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At least 1,135 records · Page 63Linked to original sources
PubMed2004

Intensity-based image registration with a guaranteed one-to-one point match.

OBJECTIVES: In this paper, we propose a novel registration technique, which combines the concepts of landmark and automatic, non-rigid intensity-based approaches. A general framework, which might be used for many different registration problems is presented. The novel approach enables the incorporation of different distance measures as well as different smoothers. METHODS: The proposed scheme minimizes a regularized distance measure subject to some interpolation constraints. The desired deformation is computed iteratively using an Euler-scheme for the first variation of the chosen objective functional. RESULTS: A fast and robust numerical scheme for the computation of the wanted minimizer is developed, implemented, and applied to various registration tasks. This includes the registration of pre- and post-intervention images of the human eye. CONCLUSIONS: A novel framework for a parameter-free, non-rigid registration scheme which allows for the additional incorporation of user-defined landmarks is proposed. It enhances the reliability of conventional approaches considerably and thereby their acceptability by practitioners in a clinical environment.

Algorithms↗
PubMed2004

Multimodal retinal image registration for optic disk segmentation.

OBJECTIVES: The analysis of the optic disk morphology with the means of the scanning laser tomography is an important step for glaucoma diagnosis. A method we developed for optic disk segmentation in images of the scanning laser tomograph is limited by noise, non-uniform illumination and presence of blood vessels. Inspired by recent medical research, we wanted to develop a tool for improving optic disk segmentation by registration of images of the scanning laser tomograph and color fundus photographs and by applying a method we developed for optic disk segmentation in color fundus photographs. METHODS: The segmentation of the optic disk for glaucoma diagnosis in images of the scanning laser tomograph is based on morphological operations, detection of anatomical structures and active contours and has been described in a previous paper. The segmentation of the optic disk in the fundus photographs is based on nonlinear filtering, Canny edge detector and a modified Hough transform. The registration is based on mutual information using simulated annealing for finding maxima. RESULTS: The registration was successful 86.8% of the time when tested on 174 images. Results of the registration have shown a very low displacement error of a maximum of about 5 pixels. The correctness of the registration was manually evaluated by measuring distances between the real vessel borders and those from the registered image. CONCLUSIONS: We have developed a method for the registration of images of the scanning laser tomograph and fundus photographs. Our first experiments showed that the optic disk segmentation could be improved by fused information from both image modalities.

Fundus Oculi↗
PubMed2004

Evaluation of computer-assisted image enhancement in minimal invasive endoscopic surgery.

OBJECTIVES: This paper focuses on the evaluation of the usage of computer-aided image processing methods for minimal invasive surgery. During video endoscopy of visceral cavities the images are displayed directly on the monitor without further processing. In the course of the operation the former good quality of the images decreases due to typical disturbances like bleeding, smoke or flying particles. These disturbances can be reduced by using image processing methods like color normalization, temporal filtering or equalization. METHODS: In this double-blinded analysis, 14 surgeons with different levels of experience evaluated 120 image pairs and 5 image sequences, directly comparing original and processed images or movies. RESULTS: Color normalization and equalization proved to significantly enhance video endoscopic images. With regard to temporal filtering, an improvement could be seen in the image sequences with filter size 5 being a greater enhancement than filter size 3. Comparing the state of experience and its influence on the results, it occurred that the experienced surgeons preferred the original color while altogether agreeing that the color-normalized images were better. CONCLUSIONS: The results obtained in the present evaluation show that the image processing methods which were used can significantly improve the quality of video endoscopic images. As a result of this, necessary lavages of the operated area are reduced and a better overview and orientation for the surgeon can be reached.

Humans↗
PubMed2004

Objective evaluation of three-dimensional image registration algorithms--tools for optimization and evaluation.

OBJECTIVE: The registration of medical volume data sets plays an important role when different images or modalities are used during computer-assisted surgical procedures. Nevertheless, it is often questionable how robust and accurate the underlying algorithms really are. Therefore, the goal is to foster the establishment of methods for an objective evaluation. METHOD: To reliably calculate the accuracy of registration algorithms, a reference transformation must be known. Due to the unknown perfect registration for real clinical data, the simulation of realistic data and successive affine transformations are employed. The simulation is based on models of the respective imaging modality where the dominant physical effects are taken into account. This gives the user full control over all simulation and transformation parameters. Finally, suitable quality measures are applied which allow a systematic evaluation of image registration accuracy by comparing the known theoretical result and the transformation calculated by the algorithm under investigation. RESULTS: During the development of a new registration algorithm, the presented method proved to be a very valuable tool for optimization and evaluation of registration accuracy, since it allows objective numerical comparison of the calculated results. CONCLUSIONS: The presented method can be used during the development of algorithms for optimization and for quantitative comparison of different registration schemes. The respective software tool can automatically generate and transform simulated but realistic data. Employing suitable numerical quality measures, an objective evaluation of registration results can be easily obtained. Still, the validity of the relatively simple models has to be verified to draw reliable conclusions with respect to real data.

