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At least 379 records · Page 21Linked to original sources

PubMed1983

Gonadotropin secretion and testicular function in golden hamsters exposed to skeleton photoperiods with ultrashort light pulses.

Both sexually mature and sexually regressed male golden hamsters were transferred to asymmetric skeleton photoperiods with night interruptions of varying duration, the short pulses occurring 14 h after "dawn." Testicular function and accompanying changes in follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone and spermatogenesis were observed. Sexually regressed animals exposed to a night-break of 6 seconds (sec) or longer exhibited maximal testicular development with a rapid rise in FSH secretion followed by a slower, more variable rise in LH. Full testicular size was achieved after 8 weeks. Night-breaks of 250 milliseconds (msec) or 1 sec induced testicular development and spermatogenesis but at a slower rate: levels of FSH and LH were still rising at the end of the experiment. Complete testicular maintenance was achieved by night-breaks of 1 sec or longer. Partial testicular regression was observed with a night-break of 250 msec. Night-breaks (60 sec) given less frequently than daily also stimulated testicular function and a night-break every 7 days increased FSH and LH secretion in sexually regressed hamsters, causing testicular development at a submaximal rate. Night-breaks given more frequently induced rapid testicular growth. Almost complete testicular maintenance of sexually mature hamsters was achieved with a 60-sec night-break at weekly intervals. Symmetric skeleton photoperiods also triggered testicular development in sexually regressed hamsters, with two 1-sec light pulses (14 h apart) being almost as effective as a normal long day. No difference in reproductive function was observed between animals on long days (14L:10D) and those exposed to maximally stimulatory skeleton photoperiods.

Animals↗

PubMed1991

Long-term effects of rigid fixation on the growing craniomaxillofacial skeleton.

Fixation of craniomaxillofacial bones with plates and screws is becoming an increasingly popular method of managing patients with maxillofacial fractures, congenital anomalies, and skeletal defects after tumor extirpation. The effects of rigid fixation on growth, however, are not well defined and remain controversial. This experimental work was designed to evaluate the effects of rigid fixation on the growing craniomaxillofacial skeleton. Eight 2-month-old beagle dogs were divided into two groups. Cephalometric analysis and computed tomography were obtained preoperatively to establish a baseline of the craniomaxillofacial skeleton. Rigid fixation using plates and screws was applied across the intact coronal and nasofrontal sutures. The contralateral side served as the control. The periosteum was elevated over the contralateral suture and replaced without any surgical intervention. The animals were killed one year after application of rigid fixation, when they had achieved full and mature skeletal growth. The skulls were evaluated both grossly and cephalometrically. There was bony growth over some of the plates, as well as sclerosis of the plated suture lines. Cephalometric analysis demonstrated consistent asymmetry between the plated and nonplated sides, with deviation of the midline toward the plated side in all of the animals. Although further studies are necessary to clarify this issue fully, we conclude from our study that rigid fixation during skeletal development can potentially alter the growth patterns of the craniomaxillofacial skeleton and should be used with caution.

Animals↗

PubMed1995

Effect of rigid microfixation on the craniomaxillofacial skeleton.

Rigid microfixation has enhanced the immediate results in pediatric craniomaxillofacial surgery. The effects of rigid fixation on the development of the craniofacial skeleton, however, remain uncertain. The long-term effects of rigid microfixation on the growing craniofacial skeleton in the rabbit model were evaluated in this study. Bifrontal craniectomies were preformed in 9-day-old rabbits. The frontal bones were replaced orthotopically and fixed both anteriorly and posteriorly with either wire osteosynthesis or titanium microplates and screws. The animals were allowed to grow to craniofacial maturity, and craniofacial development was evaluated with both cephalometric and craniometric analyses. All data were statistically analyzed through analysis of variance. Regional adverse growth effects on the craniofacial skeleton with the use of both wire and rigid fixation were observed. The adverse effects were greatest with the use of rigid fixation.

Analysis of Variance↗

PubMed2004

Immunolocalization of androgen receptor in the developing craniofacial skeleton.

