We propose a novel method to visualize the integrated birefringence information for polarization-sensitive optical coherence tomography (PS-OCT) of biological tissue. A strategy that integrates the comprehensive birefringence property in a resultant image is introduced to obtain high contrast images of the birefringent samples. Then, color-based automatic segmentation of birefringent components from 3D scanned tissue volume is proposed to isolate the 3D network of the nerve bundles in a whole mouse brain. Experimental validation and demonstrations are given by imaging ex vivo mouse tail and whole brain tissues to show the usefulness of proposed comprehensive birefringent imaging and segmentation methods. These results sufficiently demonstrate the practical usefulness of the proposed strategy of using comprehensive polarization as the imaging parameter in the PS-OCT imaging of biological samples, indicating potential applications in both pre-clinical and clinical environments where accurate identification of birefringent tissue components is important, for example the nerve identification in delicate surgical remove of the diseased tissue mass in surgery.
Swept-source optical coherence tomography (SS-OCT) is gradually out-performing spectral-domain OCT (SD-OCT) in many aspects including sensitivity, speed, and ranging distance. However, its phase-stability is generally more difficult to achieve, compared to SD-OCT, which limited the functional imaging applications of phase-sensitive SSOCT. In this study, a novel phase stabilization technique is demonstrated with significant improvement in the phase stability of an SS-OCT system that is based on micro-electromechanical (MEMS) vertical cavity surface-emitting laser (VCSEL). Without any requirements of hardware modifications, this numerical phase stabilization technique features high tolerance to acquisition jitter, and significantly reduced budget in computational effort. We demonstrate that when measured with biological tissue, this technique enables a phase sensitivity of 89 mrad in highly scattering tissue, with image ranging distance of up to 12.5 mm at A-line scan rate of 100.3 kHz. We further compare the performances delivered by the phase-stabilization approach with conventional numerical approach for accuracy and computational efficiency. Imaging result of complex signal-based optical coherence tomography angiography (OCTA) and Doppler OCTA indicate that the proposed phase stabilization technique is robust, and efficient in improving the image contrast-to-noise ratio and extending OCTA depth range. The proposed technique can be universally applied to improve phase-stability in generic SS-OCT with different scale of scan rates without special hardware or extra imaging operations.
There is an increasing demand for imaging tools in clinical dermatology that can perform in vivo wide-field morphological and functional examination from surface to deep tissue regions at various skin sites of the human body. The conventional spectral-domain optical coherence tomography-based angiography (SD-OCTA) system is difficult to meet these requirements due to its fundamental limitations of the sensitivity roll-off, imaging range as well as imaging speed. To mitigate these issues, we demonstrate a swept-source OCTA (SS-OCTA) system by employing a swept source based on a vertical cavity surface-emitting laser. A series of comparisons between SS-OCTA and SD-OCTA are conducted. Benefiting from the high system sensitivity, long imaging range, and superior roll-off performance, the SS-OCTA system is demonstrated with better performance in imaging human skin than the SD-OCTA system. We show that the SS-OCTA permits remarkable deep visualization of both structure and vasculature (up to ∼2 mm penetration) with wide field of view capability (up to 18×18 mm2), enabling a more comprehensive assessment of the morphological features as well as functional blood vessel networks from the superficial epidermal to deep dermal layers. It is expected that the advantages of the SS-OCTA system will provide a ground for clinical translation, benefiting the existing dermatological practice.
Most of current OCT-based angiography suffers from small FOV with short imaging range. Here we implement an
ultralong-range OCT system for vascular imaging based on an akinetic swept source. This swept-source OCT (SS-OCT)
system enables us to achieve up to 46 mm long imaging range with unprecedented roll-off performance. To compare
with traditional spectral domain OCT (SD-OCT) system, we demonstrated the vascular imaging of the entire mice brain
with wide FOV by this ultralong-range SS-OCT system and captured the blood flow images at different depth position,
which shows the great advantages and bright future of this ultralong-range SS-OCT in vascular imaging.
