The need for dedicated bifurcation quantitative coronary angiography (QCA) software algorithms to evaluate bifurcation lesions.

Single-vessel quantitative coronary angiography (QCA) software is inaccurate when used in bifurcation lesions due to the specific anatomical characteristics of bifurcations, including the natural step-down in diameters after every bifurcation. Dedicated bifurcation QCA software has been developed to overcome the limitations of single-vessel QCA in bifurcations. A phantom validation study has shown the superior accuracy of these bifurcation QCA algorithms compared to the single-vessel QCA software. These QCA software algorithms are currently highly recommended to assess bifurcation lesions.

Clinical validation of the new T- and Y-shape models for the quantitative analysis of coronary bifurcations: an interobserver variability study.

OBJECTIVES: This article presents the results of an interobserver validation study of our new T- and Y-shape bifurcation models including their edge segment analyses. BACKGROUND: Over the last years, the coronary artery intervention procedures have been developed more and more toward bifurcation stenting. Because traditional straight vessel quantitative coronary arteriography (QCA) is not sufficient for these measurements, the need has grown for new bifurcation analysis methods. METHODS: In this article, our two new bifurcation analysis models are presented, the Y-shape and T-shape model. These models were designed for the accurate measurement of the clinically relevant parameters of a coronary bifurcation, for different morphologies and intervention strategies and include an edge segment analysis, to accurately measure (drug-eluting) stent, stent edge, and ostial segment parameters. RESULTS: The results of an interobserver validation study of our T-shape and Y-shape analyses are presented, both containing the pre- and post-intervention analyses of each 10 cases. These results are associated with only small systematic and random errors, in the majority of the cases compliant with the QCA guidelines for straight analyses. The results for the edge segment analyses are also very good, with almost all the values within the margins that have been set by our brachytherapy directive. CONCLUSIONS: Our new bifurcation approaches including their edge segment analyses are very robust and reproducible, and therefore a great extension to the field of quantitative coronary angiography.

Dedicated bifurcation analysis: basic principles.

Over the last several years significant interest has arisen in bifurcation stenting, in particular stimulated by the European Bifurcation Club. Traditional straight vessel analysis by QCA does not satisfy the requirements for such complex morphologies anymore. To come up with practical solutions, we have developed two models, a Y-shape and a T-shape model, suitable for bifurcation QCA analysis depending on the specific anatomy of the coronary bifurcation. The principles of these models are described in this paper, as well as the results of validation studies carried out on clinical materials. It can be concluded that the accuracy, precision and applicability of these new bifurcation analyses are conform the general guidelines that have been set many years ago for conventional QCA-analyses.

QCA, IVUS and OCT in interventional cardiology in 2011.

Over the past 30 years, quantitative coronary arteriography (QCA) has been used extensively as an objective and reproducible tool in clinical research to assess changes in vessel dimensions as a result of interventions, but also as a tool to provide evidence to the interventionalist prior to and after an intervention and at follow-up when necessary. With the increasing complexities of bifurcation stenting, corresponding analytical tools for bifurcation analysis have been developed with extensive reporting schemes. Although intravascular ultrasound (IVUS) has been around for a long time as well, more recent radiofrequency analysis provides additional information about the vessel wall composition; likewise optical coherence tomography (OCT) provides detailed information about the positions of the stent struts and the quality of the stent placement. Combining the information from the X-ray lumenogram and the intravascular imaging devices is mentally a challenging task for the interventionalist. To support the registration of these intravascular images with the X-ray images, 3D QCA has been developed and registered with the IVUS or OCT images, so that at every position along the vessel of interest the luminal data and the vessel wall data by IVUS or the stent strut data by OCT can be combined. From the 3D QCA the selection of the optimal angiographic views can also be facilitated. It is the intention of this overview paper to provide an extensive description of the techniques that we have developed and validated over the past 30 years.

New approaches for the assessment of vessel sizes in quantitative (cardio-)vascular X-ray analysis.

