Optical Coherence Tomography Image Acquisition Research Articles

Method for single illumination source combined optical coherence tomography and fluorescence imaging of fluorescently labeled ocular structures in transgenic mice

In vivo imaging permits longitudinal study of ocular disease processes in the same animal over time. Two different in vivo optical imaging modalities – optical coherence tomography (OCT) and fluorescence – provide important structural and cellular data respectively about disease processes. In this Methods in Eye Research article, we describe and demonstrate the combination of these two modalities producing a truly simultaneous OCT and fluorescence imaging system for imaging of fluorescently labeled animal models. This system uses only a single light source to illuminate both modalities, and both share the same field of view. This allows simultaneous acquisition of OCT and fluorescence images, and the benefits of both techniques are realized without incurring increased costs in variability, light exposure, time, and post-processing effort as would occur when the modalities are used separately. We then utilized this system to demonstrate multi-modal imaging in a progression of samples exhibiting both fluorescence and OCT scattering beginning with resolution targets, ex vivo thy1-YFP labeled neurons in mouse eyes, and finally an in vivo longitudinal time course of GFP labeled myeloid cells in a mouse model of ocular allergy.

Optical coherence tomography (OCT) evaluation of intermediate coronary lesions in patients with NSTEMI

Coronary angiography is commonly performed following non-ST segment elevation myocardial infarction (NSTEMI) to assess the need for revascularization. Some of these patients have myocardial infarction (MI) with no obstructive coronary atherosclerosis (MINOCA). Patients without severe obstructive lesions are usually treated conservatively. However, coronary angiography has known limitations in the assessment of lesion severity. We report our experience of using coronary Optical Coherence Tomography (OCT) in a series of patients without severe obstructive coronary lesions. 165 patients underwent coronary OCT at Vancouver General Hospital. NSTEMI was the clinical presentation in 70 patients and 26 had angiographically intermediate lesions with 40%-69% diameter stenosis. Prior to OCT image acquisition, intracoronary nitroglycerin 100-200μg was administered. Blood in the vessel was displaced using contrast media by manual injections. OCT of the angiographically intermediate lesions showed larger minimal luminal area (MLA) than the angiographically severe lesions (MLA 3.3mm(2)±1.8mm(2) vs. 1.6mm(2)±0.6mm(2), p<0.001) and less severe % lumen area stenosis (54.2%±11.4% vs. 70.9%±6.8%, p=0.001). Plaque rupture or intracoronary thrombus was detected in 8/26 (31%) patients. PCI with stent deployment was performed in 16 patients (62%). In stabilized patients with NSTEMI and angiographically intermediate disease, OCT examination confirmed the lack of severe anatomical stenosis in most patients. However, OCT also identified coronary lesions with unstable features. Further research is needed to help guide management of this subgroup of patients.

IMAGE ARTIFACTS IN OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY.

To describe image artifacts of optical coherence tomography (OCT) angiography and their underlying causative mechanisms. To establish a common vocabulary for the artifacts observed. The methods by which OCT angiography images are acquired, generated, and displayed are reviewed as are the mechanisms by which each or all of these methods can produce extraneous image information. A common set of terminology is proposed and used. Optical coherence tomography angiography uses motion contrast to image blood flow and thereby images the vasculature without the need for a contrast agent. Artifacts are very common and can arise from the OCT image acquisition, intrinsic characteristics of the eye, eye motion, image processing, and display strategies. Optical coherence tomography image acquisition for angiography takes more time than simple structural scans and necessitates trade-offs in flow resolution, scan quality, and speed. An important set of artifacts are projection artifacts in which images of blood vessels seem at erroneous locations. Image processing used for OCT angiography can alter vascular appearance through segmentation defects, and because of image display strategies can give false impressions of the density and location of vessels. Eye motion leads to discontinuities in displayed data. Optical coherence tomography angiography artifacts can be detected by interactive evaluation of the images. Image artifacts are common and can lead to incorrect interpretations of OCT angiography images. Because of the quantity of data available and the potential for artifacts, physician interaction in viewing the image data will be required, much like what happens in modern radiology practice.

