Gijs van Soest

Consensus standards for acquisition, measurement, and reporting of intravascular optical coherence tomography studies: a report from the International Working Group for Intravascular Optical Coherence Tomography Standardization and Validation.

OBJECTIVES The purpose of this document is to make the output of the International Working Group for Intravascular Optical Coherence Tomography (IWG-IVOCT) Standardization and Validation available to medical and scientific communities, through a peer-reviewed publication, in the interest of improving the diagnosis and treatment of patients with atherosclerosis, including coronary artery disease. BACKGROUND Intravascular optical coherence tomography (IVOCT) is a catheter-based modality that acquires images at a resolution of ~10 μm, enabling visualization of blood vessel wall microstructure in vivo at an unprecedented level of detail. IVOCT devices are now commercially available worldwide, there is an active user base, and the interest in using this technology is growing. Incorporation of IVOCT in research and daily clinical practice can be facilitated by the development of uniform terminology and consensus-based standards on use of the technology, interpretation of the images, and reporting of IVOCT results. METHODS The IWG-IVOCT, comprising more than 260 academic and industry members from Asia, Europe, and the United States, formed in 2008 and convened on the topic of IVOCT standardization through a series of 9 national and international meetings. RESULTS Knowledge and recommendations from this group on key areas within the IVOCT field were assembled to generate this consensus document, authored by the Writing Committee, composed of academicians who have participated in meetings and/or writing of the text. CONCLUSIONS This document may be broadly used as a standard reference regarding the current state of the IVOCT imaging modality, intended for researchers and clinicians who use IVOCT and analyze IVOCT data.

Optical coherence tomography patterns of stent restenosis

BACKGROUND Stent restenosis is an infrequent but poorly understood clinical problem in the drug-eluting stent era. The aim of the study was to evaluate the morphologic characteristics of stent restenosis by optical coherence tomography (OCT). METHODS Patients (n = 24, 25 vessels) presenting with angiographically documented stent restenosis were included. Quantitative OCT analysis consisted of lumen and stent area measurement and calculation of restenotic tissue area and burden. Qualitative restenotic tissue analysis included assessment of tissue structure, backscattering and symmetry, visible microvessels, lumen shape, and presence of intraluminal material. RESULTS By angiography, restenosis was classified as diffuse, focal, and at the margins in 9, 11, and 5 vessels, respectively. By OCT, restenotic tissue structure was layered in 52%, homogeneous in 28%, and heterogeneous in 20%. The predominant backscatter was high in 72%. Microvessels were visible in 12%. Lumen shape was irregular in 28% and there was intraluminal material in 20%. The mean restenotic tissue symmetry ratio was 0.58 +/- 0.19. Heterogeneous and low scattering restenotic tissue was more frequent in focal (45.5% and 54.5%, respectively) than in diffuse (0 and 11.1%) and margin restenosis (0 and 0%) (P = .005 for heterogeneous, P = .03 for low scattering). Restenosis patients with unstable angina symptoms presented more frequently irregular lumen shape (60 vs 6.7%, P = .007). Stents implanted </=12 months ago had more frequently restenotic tissue with layered appearance (84.6% vs 16.7%, P = .003). CONCLUSIONS We demonstrate the ability of OCT to identify differential patterns of restenotic tissue after stenting. This information could help in understanding the mechanism of stent restenosis.

Atherosclerotic tissue characterization in vivo by optical coherence tomography attenuation imaging

Optical coherence tomography (OCT) is rapidly becoming the method of choice for assessing arterial wall pathology in vivo. Atherosclerotic plaques can be diagnosed with high accuracy, including measurement of the thickness of fibrous caps, enabling an assessment of the risk of rupture. While the OCT image presents morphological information in highly resolved detail, it relies on interpretation of the images by trained readers for the identification of vessel wall components and tissue type. We present a framework to enable systematic and automatic classification of atherosclerotic plaque constituents, based on the optical attenuation coefficient mu(t) of the tissue. OCT images of 65 coronary artery segments in vitro, obtained from 14 vessels harvested at autopsy, are analyzed and correlated with histology. Vessel wall components can be distinguished based on their optical properties: necrotic core and macrophage infiltration exhibit strong attenuation, mu(t)>or=10 mm(-1), while calcific and fibrous tissue have a lower mu(t) approximately 2-5mm(-1). The algorithm is successfully applied to OCT patient data, demonstrating that the analysis can be used in a clinical setting and assist diagnostics of vessel wall pathology.

Intravascular photoacoustic imaging of human coronary atherosclerosis.

We demonstrate intravascular photoacoustic imaging of human coronary atherosclerotic plaque. The data was obtained from two fresh human coronary arteries ex vivo, showing different stages of disease. A 1.25 mm diameter intravascular imaging catheter was built, comprising an angle-polished optical fiber adjacent to a 30 MHz ultrasound transducer. Specific photoacoustic imaging of lipid content, a key factor in vulnerable plaques that may lead to myocardial infarction, is achieved by spectroscopic imaging at different wavelengths between 1180 and 1230 nm. Simultaneous imaging with intravascular ultrasound was performed.