Algorithms↗
PubMed2004

Live-wires using path-graphs.

OBJECTIVES: This article discusses our new Path-Graph approach for the interactive Live-Wire segmentation method in 2D applied to pre-segmented data. Furthermore, we examine whether or not the Live-Lane extension provides advantages in combination with pre-segmentation. METHODS: We automatically over-segment the image data in a preprocessing step, using region growing with an automatic seed point generation. The Live-Wire algorithm is applied on this mosaic data by using the outlines of the homogeneous regions as the basis for graph building. We present a new definition of this underlying graph where the edges of the standard graphs are turning into vertices and the vertices of the new graph are defined by the edge connectivity in the standard graph. For better differentiation we name our new graph Path-Graph and the original defined graph Node-Graph. RESULTS: The quality evaluation is done by comparing our segmentation results with existing model data. We show that using the Path-Graph as basis for the Live-Wire algorithm instead of the Node-Graph allows for a finer segmentation. We achieve a reduction of incorrectly classified pixels by 20.66 per cent and a decrease of the mean boundary deviation by 11.61 per cent. Since savings on cost tree calculations are compensated by additional computation time required to compute the Live-Lanes, a performance loss of 2.41 per cent is measured. CONCLUSIONS: Our redefinition of the underlying graph increases the quality of the Live-Wire segmentation. The Live-Lane extension in combination with pre-segmentation is not justified for our data.

Algorithms↗
PubMed2004

MRI-based individual 3D region-of-interest atlases of the human brain: a new method for analyzing functional data.

OBJECTIVES: Introduction of a new atlas-based method for analyzing functional data which takes into account the variability of individual human brains and the partial volume, effects of functional emission computed tomography, images in complex anatomical 3D regions, as well as, describing the underlying multi-modal image processing, principles. METHODS: 3D atlas extraction is done directly by automated segmentation of individual magnetic resonance images of the patient's head. This is done in two steps: voxel-based classification of T1-weighted images for tissue differentiation (low-level processing) is followed by knowledge-based analysis of the classified images for extraction of 3D anatomical regions (high-level processing). For atlas-based quantification of co-registered functional images, 3D anatomical regions can be convoluted with an idealized point spread function of the emission computed tomography system, after which a partial volume-dependent threshold can be determined. RESULTS: Quantitative evaluation studies, based on 50 realistic software head phantoms and 24 image data sets obtained from healthy subjects and patients, show low misclassification rates and stable results for the neural network-based classification approach (mean +/- SD 3.587 +/- 0.466%, range 2.726-4.927%) as well as for the adjustable parameters of the knowledge-based approach. Computation time is <5 min for classification, <1 min for most of the extraction algorithms. The influence of the partial volume-dependent threshold is shown for an activation study. CONCLUSIONS: This new method allows 3D atlas generation without the need to warp individual image data to an anatomical or statistical brain atlas. Going beyond the purely tissue-oriented approach, partial volume effects of emission computed tomography images can be analyzed in complex anatomical 3D regions.

Algorithms↗
PubMed2004

Atlas-based recognition of anatomical structures and landmarks and the automatic computation of orthopedic parameters.

OBJECTIVE: This paper describes methods for the automatic atlas-based segmentation of bone structures of the hip, the automatic detection of anatomical point landmarks and the computation of orthopedic parameters to avoid the interactive, time-consuming pre-processing steps for the virtual planning of hip operations. METHODS: Based on the CT data of the Visible Human Data Sets, two three-dimensional atlases of the human pelvis have been built. The atlases consist of labeled CT data sets, 3D surface models of the separated structures and associated anatomical point landmarks. The atlas information is transferred to the patient data by a non-linear gray value-based registration algorithm. A surface-based registration algorithm was developed to detect the anatomical landmarks on the patient's bone structures. Furthermore, a software tool for the automatic computation of orthopedic parameters is presented. Finally, methods for an evaluation of the atlas-based segmentation and the atlas-based landmark detection are explained. RESULTS: A first evaluation of the presented atlas-based segmentation method shows the correct labeling of 98.5% of the bony voxels. The presented landmark detection algorithm enables the precise and reliable localization of orthopedic landmarks. The accuracy of the landmark detection is below 2.5 mm. CONCLUSION: The atlas-based segmentation of bone structures, the atlas-based landmark detection and the automatic computation of orthopedic measures are suitable to essentially reduce the time-consuming user interaction during the pre-processing of the CT data for the virtual three-dimensional planning of hip operations.

Algorithms↗
PubMed2004

Registration of biplane angiography and intravascular ultrasound for 3D vessel reconstruction.

