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IEEE International Symposium on Biomedical Imaging

作者： D. Loeckx F. Maes D. Vandermeulen P. Suetens Medical Image Computing ESAT/PSI Katholieke Universiteit Leuven Belgium

ISBN: (纸本)9781424441259;9781424441266

Recently, different approaches have emerged for voxel based nonrigid image registration using local instead of global similarity measures. Benefits are more accurate registration or the ability to subdivide the global similarity in local contributions. Within this article, we provide a general method to localise similarity measures using overlapping regions. Moreover, we extend the concept of partial volume estimation, introduced for mutual information (MI), to other similarity measures. We compare local and global sum of squared differences (SSD), cross correlation (CC) and MI for different sizes of the local regions. In general, local MI gives the highest accuracy, even for image pairs of the same modality. Partial volume estimation slightly improves the accuracy for local measures; the improvement is more pronounced for label images.

关键词： image registration Volume measurement Mutual information Pressure measurement Biomedical imaging Measurement standards Histograms Interpolation image databases

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The minimal entropy prior for simultaneous reconstruction and segmentation of in vivo microct trabecular bone images

The minimal entropy prior for simultaneous reconstruction an...

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IEEE International Symposium on Biomedical Imaging

作者： M. Depypere J. Nuyts K. Laperre G. Carmeliet F. Maes P. Suetens Medical Image Computing (ESAT/PSI) Katholieke Universiteit Leuven Leuven Belgium Department of Nuclear Medicine Katholieke Universiteit Leuven Leuven Belgium Laboratory of Experimental Medicine and Endocrinology Katholieke Universiteit Leuven Leuven Belgium

ISBN: (纸本)9781424439317

We present the minimal entropy prior for the iterative reconstruction of muCT projection data using the maximum a posteriori (MAP) framework. The minimal entropy prior restricts the number of intensity values in the reconstruction without requiring a priori information about the number of image tissues or tissue intensity estimates. We utilise the presented prior in the MAP framework to simultaneously reconstruct and segment trabecular bone from low quality muCT images. The MAP approach allows the straightforward incorporation of the in vivo scanner point spread function, while the entropy prior yields a segmentation that obeys to projection data.

关键词： Entropy image reconstruction image segmentation In vivo Cancellous bone Computed tomography Biomedical imaging Joints Mice image resolution

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Condylar asymmetry in children with juvenile idiopathic arthritis assessed by cone-beam computed tomography

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European Journal of Orthodontics 2008年第6期30卷 545-551页

作者： Huntjens, Elisabeth Kiss, Gabriel Wouters, Carine Carels, Carine Department of Orthodontics School of Dentistry Oral Pathology and Maxillo-Facial Surgery Katholieke Universiteit Leuven Leuven Belgium Laboratory for Medical Image Computing (Radiology - ESAT/PSI) Leuven Belgium Department of Paediatrics Unit of Paediatric Rheumatology Leuven University Hospital Gasthuisberg Belgium Department of Orthodontics School of Dentistry Oral Pathology and Maxillo-Facial Surgery Katholieke Universiteit Leuven 3000 Leuven Belgium

The purpose of this study was to determine the degree of condylar asymmetry in children with juvenile idiopathic arthritis (JIA) using cone-beam computed tomography (CBCT) and analysis software. For 20 patients (14 girls and six boys;mean age 11.21 ± 3.54 years), resultant cross-sectional images of the left and right temporomandibular joints (TMJs) were semi-automatically segmented, and exact registration of the right, with respect to the flipped left grey-level condyle, was *** inspection of the volume images in 360 degree rotation showed a wide variety of condylar destruction patterns, ranging from small erosions within the cortex to almost complete deformation of the condylar head. Because segmentation was restricted to the delineation of the cortical region, possible changes in the deeper zones were not reproduced. Descriptive statistics [median and interquartile range (IQR)] and diagrams (frequency distribution) were used to assess the results. Initial analysis of condylar volume (including both flipped left and right) showed a median value for volume of 0.844 cm³ (IQR 0.323), while the median value for volume difference between both condyles was 0.051 cm³ (IQR 0.098). Analysis of the degree of asymmetry showed a median value of 26.18 per cent (IQR 14.46). Using the CBCT-based method, it was shown that condylar asymmetry was a common feature in children with JIA. The degree of asymmetry was variable, but significant in the majority of the subjects.

