Biomedical subjects

Johan H C Reiber

Publications and source records attributed to Johan H C Reiber.

42 records · Page 3Linked to original sources

PubMed2002

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.

Coronary Vessels↗

PubMed2002

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.

Algorithms↗

PubMed2002

3-D active appearance models: segmentation of cardiac MR and ultrasound images.

A model-based method for three-dimensional image segmentation was developed and its performance assessed in segmentation of volumetric cardiac magnetic resonance (MR) images and echocardiographic temporal image sequences. Comprehensive design of a three-dimensional (3-D) active appearance model (AAM) is reported for the first time as an involved extension of the AAM framework introduced by Cootes et al. The model's behavior is learned from manually traced segmentation examples during an automated training stage. Information about shape and image appearance of the cardiac structures is contained in a single model. This ensures a spatially and/or temporally consistent segmentation of three-dimensional cardiac images. The clinical potential of the 3-D AAM is demonstrated in short-axis cardiac MR images and four-chamber echocardiographic sequences. The method's performance was assessed by comparison with manually identified independent standards in 56 clinical MR and 64 clinical echo image sequences. The AAM method showed good agreement with the independent standard using quantitative indexes of border positioning errors, endo- and epicardial volumes, and left ventricular mass. In MR, the endocardial volumes, epicardial volumes, and left ventricular wall mass correlation coefficients between manual and AAM were R2 = 0.94, 0.97, 0.82, respectively. For echocardiographic analysis, the area correlation was R2 = 0.79. The AAM method shows high promise for successful application to MR and echocardiographic image analysis in a clinical setting.

Echocardiography, Three-Dimensional↗

PubMed2002

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.

Brachytherapy↗

PubMed2002

Automatic segmentation of echocardiographic sequences by active appearance motion models.

A novel extension of active appearance models (AAMs) for automated border detection in echocardiographic image sequences is reported. The active appearance motion model (AAMM) technique allows fully automated robust and time-continuous delineation of left ventricular (LV) endocardial contours over the full heart cycle with good results. Nonlinear intensity normalization was developed and employed to accommodate ultrasound-specific intensity distributions. The method was trained and tested on 16-frame phase-normalized transthoracic four-chamber sequences of 129 unselected infarct patients, split randomly into a training set (n = 65) and a test set (n = 64). Borders were compared to expert drawn endocardial contours. On the test set, fully automated AAMM performed well in 97% of the cases (average distance between manual and automatic landmark points was 3.3 mm, comparable to human interobserver variabilities). The ultrasound-specific intensity normalization proved to be of great value for good results in echocardiograms. The AAMM was significantly more accurate than an equivalent set of two-dimensional AAMs.

Algorithms↗

PubMed2002

Impact of simultaneous pancreas and kidney transplantation on progression of coronary atherosclerosis in patients with end-stage renal failure due to type 1 diabetes.

OBJECTIVE: Mortality in type 1 diabetic patients with end-stage renal failure is high and dominated by coronary atherosclerotic events. With regard to prognosis, simultaneous transplantation of pancreas and kidney (SPK) may be superior to kidney transplantation alone (KTA) in type 1 diabetic patients, because normalization of blood glucose levels may reduce progression of coronary atherosclerosis and because it is well known that progression of coronary atherosclerosis is one of the major factors that determines clinical prognosis. However, no data are available on progression of coronary atherosclerosis after SPK. RESEARCH DESIGN AND METHODS: We performed an observational angiographic study comparing progression of coronary atherosclerosis, analyzed with quantitative coronary angiography, in patients with (n = 26) and those without (n = 6) a functioning pancreas graft after SPK, to test the hypothesis that normalization of blood glucose levels by SPK may indeed reduce progression of coronary atherosclerosis in type 1 diabetic patients and thereby improve prognosis. RESULTS: Mean follow-up was 3.9 years. Average glucose control was significantly worse for the patients without a pancreas graft than for patients with a functioning pancreas graft: 11.3 (SD 3.5) vs. 5.9 mmol/l (SD 1.1) (P = 0.03). Mean segment diameter loss (progression of diffuse coronary atherosclerosis) was 0.024 mm/year (SD 0.067) in patients with a functioning pancreas graft, compared with 0.044 mm/year (SD 0.038) in patients in whom the pancreas graft was lost. Minimum obstruction diameter loss (progression of focal coronary atherosclerosis) was 0.037 mm/year (SD 0.086) in patients with a functioning pancreas graft compared with 0.061 mm/year (SD 0.038) in patients in whom the pancreas graft was lost. Regression of atherosclerosis occurred in 38% of patients with a functioning pancreas graft compared with 0% of patients of whom the pancreas graft was lost (P = 0.035). CONCLUSIONS: Our study provides, for the first time, evidence that in patients who have undergone SPK, progression of coronary atherosclerosis in patients with a functioning pancreas graft is reduced compared with patients with pancreas graft failure. Our observation is an important part of the explanation for the observed improved mortality rates reported in type 1 diabetic patients with end-stage renal failure after SPK compared with KTA. In light of these findings described above, SPK must to be carefully considered for all diabetic transplant candidates.

Adult↗