OCT-measured plaque free wall angle is indicative for plaque burden: overcoming the main limitation of OCT?

The aim of this study was to investigate the relationship between the plaque free wall (PFW) measured by optical coherence tomography (OCT) and the plaque burden (PB) measured by intravascular ultrasound (IVUS). We hypothesize that measurement of the PFW could help to estimate the PB, thereby overcoming the limited ability of OCT to visualize the external elastic membrane in the presence of plaque. This could enable selection of the optimal stent-landing zone by OCT, which is traditionally defined by IVUS as a region with a PB < 40 %. PB (IVUS) and PFW angle (OCT and IVUS) were measured in 18 matched IVUS and OCT pullbacks acquired in the same coronary artery. We determined the relationship between OCT measured PFW (PFWOCT) and IVUS PB (PBIVUS) by non-linear regression analysis. An ROC-curve analysis was used to determine the optimal cut-off value of PFW angle for the detection of PB < 40 %. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated. There is a significant correlation between PFWOCT and PBIVUS (r(2) = 0.59). The optimal cut-off value of the PFWOCT for the prediction of a PBIVUS < 40 % is ≥220° with a PPV of 78 % and an NPV of 84 %. This study shows that PFWOCT can be considered as a surrogate marker for PBIVUS, which is currently a common criterion to select an optimal stent-landing zone.

Positive remodeling at 3 year follow up is associated with plaque-free coronary wall segment at baseline: a serial IVUS study.

AIMS: At present it is unknown what limits the arterial remodeling process during atherosclerotic plaque formation. In healthy arteries remodeling is regulated by the shear stress induced response by the endothelium. As endothelium at the plaque site is assumed to be dysfunctional, we tested the hypothesis that plaque free wall (PFW) determines vascular remodeling during atherosclerotic plaque build-up. METHODS & RESULTS: 66 human coronary ROIs (38 patients) were studied at baseline and at 3 years follow up applying intravascular ultrasound (IVUS). From the IVUS images the lumen and external elastic membrane contours were delineated to assess wall thickness (WT), vessel area (VA), Plaque Area (PA) and plaque burden (PA/VA*100%). WT < 0.5 mm was defined as normal and determined the arc of the PFW (0-360°). Positive remodeling was defined as relative difference of VA over time >5%. At baseline, IVUS-PFW was inversely related to plaque burden (p < 0.05). Positive remodeling was most frequently observed in ROIs with IVUS-PFW > 180° (i.e. larger than half of the circumference) compared to PFW < 180° (55% vs. 12%, p < 0.05). Accordingly, plaques with IVUS-PFW > 180° at baseline had the largest change in VA (1.1 ± 2.1 vs. -0.4 ± 0.6 mm(2), p < 0.05) with an odds ratio of 9.2 to develop positive remodeling. CONCLUSIONS: Our serial IVUS data show that IVUS-PFW is a determinant of vascular remodeling. ROIs with PFW > 180 at baseline had the highest probability to undergo positive remodeling.

3D reconstruction techniques of human coronary bifurcations for shear stress computations.

BACKGROUND: Heterogeneity in plaque composition in human coronary artery bifurcations is associated with blood flow induced shear stress. Shear stress is generally determined by combing 3D lumen data and computational fluid dynamics (CFD). We investigated two new procedures to generate 3D lumen reconstructions of coronary artery bifurcations for shear stress computations. METHODS: We imaged 10 patients with multislice computer tomography (MSCT) and intravascular ultrasound (IVUS). The 3D reconstruction of the main branch was based on the fusion of MSCT and IVUS. The proximal part of side branch was reconstructed using IVUS data or MSCT data, resulting in two different reconstructions of the bifurcation region. The distal part of the side branch was based on MSCT data alone. The reconstructed lumen was combined with CFD to determine the shear stress. Low and high shear stress regions were defined and shear stress patterns in the bifurcation regions were investigated. RESULTS: The 3D coronary bifurcations were successfully generated with both reconstruction procedures. The geometrical features of the bifurcation region for the two reconstruction procedures did not reveal appreciable differences. The shear stress maps showed a qualitative agreement, and the low and high shear stress regions were similar in size and average shear stress values were identical. The low and high shear stress regions showed an overlap of approximately 75%. CONCLUSION: Reconstruction of the side branch with MSCT data alone is an adequate technique to study shear stress and wall thickness in the bifurcation region. The reconstruction procedure can be applied to further investigate the effect of shear stress on atherosclerosis in coronary bifurcations.

