928 research outputs found

    2D-3D registration of CT vertebra volume to fluoroscopy projection: A calibration model assessment (doi:10.1155/2010/806094)

    Get PDF
    This study extends a previous research concerning intervertebral motion registration by means of 2D dynamic fluoroscopy to obtain a more comprehensive 3D description of vertebral kinematics. The problem of estimating the 3D rigid pose of a CT volume of a vertebra from its 2D X-ray fluoroscopy projection is addressed. 2D-3D registration is obtained maximising a measure of similarity between Digitally Reconstructed Radiographs (obtained from the CT volume) and real fluoroscopic projection. X-ray energy correction was performed. To assess the method a calibration model was realised a sheep dry vertebra was rigidly fixed to a frame of reference including metallic markers. Accurate measurement of 3D orientation was obtained via single-camera calibration of the markers and held as true 3D vertebra position; then, vertebra 3D pose was estimated and results compared. Error analysis revealed accuracy of the order of 0.1 degree for the rotation angles of about 1?mm for displacements parallel to the fluoroscopic plane, and of order of 10?mm for the orthogonal displacement.<br/

    Image processing for plastic surgery planning

    Get PDF
    This thesis presents some image processing tools for plastic surgery planning. In particular, it presents a novel method that combines local and global context in a probabilistic relaxation framework to identify cephalometric landmarks used in Maxillofacial plastic surgery. It also uses a method that utilises global and local symmetry to identify abnormalities in CT frontal images of the human body. The proposed methodologies are evaluated with the help of several clinical data supplied by collaborating plastic surgeons

    Virtuální rekonstrukce, její význam a přínos k paleobiologickému studiu fosilního člověka

    Get PDF
    Zachovalost kosterního materiálu je hlavní překážkou paleoantropologických studií. Virtuální metody se od 90. let 20. století staly důležitou součástí antropologického výzkumu, přičemž značně pomáhají překonat problémy zachovalosti, a to dvěma hlavními způsoby: zlepšují extrakci informací z fragmentárního materiálu a umožňují objektivnější rekonstrukci fragmentárních a nekompletních nálezů. Tato práce se zaměřila na virtuální rekonstrukci dvou fosilních nálezů: lebky moderního člověka Zlatý kůň (ZK; Česká republika) ze svrchního paleolitu a neandertálské pánve Regourdou 1 (R1) z Francie. Rekonstrukce lebky ZK nám umožnila revidovat pohlavní diagnózu a analyzovat její morfologickou afinitu. Na základě sekundární pohlavní diagnózy byl jedinec ZK s vysokou pravděpodobností žena a lebka vykazuje afinitu k rané svrchně paleolitické populaci. Pánev R1 vykazuje značnou asymetrii, která byla nejprve analyzována na křížové kosti v porovnání se zdravými moderními lidmi a neandertálci. Asymetrie výrazně překračuje variabilitu pozorovanou v současné populaci a mohla souviset s asymetrickým přenosem zátěže. Výrazná asymetrie byla proto zohledněna při následné rekonstrukci pánve, která nám umožnila posoudit pohlaví jedince a analyzovat transverzální rozměry pánevního kanálu a orientaci křížové kosti. Na základě...Preservation is a major obstacle in paleoanthropological studies. Since 1990s virtual methods have become an important part of anthropological research helping to overcome preservation problems in two principle ways: they improve extraction of information from a fragmentary material, and they permit a more objective reconstruction of fragmentary and incomplete remains. This thesis has focused on the virtual reconstruction of two fossil specimens: the modern human cranium from the Upper Paleolithic site of Zlatý kůň (ZK; Czech Republic) and the Neandertal Regourdou 1 (R1) pelvis (France). The reconstruction of the ZK cranium allowed us to revise sex attribution and analyze morphological affinity. Based on the secondary sex diagnosis, the ZK individual was most probably a female and exhibits a great affinity to Early Upper Paleolithic population. The R1 pelvis shows considerable asymmetry that was first analyzed on the sacrum in comparison with healthy modern humans and Neandertals. The asymmetry exceeds normal variation observed in the extant population and could have related to asymmetrical load dissipation. Therefore, the asymmetry was considered in the subsequent preliminary pelvic reconstruction which allowed us to assess sex of the individual and to analyze transverse dimensions of the pelvic...Katedra antropologie a genetiky člověkaDepartment of Anthropology and Human GeneticsPřírodovědecká fakultaFaculty of Scienc

