Interstudy reproducibility of the second generation, Fourier domain optical coherence tomography in patients with coronary artery disease and comparison with intravascular ultrasound: a study applying automated contour detection

Intravascular imaging modalities in coronary intervention: Insights from 3D-printed phantom coronary models

INTRODUCTION AND OBJECTIVES

Several studies comparing optical coherence tomography (OCT) and intravascular ultrasound (IVUS) have revealed that OCT consistently provides smaller area and diameter measurements. However, comparative assessment in clinical practice is difficult. Three-dimensional (3D) printing offers a unique opportunity to assess intravascular imaging modalities. We aim to compare intravascular imaging modalities using a 3D-printed coronary artery in a realistic simulator and to assess whether OCT underestimates intravascular dimensions, exploring potential corrections.

METHODS

A standard realistic left main anatomy with an ostial left anterior descending artery lesion was replicated using 3D printing. After provisional stenting and optimization, IVI was obtained. Modalities included 20 MHz digital IVUS, 60 MHz rotational IVUS (HD-IVUS) and OCT. We assessed luminal area and diameters at standard locations.

RESULTS

Considering all coregistered measurements, OCT significantly underestimated area, minimal diameter and maximal diameter measurements in comparison to IVUS and HD-IVUS (p<0.001). No significant differences were found between IVUS and HD-IVUS. A significant systematic dimensional error was found in OCT auto-calibration by comparing known reference diameter of guiding catheter (1.8 mm) to measured mean diameter (1.68 mm±0.04 mm). By applying a correction factor based on the reference guiding catheter area to OCT, the luminal areas and diameters became not significantly different compared to IVUS and HD-IVUS.

CONCLUSION

Our findings suggest that automatic spectral calibration method for OCT is inaccurate, with a systematic underestimation of luminal dimensions. When guiding catheter correction is applied the performance of OCT is significantly improved. These results may be clinically relevant and need to be validated.

Qualitative and quantitative evaluation of dynamic changes in non-culprit coronary atherosclerotic lesion morphology: a longitudinal OCT study

AIMS

There is limited in vivo evidence regarding the temporal evolution of non-culprit coronary plaque morphology. We aimed to evaluate changes in non-culprit plaque morphology over time by optical coherence tomography (OCT).

METHODS AND RESULTS

Seventy-two (72) patients with 257 non-culprit segments with serial OCT studies were analysed. Non-culprit 5 mm-long coronary segments from the same imaged region were matched between baseline and follow-up. OCT plaque characterisation including automated attenuation analysis was performed, and changes over a median follow-up of 6.2 months were evaluated. On segment level, lumen area decreased from baseline to follow-up, whereas fibrous cap thickness increased. Similarly, plaque attenuation indices at follow-up were significantly decreased. Minimal cap thickness per patient did not change. In 68.5% of segments, plaque morphology did not change. Favourable change was observed in 18.4% of segments and unfavourable in 12.9%. There were no robust clinical predictors of change in plaque morphology. Attenuation analysis supported the qualitative characterisation, showing significantly different attenuation between different plaque types.

CONCLUSIONS

In non-culprit coronary segments of patients with coronary artery disease under standard medical therapy, segment-level but not patient-level minimum fibrous cap thickness increases over time, with observations of both favourable and unfavourable changes in individual segments.

Intra- and interobserver reliability and intra-catheter reproducibility using frequency domain optical coherence tomography for the evaluation of morphometric stent parameters and qualitative assessment of stent strut coverage

PURPOSE

Frequency-domain optical coherence tomography (FD-OCT) is a high-resolution imaging tool (~10-15 μm), which enables near-histological in-vivo images of the coronary vessel wall. The use of the technique is increasing, both for research- and clinical purposes. This study sought to investigate the intra- and interobserver reliability, as well as the intra-catheter reproducibility of quantitative FD-OCT-assessment of morphometric stent parameters and qualitative FD-OCT-evaluation of strut coverage in 10 randomly selected 6-month follow-up Nobori® biolimus-eluting stents (N-BESs).

METHODS

Ten N-BESs (213 cross sectional areas (CSAs) and 1897 struts) imaged with OCT 6 months post-implantation were randomly selected and analyzed by 2 experienced analysts, and the same 10 N-BESs were analyzed by one of the analysts 3 months later. Further, 2 consecutive pullbacks randomly performed in another 10 N-BESs (219 CSAs and 1860 struts) were independently assessed by one of the analysts.

RESULTS

The intraobserver variability with regard to relative difference of mean luminal area and mean stent area at the CSA-level was very low: 0.1%±1.4% and 0.5%±3.2%. Interobserver variability also proved to be low: -2.1%±3.3% and 2.1%±4.6%, and moreover, very restricted intra-catheter variation was observed: 0.02%±6.8% and -0.18%±5.2%. The intraobserver-, interobserver- and intra-catheter reliability for the qualitative evaluation of strut coverage was found to be: kappa (κ)=0.91 (95% confidence interval (CI): 0.88-0.93, p<0.01), κ=0.88 (95% CI: 0.85-0.91, p<0.01), and κ=0.73 (95% CI: 0.68-0.78, p<0.01), respectively.

CONCLUSIONS

FD-OCT is a reproducible and reliable imaging tool for quantitative evaluation of stented coronary segments, and for qualitative assessment of strut coverage.

