Endoscopic Optical Coherence Tomography Imaging Research Articles

Quantification of attenuation and speckle features from endoscopic OCT images for the diagnosis of human brain glioma

Application of optical coherence tomography (OCT) in neurosurgery mostly includes the discrimination between intact and malignant tissues aimed at the detection of brain tumor margins. For particular tissue types, the existing approaches demonstrate low performance, which stimulates the further research for their improvement. The analysis of speckle patterns of brain OCT images is proposed to be taken into account for the discrimination between human brain glioma tissue and intact cortex and white matter. The speckle properties provide additional information of tissue structure, which could help to increase the efficiency of tissue differentiation. The wavelet analysis of OCT speckle patterns was applied to extract the power of local brightness fluctuations in speckle and its standard deviation. The speckle properties are analysed together with attenuation ones using a set of ex vivo brain tissue samples, including glioma of different grades. Various combinations of these features are considered to perform linear discriminant analysis for tissue differentiation. The results reveal that it is reasonable to include the local brightness fluctuations at first two wavelet decomposition levels in the analysis of OCT brain images aimed at neurosurgical diagnosis.

ATN-Res2Unet: an advanced deep learning network for the elimination of saturation artifacts in endoscopy optical coherence tomography

Endoscopic optical coherence tomography (OCT) possesses the capability to non-invasively image internal lumens; however, it is susceptible to saturation artifacts arising from robust reflective structures. In this study, we introduce an innovative deep learning network, ATN-Res2Unet, designed to mitigate saturation artifacts in endoscopic OCT images. This is achieved through the integration of multi-scale perception, multi-attention mechanisms, and frequency domain filters. To address the challenge of obtaining ground truth in endoscopic OCT, we propose a method for constructing training data pairs. Experimental in vivo data substantiates the effectiveness of ATN-Res2Unet in reducing diverse artifacts while preserving structural information. Comparative analysis with prior studies reveals a notable enhancement, with average quantitative indicators increasing by 45.4–83.8%. Significantly, this study marks the inaugural exploration of leveraging deep learning to eradicate artifacts from endoscopic OCT images, presenting considerable potential for clinical applications.

Virtual Hall sensor triggered multi-MHz endoscopic OCT imaging for stable real-time visualization.

Circumferential scanning in endoscopic imaging is crucial across various disciplines, and optical coherence tomography (OCT) is often the preferred choice due to its high-speed, high-resolution, and micron-scale imaging capabilities. Moreover, real-time and high-speed 3D endoscopy is a pivotal technology for medical screening and precise surgical guidance, among other applications. However, challenges such as image jitter and non-uniform rotational distortion (NURD) are persistent obstacles that hinder real-time visualization during high-speed OCT procedures. To address this issue, we developed an innovative, low-cost endoscope that employs a brushless DC motor for scanning, and a sensorless technique for triggering and synchronizing OCT imaging with the scanning motor. This sensorless approach uses the motor's electrical feedback (back electromotive force, BEMF) as a virtual Hall sensor to initiate OCT image acquisition and synchronize it with a Fourier Domain Mode-Locked (FDML)-based Megahertz OCT system. Notably, the implementation of BEMF-triggered OCT has led to a substantial reduction in image jitter and NURD (<4 mrad), thereby opening up a new window for real-time visualization capabilities. This approach suggests potential benefits across various applications, aiming to provide a more accurate, deployable, and cost-effective solution. Subsequent studies can explore the adaptability of this system to specific clinical scenarios and its performance under practical endoscopic conditions.

Automatic 3D reconstruction of an anatomically correct upper airway from endoscopic long range OCT images.