Male predominance in metopic and sagittal craniosynostosis and in nonsynostotic plagiocephaly suggests a role for circulating androgens in early craniofacial development. Androgens have been documented to play an important role in postnatal skeletal growth, and the androgen receptor has been recently demonstrated in human and rat osteoblast-like cell lines and in human long bones. The purpose of this study was to describe the expression of androgen receptor in the fetal craniofacial skeleton. The heads of E18 fetal CD-1 male and female mice were fixed in 10% formalin, decalcified, and embedded in paraffin. Four- to 6-mum coronal and sagittal sections were stained with a monoclonal antibody specific to androgen receptor, which was detected by an avidinbiotin conjugate and peroxidase system. The sections were then examined for androgen receptor expression patterns. Strong androgen receptor immunoreactivity was observed in the dura mater of developing fetuses. Androgen receptor expression was also noted in cells lining the osteogenic fronts and in calvarial osteoblasts. Similar androgen receptor expression patterns were found in male and female mice. Androgen receptor is abundantly expressed in fetal dura mater and calvarial bone. This study confirms the presence of androgen receptor in the murine fetal craniofacial skeleton, suggesting a potential role for the anabolic effects of androgens in the developing craniofacial skeleton.

Androgens↗

PubMed1999

Cold-hot mismatch between Tc-99m HMPAO-labeled leukocytes and Tc-99m ciprofloxacin in axial skeleton infections: a report of three cases.

Radiolabeled leukocyte scintigraphy is a well-established technique for the diagnosis of inflammation and infection with a typical presentation of a hot spot within the abnormal areas. However, in some cases of osteomyelitis of the axial skeleton, a cold defect pattern has been described. Tc-99m ciprofloxacin is a new agent claimed to be specific for imaging sites containing viable bacteria. In this report, we present three cases of proved bacterial infection of the axial skeleton with a mismatch pattern between Tc-99m ciprofloxin and tagged leukocytes. Although Tc-99m-labeled leukocyte scanning showed a cold defect, probably caused by bone marrow replacement, the Tc-99m ciprofloxacin consecutively revealed a hot spot at the site of infection. These data suggest that Tc-99m ciprofloxacin should be a better agent than radiolabeled leukocytes for detecting osteomyelitis of the axial skeleton.

Adult↗

PubMed1988

Partitioning of 238Pu, 239Pu and 241Am in skeleton and liver of U.S. Transuranium Registry autopsy cases.

The content of 238Pu, 239Pu and 241Am in the liver and skeleton was estimated from radiochemical analysis of human liver and bone samples obtained at autopsy from former actinide workers whose occupational histories were suggestive of chronic inhalation exposures, with minor skin contamination and wounds documented in a few individuals. For times estimated to be several years to a few decades post intake, 75.8 +/- 15.3% of the total 241Am in the skeleton and liver was found in the skeleton (25 cases) as compared with 63.4 +/- 24.1% for 238Pu (36 cases) and 53.2 +/- 18.2% for 239Pu (43 cases). These differences are significant at the 95% confidence level. Of these cases, 34 included data on both 238Pu and 239Pu and were divided into high and low activity subgroups. The difference in the fractionation of the two Pu isotopes was apparent only in the low activity subgroup, suggesting that the difference observed between the Pu isotopes may be an artifact of the data. The different partitioning of these three nuclides suggests that the ALIs for 238Pu and 241Am may be high by about 25-50% if only the dose to bone is considered and may be high by 12-13%, based on the weighted committed dose equivalent in target organs or tissues.

Americium↗

PubMed1989

Kinetic model of the distribution of 239Pu in the beagle skeleton.

A model is presented to analyze the retention of Pu in the major deposition organs of the beagle dog and predict the dynamic behavior of skeletal labels. The kinetic part describing the gross organ distribution was represented by a compartment model. A fit to empirical retention equations of liver and skeleton yielded skeletal clearance corresponding to turnover rates of 93.8% y-1 and 3.8% y-1 in trabecular and cortical bone, respectively. Initially about 9% of skeletal Pu is deposited in cortical bone. The blood flow changes over a period of 3000 d from an initial 0.15% of the injected dose per day to 0.05% d-1 at the end of this period. More than 100% of the injected Pu is recirculated back to the skeleton during this interval. The calculation of the label dynamics showed that nearly complete volumization of Pu was only possible assuming a very high affinity ratio of forming vs. resting surfaces and high bone turnover rates. There was a steady increase in the fractional activity of surface and secondary diffuse labels in cortical bone whereas in trabecular bone these labels showed maximum activity at about 2 y after injection. The Pu concentration on pre-existing trabecular bone surfaces that were not remodeled within 3000 d post injection increased by a factor of 3.6. The model may be applied to single bones or the skeleton as a whole. The flow of Pu in the blood can be derived in human cases where urinary excretion rates are available. With the blood flow known, the model enables one to simulate the dynamic behavior of skeletal labels even for very general conditions of human contamination, including inhalation.

