Ronald Hamers

Incomplete Stent Apposition After Implantation of Paclitaxel-Eluting Stents or Bare Metal Stents Insights From the Randomized TAXUS II Trial

Background—The clinical impact of late incomplete stent apposition (ISA) for drug-eluting stents is unknown. We sought to prospectively investigate the incidence and extent of ISA after the procedure and at 6-month follow-up of paclitaxel-eluting stents in comparison with bare metal stents (BMS) and survey the clinical significance of ISA over a period of 12 months. Methods and Results—TAXUS II was a randomized, double-blind study with 536 patients in 2 consecutive cohorts comparing slow-release (SR; 131 patients) and moderate-release (MR; 135 patients) paclitaxel-eluting stents with BMS (270 patients). This intravascular ultrasound (IVUS) substudy included patients who underwent serial IVUS examination after the procedure and at 6 months (BMS, 240 patients; SR, 113; MR, 116). The qualitative and quantitative analyses of ISA were performed by an independent, blinded core laboratory. More than half of the instances of ISA observed after the procedure resolved at 6 months in all groups. No difference in the incidence of late-acquired ISA was observed among the 3 groups (BMS, 5.4%; SR, 8.0%; MR, 9.5%; P=0.306), with a similar ISA volume (BMS, 11.4 mm3; SR, 21.7 mm3; MR, 8.5 mm3; P=0.18). Late-acquired ISA was the result of an increase of vessel area without change in plaque behind the stent. Predictive factors of late-acquired ISA were lesion length, unstable angina, and absence of diabetes. No stent thrombosis occurred in the patients diagnosed with ISA over a period of 12 months. Conclusions—The incidence and extent of late-acquired ISA are comparable in paclitaxel-eluting stents and BMS. ISA is a pure IVUS finding without clinical repercussions.

Retrospective image-based gating of intracoronary ultrasound images for improved quantitative analysis: The intelligate method

Quantitative analysis of intracoronary ultrasound (ICUS) studies is performed on a series of tomographic cross‐sectional ICUS images acquired during a motorized 0.5 mm/sec catheter pullback. Catheter displacement in the vascular lumen during the cardiac cycle causes an anatomically shuffled ICUS study, which results in a sawtooth‐shaped appearance of the coronary segment in longitudinal reconstructed views in quantitative coronary ultrasound software packages. This hampers contour detection and leads to a laborious time‐consuming semiquantitative analysis process that may produce inaccurate results. To solve these problems, in the past, online ECG‐gated acquisition hardware has been applied. This article describes a novel image‐based gating method called Intelligate, which features automatic retrospective selection of end‐diastolic frames from videotaped or digitally stored ICUS studies. Our evaluation shows that there are no quantitative differences between analysis results of hardware ECG‐gated and Intelligated ICUS studies. Catheter Cardiovasc Interv 2004;61:84–94.

Quantification of coronary plaque by 64-slice computed tomography: a comparison with quantitative intracoronary ultrasound.

Background:Noninvasive assessment of coronary atherosclerotic plaque may be useful for risk stratification and treatment of atherosclerosis. Materials and Methods:We studied 47 patients to investigate the accuracy of coronary plaque volume measurement acquired with 64-slice multislice computed tomography (MSCT), using newly developed quantification software, when compared with quantitative intracoronary ultrasound (QCU). Quantitative MSCT coronary angiography (QMSCT-CA) was performed to determine plaque volume for a matched region of interest (regional plaque burden) and in significant plaque defined as a plaque with ≥50% area obstruction in QCU, and compared with QCU. Dataset with image blurring and heavy calcification were excluded from analysis. Results:In 100 comparable regions of interest, regional plaque burden was highly correlated (coefficient r = 0.96; P < 0.001) between QCU and QMSCT-CA, but QMSCT-CA overestimated the plaque burden by a mean difference of 7 ± 33 mm3 (P = 0.03). In 76 significant plaques detected within the regions of interest, plaque volume determined by QMSCT-CA was highly correlated (r = 0.98; P < 0.001) with a slight underestimation of 2 ± 17 mm3 (P = not significant) when compared with QCU. Calcified and mixed plaque volume was slightly overestimated by 4 ± 19 mm3 (P = ns) and noncalcified plaque volume was significantly underestimated by 9 ± 11 mm3 (P < 0.001) with QMSCT-CA. Overall, the limits of agreement for plaque burden/volume measurement between QCU and QMSCT-CA were relatively large. Reproducibility for the measurements of regional plaque burden with QMSCT-CA was good, with a mean intraobserver and interobserver variability of 0% ± 16% and 4% ± 24%, respectively. Conclusions:Quantification of coronary plaque within selected proximal or middle coronary segments without image blurring and heavy calcification with 64-slice CT was moderately accurate with respect to intravascular ultrasound and demonstrated good reproducibility. Further improvement in CT resolution is required for more reliable measurement of coronary plaques using quantification software.

