Yuankai K. Tao

Methods for single-pass volumetric bidirectional blood flow imaging spectral domain optical coherence tomography using a modified hilbert transform

We demonstrate in vivo volumetric bidirectional blood flow imaging in animal models using single-pass flow imaging spectral domain optical coherence tomography. This technique uses a modified Hilbert transform algorithm to separate moving and non-moving scatterers within a depth. The resulting reconstructed image maps the components of moving scatterers flowing into and out of the imaging axis onto opposite image half-planes, enabling volumetric bidirectional flow mapping without manual segmentation.

Integration of a spectral domain optical coherence tomography system into a surgical microscope for intraoperative imaging.

PURPOSE To demonstrate an operating microscope-mounted spectral domain optical coherence tomography (MMOCT) system for human retinal and model surgery imaging. METHODS A prototype MMOCT system was developed to interface directly with an ophthalmic surgical microscope, to allow SDOCT imaging during surgical viewing. Nonoperative MMOCT imaging was performed in an Institutional Review Board-approved protocol in four healthy volunteers. The effect of surgical instrument materials on MMOCT imaging was evaluated while performing retinal surface, intraretinal, and subretinal maneuvers in cadaveric porcine eyes. The instruments included forceps, metallic and polyamide subretinal needles, and soft silicone-tipped instruments, with and without diamond dusting. RESULTS High-resolution images of the human retina were successfully obtained with the MMOCT system. The optical properties of surgical instruments affected the visualization of the instrument and the underlying retina. Metallic instruments (e.g., forceps and needles) showed high reflectivity with total shadowing below the instrument. Polyamide material had a moderate reflectivity with subtotal shadowing. Silicone instrumentation showed moderate reflectivity with minimal shadowing. Summed voxel projection MMOCT images provided clear visualization of the instruments, whereas the B-scans from the volume revealed details of the interactions between the tissues and the instrumentation (e.g., subretinal space cannulation, retinal elevation, or retinal holes). CONCLUSIONS High-quality retinal imaging is feasible with an MMOCT system. Intraoperative imaging with model eyes provides high-resolution depth information including visualization of the instrument and intraoperative tissue manipulation. This study demonstrates a key component of an interactive platform that could provide enhanced information for the vitreoretinal surgeon.

Characterization of buried glands before and after radiofrequency ablation by using 3-dimensional optical coherence tomography (with videos)

BACKGROUND Radiofrequency ablation (RFA) is an endoscopic technique used to eradicate Barretts esophagus (BE). However, such ablation can commonly lead to neosquamous epithelium overlying residual BE glands not visible by conventional endoscopy and may evade detection on random biopsy samples. OBJECTIVE To demonstrate the capability of endoscopic 3-dimensional optical coherence tomography (3D-OCT) for the identification and characterization of buried glands before and after RFA therapy. DESIGN Cross-sectional study. SETTING Single teaching hospital. PATIENTS Twenty-six male and 1 female white patients with BE undergoing RFA treatment. INTERVENTIONS 3D-OCT was performed at the gastroesophageal junction in 18 patients before attaining complete eradication of intestinal metaplasia (pre-CE-IM group) and in 16 patients after CE-IM (post-CE-IM group). MAIN OUTCOME MEASUREMENTS Prevalence, size, and location of buried glands relative to the squamocolumnar junction. RESULTS 3D-OCT provided an approximately 30 to 60 times larger field of view compared with jumbo and standard biopsy and sufficient imaging depth for detecting buried glands. Based on 3D-OCT results, buried glands were found in 72% of patients (13/18) in the pre-CE-IM group and 63% of patients (10/16) in the post-CE-IM group. The number (mean [standard deviation]) of buried glands per patient in the post-CE-IM group (7.1 [9.3]) was significantly lower compared with the pre-CE-IM group (34.4 [44.6]; P = .02). The buried gland size (P = .69) and distribution (P = .54) were not significantly different before and after CE-IM. LIMITATIONS A single-center, cross-sectional study comparing patients at different time points in treatment. Lack of 1-to-1 coregistered histology for all OCT data sets obtained in vivo. CONCLUSION Buried glands were frequently detected with 3D-OCT near the gastroesophageal junction before and after radiofrequency ablation.

