Doppler Optical Coherence Tomography Imaging Research Articles

Relationship Between Macular Vessel Density and Total Retinal Blood Flow in Primary Open-angle Glaucoma.

An association between macular vessel density (VD) and total retinal blood flow (TRBF) was demonstrated in subjects with primary open-angle glaucoma (POAG) and visual field (VF) loss. The purpose of this study was to report relationships of macular VD metrics and TRBF in POAG. A total of 24 POAG and 19 healthy control subjects participated in the study. Subjects underwent optical coherence tomography and angiography for measurements of inner retinal thickness (IRT), VD, and spacing between large vessels (SLV) and small vessels (SSV). Doppler optical coherence tomography imaging was performed for TRBF measurement. In POAG subjects, automated perimetry was performed and VF loss expressed as mean deviation was measured. Compared with the control group, POAG group had decreased VD, TRBF, IRT, and increased SLV (P<0.0001). Decreased VD (Pearson correlation, r=0.51; P<0.0001; N=43) and increased SLV (Spearman correlation, rs=-0.47; P=0.001) were correlated with decreased TRBF. Decreased VD and SSV (r≥0.39; P≤0.001; N=43) and increased SLV (rs=-0.71; P<0.0001) were associated with decreased IRT. Decreased VF mean deviation was correlated with decreased VD, SSV, IRT (r≥0.53; P≤0.001; N=24), and with increased SLV (rs=-0.84; P<0.0001). The finding of an association between macular VD and TRBF supports the role of vascular factors in the pathophysiology of POAG and potential conduct of future studies aimed at identifying multiple image-based vascular metrics for disease diagnosis.

Endovascular Cerebral Venous Sinus Imaging with Optical Coherence Tomography.

Imaging of the cerebral venous sinuses has evolved Substantially during the past 2 decades, and most recently intravascular sinus imaging with sonography has shed light on the pathophysiology of sinus thrombosis and intracranial hypertension. Optical coherence tomography is the highest resolution intravascular imaging technique available but has not been previously used in cerebral sinus imaging. The purpose of this study was to develop a preclinical animal model of endovascular optical coherence tomography cerebral venous sinus imaging and compare optical coherence tomography findings with histology. Four consecutive Yorkshire swine were selected. The superior sagittal sinus was first catheterized with a microwire, and the optical coherence tomography catheter was delivered via a monorail technique into the sinus. Luminal blood was cleared with a single arterial injection. After structural and Doppler optical coherence tomography imaging, a craniotomy was performed and the sinus and adjacent dura/veins were resected. Bland-Altman analysis was performed to compare optical coherence tomography and histology. Technically successful optical coherence tomography images were obtained in 3 of 4 swine. The luminal environment and visualization of dural arteries and draining cortical veins were characterized. The average maximum diameters of the sinus, dural arteries, and cortical veins were 3.14 mm, 135 µm, and 260 µm, respectively. Bland-Altman analysis demonstrated good agreement between histology and optical coherence tomography images. Endovascular optical coherence tomography imaging was feasible in this preclinical animal study. Adoption of this imaging technique in the human cerebral venous sinus could aid in the diagnosis, treatment, and understanding of the pathophysiology of various diseases of the sinus. Human safety and feasibility studies are needed.

9.4 MHz A-line rate optical coherence tomography at 1300\u2009nm using a wavelength-swept laser based on stretched-pulse active mode-locking

In optical coherence tomography (OCT), high-speed systems based at 1300 nm are among the most broadly used. Here, we present 9.4 MHz A-line rate OCT system at 1300 nm. A wavelength-swept laser based on stretched-pulse active mode locking (SPML) provides a continuous and linear-in-wavenumber sweep from 1240 nm to 1340 nm, and the OCT system using this light source provides a sensitivity of 98 dB and a single-sided 6-dB roll-off depth of 2.5 mm. We present new capabilities of the 9.4 MHz SPML-OCT system in three microscopy applications. First, we demonstrate high quality OCTA imaging at a rate of 1.3 volumes/s. Second, by utilizing its inherent phase stable characteristics, we present wide dynamic range en face Doppler OCT imaging with multiple time intervals ranging from 0.25 ms to 2.0 ms at a rate of 0.53 volumes/s. Third, we demonstrate video-rate 4D microscopic imaging of a beating Xenopus embryo heart at a rate of 30 volumes/s. This high-speed and high-performance OCT system centered at 1300 nm suggests that it can be one of the most promising high-speed OCT platforms enabling a wide range of new scientific research, industrial, and clinical applications at speeds of 10 MHz.

