1.7 micron optical coherence tomography for vaginal tissue characterization in vivo

Imaging the ex-vivo human cochlea using 1.3-μm and 1.7-μm optical coherence tomography

Significance

There is no clinical imaging method to visualize the soft tissues of the human cochlea, which are crucial for sound transduction and are damaged in sensorineural hearing loss. Although optical coherence tomography (OCT) has been effective in small animal models, we show for the first time that it can image through the full thickness of the ex-vivo human otic capsule and resolve cochlear microstructures despite increased scattering.

Aim

We aim to investigate whether OCT could image the cochlea through the otic capsule. We compared 1.7 and 1.3    μ m OCT to test if the reduced scattering at 1.7    μ m provided any appreciable advantage for imaging the cochleae.

Approach

OCT interferometers were built for both 1.3 and 1.7    μ m wavelengths, using identical sample and reference arm optics in both systems. Imaging was performed on two fixed human temporal bones with intact cochleae. The interferometers were designed to allow seamless switching between 1.3 and 1.7    μ m OCT without disrupting the temporal bone during imaging.

Results

We took volumetric OCT images at the base, apex, and hook regions of fixed ex-vivo human cochleae and compared the images taken at 1.3    μ m with those taken at 1.7    μ m . At both wavelengths, we could see through the otic capsule and identify cochlear structures. In some cases, 1.7    μ m OCT resulted in clearer images of the lateral wall, interior scala, and fine cochlear structures due to reduced multiple scattering at depth compared with 1.3    μ m .

Conclusions

We conclude that both 1.7    μ m and 1.3    μ m OCT can image through the human otic capsule, offering the potential for direct measurement of cochlear vibrometry or blood flow in living humans. Using 1.7    μ m light, we observed reduced multiple scattering in the otic capsule, leading to enhanced contrast of cochlear structures compared with 1.3    μ m . However, these improvements were marginal and came with trade-offs.

1.7-micron Optical Coherence Tomography Angiography for Diagnosis and Monitoring of Hereditary Hemorrhagic Telangiectasia - A Pilot Study

OBJECTIVE

Develop a multi-functional imaging system that combines 1.7 µm optical coherence tomography/angiography (OCT/OCTA) to accurately interrogate Hereditary Hemorrhagic Telangiectasia (HHT) skin lesions.

METHODS

The study involved imaging HHT skin lesions on five subjects including lips, hands, and chest. We assessed the attributes of both HHT lesions and the healthy vasculature around them in these individuals, employing quantifiable measures such as vascular density and diameter. Additionally, we performed scans on an HHT patient who had undergone anti-angiogenic therapy, allowing us to observe changes in vasculature before and after treatment.

RESULTS

The results from this pilot study demonstrate the feasibility of evaluating the HHT lesion using this novel methodology and suggest the potential of OCTA to non-invasively track HHT lesions over time. The average percentage change in density between HHT patients' lesions and control was 37%. The percentage increase in vessel diameter between lesion and control vessels in HHT patients was 23.21%.

CONCLUSION

In this study, we demonstrated that OCTA, as a functional extension of OCT, can non-invasively scan HHT lesions in vivo. We scanned five subjects with HHT lesions in various areas (lip, ear, finger, and palm) and quantified vascular density and diameter in both the lesions and adjacent healthy tissue. This non-invasive method will permit a more comprehensive examination of HHT lesions.

SIGNIFICANCE

This method of non-invasive imaging could offer new insights into the physiology, management, and therapeutics of HHT-associated lesion development and bleeding.

First Clinical Feasibility and Safety Study of a Novel Multimodality Fallopian Tube Imaging Endoscope

STUDY OBJECTIVE

We present the results of the first feasibility and safety study of a novel multi-modality falloposcope, in 19 volunteers. The falloposcope incorporated multispectral fluorescence imaging (MFI) and optical coherence tomography (OCT) for evaluation of the fallopian tubes (FT).

METHODS

Nineteen females undergoing elective salpingectomy were recruited in this IRB-approved study. During a 15-min pause in standard of care surgery, a novel falloposcope was inserted under hysteroscopic guidance and advanced into the FTs. The furthest cannulated segment (proximal, middle, distal) was noted, and acquisition of MFI and OCT images was attempted at each segment in a retrograde fashion. Surgical discard samples from each segment of both FTs were obtained per pathology discretion for ex vivo imaging. All samples were processed for histology to evaluate any device-related injury.

