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Biomedical subjects

W J Niessen

Publications and source records attributed to W J Niessen.

16 recordsLinked to original sources
PubMed2004

Registration-based interpolation.

A method is presented to interpolate between neighboring slices in a grey-scale tomographic data set. Spatial correspondence between adjacent slices is established using a nonrigid registration algorithm based on B-splines which optimizes the normalized mutual information similarity measure. Linear interpolation of the image intensities is then carried out along the directions calculated by the registration algorithm. The registration-based method is compared to both standard linear interpolation and shape-based interpolation in 20 tomographic data sets. Results show that the proposed method statistically significantly outperforms both linear and shape-based interpolation.

Algorithms↗
PubMed2004

A quantitative analysis of 3-D coronary modeling from two or more projection images.

A method is introduced to examine the geometrical accuracy of the three-dimensional (3-D) representation of coronary arteries from multiple (two and more) calibrated two-dimensional (2-D) angiographic projections. When involving more then two projections, (multiprojection modeling) a novel procedure is presented that consists of fully automated centerline and width determination in all available projections based on the information provided by the semi-automated centerline detection in two initial calibrated projections. The accuracy of the 3-D coronary modeling approach is determined by a quantitative examination of the 3-D centerline point position and the 3-D cross sectional area of the reconstructed objects. The measurements are based on the analysis of calibrated phantom and calibrated coronary 2-D projection data. From this analysis a confidence region (alpha degrees approximately equal to [35 degrees - 145 degrees]) for the angular distance of two initial projection images is determined for which the modeling procedure is sufficiently accurate for the applied system. Within this angular border range the centerline position error is less then 0.8 mm, in terms of the Euclidean distance to a predefined ground truth. When involving more projections using our new procedure, experiments show that when the initial pair of projection images has an angular distance in the range alpha degrees approximately equal to [35 degrees - 145 degrees], the centerlines in all other projections (gamma = 0 degrees - 180 degrees) were indicated very precisely without any additional centering procedure. When involving additional projection images in the modeling procedure a more realistic shape of the structure can be provided. In case of the concave segment, however, the involvement of multiple projections does not necessarily provide a more realistic shape of the reconstructed structure.

Algorithms↗
PubMed2003

Analytical guide wire motion algorithm for simulation of endovascular interventions.

Performing minimally invasive vascular interventions requires proper training, as a guide wire needs to be manipulated, by the tail, under fluoroscopic guidance. To provide a training environment, the motion of the guide wire inside the human vasculature can be simulated by computer. Such a simulation needs to be based on an algorithm that is both realistic and fast. To meet these two demands, an analytical solution to the problem of guide wire motion has been derived, using a new parametrisation of guide wire shape. The algorithm is highly generic, is entirely based on elementary physics and has good convergence properties (accuracy of 22 micron after two iterations). In an experimental validation of the algorithm in a planar model, the RMS of the spatial discrepancy between the real and simulated catheter positions was about 10% of the lumen size. Comparison of the simulated guide wire motion with 3D rotational angiography data of a real guide wire advanced in a plastic phantom of the cerebral vasculature showed that the new algorithm produced realistic results.

Algorithms↗
PubMed2002

Subchondral bone mineral density patterns representing the loading history of the wrist joint.

Ten cadaver wrists were examined with CT-Absorptiometry in order to assess bone density in the subchondral bone. In normal wrists the distal radius contained two centroids of bone density, one in the lunate fossa and another in the scaphoid fossa. Pathologically altered wrists showed a shift in bone density towards the scaphoid fossa, with the subchondral bone in the lunate fossa and distal ulna becoming less dense. Bone density patterns in the wrist reflect the long-term force transmission. As bone density alters according to loading conditions, this method can be used to determine force transmission patterns before and after wrist surgery.

Absorptiometry, Photon↗
PubMed2001

Quantitative analysis of vascular morphology from 3D MR angiograms: In vitro and in vivo results.

