High-Speed Integrated Endoscopic Photoacoustic and Ultrasound Imaging System.

Endoscopic integrated photoacoustic and ultrasound imaging has the potential for early detection of the cancer in the gastrointestinal tract. Currently, slow imaging speed is one of the limitations for clinical translation. Here, we developed a high speed integrated endoscopic PA and US imaging system, which is able to perform PA and US imaging simultaneously up to 50 frames per second. Using this system, the architectural morphology and vasculature of the rectum wall were visualized from a Sprague Dawley rat in-vivo.

1.7 micron optical coherence tomography for vaginal tissue characterization in vivo.

OBJECTIVES: Optical coherence tomography (OCT) can noninvasively visualize in vivo tissue microstructure with high spatial resolution that approaches the histologic level. Currently, OCT studies in gynecology are few and limited to a conventional 1.3 µm center wavelength swept light source which provides high spatial resolution but limited penetration depth. Here, we present a novel endoscopic OCT system with improved penetration depth and high resolution. METHODS: A novel endoscopic OCT system was developed based on a 1.7 µm swept source laser, which is capable of deeper tissue penetration due to its longer wavelength. To evaluate the performance of system, we imaged the human vaginas in vivo with both conventional 1.3 and 1.7 µm endoscopic OCT systems. RESULTS: With the 1.7 µm endoscopic OCT system, imaging depth was improved by more than 25%, allowing better visualization of the lamina propria and clear contrast of the epithelial layer from the surrounding tissues. CONCLUSION: The significantly improved performance of the novel 1.7 µm OCT imaging system demonstrates its potential use as a minimally-invasive monitoring tool of vaginal health in gynecologic practice. Lasers Surg. Med. 51:120-126, 2019. © 2018 Wiley Periodicals, Inc.

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.

Long-Range Optical Coherence Tomography of the Neonatal Upper Airway for Early Diagnosis of Intubation-related Subglottic Injury.

RATIONALE: Subglottic edema and acquired subglottic stenosis are potentially airway-compromising sequelae in neonates following endotracheal intubation. At present, no imaging modality is capable of in vivo diagnosis of subepithelial airway wall pathology as signs of intubation-related injury. OBJECTIVES: To use Fourier domain long-range optical coherence tomography (LR-OCT) to acquire micrometer-resolution images of the airway wall of intubated neonates in a neonatal intensive care unit setting and to analyze images for histopathology and airway wall thickness. METHODS: LR-OCT of the neonatal laryngotracheal airway was performed a total of 94 times on 72 subjects (age, 1-175 d; total intubation, 1-104 d). LR-OCT images of the airway wall were analyzed in MATLAB. Medical records were reviewed retrospectively for extubation outcome. MEASUREMENTS AND MAIN RESULTS: Backward stepwise regression analysis demonstrated a statistically significant association between log(duration of intubation) and both laryngeal (P < 0.001; multiple r(2) = 0.44) and subglottic (P < 0.001; multiple r(2) = 0.55) airway wall thickness. Subjects with positive histopathology on LR-OCT images had a higher likelihood of extubation failure (odds ratio, 5.9; P = 0.007). Longer intubation time was found to be significantly associated with extubation failure. CONCLUSIONS: LR-OCT allows for high-resolution evaluation and measurement of the airway wall in intubated neonates. Our data demonstrate a positive correlation between laryngeal and subglottic wall thickness and duration of intubation, suggestive of progressive soft tissue injury. LR-OCT may ultimately aid in the early diagnosis of postintubation subglottic injury and help reduce the incidences of failed extubation caused by subglottic edema or acquired subglottic stenosis in neonates. Clinical trial registered with www.clinicaltrials.gov (NCT 00544427).

Trimodality imaging system and intravascular endoscopic probe: combined optical coherence tomography, fluorescence imaging and ultrasound imaging.

In this Letter, we present a trimodality imaging system and an intravascular endoscopic probe for the detection of early-stage atherosclerotic plaques. The integrated system is able to acquire optical coherence tomography (OCT), fluorescence, and ultrasound images and simultaneously display them in real time. A trimodality intravascular endoscopic probe of 1.2 mm in diameter and 7 mm in length was fabricated based on a dual-modality optical probe that integrates OCT and fluorescence imaging functions and a miniature ultrasound transducer. The probe is capable of rotating at up to 600 rpm. Ex vivo images from rabbit aorta and human coronary arteries showed that this combined system is capable of providing high resolution, deep penetration depth and specific molecular fluorescence contrast simultaneously.

Long-range optical coherence tomography of pediatric airway during drug induced sleep endoscopy: A preliminary report.