Animals↗

PubMed1991

Radionuclide distribution dynamics in skeletons of beagles fed 90Sr: correlation with injected 226Ra and 239Pu.

Data for the bone-by-bone redistribution of 90Sr in the beagle skeleton are reported for a period of 4000 d following a midgestation-to-540-d-exposure by ingestion. The partitioned clearance model (PCM) that was originally developed to describe bone-by-bone radionuclide redistribution of 226Ra after eight semimonthly injections at ages 435-535 d has been fitted to the 90Sr data. The parameter estimates for the PCM that describe the distribution and clearance of 226Ra after deposition on surfaces following injection and analogous parameter estimates for 90Sr after uniform deposition in the skeleton as a function of Ca mass are given. Fractional compact bone masses per bone group (mi,COM) are also predicted by the model and compared to measured values; a high degree of correlation (r = 0.84) is found. Bone groups for which the agreement between the model and experimental values of mi,COM was poor had tissue-to-calcium weight ratios about 1.5 times those for bones that agreed well. Metabolically defined "surface" in PCM is initial activity fraction per Ca fraction in a given skeletal component for intravenously injected alkaline earth (Sae) radionuclides; comparisons are made to similarly defined "surface" (Sact) values from 239Pu injection studies. The patterns of Sae and Sact distribution throughout the skeleton are similar.

Administration, Oral↗

PubMedDate not supplied

Computing the centerline of a colon: a robust and efficient method based on 3D skeletons.

We present a robust and efficient algorithm for calculating the centerline of a computer-generated colon model created from helical CT image data. The centerline is an essential aid for navigating through complex anatomy such as the colon. Our algorithm involves three steps. In the first step, we generate a 3D skeleton of the binary colon volume using a fast topological thinning algorithm. In the second step, we employ a graph search algorithm to remove extra loops and branches. These loops and branches are caused by holes in the object that are artifacts produced during image segmentation. In the final step, we compute a smooth representation of the centerline by approximating the skeleton with cubic B-splines. This final step is necessary because the skeleton contains many abrupt changes in direction due to the discrete nature of image data. The user supplies two endpoints for the centerline; otherwise, the algorithm is fully automated. Experimental results demonstrate that the algorithm is not only robust but also efficient.

Algorithms↗

PubMed1998

Tracheal reconstruction using a free jejunal flap with cartilage skeleton: experimental study.

An experimental study was undertaken to evaluate the behavior of an autologous microvascularjejunal transfer with a cartilage skeleton for major tracheal reconstruction in the goat model. A 15-cm segment of the cervical trachea was replaced by a free microvascularjejunal transfer with costal cartilage skeleton as a single-stage procedure. The flap was stented for 4 weeks with an endotracheal T-tube. Bronchoscopy was done to the survivors at 6 months. The perioperative mortality rate was 40 percent, with 30 percent of the animals surviving the 30-week follow-up period. Bronchoscopy showed a smooth and appropriate lumen. Histology showed hyaline cartilage integrated within the jejunal wall and normal jejunal mucosa. The reconstruction of a large circumferential tracheal defect with a free jejunal transfer with cartilaginous skeleton remained stable, without undue mucous secretion, and the surviving animals remained asymptomatic for the follow-up.

Animals↗

PubMed1988

Preoperative indium-labeled white blood cell scintigraphy in suspected osteomyelitis of the axial skeleton.

