Effects of adaptive or fixed thresholds and different platforms on the assessment of plaque characteristics using coronary computed tomography angiography.

BACKGROUND: Coronary computed tomography angiography (CCTA) is used to evaluate components of atherosclerosis. Either adaptive or diverse, fixed Hounsfield Units (HU) are used to define components such as low attenuation (LAP), mixed (MP) and calcified plaque (CP). Comparisons of different platforms and different thresholding approaches have not been extensively evaluated. We compare two fixed threshold options to an adaptive threshold option within a specific platform and to fixed threshold options measured with another platform. METHODS: Coronary segments (n â€‹= â€‹24) of good image quality, with well-defined boundaries and representing a broad range of atheroma were analyzed for LAP, MP and CP. Thresholds for LAP vs MP and MP vs CP were either Fixed30/350, Fixed75/350 or based on an automatically determined Adaptive option. Pearson correlation and Bland-Altman analyses were undertaken. RESULTS: Within a single platform, measures were highly correlated irrespective of use of Adaptive or Fixed30/350 and Fixed75/350 thresholds (R â€‹≥ â€‹0.819, p â€‹< â€‹0.000001). The correlation slope for measures of LAP progressively diminished comparing the Adaptive versus Fixed30/350 and the Fixed75/350 versus the Fixed30/350 approaches but bias was small. Between-platform comparisons yielded less optimal results, particularly with respect to measures of LAP and with one platform yielding both very small LAP volumes and very small ranges of volumes. CONCLUSION: Measures of plaque components are highly correlated irrespective of use of Adaptive or Fixed threshold approaches within a given platform. But measures are more affected by the specific proprietary algorithms employed than by specific thresholding options, especially for LAP.

Measurement of Plaque Characteristics Using Coronary Computed Tomography Angiography: Achieving High Interobserver Performance.

BACKGROUND: Coronary computed tomography angiography (CCTA) is used to assess plaque characteristics, remodelling, and progression and regression. Few papers address standard operating procedures that ensure achievement of high interobserver reproducibility. Moreover, assessment of coronary artery bypass grafts has not been reported. METHODS: A training set of images was created of native coronary segments, spanning the full range of atheromatous disease from normal to severe, excluding totally occluded segments, and including segments with or without calcification (n = 24) and completely normal-appearing bypass grafts (n = 16). Three observers used a validated software program during a training phase to establish standard operating procedures and then to achieve high intraobserver performance based on Pearson's correlation coefficient. Subsequently, interobserver variability for the laboratory as a whole was determined with a focus on measures of plaque volume, low- attenuation plaque (LAP), mixed plaque (MP), and calcified plaque (CP). RESULTS: We found no substantive differences in analytical issues between grafts and native vessels and emphasize the aggregated data. The range of mean total plaque percent was approximately 55% of total vessel volume with maximal interobserver mean absolute differences of 2% or less. Percent of LAP, MP, and CP demonstrated interobserver standard errors of 1% to 2% and interobserver mean absolute differences of 0% to 1%. Pearson's correlations were all highly significant and ranged from 0.969 to 0.999. CONCLUSIONS: CCTA provides a rich diversity of measures of atherosclerosis in coronary and bypass segments that are highly reproducible with experience and adherence to standard operating procedures.

