Biomedical subjects

Laurent Pothuaud

Publications and source records attributed to Laurent Pothuaud.

7 recordsLinked to original sources

PubMed2005

Quality control assessment of ePTFE precoating procedure for in vitro endothelial cell seeding.

Over the past two decades, in vitro autologous endothelial cell (EC) coverage of expanded polytetrafluoroethylene (ePTFE) graft has been developed and clinically applied with success in infrainguinal bypasses. Before endothelialization, the luminal surface of the graft has to be coated with a currently used fibrinolytically inhibited fibrin glue. The aim of this work is to validate the precoating of the ePTFE (4 mm ID) ringed graft with fibrin. Twenty cm-long grafts were precoated with fibrin glue (2 operators) then fixed for microscopy investigations. Grafts were sliced into 3 regions. Thickness analysis was evaluated by image processing. Three grafts have been tested for endothelialization and observed at days 3, 8. Cell-free coated ePTFE were imaged using high-frequency ultrasound modality. Whatever the examined segment an overall homogeneous covering protein is shown. Fibrin thickness after image processing is 8.5+/-0.25 and 4.1+/-0.4 microm for two operators (P < .001). We have evaluated reproducibility and inter- and intra-variability of the operator, assessed quality controls and quality assurance all along the prosthesis and finally endothelialization and subsequent behaviour under shear stress conditions.

Bioprosthesis↗

PubMed2005

Mathematical modelling of the distribution of newly formed bone in bone tissue engineering.

New bone formation in bone substitutes is usually investigated by histomorphometric global analysis. This study provides a novel mathematical modelling approach of new bone formation in the use of osteoinductive and functionalized biomaterials for bone tissue engineering. We discuss here the repartition and the probability to get new bone formation inside Biphasic Calcium Phosphate (BCP) loaded with autologous osteogenic cells, functionalized with a cyclo RGD peptide, after implantation in rabbits for 2 and 4 weeks. This local analysis allowed us to complement classical global findings and to demonstrate that after 2 weeks of implantation, the probability of new bone formation was significantly higher in RGD-grafted BCP and that new formed bone was largely distributed from the edge to the centre of the implant. While no significant differences were obtained after 4 weeks of implantation between RGD-grafted and non-grafted materials, distribution of new bone formation inside RGD-grafted materials was significantly more homogeneous as demonstrated by our mathematical modelling approach. In conclusion, local analysis of new bone formation inside macroporous substitutes coupled with mathematical modelling constitutes a potential quantitative approach for the evaluation of the osteoconductive and osteoinductive characteristics of such biomaterials.

Algorithms↗

PubMed2004

In vivo application of 3D-line skeleton graph analysis (LSGA) technique with high-resolution magnetic resonance imaging of trabecular bone structure.

Over the last several years magnetic resonance (MR) imaging has emerged as a means of measuring in vivo 3D trabecular bone structure. In particular, MR based diagnosis could be used to complement standard bone mineral density (BMD) methods for assessing osteoporosis and evaluating longitudinal changes. The aim of this study was to demonstrate the feasibility of using the 3D-LSGA technique for the evaluation of trabecular bone structure of high-resolution MR images, particularly for assessing longitudinal changes, in vivo. First, the reproducibility of topological 3D-LSGA based measurements was evaluated in a set of seven volunteers, and coefficients of variations ranged from 3.5% to 6%. Second, high-resolution MR images of the radius in 30 postmenopausal women from a placebo controlled drug study (Idoxifene), divided into placebo ( n=9) and treated ( n=21) groups, were obtained at baseline (BL) and after 1 year of treatment (follow-up, FU). In addition, dual X-ray absorptiometry (DXA) measures of BMD were obtained in the distal radius. Standard morphological measurements based on the mean intercept length (MIL) technique as well as 3D-LSGA based measurements were applied to the 3D MR images. Significant changes from BL to FU were detected, in the treated group, using the topological 3D-LSGA based measurements, morphological measures of volume of connected trabeculae and App Tb.N from MIL analysis. The duration of the study was short, and the number of patients remaining in the study was small, hence these results cannot be interpreted with regard to a true therapeutic response. Furthermore, the site (wrist) and the drug (idoxifene) are not optimal for follow-up study. However, this paper demonstrated the feasibility of using 3D-LSGA based evaluation coupled with in vivo high-resolution MR imaging as a complementary approach for the monitoring of trabecular bone changes in individual subjects.

Adult↗

PubMed2004

A new computational efficient approach for trabecular bone analysis using beam models generated with skeletonized graph technique.

Micro-finite element (FE) analysis is a well established technique for the evaluation of the elastic properties of trabecular bone, but is limited in its application due to the large number of elements that it requires to represent the complex internal structure of the bone. In this paper, we present an alternative FE approach that makes use of a recently developed 3D-Line Skeleton Graph Analysis (LSGA) technique to represent the complex internal structure of trabecular bone as a network of simple straight beam elements in which the beams are assigned geometrical properties of the trabeculae that they represent. Since an enormous reduction of cputime can be obtained with this beam modeling approach, ranging from approximately 1,200 to 3,600 for the problems investigated here, we think that the FE modeling technique that we introduced could potentially constitute an interesting alternative for the evaluation of the elastic mechanical properties of trabecular bone.

