We demonstrate the first 1050nm MEMS-eVCSEL co-packaged with a wideband amplifier to achieve over 70nm wavelength tuning at over 30mW of output power and SMSR greater than 40dB. Ophthalmic Optical Coherence Tomography Angiography (OCTA) images acquired at 800kHz A-scan rates showcase the telecom grade 14pin butterfly co-package as a path to low cost swept source OCT engines. Device design employs a strain-compensated InGaAs/GaAsP gain region disposed on a wideband fully oxidized GaAs/AlxOy back mirror capable of tuning ranges beyond 100nm. It has been suggested the wideband fully oxidized GaAs/AlxOy back mirror may pose risk to device lifetime reliability. However, over 9000hrs of lifetime testing validates reliability and projects device lifetimes exceed 20,000hrs under continuous use.
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.
Imaging the entire human cornea with a conventional OCT system configuration requires trade-offs between resolution and depth-of-focus because the cornea is curved over a depth of approximately 4 mm. These system trade-offs result in image quality variations in the corneal image such as a bright apex surrounded by decreasing intensity as the cornea curves away from the apex. These intensity changes cause non-biological ambiguities in interpreting the image, make it difficult to see anatomy in the dim areas, and make automated surface detection difficult in the periphery. To address this problem, we developed a continuously focusing corneal OCT system coupled with a constant linear velocity (CLV) spiral scan pattern that is able to better maintain focus from the apex to the deeper cornea during a scan. The continuous focusing was implemented by introducing a focusing telescope on a motorized stage into the sample arm and matching the translation of the telescope with the CLV scan as it spiraled from the corneal apex outwards. Orthogonal B-scans prior to volume acquisition were used as a reference to estimate and correct motion that occurred during the subsequent CLV scan. A consented subject was imaged, and the resultant image showed increased intensity in the peripheral and deeper cornea and anterior chamber. Continuous focusing with CLV spiral scanning is a promising design change to OCT systems allowing adequate focus over relatively large depths such as for scanning the human cornea.
Optical coherence tomography (OCT) allows for micron scale imaging of the human retina and cornea. Previous research and commercial intraoperative OCT prototypes have been limited to live B-scan imaging because they were based on previous-generation spectral domain OCT systems. Our group has developed and reported on an intraoperative microscope integrated OCT system based on a 100 kHz commercial swept source laser. This system is capable of live 4D imaging, and with a heads up display allows for dynamic intraoperative visualization of retinal structures, tool tissue interaction, and surgical maneuvers. OCT angiography (OCTA) is an emerging OCT technology that allows for imaging of retinal vasculature without the use of potentially harmful contrast agents. This structural information can provide insights into the state and development of a wide range of ophthalmic pathologies. The addition of OCTA into intraoperative OCT could allow for monitoring of changes in retinal vasculature during surgery and imaging of traditionally non-compliant patients. In this work we provide a brief update of intraoperative 4D MIOCT across a range of pathologies, and demonstrate intraoperative OCTA for the first time. To the best of knowledge, this is the first report of intraoperative OCTA, as well as the first OCTA images ever acquired in an infant.
The en face operating stereomicroscope offers limited depth perception and ophthalmic surgeons must often rely on stereopsis and instrument shadowing to estimate motion in the axial dimension. Recent research and commercial microscope-integrated optical coherence tomography (MIOCT) systems have allowed OCT of live surgery, but these were restricted to real-time cross-sectional (B-scan) imaging which captures limited information about maneuvers that extend over 3D space. We recently reported on a four dimensional (4D: 3D imaging over time) MIOCT and HUD system with real-time volumetric rendering for human ophthalmic surgery, but this 100 kHz OCT system was restricted to 3.3 volumes/sec to achieve sufficient lateral sampling over a 5x5 mm field of view (FOV). In this work, we present a high-speed 4D MIOCT (HS 4D MIOCT) system for volumetric imaging at 800 kHz A-scan rate. The proposed system employs a temporal spectral splitting (TSS) technique in which the spectrum of a buffered 400 kHz OCT system is windowed into sub-spectra to yield A-scans with reduced axial resolution but at a doubled A-scan rate of 800 kHz. The trade-offs of TSS for B-scan and volumetric retinal imaging were characterized in healthy adult volunteers. In addition, porcine eye surgical manipulations were imaged with HS 4D MIOCT imaging at 10.85 volumes/sec with 400x96x340 (X,Y,Z) usable voxels over a 5x5 mm lateral FOV. HS 4D MIOCT was capable of imaging subtle volumetric tissue manipulations with high temporal and spatial resolution using ANSI-limited optical power and is readily translatable to the human operating suite.
