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J Declerck

Publications and source records attributed to J Declerck.

10 recordsLinked to original sources
PubMed2001

Respiratory motion compensation for 3-D freehand echocardiography.

Motion of the diaphragm during respiration causes a displacement of the heart relative to the position of a transthoracic ultrasound (US) probe. These respiration-induced shifts of cardiac position can lead to spatial misalignments of data when reconstructed in 3-D. We show how to compensate for this motion using a technique that extends the tracking of the probe to additionally monitor a marker placed on the patient umbilicus. The motion of the umbilicus is calibrated to that of the diaphragm using one additional scan. This calibration is used to correct the 3-D spatial positions of cardiac images acquired from multiple acoustic views. At both systole and diastole, segmentations of the endocardial border visually appear more consistent after our correction than with no correction. Long and short axis segmentations should intersect on the endocardium. After correction, their separation at the closest point is shown to be reduced.

Calibration↗
PubMed2000

Predictors of systolic augmentation from left ventricular preexcitation in patients with dilated cardiomyopathy and intraventricular conduction delay.

BACKGROUND: VDD pacing can enhance systolic function in patients with dilated cardiomyopathy and discoordinate contraction; however, identification of patients likely to benefit is unclear. We tested predictors of systolic responsiveness on the basis of global parameters as well as directly assessed mechanical dyssynchrony. METHODS AND RESULTS: Twenty-two DCM patients with conduction delay were studied by cardiac catheterization with a dual-sensor micromanometer to measure LV and aortic pressures during sinus rhythm and LV free-wall pacing. Pacing enhanced isovolumetric (dP/dt(max)) and ejection-phase (pulse pressure, PP) systolic function by 35+/-21% and 16.4+/-11%, respectively, and these changes correlated directly (r=0.7, P=0.001). %DeltadP/dt(max) was weakly predicted by baseline QRS (r=0.6, P<0.02), more strongly by baseline dP/dt(max) (r=0.7, P=0.001), and best by bidiscriminate analysis combining baseline dP/dt(max) < or =700 mm Hg/s and QRS > or =155 ms to predict %DeltadP/dt(max) > or =25% and %DeltaPP > or =10% (P<0.0005, chi(2)), with no false-positives. Benefit could not be predicted by %DeltaQRS. To test whether basal mechanical dyssynchrony predicted responsiveness to LV pacing, circumferential strains were determined at approximately 80 sites throughout the LV by tagged MRI in 8 DCM patients and 7 additional control subjects. Strain variance at time of maximal shortening indexed dyssynchrony, averaging 28.0+/-7.1% in normal subjects versus 201.4+/-84.3% in DCM patients (P=0.001). Mechanical dyssynchrony also correlated directly with %DeltadP/dt(max) (r=0.85, P=0.008). Conclusions-These results show that although mechanical dyssynchrony is a key predictor for pacing efficacy in DCM patients with conduction delay, combining information about QRS and basal dP/dt(max) provides an excellent tool to identify maximal responders.

Adult↗
PubMed2000

The subjective image quality of direct digital and conventional panoramic radiography.

One of the main advantages of digital imaging is the possibility of altering display options for improved image interpretation. The aim of the present study was to evaluate the subjective image quality of direct digital panoramic images and compare the results with those obtained from conventional images. Furthermore, the effect of various filter settings on image interpretation was assessed. Panoramic images were obtained with three different types of panoramic equipment (one direct digital and two conventional units) from three groups of 54 patients with a natural dentition in all quadrants. The first series of panoramic images consisted of 54 unprocessed digital images; conventional film images (n = 108) comprised the second and third series. A final series consisted of the digital images treated with three different filters ("smoothening," "sharpening," and "contrast enhancement"). All images were scored randomly by four experts in oral radiology on a 4-point rating scale. The results showed a statistically significant difference in scorings between the conventional and digital panoramic units. The main reason for poor image quality appeared to be a combination of blurring and overlapping in the panoramic image. The premolar region in the upper jaw was the region where most additional radiographs were needed.

Adolescent↗
PubMed2000

Left ventricular motion reconstruction from planar tagged MR images: a comparison.

Through recent development of MR techniques, it is now possible to assess regional myocardial wall function in a non-invasive way. Using MR tagging, space is marked with planes which deform with the tissue, providing markers for tracking the local motion of the myocardium. Numerous methods to reconstruct the three-dimensional displacement field have been developed. The aim of this article is to provide a framework to quantitatively compare the performance of four methods the authors have developed. Five sets of experiments are described, and their results are reported. Instructions are also provided to perform similar tests on any method using the same data. The experiments show that some characteristic properties of the methods, such as sensitivity to noise or spatial resolution, can be quantitatively classified. Cross-comparison of performances show what range values for these properties can be considered acceptable.

Animals↗
PubMed2000

Real-time projection MR angiography: feasibility study.

Intraarterial injections of small doses of gadopentetate dimeglumine were combined with a fast spoiled-gradient-echo magnetic resonance (MR) sequence to obtain real-time projection angiographic images of the rabbit aorta and canine coronary arteries. Arterial filling and washout, as well as venous and perfusion phases, were clearly displayed, demonstrating that arterial fluoroscopy in which an MR technique is used is feasible.

Adult↗
PubMed1998

Definition of a four-dimensional continuous planispheric transformation for the tracking and the analysis of left-ventricle motion.

Cardiologists assume that analysis of the motion of the heart (especially the left ventricle) can provide useful information about the health of the myocardium. A 4-D polar transformation is defined to describe the left-ventricle (LV) motion and a method is presented to estimate it from sequences of 3-D images. The transformation is defined in 3-D planispheric coordinates (3PC) by a small number of parameters involved in a set of simple linear equations. It is continuous and regular in time and space, and periodicity in time can be imposed. The local motion can be easily decomposed into a few canonical motions (radial motion, rotation around the long-axis, elevation). To recover the motion from original data, the 4-D polar transformation is calculated using an adaptation of the iterative closest-point algorithm. We present the mathematical framework and a demonstration of its feasability on a series of gated SPECT sequences.

Humans↗
PubMed1997

Automatic registration and alignment on a template of cardiac stress and rest reoriented SPECT images.

Single photon emission computed tomography (SPECT) imaging with 201Tl or 99mTc agent is used to assess the location or the extent of myocardial infarction or ischemia. A method is proposed to decrease the effect of operator variability in the visual or quantitative interpretation of scintigraphic myocardial perfusion studies. To effect this, the patient's myocardial images (target cases) are registered automatically over a template image, utilizing a nonrigid transformation. The intermediate steps are: 1) Extraction of feature points in both stress and rest three-dimensional (3-D) images. The images are resampled in a polar geometry to detect edge points, which in turn are filtered by the use of a priori constraints. The remaining feature points are assumed to be points on the edges of the left ventricular myocardium. 2) Registration of stress and rest images with a global affine transformation. The matching method is an adaptation of the iterative closest point algorithm. 3) Registration and morphological matching of both stress and rest images on a template using a nonrigid local spline transformation following a global affine transformation. 4) Resampling of both stress and rest images in the geometry of the template. Optimization of the method was performed on a database of 40 pairs of stress and rest images selected to obtain a wide variation of images and abnormalities. Further testing was performed on 250 cases selected from the same database on the basis of the availability of angiographic results and patient stratification.

Coronary Disease↗