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

INTRODUCTION AND OBJECTIVES 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. METHODS 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. RESULTS 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%). CONCLUSIONS 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.

Pitfalls in plaque characterization by OCT: Image artifacts in native coronary arteries

ONE OF THE GOALS OF INTRAVASCULAR IMAGING IS SPECIFIC IN VIVO IDENTIFICATION OF VULNERABLE PLAQUES, which are likely to cause acute coronary syndrome. Intravascular optical coherence tomography (OCT) is a recent technique that is used for coronary plaque characterization, and is rapidly gaining

Diagnosis of Vertical Root Fractures with Optical Coherence Tomography

The purpose of this experiment was to evaluate the ability of optical coherence tomography (OCT) to image vertical root fractures (VRFs). Twenty-five mandibular premolars were prepared to size 50. Five teeth served as controls. Group 1 (n = 10) was treated with ethylenediaminetetraacetic acid and ultrasonic irrigation, whereas group 2 (n = 10) received no further treatments. Teeth from groups 1 and 2 were fractured, and the presence of a fracture line was demonstrated microscopically. Control group teeth were not subjected to any force. Teeth were pooled and scanned with an OCT fiber. The resulting video files were blindly interpreted by 2 observers. No fractures were detected in the control teeth. The overall sensitivity for detection of VRFs with OCT was 93% for group 1 and 84% group 2, whereas the specificity was 95% for group 1 and 96% for group 2. OCT is a promising nondestructive imaging method for the diagnosis of VRFs.

Intravascular optical coherence tomography imaging at 3200 frames per second

We demonstrate intravascular optical coherence tomography (OCT) imaging with frame rate up to 3.2 kHz (192,000 rpm scanning). This was achieved by using a custom-built catheter in which the circumferential scanning was actuated by a 1.0 mm diameter synchronous motor. The OCT system, with an imaging depth of 3.7 mm (in air), is based on a Fourier domain mode locked laser operating at an A-line rate of 1.6 MHz. The diameter of the catheter is 1.1 mm at the tip. Ex vivo images of human coronary artery (78.4 mm length) were acquired at a pullback speed of 100 mm/s. True 3D volumetric imaging of the entire artery, with dense and isotropic sampling in all dimensions, was performed in <1 second acquisition time.

Photoacoustic imaging of human coronary atherosclerosis in two spectral bands

Spectroscopic intravascular photoacoustic imaging (sIVPA) has shown promise to detect and distinguish lipids in atherosclerotic plaques. sIVPA generally utilizes one of the two high absorption bands in the lipid absorption spectrum at 1.2 μm and 1.7 μm. Specific absorption signatures of various lipid compounds within the bands in either wavelength range can potentially be used to differentiate between plaque lipids and peri-adventitial lipids. With the aim to quantify any differences between the two bands, we performed combined sIVPA imaging in both absorption bands on a vessel phantom and an atherosclerotic human coronary artery ex vivo. Lipid detection in a human atherosclerotic lesion with sIVPA required lower pulse energy at 1.7 μm than at 1.2 μm (0.4 mJ versus 1.2 mJ). The imaging depth was twice as large at 1.2 μm compared to 1.7 μm. Adequate differentiation between plaque and peri-adventitial lipids was achieved at 1.2 μm only.

Second-generation optical coherence tomography in clinical practice. High-speed data acquisition is highly reproducible in patients undergoing percutaneous coronary intervention

INTRODUCTION AND OBJECTIVES The development of second-generation optical coherence tomography (i.e. Fourier domain optical coherence tomography, FD-OCT) has made it possible to perform high speed pullbacks during image acquisition without the need for transient occlusion of the coronary artery. The objective of this study was to assess the reproducibility of FD-OCT systems for characterizing plaque and evaluating stent implantation in patients undergoing a percutaneous coronary intervention. METHODS The study included 45 patients scheduled for percutaneous coronary intervention who were enrolled between May and December 2008. Image acquisition was performed by FD-OCT using a non-occlusive technique and employing pullback speeds ranging from 5 to 20 mm/s. Interstudy, interobserver and intraobserver reproducibility of plaque characterization and stent analysis were assessed. RESULTS Fourier domain imaging was successfully performed in all patients (n=45). The average flush rate was 3+/-0.4 mL/s and the contrast volume per pullback was 16.1+/-3.5 mL. The mean pullback duration and length were 3.2+/-1.2 s and 53.3+/-12.4 mm, respectively. The interstudy reproducibility for visualizing edge dissection, tissue prolapse, intrastent dissection and malapposition was excellent (k=1). The kappa values for interstudy, interobserver and intraobserver agreement on plaque characterization were 0.92, 0.82 and 0.95, respectively. CONCLUSIONS A second-generation OCT system (i.e. FD-OCT) involving high-speed data acquisition demonstrated good interstudy, interobserver and intraobserver reproducibility for characterizing plaque and evaluating stent implantation in patients undergoing a percutaneous coronary intervention.