OBJECTIVE: Drug induced sleep endoscopy (DISE) is often performed for pediatric obstructive sleep apnea (OSA) when initial diagnostic studies do not provide adequate information for therapy. However, DISE scoring is subjective and with limitations. This proof-of-concept study demonstrates the use of a novel long-range optical coherence tomography (LR-OCT) system during DISE of two pediatric patients. METHODS: LR-OCT was used to visualize the airway of pediatric patients during DISE. At the conclusion of DISE, the OCT probe was guided in the airway under endoscopic visual guidance, and cross-sectional images were acquired at the four VOTE locations. Data processing involved image resizing and alignment, followed by rendering of three-dimensional (3D) volumetric models of the airways. RESULTS: Two patients were included in this study. Patient one had 18.4%, 20.9%, 72.3%, and 97.3% maximal obstruction at velum, oropharynx, tongue base, and epiglottis, while patient two had 40.2%, 41.4%, 8.0%, and 17.5% maximal obstruction at these regions, respectively. Three-dimensional reconstructions of patients' airways were also constructed from the OCT images. CONCLUSION: This proof-of-concept study demonstrates the successful evaluation of pediatric airway during DISE using LR-OCT, which accurately identified sites and degrees of obstruction with respective 3D airway reconstruction.

Phase-resolved dynamic wavefront imaging of cilia metachronal waves.

Background: The coordination and the directional order of ciliary metachronal waves are the major factors that determine the effectiveness of mucociliary clearance (MCC). Even though metachronal waves play an essential part in immune response, clinical diagnostic tools and imaging techniques that can reliably and efficiently capture their spatial distribution and function are currently limited. Methods: We present label-free high-speed visualization of ciliary metachronal wave propagations in freshly-excised tracheal explants using a spectrally-encoded interferometric microscope over a two-dimensional (2D) plane of 0.5 mm × 0.5 mm at an acquisition rate of 50 frame-per-second. Furthermore, phase-resolved enhanced dynamic (PHRED) analysis of time-series doppler images was performed, where spatial-temporal characteristics of cilia metachronal wave motions are revealed through frequency component analysis and spatial filtering. Results: The PHRED analysis of phase-resolved Doppler (PRD) images offers a capability to distinguish the propagation direction of metachronal waves, and quantitatively assess amplitude and dominant frequency of cilia beating at each spatial location. Compared to the raw PRD images, the phase-resolved dynamic wavefront imaging (PRDWI) method showed the direction and coordination of collective cilia movement more distinctively. Conclusions: The PRDWI technique can have broad application prospects for the diagnosis of human respiratory diseases and evaluation of the curative effect of treatments and open new perspectives in biomedical sciences.

Ultrafast and hypersensitive phase imaging of propagating internodal current flows in myelinated axons and electromagnetic pulses in dielectrics.

Many ultrafast phenomena in biology and physics are fundamental to our scientific understanding but have not yet been visualized owing to the extreme speed and sensitivity requirements in imaging modalities. Two examples are the propagation of passive current flows through myelinated axons and electromagnetic pulses through dielectrics, which are both key to information processing in living organisms and electronic devices. Here, we demonstrate differentially enhanced compressed ultrafast photography (Diff-CUP) to directly visualize propagations of passive current flows at approximately 100 m/s along internodes, i.e., continuous myelinated axons between nodes of Ranvier, from Xenopus laevis sciatic nerves and of electromagnetic pulses at approximately 5 × 107 m/s through lithium niobate. The spatiotemporal dynamics of both propagation processes are consistent with the results from computational models, demonstrating that Diff-CUP can span these two extreme timescales while maintaining high phase sensitivity. With its ultrahigh speed (picosecond resolution), high sensitivity, and noninvasiveness, Diff-CUP provides a powerful tool for investigating ultrafast biological and physical phenomena.

Graph-based rotational nonuniformity correction for localized compliance measurement in the human nasopharynx.

Recent advancements in the high-speed long-range optical coherence tomography (OCT) endoscopy allow characterization of tissue compliance in the upper airway, an indicator of collapsibility. However, the resolution and accuracy of localized tissue compliance measurement are currently limited by the lack of a reliable nonuniform rotational distortion (NURD) correction method. In this study, we developed a robust 2-step NURD correction algorithm that can be applied to the dynamic OCT images obtained during the compliance measurement. We demonstrated the utility of the NURD correction algorithm by characterizing the local compliance of nasopharynx from an awake human subject for the first time.

Spatio-temporal-spectral imaging of non-repeatable dissipative soliton dynamics.