This paper presents new approaches for the assessment of the arterial and reference diameters in (cardio-)vascular X-ray images, designed to overcome the problems experienced in conventional quantitative coronary and vascular angiography approaches. In single or "straight" vessel segments, the arterial and reference diameter directions were made independent of each other in order to be able to measure the minimal lumen diameter (MLD) more accurately, especially in curved vessel segments. For ostial segments, an extension of this approach was used, to allow measurement of ostial lesions in sidebranches more proximal than using conventional methods. Furthermore, two new bifurcation approaches were developed. The validation study shows that the straight segment approach results in significant smaller MLDs (on average 0.032 mm) and the ostial approach achieves on average an increase in %DS of 3.8% and an increase in lesion length of 0.59 mm due to loosening the directional constraint. The validation of our new bifurcation approaches in phantom data as well as clinical data shows only small differences between pre- and post-intervention measurements of the reference diameters outside the bifurcation core (errors smaller than 0.06 mm) and the bifurcation core area (errors smaller than 1.4% for phantom data). In summary, these new approaches have led to further improvements in the quantitative analyses of (cardio-)vascular X-ray angiographies.

Coronary angiography enhancement for visualization.

High quality visualization on X-ray angiograms is of great significance both for the diagnosis of vessel abnormalities and for coronary interventions. Algorithms for improving the visualization of detailed vascular structures without significantly increasing image noise are currently demanded in the market. A new algorithm called stick-guided lateral inhibition (SGLI) is presented for increasing the visibility of coronary vascular structures. A validation study was set up to compare the SGLI algorithm with the conventional unsharp masking (UM) algorithm on 20 still frames of coronary angiographic images. Ten experienced QCA analysts and nine cardiologists from various centers participated in the validation. Sample scoring value (SSV) and observer agreement value (OAV) were defined to evaluate the validation result, in terms of enhancing performance and observer agreement, respectively. The mean of SSV was concluded to be 77.1 +/- 11.9%, indicating that the SGLI algorithm performed significantly better than the UM algorithm (P-value < 0.001). The mean of the OAV was concluded to be 70.3%, indicating that the average agreement with respect to a senior cardiologist was 70.3%. In conclusion, this validation study clearly demonstrates the superiority of the SGLI algorithm in the visualization of coronary arteries from X-ray angiograms.

Evaluation of patients with previous coronary stent implantation with 64-section CT.

PURPOSE: To prospectively evaluate the diagnostic accuracy of 64-section computed tomography (CT) for the assessment of in-stent or peristent restenosis, with conventional coronary angiography as the reference standard. MATERIALS AND METHODS: The study was approved by the medical ethics committee, and informed consent was obtained in all 50 enrolled patients (40 men, 10 women; mean age, 60 years +/- 11 [standard deviation]). In addition to conventional coronary angiography with quantitative coronary angiography, 64-section CT was performed. For each stent, assessability was determined and was related to stent characteristics and heart rate by using a chi(2) test. On the interpretable images of stents and peristent lumina (5.00 mm proximal and distal to the stent), the presence of significant (> or =50%) restenosis was determined. For this analysis, partially overlapping stents were considered to represent a single stent. RESULTS: Of 76 stents, 65 (86%) were determined to be assessable. Increased heart rate and overlapping positioning were associated with increased uninterpretability of the images of stents (P < .05), whereas location of the stent and thickness of the strut were not. In seven patients, stents were placed in an overlapping manner, resulting in 58 stents available for the evaluation of significant (> or =50%) in-stent restenosis. All six significant (> or =50%) in-stent restenoses were detected, and the absence of significant (> or =50%) restenosis was correctly identified in the 52 remaining stents, resulting in sensitivity and specificity of 100%. Sensitivity and specificity for the detection of significant (> or =50%) peristent stenosis were 100% and 98%, respectively. CONCLUSION: In selected patients with previous stent implantation, 64-section CT can be used to evaluate in-stent restenosis with high accuracy. Accordingly, the technique may be useful for noninvasive exclusion of in-stent or peristent restenosis, thereby avoiding invasive imaging in a considerable number of patients.