Advanced three-dimensional quantitative coronary angiographic assessment of bifurcation lesions: methodology and phantom validation.

AIMS: Validation of new three-dimensional (3-D) bifurcation quantitative coronary angiography (QCA) software. METHODS AND RESULTS: Cardiovascular Angiography Analysis System (CAAS 5v10) allows 3-D angiographic reconstructions based on two or more 2-D projection images. Measurements for minimal lumen diameter (MLD), reference vessel diameter (RVD), percent diameter stenosis (DS) and bifurcation angle (BA) were validated against precision manufactured phantom bifurcations. Length measurements were validated against angiographic measurement catheters inserted into a plexiglas bifurcation phantom. In 3-D reconstructions based on two 2-D images, acquired at variable rotation and angulation, accuracy and precision (mean difference ± SD) of the 11-segment model for MLD, RVD and DS were 0.013±0.131 mm, -0.052±0.039 mm and -1.08±5.13%, respectively; inter-observer variability was 0.141 mm, 0.058 mm and 5.42%, respectively. Adding the antero-posterior (optimal) projection to these basic reconstructions resulted in reduced variability (0.101 mm, 0.041 mm and 3.93% for MLD, RVD and DS, p<0.01 for all) and showed a trend towards improved precision (0.109 mm, 0.031 mm and 4.26%, respectively, p>0.05 for all). In basic reconstructions, accuracy and precision for BA was -1.3±5.0°, whereas inter-observer variability was 7.5°; respective measures for length were 0.15±0.26 mm and 0.54 mm. Adding the antero-posterior projection resulted in decreased precision (0.47 mm, p<0.01) and increased variability (1.03 mm, p<0.01) for length measurements; precision (5.4°) and variability (7.9°) for BA did not change significantly (p>0.30). CONCLUSIONS: Advances in the methodology of 3-D reconstruction and quantitative analysis for bifurcation lesions translated into highly accurate, precise and reproducible measures of diameter, length and BA.

In vivo assessment of the relationship between shear stress and necrotic core in early and advanced coronary artery disease.

AIMS: Atherosclerotic plaques develop at low shear stress locations in the arterial tree. However, at a certain moment, plaques encroach into the lumen causing local wall shear stress (WSS) increase. Minimal information is available on the relationship between WSS and plaque composition. We investigated in human coronary arteries in vivo the frequency with which the necrotic core and necrotic core in contact with the lumen are located at either low or high WSS regions in early and advanced plaques. METHODS AND RESULTS: We combined a 3-D reconstruction technique of coronary arteries based on angiography and intravascular ultrasound with IVUS-virtual histology (IVUS-VH) data. With IVUS-VH the necrotic core was determined. The lumen of these 3-D reconstructions served as input for the computational fluid dynamics. Per cross-section the WSS at the regions with major necrotic core and necrotic core in contact with the lumen were compared to the median WSS in the cross-section. Ten human coronary arteries were studied. Only cross-sections with average wall thickness >0.5 mm were included in the analysis. In early plaques (plaque burden <40%), the necrotic core was most frequently located at WSS smaller than the median (61%) contrasting the advanced plaques (plaque burden >40%), being located at WSS higher than the median (60%, p<0.05 Mann-Whitney U test). Necrotic core in contact with the lumen was most often exposed to high WSS, being most pronounced in advanced disease (61%, p<0.05). CONCLUSIONS: With the advancement of disease, necrotic core is less often located at low WSS regions, but exposed to high WSS, which is probably the result of lumen narrowing. Necrotic core in contact with the lumen was most frequently exposed to high WSS.

Advances in two-dimensional quantitative coronary angiographic assessment of bifurcation lesions: improved small lumen diameter detection and automatic reference vessel diameter derivation.