Video-rate volumetric optical coherence tomography (vOCT) is relatively young in the field of OCT imaging but has great potential in biomedical applications. Due to the recent development of the MHz range swept laser sources, vOCT has started to gain attention in the community. Here, we report the first in vivo video-rate volumetric OCT-based microangiography (vOMAG) system by integrating an 18-kHz resonant microelectromechanical system (MEMS) mirror with a 1.6-MHz FDML swept source operating at ∼1.3 μm wavelength. Because the MEMS scanner can offer an effective B-frame rate of 36 kHz, we are able to engineer vOMAG with a video rate up to 25 Hz. This system was utilized for real-time volumetric in vivo visualization of cerebral microvasculature in mice. Moreover, we monitored the blood perfusion dynamics during stimulation within mouse ear in vivo. We also discussed this system’s limitations. Prospective MEMS-enabled OCT probes with a real-time volumetric functional imaging capability can have a significant impact on endoscopic imaging and image-guided surgery applications.
We demonstrate in vivo volumetric optical microangiography at ∼200 volumes/s by the use of 1.6 MHz Fourier domain mode-locking swept source optical coherence tomography and an effective 36 kHz microelectromechanical system (MEMS) scanner. We propose an intervolume analysis strategy to contrast the dynamic blood flow signal from the static tissue background. The proposed system is demonstrated by imaging cerebral blood flow in mice in vivo. For the first time, imaging speed, sensitivity, and temporal resolution become possible for a direct four-dimensional observation of microcirculations within live body parts.
Routine procedures in standard histopathology involve laborious steps of tissue processing and staining for final examination. New techniques which can bypass these procedures and thus minimize the tissue handling error would be of great clinical value. Coherent anti-Stokes Raman scattering (CARS) microscopy is an attractive tool for label-free biochemical-specific characterization of biological specimen. However, a vast majority of prior works on CARS (or stimulated Raman scattering (SRS)) bioimaging restricted analyses on a narrowband or well-distinctive Raman spectral signatures. Although hyperspectral SRS/CARS imaging has recently emerged as a better solution to access wider-band spectral information in the image, studies mostly focused on a limited spectral range, e.g. CH-stretching vibration of lipids, or non-biological samples. Hyperspectral image information in the congested fingerprint spectrum generally remains untapped for biological samples. In this regard, we further explore ultrabroadband hyperspectral multiplex (HM-CARS) to perform chemoselective histological imaging with the goal of exploring its utility in stain-free clinical histopathology. Using the supercontinuum Stokes, our system can access the CARS spectral window as wide as >2000cm-1. In order to unravel the congested CARS spectra particularly in the fingerprint region, we first employ a spectral phase-retrieval algorithm based on Kramers–Kronig (KK) transform to minimize the non-resonant background in the CARS spectrum. We then apply principal component analysis (PCA) to identify and map the spatial distribution of different biochemical components in the tissues. We demonstrate chemoselective HM-CARS imaging of a colon tissue section which displays the key cellular structures that correspond well with standard stained-tissue observation.
Optical imaging based on time-stretch process has recently been proven as a powerful tool for delivering ultra-high
frame rate (< 1MHz) which is not achievable by the conventional image sensors. Together with the capability of optical
image amplification for overcoming the trade-off between detection sensitivity and speed, this new imaging modality is
particularly valuable in high-throughput biomedical diagnostic practice, e.g. imaging flow cytometry. The ultra-high
frame rate in time-stretch imaging is attained by two key enabling elements: dispersive fiber providing the time-stretch
process via group-velocity-dispersion (GVD), and electronic digitizer. It is well-known that many biophotonic
applications favor the spectral window of ~1μm. However, reasonably high GVD (< 0.1 ns/nm) in this range can only be
achieved by using specialty single-mode fiber (SMF) at 1μm. Moreover, the ultrafast detection has to rely on the state-of-
the-art digitizer with significantly wide-bandwidth and high sampling rate (e.g. <10 GHz, <40 GS/s). These stringent
requirements imply the prohibitively high-cost of the system and hinder its practical use in biomedical diagnostics. We
here demonstrate two cost-effective approaches for realizing time-stretch confocal microscopy at 1μm: (i) using the
standard telecommunication SMF (e.g. SMF28) to act as a few-mode fiber (FMF) at 1μm for the time-stretch process,
and (ii) implementing the pixel super-resolution (SR) algorithm to restore the high-resolution (HR) image when using a
lower-bandwidth digitizer. By using a FMF (with a GVD of ~ 0.15ns/nm) and a modified pixel-SR algorithm, we can
achieve time-stretch confocal microscopy at 1μm with cellular resolution (~ 3μm) at a frame rate 1 MHz.
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