Optical Density of Subretinal Fluid in Retinal Detachment.

To investigate the changes over time in optical density (OD) characteristics of subretinal fluid (SRF) in rhegmatogenous retinal detachment (RRD) and their clinical relevance. The study included patients with first-onset RRD and no history of intraocular illness who underwent optical coherence tomography (OCT) and whose OCT scans showed sufficient SRF for sampling (08/2013-09/2014). The highest quality B-scan (as graded by the OCT image acquisition software) containing SRF was analyzed. Optical density measurements were obtained using ImageJ. Optical density ratios (ODRs) were calculated as SRF OD divided by vitreous OD. Time from onset of RRD was determined by first signs of visual loss as described in the patient's anamnesis. Patients were divided into three groups by RRD duration: acute (≤1 week), subacute (between 1 week and 1 month), and chronic (>1 month). Thirty-five eyes (34 patients) met the inclusion criteria. The ODR measurement was significantly associated with RRD duration. The ODR had a significant (P < 0.0001) association with the 3-month postoperative visual acuity (VA). Vitreous OD did not differ significantly between the three groups. The increase over time in the ODR of the SRF in RRD might reflect a change in SRF composition and state of the retina. This, together with a significant association between preoperative ODR values and postoperative VA suggest its potential as a biological prognostic marker.

Serum n-3 to n-6 polyunsaturated fatty acids ratio correlates with coronary plaque vulnerability: an optical coherence tomography study

A low ratio of eicosapentaenoic acid to arachidonic acid (EPA/AA) has been demonstrated to be associated with a higher risk of cardiovascular events. Optical coherence tomography (OCT) is useful for the assessment of coronary plaque vulnerability. The purpose of this study was to evaluate the association between EPA/AA ratio and coronary plaque vulnerability. This study involved 58 patients with stable angina pectoris undergoing percutaneous coronary intervention. OCT image acquisition was performed before the procedure in the culprit lesions. We assessed lipid-rich plaque length and arc, fibrous cap thickness, frequency of thin-cap fibroatheroma (TCFA), thrombus, ruptured plaque, macrophage infiltration, and microvessels using OCT. Patients were divided into two groups according to the median value of serum EPA/AA ratio: a low-EPA/AA group (n = 29, EPA/AA ratio <0.36) and a high-EPA/AA group (n = 29, EPA/AA ratio ≥0.36). In qualitative analyses, TCFA (35.4 vs 6.9 %, P = 0.0095), macrophage infiltration (48.3 vs 13.8 %, P = 0.0045), and microvessels (44.8 vs 10.3 %, P = 0.0033) were more frequently observed in the low-EPA/AA group. In quantitative analyses, the low-EPA/AA group had wider maximum lipid arc (114.0 ± 94.8° vs 56.4 ± 66.0°, P = 0.0097), longer lipid length (4.8 ± 4.5 vs 1.6 ± 2.6 mm, P = 0.0037), and thinner fibrous cap (69.3 ± 28.3 vs 113.3 ± 46.6 μm, P = 0.005) compared with the high-EPA/AA group. EPA/AA ratio was positively correlated with fibrous cap thickness (r = 0.46, P = 0.007). In a multivariate model, an EPA/AA ratio <0.36 was associated with the presence of TCFA (odds ratio 6.41, 95 % confidence interval 1.11-61.91, P = 0.0371). In our detailed OCT analysis, lower EPA/AA ratio was associated with higher vulnerability of coronary plaques to rupture.

