148 research outputs found
Extending and applying active appearance models for automated, high precision segmentation in different image modalities
In this paper, we present a set of extensions to the deformable template model: Active Appearance Model (AAM) proposed by Cootes et al. AAMs distinguish themselves by learning a priori knowledge through observation of shape and texture variation in a training set. This is used to obtain a compact object class description, which can be employed to rapidly search images for new object instances. The proposed extensions concern enhanced shape representation, handling of homogeneous and heterogeneous textures, refinement optimization using Simulated Annealing and robust statistics. Finally, an initialization scheme is designed thus making the usage of AAMs fully automated. Using these extensions it is demonstrated that AAMs can segment bone structures in radiographs, pork chops in perspective images and the left ventricle in cardiovascular magnetic resonance images in a robust, fast and accurate manner. Subpixel landmark accuracy was obtained in two of the three cases
Indirect Image Registration with Large Diffeomorphic Deformations
The paper adapts the large deformation diffeomorphic metric mapping framework
for image registration to the indirect setting where a template is registered
against a target that is given through indirect noisy observations. The
registration uses diffeomorphisms that transform the template through a (group)
action. These diffeomorphisms are generated by solving a flow equation that is
defined by a velocity field with certain regularity. The theoretical analysis
includes a proof that indirect image registration has solutions (existence)
that are stable and that converge as the data error tends so zero, so it
becomes a well-defined regularization method. The paper concludes with examples
of indirect image registration in 2D tomography with very sparse and/or highly
noisy data.Comment: 43 pages, 4 figures, 1 table; revise
Object localization using deformable templates
Object localization refers to the detection, matching and segmentation of objects in
images. The localization model presented in this paper relies on deformable templates
to match objects based on shape alone. The shape structure is captured by a prototype
template consisting of hand-drawn edges and contours representing the object to be
localized. A multistage, multiresolution algorithm is utilized to reduce the computational
intensity of the search. The first stage reduces the physical search space dimensions
using correlation to determine the regions of interest where a match it likely to occur.
The second stage finds approximate matches between the template and target image at
progressively finer resolutions, by attracting the template to salient image features using
Edge Potential Fields. The third stage entails the use of evolutionary optimization to
determine control point placement for a Local Weighted Mean warp, which deforms the
template to fit the object boundaries. Results are presented for a number of applications,
showing the successful localization of various objects. The algorithm’s invariance to
rotation, scale, translation and moderate shape variation of the target objects is clearly
illustrated
Unbiased diffeomorphic atlas construction for computational anatomy
pre-printConstruction of population atlases is a key issue in medical image analysis, and particularly in brain mapping. Large sets of images are mapped into a common coordinate system to study intra-population variability and inter-population differences, to provide voxel-wise mapping of functional sites, and help tissue and object segmentation via registration of anatomical labels. Common techniques often include the choice of a template image, which inherently introduces a bias. This paper describes a new method for unbiased construction of atlases in the large deformation diffeomorphic setting. A child neuroimaging autism study serves as a driving application. There is lack of normative data that explains average brain shape and variability at this early stage of development. We present work in progress toward constructing an unbiased MRI atlas of two year of children and the building of a probabilistic atlas of anatomical structures, here the caudate nucleus. Further, we demonstrate the segmentation of new subjects via atlas mapping. Validation of the methodology is performed by comparing the deformed probabilistic atlas with existing manual segmentations
Correspondence evaluation in local shape analysis and structural subdivision
journal articleRegional volumetric and local shape analysis has become of increasing interest to the neuroimaging community due to the potential to locate morphological changes. In this paper we compare three common correspondence methods applied to two studies of hippocampal shape in schizophrenia: correspondence via deformable registration, spherical harmonics (SPHARM) and Minimum Description Length (MDL) optimization. These correspondence methods are evaluated in respect to local statistical shape analysis and structural subdivision analysis. Results show a non-negligible influence of the choice of correspondence especially in studies with low numbers of subjects. The differences are especially striking in the structural subdivision analysis and hints at a possible source for the diverging findings in many subdivision studies. Our comparative study is not meant to be exhaustive, but rather raises awareness of the issue and shows that assessing the validity of the correspondence is an important step
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