A new quantitative analysis system for the evaluation of coronary bifurcation lesions: comparison with current conventional methods.

BACKGROUND: Objective conventional quantitative angiographic systems are designed to automatically follow the contours of straight vascular segments and not of bifurcations. Recently a new analysis method was specifically developed for bifurcation lesions, able to automatically divide the lesion into three separate segments. In this study, we aimed to assess whether the smaller interaction required by the analyst could reduce the analysis time and inter and intra observer variability when compared with a conventional analysis. METHOD: We used a dedicated system (QVA-CMS V. 6.0 with the Bifurcation Module, MEDIS, Leiden, The Netherlands) applying a minimum cost algorithm tuned to detect the contours of the proximal main vessel (PMV), distal main vessel (DMV), and side-branch (SB). We assessed the intra- and the interobserver agreement in measurements of minimal lumen diameter (MLD) and percentage diameter stenosis (%DS) of the PMV and DMV, as well as of the SB ostium in 30 angiograms of patients before and after percutaneous coronary angioplasty with stenting of both branches. The consensus between measurements by two observers and by the same observer was analyzed using the intra- and interclass correlation coefficient and the reliability coefficients for all measurements. Bland-Altman plots before and after PCI were also generated to assess the relationship between variability and absolute measurements. RESULTS: Before PCI, intra- and interobserver variabilities were consistently lower for the new QVA system, with a significant difference for lesion length in the SB. Post-PCI data showed a greater variability in the assessment of diameter stenosis with both techniques. The time for analysis was significantly lower both before and after PCI for QVA compared with quantitative coronary angiography (QCA) (4.7 +/- 1.1 min versus 6.2 +/- 1.3 min, P < 0.0001). CONCLUSION: Our results demonstrate that this new quantitative bifurcation analysis system can be consistently applied to the analysis of bifurcation lesions before and after angioplasty, with an intra- and interobserver reproducibility equal to or better than the conventional analysis system with a significantly shorter analysis time.

Is there an effect of flat-panel-based imaging systems on quantitative coronary and vascular angiography?

OBJECTIVES: To study the possible effects on quantitative coronary or vascular analyses (QCA and QVA) on images of a flat-panel-based (FP-based) system. BACKGROUND: Since a few years, more and more cardiovascular X-ray imaging systems are equipped with flat-panel detectors, replacing the conventional image intensifiers in combination with CCD cameras for the creation of the angiographic images. METHODS: To assess any differences in QCA and QVA results from these two types of digital X-ray imaging systems, we performed a quantitative comparison study on images of the Medis coronary and vascular phantom, respectively. All phantom images were acquired on both a FP-based and an image intensifier-based (II-based) imaging system with different system settings (3 different kV-levels and 4 field of view sizes). RESULTS: The QCA and QVA results showed that all the systematic and random errors for the subsets of the FP-based and II-based systems were very small and satisfy the QCA and QVA reference guidelines, though some of the subsets of the FP-based and II-based coronary and vascular phantom images demonstrate a statistically significant difference. However, given the small magnitude of these under- and overestimations under phantom conditions, these differences are considered clinically irrelevant. CONCLUSIONS: The image characteristics of the FP-based images do not have any significant influence on the results of QCA and QVA analyses. As a consequence, a further optimization of the contour detection algorithm is not necessary for FP-based images, and data from both II-based and FP-based X-ray imaging systems can be used collectively in (multicenter) clinical trials.

A new approach to contour detection in x-ray arteriograms: the wavecontour.