RESULTS

The falloposcope was inserted into the FTs of 12 patients and successfully cannulated the entire length of the tube to the distal segment in one-third (4/12) of attempts. OCT and/or MFI images were obtained of all but one cannulated FT. Cannulation failure was attributed to proximal anatomy or obstruction, tortuosity of the FT, and limited study time. There were no adverse events related to the falloposcopy procedure. Focal epithelial cell denudation in the proximal segments of three patients, without no stromal involvement, was observed by histological examination. OCT images acquired in vivo showed characteristic tissue microstructures but were more susceptible to artifacts compared to ex vivo images.

CONCLUSIONS

The results of this first-in-human study suggest that falloposcopy with a novel multimodality imaging endoscope is feasible and safe. Future procedural and design modifications will be implemented to improve image quality and cannulation success rates.

Motion Artifact Correction for OCT Microvascular Images Based on Image Feature Matching

Optical coherence tomography angiography (OCTA), a functional extension of optical coherence tomography (OCT), is widely employed for high-resolution imaging of microvascular networks. However, due to the relatively low scan rate of OCT, the artifacts caused by the involuntary bulk motion of tissues severely impact the visualization of microvascular networks. This study proposes a fast motion correction method based on image feature matching for OCT microvascular images. First, the rigid motion-related mismatch between B-scans is compensated through the image feature matching based on the improved oriented FAST and rotated BRIEF algorithm. Then, the axial motion within A-scan lines in each B-scan image is corrected according to the displacement deviation between the detected boundaries achieved by the Scharr operator in a non-rigid transformation manner. Finally, an optimized intensity-based Doppler variance algorithm is developed to enhance the robustness of the OCTA imaging. The experimental results demonstrate the effectiveness of the method.

KTA-OPO for 1742 nm laser generation driven by a composite Nd:YVO4-based self-Raman laser

In this work, a double-end diffusion bonded Nd:YVO4 self-Raman laser was designed to drive an intracavity, noncritically-phase-matched KTiOAsO4 (KTA) optical parametric oscillator (OPO). Both conversion efficiency and output power at 1.7 µm (the wavelength of the OPO signal field) were improved by effectively reducing the thermal lens effect and increasing the effective length of self-Raman medium. At an incident pump power of 15.4 W, the output power for 1742 nm output laser reached 2.16 W with a conversion efficiency of 14%, and the output having a pulse width of 10.5 ns and a pulse repetition frequency of 90 kHz. The competition between the OPO and cascaded Raman laser was observed when the incident pump power was above 12.4 W. The results highlight that in order to improve output power at 1742 nm, it is critical that both the cascaded, second-Stokes field at 1313 nm and the signal field generated at 1534 nm from the 1064 nm field driving the KTA-OPO be minimized, if not completely suppressed. This laser system combining the processes of stimulated Raman scattering and optical parametric oscillation for the generation of laser emission at 1742 nm may find significant application across a broad range of fields including biological engineering, laser therapy, optical coherence tomography and for the generation of mid-infrared laser wavelengths.

Optical coherence elastography and its applications for the biomechanical characterization of tissues

The biomechanical characterization of the tissues provides significant evidence for determining the pathological status and assessing the disease treatment. Incorporating elastography with optical coherence tomography (OCT), optical coherence elastography (OCE) can map the spatial elasticity distribution of biological tissue with high resolution. After the excitation with the external or inherent force, the tissue response of the deformation or vibration is detected by OCT imaging. The elastogram is assessed by stress-strain analysis, vibration amplitude measurements, and quantification of elastic wave velocities. OCE has been used for elasticity measurements in ophthalmology, endoscopy, and oncology, improving the precision of diagnosis and treatment of disease. In this article, we review the OCE methods for biomechanical characterization and summarize current OCE applications in biomedicine. The limitations and future development of OCE are also discussed during its translation to the clinic.