Phase unwrapping for Doppler spectral domain optical coherence tomography flow measurement.

Doppler optical coherence tomography (OCT) offers additional flow velocity information, which extends the application of OCT. Phase wrapping is the inherent problem that limits measureable range of Doppler OCT. We propose a phase unwrapping method which is suitable for correcting phase in Doppler OCT images. Points (pixels) in flow region are divided into groups according to the radial distance. Points in the same group are supposed to have close velocity. Phase unwrapping algorithm begins at the boundary layer group and is performed sequentially toward the center. Using the proposed criterion, points in a group are separated into two categories, signal points and noise points. Wrapping rounds are determined for signal points phase unwrapping. Mean value of the corrected signal points replaces the noise points for noise reduction. The method is validated with capillary tube flow phantom and in vivo blood flow.

Relating glaucomatous visual field loss to retinal oxygen delivery and metabolism.

To test the hypothesis that visual field (VF) loss is associated with decreased retinal blood flow, oxygen delivery and metabolism, and with increased retinal oxygen extraction fraction (OEF) in glaucomatous individuals. Glaucomatous subjects underwent automated perimetry, dual wavelength scanning laser ophthalmoscopy and Doppler optical coherence tomography imaging in order to measure mean deviation, central retinal arterial and venous diameter equivalents (CRAE and CRVE), oxygen saturation levels and total retinal blood flow (TRBF), respectively. Retinal oxygen delivery, metabolism and extraction fraction were derived from measurements of oxygen saturation and blood flow. Twenty eyes of 14 subjects were included in the study. Mean deviation was on average -13.76±8.70 dB. Mean CRAE and CRVE were 126±28 and 191±35μm, respectively. Mean TRBF and oxygen delivery were 34.3± 11.7μl/min and 6.5±2.6μl O2 /min, respectively. Mean oxygen metabolism and extraction fraction were 2.1±0.94μl O2 /min and 0.34±0.15, respectively. Visual field (VF) loss was associated with reduced CRAE and CRVE, TRBF and oxygen delivery and associated with increased OEF. Combined measurements of retinal blood flow and oxygen saturation in glaucomatous individuals suggest VF loss is associated with impaired oxygen delivery and augmented OEF.

Automatic boundary segmentation of vascular Doppler optical coherence tomography images based on cascaded U-net architecture

Doppler optical coherence tomography (OCT) imaging of vessels after anastomosis procedures can provide high resolution structure and blood flow imaging of the vessel simultaneously for objective surgical evaluation. Automatic boundary segmentation of the outer vessel wall boundary and its inner lumen contour is a very crucial and fundamental step for the responsive and complicated quantitative analysis required in future clinical applications of Doppler OCT imaging. In this work, we proposed a cascaded U-net (CU-net) architecture to segment the vascular intensity image and its corresponding phase image for the outer vessel wall boundary and the inner blood flowing lumen contour, respectively. CU-net architecture was developed by training two specific U-net frameworks in coordination: the first performs intensity image segmentation while the second performs phase image segmentation. Output of the first framework was sent to the input of the second framework as a mask to select area of interests. Model training time can be reduced effectively by cascading two U-net frameworks. Testing segmentation accuracy for outer vessel wall boundary and inner lumen contour were calculated to be 96.7%±0.2% and 94.8%±0.2%, respectively. The CU-net architecture requires no pre-processing on noises inherent with OCT images, such as random noise and speckle noise. The segmentation was automatic and end-to-end. 250 Doppler OCT images from one in-vivo mouse femoral artery imaging were successfully segmented automatically with an average processing time of 0.68s including both the outer vessel boundary and inner lumen contour. Thrombosis morphology, the inner blood flowing lumen area, and its radius variation were quantitatively analyzed based on the segmentation results, demonstrating the potential for clinical objective evaluation.