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Statistically deformable face models for cranio-facial reconstruction

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Journal of computing and Information Technology 2006年第1期14卷 21-30页

作者： Claes, Peter Vandermeulen, Dirk De Greef, Sven Willems, Guy Suetens, Paul Katholieke Universiteit Leuven Medical Image Computing - ESAT/PSI Belgium Katholieke Universiteit Leuven Centre of Forensic Ontology Belgium

Forensic facial reconstruction aims at estimating the facial outlook associated to an unknown skull specimen. Estimation is based on tabulated average values of soft tissue thicknesses measured at a sparse set of landmarks on the skull. Traditional 'plastic' methods apply modeling clay or plasticine on a cast of the skull approximating the estimated tissue depths at the landmarks and interpolating in between. Current computerized techniques mimic this landmark interpolation procedure using a single facial surface template. However, the resulting reconstruction is biased by the specific choice of the template and no face-specific regularization is present. We reduce the bias by using a flexible statistical model of a dense set of facial surface points combined with an associated sparse set of skull landmarks. The statistical model also provides a probability value, which can be used to regularize the reconstruction towards more plausible outlooks. The reconstruction is obtained by fitting the model skull landmarks to the corresponding landmarks indicated on a digital copy of the skull to be reconstructed. The fitting process alternates between changing the face-specific statistical model parameters and interpolating the remaining landmark fit error using a minimal bending Thin-Plate Spline (TPS)-based deformation. Furthermore, estimated properties of the skull specimen (BMI, age and gender e.g.) can be incorporated as conditions on the reconstruction by removing property-related shape variation from the statistical model description before the fitting process. This iterative statistical model-based reconstruction process is shown by experiment to converge to a realistic reconstruction of the face, independent of the initial template.

关键词： Interpolation

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Removal of Plaque and Stent Artifacts in Subtraction CT Angiography Using Nonrigid Registration and a Volume Penalty

Removal of Plaque and Stent Artifacts in Subtraction CT Angi...

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Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)

作者： D. Loeckx S. Drisis F. Maes D. Vandermeulen G. Marchal P. Suetens Medical Image Computing (ESAT/PSI) Faculty of Engineering University of Hospital Gasthuisberg Leuven Belgium Department of Radiology Faculty of Medicine University of Hospital Gasthuisberg Leuven Belgium

Computed tomography angiography (CTA) is an established tool for vascular imaging. However, high-intense structures in the contrast image can seriously hamper luminal visualisation. This can be solved by subtraction CTA, where a native image is subtracted from the contrast image. However, patient and organ motion limit the application of this technique. Within this paper, a fully automated intensity-based nonrigid 3D registration algorithm for subtraction CT angiography is presented, using a penalty term to avoid volume change during registration. Visual and automated validation on four clinical datasets clearly show that the algorithm strongly reduces motion artifacts in subtraction CTA. Most artifacts disappear, also artifacts caused by minimal displacement of stents or calcified plaques, allowing a 2D and 3D artifact-free visualisation of the vessel lumen. This enables a quick overview of the whole vascular structure and opens the possibility to the visualisation of smaller vessels

关键词： Angiography Computed tomography Visualization Spatial resolution Biomedical imaging Computer displays Rendering (computer graphics) Automatic control Biomedical engineering Radiology

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Automatic identification of muscle insertion sites in MR images using atlas-based, non-rigid registration

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Gait & Posture 2006年 24卷 S71-S72页

作者： Lennart Scheys Ilse Jonkers Dirk Loeckx Arthur Spaepen Paul Suetens Medical Image Computing—ESAT/PSI U.Z. Gasthuisberg Leuven Belgium Department of Biomedical Kinesiology FABER/K.U.Leuven Leuven Belgium

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Subtraction CT angiography using non-rigid registration: The impact of similarity measure and image pre-processing

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International Congress Series 2005年 1281卷 328-333页

作者： Drisis, S. Srivastava, S. Seghers, D. Coudyzer, W. Maes, F. Suetens, P. Marchal, G. Radiology Department Gasthuisberg University Hospital Belgium Medical Image Computing PSI ESAT KU Leuven Belgium

Subtraction CT Angiography is susceptible to motion artifacts especially when abdomen is the area under examination. The purpose of this study was to compare two non-rigid registration algorithms, one, using maximization of mutual information and the other, using sum of squared differences as a similarity measure and to evaluate their registration performance. Furthermore the impact of pre-processing of the images (native images versus edge weighted images) on the registration quality for registration of the abdomen prior to subtraction was assessed. Maximization of the mutual information performed better than sum of squared differences and edge weighted images performed better than native images especially when plaques were considered. Edge weighted images preserve the volume of plaques and bones, thus increasing the registration performance for subtraction CT angiography. © 2005 CARS and Elsevier B.V.