Endoscopic airway optical coherence tomography (OCT) is a non-invasive and high resolution imaging modality for the diagnosis and analysis of airway-related diseases. During OCT imaging of the upper airway, in order to reliably characterize its 3D structure, there is a need to automatically detect the airway lumen contour, correct rotational distortion and perform 3D airway reconstruction. Based on a long-range endoscopic OCT imaging system equipped with a magnetic tracker, we present a fully automatic framework to reconstruct the 3D upper airway model with correct bending anatomy. Our method includes an automatic segmentation method for the upper airway based on dynamic programming algorithm, an automatic initial rotation angle error correction method for the detected 2D airway lumen contour, and an anatomic bending method combined with the centerline detected from the magnetically tracked imaging probe. The proposed automatic reconstruction framework is validated on experimental datasets acquired from two healthy adults. The result shows that the proposed framework allows the full automation of 3D airway reconstruction from OCT images and thus reveals its potential to improve analysis efficiency of endoscopic OCT images.

Triple-clad W-type fiber mitigates multipath artifacts in multimodal optical coherence tomography.

Multimodal endoscopic optical coherence tomography (OCT) can be implemented with double-clad fiber by using the presumed single-mode core for OCT and the higher numerical aperture cladding for a secondary modality. However, the quality of OCT in double-clad fiber (DCF) based systems is compromised by the introduction of multipath artifacts that are nt present in single-mode fiber OCT systems. Herein, the mechanisms for multipath artifacts in DCF are linked to its modal contents using a commercial software package and experimental measurement. A triple-clad W-type fiber is proposed as a method for achieving multimodal imaging with single-mode quality OCT in an endoscopic system. Simulations of the modal contents of a W-type fiber are compared to DCF and single-mode fiber. Finally, a W-Type fiber rotary catheter is used in a DCF-based endoscopic OCT and autofluorescence imaging (AFI) system to demonstrate multipath artifact free OCT and AFI of a human fingertip.

Scanning optimization of an electrothermally-actuated MEMS mirror for applications in optical coherence tomography endoscopy

Probe is an important component of the optical coherence tomography (OCT) system. Electrothermally-actuated micro-electromechanical (MEMS) mirrors are especially suitable for OCT endoscopic imaging due to their large scan angle, low driving voltage and high fill factor. However, endoscopic OCT imaging quality would be seriously affected by the nonlinear scanning characteristics of electrothermal MEMS mirrors as well as the distortion due to the need of placing the MEMS mirror on a 45° slope. In this work, an open-loop control method based on the transfer function of the MEMS mirror is proposed to optimize the overall optical trajectory scanned on the sample under a MEMS OCT probe. The transfer function of the electrothermal MEMS mirror is established and the relation between the MEMS mirror’s tilt angle and the final scanning trajectory on the sample is calculated. A PID control model based on the transfer function is developed and employed to generate the driving voltage signals that can be applied to the MEMS mirror for obtaining undistorted scanning trajectories on the sample. Experiments show that the proposed method can correct the scanning nonlinearity and the distortion without adding extra hardware. For instance, the linear scanning ratio is improved from 72% up to 98%; the fan-shaped distortion is reduced by a factor 3–5. This method is also applied to a swept-source OCT system and the image distortions are compensated effectively.

Stick-slip nonuniform rotation distortion correction in distal scanning optical coherence tomography catheters

We present a robust and fiducial-marker-free algorithm that can identify and correct stick-slip distortion caused by nonuniform rotation (or beam scanning) in distally scanned catheters for endoscopic optical coherence tomography (OCT) images. This algorithm employs spatial frequency analysis to select and remove distortions. We demonstrate the feasibility of this algorithm on images acquired from ex vivo rat colon with a distally scanned DC motor-based endoscope. The proposed algorithm can be applied to general endoscopic OCT images for correcting nonuniform rotation distortion.