Artifacts in speckle tracking and multi-aperture Doppler OCT imaging of lateral motion.

In optical coherence tomography (OCT), lateral motion is determined either by speckle tracking or by multi-aperture Doppler OCT. Here we show that both methods may provide incorrect results because, outside the focal plane, non-uniform axial motion is misinterpreted as lateral motion. First, we demonstrate the existence of this artifact by means of a simulation for speckle tracking. Then the physical origin of the artifact and its mathematical relation to defocus and axial motion are explained. It is shown that speckle tracking and multi-aperture Doppler OCT are equally affected by the artifact, which has a considerable effect, even for a defocus of less than one Rayleigh length.

Boundary segmentation based on modified random walks for vascular Doppler optical coherence tomography images

Vascular Doppler optical coherence tomography (DOCT) images with weak boundaries are usually difficult for most algorithms to segment. We propose a modified random walk (MRW) algorithm with a novel regularization for the segmentation of DOCT vessel images. Based on MRW, we perform automatic boundary detection of the vascular wall from intensity images and boundary extraction of the blood flowing region from Doppler phase images. Dice, sensitivity, and specificity coefficients were adopted to verify the segmentation performance. The experimental study on DOCT images of the mouse femoral artery showed the effectiveness of our proposed method, yielding three-dimensional visualization and quantitative evaluation of the vessel.

Endoscopic optical coherence tomography with wide field-of-view for the morphological and functional assessment of the human tympanic membrane.

.An endoscopic optical coherence tomography (OCT) system with a wide field-of-view of 8 mm is presented, which combines the image capability of endoscopic imaging at the middle ear with the advantages of functional OCT imaging, allowing a morphological and functional assessment of the human tympanic membrane. The endoscopic tube has a diameter of 3.5 mm and contains gradient-index optics for simultaneous forward-viewing OCT and video endoscopy. The endoscope allows the three-dimensional visualization of nearly the entire tympanic membrane. In addition, the oscillation of the tympanic membrane is measured spatially resolved and in the frequency range between 500 Hz and 5 kHz with 125 Hz resolution, which is realized by phase-resolved Doppler OCT imaging during acoustical excitation with chirp signals. The applicability of the OCT system is demonstrated in vivo. Due to the fast image acquisition, structural and functional measurements are only slightly affected by motion artifacts.

Comparative Study of Optical Coherence Tomography Angiography and Phase-Resolved Doppler Optical Coherence Tomography for Measurement of Retinal Blood Vessels Caliber.

PurposeTo compare the accuracy of Doppler optical coherence tomography (DOCT) and OCT angiography (OCTA) for measuring retinal blood vessel caliber at different flow rates.MethodsA research-grade 1060-nm OCT system with 3.5-μm axial resolution in retinal tissue and 92,000 A scan/s image acquisition rate was used in this study. DOCT and OCTA measurements were acquired both from a flow phantom and in vivo from retinal blood vessels in six male Brown Norway rats. The total retinal blood flow (TRBF) was modified from baseline to 70% and 20% of baseline by reducing the ocular perfusion pressure (OPP). The retinal blood vessel caliber (RBVC) was measured from OCTA and DOCT images. The caliber measurements were conducted by two separate graders using a custom MATLAB-based image processing algorithm.ResultsThe RBVC measured with OCTA and DOCT for normal blood flow rates were not significantly different (56.69 ± 12.17 and 57.17 ± 9.46 μm, P = 0.27, respectively). However, significant differences were detected when TRBF was reduced to 70% (55.69 ± 11.56 vs. 50.62 ± 8.85 μm, P < 0.01) and 20% (50.29 ± 9.29 vs. 44.88 ± 7.13 μm, P < 0.01) of baseline.ConclusionsReduced TRBF resulted in inaccuracy of the RBVC measurements with DOCT in both the phantom and animal study. This result suggests that OCTA is a more accurate tool for RBVC evaluation when applied to retinal diseases associated with reduced TRBF, such as glaucoma and diabetic retinopathy.Translational RelevanceResults from this study are directly applicable to clinical studies of retinal blood flow measured with OCTA and DOCT.