INTRODUCTION: L'angiographie cardiaque par tomodensitométrie (TDM) est utilisée pour évaluer les caractéristiques, le remodelage, la progression et la régression de la plaque. Peu d'articles portent sur les procédures opérationnelles normalisées qui permettent d'atteindre une reproductibilité inter-observateurs élevée. De plus, les greffons de pontage aorto-coronarien n'ont pas fait l'objet d'évaluation. MÉTHODOLOGIE: Un ensemble de formation composé d'images de segments d'artères coronaires natives couvrant l'ensemble de la maladie athéromateuse, c'est-à-dire de normale à sérieuse, à l'exclusion des segments totalement obstrués, mais y compris les segments calcifiés ou non (n = 24) et les greffons de pontage qui apparaissent complètement normaux (n = 16) a été créé. Trois observateurs ont utilisé un programme informatique validé durant la phase de formation pour établir des procédures opérationnelles normalisées et ensuite pour atteindre une performance intra-observateurs élevée en fonction du coefficient de corrélation de Pearson. Subséquemment, la variabilité inter-observateurs du laboratoire dans son ensemble a été déterminée plus particulièrement par les mesures du volume de la plaque, la plaque de faible atténuation (PFA), la plaque mixte (PM) et la plaque calcifiée (PC). RÉSULTATS: Nous n'avons constaté aucune différence dans les difficultés analytiques entre les greffons et les vaisseaux natifs et faisons valoir les données regroupées. La fourchette du pourcentage total moyen de la plaque était approximativement de 55 % du volume total du vaisseau avec des différences inter-observateurs absolues moyennes maximales de 2 % ou moins. Le pourcentage de la PFA, de la PM et de la PC a démontré des erreurs types inter-observateurs de 1 % à 2 % et des différences absolues moyennes inter-observateurs de 0 % à 1 %. Les corrélations de Pearson étaient toutes hautement significatives et allaient de 0,969 à 0,999. CONCLUSIONS: La TDM offre une riche diversité de mesures de l'athérosclérose dans les segments d'artères coronaires et de pontage qui, avec l'expérience et le respect des procédures opérationnelles normalisées, sont très reproductibles.

Redefining the normal angiogram using population-derived ranges for coronary size and shape: validation using intravascular ultrasound and applications in diverse patient cohorts.

OBJECTIVES: To develop a method for quantitating coronary angiographic abnormalities of segmental size and shape (tapering) in comparison to gender- and segment-specific, population derived, normal values. BACKGROUND: In the absence of obvious focal stenoses, remodeling renders the angiogram insensitive to the presence of atherosclerosis and invalidates use of a "normal reference segment" for calculation of percent diameter stenosis. METHODS: Equations were created for detection of size/shape abnormalities of coronary angiographic segments. After validation using intravascular ultrasound (IVUS), the equations were applied to a cohort of segments judged to be completely normal by a panel of highly experienced, core laboratory technicians; and a cohort of patients judged by an experienced interventionalist to have completely normal coronaries. RESULTS: In patients assessed by core technicians, 53% (162/303) of males, 39% (209/538) of normal segments in males, 60% (56/94) of females, and 40% (81/205) of normal segments in females had quantifiable abnormalities. In patients with normal coronaries as judged by an experienced interventionalist, 100% of males (n = 14) and females (n = 19), 37% (67/182) of segments in males and 43% (105/247) of segments in females had abnormalities. The left main segment was most commonly abnormal. CONCLUSIONS: We propose a set of equations validated using IVUS and based on gender- and segment-specific normal values for coronary angiographic size and shape that markedly improves the sensitivity of the coronary angiogram for detection of abnormalities. The method should replace the unfounded practice of labeling coronary angiograms as "normal" based solely on the failure to detect focal stenoses.

Validation of a new ultrasound method for the measurement of carotid artery intima medial thickness and plaque dimensions.

BACKGROUND: Carotid ultrasound is an accepted method for the detection of subclinical atherosclerosis. Valid methods that allow quantitation of carotid atheroma burden may be useful for stratifying risk. OBJECTIVE: To validate the results of intima medial thickness (IMT) and plaque measurements using a newly created software algorithm by comparing them with those obtained using a previously validated method. METHODS: Carotid ultrasound videotapes (n=24) were analyzed by experienced observers using a validated method and a new method. Ultrasound parameters were compared by measuring the difference +/- SD to yield indexes of accuracy and precision. Performance was also assessed using correlation and Bland-Altman analyses. RESULTS: Average IMT (n=24), plaque area (n=46), and several indexes that integrate IMT and plaque measurements were all found to be comparable with measurements obtained using the previously validated method. For example, the plaque area showed excellent accuracy and precision (-0.17+/-2.0 mm2, P=0.56), excellent correlation (r=0.98, standard error of the estimate = 2.01 mm2, P<0.001) and no evidence of bias using Bland-Altman analyses (Spearman's rho = 0.04, P=0.82). CONCLUSIONS: A new algorithm for the quantitation of carotid atheroma burden yields results that are comparable with those of a previously validated and widely used method. Availability of valid tools for measuring carotid ultrasound should facilitate the incorporation of this procedure into clinical risk stratification paradigms.