Thermo-elastic optical coherence tomography.

The absorption of nanosecond laser pulses induces rapid thermo-elastic deformation in tissue. A sub-micrometer scale displacement occurs within a few microseconds after the pulse arrival. In this Letter, we investigate the laser-induced thermo-elastic deformation using a 1.5 MHz phase-sensitive optical coherence tomography (OCT) system. A displacement image can be reconstructed, which enables a new modality of phase-sensitive OCT, called thermo-elastic OCT. An analysis of the results shows that the optical absorption is a dominating factor for the displacement. Thermo-elastic OCT is capable of visualizing inclusions that do not appear on the structural OCT image, providing additional tissue type information.

Spectroscopic thermo-elastic optical coherence tomography for tissue characterization.

Optical imaging techniques that provide free space, label free imaging are powerful tools in obtaining structural and biochemical information in biological samples. To date, most of the optical imaging technologies create images with a specific contrast and require multimodality integration to add additional contrast. In this study, we demonstrate spectroscopic Thermo-elastic Optical Coherence Tomography (TE-OCT) as a potential tool in tissue identification. TE-OCT creates images based on two different forms of contrast: optical reflectance and thermo-elastic deformation. TE-OCT uses short laser pulses to induce thermo-elastic tissue deformation and measures the resulting surface displacement using phase-sensitive OCT. In this work we characterized the relation between thermo-elastic displacement and optical absorption, excitation, fluence and illumination area. The experimental results were validated with a 2-dimensional analytical model. Using spectroscopic TE-OCT, the thermo-elastic spectra of elastic phantoms and tissue components in coronary arteries were extracted. Specific tissue components, particularly lipid, an important biomarker for identifying atherosclerotic lesions, can be identified in the TE-OCT spectral response. As a label-free, free-space, dual-contrast, all-optical imaging technique, spectroscopic TE-OCT holds promise for biomedical research and clinical pathology diagnosis.

Biomechanical Stress Profiling of Coronary Atherosclerosis: Identifying a Multifactorial Metric to Evaluate Plaque Rupture Risk.

OBJECTIVES: The purpose of this study was to derive a biomechanical stress metric that was based on the multifactorial assessment of coronary plaque morphology, likely related to the propensity of plaque rupture in patients. BACKGROUND: Plaque rupture, the most frequent cause of coronary thrombosis, occurs at locations of elevated tensile stress in necrotic core fibroatheromas (NCFAs). Finite element modeling (FEM), typically used to calculate tensile stress, is computationally intensive and impractical as a clinical tool for locating rupture-prone plaques. This study derived a multifactorial stress equation (MSE) that accurately computes peak stress in NCFAs by combining the influence of several morphological parameters. METHODS: Intravascular ultrasound and optical frequency domain imaging were conducted in 30 patients, and plaque morphological parameters were defined in 61 NCFAs. Multivariate regression analysis was applied to derive the MSE and compute a peak stress metric (PSM) that was based on the analysis of plaque morphological parameters. The accuracy of the MSE was determined by comparing PSM with FEM-derived peak stress values. The ability of the PSM in locating plaque rupture sites was tested in 3 additional patients. RESULTS: The following parameters were found to be independently associated with peak stress: fibrous cap thickness (p < 0.0001), necrotic core angle (p = 0.024), necrotic core thickness (p < 0.0001), lumen area (p < 0.0001), necrotic core including calcium areas (p = 0.017), and plaque area (p = 0.003). The PSM showed excellent correlation (R = 0.85; p < 0.0001) with FEM-derived peak stress, thus confirming the accuracy of the MSE. In only 56% (n = 34) of plaques, the thinnest fibrous cap thickness was a determining parameter in identifying the cross section with highest PSM. In coronary segments with plaque ruptures, the MSE precisely located the rupture site. CONCLUSIONS: The MSE shows potential to calculate the PSM in coronary lesions rapidly. However, further studies are warranted to investigate the use of biomechanical stress profiling for the prognostic evaluation of patients with atherosclerosis.