The cases of six patients with suspected osteomyelitis of the axial skeleton who underwent preoperative indium-labeled white blood cell scintigraphy (In-WBC) were reviewed retrospectively. Five of these patients had undergone previous spinal surgery, and all six patients complained of back pain. Four of these six patients were proven to have osteomyelitis by culture and histopathology. The sensitivity, specificity, and accuracy of In-WBC scintigraphy in detecting osteomyelitis of the axial skeleton was 25%, 50%, and 33%, respectively. Our preliminary experience in six patients with suspected osteomyelitis of the axial skeleton suggests that In-WBC scintigraphy is neither sensitive nor specific in predicting infection.

Humans↗

PubMed2005

Repair of the immature and mature craniofacial skeleton with a carbonated calcium phosphate cement: assessment of biocompatibility, osteoconductivity, and remodeling capacity.

BACKGROUND: The apatite compounds used most commonly in craniofacial reconstruction are highly crystalline and biologically inert ceramics. Because their capacity to be replaced by native bone is limited, they have found little application in repair of the growing craniofacial skeleton. Carbonated calcium phosphate cements more closely resemble the mineral phase of bone, thereby offering enhanced bioresorption and osteoconductivity, but their fate in the immature and mature craniofacial skeleton has not been investigated. METHODS: The authors hypothesized that the capacity for cell-mediated remodeling of carbonated calcium phosphate cements is based on (1) their crystallographic and compositional similarity to the mineral phase of bone and (2) the osteogenic capacity of the host. Four noncritical-sized calvarial defects were created in six 3-week-old and six 16-week-old Yorkshire pigs. The defects were repaired with autologous bone, sintered carbonated calcium phosphate cement disks with a higher crystal order, or carbonated calcium phosphate cement (Norian CRS; Synthes Maxillofacial, West Chester, Pa.). The fourth defect was left empty as a control. Specimens were harvested at 30 and 90 days postoperatively. RESULTS: Empty defects healed with dense fibroconnective tissue in all groups. Autologous bone grafts underwent complete remodeling and replacement with woven bone at both time points. Sintered carbonated calcium phosphate disks demonstrated no bony ingrowth or remodeling. In immature animals, carbonated calcium phosphate cement implants were progressively replaced with woven bone through osteoclast-mediated resorption and osteoblast-mediated bone formation. Only minimal remodeling of the carbonated calcium phosphate cement implants was observed in skeletally mature animals. CONCLUSIONS: The results of these experiments suggest that the extent of remodeling of carbonated calcium phosphate cement is dependent on both the composition of the implant itself and the osteogenic capacity of the host and that carbonated calcium phosphate cement may be used successfully for inlay applications in the immature craniofacial skeleton.

Animals↗

PubMed1989

Automated site-directed drug design: the concept of spacer skeletons for primary structure generation.

This paper examines the problem of automated structure generation at specified binding sites. The objective is to obtain molecular graphs that span the binding site and incorporate predicted ligand points at their vertices. Three approaches are considered: brute-force techniques, subgraph addition and spacer skeletons. Spacer skeletons are assemblies of molecular subgraphs and are used to reduce the combinatorial problems of structure generation to a practicable level for future analysis. This description is restricted to structure generation in two dimensions. Assemblies of rings are examined for planarity by searching the Cambridge Structural Database. Appropriate spacer skeletons may then be fitted to arrays of site points.

Computer Simulation↗

PubMed2006

Skeleton and fractal scaling in complex networks.

We find that the fractal scaling in a class of scale-free networks originates from the underlying tree structure called a skeleton, a special type of spanning tree based on the edge betweenness centrality. The fractal skeleton has the property of the critical branching tree. The original fractal networks are viewed as a fractal skeleton dressed with local shortcuts. An in silico model with both the fractal scaling and the scale-invariance properties is also constructed. The framework of fractal networks is useful in understanding the utility and the redundancy in networked systems.

Escherichia coli↗

PubMed1998

A comparison of two algorithms for electron-density map improvement by introduction of atomicity: skeletonization, and map sorting followed by refinement.