Side-viewing endoscopic imaging probe for swept source optical coherence tomography

Endoscopic optical coherence tomography (OCT) has many promising applications in the fields of medical research and clinical diagnosis. In this letter, we present a side-viewing endoscopic OCT probe based on a gradient index (GRIN) lens with an air gap. By adjusting the length of the air gap the optical performance of the probe can be flexibly tuned. The quantitative relationships between the optical performance parameters of the probe and its structural parameters are theoretically analyzed by using the ABCD beam transfer matrix theory. The developed probe has a maximum diameter of 1.4 mm and a rigid length of 11 mm. The working distance and the spot size of the probe are measured to be 2.71 mm and 21.24 μm respectively. An endoscopic swept source OCT (SS-OCT) imaging system with an adjustable axial scan rate is built which can flexibly match the rotational scanning speed of the probe. The circumferential OCT images of the tape and the biological tissue are acquired and reconstructed.

Automatic three-dimensional segmentation of endoscopic airway OCT images

Automatic delineation and segmentation of airway structures from endoscopic optical coherence tomography (OCT) images improve image analysis efficiency and thus has been of particular interest. Conventional two-dimensional automatic segmentation methods, such as the dynamic programming approach, ensures the edge-continuity in the xz-direction (intra-B-scan), but fails to preserve the surface-continuity when concerning the y-direction (inter-B-scan). To solve this, we present a novel automatic three-dimensional (3D) airway segmentation strategy. Our segmentation scheme includes an artifact-oriented pre-processing pipeline and a modified 3D optimal graph search algorithm incorporating adaptive tissue-curvature adjustment. The proposed algorithm is tested on endoscopic airway OCT image data sets acquired by different swept-source OCT platforms, and on different animal and human models. With our method, the results show continuous surface segmentation performance, which is both robust and accurate.

Miniature all-fiber axicon probe with extended Bessel focus for optical coherence tomography.

The trade-off between lateral resolution and depth of focus (DOF) severely limits the capability of endoscopic optical coherence tomography (OCT) for high-resolution deep-tissue imaging. To address this issue, we developed a novel miniature all-fiber axicon OCT probe by inserting a segment of gradient-index (GRIN) fiber between a piece of single-mode fiber (SMF) and an axicon polished from a no-core fiber. The GRIN lens served as a beam expander extending the probe DOF by 5.2 times while maintaining a high lateral resolution of 2 μm. The DOF extension was experimentally verified by measuring the axial profile of the probe output beam and further by imaging multilayered polymer tapes and onion samples. The designed probe with a tight focus over a large DOF holds great potential in endoscopic OCT imaging of deep tissues at the cellular level.

Multimodality endoscopic optical coherence tomography and fluorescence imaging technology for visualization of layered architecture and subsurface microvasculature.

Endoscopic imaging technologies, such as endoscopic optical coherence tomography (OCT) and near-infrared fluorescence, have been used to investigate vascular and morphological changes as hallmarks of early cancer in the gastrointestinal tract. Here we developed a high-speed multimodality endoscopic OCT and fluorescence imaging system. Using this system, the architectural morphology and vasculature of the rectum wall were obtained simultaneously from a Sprague Dawley rat in vivo. This multimodality imaging strategy in a single imaging system permits the use of a single imaging probe, thereby improving prognosis by early detection and reducing costs.

Endoscopic optical coherence tomography with a flexible fiber bundle.

We demonstrate in vivo endoscopic optical coherence tomography (OCT) imaging in the forward direction using a flexible fiber bundle (FB). In comparison to current conventional forward-looking probe schemes, our approach simplifies the endoscope design by avoiding the integration of any beam steering components in the distal probe end due to two-dimensional scanning of a focused light beam over the proximal FB surface. We describe the challenges that arise when OCT imaging with an FB is performed, such as multimoding or cross coupling. The performance of different FBs varying in parameters, such as numerical aperture, core size, core structure, and flexibility, was consequently compared, and image quality degrading artifacts were described in detail. Based on our findings, we propose an optimal FB design for endoscopic OCT imaging.