High speed photo-mediated ultrasound therapy integrated with OCTA

Photo-mediated Ultrasound Therapy (PUT), as a new anti-vascular technique, can promote cavitation activity to selectively destruct blood vessels with a significantly lower amount of energy when compared to energy level required by other laser and ultrasound treatment therapies individually. Here, we report the development of a high speed PUT system based on a 50-kHz pulsed laser to achieve faster treatment, decreasing the treatment time by a factor of 20. Furthermore, we integrated it with optical coherence tomography angiography (OCTA) for real time monitoring. The feasibility of the proposed OCTA-guided PUT was validated through in vivo rabbit experiments. The addition of OCTA to PUT allows for quantitative prescreening and real time monitoring of treatment response, thereby enabling implementation of individualized treatment strategies.

Optical coherence tomography evaluation of vaginal epithelial thickness during CO2 laser treatment: A pilot study

Genitourinary syndrome of menopause (GSM) negatively affects more than half of postmenopausal women. Energy-based therapy has been explored as a minimally invasive treatment for GSM; however, its mechanism of action and efficacy is controversial. Here, we report on a pilot imaging study conducted on a small group of menopause patients undergoing laser treatment. Intravaginal optical coherence tomography (OCT) endoscope was used to quantitatively monitor the changes in the vaginal epithelial thickness (VET) during fractional-pixel CO2 laser treatment. Eleven patients with natural menopause and one surgically induced menopause patient were recruited in this clinical study. Following the laser treatment, 6 out of 11 natural menopause patient showed increase in both proximal and distal VET, while two natural menopause patient showed increase in VET in only one side of vaginal tract. Furthermore, the patient group that showed increased VET had thinner baseline VET compared to the patients that showed decrease in VET after laser treatment. These results demonstrate the potential utility of intravaginal OCT endoscope in evaluating the vaginal tissue integrity and tailoring vaginal laser treatment on a per-person basis, with the potential to monitor other treatment procedures.

Intraoperative In Vivo Imaging Modalities in Head and Neck Cancer Surgical Margin Delineation: A Systematic Review

Surgical margin status is one of the strongest prognosticators in predicting patient outcomes in head and neck cancer, yet head and neck surgeons continue to face challenges in the accurate detection of these margins with the current standard of care. Novel intraoperative imaging modalities have demonstrated great promise for potentially increasing the accuracy and efficiency in surgical margin delineation. In this current study, we collated and analyzed various intraoperative imaging modalities utilized in head and neck cancer to evaluate their use in discriminating malignant from healthy tissues. The authors conducted a systematic database search through PubMed/Medline, Web of Science, and EBSCOhost (CINAHL). Study screening and data extraction were performed and verified by the authors, and more studies were added through handsearching. Here, intraoperative imaging modalities are described, including optical coherence tomography, narrow band imaging, autofluorescence, and fluorescent-tagged probe techniques. Available sensitivities and specificities in delineating cancerous from healthy tissues ranged from 83.0% to 100.0% and 79.2% to 100.0%, respectively, across the different imaging modalities. Many of these initial studies are in small sample sizes, with methodological differences that preclude more extensive quantitative comparison. Thus, there is impetus for future larger studies examining and comparing the efficacy of these intraoperative imaging technologies.

Visualization of ex vivo rabbit olfactory mucosa and foramina with three-dimensional optical coherence tomography

There is increasing interest in developing a minimally invasive imaging modality to safely evaluate dynamic microscopic changes of the olfactory mucosa and cribriform foramina. Herein, we utilized three-dimensional (3D) optical coherence tomography (OCT) to characterize the ex vivo stratified substructure of olfactory mucosa in rabbits and create 3D reconstructed images of olfactory foramina. Olfactory mucosa and cribriform plates from four New Zealand White rabbits were dissected and imaged using two swept-source OCT systems: (1) 1.3-µm (μm) center wavelength, 100-nm bandwidth, 200-kHz sweep rate, and (2) 1.7-μm center wavelength, 120-nm bandwidth, 90-kHz sweep rate. Volumetric OCT images were compiled to create a 3D reconstruction of the cribriform plate. The ability of OCT to distinguish the olfactory mucosa substructure and foramina was compared to histology. To estimate imaging penetration depth of each system, the first-order exponential decays of depth-resolved intensity were calculated and compared using a paired t-test. Three-dimensional OCT depicted the stratified layered structures within the olfactory mucosa correlating with histology. The epithelium and lamina propria were measured to be 32 μm and 107 μm in 1.3-μm OCT compared to 30 μm and 105 μm in histology. Olfactory foramina were visualized via 3D reconstruction. The 1.7-μm system provided greater depth penetration compared to the 1.3-μm system, allowing for improved foramina visualization. We have shown that OCT can be used to image non-pathologic olfactory mucosa and foramina. Implications for this work include diagnostic and therapeutic potentials for neurorhinological and neurodegenerative diseases.