A novel approach for quantitative analysis of intracoronary optical coherence tomography: High inter-observer agreement with computer-assisted contour detection

Objective: This study aims to examine observer‐related variability of quantitative optical coherence tomography (OCT) derived measurements from both in vitro and in vivo pullback data. Background: Intravascular OCT is a new imaging modality using infrared light and offering 10 times higher image resolution (15 μm) compared to intravascular ultrasound. The quantitative analysis of in vivo intracoronary OCT imaging is complicated by the presence of blood, motion artifacts and the large quantity of information that has to be processed. Methods: We developed a standardized, automated quantification process for intracoronary OCT pullback data with inter‐observer variability assessed both in vitro by using postmortem human coronary arteries and in vivo by studying simple and complex coronary pathology and outcomes following stent implantation. The consensus between measurements by two observers was analyzed using the intraclass and interclass correlation coefficient and the reliability coefficients. Bland–Altman plots were generated to assess the relationship between variability and absolute measurements. Results: In vitro OCT assessment was performed in nine postmortem coronary arteries. The time needed for semiautomated contour detection of a 15‐mm long coronary segment was ∼40 min. The absolute and relative difference between lumen area measurements derived from two observers was low [0.02 ± 0.10 mm2; (0.3 ± 0.5)% respectively] with excellent correlation confirmed by linear regression analysis (R2 = 0.99; P < 0.001). Similarly, in vivo measurements demonstrated a high correlation with the main source of inter‐observer variation occurring as a result of coronary dissection and motion artifact. The absolute and relative difference between measurements were 0.11 ± 0.33 mm2 (1.57 ± 0.05)% for lumen area (R2 = 0.98; P < 0.001), 0.17 ± 0.68 mm2 (1.44 ± 0.08)% for stent area (R2 = 0.94; P < 0.001), and 0.26 ± 0.72 mm2 (14.08 ± 0.37)% for neointimal area (R2 = 0.78; P < 0.001). Conclusions: Highly accurate computer‐assisted quantitative analysis ofintracoronary OCT pullbacks is feasible with low inter‐observer variability. The presented approach allows for observer independent analysis of detailed vessel structures, and may be a valuable tool for future longitudinal studies incorporating OCT.

Three‐dimensional and quantitative analysis of atherosclerotic plaque composition by automated differential echogenicity

To validate automated and quantitative three‐dimensional analysis of coronary plaque composition using intracoronary ultrasound (ICUS).

Fully Automatic Three-Dimensional Quantitative Analysis of Intracoronary Optical Coherence Tomography: Method and Validation

Objectives and background: Quantitative analysis of intracoronary optical coherence tomography (OCT) image data (QOCT) is currently performed by a time‐consuming manual contour tracing process in individual OCT images acquired during a pullback procedure (frame‐based method). To get an efficient quantitative analysis process, we developed a fully automatic three‐dimensional (3D) lumen contour detection method and evaluated the results against those derived by expert human observers. Methods: The method was developed using Matlab (The Mathworks, Natick, MA). It incorporates a graphical user interface for contour display and, in the selected cases where this might be necessary, editing. OCT image data of 20 randomly selected patients, acquired with a commercially available system (Lightlab imaging, Westford, MA), were pulled from our OCT database for validation. Results: A total of 4,137 OCT images were analyzed. There was no statistically significant difference in mean lumen areas between the two methods (5.03 ± 2.16 vs. 5.02 ± 2.21 mm2; P = 0.6, human vs. automated). Regression analysis showed a good correlation with an r value of 0.99. The method requires an average 2–5 sec calculation time per OCT image. In 3% of the detected contours an observer correction was necessary. Conclusion: Fully automatic lumen contour detection in OCT images is feasible with only a select few contours showing an artifact (3%) that can be easily corrected. This QOCT method may be a valuable tool for future coronary imaging studies incorporating OCT.

Monitoring in vivo absorption of a drug-eluting bioabsorbable stent with intravascular ultrasound-derived parameters a feasibility study.

OBJECTIVES The aim of this study was to investigate the feasibility of using quantitative differential echogenicity to monitor the in vivo absorption process of a drug-eluting poly-l-lactic-acid (PLLA) bioabsorbable stent (BVS, Abbott Vascular, Santa Clara, California). BACKGROUND A new bioabsorbable, balloon-expanded coronary stent was recently evaluated in a first-in-man study. Little is known about the absorption process in vivo in diseased human coronary arteries. METHODS In the ABSORB (Clinical Evaluation of the BVS everolimus eluting stent system) study, 30 patients underwent treatment with the BVS coronary stent system and were examined with intracoronary ultrasound (ICUS) after implantation, at 6 months and at 2-year follow-up. Quantitative ICUS was used to measure dimensional changes, and automated ICUS-based tissue composition software (differential echogenicity) was used to quantify plaque compositional changes over time in the treated regions. RESULTS The BVS struts appeared as bright hyperechogenic structures and showed a continuous decrease of their echogenicity over time, most likely due to the polymer degradation process. In 12 patients in whom pre-implantation ICUS was available, at 2 years the percentage-hyperechogenic tissue was close to pre-implantation values, indicating that the absorption process was either completed or the remaining material was no longer differentially echogenic from surrounding tissues. CONCLUSIONS Quantitative differential echogenicity is a useful plaque compositional measurement tool. Furthermore, it seems to be valuable for monitoring the absorption process of bioabsorbable coronary stents made of semi-crystalline polymers.

