, S. Zhong, J. Lin, W. Chen, M. Luo, J. Zhong, Y. Yu, Z. Peng, S. Cheng, "Full-range Fourier-domain optical coherence tomography based on Mach–Zehnder interferometer", Opt. Lasers Engin. 124, 105794 (2020). CrossRef R. Juarez-Salazar, C. Robledo-Sanchez, F. Guerrero-Sanchez, A. Rangel-Huerta, "Generalized phase-shifting algorithm for inhomogeneous phase shift and spatio-temporal fringe visibility variation", Opt. Express 22, 4738 (2014). CrossRef R. Juarez-Salazar, C. Robledo-Sánchez, C. Meneses-Fabian, F. Guerrero-Sánchez, L. M. Arévalo Aguilar, "Generalized phase-shifting interferometry by parameter estimation with the least squares method", Opt. Lasers Engin. 51, 626 (2013). CrossRef M.A. Herráez, D.R. Burton, M.J. Lalor, M.A. Gdeisat, "Fast two-dimensional phase-unwrapping algorithm based on sorting by reliability following a noncontinuous path", Appl. Opt. 41, 7437 (2002). CrossRef Z. Wang, A.C. Bovik, "A universal image quality index", IEEE Signal Proc. Lett. 9, 81 (2002). CrossRef

Long-range Fourier domain optical coherence tomography of the pediatric subglottis

The depth reflectivity profile of Fourier domain optical coherence tomography (FD-OCT) is estimated from the inverse Fourier transform of the spectral interference signals (interferograms). As a result, the axial resolution is fundamentally limited by the coherence length of the light source. We demonstrate that using the autoregressive spectral estimation technique instead of the inverse Fourier transform, to analyze the spectral interferograms can improve the axial resolution. We name this method spectral estimation OCT (SE-OCT). SE-OCT breaks the coherence length limitation and improves the axial resolution by a factor of up to 4.7 compared with FD-OCT. Furthermore, SE-OCT provides complete sidelobe suppression in the depth point-spread function, further improving the image quality. We demonstrate that these technical advances enables clear identification of corneal endothelium anatomical details ex vivo that cannot be identified using the corresponding FD-OCT. Given that SE-OCT can be implemented in the FD-OCT devices without any hardware changes, the new capabilities provided by SE-OCT are likely to offer immediate improvements to the diagnosis and management of diseases based on OCT imaging.

Aim:To report the evolution of pattern scanning laser (Pascal) photocoagulation burns in the treatment of diabetic retinopathy, using Fourier-domain optical coherence tomography (FD-OCT) and fundus autofluorescence (AF), and to evaluate...

Optical design of a spectrometer for all-reflective optics based line scan Fourier domain optical coherence tomography (FD-OCT) imaging has been reported in this work for high-speed scanning. FD-OCT imaging data acquisition offers significantly improved imaging speed in the depth direction compared to conventional time domain optical coherence tomography (TD-OCT). On the other hand, line focused scanning improve imaging speed in the transverse direction compare to commonly used flying spot scanning. Combination of FD-OCT acquisition and line focused scanner can give higher imaging speed. Spectrometer is a critical submodule in FD-OCT system. Apart from the spectrometer optical resolution, and detector array resolution, the chromatic aberration should be considered to design a high-quality FD-OCT imaging spectrometer. The proposed imaging spectrometer consists of a planer reflective grating, off-axis parabolic cylindrical mirror and a CCD array detector. Mirror focusing reduces the chromatic aberration because of its insensitivity to the wavelength of the laser beam, therefore the spectrometer image quality enhanced by the reflective optics focusing. Spot profile fall-off characteristic was analyzed by using ZEMAX optical design software.

Standard high-speed Fourier domain optical coherence tomography (FD-OCT) and a modified version of FD-OCT; a line-field FD-OCT (LF-FDOCT) are demonstrated. LF-FDOCT is using the principle of FD-OCT for its depth resolution and a one-dimensional imaging optics for its one-dimensional lateral resolution. A mechanical C-scan drived by a galvano scanner is introduced into the FD-FDOCT, which shows a cross sectional OCT image without any mechanical scanning. The improved version of FD-OCT visualizes the three-dimensional structure of a sample with only one-dimensional scanning. Both standard FD-OCT and LF-FDOCT are applied to dermatological applications and visualize the inner structure of an in vivo human fingerpad.

To use Fourier-domain optical coherence tomography (FD-OCT) to study the effect of artificial tears on the tear meniscus in patients with dry eyes. The lower tear meniscus of 16 consecutive patients with dry eyes was imaged by an FD-OCT system (RTVue; Optovue, Inc., Fremont, CA). Baseline and five serial pairs of measurements were taken after the instillation of artificial tears (Optive; Allergan, Irvine, CA) at 1, 2, 5, 10, and 15 minutes. The lower meniscus height, depth, and area were measured with a computer caliper. Baseline meniscus measurements were 235.5 ± 150.0 μm, 138.1 ± 78.7 μm, and 0.020 ± 0.022 mm(2) for height, depth, and area, respectively. After instillation of artificial tears, all lower tear meniscus parameters remained significantly elevated for 5 minutes and returned to baseline by 10 minutes. FD-OCT is able to quantify a dramatic initial increase in tear meniscus, followed by a decay back to baseline values after approximately 5 minutes. FD-OCT may be useful in objectively quantifying the dynamic efficacy of dry eye treatments.

We implemented the fast Gaussian gridding (FGG) based nonuniform fast Fourier transform (NUFFT) and complex OCT processing on the graphics processing unit (GPU) architecture for high-speed, real-time Fourier-domain optical coherence tomography (FD-OCT). The Vander monde matrix based non-uniform discrete Fourier transform (NUDFT) as well as the linear/cubic interpolation with fast Fourier transform (InFFT) methods are also implemented on GPU to compare their performance in terms of image quality and processing speed. The GPU accelerated NUDFT/NUFFT are applied to process both the standard half-range FDOCT and complex full-range FD-OCT (C-FD-OCT). GPU-NUFFT provides a very close approximation to GPU-NUDFT in terms of image quality but offers >10 times higher processing speed. Compared with the GPU-InFFT methods, GPU-NUFFT has improved sensitivity fall-off, higher local signal-to-noise ratio and immunity to side lobe artifacts caused by the interpolation error. Using a high speed CMOS line-scan camera, we demonstrated the real-time processing and display of GPU-NUFFT based C-FD-OCT at a camera-limited rate of 122 k line/s (1024 pixel/A-scan).

Blood flow measurement with spectrometer-based Fourier domain optical coherence tomography (FD-OCT) is limited by the motion-induced signal fading and the resulting reduction of flow sensitivity. Therefore, we have numerically simulated the signal power decrease of an obliquely moved scattering layer as a function of the absolute sample velocity composed of an axial and transverse component. In contrast to the prevalent expectance, the resulting signal damping is not only the sum of axial and transverse effect. In this study, we take advantage of the signal decay and present the feasibility to quantify high flow velocities at which the standard Doppler OCT does not work any longer. For the validation of our approach, a flow phantom model consisting of a 1%-Intralipid solution and a 320 μm glass capillary was used. With this phantom study, depth-resolved flow was visualized and the quantitative velocities were extracted from the OCT images without phase information.

AimTo assess circumpapillary retinal vessel density (RVD) profiles and correlate them with retinal nerve fibre layer (RNFL) thickness measured by Fourier domain optical coherence tomography (FD-OCT).MethodsRNFL thickness of 106 healthy...