OBJECTIVES: We sought to develop a novel approach (the Wavecontour) for the detection of contours in vascular x-ray images, designed to eliminate any systematic underestimation or overestimation for vessel sizes in the range of 0.5 to 15 mm and further minimize the influence of the user-defined start points and end points. MATERIALS AND METHODS: This method is based on the Wavefront Propagation principle in a 2-stage approach. Two validation experiments were performed: a Plexiglas phantom study (tube sizes ranging from 0.51 to 9.9 mm) and an in vivo patient study (114 patients with various degrees of stenosis). RESULTS: The phantom study demonstrated an accuracy of 0.007 mm and a precision of 0.072 mm. The patient study showed a high similarity between the detected and the expert-drawn contours: 93% for a threshold of 1.0 pixel and 81% for a threshold of 0.5 pixels. Furthermore, the contours are robust in complex lesions and are almost independent in the middle part of the segment from the user-defined start point and end point. A variation of only 0.6 pixels exists in the middle 60% of the contours. CONCLUSIONS: Our new Wavecontour approach performs very well on phantom images as well as on clinical data over the whole range of 0.5 to 15 mm and results in more robust QCA/QVA analyses.

Cardiac multidetector-row computed tomography in patients with unstable angina.

Ideally, information on coronary artery stenosis and left ventricular (LV) function is obtained in patients who have unstable angina to allow optimal risk stratification. The value of multidetector-row computed tomography (MDCT) was evaluated for a simultaneous assessment of coronary artery disease and global/regional LV function using a single acquisition. Twenty-five patients who had unstable angina underwent a single multidetector-row computed tomographic acquisition using a 4-slice multidetector-row computed tomographic system. Based on retrospective electrocardiographic gating, images and cine movies were reconstructed, which allowed 2 independent observers to analyze the 9 major coronary artery segments and global/regional LV function. Conventional angiography (with quantitative analysis) and echocardiography served as standards of reference, which were performed /=50%) coronary artery stenosis was detected with sensitivities, specificities, and positive and negative predictive values of 95%, 91%, 85%, and 97% for observer 1 and 89%, 87%, 79%, and 94% for observer 2, respectively; the interobserver kappa value was 0.73. MDCT showed excellent agreement with echocardiography for regional wall motion (90%; kappa = 0.88) and LV ejection fraction (correlation 0.95%, mean difference 0.7 +/- 3.9). Thus, MDCT can simultaneously assess coronary artery disease and LV function in patients who have unstable angina. High accuracies in excluding significant coronary artery disease and in confirming normal LV function were observed, suggesting potential clinical use for screening of patients who present with symptoms of unstable angina.

Validation of a new method for the detection of pathlines in vascular x-ray images.

This article presents the validation of a new pathline approach, based on the wavefront propagation principle, on a large variety of vascular images. The purpose of the novel approach, called wavepath, was to minimize the variability of the measurements in the quantitative vascular analysis by reducing the variability that is introduced by manually placing the start and end points of the vessel segment. This results in a robust and reproducible pathline detection that is subsequently used in the analysis and lesion quantification. The validation study that was performed concerned a large variety of vessel segments and showed that the approach results in a pathline that is totally constant in its middle part. This holds not only for the straight segment version but also for the bifurcation version and ostial version of the algorithm. Moreover, the average number of additional points per pathline needed to guide the wavepath through the correct vessel is minimized to 0 for the straight segments, 0.06 for aortic bifurcations, 0.25 for carotid bifurcations, and 0.08 for the ostial segments. In conclusion, our new approach performs very well in all types of vascular x-ray images, resulting in a stable and robust pathline detection.

A novel approach for the detection of pathlines in X-ray angiograms: the wavefront propagation algorithm.

This article presents a new pathline approach, based on the wavefront propagation principle, and developed in order to reduce the variability in the outcomes of the quantitative coronary artery analysis. This novel approach, called wavepath, reduces the influence of the user-defined start- and endpoints of the vessel segment and is therefore more robust and improves the reproducibility of the lesion quantification substantially. The validation study shows that the wavepath method is totally constant in the middle part of the pathline, even when using the method for constructing a bifurcation or sidebranch pathline. Furthermore, the number of corrections needed to guide the wavepath through the correct vessel is decreased from an average of 0.44 corrections per pathline to an average of 0.12 per pathline. Therefore, it can be concluded that the wavepath algorithm improves the overall analysis substantially.

