Reproducibility of IVUS border detection for carotid atherosclerotic plaque assessment

Abstract

Plaque composition is a potentially important diagnostic feature for carotid artery stenting (CAS). The purpose of this investigation is to evaluate the reproducibility of manual border correction in intravascular ultrasound with virtual histology (VH IVUS) images. Three images each were obtained from 51 CAS datasets on which automatic border detection was corrected manually by two trained observers. Plaque was classified using the definitions from the CAPITAL (Carotid Artery Plaque Virtual Histology Evaluation) study, listed in order from least to most pathological: no plaque, pathological intimal thickening, fibroatheroma, fibrocalcific, calcified fibroatheroma, thin-cap fibroatheroma, and calcified thin-cap fibroatheroma. Inter-observer variability was quantified using both weighted and unweighted Kappa statistics. Bland-Altman analysis was used to compare the cross-sectional areas of the vessel and lumen. Agreement using necrotic core percentage as the criterion was evaluated using the unweighted Kappa statistic. Agreement between classifications of plaque type was evaluated using the weighted Kappa statistic. There was substantial agreement between the observers based on necrotic core percentage (κ = 0.63), while the agreement was moderate (κquadratic = 0.60) based on plaque classification. Due to the time-consuming nature of manual border detection, an improved automatic border detection algorithm is necessary for using VH IVUS as a diagnostic tool for assessing the suitability of patients with carotid artery occlusive disease for CAS.

The association between expansive arterial remodeling detected by high-resolution MRI in carotid artery stenosis and clinical presentation

“…27 However, CA ultrasonography, multidetector CT angiography, 13,21 and MRI are better suited for screening patients for unstable plaque in the clinical setting because they are less invasive. Ultrasonography has many methodological advantages such as noninvasiveness, ease of use, and suitability for repeated imaging.…”

Virtual Histology Intravascular Ultrasound Evaluation of Atherosclerotic Carotid Artery Stenosis: Time for Fully Quantitative Image Analysis

“…4 Nevertheless, most of the exemplary raw data images in Figure 1 of their article 1 clearly do not meet these criteria. 5 Furthermore, as seen in Figure 1C of the article, 1 areas of dense calcification (coded in white) are typically surrounded by red-colored tissue, which is particularly visible behind the calcium. The first limitation is best demonstrated in Figure 1B, in which a segment of the plaque between 11 and 5 o'clock outward to the 5-mm radius from the center of the ultrasound probe is not visualized at all as it is out of the VH-IVUS imaging field.…”

“…4,5,7 As intraluminal blood is coded as fibrofatty or fibrous tissue by the VH software, 4,7 this becomes a false fibrous cap (FC) when included in the plaque on image processing. 4,5,7 As intraluminal blood is coded as fibrofatty or fibrous tissue by the VH software, 4,7 this becomes a false fibrous cap (FC) when included in the plaque on image processing.…”

“…1 Although at present no simultaneous acquisition of ChromaFlo and VH images is feasible, the ChromaFlo images (if acquired) can be systematically matched with the VH-IVUS frames, enabling an improved (albeit laborious) detection of the luminal plaque border and thus improved recognition of whether confluent NC is in direct contact (within the IVUS resolution) with the lumen. 5,13 While the latter would have been (rightly) limited by the authors using agreement between two observers for image classification, the former may have significantly affected the pivotal data from this study [''if a vulnerable plaque (phenotype) was present in just 2 consecutive frames, the lesion was not considered to be vulnerable.'' 5,13 While the latter would have been (rightly) limited by the authors using agreement between two observers for image classification, the former may have significantly affected the pivotal data from this study [''if a vulnerable plaque (phenotype) was present in just 2 consecutive frames, the lesion was not considered to be vulnerable.''…”

“…19 Over the recent years, it has become clear that risk stratification by carotid stenosis severity (or by IVUS-determined plaque burden 19 ) is not relevant in a contemporary population because carotid stenosis severity once it exceeds 50% is not predictive of the symptomatic lesion status. For meaningful, large-scale data, this interest needs to be met with reproducible VH-IVUS parameters 12 that largely eliminate important shortcomings 5,13 of the present analytical algorithms and whose observer-dependence is minimized. 19 Although noninvasive carotid plaque imaging modalities appear attractive as carotid stenosis risk stratification tools, their axial resolution is 2 to 3-fold lower than that of IVUS, [22][23][24] longitudinal resolution is several-fold lower, 23,24 and reproducibility for identification of plaque features can be only moderate.…”