Tomografía de coherencia óptica de segunda generación en la práctica clínica. La adquisición de datos de alta velocidad muestra una reproducibilidad excelente en pacientes tratados con intervenciones coronarias percutáneas / Second-generation optical coherence tomography in clinical practice. High-speed data acquisition is highly reproducible in patients undergoing percutaneous coronary intervention

Introducción y objetivos. Se ha desarrollado una segunda generación de sistemas de tomografía de coherencia óptica (OCT) (dominio de Fourier, OCT-DF) que permiten las retiradas a alta velocidad sin necesidad de ocluir transitoriamente la arteria coronaria durante la obtención de imágenes. El objetivo de este estudio es evaluar la reproducibilidad de los sistemas de OCT-DF para la caracterización de la placa y la evaluación de la implantación del stent en pacientes a los que se practican intervenciones coronarias percutáneas. Métodos. Entre mayo y diciembre de 2008, se incluyó en el estudio a 45 pacientes para los que se había programado una intervención coronaria percutánea. La adquisición de la OCT-DF se realizó con una técnica no oclusiva con velocidades de retirada de entre 5 y 20 mm/s. Se evaluó la reproducibilidad entre estudios, entre observadores y en el observador para la caracterización de la placa y el análisis de los stents. Resultados. La obtención de imágenes de dominio de Fourier se realizó satisfactoriamente en todos los pacientes (n = 45). El ritmo de infusión medio fue de 3 ± 0,4 ml/s y el volumen de contraste por retirada, 16,1 ± 3,5 ml. La media de duración y longitud de la retirada fue de 3,2 ± 1,2 s y 53,3 ± 12,4 mm. La reproducibilidad entre estudios, en cuanto a la visualización de la disección del borde, el prolapso tisular, la disección en el stent y la mala aposición, fue excelente (k = 1). Los valores de kappa para la coincidencia entre estudios, entre observadores y en el observador en la caracterización de la placa fueron 0,92, 0,82 y 0,95 respectivamente. Conclusiones. La tecnología de OCT de segunda generación, que obtiene datos a alta velocidad, muestra buena reproducibilidad entre estudios, entre observadores y en el observador para la caracterización de la placa y evaluar la implantación del stent en pacientes a los que se practican intervenciones coronarias percutáneas (AU)

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 (AU)

Comparación cuantitativa ex vivo e in vivo de las dimensiones del lumen medidas por tomografía de coherencia óptica y ecografía intravascular en arterias coronarias humanas / Quantitative Ex Vivo and in Vivo Comparison of lumen Dimensions Measured by optical Coherence tomography and intravascular ultrasound in Human Coronary arteries

Introducción y objetivos. La relación entre las dimensiones del lumen medidas por ecografía intravascular (IVUS) y tomografía de coherencia óptica (OCT) en arterias coronarias humanas no es bien conocida. Los objetivos son comparar las dimensiones del lumen en IVUS, OCT e histología en arterias coronarias humanas ex vivo, y comparar in vivo las dimensiones del lumen obtenidas en pacientes con IVUS, OCT con oclusión y OCT sin oclusión. Métodos. Estudio ex vivo: el área luminal se midió en secciones anatómicas correspondientes en IVUS, OCT e histología en arterias coronarias humanas. Estudio in vivo: el área luminal se midió en regiones correspondientes en IVUS y OCT con y sin oclusión. Resultados. Ex vivo: en las 8 muestras estudiadas, el área del lumen fue más grande en IVUS y OCT que en histología ¿diferencia media, 0,8 ± 1 mm2 (28%) para OCT y 1,3 ± 1,1 mm2 (40%) para IVUS¿. In vivo: en los cinco vasos analizados las dimensiones del lumen fueron más grandes en IVUS que en OCT ¿diferencia área media del lumen, 1,67 ± 0.54 mm2 (33,7%) para IVUS y OCT con oclusión y 1,11 ± 0.53 mm2 (21,5%) para IVUS y OCT sin oclusión¿. Las dimensiones del lumen fueron más grandes en OCT sin oclusión que en OCT con oclusión ¿diferencia media, 0,61 ± 0,23 mm2 (13%). Conclusiones. En arterias coronarias humanas fijadas, IVUS y OCT sobrestimaron el área del lumen en comparación con la histología. In vivo, las dimensiones del lumen fueron más grandes en IVUS que en OCT con o sin oclusión. La técnica de adquisición de OCT (con o sin oclusión) influye en las dimensiones del lumen (AU)

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 mm2 (28%) for OCT and 1.3±1.1 mm2 (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 mm2 (33.7%) for IVUS relative to OCT with occlusion and 1.11±0.53 mm2 (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 mm2 (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 (AU)