A 3D model-based approach for quantification of vascular morphology from several MRA acquisition protocols was evaluated. Accuracy, reproducibility, and influence of the image acquisition techniques were studied via in vitro experiments with ground truth diameters and the measurements of two expert readers as reference. The performance of the method was similar to or more accurate than the manual assessments and reproducibility was also improved. The methodology was applied to stenosis grading of carotid arteries from CE MRA data. In 11 patients, the approach was compared to manual scores (NASCET criterion) on CE MRA and DSA images, with the result that the model-based technique correlates better with DSA than the manual scores. Spearman's correlation coefficient was 0.91 (P < 0.001) for the model-based technique and DSA vs. 0.80 and 0.84 (P < 0.001) between the manual scores and DSA. From the results it can be concluded that the approach is a promising objective technique to assess geometrical vascular parameters, including degree of stenosis. Magn Reson Med 45:311-322, 2001.

Algorithms↗
PubMed2001

Quantitative evaluation of convolution-based methods for medical image interpolation.

Interpolation is required in a variety of medical image processing applications. Although many interpolation techniques are known from the literature, evaluations of these techniques for the specific task of applying geometrical transformations to medical images are still lacking. In this paper we present such an evaluation. We consider convolution-based interpolation methods and rigid transformations (rotations and translations). A large number of sinc-approximating kernels are evaluated, including piecewise polynomial kernels and a large number of windowed sinc kernels, with spatial supports ranging from two to ten grid intervals. In the evaluation we use images from a wide variety of medical image modalities. The results show that spline interpolation is to be preferred over all other methods, both for its accuracy and its relatively low computational cost.

Brain Mapping↗
PubMed2001

Three-dimensional modeling for functional analysis of cardiac images: a review.

Three-dimensional (3-D) imaging of the heart is a rapidly developing area of research in medical imaging. Advances in hardware and methods for fast spatio-temporal cardiac imaging are extending the frontiers of clinical diagnosis and research on cardiovascular diseases. In the last few years, many approaches have been proposed to analyze images and extract parameters of cardiac shape and function from a variety of cardiac imaging modalities. In particular, techniques based on spatio-temporal geometric models have received considerable attention. This paper surveys the literature of two decades of research on cardiac modeling. The contribution of the paper is three-fold: 1) to serve as a tutorial of the field for both clinicians and technologists, 2) to provide an extensive account of modeling techniques in a comprehensive and systematic manner, and 3) to critically review these approaches in terms of their performance and degree of clinical evaluation with respect to the final goal of cardiac functional analysis. From this review it is concluded that whereas 3-D model-based approaches have the capability to improve the diagnostic value of cardiac images, issues as robustness, 3-D interaction, computational complexity and clinical validation still require significant attention.

Diagnostic Imaging↗
PubMed2001

Reduction of patient motion artifacts in digital subtraction angiography: evaluation of a fast and fully automatic technique.

The performance of an automatic technique for the reduction of patient motion artifacts in digital subtraction angiography was evaluated. Four observers assessed the quality of 104 cerebral digital subtraction angiographic images that were processed by means of both the automatic technique and manual pixel shifting. The automatic technique resulted in better image quality and was considerably less time-consuming.

Adult↗
PubMed2000

Fast delineation and visualization of vessels in 3-D angiographic images.

A method is presented which aids the clinician in obtaining quantitative measures and a three-dimensional (3-D) representation of vessels from 3-D angiographic data with a minimum of user interaction. Based on two user defined starting points, an iterative procedure tracks the central vessel axis. During the tracking process, the minimum diameter and a surface rendering of the vessels are computed, allowing for interactive inspection of the vasculature. Applications of the method to CTA, contrast enhanced (CE)-MRA and phase contrast (PC)-MRA images of the abdomen are shown. In all applications, a long stretch of vessels with varying width is tracked, delineated, and visualized, in less than 10 s on a standard clinical workstation.

Algorithms↗
PubMed2000

Objective quantification of the motion of soft tissues in the orbit.

Orbital soft-tissue motion analysis aids in the localization and diagnosis of orbital disorders. A technique has been developed to objectively quantify and visualize motion in the orbit during gaze. T1-weighted MR volume sequences are acquired during gaze and soft-tissue motion is quantified using optical flow techniques. The flow field is visualized using color-coding: orientation of the flow vector is coded by hue and magnitude by saturation of the pixel. Current clinical circumstances limit MR image acquisition to short sequences and short acquisition times. The effect of these limitations on the performance of optical flow computation has been studied for four representative optical flow algorithms: on short (nine frames) and long (21 frames) simulated sequences of rotation of a magnetic resonance (MR) imaged object, on short measured MR sequences of controlled rotation of the same object and on short MR sequences of motion in the orbit. On the short simulated and motion-controlled sequences, the Lucas and Kanade algorithm showed the best performance with respect to both accuracy and robustness. These motion estimates were accurate to within 20%. Motion in the orbit ranged between 0.05 and 0.25 mm/degree gaze. Color-coding was found to be attractive as a visualization technique, because it shows both magnitude and orientation of all flow vectors without cluttering.