Algorithms↗

PubMed2003

Semi-automated evaluation of the cortico-medullar index on radius radiographs: a study in prepubertal girls.

The aim of the study was to validate a non-invasive method allowing a semi-automatic cortico-medullar index (CMI) computation from standard radiographs. Fifty-five radiographs of the non-dominant radius of prepubertal girls (aged 10.12+/-1.47 years) were scanned (100 microm scanning resolution) by the same observer. To detect the grey level peaks, we used the Deriche's recursive filter applied to the grey level gradients and we defined the cortical areas by thresholding (iterative contour detection). The CMI was calculated as cortical areas divided by the total bone area. The reproducibility was tested through the analysis of ten radiographs scanned twice, on 5, 10, 15, 20, 30 and 40 lines at each side of a reference line located at the distal third part of the radius. We used the root mean square coefficient of variation (RMS-CV) as verification. Dual-Energy X-ray (DXA) was used for densitometry measurements of the whole body, and non dominant radius (mid-, distal third and ultra distal). The result attaining the best reproducibility concerned the 15-line position (Mean CMI=0.58+/-0.005 with a 1.36% RMS-CV). CMI correlated significantly with Bone Mineral Density (BMD) (r=0.40, 0.33 and 0.50, P<0.01, respectively, at the whole body, mid- and third distal of the radius), Bone Mineral Content (BMC) (r=0.32, 0.36, 0.34 and 0.35, respectively, at the whole body (P=0.01), mid- (P=0.007), third distal (P=0.01) and ultra distal of the radius (P=0.01)) but not with BMD at the ultra distal of the radius (r=-0.01, P=0.9). This semi-automated new method has been easily implemented, reproducible, and therefore, could be useful tool for the bone CMI computation.

Absorptiometry, Photon↗

PubMed2002

Combination of topological parameters and bone volume fraction better predicts the mechanical properties of trabecular bone.

Trabecular bone structure may complement bone volume/total volume fraction (BV/TV) in the prediction of the mechanical properties. Nonetheless, the direct in vivo use of information pertaining to trabecular bone structure necessitates some predictive analytical model linking structure measures to mechanical properties. In this context, the purpose of this study was to combine BV/TV and topological parameters so as to better estimate the mechanical properties of trabecular bone. Thirteen trabecular bone mid-sagittal sections were imaged by magnetic resonance (MR) imaging at the resolution of 117 x 117x 300 microm(3). Topological parameters were evaluated in applying the 3D-line skeleton graph analysis (LSGA) technique to the binary MR images. The same images were used to estimate the elastic moduli by finite element analysis (FEA). In addition to the mid-sagittal section, two cylindrical samples were cored from each vertebra along vertical and horizontal directions. Monotonic compression tests were applied to these samples to measure both vertical and horizontal ultimate stresses. BV/TV was found as a strong predictor of the mechanical properties, accounting for 89-94% of the variability of the elastic moduli and for 69-86% of the variability of the ultimate stresses. Topological parameters and BV/TV were combined following two analytical formulations, based on: (1) the normalization of the topological parameters; and on (2) an exponential fit-model. The normalized parameters accounted for 96-98% of the variability of the elastic moduli, and the exponential model accounted for 80-95% of the variability of the ultimate stresses. Such formulations could potentially be used to increase the prediction of the mechanical properties of trabecular bone.

Adult↗

PubMed2002

Three-dimensional-line skeleton graph analysis of high-resolution magnetic resonance images: a validation study from 34-microm-resolution microcomputed tomography.

The resolution achievable in vivo by magnetic resonance imaging (MRI) techniques is not sufficient to depict precisely individual trabeculae and, thus, does not permit the quantification of the "true" trabecular bone morphology and topology. Nevertheless, the characterization of the "apparent" trabecular bone network derived from high-resolution MR images (MRIs) and their potential to provide information in addition to bone mineral density (BMD) alone has been established in studies of osteoporosis. The aim of this work was to show the ability of the three-dimensional-line skeleton graph analysis (3D-LSGA) to characterize high-resolution MRIs of trabecular bone structure. Fifteen trabecular bone samples of the distal radius were imaged using the high-resolution MRI (156 x 156 x 300 microm3) and microcomputed tomography (microCT; 34 x 34 x 34 microm3). After thresholding, the 3D skeleton graph of each binary image was obtained. To remove the assimilated-noise branches of the skeleton graph and smooth this skeleton graph before it was analyzed, we defined a smoothing length criterion (l(c)), such that all "termini" branches having a length lower than l(c) were removed. Local topological and morphological LSGA measurements were performed from MRIs and microCT images of the same samples. The correlations between these two sets of measurements were dependent on the smoothing criterion l(c), reaching R2 = 0.85 for topological measurements and R2 = 0.57-0.64 for morphological measurements. 3D-LSGA technique could be applied to in vivo high-resolution MRIs of trabecular bone structure, giving an indirect characterization of the microtrabecular bone network.

Adult↗