Multi-laboratory inter-institute reproducibility study of IVOCT and IVUS assessments using published consensus document definitions

AIMS

The aim of this study was to investigate the reproducibility of intravascular optical coherence tomography (IVOCT) assessments, including a comparison to intravascular ultrasound (IVUS). Intra-observer and inter-observer variabilities of IVOCT have been previously described, whereas inter-institute reliability in multiple laboratories has never been systematically studied.

METHODS AND RESULTS

In 2 independent laboratories with intravascular imaging expertise, 100 randomized matched data sets of IVOCT and IVUS images were analysed by 4 independent observers according to published consensus document definitions. Intra-observer, inter-observer, and inter-institute variabilities of IVOCT qualitative and quantitative measurements vs. IVUS measurements were assessed. Minor inter- and intra-observer variability of both imaging techniques was observed for detailed qualitative and geometric analysis, except for inter-observer mixed plaque identification on IVUS (κ = 0.70) and for inter-observer fibrous cap thickness measurement reproducibility on IVOCT (ICC = 0.48). The magnitude of inter-institute measurement differences for IVOCT was statistically significantly less than that for IVUS concerning lumen cross-sectional area (CSA), maximum and minimum lumen diameters, stent CSA, and maximum and minimum stent diameters (P < 0.001, P < 0.001, P < 0.001, P = 0.02, P < 0.001, and P = 0.01, respectively). Minor inter-institute measurement variabilities using both techniques were also found for plaque identification.

CONCLUSION

In the measurement of lumen CSA, maximum and minimum lumen diameters, stent CSA, and maximum and minimum stent diameters by analysts from two different laboratories, reproducibility of IVOCT was more consistent than that of IVUS.

Assessment and Quantitation of Stent Results by Intracoronary Optical Coherence Tomography

Optical coherence tomography evaluation of poststent results includes stent expansion as the absolute minimum stent area ratio by comparing the minimum stent area with the proximal and distal reference lumen areas or mean stent area defined as the total stent volume divided by the analyzed stent length; stent strut malapposition defined when the distance from the center of the blooming artifact and the surface of plaque is greater than the sum of stent thickness and polymer thickness; tissue protrusion through the stent struts; semiquantitative residual thrombus evaluation; and stent edge dissection.

Clinical validation of an algorithm for rapid and accurate automated segmentation of intracoronary optical coherence tomography images

OBJECTIVES

The analysis of intracoronary optical coherence tomography (OCT) images is based on manual identification of the lumen contours and relevant structures. However, manual image segmentation is a cumbersome and time-consuming process, subject to significant intra- and inter-observer variability. This study aims to present and validate a fully-automated method for segmentation of intracoronary OCT images.

METHODS

We studied 20 coronary arteries (mean length=39.7±10.0 mm) from 20 patients who underwent a clinically-indicated cardiac catheterization. The OCT images (n=1812) were segmented manually, as well as with a fully-automated approach. A semi-automated variation of the fully-automated algorithm was also applied. Using certain lumen size and lumen shape characteristics, the fully- and semi-automated segmentation algorithms were validated over manual segmentation, which was considered as the gold standard.

RESULTS

Linear regression and Bland-Altman analysis demonstrated that both the fully-automated and semi-automated segmentation had a very high agreement with the manual segmentation, with the semi-automated approach being slightly more accurate than the fully-automated method. The fully-automated and semi-automated OCT segmentation reduced the analysis time by more than 97% and 86%, respectively, compared to manual segmentation.

CONCLUSIONS

In the current work we validated a fully-automated OCT segmentation algorithm, as well as a semi-automated variation of it in an extensive "real-life" dataset of OCT images. The study showed that our algorithm can perform rapid and reliable segmentation of OCT images.

Comparison of longitudinal geometric measurement in human coronary arteries between frequency-domain optical coherence tomography and intravascular ultrasound

Previous studies have demonstrated the higher accuracy of frequency-domain optical coherence tomography (FD-OCT) for quantitative measurements in comparison with intravascular ultrasound (IVUS). However, those analyses were based on the cross-sectional images. The aim of this study was to assess the accuracy of FD-OCT for longitudinal geometric measurements of coronary arteries in comparison with IVUS. Between October 2011 and March 2012, we performed prospective FD-OCT and IVUS examinations in consecutive 77 patients who underwent percutaneous coronary intervention with single stent. Regression analysis and Bland-Altman analysis revealed an excellent correlation between the FD-OCT-measured stent lengths and IVUS-measured stent lengths (r = 0.986, p < 0.001; mean difference = -0.51 mm). There was an excellent agreement between the actual stent lengths and the FD-OCT-measured stent lengths (r = 0.993, p < 0.001) as well as between the actual stent lengths and the IVUS-measured stent lengths (r = 0.981, p < 0.001). The difference between the actual stent lengths and the FD-OCT-measured stent lengths was significantly smaller than that between the actual stent lengths and the IVUS-measured stent lengths (0.15 ± 0.68 vs. 0.70 ± 1.15 mm, p < 0.001). Both FD-OCT (mean difference = -0.04 and -0.04 mm, respectively) and IVUS (mean difference = -0.06 and -0.06 mm, respectively) showed an excellent intra-observer and inter-observer reproducibility for the stent length measurements. In conclusion, FD-OCT provides accurate longitudinal measurement with excellent intra-observer and inter-observer reproducibility. FD-OCT might be a reliable technique for longitudinal geometric measurement in human coronary arteries.