ES 07.04 Endoscopic Options for Solitary Pulmonary Nodules

World-wide, aside from men in France, Spain and the Netherlands, peripherally located adenocarcinomas have now overtaken squamous cell carcinoma as the predominant lung cancer cell type. With the implementation of lung cancer screening programs using low dose CT and increasing use of CT imaging for clinical investigations, a large number of people are found to have lung nodules. In contrast to symptomatic lung cancer, the size of screening CT detected or incidental lung nodules suspicious of malignancy is much smaller. Over 75% of screening CT detected lung cancers are ≤20 mm with 20% to 47% of the lung cancers found in the first screening CT and 33% to 62% of lung cancers found in annual repeat screening CT are ≤10 mm.1-4 Because of the small size of these lesions, currently only 20% to 34% of screening CT detected lung cancers are diagnosed by endoscopy. The diagnostic yield of bronchoscopic biopsies is modest.1,2 In the real world setting, even with advanced bronchoscopic methods such as navigation bronchoscopy and radial ultrasound, the diagnostic yield of peripheral lung lesions is less than 60%.5,6 Several factors account for the suboptimal diagnostic yield. The diameter of the airways leading to the lesion may be smaller than the 1.4 mm diameter radial EBUS probe. The lesion may be eccentric rather than perpendicular to the biopsy forceps. Removable of the imaging probe from a guide sheath and re-insertion of biopsy forceps or needle may cause displacement or migration of the guide sheath to a different airway. To improve the diagnostic accuracy, other methods are being developed for endoscopic detection and biopsy of peripheral lung lesions ≤20 mm. Bronchoscopic transparenchymal approach to access peripheral lung nodules from more central airways and real time fluoroscopic transbronchial guidance systems are under evaluation.7,8 Flexible 21G peripheral needles are becoming commercially available for transbronchial aspiration or core biopsy. Small optical imaging probes < 0.5 mm that can be inserted within a 21G needle to confirm abnormal pathology in real time using optical frequency domain imaging9,10 or diffuse reflectance spectroscopy before taking a biopsy. These newer endoscopic approaches hold promise to improve diagnostic accuracy while maintaining the advantage of lower complication rates such as pneumothorax and bleeding compares to CT guided transthoracic lung biopsy. 1. National Lung Screening Research Team, Church TR, Black WC, et al. Results of initial low-dose computed tomographic screening for lung cancer. N Engl J Med. 2013 May 23;368(21):1980-91. 2. Aberle DR, DeMello S, Berg CD, et al. Results of the two incidence screenings in the National Lung Screening Trial. N Engl J Med 2013; 369(10):920-31. 3. McWilliams A, Tammemagi MC, Mayo et al. Probability of cancer in pulmonary nodules detected on first screening CT. N Engl J Med 2013;369:910-9.4. Horeweg N, van Rosmalen J, Heuvelmans MA, et al. Lung cancer probability in patients with CT- detected pulmonary nodules: a prespecified analysis of data from the NELSON trial of low-dose CT screening. Lancet Oncol. 2014 Nov;15(12):1332-41. 5. Ost DE, Ernst A, Lei X, et al. AQuIRE Bronchoscopy Registry. Diagnostic yield and complications of bronchoscopy for peripheral lung lesions. Results of the AQuIRE Registry. Am J Respir Crit Care Med. 2016 Jan 1;193(1):68-77. 6. Ali MS, Trick W, Mba BI, et al. Radial endobronchial ultrasound for the diagnosis of peripheral pulmonary lesions: A systematic review and meta-analysis. Respirology. 2017; 22(3):443-453. 7. Herth FJ, Li S, Jiayuan Sun J, Nader D. Bronchoscopic TransParenchymal Nodule Access: Evaluation of safety and feasibility of Archimedes System. Am J Respir Crit Care Med 2017;195:A7597. 8. Stoy SP, Whitten PE, Al-Zubaidi A, Hogarth K. Bronchoscopic peripheral lung nodule navigation by a novel Live fluoroscopic overlay guidance technology. Am J Respir Crit Care Med 2017;195:A2865. 9. Tan KM, Shishkov M, Chee A, et al. Flexible transbronchial optical frequency domain imaging smart needle for biopsy guidance. Biomed Opt Express 2012; 3::1947-1954. 10. Pahlevaninezhad H, Lee AM, A. R, et al. Endoscopic Doppler optical coherence tomography and autofluorescence imaging of peripheral pulmonary nodules and vasculature. Biomedical Optics xpress. 2015; 6(10):4191-9. Endoscopic biopsy

In vivo endoscopic Doppler optical coherence tomography imaging of the colon.