关键词： Mutual information Non-rigid registration Subtraction CT angiography

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Very fast soft tissue predictions with mass tensor model for maxillofacial surgery planning systems

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International Congress Series 2005年 1281卷 491-496页

作者： Mollemans, Wouter Schutyser, Filip Nadjmi, Nasser Suetens, Paul Medical Image Computing (Radiology-ESAT/PSI) University Hospital Gasthuisberg B-3000 Leuven Herestraat 4 Belgium Eeuwfeestkliniek 2018 Antwerpen Harmoniestraat 68 Belgium

Maxillofacial surgery treats abnormalities of the skeleton of the head. Skull remodelling implies osteotomies, bone fragment repositioning, restoration of bone defects and inserting implants. In this field there is a huge demand from the surgeons to be able to predict the new facial outlook after surgery. Besides the big interests for the surgeon during planning, it is also an essential tool to improve the communication between surgeon and patient. Mass Spring Models (MSM) are widely used to simulate the deformation behavior of soft tissues. The usage of these models has however some serious disadvantages. Most important is that the MSM has no real bio-mechanical foundation. The Finite Element Model (FEM) on the other hand has a strong bio-mechanical foundation but the high computational cost and a difficult architecture make it not very useful for fast simulators. In this paper we present the usage of a Mass Tensor Model (MTM) to simulate the soft tissue deformations after bone displacement. This model tries to combine the advantages of FEM and MSM. Moreover by combining this MTM with a new static solution scheme and a dynamic threshold, we were able to reduce the calculation time seriously when compared to MSM or FEM. © 2005 CARS and Elsevier B.V.

关键词： Mass tensor Maxillofacial Planning systems Soft tissue modelling

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Robust and accurate partial surface registration based on variational implicit surfaces for automatic 3D model building

Robust and accurate partial surface registration based on va...

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International Conference on 3D Imaging, Modeling, Processing, Visualization and Transmission (3DIMPVT)

作者： P. Claes D. Vandermeulen L. Van Gool P. Suetens ESAT/PSI/Medical Image Computing Katholieke Universiteit Leuven Belgium ESAT/PSI/VISICS Katholieke Universiteit Leuven Belgium

Three-dimensional models are often assembled from several partial reconstructions from unknown viewpoints. In order to provide a fully automatic, robust and accurate method for aligning and integrating partial reconstructions without any prior knowledge of the relative viewpoints of the sensor or the geometry of the imaging process, we propose a 4-step registration and integration algorithm based on a common Variational Implicit Surface (VIS) representation of the partial surface reconstructions. First, a global crude registration without a priori knowledge is performed followed by a pose refinement of partial reconstruction pairs. Pair-wise registrations are converted into a multi-view registration, before a final integration of the reconstructions into one entity or model occurs. Furthermore, making use of the smoothing properties of the VIS representations, the algorithm proves to be robust against noise in the reconstruction data. Experimental results on real-live, as well as noiseless and noisy simulated data are presented to show the feasibility, the accuracy and robustness of our registration scheme.

关键词： image reconstruction Surface reconstruction Biomedical imaging Geometry Smoothing methods Noise robustness Cameras image sensors Assembly systems Calibration

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Partial surface integration based on variational implicit functions and surfaces for 3D model building

Partial surface integration based on variational implicit fu...

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International Conference on 3D Imaging, Modeling, Processing, Visualization and Transmission (3DIMPVT)

作者： P. Claes D. Vandermeulen L. Van Gool P. Suetens ESAT/PSI/Medical Image Computing Katholieke Universiteit Leuven Belgium ESAT/PSI/VISICS Katholieke Universiteit Leuven Belgium

Most three-dimensional acquisition systems generate several partial reconstructions that have to be registered and integrated for building a complete 3D model. In this paper, we propose a volumetric shape integration method, consisting of weighted signed distance functions represented as variational implicit functions (VIF) or surfaces (VIS). Texture integration is solved similarly by using three weighted color junctions also based on VIFs. Using these continuous (not grid-based) representations solves current limitations of volumetric methods: no memory inefficient and resolution limiting grid representation is required. The built-in smoothing properties of the VIS representations also improve the robustness of the final integration against noise in the input data. Experimental results are performed on real-live, noiseless and noisy synthetic data of human faces in order to show the robustness and accuracy of the integration algorithm.

关键词： Biomedical imaging image reconstruction Shape Noise robustness Data mining Surface reconstruction Colored noise Smoothing methods Humans Face

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