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Biomedical subjects

C Zannoni

Publications and source records attributed to C Zannoni.

36 records · Page 2Linked to original sources
PubMed1999

Spatial positioning of an hip stem solid model within the CT data set of the host bone.

A new protocol is proposed which allows the spatial registration of a prosthetic hip stem solid model with the CT data set of the host bone collected pre-operatively using a limited number of reference landmarks taken from post-operative images. Although based on well know algorithms, such as the Single Value Decomposition, this method opens new possibilities to the three-dimensional modelling of operated bones. In a preliminary experiment based on a synthetic human femur replica the proposed protocol achieved a global accuracy of 1.53 mm (root mean square error of the centre location of ten control sections) using only six CT post-operative slices. This methodology allows an accurate three-dimensional modelling of operated bone which have been implanted with high density metallic devices which produce relevant artefacts in post-operative CT images.

Algorithms↗
PubMed1999

CT data sets surface extraction for biomechanical modeling of long bones.

In modelling applications such as custom-made implants design is useful to have a surface representation of the anatomy of bones rather than the voxel-based representation generated by tomography systems. A voxel-to-surface conversion process is usually done by a 2D segmentation of the images stack. However, other methods allow a direct 3D segmentation of the CT or MRI data set. In the present work, two of these methods, namely the Standard Marching Cube (SMC) and the Discretized Marching Cube (DMC) algorithms, were compared in terms of local accuracy when used to reconstruct the geometry of a human femur. The SMC method was found to be more accurate than the DMC method. The SMC method was capable of reconstructing the inner and outer geometry of a human femur with a peak error lower than 0.9 mm and an average error comparable to the pixel size (0.3 mm). However, the large number of triangles generated by the algorithm may limit its adoption in many modelling applications. The peak error of the DMC algorithm was 1.6 mm but it produced approximately 70% less triangles than the SMC method. From the results of this study, it may be concluded that three dimensional segmentation algorithms are useful not only in visualisation applications but also in the creation of geometry models.

Algorithms↗
PubMed1999

NMR spectra from Monte Carlo simulations of polymer dispersed liquid crystals.

We present the calculation of NMR line shapes, including dynamical effects, of polymer dispersed liquid crystals starting from the Monte Carlo configurations simulated for a lattice spin model. We consider droplets with radial, bipolar, and random boundary conditions and examine to what extent their predicted deuterium NMR spectra differ in the presence of molecular motion.

Journal Article↗
PubMed1998

TRI2SOLID: an application of reverse engineering methods to the creation of CAD models of bone segments.

For many biomechanical engineering activities it would be useful to have the three dimensional (3D) geometry of bone segments available in form of vectorial models within computer aided design (CAD) environments. In this paper a new method for the semi-automatic conversion of a stack of CT images of a femur into a CAD solid model is described. This method is relatively simple, accurate, and requires only a 3D CAD plus a few additional programs available in the public domain. The proposed method was used to convert the CT scan data set of a human femur into a valid CAD model; the resulting solid was two times more accurate than that obtained using the commonly used procedure based on 2D segmentation.

Algorithms↗
PubMed1998

Material properties assignment to finite element models of bone structures: a new method.

Finite element analysis (FEA) is widely adopted to investigate the mechanical behaviour of bone structures. Computed tomography (CT) data are frequently used to generate FE models of bone. If properly calibrated, CT images are capable of providing accurate information about the bone morphology and tissue density. The aim of this work was to develop a special program able to read a CT data set as well as the FEA mesh generated from it, and to assign to each element of the mesh the material properties derived from the bone tissue density at the element location. The program was tested on phantom data sets and was adopted to evaluate the effects of the discrete description of the bone material properties. A three-dimensional FE model was generated automatically from a 16 bit CT data set of a distal femur acquired in vivo. The strain energy density (SED) was evaluated for each model element for increasing model complexity (number of different material cards assigned to the model). The computed SED were strongly dependent on the material mapping strategy.

Algorithms↗
PubMed1998

Optimal CT scanning plan for long-bone 3-D reconstruction.