Dissipative solitons (DSs) are multi-dimensionally localized waves that arise from complex dynamical balances in far-from-equilibrium nonlinear systems and widely exist in physics, chemistry and biology. Real-time observations of DS dynamics across many dimensions thus have a broad impact on unveiling various nonlinear complexities in different fields. However, these observations are challenging as DS transitions are stochastic, non-repeatable and often strongly coupled across spatio-temporal-spectral (STS) domains. Here we report multi-dimensional (space xy + discrete time t + wavelength λ) DS dynamics imaged by STS compressed ultrafast photography, enabling imaging at up to trillions of frames per second. Various transient and random phenomena of multimode DSs are revealed, highlighting the importance of real-time multi-dimensional observation without the need for event repetition in decomposing the complexities of DSs.

Harnessing a multi-dimensional fibre laser using genetic wavefront shaping.

The multi-dimensional laser is a fascinating platform not only for the discovery and understanding of new higher-dimensional coherent lightwaves but also for the frontier study of the complex three-dimensional (3D) nonlinear dynamics and solitary waves widely involved in physics, chemistry, biology and materials science. Systemically controlling coherent lightwave oscillation in multi-dimensional lasers, however, is challenging and has largely been unexplored; yet, it is crucial for both designing 3D coherent light fields and unveiling any underlying nonlinear complexities. Here, for the first time, we genetically harness a multi-dimensional fibre laser using intracavity wavefront shaping technology such that versatile lasing characteristics can be manipulated. We demonstrate that the output power, mode profile, optical spectrum and mode-locking operation can be genetically optimized by appropriately designing the objective function of the genetic algorithm. It is anticipated that this genetic and systematic intracavity control technology for multi-dimensional lasers will be an important step for obtaining high-performance 3D lasing and presents many possibilities for exploring multi-dimensional nonlinear dynamics and solitary waves that may enable new applications.

Spatial mapping of tracheal ciliary beat frequency using real time phase-resolved Doppler spectrally encoded interferometric microscopy.

Ciliary motion in the upper airway is the primary mechanism by which the body transports foreign particulates out of the respiratory system in order to maintain proper respiratory function. The ciliary beating frequency (CBF) is often disrupted with the onset of disease as well as other conditions, such as changes in temperature or in response to drug administration. Current imaging of ciliary motion relies on microscopy and high-speed cameras, which cannot be easily adapted to in-vivo imaging. M-mode optical coherence tomography (OCT) imaging is capable of visualization of ciliary activity, but the field of view is limited. We report on the development of a spectrally encoded interferometric microscopy (SEIM) system using a phase-resolved Doppler (PRD) algorithm to measure and map the ciliary beating frequency within an en face region. This novel high speed, high resolution system allows for visualization of both temporal and spatial ciliary motion patterns as well as propagation of metachronal wave. Rabbit tracheal CBF ranging from 9 to 13 Hz has been observed under different temperature conditions, and the effects of using lidocaine and albuterol have also been measured. This study is the stepping stone to in-vivo studies and the translation of imaging spatial CBF to clinics.

Real-time frequency-encoded spatiotemporal focusing through scattering media using a programmable 2D ultrafine optical frequency comb.

Optical wavefront shaping is a powerful tool for controlling photons in strongly scattering media. Its speed, however, has been the bottleneck for in vivo applications. Moreover, unlike spatial focusing, temporal focusing from a continuous-wave source has rarely been exploited yet is highly desired for nonlinear photonics. Here, we present a novel real-time frequency-encoded spatiotemporal (FEST) focusing technology. FEST focusing uses a novel programmable two-dimensional optical frequency comb with an ultrafine linewidth to perform single-shot wavefront measurements, with a fast single-pixel detector. This technique enables simultaneous spatial and temporal focusing at microsecond scales through thick dynamic scattering media. This technology also enabled us to discover the large-scale temporal shift, a new phenomenon that, with the conventional spatial memory effect, establishes a space-time duality. FEST focusing opens a new avenue for high-speed wavefront shaping in the field of photonics.

Optical Vaginal Biopsy Using Optical Coherence Tomography.