Low molecular weight dextran provides similar optical coherence tomography coronary imaging compared to radiographic contrast media

Optical coherence tomography (OCT) coronary imaging requires displacement of red blood cells from the vessel lumen. This is usually accomplished using radiographic contrast. Low molecular weight dextran has low cost and is safe in low volumes. In the present study, we compared dextran with contrast for coronary OCT imaging. Fifty-one vessels in 26 patients were sequentially imaged using manual injection of radiographic contrast (iodixanol) and dextran. OCT images were analyzed at 1 mm intervals to determine the image clarity (defined as a visible lumen border > 270°) and to measure the lumen area and lumen diameter. To correct for the refractive index of dextran, the dextran area measurements were multiplied by 1.117 and the dextran length measurements were multiplied by 1.057. A total of 3,418 cross-sections (1,709 with contrast and 1,709 with dextran) were analyzed. There were no complications related to OCT imaging or to contrast or dextran administration. Clear image segments were observed in 97.0% vs. 96.7% of the cross-sections obtained with contrast and dextran, respectively (P = 0.45). The mean lumen areas were also similar: 6.69 ± 1.95 mm(2) with iodixanol vs. 7.06 ± 2.06 mm(2) with dextran (correlation coefficient 0.984). The image quality and measurements during OCT image acquisition are similar for dextran and contrast. Dextran could be used instead of contrast for OCT imaging, especially in patients in whom contrast load minimization is desired.

Optical Coherence Tomography after Carotid Stenting: Rate of Stent Malapposition, Plaque Prolapse and Fibrous Cap Rupture According to Stent Design

This study aims to evaluate the rate of stent malapposition, plaque prolapse and fibrous cap rupture detected by optical coherence tomography (OCT) imaging according to carotid stent design. It was a prospective single-centre study. Forty consecutive patients undergoing protected carotid artery stenting (CAS) and high-definition OCT image acquisition were enrolled in the study. OCT frames were analysed off-line, in a dedicated core laboratory by two independent physicians. Cross-sectional OCT images within the stented segment of the internal carotid artery were evaluated at 1-mm intervals for the presence of strut malapposition, plaque prolapse and fibrous cap rupture according to stent design. Closed-cell design stents (CC) were used in 17 patients (42.5%), open-cell design stents (OC) in 13 (32.5%) and hybrid design stents (Hyb) in 10 (25%). No procedural or post-procedural neurological complications occurred (stroke/death 0% at 30 days). On OCT analysis the frequencies of malapposed struts were higher with CC compared to OC and Hyb (34.5% vs 15% and 16.3%, respectively; p < 0.01). Plaque prolapse was more frequent with OC vs CC (68.6% vs 23.3%; p < 0.01) and vs Hyb stents (30.8%; p < 0.01). Significant differences were also noted in the rates of fibrous cap rupture between CC and OC (24.2% vs 43.8%; p < 0.01), and between CC and Hyb (24.2% vs 39.6%; p < 0.01), but not between OC and Hyb stents (p = 0.4). Intravascular OCT after CAS revealed that micro-defects after stent deployment are frequent and are related to the design of implanted stents. Stent malapposition is more frequent with CC stents, while plaque prolapse is more common with OC stents. It remains, however, unknown whether these figures now detected with OCT are of any clinical and prognostic significance.

Rapid radial optical coherence tomography image acquisition

We demonstrate how compressive sampling can be used to expedite volumetric optical coherence tomography (OCT) image acquisition. We propose a novel method to interpolate OCT volumetric images from data acquired by radial B-scans in the Cartesian coordinate system. Due to the inherent polar symmetry in the human eye, the (r, θ, z) coordinate system provides a natural domain to perform the interpolation. We demonstrate that the method has minimal effect on image quality even when up to 88% of the data is not acquired. The potential outcome of this work could lead to significant reductions in OCT volume acquisition time in clinical practice.

Safety and Feasibility of Intravascular Optical Coherence Tomography Using a Nonocclusive Technique to Evaluate Carotid Plaques Before and After Stent Deployment