Intravascular polarization-sensitive optical coherence tomography based on polarization mode delay

Intravascular polarization-sensitive optical coherence tomography (IV-PSOCT) provides depth-resolved tissue birefringence which can be used to evaluate the mechanical stability of a plaque. In our previous study, we reported a new strategy to construct polarization-sensitive optical coherence tomography in a microscope platform. Here, we demonstrated that this technology can be implemented in an endoscope platform, which has many clinical applications. A conventional intravascular OCT system can be modified for IV-PSOCT by introducing a 12-m polarization-maintaining fiber-based imaging probe. Its two polarization modes separately produce OCT images of polarization detection channels spatially distinguished by an image separation of 2.7 mm. We experimentally validated our IV-PSOCT with chicken tendon, chicken breast, and coronary artery as the image samples. We found that the birefringent properties can be successfully visualized by our IV-PSOCT.

Advances in Endoscopic Photoacoustic Imaging

Photoacoustic (PA) imaging is able to provide extremely high molecular contrast while maintaining the superior imaging depth of ultrasound (US) imaging. Conventional microscopic PA imaging has limited access to deeper tissue due to strong light scattering and attenuation. Endoscopic PA technology enables direct delivery of excitation light into the interior of a hollow organ or cavity of the body for functional and molecular PA imaging of target tissue. Various endoscopic PA probes have been developed for different applications, including the intravascular imaging of lipids in atherosclerotic plaque and endoscopic imaging of colon cancer. In this paper, the authors review representative probe configurations and corresponding preclinical applications. In addition, the potential challenges and future directions of endoscopic PA imaging are discussed.

1.7-Micron Optical Coherence Tomography Angiography for Characterization of Skin Lesions-A Feasibility Study

Optical coherence tomography (OCT) is a non-invasive diagnostic method that offers real-time visualization of the layered architecture of the skin in vivo. The 1.7-micron OCT system has been applied in cardiology, gynecology and dermatology, demonstrating an improved penetration depth in contrast to conventional 1.3-micron OCT. To further extend the capability, we developed a 1.7-micron OCT/OCT angiography (OCTA) system that allows for visualization of both morphology and microvasculature in the deeper layers of the skin. Using this imaging system, we imaged human skin with different benign lesions and described the corresponding features of both structure and vasculature. The significantly improved imaging depth and additional functional information suggest that the 1.7-micron OCTA system has great potential to advance both dermatological clinical and research settings for characterization of benign and cancerous skin lesions.

A review of low-cost and portable optical coherence tomography

Optical coherence tomography (OCT) is a powerful optical imaging technique capable of visualizing the internal structure of biological tissues at near cellular resolution. For years, OCT has been regarded as the standard of care in ophthalmology, acting as an invaluable tool for the assessment of retinal pathology. However, the costly nature of most current commercial OCT systems has limited its general accessibility, especially in low-resource environments. It is therefore timely to review the development of low-cost OCT systems as a route for applying this technology to population-scale disease screening. Low-cost, portable and easy to use OCT systems will be essential to facilitate widespread use at point of care settings while ensuring that they offer the necessary imaging performances needed for clinical detection of retinal pathology. The development of low-cost OCT also offers the potential to enable application in fields outside ophthalmology by lowering the barrier to entry. In this paper, we review the current development and applications of low-cost, portable and handheld OCT in both translational and research settings. Design and cost-reduction techniques are described for general low-cost OCT systems, including considerations regarding spectrometer-based detection, scanning optics, system control, signal processing, and the role of 3D printing technology. Lastly, a review of clinical applications enabled by low-cost OCT is presented, along with a detailed discussion of current limitations and outlook.

