Biomedical subjects

Bert Verdonck

Publications and source records attributed to Bert Verdonck.

6 recordsLinked to original sources

PubMed2003

Blood pool contrast-enhanced MRA: improved arterial visualization in the steady state.

Blood pool agents (BPAs) for contrast-enhanced magnetic resonance angiography (CE-MRA) allow prolonged imaging during the steady state when the agent is distributed through the complete vascular system. This increases both the spatial resolution and the contrast resolution. However, simultaneous venous and arterial enhancement hampers interpretation. For the pelvic region of the vasculature, it is shown that arterial visualization in this equilibrium phase can be improved if the central arterial axis (CAA) is known. However, manually obtaining this axis is not feasible in clinical practice. Therefore, a method is presented that utilizes images acquired during the first pass of the contrast agent to find the CAA in the steady-state data with minimum user initialization. The accuracy of the resulting CAA is compared with tracings of three observers in six patient datasets. It was found that the mean difference between the semiautomatic method and the manual delineation is 1.32 mm in the steady-state data, and that the resulting CAA was always within the arterial lumen, which is an important prerequisite for both improved visualization and segmentation.

Algorithms↗

PubMed2002

The reliability of quantitative analysis on digital images of the scoliotic spine.

Although analysis of scoliotic deformity is still studied extensively by means of conventional roentgenograms, computer-assisted digital analysis may allow a faster, more accurate and more complete evaluation of the scoliotic spine. In this study, a new computer-assisted measurement method was evaluated. This method uses digital reconstruction images for quantitative analysis of the scoliotic spine. The aim of the current study was to determine the reliability of the computer-assisted measuring method, which was done by establishing coefficients of repeatability for a variety of measurements. Measurements were carried out by five observers on 30 frontal and 10 lateral scoliotic digital reconstruction images. Each image was measured on three separate occasions by placing anatomical vertebral landmarks and drawing lines with a computer pointing device. The computer then calculated a number of geometrical shape parameters from scale calibration, landmarks and lines. The intra- and interobserver results were subjected to an analysis of variance to assess the level of agreement, and the means and standard deviations were calculated. The coefficient of repeatability (CR) was taken to be equal to two standard deviations. The mean intraobserver CR was found to be 3.1 degrees for the Cobb angle on the frontal digital image and 3.3 degrees for the kyphosis Cobb angle on the lateral overview. The mean difference in the intraobserver CR of the Cobb angle between measurements made by placing landmarks and those made by drawing lines was not statistically significant (P>0.05). The mean intraobserver CR for the other parameters can be summarized as follows: for lateral deviation it was 0.8 mm, for axial rotation 4.0 degrees and for length of the spine 3.3 mm. The interobserver bias was negligible. It can be concluded that the reliability of our new method for quantifying geometrical variables on digital reconstruction images is better than measurements on conventional roentgenograms in previously published reports. The presented method is therefore considered to be more accurate for research of spinal deformities and more adequate for clinical management of scoliosis.

Adolescent↗

PubMed2002

Digital radiography of scoliosis with a scanning method: radiation dose optimization.

The aim of this study was optimization of the radiation dose-image quality relationship for a digital scanning method of scoliosis radiography. The examination is performed as a digital multi-image translation scan that is reconstructed to a single image in a workstation. Entrance dose was recorded with thermoluminescent dosimeters placed dorsally on an Alderson phantom. At the same time, kerma area product (KAP) values were recorded. A Monte Carlo calculation of effective dose was also made. Image quality was evaluated with a contrast-detail phantom and Visual Grading. The radiation dose was reduced by lowering the image intensifier entrance dose request, adjusting pulse frequency and scan speed, and by raising tube voltage. The calculated effective dose was reduced from 0.15 to 0.05 mSv with reduction of KAP from 1.07 to 0.25 Gy cm(2) and entrance dose from 0.90 to 0.21 mGy. The image quality was reduced with the Image Quality Figure going from 52 to 62 and a corresponding reduction in image quality as assessed with Visual Grading. The optimization resulted in a dose reduction to 31% of the original effective dose with an acceptable reduction in image quality considering the intended use of the images for angle measurements.

Adolescent↗

PubMed2002

3D MRA coronary axis determination using a minimum cost path approach.

A method is introduced to automatically find the coronary axis based on two or more user-defined points, even in the presence of a severe stenosis. The coronary axis is determined by finding a minimum cost path (MCP) in a feature image in which the tubular-like structures are enhanced. The results of the proposed method were compared with manually drawn central axes to estimate the accuracy. In 32 3D TFE-EPI acquisitions of patients and volunteers, 14 right coronary arteries (RCAs), 15 left anterior descending arteries (LADs), and eight left circumflex arteries (LCXs) were manually tracked twice by two operators to determine a reference axis and to assess the inter- and intra-user variability. On average, the maximum distance to the reference axis, based on only two user-defined points, is less than 1.5 mm; the average distance is around 0.65 mm, which is less than the average in-plane resolution. The results of the method are comparable to those of the manual operators.

Coronary Stenosis↗

PubMed2002

Semi-automatic landmark detection in digital X-ray images of the spine.

Quantitative diagnosis of 3D scoliotic deformities depends on a number of dedicated measurements. Existing methods rely on the manual determination of a series of anatomical landmarks in X-ray images. We have developed an automatic method to alleviate the burden of this tedious task. Our method looks for a compromise between local image information and global prior constraints and finds the most probable points using dynamic programming optimization. Remaining errors can be quickly corrected by effective user interaction. The first results are promising.

Humans↗

PubMed2002

3D reconstruction and analysis of the vertebral body line.

Quantitative analysis of 3D spinal deformities includes measurements related to individual vertebrae and measurements related to the overall shape of the spine. For the latter aspect, we propose to build a 3D model of the line that connects all vertebrae centres. We present two methods that allow reconstructing this vertebral body line in a quick and easy way. Various new descriptors of the spinal shape can be automatically computed. A study is under way to assess their clinical relevance and reliability.

Humans↗