Colorectal cancer (CRC) remains the second deadliest cancer in the United States. Several screening methods exist; however, detection of small polyps remains a challenge. Optical coherence tomography (OCT) has been demonstrated to be capable of detecting lesions as small as 1 mm in the mouse colon, but detection is based on measuring a doubling of the mucosa thickness. The colon microvasculature may be an attractive biomarker of early tumor development because tumor vessels are characterized by irregular structure and dysfunction. Our goal was to develop an endoscopic method of detecting and segmenting colon vessels using Doppler OCT to enable future studies for improving early detection and development of novel chemopreventive agents. We conducted in vivo colon imaging in an azoxymethane (AOM)-treated mouse model of colorectal cancer using a miniature endoscope and a swept-source OCT system at 1,040 nm with a 16 kHz sweep rate. We applied the Kasai autocorrelation algorithm to laterally oversampled OCT B-scans to resolve vascular flow in the mucosa and submucosa. Vessels were segmented by applying a series of image processing steps: (i) intensity thresholding; (ii) two-dimensional matched filtering; and (iii) histogram segmentation. We observed differences in the vessels sizes and spatial distribution in a mature adenoma compared to surrounding undiseased tissue and compared the results with histology. We also imaged flow in four young mice (two AOM-treated and two control) showing no significant differences, which is expected so early after carcinogen exposure. We also present flow images of adenoma in a living mouse and a euthanized mouse to demonstrate that no flow is detected after euthanasia. We present, to the best of our knowledge, the first Doppler OCT images of in vivo mouse colon collected with a fiber-based endoscope. We also describe a fast and robust image processing method for segmenting vessels in the colon. These results suggest that Doppler OCT is a promising imaging modality for vascular imaging in the colon that requires no exogenous contrast agents. Lasers Surg. Med. 49:249-257, 2017. © 2016 Wiley Periodicals, Inc.

Fully distributed absolute blood flow velocity measurement for middle cerebral arteries using Doppler optical coherence tomography.

Doppler optical coherence tomography (DOCT) is considered one of the most promising functional imaging modalities for neuro biology research and has demonstrated the ability to quantify cerebral blood flow velocity at a high accuracy. However, the measurement of total absolute blood flow velocity (BFV) of major cerebral arteries is still a difficult problem since it is related to vessel geometry. In this paper, we present a volumetric vessel reconstruction approach that is capable of measuring the absolute BFV distributed along the entire middle cerebral artery (MCA) within a large field-of-view. The Doppler angle at each point of the MCA, representing the vessel geometry, is derived analytically by localizing the artery from pure DOCT images through vessel segmentation and skeletonization. Our approach could achieve automatic quantification of the fully distributed absolute BFV across different vessel branches. Experiments on rodents using swept-source optical coherence tomography showed that our approach was able to reveal the consequences of permanent MCA occlusion with absolute BFV measurement.

In Vivo Coregistered Doppler Optical Coherence Tomography and Autofluorescence Imaging of Peripheral Lung Cancers

In Vivo Coregistered Doppler Optical Coherence Tomography and Autofluorescence Imaging of Peripheral Lung Cancers

Endoscopic Doppler optical coherence tomography and autofluorescence imaging of peripheral pulmonary nodules and vasculature.