AIMS: To validate a new two dimensional (2-D) bifurcation quantitative coronary angiography (QCA) software. METHODS AND RESULTS: In the latest edition of the Cardiovascular Angiography Analysis System (CAAS 5.9; Pie Medical Imaging, Maastricht, The Netherlands) video-densitometric information is dynamically integrated into the edge-detection algorithm of 11- and 6-segment models to reduce overestimation of small diameters. Furthermore, automatic reference obstruction analysis was optimised. Values of the minimal lumen diameter (MLD), reference vessel diameter (RVD), percent diameter stenosis (DS) and bifurcation angle (BA) for the different bifurcation segment models were validated against precision manufactured plexiglass phantoms. In anteroposterior views, accuracy and precision (mean difference±SD) of 11- and 6-segment models for MLD were 0.013±0.082 mm vs. 0.003±0.100 mm, for RVD -0.030±0.047 mm vs. -0.029±0.045 mm and for DS -0.48±3.66% vs. -0.11±3.97%. In smaller vessel segments (true MLD <0.7 mm), MLD overestimation was reduced. Inter-observer variability for MLD, RVD and DS for either model was ≤0.052 mm, ≤0.043 mm and ≤2.24%, respectively. Agreement between models for MLD, RVD and DS was ±0.076 mm, ±0.021 mm and ±2.53%, respectively. Accuracy and precision for BA were -2.6±3.5°, and variability was ≤1.2°. Accuracy and precision for diameter-derived parameters were slightly decreased in projections with 30° rotation; BA precision dropped to 6.2°. CONCLUSIONS: MLD quantification is improved for true MLD <0.7 mm, resulting in highly accurate and precise diameter measurements over the entire range of phantom diameters. Automatic reference obstruction analysis provides highly accurate, precise and reproducible RVD and DS measurements.

Validity and variability in visual assessment of stenosis severity in phantom bifurcation lesions: a survey in experts during the fifth meeting of the European Bifurcation Club.

OBJECTIVES: To investigate the adequacy of visual estimate regarding the percent diameter stenosis (DS) in bifurcation lesions. BACKGROUND: Quantitative coronary angiography (QCA) is more accurate and precise compared to visual estimate in assessing stenosis severity in single-vessel lesions. METHODS: Thirty-six experts in the field of bifurcation PCI visually assessed the DS in cine images of five precision manufactured phantom bifurcation lesions, experts being blinded to the true values. Expert DS estimates were compared with the true values and they were also used to define the Medina class of each individual bifurcation. Results were pooled together both for proximal main vessel (PMV), distal main vessel (DMV) and side-branch (SB) segments and for vessel segments with similar DS values. RESULTS: Individual performance was highly variable among observers; pooled values and range of accuracy and precision were 2.79% (-6.67% to 17.33%) and 8.69% (4.31-16.25%), respectively. On average, DS was underestimated in the PMV (-1.08%, P = 0.10) and overestimated in the DMV (3.86% P < 0.01) and SB segments (5.58%, P < 0.01). Variability in visual estimates was significantly larger in lesions of medium severity compared to the clearly obstructive ones (P < 0.01); the latter were consistently overestimated. Inter-observer agreement was moderate (κ = 0.55) over the entire number of estimates. However, if the segments with true DS = 0% were excluded, agreement was diminished (κ = 0.27). Inter-observer agreement in Medina class was rather low (κ = 0.21). True bifurcation lesions were misclassified as non-true ones in 14/180 estimates. CONCLUSIONS: Visual assessment by experts is more variable and less precise in the analysis of bifurcation lesions compared to bifurcation QCA software.

Detection and quantification of coronary atherosclerotic plaque by 64-slice multidetector CT: a systematic head-to-head comparison with intravascular ultrasound.

OBJECTIVE: We evaluated the ability of 64-slice multidetector computed tomography (MDCT)-derived plaque parameters to detect and quantify coronary atherosclerosis, using intravascular ultrasound (IVUS) as the reference standard. METHODS: In 32 patients, IVUS and 64-MDCT was performed. The MDCT and IVUS datasets of 44 coronary arteries were co-registered using a newly developed fusion technique and quantitative parameters were derived from both imaging modalities. The threshold of >0.5 mm of maximum wall thickness was used to establish plaque presence on MDCT and IVUS. RESULTS: We analyzed 1364 coregistered 1-mm coronary cross-sections and 255 segments of 5-mm length. Compared with IVUS, 64-MDCT enabled correct detection in 957 of 1109 cross-sections containing plaque (sensitivity 86%). In 180 of 255 cross-sections atherosclerosis was correctly excluded (specificity 71%). On the segmental level, MDCT detected 213 of 220 segments with any atherosclerotic plaque (sensitivity 96%), whereas the presence of any plaque was correctly ruled out in 28 of 32 segments (specificity 88%). Interobserver agreement for the detection of atherosclerotic cross-sections was moderate (Cohen's kappa coefficient K=0.51), but excellent for the atherosclerotic segments (K=1.0). Pearson's correlation coefficient for vessel plaque volumes measured by MDCT and IVUS was r=0.91 (p<0.001). Bland-Altman analysis showed a slight non-significant underestimation of any plaque volume by MDCT (p=0.5), with a trend to underestimate noncalcified and overestimate mixed/calcified plaque volumes (p=0.22 and p=0.87 respectively). CONCLUSION: MDCT is able to detect and quantify atherosclerotic plaque. Further improvement in CT resolution is necessary for more reliable assessment of very small and distal coronary plaques.