To evaluate the safety and feasibility of optical coherence tomography (OCT) in patients with carotid stenosis undergoing carotid artery stenting (CAS). In a prospective study, 25 consecutive patients (15 men; mean age 74±4 years) undergoing protected CAS were enrolled and underwent high-definition (homoaxial resolution 10 µm) OCT image acquisition before stent deployment, immediately after stent placement, and following postdilation of the stent (3 scans/patient). Pullbacks were started during a nonocclusive flush, mechanically injecting 24 mL of 50% diluted contrast at 6 mL/s to displace blood from the artery. Two independent physicians judged the quality of images on a predefined 1-10 scale. The proportions of specific agreement and kappa values (κ) were calculated. No procedural or in-hospital neurological complications occurred (any stroke/death 0%). The technical success of OCT pullbacks was 97.3% (73/75). The total amount of contrast was 86±18 mL/patient. No significant alteration in glomerular filtration rate or any other significant adverse event occurred. The images obtained were of high quality (mean value 8.1 out of 10), with good inter- and intraobserver agreement (κ = 0.81-0.87 and κ = 0.95, respectively). OCT images revealed innovative features such as rupture of the fibrous cap, plaque prolapse, and stent malapposition in a high percentage of the patients (range 24%-100%). Intravascular OCT during a nonocclusive flush appears to be feasible and safe in carotid arteries. Since some original and unexpected information after CAS has been made available for the first time at such a high definition, future studies with OCT should focus on the interaction between carotid plaque and stent design, which might revolutionize our understanding of the mechanisms of carotid stenting, as well as influence our clinical policies.

Differential Optical Density of Subretinal Spaces

We investigated the optical density characteristics of 3subretinal spaces in neovascular age-related macular degeneration (AMD), diabetic retinopathy (DR), rhegmatogenous retinal detachment (RRD), central serous retinopathy (CSR), retinoschisis (RS), and pseudophakic cystoids macular edema (PCME). Patients in whom subretinal fluid (SRF) was detected by optical coherence tomography (OCT), and whose earliest OCT scans showed sufficient SRF for sampling that did not include tissue edges, were chosen for study. The highest quality B-scan containing SRF (as graded by the OCT image acquisition software) was analyzed. Optical density measurements were obtained using ImageJ, an open code Java-based image processing software. The diagnoses of the 71 patients who met the inclusion criteria were AMD in 17, DR in 7, RRD in 18, CSR in 17, RS in 8, and PCME in 4. Optical density ratios (ODRs) were calculated as SRF OD divided by vitreous OD. ODRs were significantly higher in patients with AMD, DR, CSR, and PCME than in those with RRD and RS. No significant difference in vitreous reflectivity was detected between the former and latter patients. The finding that disease states produce significant changes in optical density ratios calls for further investigation of the possible usefulness of the parameter in differentiating between disease states, determining the outcome of various retinal diseases, and designing therapies aimed at treating the disease by correcting the abnormal density.

Rapid Volumetric OCT Image Acquisition Using Compressive Sampling

Acquiring three dimensional image volumes with techniques such as Optical Coherence Tomography (OCT) relies on reconstructing the tissue layers based on reflection of light from tissue interfaces. One B-mode scan in an image is acquired by scanning and concatenating several A-mode scans, and several contiguous slices are acquired to assemble a full 3D image volume. In this work, we demonstrate how Compressive Sampling (CS) can be used to accurately reconstruct 3D OCT images with minimal quality degradation from a subset of the original image. The full 3D image is reconstructed from sparsely sampled data by exploiting the sparsity of the image in a carefully chosen transform domain. We use several sub-sampling schemes, recover the full 3D image using CS, and show that there is negligible effect on clinically relevant morphometric measurements of the optic nerve head in the recovered image. The potential outcome of this work is a significant reduction in OCT image acquisition time, with possible extensions to speeding up acquisition in other imaging modalities such as ultrasound and MRI.

