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At least 217 records · Page 12Linked to original sources
PubMed2003

The dual-bootstrap iterative closest point algorithm with application to retinal image registration.

Motivated by the problem of retinal image registration, this paper introduces and analyzes a new registration algorithm called Dual-Bootstrap Iterative Closest Point (Dual-Bootstrap ICP). The approach is to start from one or more initial, low-order estimates that are only accurate in small image regions, called bootstrap regions. In each bootstrap region, the algorithm iteratively: 1) refines the transformation estimate using constraints only from within the bootstrap region; 2) expands the bootstrap region; and 3) tests to see if a higher order transformation model can be used, stopping when the region expands to cover the overlap between images. Steps 1): and 3), the bootstrap steps, are governed by the covariance matrix of the estimated transformation. Estimation refinement [Step 2)] uses a novel robust version of the ICP algorithm. In registering retinal image pairs, Dual-Bootstrap ICP is initialized by automatically matching individual vascular landmarks, and it aligns images based on detected blood vessel centerlines. The resulting quadratic transformations are accurate to less than a pixel. On tests involving approximately 6000 image pairs, it successfully registered 99.5% of the pairs containing at least one common landmark, and 100% of the pairs containing at least one common landmark and at least 35% image overlap.

Algorithms↗
PubMed2000

A mouse fibroblast cell model to study human papillomavirus-associated tumorigenesis.

Cervical cancer represents the second most common cancer in women worldwide. About 90% of cervical cancer contain high-risk human papillomavirus (HPV) DNA, most often HPV type 16. Animal models and mostly laboratory mice are excellent for carrying out diverse immunological studies. We transfected a fibroblast cell line, 3T3-A31, with human papillomavirus type 16 genome to develop an in vivo/in vitro malignant transformant model. Isolated clones inoculated to immunocompetent mice displayed a tumorigenic phenotype. Small clusters of metastatic cells were found in the liver of animal 45 days after receiving the inoculum. Integrated viral DNA and expression of E7 viral oncogene from the high-risk HPV-16 were demonstrated both in transfectans and tumor-derived cells. The observed high-grade neovascularization was correlated with the upregulation of vascular endothelial growth factor (VEGF) mRNA on HPV-16 transformed fibroblast cells. These observations emphasize the association between papillomavirus expression and progression to malignancy.

Animals↗
PubMedDate not supplied

Genetic parameters for litter size in sheep: natural versus hormone-induced oestrus.

The litter size in Suffolk and Texel-sheep was analysed using REML and Bayesian methods. Litters born after hormonal induced oestrus and after natural oestrus were treated as different traits in order to estimate the genetic correlation between the traits. Explanatory variables were the age of the ewe at lambing, period of lambing, a year*flock-effect, a permanent environmental effect associated with the ewe, and the additive genetic effect. The heritability estimates for litter size ranged from 0.06 to 0.13 using REML in bi-variate linear models. Transformation of the estimates to the underlying scale resulted in heritability estimates from 0.12 to 0.17. Posterior means of the heritability of litter size in the Bayesian approach with bi-variate threshold models varied from 0.05 to 0.18. REML estimates of the genetic correlations between the two types of litter size ranged from 0.57 to 0.64 in the Suffolk and from 0.75 to 0.81 in the Texel. The posterior means of the genetic correlation (Bayesian analysis) were 0.40 and 0.44 for the Suffolk and 0.56 and 0.75 for the Texel in the sire and animal model respectively. A bivariate threshold model seems appropriate for the genetic evaluation of prolificacy in the breeds concerned.

Animals↗
PubMed2002

Radiometry in line-shape modeling of Fourier-transform spectrometers.

A radiometric model of the instrument line shape (ILS) of Fourier-transform spectrometers is presented. We show first that common line-shape models are based on distribution of the radiant intensity in the interferometer. The complete steps between the source and the ILS are exposed as the core of the model. Relationships between the ILS, the spectrum as measured by the instrument, and the spectrum as emitted by the scene are demonstrated from the ILS model. Then the formal radiometric modeling of the ILS is derived, including the contribution of the aperture of the optical system. The particular case of a centered circular aperture with a uniform Lambertian radiance in the field of view is discussed. Conditions are deduced to ensure that the only spectral variation of the ILS is a scaling with wave number, as is usually assumed in current line-shape models. The ILS dependence on the scene is also discussed, and the effect of taking into account the radiometry on the ILS is estimated for the case of an ideal thin lens used as a collimator.

