Biomedical subjects

A Laib

Publications and source records attributed to A Laib.

24 records · Page 2Linked to original sources

PubMed1998

Assessment of cancellous bone mechanical properties from micro-FE models based on micro-CT, pQCT and MR images.

Recently, new micro-finite element (micro-FE) techniques have been introduced to calculate cancellous bone mechanical properties directly from high-resolution images of its internal architecture. Also recently, new peripheral quantitative computed tomography (pQCT) and magnetic resonance (MR) imaging techniques have been developed that can create images of whole bones in vivo with enough detail to visualize the internal cancellous bone architecture. In this study we aim to investigate if the calculation of cancellous bone mechanical properties from micro-FE models based on such new pQCT and MR images is feasible. Three bone specimens were imaged with the pQCT scanning system and the MR-imaging system. The specimens were scanned a second time using a micro-CT scanner with a much higher resolution. Digitized reconstructions were made based on each set of images and converted to micro-FE models from which the bone elastic properties were calculated. It was found that the results of both the pQCT and the MR-based FE-models compared well to those of the more accurate micro-CT based models in a qualitative sense, but correction factors will be needed to get accurate values.

Bone and Bones↗

PubMed1998

Mechanical analysis of bone and its microarchitecture based on in vivo voxel images.

Prevention of osteoporotic fractures requires accurate methods to detect the increase in bone fragility at an early disease stage as well as effective therapies to reduce the risk of bone fractures. Presently the prediction of the patient-specific bone fracture risk is primarily based on bone density, since this is the only parameter which can routinely be measured in vivo. However, these predictions might not always be precise because the fracture risk is also determined by the bone microarchitecture and the bone's loading conditions. The aim of this paper is to introduce and evaluate new methods which could contribute to a better quantification of bone fracture risk. Recently, a new approach, combining computational engineering methods (finite element (FE) method) and 3D high-resolution imaging techniques, has been introduced which can account not only for bone density but also for microarchitecture and loading conditions. High-resolution imaging techniques allow acquisition of 3D images of the bone microarchitecture, whereas FE methods applied to these images allow very precise calculation of the mechanical properties of bone. However, such a detailed FE analysis was not feasible for bone in vivo mainly because the resolution was not sufficient to measure the bone microarchitecture. It is shown here, from preliminary results, that the FE approach based on high-resolution images from a new CT scanner now allows prediction of the mechanical behavior of peripheral bones in vivo. It is expected that, eventually, the FE approach will lead to a better patient-specific fracture risk prediction than earlier methods based on bone density alone. Hence, with this new approach, it might be possible to detect the increase in bone fragility at an early stage of osteoporosis and it might also be possible to evaluate treatments more accurately.

Biomechanical Phenomena↗

PubMed1997

Ridge number density: a new parameter for in vivo bone structure analysis.

An advanced analysis of the mechanical properties of bone should include information about the microarchitecture of cancellous bone in addition to its density. It has recently been shown that high-resolution quantitative computed tomography and magnetic resonance imaging have the potential to assess such information in a noninvasive way in patients. Both techniques, however, lack sufficient spatial resolution to image the individual trabeculae with true precision. In this work, a new parameter, Ridge number density (RND), is introduced. RND is a measure for the trabecular number, which can be extracted directly from high-resolution three-dimensional (3D) images of patients. We applied the RND technique to a test group of nine healthy, postmenopausal women measured repetitively with a high-resolution 3D peripheral quantitative computed tomography (3D-pQCT) system with 165 x 165 x 165 microm3 voxel size. Simultaneously with the RND determination, the trabecular bone density (TBD) was also assessed in the same volume of interest. The examination site was the distal radius. The intersubject variability of the measured test group was 10.5% for RND and 26.3% for TBD. The root mean square error between first and second examinations (midterm reproducibility) was 1.6% and 1.1%, respectively. RND is determined independently from TBD and pertains to the structure of the cancellous bone. As such, it might add crucial information in cases where bone mass or bone density measurements alone give ambiguous results.

Bone Density↗

PubMed1996

Resolution dependency of microstructural properties of cancellous bone based on three-dimensional mu-tomography.

Micro-computed tomography (microCT) is an emerging technique for the non-destructive assessment and analysis of the three-dimensional cancellous bone architecture. However, the procedures the procedures and applications used to quantify bone structures are not yet standardized. The aim of this study was to provide more insight in the resolution-dependency of microstructural properties of three-dimensional trabecular bone. Ten iliac crest bone biopsies were measured using a newly devised microCT system providing a nominal isotropic resolution of 14 microns. To study the resolution dependency the measured data were reconstructed on reduced image arrays with reduction factors ranging from 2 to 20. To assess the structural properties, morphometric parameters were computed based on a truly three-dimensional approach. The results showed a strong resolution dependency of the structural properties and that, if very precise results are needed, only the highest resolution will predict the correct values. Nevertheless, since the properties either decrease or increase monotonously up to a nominal resolution of about 175 microns, the values appear to be restorable using a suitable calibration procedure.

Bone Matrix↗

PubMedDate not supplied

Comparison of structure extraction methods for in vivo trabecular bone measurements.

In vivo trabecular bone structure measurements have become available recently using high resolution quantitative computed tomography (3D-QCT) or magnetic resonance imaging. In this work different structure extraction and morphometric evaluation techniques are compared, which are of potential use for in vivo assessment of human cancellous bone structure. Given the spatial resolution of actual in vivo examination procedures, best results are obtained by extracting first the skeleton of the structure and applying model independent 3D techniques to calculate trabecular number, then deriving mean trabecular thickness and separation from densitometric bone volume fraction and Tb.N*. Traditional histomorphometric methods based on bone surface and volume ratios and assuming a plate model performed less well.

Bone Density↗

PubMedDate not supplied

Mutation of the ectodysplasin-A gene results in bone defects in mice.

Anhidrotic ectodermal dysplasia (EDA) is an X-linked, recessive genetic disease characterized by dysfunctional sweat glands, poorly developed teeth, and premature balding in human beings. This disorder results from mutations in the gene for ectodysplasin-A, a type II transmembrane protein with tumour necrosis factor-alpha domains. An animal model of EDA, the Tabby mouse, also has mutations in the ectodysplasin-A gene and defects similar to those of human beings with EDA. In addition to these defects, Tabby mice acquire deformities in the distal portion of their tails at 10-12 weeks of age. Whole-mount staining of the skeleton with Alizarin Red and Alcian Blue revealed that the tail defect resulted from vertebral fractures just distal to the epiphysis. Histological analysis demonstrated that the structure of both the epiphysis and the subepiphyseal zone of the tail vertebrae was dysplastic while the shaft of the diaphysis was relatively normal. The overall structure of the trabecular bone of these animals was examined through 3-dimensional microcomputed tomography of the tibia. This analysis indicated that Tabby mice had a mild increase in the interconnectivity of the intertwined trabecular bone network but that individual trabeculae were relatively normal. Since it has been determined recently that the ectodysplasin-A gene is expressed in the osteoblasts of developing human embryos, it appears likely that this gene plays a role in normal bone development.

Animals↗