INTEGRATED CLINICAL EVALUATION OF TYPE 2A IDIOPATHIC JUXTAFOVEOLAR RETINAL TELANGIECTASIS

To describe spectral high-resolution optical coherence tomography (OCT) findings correlated with fundus autofluorescence (FAF), confocal blue reflectance (CBR), and fluorescein angiography (FA) patterns in patients affected by Type 2A idiopathic juxtafoveolar retinal telangiectasis. We reviewed OCT, FA, CBR, and FAF images of both eyes from 11 patients affected by Type 2A idiopathic juxtafoveolar retinal telangiectasis. One eye had Stage 2 disease, 13 eyes had Stage 3 disease, 5 eyes had Stage 4 disease, and 3 eyes had Stage 5 disease. All the imaging modalities were obtained with a combined instrument for confocal scanning laser ophthalmoscopy and Spectral-domain OCT. Simultaneous acquisition of OCT images with FA, CBR, and FAF images was achieved with perfect point-to-point correspondence. Increased parafoveal CBR was observed in all but 2 eyes that had Stage 5 disease. A correspondence of hyperautofluorescence on FAF and anatomical localization of the intraretinal cyst was observed in the 16 eyes where the cyst was visible by OCT. All eyes showed some alterations of the plexiform layers. A correspondence between increased CBR and late-phase FA hyperfluorescence occurred in the 4 eyes with focal and oval CBR pattern, whereas none of the 10 eyes with ring-pattern lesions had this correspondence. Patterns of increased CBR corresponded to areas of increased FAF in 94% of eligible eyes. The simultaneous acquisition of Spectral-domain OCT and reference images (FA, FAF, and CBR) with point-to-point correlation may further add to the understanding of morphologic alterations in Type 2A idiopathic juxtafoveolar retinal telangiectasis.

Quantitative Ex Vivo and In Vivo Comparison of Lumen Dimensions Measured by Optical Coherence Tomography and Intravascular Ultrasound in Human Coronary Arteries

The relationship between the lumen dimensions obtained in human coronary arteries using intravascular ultrasound (IVUS) and those obtained using optical coherence tomography (OCT) is not well understood. The objectives were to compare the lumen measurements obtained ex vivo in human coronary arteries using IVUS, OCT and histomorphometry, and in vivo in patients using IVUS and OCT with and without balloon occlusion. Ex vivo study: the lumen areas of matched anatomical sections of human coronary arteries were measured using IVUS, OCT and histology. In vivo study: the lumen areas in matched sections were measured using IVUS and OCT with and without occlusion. Ex vivo: in the eight specimens studied, the lumen area obtained using OCT and IVUS was larger than that obtained using histomorphometry: mean difference 0.8+/-1 mm(2) (28%) for OCT and 1.3+/-1.1 mm(2) (40%) for IVUS. In vivo: in the five vessels analyzed, the lumen area obtained using IVUS was larger than that obtained using OCT: mean difference 1.67+/-0.54 mm(2) (33.7%) for IVUS relative to OCT with occlusion and 1.11+/-0.53 mm(2) (21.5%) relative to OCT without occlusion. The lumen area obtained using OCT without occlusion was larger than that obtained using OCT with occlusion: mean difference 0.61+/-0.23 mm(2) (13%). In fixed human coronary arteries, both IVUS and OCT overestimated the lumen area compared with histomorphometry. In vivo the lumen dimensions obtained using IVUS were larger than those obtained using OCT, with or without occlusion. Moreover, the OCT image acquisition technique (i.e. with or without occlusion) also had an impact on lumen measurement.

Safety and feasibility of a new non-occlusive technique for facilitated intracoronary optical coherence tomography (OCT) acquisition in various clinical and anatomical scenarios

To facilitate OCT images acquisition we developed a novel, simplified, non-occlusive technique based on manual infusion of a viscous isosmolar solution. The aims of the present study was to address the safety and efficacy of non-occlusive OCT images acquisition modality in a patient population with complex coronary lesions, and in various clinical scenarios. OCT assessment was performed with the LightLab OCT Imagewire in 64 patients. The imaging acquisition technique was aimed at target lesion and proximal and distal reference segments. OCT images were deemed of good quality if they allowed both an accurate measurement of luminal area and a qualitative classification of the superficial plaque components.In 60 patients (93.7%), the procedure was successful. The mean images acquisition time was 5.3+/-1.4 minutes. No major complications such as death, myocardial infarction or major arrhythmias were recorded. The average length of imaged segments was 28.6+/-6.1 mm and 95.1% of the imaged segments were deemed of sufficient quality to evaluate luminal area and plaque morphology (intra-observer and inter-observer variability 0.71, p<0.0001 and 0.68, p<0.0001 respectively).Conclusions. The non-occlusive modality of OCT image acquisition is safe and effective, and promises to simplify the complex current occlusive technique, leading to a marked reduction of procedural time.