Journal Article↗
PubMed1987

Enhancement of transformation and continuous inhibition of intercellular communication by 1-oleoyl-2-acetyl glycerol in BALB/c 3T3 cells.

Tumour-promoting phorbol esters and diacylglycerols have a variety of biochemical and biological effects in common in a number of cell culture systems; thus, it has been suggested that diacylglycerols are endogenous functional analogues of phorbol esters. In order to examine more directly the possible relevance of these functional analogues in tumour promotion, we have studied the promoting effect of 1-oleoyl-2-acetyl glycerol (OAG) in the two-stage transformation model with BALB/c 3T3 cells, which is designed to simulate in vivo two-stage carcinogenesis. When BALB/c 3T3 cells were treated once with a low dose of 3-methylcholanthrene (MCA), almost no increase in cell transformation occurred. However, repeated application of OAG after MCA treatment enhanced cell transformation. OAG enhanced transformation to a lesser extent than a potent promoter of in vivo and in vitro carcinogenesis, phorbol-12,13-didecanoate. OAG also continuously inhibited junctional intercellular communication when BALB/c 3T3 cells were treated daily at confluence. These results indicate that diacylglycerols mimic phorbol esters in promoting cell transformation and that the enhancement may be related to an inhibitory effect on intercellular communication.

Animals↗
PubMed1999

Generalized proportional hazards model based on modified partial likelihood.

The proportional hazards (Cox) model is generalized by assuming that at any moment the ratio of hazard rates is depending not only on values of covariates but also on resources used until this moment. Relations with generalized multiplicative, frailty and linear transformation models are considered. A modified partial likelihood function is proposed, and properties of the estimators are investigated.

Humans↗
PubMedDate not supplied

Case management: a formula for resource conservation.

Case management as a concept of efficiency and effectiveness has demonstrated its applicability in acute care. This article addresses one model of case management that integrates the traditional structure of independently functioning, nonrevenue-producing activities of quality, risk, and utilization management under the comprehensive umbrella of quality resource management. The model transformed existing full-time equivalent services at an acute care hospital in Florida into value-added services on behalf of patients, physicians, the hospital, and payers and presented a practical approach to organizing a case management program. Issues in the transformation process also are addressed.

Case Management↗
PubMed2001

Thermo-debonding mechanisms in dentin bonding systems using finite element analysis.

The finite element method (FEM) has been extensively used in evaluating the interfacial status of biomaterials. We used FEM to explore the microscopic debonding mechanism of the dentin/hybrid layer/resin adhesive interface. The stress status of the local material was used as an index to judge whether the adhesive interface would develop a debonding mechanism. To generate the local stress concentration, the thermal boundary condition was applied to the model which has the phenomenon of the coefficient of thermal expansion (CTE) mismatch. The thermal boundary condition was used to emulute a previous study conducted with a laser thermoacoustic technique (LTAT). The materials, Scotchbond MP, Optibond, and Tenure bonding systems, used in the previous experiment were also tested in this study. The results show that interfacial debonding in the finite element model occurred through the hybrid layer for both the Scotchbond MP and Tenure systems, as well as within the adhesive layer itself for the Optibond system. These findings are compatible with observations by SEM obtained by LTAT. Another transformed model was created to test the "elastic cavity wall" concept. The result also confirms the importance of the elastic cavity wall concept. These compatible results between FEM and LTAT indicate that FEM can be a very useful supplement to thermoacoustic testing.

Biocompatible Materials↗
PubMed2004

Activation of antioxidant pathways in ras-mediated oncogenic transformation of human surface ovarian epithelial cells revealed by functional proteomics and mass spectrometry.

