34 research outputs found
Surface interpolation from sparse cross-sections using region correspondence G.M. Treece, R.W. Prager
3D ultrasound examination of large organs G.M. Treece, R.W. Prager,
No full textFreehand 3D ultrasound is particularly appropriate for the measurement of organ volumes. For small organs, which can be fully examined with a single sweep of the ultrasound probe, the results are known to be much more accurate than those using conventional 2D ultrasound. However, large or complex shaped organs are difficult to quantify in this manner because multiple sweeps are required to cover the entire organ. Typically, there are significant registration errors between the various sweeps, which generate artifacts in an interpolated voxel array, making segmentation of the organ very difficult. This report describes how sequential freehand 3D ultrasound can be used to measure the volume of large organs without the need for an interpolated voxel array. The method is robust to registration errors and sweep orientation, as demonstrated in simulation and also using in vivo scans of a human liver, where a volume measurement precision of ±5 % is achieved
Trabecular and cortical bone structure of the talus and distal tibia in Pan and Homo.
No full textObjectives: Internal bone structure, both cortical and trabecular bone, remodels in response to loading and may provide important information regarding behavior. The foot is well suited to analysis of internal bone structure because it experiences the initial substrate reaction forces, due to its proximity to the substrate. Moreover, as humans and apes differ in loading of the foot, this region is relevant to questions concerning arboreal locomotion and bipedality in the hominoid fossil record.
Materials and methods: We apply a whole-bone/epiphysis approach to analyze trabecular and cortical bone in the distal tibia and talus of Pan troglodytes and Homo sapiens. We quantify bone volume fraction (BV/TV), degree of anisotropy (DA), trabecular thickness (Tb.Th), bone surface to volume ratio (BS/BV), and cortical thickness and investigate the distribution of BV/TV and cortical thickness throughout the bone/epiphysis.
Results: We find that Pan has a greater BV/TV, a lower BS/BV and thicker cortices than Homo in both the talus and distal tibia. The trabecular structure of the talus is more divergent than the tibia, having thicker, less uniformly aligned trabeculae in Pan compared to Homo. Differences in dorsiflexion at the talocrural joint and in degree of mobility at the talonavicular joint are reflected in the distribution of cortical and trabecular bone.
Discussion: Overall, quantified trabecular parameters represent overall differences in bone strength between the two species, however, DA may be directly related to joint loading. Cortical and trabecular bone distributions correlate with habitual joint positions adopted by each species, and thus have potential for interpreting joint position in fossil hominoids
How does the femoral cortex depend on bone shape? A methodology for the joint analysis of surface texture and shape
No full textA study of similarity measures for in vivo 3D ultrasound volume registration
No full textMost of the conventional ultrasound machines in hospitals work in two dimensions. However, there are some applications where doctors would like to be able to gather ultrasound data as a three-dimensional (3D) block rather than a two-dimensional (2D) slice. Two different types of 3D ultrasound have been developed to meet this requirement. One type involves a special probe that can record a fixed block of data, either by having an internal sweeping mechanism or by using electronic steering. The other type of 3D ultrasound uses a conventional 2D ultrasound probe together with a position sensor and is called freehand 3D ultrasound. A natural progression of the mechanically-swept 3D ultrasound system is to combine it with the free hand sensor. This results in an extended field of view. There are two major problems with using a position sensor. Firstly, line-of-sight needs to be maintained between the sensor and the reference point. Secondly, the multiple volumes rarely register because of tissue displacement and deformation. Therefore, the objective of this paper is to get rid of the inconvenient position sensor and to use an automatic image-based registration technique. We provide an experimental study of several intensity-based similarity measures for the registration of 3D ultrasound volumes. Rather than choosing a conventional voxel array to represent the 3D blocks, we use corresponding vertical and horizontal image slices from the blocks to be matched. This limits the amount of data thus making the calculation of the similarity measure less computationally expensive
Particle swarm optimization for in vivo 3D ultrasound volume registration