High shear stress induces a strain increase in human coronary plaques over a 6-month period.

AIMS: Atherosclerotic plaques develop in low shear stress regions. In the more advanced phase of the disease, plaques are exposed to altered shear stress levels, which could influence plaque composition. We investigated changes in plaque composition in human coronary arteries over a 6-month period and how these changes are related to shear stress. METHODS AND RESULTS: We took images of eight coronary arteries to obtain the 3D shape of the arteries. Lumen data were combined with computational fluid dynamics to obtain shear stress. Palpography was applied to measure strain at baseline and at 6-month follow-up. The change in strain from baseline to follow-up served as a marker for the change in plaque composition. We identified 17 plaques, and each plaque was divided into four regions: the upstream, throat, shoulder and downstream region. Shear stress and strain in the downstream region was significantly lower than in the other regions. There was no significant change in strain for the four different plaque regions. However, we observed that those plaque regions exposed to high shear stress showed a significant increase in strain. CONCLUSIONS: Plaque regions exposed to high shear stress showed an increase in strain over time. This indicates that shear stress may modulate plaque composition in human coronary arteries.

Two-dimensional quantitative coronary angiographic models for bifurcation segmental analysis: in vitro validation of CAAS against precision manufactured plexiglas phantoms.

BACKGROUND: Quantitative coronary angiography (QCA) analysis for bifurcation lesions needs to be standardized. OBJECTIVES: In vitro validation of two models for bifurcation QCA segmental analysis. METHODS: In the latest edition of the Cardiovascular angiography analysis system (CAAS 5v8, Pie Medical Imaging, Maastricht, The Netherlands) a 6-segment model for two-dimensional coronary bifurcation analysis was implemented next to the currently available 11-segment model. Both models were validated against 6 precision manufactured plexiglas phantoms, each of them mimicking a vessel with three successive bifurcation lesions with variable anatomy and Medina class. The phantoms were filled with 100% contrast agent and imaged with a biplane gantry. Images acquired in antero-posterior (AP) direction by either C-arm and at 30° right and left anterior oblique angulation were analyzed by two independent analysts, blinded to the actual dimensions. Manual correction of the contours was not allowed. Measurements for minimal lumen diameter (MLD), reference vessel diameter (RVD), percent diameter stenosis (DS) and bifurcation angle (BA) were compared with the true phantom dimensions. RESULTS: In AP views the accuracy and precision (mean difference ± SD) of 11- and 6-segment model for MLD, RVD, and DS were 0.065 ± 0.128 mm vs. 0.058 ± 0.142 mm, -0.021 ± 0.032 mm vs. -0.022 ± 0.030 mm, and -2.45% ± 5.07% vs. -2.28% ± 5.29%, respectively. Phantom MLD values ≤ 0.7 mm were systematically overestimated; if excluded, MLD accuracy and precision became 0.015 ± 0.106 mm and 0.004 ± 0.125 mm for the 11- and 6-segment model, respectively. Accuracy and precision for BA were -2.2° ± 3.3°. Interobserver variability for MLD, RVD, DS, and BA for either model was ≤ 0.049 mm, ≤ 0.056 mm, ≤ 2.77%, and 1.6°, respectively. Agreement between models for MLD, RVD, and DS was ± 0.079 mm, ± 0.011 mm, and ± 2.07%. Accuracy and precision for diameter-derived parameters were slightly decreased in angulated projections; precision for BA measurements dropped to 6.1°. CONCLUSIONS: The results of both models are highly reproducible and for phantom MLD values >0.7 mm in excellent agreement with the true dimensions.