UNLABELLED: If planned and applied correctly, intra-vascular brachytherapy (IVB) can significantly reduce the risk of restenosis after interventional treatment of stenotic arteries. OBJECTIVES: In order to facilitate computer-based IVB planning, a three-dimensional reconstruction of the stenotic artery based on intravascular ultrasound (IVUS) sequences is desirable. METHODS: To attain a 3D reconstruction, the frames of the IVUS sequence are properly aligned in space and completed with additional intermediate frames generated by interpolation. The alignment procedure uses additional information that is obtained from biplane X-ray angiography performed simultaneously during the capturing of the IVUS sequence. After IVUS images and biplane angiography data are acquired from the patient, the vessel-wall borders and the IVUS catheter are detected by an active contour algorithm. Next, the twist between adjacent IVUS frames is determined by a sequential triangulation method combined with stochastic analysis. RESULTS: The above procedure results in a 3D volume-model of the vessel, which also contains information from the IVUS modality. This data is sufficient for computer-based intravascular brachytherapy planning. CONCLUSION: The proposed methodology can be used to improve the current state-of-the-art IVB treatment planning by enabling computerized dosage computations on a highly accurate 3D model.

Algorithms↗
PubMed2004

Light fields for minimal invasive surgery using an endoscope positioning robot.

OBJECTIVES: To generate a fast and robust 3-D visualization of the operation site during minimal invasive surgery. METHODS: Light fields are used to model and visualize the 3-D operation site during minimal invasive surgery. An endoscope positioning robot provides the position and orientation of the endoscope. The a priori un-known transformation from the endoscope plug to the endoscope tip (hand-eye transformation) can either be determined by a three-step algorithm, which includes measuring the endoscope length by hand or by using an automatic hand-eye calibration algorithm. Both methods are described in this paper and their respective computation times and accuracies are compared. RESULTS: Light fields were generated during real operations and in the laboratory. The comparison of the two methods to determine the unknown hand-eye transformation was done in the laboratory. The results which are being presented in this paper are: rendered images from the generated light fields, the calculated extrinsic camera parameters and their accuracies with respect to the applied hand-eye calibration method, and computation times. CONCLUSION: Using an endoscope positioning robot and knowing the hand-eye transformation, the fast and robust generation of light fields for minimal invasive surgery is possible.

Algorithms↗
PubMed2004

Establishing an international reference image database for research and development in medical image processing.

INTRODUCTION: The lack of comparability of evaluation results is one of the major obstacles of research and development in Medical Image Processing (MIP). The main reason for that is the usage of different image datasets with different quality, size and Gold standard. OBJECTIVES: Therefore, one of the goals of the Working Group on Medical Image Processing of the European Federation for Medical Informatics (EFMI WG MIP) is to develop first parts of a Reference Image Database. METHODS: Kernel of the concept is to identify highly relevant medical problems with significant potential for improvement by MIP, and then to provide respective reference datasets. The EFMI WG MIP has primarily the role of a specifying group and an information broker, while the provider user relationships are defined by bilateral co-operation or license agreements. RESULTS: An explorative database prototype has been implemented using the MySQL database software on the Web. Templates for provider user agreements have been worked out and already applied for own 'pre-RID-MIP' co-operations of the authors. DISCUSSION AND CONCLUSION: First steps towards a comprehensive reference image database have been done. Issues like funding, motivation, management, provision of Gold standards and evaluation guidelines are to be solved. Due to the interest from research groups and industry the efforts will be continued.

Databases as Topic↗
PubMed2004

HELEN, a modular framework for representing and implementing clinical practice guidelines.

OBJECTIVES: In order to implement clinical practice guidelines for the Department of Neonatology of the Heidelberg University Medical Center we developed a modular framework consisting of tools for authoring, browsing and executing encoded clinical practice guidelines (CPGs). METHODS: Based upon a comprehensive analysis of literature, we set up requirements for guideline representation systems. Additionally, we analyzed further aspects such as the critical appraisal and known bridges and barriers for implementing CPGs. Thereafter we went through an evolutionary spiral model to develop a comprehensive ontology. Within this model each cycle focuses on a certain topic of management and implementation of CPGs. RESULTS: In order to bring the resulting ontology into practice we developed a framework consisting of a tool for authoring, a server for web-based browsing, and an engine for the execution of certain elements of CPGs. Based upon this framework we encoded and implemented several CPGs in varying medical domains. CONCLUSIONS: This paper shall present a practical framework for both authors and implementers of CPGs. We have shown the fruitful combination of different knowledge representations such as narrative text and algorithm for implementing CPGs. Finally, we introduced a possible approach for the explicit adaptation of CPGs in order to provide institution-specific recommendations and to support sharing with other medical institutions.

Academic Medical Centers↗
PubMed2004

Public sphere and the sustainability of the bioinformatics promise.

The literature about genomics and bioinformatics achievements in high-impact journals such as Nature and Science has raised disproportionate expectations amongst the general public about fast and revolutionary drugs and breakthroughs in biomedicine. However, the yield obtained by database mining activities has been modest, as reported in the February 2001 issues of these journals featuring the completion of human genome draft sequences by the Human Genome Project Consortium and the company Celera. I have compared changes in rethoric employed by molecular biologists in 2001 and in April 2003, when the final sequence was announced. The comparison suggests that researchers are concerned about the sustainability of society's investment in this field, though not explicitly.

Bibliometrics↗