We present the first endoscopic Doppler optical coherence tomography and co-registered autofluorescence imaging (DOCT-AFI) of peripheral pulmonary nodules and vascular networks in vivo using a small 0.9 mm diameter catheter. Using exemplary images from volumetric data sets collected from 31 patients during flexible bronchoscopy, we demonstrate how DOCT and AFI offer complementary information that may increase the ability to locate and characterize pulmonary nodules. AFI offers a sensitive visual presentation for the rapid identification of suspicious airway sites, while co-registered OCT provides detailed structural information to assess the airway morphology. We demonstrate the ability of AFI to visualize vascular networks in vivo and validate this finding using Doppler and structural OCT. Given the advantages of higher resolution, smaller probe size, and ability to visualize vasculature, DOCT-AFI has the potential to increase diagnostic accuracy and minimize bleeding to guide biopsy of pulmonary nodules compared to radial endobronchial ultrasound, the current standard of care.

Phase-Resolved Doppler Optical Coherence Tomographic Features in Retinal Angiomatous Proliferation.

To study patients diagnosed with retinal angiomatous proliferation (RAP) based on conventional imaging techniques with phase-resolved Doppler optical coherence tomography (OCT) to detect and localize blood flow in RAP lesions; and to compare these findings to conventional imaging, which are mostly invasive and give limited information concerning intra- and transretinal blood flow. Single-center, consecutive observational case series. Twelve treatment-naïve patients diagnosed with RAP based on fundus examination, fluorescein angiography, and indocyanine green angiography were included. Median age was 79 years (range 65-90). Patients were imaged with an experimental 1040nm swept-source phase-resolved Doppler OCT instrument. Abnormal flow was defined as intraretinal neovascularization or retinal choroidal anastomosis. In 11 patients adequate phase-resolved Doppler OCT images were obtained showing abnormal blood flow in the RAP lesion. In 4 patients a retinal choroidal anastomosis was found, 3 patients showed intraretinal neovascularization connected with a pigment epithelial detachment, 2 patients showed only intraretinal neovascularization, and in 2 patients flow was limited to the subretinal or sub-retinal pigment epithelial space. Phase-resolved Doppler OCT is able to detect and localize abnormal blood flow within RAP lesions. Blood flow was mostly confined to the intraretinal structures with or without a connecting pigment epithelial detachment; in one-third of patients a retinal choroidal anastomosis was detected. The potential of angiography with phase-resolved Doppler OCT to accurately distinguish between normal and pathologic blood flow in addition to structural OCT data without invasive procedures will help to further elucidate both retinal andchoroidal vascular pathologies like RAP.

Noninvasive vascular imaging of polypoidal choroidal vasculopathy by Doppler optical coherence tomography.

To noninvasively investigate the vascular architecture of polypoidal lesions in polypoidal choroidal vasculopathy (PCV) using Doppler optical coherence tomography (OCT), and to evaluate the clinical usefulness of Doppler OCT for the assessment of therapeutic effects in PCV. Fifteen eyes of 15 patients with treatment-naïve PCV were prospectively studied. Vascular imaging was obtained using 1060-nm swept-source Doppler OCT, and compared with indocyanine green angiography (ICGA) images. The therapeutic effect of three consecutive intravitreal aflibercept injections was evaluated with ICGA and Doppler OCT. In Doppler OCT images, polypoidal lesions were clearly detected at the corresponding locations of lesions in the ICGA images. By being insensitive to dye leakage, Doppler OCT identified the complicated vascular structure in the polypoidal lesions. The identified mean area of the polypoidal lesions in the Doppler OCT images (0.04 mm(2)) was significantly smaller than that of the ICGA images (0.13 mm(2)). Polypoidal lesions were located in the retinal pigment epithelial detachment in 13 eyes, in the choroid in one eye, and in both the retinal pigment epithelial detachment and choroid in one eye. After intravitreal aflibercept treatment, areas of polypoidal lesions in the ICGA images were decreased in 14 of 15 eyes. This therapeutic effect was clearly confirmed in the Doppler OCT images. Doppler OCT imaging clearly detected fine vascular structures at the polypoidal lesions in PCV. Doppler OCT might be useful for the diagnosis and evaluation of therapeutic effects in PCV.