No full textAs three-dimensional (3D) ultrasound is becoming more and more popular, there has been increased interest in using a position sensor to track the trajectory of the 3D ultrasound probe during the scan. One application is the improvement of image quality by fusion of multiple scans from different orientations. With a position sensor mounted on the probe, the clinicians face additional difficulties, for example, maintaining a line-of-sight between the sensor and the reference point. Therefore, the objective of this paper is to register the volumes using an automatic image-based registration technique. In this paper, we employ the particle swarm optimization (PSO) technique to calculate the six rigid-body transformation parameters (three for translation and three for rotation) between successive volumes of 3D ultrasound data. We obtain vertical and horizontal slices through the acquired volumes and then use an intensity-based similarity measure as a fitness function for each particle. We considered various settings in the PSO to find a set of parameters to give the best convergence. We found the visually acceptable registration when the initial orientations of the particles were confined to within a few degrees of the orientations obtained from position sensor
Regularised marching tetrahedra: improved iso-surface extraction
No full textMarching cubes is a simple and popular method for extracting iso-surfaces from implicit functions or discrete three-dimensional (3-D) data. However, it does not guarantee the surface to be topologically consistent with the data, and it creates triangulations which contain many triangles of poor aspect ratio. Marching tetrahedra is a variation of marching cubes, which overcomes this topological problem. Improvement in triangle aspect ratio has generally been achieved by mesh simplification, a group of algorithms designed to reduce the large number of triangles. Vertex clustering is one of the simplest of these algorithms, but does not in general maintain the topology of the original mesh. We present a new algorithm, regularised marching tetrahedra, which combines marching tetrahedra and vertex clustering to generate iso-surfaces which are topologically consistent with the data and contain a number of triangles appropriate to the sampling resolution (typically 70 % fewer than marching tetrahedra) with significantly improved aspect ratios. This improvement in aspect ratio greatly enhances the display of the surface, particularly when it is rendered using simple interpolated shading. Surface triangulations are shown for implicit surfaces, thresholded medical data, and surface
Deverbal nominals in Kiswahili: Underspecification morphology and the lexicon
No full textThis study provides an explicit account of the lexical entries and rules required to generate five common types of Kiswahili nouns based on verbal roots and stems, as illustrated by the data below, all derived from -kata 'cut'. (UNFORMATTED TABLE OR EQUATION FOLLOWS)\vbox{\halign{#\hfil&&\enspace#\hfil\cr&a.&Action Nominals in -{\it o}:&{\it mkato/mikato\/}&`cut(s)'\cr&b.&Transitive Verbals in -{\it a}:&{\it mkata/wakata}&`cutter(s)'\cr&c.&Relic Agentives in -{\it i}:&{\it mkati/wakati}&`cutter(s)'\cr&d.&Productive Agentives in -{\it aji}:&{\it mkataji/wakataji}&`cutter(s)'\cr&e.&Patient Nominals in -{\it e}:&{\it mkate/mikate}&`lump(s), loaf/loaves'\cr}}(TABLE/EQUATION ENDS)Underspecification Theory as developed by Archangeli & Pulleyblank (1986) is adopted to aid in this descriptive task. A rigorous analysis of the Kiswahili phoneme set is provided in this framework, with underspecified and fully specified representations of all phonemes as well as explicit default and complement rules. A detailed account of various types of prefix allomorphy is included, both for inherent nouns and for derived nominals.The apparent simplicity of the data above is deceptive, even disregarding the account provided of the stem and suffix allomorphy associated with the Relic Agentives. Issues confronted in the description include semantic drift, blocking, percolation, questions of derivational source, and archaic roots. A particular focus of the study is to streamline the lexical entries by avoiding the explicit specification of redundant features of all kinds.An innovation in the research is the application of the principles of Underspecification Theory beyond the phonology to capture redundancies in and among the morphological, semantic, and syntactic features and representations. To develop and illustrate this approach, a set of four binary morphological features is proposed to capture the Kiswahili noun-class system. A further innovation is the use of Lexical Cross-References (LXRefs) which capture generalizations relating to morphological complexes while allowing redundant information to be filled in automatically.Made available in DSpace on 2011-05-07T13:59:06Z (GMT). No. of bitstreams: 2
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