One core laboratory at two international sites, is that feasible? An inter-core laboratory and intra-observer variability study.

To assess the magnitude of differences in QCA outcomes between two cooperating core laboratories in a single trial, we have carried out an inter-core laboratory variability study. Two QCA experts at the Montreal Heart Institute and Heart Core Leiden both analyzed 32 lesions (pre- and post-intervention) in accordance with previously agreed upon standard operating procedures. One of the experts analyzed the whole image set twice to determine the intraobserver variability. The inter-core laboratory differences in the acute gain (n = 31 pairs) are non-significant. The systematic errors of the individual measurements (n = 63 analyses) show an excellent intraclass correlation coefficient of reliability (>75%), except for the stent length (67.7%). The corresponding random errors are small. In general, the intra-observer systematic and random errors are both slightly smaller than those for the inter-core laboratory study. QCA analyses in clinical trials can be carried out in core laboratories at two different locations if and only if highly standardized conditions are maintained.

Advanced contour detection for three-dimensional intracoronary ultrasound: a validation--in vitro and in vivo.

Intracoronary ultrasound (ICUS) provides high-resolution transmural images of the arterial wall. By performing a pullback of the ICUS transducer and three-dimensional reconstruction of the images, an advanced assessment of the lumen and vessel wall morphology can be obtained. To reduce the analysis time and the subjectivity of boundary tracing, automated segmentation of the image sequence must be performed. The Quantitative Coronary Ultrasound-Clinical Measurement Solutions (QCU-CMS) (semi)automated analytical software package uses a combination of transversal and longitudinal model- and knowledge-guided contour detection techniques. On multiple longitudinal sections through the pullback stack, the external vessel contours are detected simultaneously, allowing mutual guidance of the detection in difficult areas. Subsequently, luminal contours are detected on these longitudinal sections. Vessel and luminal contour points are transformed to the individual cross-sections, where they guide the vessel and lumen contour detection on these transversal images. The performance of the software was validated stepwise. A set of phantoms was used to determine the systematic and random errors of the contour detection of external vessel and lumen boundaries. Subsequently, the results of the contour detection as obtained in in vivo image sets were compared with expert manual tracing, and finally the contour detection in in vivo image sequences was compared with results obtained from another previously validated ICUS quantification system. The phantom lumen diameters were underestimated by 0.1 mm, equally by the QCU-CMS software and by manual tracing. Comparison of automatically detected contours and expert manual contours, showed that lumen contours correspond very well (systematic and random radius difference: -0.025 +/- 0.067 mm), while automatically detected vessel contours slightly overestimated the expert manual contours (radius difference: 0.061 +/- 0.037 mm). The cross-sectional vessel and lumen areas as detected with our system and with the second computerized system showed a high correlation (r = 0.995 and 0.978, respectively). Thus, use of the new QCU-CMS analytical software is feasible and the validation data suggest its application for the analysis of clinical research.

A novel measurement technique to assess the effects of coronary brachytherapy in clinical trials.

This paper presents a novel measurement technique to assess the effects of coronary brachytherapy. This new technique is based upon the conventional quantitative coronary analysis (QCA) technique, which is accepted worldwide as an accurate and reliable analysis tool for clinical trials. This paper provides the definitions and main issues important for correct brachytherapy analysis. Based on these definitions, this novel technique is implemented as an extension of conventional QCA software, as a multisegmental analysis tool. It allows to follow the influence of radiation on restenosis, and the mutual relation between intervention devices. A pilot interobserver study was performed to assess the reliability and reproducibility of the brachytherapy analysis tool, using 15 patient cases. The validation results show that the segment lengths, minimum lumen diameter, and reference diameters of the user-defined and derived (sub)segments can be assessed reproducible. However, these good results can only be obtained, when strict and extensive image acquisition and image analysis protocols are followed. From this pilot validation study presented in this paper and only based on a small number of patients, we may conclude that the software can be applied to clinical trials.