RESUMEN

Biomedical scientific research in the Netherlands has a good reputation worldwide. Quantitatively, the university medical centres (UMCs) deliver about 40 % of the total number of scientific publications of this research. Analysis of the bibliometric output data of the UMCs shows that their research is highly cited. These output-based analyses also indicate the high impact of cardiovascular scientific research in these centres, illustrating the strength of this research in the Netherlands. A set of six joint national cardiovascular research topics selected by the UMCs can be recognised. At the top are heart failure, rhythm disorder research and atherosclerosis. National collaboration of top scientists in consortia in these three areas is successful in acquiring funding of large-scale programs. Our observations suggest that funding national consortia of experts focused on a few selected research topics may increase the international competitiveness of cardiovascular research in the Netherlands.

RESUMEN

One prerequisite for standard clinical use of intravascular ultrasound imaging is rapid evaluation of the data. The main quantities to be extracted from the data are the size and the shape of the lumen. Until now, no accurate, robust and reproducible method to obtain the lumen boundaries from intravascular ultrasound images has been described. In this study, 21 different (semi-)automated binary-segmentation methods for determining the lumen are compared with manual segmentation to find an alternative for the laborious and subjective procedure of manual editing. After a preprocessing step in which the catheter area is filled with lumen-like grey values, all approaches consist of two steps: (i) smoothing the images with different filtering methods and (ii) extracting the lumen by an object definition method. The combination of different filtering methods and object definition methods results in a total of 21 methods and 80 experiments. The results are compared with a reference image, obtained from manual editing, by use of four different quality parameters--two based on squared distances and two based on Mahalanobis distances. The evaluation has been carried out on 15 images, of which seven are obtained before balloon dilation and eight after balloon dilation. While for the post-dilation images no definite conclusions can be drawn, an automated contour model applied to images smoothed with a large kernel appears to be a good alternative to manual contouring. For pre-dilation images a fully automated active contour model, initialized by thresholding, preceded by filtering with a small-scale median filter is the best alternative for manual delineation. The results of this method are even better than manual segmentation, i.e. they are consistently closer to the reference image than the average distance of all individual manual segmentations.

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The hypothesis that cholesterol consumption alters hepatic sphingomyelin homeostasis was tested. Rats were fed a purified diet with or without added cholesterol (1 g/100 g) for up to 21 d. In accordance with previous work, cholesterol consumption significantly increased hepatic, whole plasma and VLDL cholesterol concentrations. Dietary cholesterol also raised the amount of sphingomyelin in the VLDL fraction, which was associated with a decrease in hepatic sphingomyelin concentrations. We suggest that the increase in hepatic VLDL secretion after cholesterol consumption imposed an increase in the demand for sphingomyelin in the liver because this phospholipid is a structural component of VLDL. Determination of the activity of two key enzymes of sphingomyelin homeostasis revealed that cholesterol consumption reduced the activity of acid sphingomyelinase in the liver but did not affect that of serine palmitoyltransferase. These enzyme data indicate that the extra sphingomyelin needed after cholesterol loading results from a decrease in the rate of its catabolism in the liver.

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At 30 MHz, the intravascular ultrasound backscatter of blood confounds the discrimination of the lumen from the arterial wall. This study validates a subtraction method which creates a still-frame image with a sharp demarcation of the lumen. The method involves subtraction of consecutive images and 2D ensemble averaging of the absolute pixel values. Subtraction exploits the dynamic properties of flowing red blood cells. Three phantom arteries were used, with erythrocytes in their lumens and wall. For this reason, it was not possible, in one single original image, to discriminate the blood in the lumen from the phantom wall. Based on 26 consecutive original images, in the mean subtraction image contrast between lumen and phantom wall grey values increased eightfold from 10.9 (5.3-19.2) (mean and range) in the original image to 87.7 (73.6-107.0) (P < 0.001). A sufficiently large contrast increase to allow automatic segmentation was obtained by using five original images (0.3-s acquisition time) for any single mean subtraction image. Low blood flow velocities (down to 0.5 cm/s) did not alter this result. Automatic segmentation of the lumen allowed fast 3D reconstruction of the lumen in all three phantom arteries. In phantom arteries, the intravascular ultrasound image subtraction technique improved contrast between lumen and wall which enabled automated lumen segmentation and fast 3D visualization of both the lumen and defects in the wall.

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