Cellular transformation is a complex process involving genetic alterations associated with multiple signaling pathways. Development of a transformation model using defined genetic elements has provided an opportunity to elucidate the role of oncogenes and tumor suppressor genes in the initiation and development of ovarian cancer. To study the cellular and molecular mechanisms of Ras-mediated oncogenic transformation of ovarian epithelial cells, we used a proteomic approach involving two-dimensional electrophoresis and mass spectrometry to profile two ovarian epithelial cell lines, one immortalized with SV40 T/t antigens and the human catalytic subunit of telomerase and the other transformed with an additional oncogenic ras(V12) allele. Of approximately 2200 observed protein spots, we have identified >30 protein targets that showed significant changes between the immortalized and transformed cell lines using peptide mass fingerprinting. Among these identified targets, one most notable group of proteins altered significantly consists of enzymes involved in cellular redox balance. Detailed analysis of these protein targets suggests that activation of Ras-signaling pathways increases the threshold of reactive oxidative species (ROS) tolerance by up-regulating the overall antioxidant capacity of cells, especially in mitochondria. This enhanced antioxidant capacity protects the transformed cells from high levels of ROS associated with the uncontrolled growth potential of tumor cells. It is conceivable that an enhanced antioxidation capability may constitute a common mechanism for tumor cells to evade apoptosis induced by oxidative stresses at high ROS levels.

Antioxidants↗
PubMed2001

Regression modeling of competing crude failure probabilities.

In a randomized trial of tamoxifen therapy for breast cancer, women can experience tumor recurrence or die from competing causes. One goal of analysis is to describe the effect of tamoxifen on the probabilities of recurrence or death from other causes. To this end, we propose a semi-parametric transformation model for the crude failure probabilities of a competing risk, conditional on covariates. The model is developed as an extension of the standard approach to survival data with independent right censoring. Estimation of the regression coefficients is achieved with a rank-based least squares criterion. Simulations show that the procedure works well with practical sample sizes. A separate estimating function is developed for the baseline parameter. Prediction of covariate-adjusted failure probabilities is considered. The methodology is motivated and illustrated with data from the tamoxifen trial.

Journal Article↗
PubMed2000

Molecular dynamics simulation of a glissile dislocation interface propagating a martensitic transformation.

The method of Parrinello and Rahman is generalized to include slip in addition to deformation of the simulation cell. Equations of motion are derived, and a microscopic expression for traction is introduced. Lagrangian constraints are imposed so that the combination of deformation and slip conform to the invariant plane shear characteristic of martensites. Simulation of a model transformation demonstrates the nucleation and propagation of a glissile dislocation interface.

Journal Article↗
PubMed2004

A model of acoustic interspeaker variability based on the concept of formant-cavity affiliation.

A method is proposed to model the interspeaker variability of formant patterns for oral vowels. It is assumed that this variability originates in the differences existing among speakers in the respective lengths of their front and back vocal-tract cavities. In order to characterize, from the spectral description of the acoustic speech signal, these vocal-tract differences between speakers, each formant is interpreted, according to the concept of formant-cavity affiliation, as a resonance of a specific vocal-tract cavity. Its frequency can thus be directly related to the corresponding cavity length, and a transformation model can be proposed from a speaker A to a speaker B on the basis of the frequency ratios of the formants corresponding to the same resonances. In order to minimize the number of sounds to be recorded for each speaker in order to carry out this speaker transformation, the frequency ratios are exactly computed only for the three extreme cardinal vowels [i, a, u] and they are approximated for the remaining vowels through an interpolation function. The method is evaluated through its capacity to transform the (F1,F2) formant patterns of eight oral vowels pronounced by five male speakers into the (F1,F2) patterns of the corresponding vowels generated by an articulatory model of the vocal tract. The resulting formant patterns are compared to those provided by normalization techniques published in the literature. The proposed method is found to be efficient, but a number of limitations are also observed and discussed. These limitations can be associated with the formant-cavity affiliation model itself or with a possible influence of speaker-specific vocal-tract geometry in the cross-sectional direction, which the model might not have taken into account.

