Browsing by Subject "skeleton"

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    A Combined Skeleton Model
    (2014-12-10) Miller, Daniel Evan
    Skeleton representations are a fundamental way of representing a variety of solid models. They are particularly important for representing certain biological models and are often key to visualizing such data. Several methods exist for extracting skeletal models from 3D data sets. Unfortunately, there is usually not a single correct definition for what makes a good skeleton, and different methods will produce different skeletal models from a given input. Furthermore, for many scanned data sets, there also is inherent noise and loss of data in the scanning process that can reduce ability to identify a skeleton. In this document, I propose a method for combining multiple algorithms' skeleton results into a single composite skeletal model. This model leverages various aspects of the geometric and topological information contained in the different input skeletal models to form a single result that may limit the error introduced by particular inputs by means of a confidence function. Using such an uncertainty based model, one can better understand, refine, and de-noise/simplify the skeletal structure. The following pages describe methods for forming this composite model and also examples of applying it to some real-world data sets.
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    Mechanisms of impaired osteoblast function during disuse
    (Texas A&M University, 2004-11-15) Allen, Matthew Robert
    Prolonged periods of non-weightbearing activity result in a significant loss of bone mass which increases the risk of fracture with the initiation of mechanical loading. The loss of bone mass is partially driven by declines in bone formation yet the mechanisms responsible for this decline are unclear. To investigate the limitations of osteoblasts during disuse, marrow ablation was superimposed on hindlimb unloaded mice. Marrow ablation is a useful model to study osteoblast functionality as new cancellous bone is rapidly formed throughout the marrow of a long bone while hindlimb unloading is the most common method used to produce skeletal unloading. The specific hypotheses of this study were aimed at determining if changes in osteoblast functionality, differentiation, and/or proliferation were compromised in non-weightbearing bone in response to a bone formation stimulus. Additionally, the influence of having compromised osteoblast functionality at the time of stimulation was assessed in non-weightbearing bones. Key outcome measures used to address these hypotheses included static and dynamic cancellous bone histomorphometry, bone densitometry, and real-time polymerase chain reaction (PCR) analyses of gene expression. The results document similar ablation-induced increases of cancellous bone in both weightbearing and unloaded animals. Similarly, there was no influence of load on ablation-induced increases in cancellous bone forming surface or mineral apposition rate. Unloading did significantly attenuate the ablation-induced increase in bone formation rate, due to reduced levels of total surface mineralization. When osteoblast functionality was compromised prior to marrow ablation, bone formation rate increases were also attenuated in ablated animals due to reduced mineralization. Additionally, increases in forming surface were attenuated as compared to unloaded animals having normal osteoblast function at the time of ablation. Collectively, these data identify mineralization as the limiting step in new bone formation during periods of disuse. The caveat, however, is that when bone formation is stimulated after a period of unloading sufficient to compromise osteoblast functionality, increases in osteoblast recruitment to the bone surface are compromised.