Visualization of dynamic boiling processes using high-speed optical coherence tomography

Investigating microscale nucleate boiling processes with high heat flux requires experimental visualization and quantification with high spatial resolution in the micrometer range as well as a sufficient temporal resolution. Numerous measurement techniques are employed for providing comprehensive experimental data on microscale boiling processes and other multiphase flows. In this context, optical coherence tomography (OCT) has been introduced recently for the visualization of quasistatic growing vapor bubbles in turbid fluids with a high spatial resolution. Since OCT detects backscattered light, only one optical access is necessary and OCT is feasible for measurements in turbid media, where other imaging techniques fail. Within this study, a high-speed OCT system is utilized for visualizing dynamic nucleate boiling processes at a heated surface with a frame rate of about 234 Hz. The bubble contour is extracted out of the OCT images using segmentation and tracking algorithm, which provide bubble contours and the course of the bubble area for individual vapor bubbles over time. Additionally, high-speed Doppler OCT imaging is presented revealing the velocity component of the fluid in beam direction up to 30 mm/s unambiguously. The present proof of principle study suggests high-speed OCT imaging as a promising and alternative technique for the simultaneous measurement of bubble geometries and fluid velocities in dynamic processes with a high spatial resolution of 16 µm. Due to the ongoing development and availability of ultra high-speed OCT systems, the perspective temporal resolution will be comparable to the frame rates provided by presently established techniques, such as particle image velocimetry or high-speed camera imaging.

Three-dimensional Vascular Imaging of Proliferative Diabetic Retinopathy by Doppler Optical Coherence Tomography

To evaluate the 3-dimensional architecture of neovascularization in proliferative diabetic retinopathy using Doppler optical coherence tomography (OCT). Prospective, nonrandomized clinical trial. Seventeen eyes of 14 patients with proliferative diabetic retinopathy were prospectively studied. Prototype Doppler OCT was used to evaluate the 3-dimensional vascular architecture at vitreoretinal adhesions. Proliferative membranes were detected in all eyes with proliferative diabetic retinopathy by standard OCT images. Doppler OCT images detected blood flow by neovascularization of the disc in 12 eyes and neovascularization elsewhere in 11 eyes. Doppler OCT images showed the 3-dimensional extent of new vessels at various stages of neovascularization, and the extent of new vessels could be clearly confirmed at vitreoretinal adhesions. Doppler OCT is useful for the detection and evaluation of the 3-dimensional vascular structure of neovascularization, and can assist in the noninvasive assessment of proliferative diabetic retinopathy.

Gold Nanorods as a Contrast Agent for Doppler Optical Coherence Tomography

PurposeTo investigate gold nanorods (GNRs) as a contrast agent to enhance Doppler optical coherence tomography (OCT) imaging of the intrascleral aqueous humor outflow.MethodsA serial dilution of GNRs was scanned with a spectral-domain OCT device (Bioptigen, Durham, NC) to visualize Doppler signal. Doppler measurements using GNRs were validated using a controlled flow system. To demonstrate an application of GNR enhanced Doppler, porcine eyes were perfused at constant pressure with mock aqueous alone or 1.0×1012 GNR/mL mixed with mock aqueous. Twelve Doppler and volumetric SD-OCT scans were obtained from the limbus in a radial fashion incremented by 30°, forming a circular scan pattern. Volumetric flow was computed by integrating flow inside non-connected vessels throughout all 12 scans around the limbus.ResultsAt the GNR concentration of 0.7×1012 GNRs/mL, Doppler signal was present through the entire depth of the testing tube without substantial attenuation. A well-defined laminar flow profile was observed for Doppler images of GNRs flowing through the glass capillary tube. The Doppler OCT measured flow profile was not statistically different from the expected flow profile based upon an autoregressive moving average model, with an error of −0.025 to 0.037 mm/s (p = 0.6435). Cross-sectional slices demonstrated the ability to view anterior chamber outflow ex-vivo using GNR-enhanced Doppler OCT. Doppler volumetric flow measurements were comparable to flow recorded by the perfusion system.ConclusionsGNRs created a measureable Doppler signal within otherwise silent flow fields in OCT Doppler scans. Practical application of this technique was confirmed in a constant pressure ex-vivo aqueous humor outflow model in porcine eyes.