Ultrahigh speed endoscopic optical coherence tomography using micromotor imaging catheter and VCSEL technology

We developed a micromotor based miniature catheter with an outer diameter of 3.2 mm for ultrahigh speed endoscopic swept source optical coherence tomography (OCT) using a vertical cavity surface-emitting laser (VCSEL) at a 1 MHz axial scan rate. The micromotor can rotate a micro-prism at several hundred frames per second with less than 5 V drive voltage to provide fast and stable scanning, which is not sensitive to the bending of the catheter. The side-viewing probe can be pulled back to acquire a three-dimensional (3D) data set covering a large area on the specimen. The VCSEL provides a high axial scan rate to support dense sampling under high frame rate operation. Using a high speed data acquisition system, in vivo 3D-OCT imaging in the rabbit GI tract and ex vivo imaging of a human colon specimen with 8 μm axial resolution, 8 μm lateral resolution and 1.2 mm depth range in tissue at a frame rate of 400 fps was demonstrated.

Integrative Advances for OCT-Guided Ophthalmic Surgery and Intraoperative OCT: Microscope Integration, Surgical Instrumentation, and Heads-Up Display Surgeon Feedback

Microscope-integrated intraoperative OCT (iOCT) allows live cross-sectional imaging concurrent with ophthalmic surgery and dynamic visualization of tissue-instrument interactions. However, limited volumetric data acquisition rates and three-dimensional rendering and display remain critical barriers to iOCT-guided surgical maneuvers. We present a microscope-integrated iOCT system with heads-up display (HUD) and novel semi-transparent ophthalmic surgical instruments. Cross-sectional iOCT imaging of surgical maneuvers using real-time HUD feedback and novel instrumentation is used to demonstrate the utility of real-time cross-sectional imaging for surgical guidance.

High-speed complex conjugate resolved retinal spectral domain optical coherence tomography using sinusoidal phase modulation.

We demonstrate high-speed complex conjugate artifact (CCA) resolved imaging of human retina in vivo using spectral domain optical coherence tomography. This technique utilizes sinusoidal reference mirror modulation to implement high-speed integrating buckets acquisition and a quadrature projection reconstruction algorithm in postprocessing. This method is illustrated experimentally using sets of four integrating bucket phase scans, acquired at 52 kHz, for DC suppression of 73 dB and complex conjugate suppression of 35 dB. Densely sampled (3000 A-scans/image, acquired at 4.3 images/s) full-depth in vivo images of optic nerve head show CCA suppression for most image reflections to the noise floor.

Velocity-resolved 3D retinal microvessel imaging using single-pass flow imaging spectral domain optical coherence tomography

We demonstrate in vivo velocity-resolved, volumetric bidirectional blood flow imaging in human retina using single-pass flow imaging spectral domain optical coherence tomography (SPFI-SDOCT). This technique uses previously described methods for separating moving and non-moving scatterers within a depth by using a modified Hilbert transform. Additionally, a moving spatial frequency window is applied, creating a stack of depth-resolved images of moving scatterers, each representing a finite velocity range. The resulting velocity reconstruction is validated with and strongly correlated to velocities measured with conventional Doppler OCT in flow phantoms. In vivo velocity-resolved flow mapping is acquired in healthy human retina and demonstrate the measurement of vessel size, peak velocity, and total foveal blood flow with OCT.

Microscope-integrated intraoperative OCT with electrically tunable focus and heads-up display for imaging of ophthalmic surgical maneuvers

We present novel optical and mechanical designs for a microscope-integrated intraoperative optical coherence tomography (iOCT) system with enhanced function and ergonomics for visualization of ophthalmic surgical maneuvers. Integration of an electrically tunable lens allows rapid focal plane adjustment and iOCT imaging of both anterior and posterior segment tissue microstructures while maintaining parfocality with the ophthalmic surgical microscope. We demonstrate novel visualization of instrument positions relative to tissue layers of interest as colormap overlays onto en face OCT data, which may provide integrative display of volumetric information during surgical maneuvers. Finally, we implement a heads-up display system to provide real-time feedback as proof-of-principle for iOCT-guided ophthalmic surgery.