    Aerospace Medicine and Biology: A continuing supplement 180, May 1978

    Get PDF
    This special bibliography lists 201 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1978

    Mechanical response of the porcine cervical spine to acute and repetitive anterior-posterior shear

    Get PDF
    Approximately 80% of the population will experience low-back pain within their lifetime. Significant research efforts have focused on compressive loading as an injury mechanism that could lead to low-back pain and injury. However, the influence of shear loading, and its relationship to vertebral tissue tolerances as well as modulating factors for these tolerances have not been studied as extensively. The primary objective of this thesis was to produce a series of investigations that begin to determine the roles of different modulating factors such as posture, compression, bone density, bone morphology, and repetitive load magnitude on measured vertebral joint shear failure tolerances. The thesis comprises four independent studies using in vitro mechanical testing, imaging modalities, and finite element modeling. Each of the in vitro studies within this thesis used a validated porcine cervical model as a surrogate for the human lumbar spine. The first study employed in vitro mechanical testing to investigate the combined roles of flexion/extension postural deviation and compressive load on the measured ultimate shear failure tolerances. Peripheral quantitative computed tomography scans of the pars interarticularis and measurements of vertebral bone morphology were used in the second investigation along with in vitro mechanical testing to identify the morphological characteristics that can be used to predict ultimate shear failure tolerances. The influence of sub-maximal shear load magnitude on the cumulative shear load and number of loading cycles sustained prior to failure were investigated with in vitro mechanical testing in the third study. Finally, a finite element model of the porcine C3-C4 functional spinal unit was used to investigate the plausibility of hypotheses, developed from previous research and the findings of the first investigation for this thesis, surrounding alterations in measured ultimate shear failure tolerances as a function of changes in facet interaction. Results from the first investigation showed that there was no statistically significant interaction between postural deviation and compressive force on ultimate shear failure tolerance. However, ultimate shear failure tolerance was reduced (compared to neutral) by 13.2% with flexed postures, and increased (compared to neutral) by 12.8% with extended postures. Each 15% increment (up to a maximum of 60% of predicted compressive failure tolerance) in compressive force was met with an average 11.1% increase in ultimate shear failure tolerance. It was hypothesized that alterations in flexion/extension posture and/or compressive force altered the location for the force centroid of facet contact. These changes in the location of facet contact were hypothesized to produce subsequent changes in the bending moment at the pars interarticularis that altered the measured ultimate shear failure tolerance. The three leading factors for calculating of measured ultimate shear failure tolerance were the pars interarticularis length for the cranial vertebra, the average facet angle measured in the transverse plane, and cortical bone area through the pars interarticularis. A bi-variate linear regression model that used the cranial vertebra’s pars interarticularis length and average facet angle as inputs was developed to nondestructively calculate ultimate shear failure tolerances of the porcine cervical spine. Longer pars interarticularis lengths and facets oriented closer to the sagittal plane were associated with higher measured ultimate shear failure tolerances. Fractures observed in this investigation were similar to those reported for studies performed with human specimens and also similar to reported spondylolitic fractures associated with shear loading in humans. This provided additional evidence that the porcine cervical spine is a suitable surrogate in vitro model for studying human lumbar spine mechanics. Altered sub-maximal shear load magnitude create a non-linear decrease in both the number of cycles and the cumulative shear load sustained prior to failure. These findings suggested that estimates of cumulative shear load should assign greater importance to higher instantaneous shear loads. This was due to an increased injury potential at higher instantaneous shear loads. Cumulative load sustained prior to failure was used to develop a tissue-based weighting factor equation that would apply nonlinearly increased weight to higher shear load magnitudes in estimates of cumulative shear load. A finite element model of the porcine C3-C4 functional spinal unit was created, and simulations were performed using similar boundary conditions as the comparable in vitro tests, to assess the plausibility of the moment arm hypothesis offered within the first investigation of this thesis. Moment arm length between the force centroid of facet contact and the location of peak stress within the pars interarticularis was increased for flexed postures and decreased for extended postures. Alterations in moment arm length were larger for postural deviation than compressive force, suggesting a secondary mechanism to explain the observed increase in shear failure tolerance with higher compressive loads from the first investigation. One such possibility was the increase in the number of contacting nodes with higher compressive forces. Alterations in moment arm length were able to explain 50% of the variance in measured ultimate shear failure tolerances from the first study. Thus, the finite element model was successful in demonstrating the plausibility of moment arm length between the force centroid of facet contact and the pars interarticularis as a modulator of measured ultimate shear failure tolerance. This thesis has developed the basis for understanding how failure of the vertebral joint exposed to shear loading can be modulated. In particular, this thesis has developed novel equations to predict the ultimate shear failure tolerance measured during in vitro testing, and to determine appropriate weighting factors for sub-maximal shear forces in calculations of cumulative shear load. Evidence presented within this thesis also provides support for the long-standing moment arm hypothesis for modulation of shear injury potential