Adult↗
PubMed1999

The deletion of transforming growth factor-beta-induced myofibroblasts depends on growth conditions and actin organization.

Myofibroblasts are important but transient mediators of normal wound contraction and are characterized phenotypically by their high levels of alpha-smooth-muscle actin (SMA). During wound maturation, these cells disappear. We have examined the mechanisms that lead to myofibroblast deletion in a fibroblast culture model. Transforming growth factor-beta (TGF-beta) was used to increase SMA content in gingival fibroblasts (three- to sixfold). After replating TGF-beta-induced cells at low density with serum, there was a fivefold decrease in SMA protein content, SMA protein synthesis, and SMA mRNA as cells proliferated. These reductions were due to reduced SMA mRNA stability. For TGF-beta-induced cells plated at high density without serum (ie, quiescent conditions), protein content was reduced by only 20% over 12 days. TGF-beta protected SMA-positive cells against apoptosis in serum-free cultures. Those cells that were protected against apoptosis exhibited well-developed stress fibers enriched in SMA. We conclude that, in quiescent myofibroblasts, SMA protein turnover is slow, and cells are long-lived. In proliferative conditions SMA protein and mRNA turn over quickly, and the myofibroblast phenotype dissipates. The reduced apoptosis of myofibroblasts in quiescent conditions is due in part to the organization of SMA into stress fibers.

Actins↗
PubMed2006

Mechanisms of pericyte recruitment in tumour angiogenesis: a new role for metalloproteinases.

Pericytes occur in tumour blood vessels and are critical for the development of a functional vascular network. Targeting tumour pericytes is a promising anti-angiogenic therapy but requires identifying the mechanisms of their recruitment in tumour and addressing whether these mechanisms can be selectively harnessed. Among the pathways involved in pericyte recruitment during embryonic development, the contribution of platelet-derived growth factor B and sphingosine 1-phosphate is confirmed in tumour angiogenesis. The effect of angiopoietin 1 depends on the tumour model. Transforming growth factor-beta1 enhances tumour vascularization and microvessel maturation. Recent reports suggest a participation of matrix metalloproteinases (MMP) in tumour pericyte recruitment that is consistent with the effect of certain MMPs in the development of microvasculature in embryonic development and in in vitro models of vascular remodelling. Here, we discuss the possibility for MMPs to contribute to pericyte recruitment at six levels: (1) direct promotion of pericyte invasion by extracellular matrix degradation; (2) stimulation of pericyte proliferation and protection against apoptosis by modification of the ECM; (3) activation of pericytes through the release of growth factor bound to the ECM; (4) transactivation of angiogenic cell surface receptor; (5) propagation of angiogenic signalling as cofactor; and (6) recruitment of bone marrow-derived stem cells.

Angiopoietin-1↗
PubMed2003

CT-MRI automatic surface-based registration schemes combining global and local optimization techniques.

Medical image registration is commonly required in order to combine the complementary information provided by different medical imaging modalities. In this paper, a new automatic registration scheme is proposed to register 3-D CT-MR head images and is currently tested on a clinical environment. The proposed scheme, after the preprocessing and the outer surface extraction of the data, is based on the use the rigid transformation method, in conjunction with a combination of global and local optimization techniques. Analytically, the paper exploits the optimization efficiency of three widely used optimization techniques, in obtaining the parameters of the rigid transformation model: the Downhill Simplex Method, the Genetic Algorithms and the Simulated Annealing. These optimization techniques are further combined by the sequential application of the Powell optimization method in order to refine the registration and increase its accuracy. A comparative study involving these optimization techniques in conjunction with the rigid transformation, and two other methods, the ICP and the manual methods, is also presented, for a sufficient number of clinical CT-MR brain images. Finally, quantitative and qualitative results are also presented to validate the performance of these automatic surface-based registration schemes, in terms of consistency and accuracy. Throughout of this study, the automatic registration scheme comprising of the rigid transformation in conjunction with the Simulated Annealing method sequentially combined with the Powell method has been performed superior regarding all the other compared registration schemes.