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.

Endometrium imaging using real-time rotational optical coherence tomography imaging system: A pilot, prospective and ex-vivo study

This study aimed to evaluate a novel real-time rotational optical coherence tomography (OCT) imaging system (OCTIS) with a fiber-optic probe to look at endometrium and to correlate the OCTIS images with standard histology. OCT could obtain real-time images resembling histological examination. With recent development of customized probes, it allows OCT to be used in the field of gynecology.This is a pilot, prospective, ex-vivo and observational study. Women underwent hysterectomy for various gynecological conditions were recruited and OCTIS images were obtained from endometrium of 15 fresh uterus specimens immediately after hysterectomy. The excised uterus was cut open and OCTIS imaging was obtained. The scanned region of endometrium was excised for histological examination and OCTIS images were precisely compared to corresponding histological images and ultrasound images. Blinded qualitative analysis on OCTIS images was performed by 2 assessors to determine inter-rating reliability on the histopathological diagnosis.Epithelium, glands, cysts, and stroma of endometrium were clearly seen by the OCTIS. Different phases of menstrual cycle of normal endometrium could be differentiated and pathological condition such as hyperplastic and dysplasic endometrium, which corresponded well with histological findings, could be identified. The inter-rater reliability between assessors on overall OCTIS endometrium and neoplastic OCTIS endometrium was moderate (Kendall τb of 0.58) and substantial (Kendall τb of 0.76), respectively.OCTIS can provide real-time, high-resolution and rotational imaging modality to view endometrial structure with high consistency with histological examination and satisfactory agreement between observers. It has a great potential to be developed in the clinical use of endometrial assessment for gynecological applications.

Endometrial Vascularization Characterized by Optical Coherence Tomography and Immunohistochemistry in Women Undergoing In Vitro Fertilization-Embryo Transfer Treatment

Background and objective: Endometrial angiogenesis is a prerequisite for successful pregnancy. Optical coherence tomography (OCT) is a non-invasive physically optical imaging technique widely used in ophthalmology and cardiology. However, there is no study using OCT to evaluate endometrium. The aim of this study was to use OCT and traditionally histological methods to investigate endometrial vascularization in women undergoing in vitro fertilization-embryo transfer (IVF-ET) treatment and to determine the association with the pregnancy outcome. Methods: A total of 47 women were included in this study. OCT was used to assess endometrial vascularization by determining the high signal areas precisely on the seventh day after luteinizing hormone surge in non-conception natural cycles. Endometrial biopsies were obtained following OCT and immunohistochemistry was used to determine micro vessel and expression of vascular endothelial growth factor-A (VEGF-A) in the luminal epithelium, glandular epithelium and stroma, separately. Micro vessel counting was performed and the result was expressed as micro vessel density (MVD). A semi-quantitative H-score was used to determine the staining intensity of VEGF-A. Results: In women who successfully conceived after embryo transfer, the proportion of extensive high signal area in the uterine body detected by OCT (80%, 8/10), MVD (median number of micro vessels/mm² of 10, range 4–17) and stromal expression of VEGF-A (median H-score of 189, range 72–395) were found to be significantly higher than those of women who did not conceive after embryo transfer in the subsequent IVF-ET treatment (OCT: 30%, 3/10; MVD: median number of micro vessels/mm² of 7, range 4–10; VEGF-A: median H-score of 125, range 86–299, respectively). In addition, a significantly higher stromal expression of VEGF-A (median H-score of 196, range 84–395) and MVD (median number of micro vessels/mm² of 9, range 5–16) was found in women with extensive high signal area in uterine body, compared to those with focal or no high signal area (stromal VEGF-A: median H-score of 135, range 92–302; MVD: number of micro vessels/mm² of 6, range 4-11). Conclusions: Both immunohistochemistry and OCT demonstrated significant difference in vascularization of the peri-implantation endometrium between subjects who did and did not conceive after IVF-ET treatment. Our findings also suggest OCT appears to be a promising non-invasive or minimally invasive alternative to study endometrial vascularity in women with reproductive failure.