    DYNAMIC MEASUREMENT OF THREE-DIMENSIONAL MOTION FROM SINGLE-PERSPECTIVE TWO-DIMENSIONAL RADIOGRAPHIC PROJECTIONS

    Get PDF
    The digital evolution of the x-ray imaging modality has spurred the development of numerous clinical and research tools. This work focuses on the design, development, and validation of dynamic radiographic imaging and registration techniques to address two distinct medical applications: tracking during image-guided interventions, and the measurement of musculoskeletal joint kinematics. Fluoroscopy is widely employed to provide intra-procedural image-guidance. However, its planar images provide limited information about the location of surgical tools and targets in three-dimensional space. To address this limitation, registration techniques, which extract three-dimensional tracking and image-guidance information from planar images, were developed and validated in vitro. The ability to accurately measure joint kinematics in vivo is an important tool in studying both normal joint function and pathologies associated with injury and disease, however it still remains a clinical challenge. A technique to measure joint kinematics from single-perspective x-ray projections was developed and validated in vitro, using clinically available radiography equipmen

    Texture analysis of the radiographic trabecular bone pattern in osteoporosis

    Get PDF
    Texture is an image property which is difficult to grasp. It can be described as a "homogeneous visual pattern"l. but there exists no formal definition of texture. Intuitively people can discriminate between different textures. referring to visual clues like coarseness, orientation. periodicity, and regularity. Using such concepts, several authors have tried to quantify these aspects of texture'. However. texture encompasses more than these more or less random aspects to which the human eye is sensitive. Therefore, the majority of texture analysis algorithms is based on an image model. in which certain characteristics of the image texture are condensed. Using this image model, texture features can be derived, most of which cannot be related to visual image features. Texture analysis methods are able, in contrast to a human observer, to quantIfy textures objectively. Therefore. texture features can be used for the purpose of characterization, discrimination, and segmentation of textures in. for example, aerial and satellite imagery. Most texture analysis methods have been developed and tested on textures from the collection of texture images in Brodatz' before putting them mto use in a more realistic environment. Since the early seventies, texture analysis methods have also been applied In medical images. For example, Sulton et a!. tried to categorize different stages of pulmonary disease in radiographs4 Since then, the field of application of texture analysis methods in radiology has expanded from chest radiographs to mammograms and bone radiographs. The goal of our study is twofold: in the first place to assess the suitability of different texture analysis methods for usc in radiographs, secondly to select or develop texture features which are able to quantify the changes in the radiographic trabecular pattern occurring in osteoporosis. Osteoporosis is defined as "a disease characterized by low bone mass and microarchitectural changes of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk." (WHO, 1994)
    corecore