Broadband rotary joint for high-speed ultrahigh-resolution endoscopic OCT imaging at 800 nm

We report the development of a broadband rotary joint for high-speed ultrahigh-resolution endoscopic optical coherence tomography (OCT) imaging in the 800nm spectral range. This rotary joint features a pair of achromatic doublets in order to achieve broadband operation for a 3dB bandwidth over 150nm. The measured one-way throughput of the rotary joint is greater than 80%, while the fluctuation of the double-pass coupling efficiency during 360deg rotation is less than ±5% at a near video-rate speed of 20 revolutions/s (rps). The rotary joint is used in conjunction with a diffractive-optics-based endoscope and 800nm spectral domain OCT system and achieved an ultrahigh axial resolution of ∼2.4 μm in air. The imaging performance is demonstrated by 3D circumferential imaging of a mouse colon in vivo.

Super-achromatic monolithic microprobe for ultrahigh-resolution endoscopic optical coherence tomography at 800\u2009nm

Endoscopic optical coherence tomography (OCT) has emerged as a valuable tool for advancing our understanding of the histomorphology of various internal luminal organs and studying the pathogenesis of relevant diseases. To date, this technology affords limited resolving power for discerning subtle pathological changes associated with early diseases. In addition, it remains challenging to access small luminal organs or pass through narrow luminal sections without potentially causing trauma to tissue with a traditional OCT endoscope of a 1-1.5 mm diameter. Here we report an ultracompact (520 µm in outer diameter and 5 mm in rigid length) and super-achromatic microprobe made with a built-in monolithic fiber-optic ball lens, which achieves ultrahigh-resolution (1.7 µm axial resolution in tissue and 6 µm transverse resolution) for endoscopic OCT imaging at 800 nm. Its performance and translational potential are demonstrated by in vivo imaging of a mouse colon, a rat esophagus, and small airways in sheep.

In‐line optical fiber metallic mirror reflector for monolithic common path optical coherence tomography probes

Endoscopic optical coherence tomography probes suffer from various artifacts due to dispersion imbalance and polarization mismatch between reference and sample arm light. Such artifacts can be minimized using a common path approach. In this work, we demonstrate a miniaturized common path probe for optical coherence tomography using an inline fiber mirror. A common path optical fiber probe suitable for performing high-resolution endoscopic optical coherence tomography imaging was developed. To achieve common path functionality, an inline fiber mirror was fabricated using a thin gold layer. A commercially available swept source engine was used to test the designed probe in a cadaver human coronary artery ex vivo. We achieved a sensitivity of 104 dB for this probe using a swept source optical coherence tomography system. To test the probe, images of a cadaver human coronary artery were obtained, demonstrating the quality that is comparable to those obtained by OCT systems with separate reference arms. Additionally, we demonstrate recovery of ranging depth by use of a Michelson interferometer in the detection path. We developed a miniaturized monolithic inline fiber mirror-based common path probe for optical coherence tomography. Owing to its simplicity, our design will be helpful in endoscopic applications that require high-resolution probes in a compact form factor while reducing system complexity. Lasers Surg. Med. 50:230-235, 2018. © 2017 Wiley Periodicals, Inc.

Miniaturized Fourier-plane fiber scanner for OCT endoscopy

A forward-looking endoscopic optical coherence tomography (OCT) probe featuring a Fourier-plane fiber scanner is designed, manufactured and characterized. In contrast to common image-plane fiber scanners, the Fourier-plane scanner is a telecentric arrangement that eliminates vignetting and spatial resolution variations across the image plane. To scan the OCT beam in a spiral pattern, a tubular piezoelectric actuator is used to resonate an optical fiber bearing a collimating GRIN lens at its tip. The free-end of the GRIN lens sits at the back focal plane of an objective lens, such that its rotation replicates the beam angles in the collimated region of a classical telecentric 4f optical system. Such an optical arrangement inherently has a low numerical aperture combined with a relatively large field-of-view, rendering it particularly useful for endoscopic OCT imaging. Furthermore, the optical train of the Fourier-plane scanner is shorter than that of a comparable image-plane scanner by one focal length of the objective lens, significantly shortening the final arrangement. As a result, enclosed within a 3D printed housing of 2.5 mm outer diameter and 15 mm total length, the developed probe is the most compact forward-looking endoscopic OCT imager to date. Due to its compact form factor and compatibility with real-time OCT imaging, the developed probe is also ideal for use in the working channel of flexible endoscopes as a potential optical biopsy tool.

