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.
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.
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 surgery is typically performed through an en-face only surgical microscope that provides limited depth information. This work introduces a high speed (400 kHz) microscope integrated optical coherence tomography (MIOCT) system which provides real time volumetric “4D” visualization via a heads-up stereoscopic display. The MIOCT system provides sub retinal visualization of tools and enables surgeons to perform delicate manipulation of retinal structures during mock surgical procedures. Following these mock surgical procedures in porcine eyes, this system will be readily translated into human ophthalmic microsurgery.
Microscope-integrated optical coherence tomography (MIOCT) systems allow for 4D visualization of thin,
semi-transparent structures during ophthalmic microsurgery. While these visualizations have greatly
increased the information available to surgeons, new surgical techniques, such as subretinal injections of
gene therapies, would benefit from quantitative measurements of structures imaged using OCT. Calibration
of true scan dimensions in OCT is complicated by inter-patient ocular variability as well as poor control of
scanner-patient alignment. We introduce novel measurement techniques for calibration and de-warping of
OCT imagery which allows for accurate measurement of intraocular structures including subretinal
microinjection bleb volumes in the ocular posterior segment.
High speed optical coherence tomography (OCT) systems with A-scan rates greater than 100 kHz allow for 4D visualizations in applications such as intraoperative OCT. However, traditional triangle or sawtooth waveforms used to drive galvanometer scanners often have frequency content that exceeds the bandwidth of the scanners, leading to distorted scans. Sinusoidal waveforms used to drive resonant scanners also lead to distorted scans due to the nonlinear scan velocity. Additionally, with raster scan patterns, the scanner needs time to stop and reverse direction in between B-scans, leading to significant acquisition dead time. Continuous scan patterns such as constant frequency spiral scanning or Lissajous scanning no longer have acquisition dead times, but suffer from non-uniform sampling across the imaging plane. We previously introduced constant linear velocity (CLV) spiral scanning as a novel scan pattern to maximize the data acquisition efficiency of high speed OCT systems. While this continuous scan pattern has no acquisition dead time and produces more uniform sampling compared to raster scanning, it required significant processing time. We introduce a processing pipeline implemented using CUDA in C++, which drastically reduces the amount of processing time needed, allowing real time visualization of 4D OCT data. To demonstrate its potential utility, we used CLV scanning with a 100 kHz swept-source OCT system to image retinas of enucleated porcine eyes undergoing mock ophthalmic surgery movements. Additionally, we rendered these volumes in virtual reality (VR) in real time, allowing for interactive manipulation and sectioning.
Ophthalmic surgery involves manipulation of delicate, layered tissue structures on milli- to micrometer scales. Traditional surgical microscopes provide an inherently two-dimensional view of the surgical field with limited depth perception which precludes accurate depth-resolved visualization of these tissue layers, and limits the development of novel surgical techniques. We demonstrate multimodal swept-source spectrally encoded scanning laser ophthalmoscopy and optical coherence tomography (SS-SESLO-OCT) to address current limitations of image-guided ophthalmic microsurgery. SS-SESLO-OCT provides inherently co-registered en face and cross-sectional field-of-views (FOVs) at a line rate of 400 kHz and >2 GPix/s throughput. We show in vivo imaging of the anterior segment and retinal fundus of a healthy volunteer, and preliminary results of multi-volumetric mosaicking for ultrawide-field retinal imaging with 90° FOV. Additionally, a scan-head was rapid-prototyped with a modular architecture which enabled integration of SS-SESLO-OCT with traditional surgical microscope and slit-lamp imaging optics. Ex vivo surgical maneuvers were simulated in cadaveric porcine eyes. The system throughput enabled volumetric acquisition at 10 volumes-per-second (vps) and allowed visualization of surgical dynamics in corneal sweeps, compressions, and dissections, and retinal sweeps, compressions, and elevations. SESLO en face images enabled simple real-time co-registration with the surgical microscope FOV, and OCT cross-sections provided depth-resolved visualization of instrument-tissue interactions. Finally, we demonstrate novel augmented-reality integration with the surgical view using segmentation overlays to aid surgical guidance. SS-SESLO-OCT may benefit clinical diagnostics by enabling aiming, registration, and mosaicking; and intraoperative imaging by allowing for real-time surgical feedback, instrument tracking, and overlays of computationally extracted biomarkers of disease.