Visualization of real-time intraoperative maneuvers with a microscope-mounted spectral domain optical coherence tomography system.

The advent of optical coherence tomography (OCT) has revolutionized our diagnostic and therapeutic capabilities in ophthalmology and vitreoretinal disease. In the clinic setting, OCT has touched nearly every aspect of vitreoretinal disease. More recently, OCT has been introduced the operating room theater. Intraoperative OCT (iOCT) has been used to successfully further our understanding of optic pit maculopathy, macular holes, epiretinal membranes, and retinopathy of prematurity.1–6 Limited systems are available for intraoperative use. All commercially available systems are handheld OCT devices or modified tabletop units, which allow for intraoperative imaging but require cessation of the surgical procedure to complete imaging. This precludes real-time feedback to the surgeon of the anatomical impact of surgical maneuvers and increases the duration of the surgical procedure. A microscope-mounted/integrated OCT (MMOCT) system allows for the integration of OCT into the real-time surgical platform.7,8 At the time of this report, two unique prototype systems have been described in the literature.5,7,8 Using a prototype MMOCT system, we previously demonstrated the feasibility of intraoperative imaging of surgical instruments, retinal effects of surgical contact, and primarily static surgical steps.7 To further seamlessly integrate OCT into the surgical platform, visualization of intraoperative motion and manipulation will be critical. Another critical component of integration will include the rapid localization of the surgical area of interest with the intraoperative spectral domain OCT (SD-OCT) device and quantitative information regarding the relative locations of the surgical instruments to the retinal tissue layers of interest. In this report, we describe a novel technique for visualizing intraoperative motion of surgical instruments with an MMOCT system.

Structural markers observed with endoscopic 3-dimensional optical coherence tomography correlating with Barrett's esophagus radiofrequency ablation treatment response (with videos)

BACKGROUND Radiofrequency ablation (RFA) is effective for treating Barretts esophagus (BE) but often involves multiple endoscopy sessions over several months to achieve complete response. OBJECTIVE Identify structural markers that correlate with treatment response by using 3-dimensional (3-D) optical coherence tomography (OCT; 3-D OCT). DESIGN Cross-sectional. SETTING Single teaching hospital. PATIENTS Thirty-three patients, 32 male and 1 female, with short-segment (<3 cm) BE undergoing RFA treatment. INTERVENTION Patients were treated with focal RFA, and 3-D OCT was performed at the gastroesophageal junction before and immediately after the RFA treatment. Patients were re-examined with standard endoscopy 6 to 8 weeks later and had biopsies to rule out BE if not visibly evident. MAIN OUTCOME MEASUREMENTS The thickness of BE epithelium before RFA and the presence of residual gland-like structures immediately after RFA were determined by using 3-D OCT. The presence of BE at follow-up was assessed endoscopically. RESULTS BE mucosa was significantly thinner in patients who achieved complete eradication of intestinal metaplasia than in patients who did not achieve complete eradication of intestinal metaplasia at follow-up (257 ± 60 μm vs 403 ± 86 μm; P < .0001). A threshold thickness of 333 μm derived from receiver operating characteristic curves corresponded to a 92.3% sensitivity, 85% specificity, and 87.9% accuracy in predicting the presence of BE at follow-up. The presence of OCT-visible glands immediately after RFA also correlated with the presence of residual BE at follow-up (83.3% sensitivity, 95% specificity, 90.6% accuracy). LIMITATIONS Single center, cross-sectional study in which only patients with short-segment BE were examined. CONCLUSION Three-dimensional OCT assessment of BE thickness and residual glands during RFA sessions correlated with treatment response. Three-dimensional OCT may predict responses to RFA or aid in making real-time RFA retreatment decisions in the future.