Automatic and robust segmentation of endoscopic OCT images and optical staining.

We report a generic method for automatic segmentation of endoscopic optical coherence tomography (OCT) images. In this method, OCT images are first processed with L1 -L0 norm minimization based de-noising and smoothing algorithms to increase the signal-to-noise ratio (SNR) and enhance the contrast between adjacent layers. The smoothed images are then formulated into cost graphs based on their vertical gradients. After that, tissue-layer segmentation is performed with the shortest path search algorithm. The efficacy and capability of this method are demonstrated by automatically and robustly identifying all five interested layers of guinea pig esophagus from in vivo endoscopic OCT images. Furthermore, thanks to the ultrahigh resolution, high SNR of endoscopic OCT images and the high segmentation accuracy, this method permits in vivo optical staining histology and facilitates quantitative analysis of tissue geometric properties, which can be very useful for studying tissue pathologies and potentially aiding clinical diagnosis in real time.

Optimal operational conditions for supercontinuum-based ultrahigh-resolution endoscopic OCT imaging.

We investigated the optimal operational conditions for utilizing a broadband supercontinuum (SC) source in a portable 800 nm spectral-domain (SD) endoscopic OCT system to enable high resolution, high-sensitivity, and high-speed imaging in vivo. A SC source with a 3-dB bandwidth of ∼246 nm was employed to obtain an axial resolution of ∼2.7 μm (in air) and an optimal detection sensitivity of ∼-107 dB with an imaging speed up to 35 frames/s (at 70 k A-scans/s). The performance of the SC-based SD-OCT endoscopy system was demonstrated by imaging guinea pig esophagus in vivo, achieving image quality comparable to that acquired with a broadband home-built Ti:sapphire laser.

Simultaneous dual-band optical coherence tomography for endoscopic applications.

Dual-band optical coherence tomography (OCT) can greatly enhance the imaging contrast with potential applications in functional (spectroscopic) analysis. A new simultaneous dual-band Fourier domain mode-locked swept laser configuration for dual-band OCT is reported. It was based on a custom-designed dual-channel driver to synchronize two different wavelength bands at 1310 and 1550 nm, respectively. Two lasing wavelengths were swept simultaneously from 1260 to 1364.8 nm for the 1310-nm band and from 1500 to 1604 nm for the 1550-nm band at an A-scan rate of 45 kHz. Broadband wavelength-division multiplexing was utilized to couple two wavelength bands into a common catheter for circumferential scanning to form dual-band OCT. The proposed dual-band OCT scheme was applied to endoscopic OCT imaging of mouse esophageal wall ex vivo and human fingertip in vivo to justify the feasibility of the proposed imaging technique. The proposed dual-band OCT system is fast and easy to be implemented, which allows for in vivo high-speed biomedical imaging with potential applications in spectroscopic investigations for endoscopic imaging.

Diffractive catheter for ultrahigh-resolution spectral-domain volumetric OCT imaging

We present a novel design for an endoscopic imaging catheter utilizing diffractive optics for ultrahigh-resolution optical coherence tomography (OCT) imaging at 800 nm. A diffractive microlens was developed to alleviate severe chromatic aberration when a broadband light source was employed at the 800 nm wavelength range. Combined with a home-built fiber rotary joint and a broadband Ti:sapphire laser, the imaging catheter achieved a lateral resolution of 6.2 μm and an axial resolution of 3.0 μm in air. The performance of the catheter was demonstrated by three-dimensional full-circumferential endoscopic OCT imaging of guinea pig esophagus in vivo.