Based on the Point Distribution Model (PDM), Active Shape Model (ASM) is an iterative algorithm used to detect structures of interest from images. However, current ASM methods are sensitive to image ...noise that may trap the ASM to false edges and/or lead to a structure not within the shape space defined by the PDM. Such problems are particularly serious when segmenting 3D anatomical surface structures from 3D medical images. In this paper, the authors propose two strategies to improve the performance of 3D ASM: (a) developing a robust edge-identification algorithm to reduce the risk of detecting false edges, and (b) integrating the edge-fitting error and statistical shape model defined by a PDM into a unified cost function. They apply the proposed ASM to the challenging tasks of detecting the left hippocampus and caudate surfaces from a subset of 3D pediatric MR images and compare its performance with a recently reported atlas-based method.
Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2009.
Title from electronic title page (viewed Mar. 10, 2010). "... in partial fulfillment of the requirements for the degree of Doctor ...of Philosophy in the Department of Computer Science." Discipline: Computer Science; Department/School: Computer Science.
To evaluate the integration and accuracy of A (amplitude)-mode ultrasound-based surface matching for noninvasive registration of the head into a frameless computer-aided surgery system for ...otorhinology and skull base surgery.
Experimental study and case series.
Academic medical center.
Twelve patients underwent anterior and paranasal skull base surgery with the routine use of a computer-aided surgery system.
A computer-aided surgery system, based on an optoelectronic localizer, was used to track the skull and the surgical tools, including the A-mode ultrasound probe. The A-mode probe was a 10-MHz immersion transducer. An acoustic lens attached to the transducer focused the ultrasonic beam to a depth of 1 to 10 mm. Accuracy tests were performed for the ultrasound setup. Different surface point distributions were evaluated with respect to matching accuracy on a human cadaver skull specimen equipped with fiducial markers. The matching comparison was based on the fiducial registration error. For the clinical evaluation, the laboratory setup was transferred to the operating room.
Noninvasive registration of the skull by using A-mode ultrasound in computer-aided surgery (practical and clinical measurements).
The accuracy tests on the human skull specimen revealed that the mean +/- SD fiducial registration error was 1.00 +/- 0.19 mm in the best series for A-mode ultrasound surface matchings and was robust with respect to different sets of surface points. The mean +/- SD root mean square error from the 12 A-mode ultrasound matchings in the patient study was 0.49 +/- 0.20 mm.
A-mode ultrasound surface matching can be used as a noninvasive and accurate registration procedure in computer-aided surgery of the head.
This dissertation describes a novel shape description scheme that incorporates variability of an object population into the generation of a characteristic 3D shape model. Knowledge about the ...biological variability of anatomical objects is essential for statistical shape analysis and discrimination between healthy and pathological structures. The proposed shape representation is based on a fine-scale spherical harmonics (SPHARM) description and a coarse-scale m-rep description. The SPHARM description describes the object boundary as a weighted series of spherical harmonics. The correspondence on the boundary is defined by a first-order ellipsoid normalized parameterization. The medial m-rep description is composed of a net of medial primitives with fixed graph properties. A m rep model is computed automatically from the shape space of a training population of SPHARM objects. Pruned 3D Voronoi skeletons are used to determine a common medial branching topology in a stable way. An intrinsic coordinate system and an implicit correspondence between objects are defined on the medial manifold. My novel representation scheme describes shape and shape changes in a meaningful and intuitive manner. Several experimental studies of shape asymmetry and shape similarity in biological structures demonstrate the power of the new representation to describe global and local form. The clinical importance of shape measurements is shown in the presented applications. The contributions made in this dissertation include the development of a novel automatic pruning scheme for 3D Voronoi skeletons. My experiments showed that only a small number of skeletal sheets are necessary to describe families of even quite complex objects. This work is also the first to compute a common medial branching topology of an object population, which deals with the sensitivity of the branching topology to small shape variations. The sensitivity of the medial descriptions to small boundary perturbations, a fundamental problem of any skeletonization technique, is approached with a new sampling technique.
Diffusion tensor imaging provides important information on tissue structure and orientation of fiber tracts in brain white matter in vivo. It results in diffusion tensors, which are \(3\times3\) ...symmetric positive definite (SPD) matrices, along fiber bundles. This paper develops a functional data analysis framework to model diffusion tensors along fiber tracts as functional data in a Riemannian manifold with a set of covariates of interest, such as age and gender. We propose a statistical model with varying coefficient functions to characterize the dynamic association between functional SPD matrix-valued responses and covariates. We calculate weighted least squares estimators of the varying coefficient functions for the log-Euclidean metric in the space of SPD matrices. We also develop a global test statistic to test specific hypotheses about these coefficient functions and construct their simultaneous confidence bands. Simulated data are further used to examine the finite sample performance of the estimated varying coefficient functions. We apply our model to study potential gender differences and find a statistically significant aspect of the development of diffusion tensors along the right internal capsule tract in a clinical study of neurodevelopment.
With great potential in studying neuro-development, neuro-degeneration, and the aging process, longitudinal image data is gaining increasing interest and attention in the neuroimaging community. In ...this paper, we present a parametric nonlinear model to statistically study multivariate longitudinal data with asymptotic properties. We demonstrate our preliminary results in a combined study of two longitudinal neuroimaging data sets of early brain development to cover a wider time span and to gain a larger sample size. Such combined analysis of multiple longitudinal image data sets has not been conducted before and presents a challenge for traditional analysis methods. To our knowledge, this is the first multivariate nonlinear longitudinal analysis to study early brain development. Our methodology is generic in nature and can be applied to any longitudinal data with nonlinear growth patterns that can not easily be modeled by linear methods.
Viscoelastic Response (VisR) ultrasound is a new Acoustic Radiation Force (ARF)-based imaging method that uses two successive ARF excitations, delivered to the same region of excitation, to ...approximate a creep response in tissue and thereby estimate viscoelastic property. The viscoelasticity of dystrophic muscle is altered over time by ongoing necrotic, fatty, and fibrous degenerative changes. Evaluating such changes by VisR in the Golden Retriever Muscular Dystrophy (GRMD) canine model, with comparison to matched MRI and histology, is the purpose of this work. In a cross-sectional study, in vivo VisR imaging was performed on the vastus lateralis (VL) and cranial sartorius (CS) muscles in 20 dogs (n=10 control and GRMD age-matched pairs) aged 3, 6, 12, 24, or 60 months. Following VisR, T2-weighted MRI imaging was performed, and run percentage (RP) was calculated to reflect heterogeneity. Finally, muscle tissue samples were acquired by open surgical biopsy, sectioned, and stained, and percent collagen and fat were calculated from digital microscopy. In the VL, SD of VisR τ was consistently larger in GRMD versus age-matched control dogs (p=0.001, Wilcoxon two-sample test). This VisR result was consistent with higher MRI RP measures and higher histology percent collagen. Similarly in the CS, SD of VisR τ was larger in GRMD than control (p=0.001), consistent with higher MRI RP and with histology percent collagen. These results suggest that VisR measures of τ SD reflect heterogeneity due to collagen deposition in dystrophic muscles.
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