A comparison has been made of two methods for electron-density map improvement by the introduction of atomicity, namely the iterative skeletonization procedure of the CCP4 program DM [Cowtan & Main (1993). Acta Cryst. D49, 148-157] and the pseudo-atom introduction followed by the refinement protocol in the program suite DEMON/ANGEL [Vellieux, Hunt, Roy & Read (1995). J. Appl. Cryst. 28, 347-351]. Tests carried out using the 3.0 A resolution electron density resulting from iterative 12-fold non-crystallographic symmetry averaging and solvent flattening for the Pseudomonas aeruginosa ornithine transcarbamoylase [Villeret, Tricot, Stalon & Dideberg (1995). Proc. Natl Acad. Sci. USA, 92, 10762-10766] indicate that pseudo-atom introduction followed by refinement performs much better than iterative skeletonization: with the former method, a phase improvement of 15.3 degrees is obtained with respect to the initial density modification phases. With iterative skeletonization a phase degradation of 0.4 degrees is obtained. Consequently, the electron-density maps obtained using pseudo-atom phases or pseudo-atom phases combined with density-modification phases are much easier to interpret. These tests also show that for ornithine transcarbamoylase, where 12-fold non-crystallographic symmetry is present in the P1 crystals, G-function coupling leads to the simultaneous decrease of the conventional R factor and of the free R factor, a phenomenon which is not observed when non-crystallographic symmetry is absent from the crystal. The method is far less effective in such a case, and the results obtained suggest that the map sorting followed by refinement stage should be by-passed to obtain interpretable electron-density distributions.

Algorithms↗

PubMed2000

Interpolation of 3-D binary images based on morphological skeletonization.

In this paper, the morphological skeleton interpolation (MSI) algorithm is presented. It is an efficient, shape-based interpolation method used for interpolating slices in a three-dimensional (3-D) binary object. It is based on morphological skeletonization, which is used for two-dimensional (2-D) slice representation. The proposed morphological skeleton matching process provides translation, rotation, and scaling information at the same time. The interpolated slices preserve the shape of the original object slices, when the slices have similar shapes. It can also modify the shape of an object when the successive slices do not have similar shapes. Applications on artificial and real data are also presented.

Algorithms↗

PubMed2006

Finite element modeling of the head skeleton with a new local quantitative assessment approach.

The present study was undertaken to build a finite element model of the head skeleton and to perform a new assessment approach in order to validate it. The application fields for such an improved model are injury risk prediction as well as surgical planning. The geometrical reconstruction was performed using computed tomography scans and a total of 4680 shell elements were meshed on the median surface of the head skeleton with the particular characteristic of adapted mesh density and real element thickness. The assessment protocol of the finite element model was achieved using a quasi-static experimental compression test performed on the zygomatic bone area of a defleshed isolated head. Mechanical behavior of the finite element model was compared to the real one and the assessment approach was divided into two steps. First, the mechanical properties of the anatomical structure were identified using the simulation and then the simulated displacement field was compared to local displacement measurement performed during test using a digital correlation method. The assessment showed that the head skeleton model behaved qualitatively like the real structure. Quantitatively, the local relative error varied from 8% up to 70%.

Aged, 80 and over↗

PubMed2006

Sex-difference in the ossification rate of the appendicular skeleton in Capra pyrenaica Schinz, 1838, and its utility in the sex identification of long bones.

The main goal of our work is to quantify differences in the rate of ossification in post-cranial Iberian ibex skeletons, related to sex. Another objective is to improve criteria for assessing the sex of post-cranial bones by combining the degree of ossification of the distal epiphysis and biometrical data. Forty Capra pyrenaica skeletons were examined in order to determine the degree of ossification by means of an Ossification Index. Our results evidence that sexual differences in the rate of ossification become visible at 6 months of age. On average, females complete their bone development 2 years before males do. Finally, by means of lineal classification functions which take into account both biometrical and anatomical criteria, we can achieve, in average, a 95.5% of correct sex discrimination within a sample consisting of ibex metacarpi and metatarsi from individuals aging from <1 to 12 years. Therefore, we conclude that the rhythm of ossification in the post-cranial skeleton of C. pyrenaica may be used as a criterion for assessing the sex of skeletal remains and could be applicable to other dimorphic ungulates. Nevertheless, the results obtained for specimens belonging to a particular population may have limited application to other populations with different medium sizes and living at particular densities within habitats with variable quality.

Animals↗