Surgical interventions for ocular diseases involve manipulations of semi-transparent structures in the eye, but limited
visualization of these tissue layers remains a critical barrier to developing novel surgical techniques and improving clinical
outcomes. We addressed limitations in image-guided ophthalmic microsurgery by using microscope-integrated
multimodal intraoperative swept-source spectrally encoded scanning laser ophthalmoscopy and optical coherence
tomography (iSS-SESLO-OCT). We previously demonstrated in vivo human ophthalmic imaging using SS-SESLO-OCT,
which enabled simultaneous acquisition of en face SESLO images with every OCT cross-section. Here, we integrated our
new 400 kHz iSS-SESLO-OCT, which used a buffered Axsun 1060 nm swept-source, with a surgical microscope and
TrueVision stereoscopic viewing system to provide image-based feedback. In vivo human imaging performance was
demonstrated on a healthy volunteer, and simulated surgical maneuvers were performed in ex vivo porcine eyes. Denselysampled
static volumes and volumes subsampled at 10 volumes-per-second were used to visualize tissue deformations and
surgical dynamics during corneal sweeps, compressions, and dissections, and retinal sweeps, compressions, and elevations.
En face SESLO images enabled orientation and co-registration with the widefield surgical microscope view while OCT
imaging enabled depth-resolved visualization of surgical instrument positions relative to anatomic structures-of-interest.
TrueVision heads-up display allowed for side-by-side viewing of the surgical field with SESLO and OCT previews for
real-time feedback, and we demonstrated novel integrated segmentation overlays for augmented-reality surgical guidance.
Integration of these complementary imaging modalities may benefit surgical outcomes by enabling real-time intraoperative
visualization of surgical plans, instrument positions, tissue deformations, and image-based surrogate biomarkers correlated
with completion of surgical goals.
Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) enable noninvasive in vivo diagnostic
imaging and provide complementary en face and depth-resolved visualization of ophthalmic structures, respectively. We
previously demonstrated concurrent multimodal swept-source spectrally encoded scanning laser ophthalmoscopy and
OCT (SS-SESLO-OCT) at 1060 nm using a swept-source and double clad fiber coupler. Here, we present system
enhancements and novel designs for a modular SS-SESLO-OCT scan-head that can be coupled to ophthalmic surgical
microscope-integrated and slit-lamp imaging optics. Multimodal SS-SESLO-OCT was demonstrated using a custom-built
swept-source OCT engine with a 200 kHz 1060 nm source that was optically buffered for concurrent SESLO and OCT
imaging at 100% duty cycle and 400 kHz sweep-rate. A shared optical relay and fast-axis galvanometer ensured inherent
co-registration between SESLO and OCT field-of-views and concurrent acquisition of an en face SESLO image with each
OCT cross-section. SESLO and OCT frames were acquired at 200 fps with 2560 x 2000 pix. (spectral x lateral). We show
in vivo human ophthalmic imaging data using surgical microscope-integrated and slit-lamp imaging relays to demonstrate
the utility of our SS-SESLO-OCT design. Our self-contained modular scan-head can be used for either intraoperative
guidance or clinical diagnostics and reduces the complexity, cost, and maintenance required for clinical translation of these
technologies. We believe concurrent multimodal SS-SESLO-OCT may benefit 1) intraoperative imaging by allowing for
real-time surgical feedback, instrument tracking, and overlays of computationally extracted image-based surrogate
biomarkers of disease, and 2) slit-lamp imaging by enabling aiming, image registration, and multi-field mosaicking.
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