Algorithms↗
PubMed1999

Model-based quantitation of 3-D magnetic resonance angiographic images.

Quantification of the degree of stenosis or vessel dimensions are important for diagnosis of vascular diseases and planning vascular interventions. Although diagnosis from three-dimensional (3-D) magnetic resonance angiograms (MRA's) is mainly performed on two-dimensional (2-D) maximum intensity projections, automated quantification of vascular segments directly from the 3-D dataset is desirable to provide accurate and objective measurements of the 3-D anatomy. A model-based method for quantitative 3-D MRA is proposed. Linear vessel segments are modeled with a central vessel axis curve coupled to a vessel wall surface. A novel image feature to guide the deformation of the central vessel axis is introduced. Subsequently, concepts of deformable models are combined with knowledge of the physics of the acquisition technique to accurately segment the vessel wall and compute the vessel diameter and other geometrical properties. The method is illustrated and validated on a carotid bifurcation phantom, with ground truth and medical experts as comparisons. Also, results on 3-D time-of-flight (TOF) MRA images of the carotids are shown. The approach is a promising technique to assess several geometrical vascular parameters directly on the source 3-D images, providing an objective mechanism for stenosis grading.

Algorithms↗
PubMed1998

Selection of task-dependent diffusion filters for the post-processing of SPECT images.

Iterative reconstruction from single photon emission computed tomography (SPECT) data requires regularization to avoid noise amplification and edge artefacts in the reconstructed image. This is often accomplished by stopping the iteration process at a relatively low number of iterations or by post-filtering the reconstructed image. The aim of this paper is to develop a method to automatically select an optimal combination of stopping iteration number and filters for a particular imaging situation. To this end different error measures between the distribution of a phantom and a corresponding filtered SPECT image are minimized for different iteration numbers. As a study example, simulated data representing a brain study are used. For post-reconstruction filtering, the performance of 3D linear diffusion (Gaussian filtering) and edge preserving 3D nonlinear diffusion (Catté scheme) is investigated. For reconstruction methods which model the image formation process accurately, error measures between the phantom and the filtered reconstruction are significantly reduced by performing a high number of iterations followed by optimal filtering compared with stopping the iterative process early. Furthermore, this error reduction can be obtained over a wide range of iteration numbers. Only a negligibly small additional reduction of the errors is obtained by including spatial variance in the filter kernel. Compared with Gaussian filtering, Catté diffusion can further reduce the error in some cases. For the examples considered, using accurate image formation models during iterative reconstruction is far more important than the choice of the filter.

Biophysical Phenomena↗
PubMed1998

Geodesic deformable models for medical image analysis.

In this paper implicit representations of deformable models for medical image enhancement and segmentation are considered. The advantage of implicit models over classical explicit models is that their topology can be naturally adapted to objects in the scene. A geodesic formulation of implicit deformable models is especially attractive since it has the energy minimizing properties of classical models. The aim of this paper is twofold. First, a modification to the customary geodesic deformable model approach is introduced by considering all the level sets in the image as energy minimizing contours. This approach is used to segment multiple objects simultaneously and for enhancing and segmenting cardiac computed tomography (CT) and magnetic resonance images. Second, the approach is used to effectively compare implicit and explicit models for specific tasks. This shows the complementary character of implicit models since in case of poor contrast boundaries or gaps in boundaries e.g. due to partial volume effects, noise, or motion artifacts, they do not perform well, since the approach is completely data-driven.

Animals↗
PubMed1997

Automated lumen definition from 30 MHz intravascular ultrasound images.

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.

Catheterization↗
PubMedDate not supplied

Registration, segmentation, and visualization of multimodal brain images.

This paper gives an overview of the studies performed at our institute over the last decade on the processing and visualization of brain images, in the context of international developments in the field. The focus is on multimodal image registration and multimodal visualization, while segmentation is touched upon as a preprocessing step for visualization. The state-of-the-art in these areas is discussed and suggestions for future research are given.

Brain↗