Reproducible coronary plaque quantification by multislice computed tomography

Background: The aim of this study was to investigate reproducibility and accuracy of computer‐assisted coronary plaque measurements by multislice computed tomography coronary angiography (QMSCT‐CA). Methods and Results: Forty‐eight patients undergoing MSCT‐CA and coronary arteriography for symptomatic coronary artery disease and quantitative intravascular ultrasound (IVUS, QCU) were examined. Two investigators performed the QMSCT‐CA twice and a third investigator performed the QCU, all blinded for each others results. There was no difference found for the matched region of interest (ROI) lengths (QCU 29.4 ± 13 mm vs. QMSCT‐CA 29.6 ± 13 mm, P = 0.6; total length = 1,400 mm). The comparison of volumetric measurements showed (lumen QCU 267 ± 139 mm3 vs. mean QMSCT‐CA 177 ± 91 mm3, P << 0.001; vessel 454 ± 194 mm3 vs. 398 ± 187 mm3, P << 0.001; and plaque 189 ± 93 mm3 vs. 222 ± 121 mm3; investigator 1, P = 0.02; and investigator 2, P = 0.07) significant differences. Automated lumen detection was also applied for QMSCT‐CA (218 ± 112 mm3, P << 0.001 vs. QCU). The interinvestigator variability measurements for QMSCT‐CA showed no significant differences. Conclusion: QMSCT‐CA systematically underestimates absolute coronary lumen‐ and vessel dimensions when compared with QCU. However, repeated measurements of coronary plaque by QMSCT‐CA showed no statistically significant differences, although, the outcome showed a scattered result. Automated lumen detection for QMSCT‐CA showed improved results when compared with those of human investigators.

Non-invasive visualization of coronary atherosclerosis: State-of-art

Coronary artery disease remains the leading cause of death in the Western world. Non-invasive coronary artery imaging challenges any diagnostic modality because the coronary arteries are small and tortuous, whereas cardiac contraction and respiration cause motion artifacts. Therefore, non-invasive coronary imaging requires high spatial and temporal resolution. This review discusses the feasible applications in coronary imaging of magnetic resonance imaging and multi-slice computed tomography (MSCT), which are currently the only non-invasive diagnostic modalities for direct coronary atherosclerosis imaging. Particular attention and focus is devoted to the potential indications and clinical impact of MSCT due to its fast development and the robust results recently reported. MSCT of the coronary arteries is a promising imaging modality for the assessment of the coronary lumen and wall.

Adjustment method for mechanical Boston scientific corporation 30 MHz intravascular ultrasound catheters connected to a Clearview console. Mechanical 30 MHz IVUS catheter adjustment.

Intracoronary ultrasound (ICUS) is often used in studies evaluating new interventional techniques. It is important that quantitative measurements performed with various ICUS imaging equipment and materials are comparable. During evaluation of quantitative coronary ultrasound (QCU) software, it appeared that Boston Scientific Corporation (BSC) 30 MHz catheters connected to a Clearview® ultrasound console showed smaller dimensions of an in vitro phantom model than expected. In cooperation with the manufacturer the cause of this underestimation was determined, which is described in this paper, and the QCU software was extended with an adjustment. Evaluation was performed by performing in vitro measurements on a phantom model consisting of four highly accurate steel rings (perfect reflectors) with diameters of 2, 3, 4 and 5 mm. Relative differences (unadjusted) of the phantom were respectively: 15.92, 13.01, 10.10 and 12.23%. After applying the adjustment: −0.96, −1.84, −1.35 and −1.43%. In vivo measurements were performed on 24 randomly selected ICUS studies. These showed differences for not adjusted vs. adjusted measurements of lumen-, vessel- and plaque volumes of −10.1 ± 1.5, −6.7 ± 0.9 and −4.4 ± 0.6%. An off-line adjustment formula was derived and applied on previous numerical QCU output data showing relative differences for lumen- and vessel volumes of 0.36 ± 0.51 and 0.13 ± 0.31%. 30 MHz BSC catheters connected to a Clearview® ultrasound console underestimate vessel dimensions. This can retrospectively be adjusted within QCU software as well as retrospectively on numerical QCU data using a mathematical model.