Optical coherence tomography (OCT) allows for micron scale imaging of the human retina and cornea. Current generation research and commercial intrasurgical OCT prototypes are limited to live B-scan imaging. Our group has developed an intraoperative microscope integrated OCT system capable of live 4D imaging. With a heads up display (HUD) 4D imaging allows for dynamic intrasurgical visualization of tool tissue interaction and surgical maneuvers. Currently our system relies on operator based manual tracking to correct for patient motion and motion caused by the surgeon, to track the surgical tool, and to display the correct B-scan to display on the HUD. Even when tracking only bulk motion, the operator sometimes lags behind and the surgical region of interest can drift out of the OCT field of view. To facilitate imaging we report on the development of a fast volume based tool segmentation algorithm. The algorithm is based on a previously reported volume rendering algorithm and can identify both the tool and retinal surface. The algorithm requires 45 ms per volume for segmentation and can be used to actively place the B-scan across the tool tissue interface. Alternatively, real-time tool segmentation can be used to allow the surgeon to use the surgical tool as an interactive B-scan pointer.
Conventional optical coherence tomography (OCT) systems have working distances of about 25 mm, and require cooperative subjects to immobilize and fixate on a target. Handheld OCT probes have also been demonstrated for successful imaging of pre-term infants and neonates up to ~1 year old. However, no technology yet exists for OCT in young children due to their lack of attention and inherent fear of large objects close to their face. In this work, we demonstrate a prototype retinal swept-source OCT system with a long working distance (from the last optical element to the subject’s eye) to facilitate pediatric imaging. To reduce the footprint and weight of the system compared to the conventional 4f scheme, a novel 2f scanning configuration was implemented to achieve a working distance of 348mm with a +/- 8° scanning angle prior to cornea. Employing two custom-designed lenses, the system design resolution was nearly diffraction limited throughout a -8D to +5D refractive corrections. A fixation target displayed on a LCD monitor and an iris camera were used to facilitate alignment and imaging. Our prototype was tested in consented adult subjects and has the potential to facilitate imaging of young children. With this apparatus, young children could potentially sit comfortably in caretaker’s lap while viewing entertainment on the fixation screen designed to direct their gaze into the imaging apparatus.
Ophthalmic surgeons manipulate micron-scale tissues using stereopsis through an operating microscope and instrument
shadowing for depth perception. While ophthalmic microsurgery has benefitted from rapid advances in instrumentation
and techniques, the basic principles of the stereo operating microscope have not changed since the 1930’s. Optical
Coherence Tomography (OCT) has revolutionized ophthalmic imaging and is now the gold standard for preoperative and
postoperative evaluation of most retinal and many corneal procedures. We and others have developed initial microscope-integrated
OCT (MIOCT) systems for concurrent OCT and operating microscope imaging, but these are limited to 2D
real-time imaging and require offline post-processing for 3D rendering and visualization. Our previously presented 4D
MIOCT system can record and display the 3D surgical field stereoscopically through the microscope oculars using a
dual-channel heads-up display (HUD) at up to 10 micron-scale volumes per second. In this work, we show that 4D
MIOCT guidance improves the accuracy of depth-based microsurgical maneuvers (with statistical significance) in mock
surgery trials in a wet lab environment. Additionally, 4D MIOCT was successfully performed in 38/45 (84%) posterior
and 14/14 (100%) anterior eye human surgeries, and revealed previously unrecognized lesions that were invisible
through the operating microscope. These lesions, such as residual and potentially damaging retinal deformation during
pathologic membrane peeling, were visualized in real-time by the surgeon. Our integrated system provides an enhanced
4D surgical visualization platform that can improve current ophthalmic surgical practice and may help develop and
refine future microsurgical techniques.