Algorithms↗
PubMed2004

Temporally asymmetric learning supports sequence processing in multi-winner self-organizing maps.

We examine the extent to which modified Kohonen self-organizing maps (SOMs) can learn unique representations of temporal sequences while still supporting map formation. Two biologically inspired extensions are made to traditional SOMs: selection of multiple simultaneous rather than single "winners" and the use of local intramap connections that are trained according to a temporally asymmetric Hebbian learning rule. The extended SOM is then trained with variable-length temporal sequences that are composed of phoneme feature vectors, with each sequence corresponding to the phonetic transcription of a noun. The model transforms each input sequence into a spatial representation (final activation pattern on the map). Training improves this transformation by, for example, increasing the uniqueness of the spatial representations of distinct sequences, while still retaining map formation based on input patterns. The closeness of the spatial representations of two sequences is found to correlate significantly with the sequences' similarity. The extended model presented here raises the possibility that SOMs may ultimately prove useful as visualization tools for temporal sequences and as preprocessors for sequence pattern recognition systems.

Computer Simulation↗
PubMed1998

Characterization of Wnt-1 and Wnt-2 induced growth alterations and signaling pathways in NIH3T3 fibroblasts.

Members of the Wnt family induce mouse mammary tumors and partially transform mammary epithelial cells in culture. However, their mechanism of transformation remains to be elucidated. In NIH3T3 mouse embryo fibroblasts, a standard transformation model, Wnt-1 and Wnt-2 were shown to induce altered properties including increased saturation density and growth in soft agar. Such cells also exhibited increased cell-cell adhesiveness. However, unlike oncogenes such as PDGFB or ras, Wnt-1 and -2 failed to induce detectable transformed foci following transfection, and stable NIH3T3 transfectants lacked tumor forming capacity. Wnt-1 and -2 transfectants exhibited increased uncomplexed, cytosolic beta-catenin, which was not observed with PDGFB, ras or erbB2 transfectants. In transient transfection, Wnt-1 and -2 induced a rapid increase in cytosolic beta-catenin but no detectable increase in the phosphorylated activated forms of MAP kinase. In contrast, ras was a potent activator of MAP kinase but had no effect on free beta-catenin levels. These findings establish that both Wnt signaling and pattern of growth alterations differ from those of oncogenes which activate proliferative signaling pathways in NIH3T3 cells.

3T3 Cells↗
PubMed1988

Autocrine production of pre-B-cell stimulating activity by a variety of transformed murine pre-B-cell lines.

Current evidence suggests that the proliferation and differentiation of normal pre-B-cells may be regulated by interactions with mesenchymally derived stromal cells. The nature of these cell-cell interactions has not yet been fully elucidated, but the involvement of pre-B-cell stimulating factors produced by various mesenchymal cell lines has recently been demonstrated in the murine system. In this model, transformed pre-B-cells differ from their normal counterparts in their acquisition of autonomous growth potential, as seen by an ability to be maintained in vitro in the absence of mesenchymal cell feeders. To test the hypothesis that autonomy might be associated with autocrine growth factor production, we tested the ability of a spontaneous pre-B-cell transformant (H9 cells) and two independently derived Abelson murine leukemia virus transformed pre-B-cell lines to produce pre-B-cell stimulating factors. All three lines released activities that stimulated the proliferation of themselves or H9 cells when cultured at low cell densities. One of the three transformed pre-B-cell lines could also substitute for mesenchymal feeders to stimulate normal pre-B-cells. Time course studies of an evolving Abelson murine leukemia virus transformant showed that the production of an autocrine pre-B-cell growth factor increased concomitantly with the acquisition of autonomous growth potential suggesting a relationship between these two phenotypic changes. Preliminary characterization of the growth factor responsiveness of H9 cells and the nature of the autostimulatory activity produced by this line suggested its nonidentity with any known hemopoietic growth factor. Activation of autocrine growth factor production appears to be a common event in the evolution of malignant pre-B-cells arising through different oncogenic mechanisms and may therefore be relevant to the pathogenesis of human acute lymphoid leukemia.

Abelson murine leukemia virus↗