Novel bifurcation phantoms for validation of quantitative coronary angiography algorithms.

BACKGROUND: Validation is lacking for two- and three-dimensional (2D and 3D) bifurcation quantitative coronary angiography (QCA) algorithms. METHODS: Six plexiglas phantoms were designed, each of them mimicking a coronary vessel with three successive bifurcations lesions, wherein at least one vessel segment had a percent diameter stenosis (DS) of ≥60%. The five most frequently occurring Medina classes (1,1,1), (1,1,0), (0,1,0), (0,1,1), and (1,0,0) were used in the design. Diameters of the daughter vessels in every bifurcation were dictated by the scaling law of Finet. Lesions were cosinus-shaped in longitudinal view and circular-shaped in cross-sectional view. At the level of the carina, lesions were becoming eccentric, favoring "plaque" at the outer bifurcation walls. Adjacent bifurcation lesions were kept distant by nontapering, stenosis-free segments of ≥10 mm length. The direction of the side branch relative to the main vessel was based on relevant literature. The phantoms were precision manufactured using computer-aided design and machining techniques. Because of the high drilling accuracy (within 10 µm), the 3D luminal surface description of the phantom could be used to determine the true lumen dimensions and bifurcation angle (BA) values of the final geometry. RESULTS: Our series of bifurcation phantoms comprised 33 narrowed and 21 stenosis-free vessel segments with a mean true minimal lumen diameter (MLD) value of 0.98 ± 0.40 mm (range, 0.53-1.96 mm) and 2.29 ± 0.74 mm (range, 1.40-4.00 mm), respectively. Overall, the mean true values for MLD, reference diameter, and DS were 1.49 ± 0.85 mm, 2.70 ± 0.71 mm, and 40.9% ± 34.2%. The mean true values for the proximal and the distal BA were 123.6° ± 19.0° and 69.6° ± 19.9°, respectively. CONCLUSIONS: Six plexiglas phantoms containing a total of 18 bifurcations lesions with variable anatomy and Medina class were designed and precision manufactured to facilitate the validation of bifurcation QCA algorithms.

In vivo validation of CAAS QCA-3D coronary reconstruction using fusion of angiography and intravascular ultrasound (ANGUS).

OBJECTIVES: The CAAS QCA-3D system (Pie Medical Imaging BV, the Netherlands) was validated against 3D reconstructions based on fusion of angiography and intravascular ultrasound (ANGUS), allowing slice by slice validation of the lumen areas and 3D geometric values. BACKGROUND: Accurate online 3D reconstruction of human coronary arteries is of outmost importance during clinical practice in the catheterization laboratory. The CAAS QCA-3D system provides technology to 3D reconstruct human coronary arteries based on two or more angiographic images, but was not validated in realistic arteries before. METHODS: Ten patients were imaged using biplane angiography and an ECG gated (TomTec) intravascular ultrasound (IVUS) pullback (stepsize 0.5 mm, Boston Scientific). The coronary arteries were 3D reconstructed based on (a) fusion of biplane angiography and IVUS (ANGUS) and (b) CAAS QCA-3D using the biplane angiography images. For both systems the length, the curvature and the lumen areas at 0.5 mm spacing were calculated and compared. RESULTS: Bland-Altman analysis indicated that the CAAS QCA-3D system underestimated the lumen areas systematically by 0.45 +/- 1.49 mm2. The segment length was slightly underestimated by the CAAS QCA-3D system (62.1 +/- 11.3 vs. 63.2 +/- 11.4 mm; P < 0.05), while the curvature of the analyzed segments were not statistically different. CONCLUSIONS: The CAAS QCA-3D system allows 3D reconstruction of human coronary arteries based on biplane angiography. Validation against the ANGUS system showed that both the 3D geometry and lumen areas are highly correlated which makes the CAAS QCA-3D system a promising tool for applications in the catheterization laboratory and opens possibilities for computational fluid dynamics.

Strain distribution over plaques in human coronary arteries relates to shear stress.