The first generation of intrasurgical optical coherence tomography (OCT) systems displayed OCT data onto a separate computer monitor, requiring surgeons to look away from the surgical microscope. In order to provide real-time OCT feedback without requiring surgeons to look away during surgeries, recent prototype research and commercial intrasurgical OCT systems have integrated heads-up display (HUD) systems into the surgical microscopes to allow the surgeons to access the OCT data and the surgical field through the oculars concurrently. However, all current intrasurgical OCT systems with a HUD are only capable of imaging through one ocular limiting the surgeon’s depth perception of OCT volumes. Stereoscopy is an effective technology to dramatically increase depth perception by presenting an image from slightly different angles to each eye. Conventional stereoscopic HUD use a pair of micro displays which require bulky optics. Several new approaches for HUDs are reported to use only one micro display at the expense of image brightness or increased footprint. Therefore, these techniques for HUD are not suitable to be integrated into microscopes. We have developed a novel stereoscopic HUD which uses spatial multiplexing to project stereo views into both oculars simultaneously with only one micro-display and three optical elements for our microscope-integrated OCT system. Simultaneous stereoscopic views of OCT volumes are computed in real time by GPU-enabled OCT system software. We present, to our knowledge, the first microscope integrated stereoscopic HUD used for intrasurgical OCT with a novel optical design for stereoscopic viewing devices and report on its preliminary use in human vitreoretinal surgeries.
Confocal microscopy has shown potential as an imaging technique to detect precancer. Imaging cellular features throughout the depth of epithelial tissue may provide useful information for diagnosis. However, the current in vivo axial scanning techniques for confocal microscopy are cumbersome, time-consuming, and restrictive when attempting to reconstruct volumetric images acquired in breathing patients. Chromatic dispersion confocal microscopy (CDCM) exploits severe longitudinal chromatic aberration in the system to axially disperse light from a broadband source and, ultimately, spectrally encode high resolution images along the depth of the object. Hyperchromat lenses are designed to have severe and linear longitudinal chromatic aberration, but have not yet been used in confocal microscopy. We use a hyperchromat lens in a stage scanning confocal microscope to demonstrate the capability to simultaneously capture information at multiple depths without mechanical scanning. A photonic crystal fiber pumped with a 830nm wavelength Ti:Sapphire laser was used as a supercontinuum source, and a spectrometer was used as the detector. The chromatic aberration and magnification in the system give a focal shift of 140μm after the objective lens and an axial resolution of 5.2-7.6μm over the wavelength range from 585nm to 830nm. A 400x400x140μm3 volume of pig cheek epithelium was imaged in a single X-Y scan. Nuclei can be seen at several depths within the epithelium. The capability of this technique to achieve simultaneous high resolution confocal imaging at multiple depths may reduce imaging time and motion artifacts and enable volumetric reconstruction of in vivo confocal images of the epithelium.
We present chromatic confocal microscopy as a technique to axially scan the sample by spectrally encoding depth
information to avoid mechanical scanning of the lens or sample. We have achieved an 800 μm focal shift over a range of
680-1080 nm using a hyperchromat lens as the imaging lens. A more complex system that incorporates a water
immersion objective to improve axial resolution was built and tested. We determined that increasing objective
magnification decreases chromatic shift while improving axial resolution. Furthermore, collimating after the
hyperchromat at longer wavelengths yields an increase in focal shift.
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