SignificanceImaging deep structures with optical coherence tomography (OCT) is difficult in highly scattering biological tissue, such as the sclera. There is a need to visualize the suprachoroidal space and choroid through the sclera to study suprachoroidal drug delivery.AimWe aim to develop optical methods to image through the highly scattering sclera with a custom-built OCT system to visualize the suprachoroidal space and drug delivery within.ApproachWe developed a custom handheld OCT scanner to image the anterior segment and suprachoroidal space in ex vivo eye models. Tartrazine (Yellow 5) solution, which has been shown to optically clear biological tissue in the visible regime, was tested as a clearing agent to optimize near infrared OCT imaging through the sclera.ResultsTartrazine dramatically increased OCT signal return from the deeper sclera and choroid and thus enabled visualization of the suprachoroidal drug delivery after transscleral injection.ConclusionsWe demonstrated successful optical clearing of the thick, porcine sclera with a compact handheld OCT system to image the suprachoroidal space. We believe there is broader potential to use optical clearing with handheld OCT for a variety of previously inaccessible, highly scattering tissue samples.
In fields such as virtual/augmented reality, robotic vision, facial recognition, and biomedical imaging, the demand for accurate, fast coherent 3D surface imaging technology is increasing. However, current technologies like FMCW LiDAR have limitations in terms of low spectral bandwidth efficiency and high cost. We demonstrate a novel approach using synthetic wavelength phase unwrapping and line-scan off-axis holography. Our system achieved fast 3D surface imaging with a non-ambiguous depth range of 22.3mm. We validated system performance using a 3D-printed test target and a U.S. copper penny.
Extending OCT into meter-scale working distances has potential applications in robotic vision, surgical planning and assistance, and non-invasive medical imaging. However, long-range imaging significantly decreases the numerical aperture (NA) of the system unless a much larger aperture is used. This diminishes the signal and requires the use of Gaussian beam theory for accurate determination of the beam profile and focusing behavior. We demonstrate and experimentally validate theory for focusing a laser source to optimize both resolution and signal and discuss the impact of the “focal shift” effect in which the geometric focus of the objective and Gaussian beam waist diverge at low NA.
Real-time volumetric microscope-integrated OCT (MIOCT) visualization of ophthalmic surgeries is limited by the narrow field of view of OCT relative to the movement of the surgical instruments, requiring extensive manual repositioning by a trained operator. We developed a computer vision system for instrument tracking that utilizes a microscope video camera and a deep-learning object detector trained on synthetic data, which consisted of 3D rendered models of surgical instruments alongside an eye model. This system was then tested in a clinical MIOCT platform, providing high fidelity, video-rate (>40 Hz) object tracking of a cataract surgery instrument over a model eye phantom.
Microscope-integrated optical coherence tomography (MIOCT) is an emerging multimodal imaging technology in which live volumetric OCT (“4D-OCT”) is displayed simultaneous with standard stereo color microscopy. 4D-OCT provides ophthalmic surgeons with many visual cues not available in microscopy, but it cannot serve as a replacement due to lack of color features. In this work, we demonstrate progress toward a unified solution by fusion of data from both modalities, guided by segmented 3D features, yielding a more efficient visualization combining important cues from both modalities.
KEYWORDS: Scattering, Tissues, Monte Carlo methods, Polarization, Laparoscopy, RGB color model, Light scattering, In vivo imaging, Visualization, Solid state lighting
Peritoneal metastases are characterized by significant disruptions in the extracellular matrix. Hence, the scattering cross sections of malignant and benign lesions and surrounding background tissues are distinct. In this work, Monte Carlo based regression was used to develop an empirical relation to extract the scattering power of tissue based on co- and cross-polarized RGB reflectance images of tissue. The empirical relation improved the sensitivity of lesion detection, and discrimination accuracy of malignant and benign lesions. The proposed empirical equation is both accurate and simple, paving the way for real-time diagnostic applications.
KEYWORDS: Laparoscopy, Yield improvement, Polarization, Collagen, Visualization, Cancer, In vivo imaging, Scattering, Monte Carlo methods, Light scattering
While white light laparoscopy (WLL) has been established as a method that yields improved detection of peritoneal metastatic lesions over radiographic imaging, its sensitivity and specificity remain sub-optimal, leading to thousands of cancer patients that are over- or under- treated every year. We present studies that establish the sensitivity of polarization enhanced (PEL) laparoscopy to changes in the cross-section and alignment of scattering centers using phantoms and report on our initial in vivo human feasibility trial. The design of our PEL probe is simple and highly compatible with current laparoscopes, the standard of patient care and the established procedure flow for WLL. It comprises of a sheath inserted on the WLL laparoscope to provide linearly polarized illumination and a modified detection optical path that allows for recording of co- and cross-polarized images relative to the incident illumination. The sum of these images is equivalent to WLL, while their difference corresponds to PEL. Using PDMS phantoms with features that contain either TiO2 and ZnO2 particles, we demonstrate the enhanced sensitivity of PEL to scattering cross-section differences. Measurements performed with collagen gels that are being stretched reveal improved sensitivity of PEL (over WLL) to collagen fiber alignment. Our initial feasibility study results support the improved diagnostic potential of PEL. In fact, a Monte Carlo-based analysis approach that utilizes the color content of the PEL images indicates that PEL yields improved contrast for detection and differentiation of benign and malignant metastatic lesions. These studies provide strong motivation for further development of PEL imaging as an approach that may improve significantly the detection of peritoneal metastatic lesions.
Microscope-integrated optical coherence tomography (MIOCT) is an emerging multimodal imaging technology in which live volumetric OCT (“4D-OCT”) is displayed simultaneously with standard stereo color microscopy. 4D-OCT provides ophthalmic surgeons with many visual cues not available in microscopy, but it cannot serve as a replacement due to lack of color features. In this work, we demonstrate progress toward a unified solution by fusion of data from both modalities, guided by segmented 3D features, yielding a more efficient visualization combining important cues from both modalities.
Ophthalmic microsurgery involves the manipulation of thin, semi-transparent structures and has traditionally been performed using stereoscopic microscopes that provide an en face view of the surgical field. However, new therapeutic interventions such as subretinal injections require precise tool placement and dosing that are difficult to determine from the traditional microscope view. Optical coherence tomography (OCT) provides micron scale cross-sectional imaging and has become a gold standard in clinical ophthalmology settings, but its use in surgery has been more limited. The high-speed 400 kHz intraoperative system presented here provides valuable image guidance and quantitative metrics for a variety of human surgeries.
An experimental polarization enhanced laparoscopy (PEL) imaging system was developed to improve the visualization of peritoneal cancer lesions compared to conventional white light laparoscopy (WLL). The design modifications provide sensitivity to backscatter depolarization in tissue. Phantom studies demonstrated the sensitivity of PEL to altered scattering cross section and collagen organization. Implementation of the PEL for biopsy tissue study illustrated the feasibility and potential of PEL to improve the contrast between malignant lesions, and background tissue based on differences in their depolarization properties.
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