Once plaques intrude into the lumen, the shear stress they are exposed to alters with hitherto unknown consequences for plaque composition. We investigated the relationship between shear stress and strain, a marker for plaque composition, in human coronary arteries. We imaged 31 plaques in coronary arteries with angiography and intravascular ultrasound. Computational fluid dynamics was used to obtain shear stress. Palpography was applied to measure strain. Each plaque was divided into four regions: upstream, throat, shoulder, and downstream. Average shear stress and strain were determined in each region. Shear stress in the upstream, shoulder, throat, and downstream region was 2.55+/-0.89, 2.07+/-0.98, 2.32+/-1.11, and 0.67+/-0.35 Pa, respectively. Shear stress in the downstream region was significantly lower. Strain in the downstream region was also significantly lower than the values in the other regions (0.23+/-0.08% vs. 0.48+/-0.15%, 0.43+/-0.17%, and 0.47+/-0.12%, for the upstream, shoulder, and throat regions, respectively). Pooling all regions, dividing shear stress per plaque into tertiles, and computing average strain showed a positive correlation; for low, medium, and high shear stress, strain was 0.23+/-0.10%, 0.40+/-0.15%, and 0.60+/-0.18%, respectively. Low strain colocalizes with low shear stress downstream of plaques. Higher strain can be found in all other plaque regions, with the highest strain found in regions exposed to the highest shear stresses. This indicates that high shear stress might destabilize plaques, which could lead to plaque rupture.

Coronary plaque composition as assessed by greyscale intravascular ultrasound and radiofrequency spectral data analysis.

OBJECTIVES: (i) To explore the relation between greyscale intravascular ultrasound (IVUS) plaque qualitative classification and IVUS radiofrequency data (RFD) analysis tissue types; (ii) to evaluate if plaque composition as assessed by RFD analysis can be predicted by visual assessment of greyscale IVUS images. METHODS: In 120 IVUS-RFD cross-sections, a sector of the plaque with homogenous tissue composition (e.g., fibrous, fibrofatty, necrotic core, and dense calcium) was selected. Two experienced observers analyzed twice the corresponding greyscale IVUS images to: (1) classify the selected sectors according to greyscale IVUS plaque type classification and (2) predict the tissue type expected in the sector by RFD analysis. RESULTS: In the greyscale IVUS plaque type classification, the observers agreed in 90/120 sectors (kappa = 0.64). Calcified, soft and mixed plaques by greyscale IVUS classification were mainly composed of dense calcium, fibrofatty, and necrotic core, respectively, in the RFD analysis. The plaques classified in greyscale IVUS as fibrous were actually fibrous tissue by IVUS RFD in only 30% of the cases. Overall, high interobserver variability in the prediction of RFD results by visual assessment of greyscale IVUS images (kappa = 0.23 for observer 1 and 0.55 for observer 2) was found. Sensitivities for detection of calcified tissue and NC by greyscale IVUS visual assessment were 88% and 58%, respectively. CONCLUSIONS: High interobserver variability in the prediction of tissue type by visual assessment of greyscale IVUS images was observed. This underlines the need of quantitative methods for the analysis of the ultrasound characteristics of coronary plaque components.

A new imaging technique to study 3-D plaque and shear stress distribution in human coronary artery bifurcations in vivo.

OBJECTIVE: Bifurcations of coronary arteries are predilection sites for atherosclerosis and expansive remodeling, the latter being associated with plaque vulnerability. Both are related to blood flow-induced shear stress (SS). We present a new approach to generate 3-D reconstructions of coronary artery bifurcations in vivo and investigate the relationship between SS, wall thickness (WT) and remodeling. METHODS: The patient specific 3-D reconstruction of the main branch of the bifurcation was obtained by combining intravascular ultrasound and biplane angiography, and the 3-D lumen of the side branch was based on biplane angiography only. The two data sets were fused and computational methods were applied to determine the SS distribution, using patient derived flow and viscosity data. The intravascular ultrasound data allowed us to measure local WT and remodeling in the main branch. RESULTS: The lumen reconstruction procedure was successful and it was shown that the impact of the side branch on SS distribution in the main branch diminished within 3mm. Distal to the bifurcation, two continuous regions in the main branch were identified. In the proximal region, we observed lumen preservation, and expansive remodeling. Although a plaque was observed in the low SS region at the non-divider wall, no relationship between SS and WT was found. In the distal region, we observed lumen narrowing and a significant positive relationship between SS and WT. CONCLUSIONS: A new imaging technique was applied to generate a 3-D reconstruction of a human coronary artery bifurcation in vivo. The observed relationship between SS, WT and remodeling in this specific patient illustrates the spatial heterogeneity of the atherosclerosis in the vicinity of arterial bifurcations.