OBJECTIVE: Optical coherence tomography is a noninvasive technology that visualizes tissue microstructure with high spatial resolution. We designed a novel vaginal system that demonstrates a clear distinction between vaginal tissues planes. In this study, we sought to compare vaginal tomographic images of premenopausal, perimenopausal, and postmenopausal women, demonstrate feasibility of tracking vaginal tissue changes after treatment with fractional-pixel CO2 laser therapy, and obtain a histologic correlation of these findings. METHODS: Enrolled subjects underwent imaging and were divided into 3 groups based on menopausal status. Women with genitourinary syndrome of menopause who received fractional-pixel CO2 laser therapy were assessed before and after treatment. A cadaveric vagina was used to obtain tomographic and histologic images to assess for accuracy. Our primary outcome was mean vaginal epithelial thickness. Statistical analysis was performed using analysis of variance and t tests, respectively. RESULTS: Among 6 women, the mean vaginal epithelial thickness decreased with menopause (P < 0.01). Although change in epithelial thickness after fractional-pixel CO2 laser treatment varied between the 2 subjects evaluated, it increased significantly for the subject who reported improvement of vaginal symptoms (P < 0.01). Using a cadaveric specimen, optical biopsy was correlated to an hematoxylin and eosin-stained biopsy of the same vaginal site. CONCLUSIONS: This study establishes feasibility of optical coherence tomography in providing an optical biopsy of the vaginal epithelium and lamina propria. In addition, it demonstrates vaginal changes as women enter menopause. This report is the initial phase of a longitudinal cohort study to evaluate changes in vaginal microstructure after energy-based treatment.

Characterization of oviduct ciliary beat frequency using real time phase resolved Doppler spectrally encoded interferometric microscopy.

Ciliary activity, characterized by the coordinated beating of ciliary cells, generates the primary driving force for oviduct tubal transport, which is an essential physiological process for successful pregnancies. Malfunction of the cilium in the fallopian tube, or oviduct, may increase the risk of infertility and tubal pregnancy that can result in maternal death. While many ex-vivo studies have been carried out using bright field microscopy, this technique is not feasible for the in-vivo investigation of oviduct ciliary beating frequency (CBF). Optical coherence tomography (OCT) has been able to provide in-vivo CBF imaging in a mouse model, but its resolution may be insufficient to resolve the spatial and temporal features of the cilium. Our group has recently developed the phase resolved Doppler (PRD) OCT method to visualize ciliary strokes at ultra-high displacement sensitivity. However, the cross-sectional field of view (FOV) may not be ideal for visualizing the surface dynamics of ciliated tissue. In this study, we report on the development of phase resolved Doppler spectrally encoded interferometric microscopy (PRD-SEIM) to visualize the oviduct ciliary activity within an en face FOV. This novel real time imaging system offers micrometer spatial resolution, sub-nanometer displacement sensitivity, and the potential for in-vivo endoscopic adaptation. The feasibility of the approach has been validated through ex-vivo experiments where the porcine oviduct CBF has been measured across different temperature conditions and the application of a drug. CBF ranging from 8 to 12 Hz have been observed at different temperatures, while administration of lidocaine decreased the CBF and deactivated the motile cilia. This study will serve as a stepping stone to in-vivo oviduct ciliary endoscopy and future clinical translations.

Multimodal endoscopy for colorectal cancer detection by optical coherence tomography and near-infrared fluorescence imaging.

While colonoscopy is the gold standard for diagnosis and classification of colorectal cancer (CRC), its sensitivity and specificity are operator-dependent and are especially poor for small and flat lesions. Contemporary imaging modalities, such as optical coherence tomography (OCT) and near-infrared (NIR) fluorescence, have been investigated to visualize microvasculature and morphological changes for detecting early stage CRC in the gastrointestinal (GI) tract. In our study, we developed a multimodal endoscopic system with simultaneous co-registered OCT and NIR fluorescence imaging. By introducing a contrast agent into the vascular network, NIR fluorescence is able to highlight the cancer-suspected area based on significant change of tumor vascular density and morphology caused by angiogenesis. With the addition of co-registered OCT images to reveal subsurface tissue layer architecture, the suspected regions can be further investigated by the altered light scattering resulting from the morphological abnormality. Using this multimodal imaging system, an in vivo animal study was performed using a F344-ApcPircUwm rat, in which the layered architecture and microvasculature of the colorectal wall at different time points were demonstrated. The co-registered OCT and NIR fluorescence images allowed the identification and differentiation of normal colon, hyperplastic polyp, adenomatous polyp, and adenocarcinoma. This multimodal imaging strategy using a single imaging probe has demonstrated the enhanced capability of identification and classification of CRC compared to using any of these technologies alone, thus has the potential to provide a new clinical tool to advance gastroenterology practice.

PMN-PT/Epoxy 1-3 composite based ultrasonic transducer for dual-modality photoacoustic and ultrasound endoscopy.

