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.
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 angiography (OCTA) is an extension of OCTA that allows for non-invasive imaging of the retinal microvasculature. OCTA imaging of adult retinal diseases is area of active research in ophthalmology as OCTA can provide insight into the pathogenesis of many retinal diseases. Like these adult diseases, pediatric diseases such as retinopathy of prematurity (ROP) have a primarily vascular pathogenesis. However, table top OCTA systems require compliant, seated subjects and cannot be used on infants and young children. In this manuscript we describe the development of a non-contact handheld OCTA (HH-OCTA) probe for imaging of young children and infants in the operating room. The probe utilizes a novel, diverging light on the scanner optical design that provides improved performance over a traditional OCT scanner design. While most handheld OCT probes are designed to be held by the side of the case or by a handle, our operators tend to prefer to grip probes by the tip of the probe for supine imagine. The ergonomics of the HH-OCTA probe were designed to match this grip. The HH-OCTA probe used a 200 kHz OCT engine, has a motorized stage that provides +10 to -10 D refractive error correction, and weighs 700g. Initial OCTA imaging was performed in 9 children or infants during exam under anesthesia. The HH-OCTA images provide visualization of the retinal microvasculature in both normal and pathological eyes.
Optical coherence tomography (OCT) allows for non-contact, high resolution, volumetric imaging of biological tissue and has become an indispensable ophthalmic imaging technique. However, conventional, commercial OCT systems require a cooperative, sitting patient typically stabilized by a head and/or chin rests. Additionally, current clinical systems are designed for imaging either the anterior or posterior segment of the eye exclusively. While these limitations are not severe in the ophthalmic clinic, they do limit the use of OCT in other more challenging medical environments where novel “whole eye” imaging could provide value, such as in the military theater or emergency department (ED). One solution to eliminate the need for a patient to sit upright and be stabilized during imaging would be a hand-held probe positioned and stabilized by the photographer or physician. Here we describe a hand-held OCT probe for simultaneous imaging of the anterior chamber (13.3 mm diameter field-of-view) and posterior segment (40° as measured from the pupil nodal point) simultaneously. The use of polarization multiplexing allows for two independent imaging channels which enable a wide posterior segment field-of-view and the ability to control the posterior segment path length and focal depth independently from the anterior chamber channel. Additionally, the probe was designed for a relatively compact form factor.
OCT is the gold standard for clinical diagnosis and treatment of many retinal diseases. Most clinical OCT systems are table top systems that can only image seated, compliant patients that can fixate. These systems are incapable of imaging several important patient populations including bedridden patients and infants. In this work we describe the use of a custom, light weight, handheld OCT probe based on a high speed swept source engine for imaging in the intensive care nursery. The probe uses custom optics, optomechanics, and a MEMS mirror to achieve a weight of only 211g. The portability and imaging speed of this probe facilitates repeat, volumetric, bedside imaging in a challenging imaging environment. To date we have imaged over 43 pre-term and full-term infants in the intensive care nursery, with some patients having up to 15 imaging sessions starting at 30 weeks post menstrual age. Volumetric OCT enables visualization of the complex 3D structures associated with retinal pathology that is unavailable to slower, B-scan based probes. Repeat imaging shows the development of both normal and diseased retinal structures. We believe that OCT imaging of these infants will reveal retinal abnormalities, enable further study of pediatric retinal diseases, and allow for better management and prediction of future visual outcomes.
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