Virtual histology and remodelling index allow in vivo identification of allegedly high-risk coronary plaques in patients with acute coronary syndromes: a three vessel intravascular ultrasound radiofrequency data analysis.

BACKGROUND: Virtual histology (VH) uses intravascular ultrasound (IVUS) radiofrequency spectral analysis to locally identify the morphology and composition of atherosclerotic plaques. We sought to explore in vivo the relation between IVUS-derived thin cap fibro-atheroma (IDTCFA) and remodelling index in patients with acute coronary syndromes using IVUS-VH. METHODS AND RESULTS: Twenty-one patients (63 vessels) were enrolled. When compared to cross sectional areas (CSAs) without necrotic core in contact with the lumen (NCCL), CSAs with NCCL had a larger plaque burden 42.8+/-11.5% vs. 32.8+/-11.5%, p<0.001; higher overall necrotic core content [13.8+/-10.7% vs. 2.3+/-7.9% (p<0.001)] and calcified tissue [4.7+/-6.5 vs. 0.66+/-2.1% (p<0.001)]. On average there were 2 IVUS-derived thin cap fibro-atheroma (IDTCFA) per patient. Nearly half of the IDTCFAs had positive remodelling. CONCLUSIONS: CSAs with NCCL had worse morphological profiles than those with no NCCL. The simultaneous and more detailed assessment of IDTCFA and remodelling index identifies a reduced number of allegedly high-risk plaques. The findings of this study may have important clinical implications, since they shed light into a possible method of identiying potentially high-risk plaques suitable for pharmacological and/or local treatment.

Geometry guided data averaging enables the interpretation of shear stress related plaque development in human coronary arteries.

The average low shear stress (SS) is known to determine predilection sites of atherosclerotic plaques. However, as plaques encroach into the lumen and thereby increase SS, interpretation of patient-specific data obtained at one moment in time regarding the influence of SS in the generation of atherosclerosis is not straightforward. This study aims to compare two methods of data analysis for the aid of data interpretation: (a) point-wise analysis of the raw data, (b) global analysis: to assess the history related natural SS distribution in coronary arteries by averaging the data in the axial vessel direction. Normal to mildly diseased human coronary arteries were investigated applying a combination of 3-D reconstruction technique and computational fluid dynamics (CFD). Point-wise analysis relating local wall thickness to local SS showed in only 4% of the cases an inverse relationship. In contrast, averaging the data in the axial vessel direction, showed in 38% a significant inverse relation between wall thickness and SS, resulting in an average negative slope of -0.70+/-0.46 mm/Pa. These data suggest that using a geometry guided way of data averaging may reveal history related effects of SS, which in part explains localization of atherosclerotic plaques.

A biplane angiographic study on cardiac motion of coronary artery stents: options to minimize the target volume for high-precision external beam radiotherapy of coronary artery in-stent restenosis.

PURPOSE: High-precision external beam radiotherapy (EBRT) has been suggested as a potential alternative to endovascular brachytherapy for the treatment of coronary artery in-stent restenosis. The purpose of our study was to investigate and compare different options to define a smallest feasible target volume. METHODS AND MATERIALS: The cardiac motion of 17 coronary artery stents in 17 patients was studied by use of biplane conventional angiography, recorded during breath-hold. Each stent was reconstructed in three dimensions by use of biplane sets of frames covering an entire cardiac cycle. The volume traversed by the stent during the entire or part of the cardiac cycle was determined. Four options to define the stent-traversed volume (STV) as a target for high-precision EBRT were investigated. RESULTS: The mean STV during the entire cardiac cycle was 3.5 cm3; the STV represented less than 1% of the heart volume in all patients. The STV during the diastolic and systolic phase resulted in a mean reduction of 26.6% and 29.1%, respectively, compared with the STV during the entire cardiac cycle. The smallest STV, measured during a 160-ms interval within the cardiac cycle, resulted in a mean maximal reduction of 75.9% compared with the STV during the entire cardiac cycle. CONCLUSIONS: The STV during the entire cardiac cycle represents a small potential target volume for high-precision EBRT. A significant reduction of this target volume is possible in case of definition during a selected interval within the cardiac cycle.