Endoscopic dual-modality photoacoustic (PA) and ultrasound (US) imaging has the capability of providing morphology and molecular information simultaneously. An ultrasonic transducer was applied for detecting PA signals and performing US imaging which determines the sensitivity and performance of a dual-modality PA/US system. In our study, a miniature single element 32-MHz lead magnesium niobate-lead titanate (PMN-PT) epoxy 1-3 composite based ultrasonic transducer was developed. A miniature endoscopic probe based on this transducer has been fabricated. Using the dual modality PA/US system with a PMN-PT/epoxy 1-3 composite based ultrasonic transducer, phantom and in vivo animal studies have been conducted to evaluate the performance. The preliminary results show enhanced bandwidths of the new ultrasonic transducer and improved signal-to-noise ratio of PA and US images of rat colorectal wall compared with PMN-PT and lead zirconate titanate (PZT) composite based ultrasonic transducers.

Dynamic programming and automated segmentation of optical coherence tomography images of the neonatal subglottis: enabling efficient diagnostics to manage subglottic stenosis.

Subglottic stenosis (SGS) is a challenging disease to diagnose in neonates. Long-range optical coherence tomography (OCT) is an optical imaging modality that has been described to image the subglottis in intubated neonates. A major challenge associated with OCT imaging is the lack of an automated method for image analysis and micrometry of large volumes of data that are acquired with each airway scan (1 to 2 Gb). We developed a tissue segmentation algorithm that identifies, measures, and conducts image analysis on tissue layers within the mucosa and submucosa and compared these automated tissue measurements with manual tracings. We noted small but statistically significant differences in thickness measurements of the mucosa and submucosa layers in the larynx (p < 0.001), subglottis (p = 0.015), and trachea (p = 0.012). The automated algorithm was also shown to be over 8 times faster than the manual approach. Moderate Pearson correlations were found between different tissue texture parameters and the patient's gestational age at birth, age in days, duration of intubation, and differences with age (mean age 17 days). Automated OCT data analysis is necessary in the diagnosis and monitoring of SGS, as it can provide vital information about the airway in real time and aid clinicians in making management decisions for intubated neonates.

Automated 3D segmentation of methyl isocyanate-exposed rat trachea using an ultra-thin, fully fiber optic optical coherence endoscopic probe.

Development of effective rescue countermeasures for toxic inhalational industrial chemicals, such as methyl isocyanate (MIC), has been an emerging interest. Nonetheless, current methods for studying toxin-induced airway injuries are limited by cost, labor time, or accuracy, and only provide indirect or localized information. Optical Coherence Tomography (OCT) endoscopic probes have previously been used to visualize the 3-D airway structure. However, gathering such information in small animal models, such as rat airways after toxic gas exposure, remains a challenge due to the required probe size necessary for accessing the small, narrow, and partially obstructed tracheas. In this study, we have designed a 0.4 mm miniature endoscopic probe and investigated the structural changes in rat trachea after MIC inhalation. An automated 3D segmentation algorithm was implemented so that anatomical changes, such as tracheal lumen volume and cross-sectional areas, could be quantified. The tracheal region of rats exposed to MIC by inhalation showed significant airway narrowing, especially within the upper trachea, as a result of epithelial detachment and extravascular coagulation within the airway. This imaging and automated reconstruction technique is capable of rapid and minimally-invasive identification of airway obstruction. This method can be applied to large-scale quantitative analysis of in vivo animal models.

In vivo imaging of the internal nasal valve during different conditions using optical coherence tomography.

OBJECTIVE: Previously, we proposed long-range optical coherence tomography (LR-OCT) to be an effective method for the quantitative evaluation of the nasal valve geometry. Here, the objective was to quantify the reduction in the internal nasal valve angle and cross-sectional area that results in subjective nasal airway obstruction and to evaluate the dynamic behavior of the valve during respiration using LR-OCT. METHODS: For 16 healthy individuals, LR-OCT was performed in each naris during: 1) normal respiration, 2) peak forced inspiration, 3) lateral nasal wall depression (to the onset of obstructive symptoms), and 4) after application of a topical decongestant. The angle and the cross-sectional area of the valve were measured. RESULTS: A reduction of the valve angle from 18.3° to 14.1° (11° in Caucasians and 17° in Asians) and a decrease of the cross-sectional area from 0.65 cm2 to 0.55 cm2 led to subjective nasal obstruction. Forceful breathing did not significantly change the internal nasal valve area in healthy individuals. Application of nasal decongestant resulted in increased values. CONCLUSION: LR-OCT proved to be a fast and readily performed method for the evaluation of the dynamic behavior of the nasal valve. The values of the angle and the cross-sectional area of the valve were reproducible, and changes in size could be accurately delineated. LEVEL OF EVIDENCE: 2b. Laryngoscope, 128:E105-E110, 2018.