Digital computed tomographic (CT) data are widely used in three-dimensional (3-D) reconstruction of bone geometry and density features for 3-D) modeling purposes. During in vivo CT data acquisition the number of scans must be limited in order to protect patients from the risks related to X-ray absorption. Aim of this work is to automatically define, given a finite number of CT slices, the scanning plan which returns the optimal 3-D) reconstruction of a bone segment from in vivo acquired CT images. An optimization algorithm based on a Discard-Insert-Exchange technique has been developed. In the proposed method the optimal scanning sequence is searched by minimizing the overall reconstruction error of a two-dimensional (2-D) prescanning image: an anterior-posterior (AP) X-ray projection of the bone segment. This approach has been validated in vitro on three different femurs. The 3-D reconstruction errors obtained through the optimization of the scanning plan on the 2-D) prescanning images and on the corresponding 3-D data sets have been compared. Two-dimensional and 3-D data sets have been reconstructed by linear interpolation along the longitudinal axis. Results show that direct 3-D optimization yields root mean square reconstruction errors which are only 4%-7% lower than the 2-D-optimized plan, thus proving that 2-D-optimization provides a good suboptimal scanning plan for 3-D reconstruction. Further on, 3-D reconstruction errors given by the optimized scanning plan and a standard radiological protocol for long bones have been compared. Results show that the optimized plan yields 20%-50% lower 3-D reconstruction errors.

Algorithms↗
PubMed1986

O2-dependent lipid peroxidation does not affect the molecular order in hepatoma microsomes.

Microsomal membranes from rat liver and from the fast-growing Morris hepatoma 3942A have been peroxidized to different extents and the order parameter of the membranes measured by fluorescence depolarization of the probe 1,6-diphenyl-1,3,5-hexatriene. The data have been analysed by applying a mathematical approach that takes into account simultaneously static and dynamic fluorescence parameters. It appears that tumour membranes are more ordered than the control and their order parameter does not increase with greater exposure to the action of O2 radicals in contrast to liver membranes. The fatty acid composition of the membrane lipids has been studied under different experimental conditions and correlated to the behaviour of the physical parameter.

Animals↗
PubMed1984

Lipid peroxidation and fluidity of plasma membranes from rat liver and Morris hepatoma 3924A.

Plasma membranes isolated from the fast-growing, maximal-deviation, Morris hepatoma 3924A exhibit remarkable changes in lipid composition, lipid peroxidation and to some extent in the physical state with respect to rat liver plasmalemmas. A correlation appears to exist between the lower phospholipid: protein ratio, higher cholesterol: phospholipid ratio, lower rate of lipid peroxidation and decrease in fluidity in tumor plasma membranes.

Animals↗
PubMed1984

Lipid composition, physical state, and lipid peroxidation of tumor membranes.

Studies were carried out on microsomes isolated from the highly differentiated (slow-growing) Morris hepatoma 9618A, on microsomes and plasma membranes from the poorly differentiated (fast-growing) Morris hepatoma 3924A, and rat liver used as control. The lipid composition (phospholipid and cholesterol content, degree of fatty acid unsaturation) and peroxidation of such membranes has been correlated with the order and fluidity of the membrane bilayer. The results indicate that substrate availability is the rate-limiting step in microsomal and plasma membrane lipid peroxidation of hepatoma 3924A. From diphenylhexatriene fluorescence depolarization measurements it appears that the changes in lipid composition cause an increase in the order of the lipid bilayer on going from the control to hepatoma 9618A and 3924A microsomes, while fluidity is virtually unchanged. Conversely, for similar chemical changes, in plasma membranes from hepatoma 3924A the order is nearly the same and there is a decrease in fluidity. The changes in the above parameters of tumor membranes might be partly related to the loss of protective enzymes against oxygen radicals. This is supported by the observation that inhibition of liver superoxide dismutase and glutathione reductase, by treatment of rats with diethyldithiocarbamate and chloroethyl nitrosourea, respectively, renders the microsomal membranes more resistant to lipid peroxidation in vitro.

Adenosine Diphosphate↗
PubMedDate not supplied

Analysis of titanium induced CT artifacts in the development of biomechanical finite element models.

X-ray computerized tomography (CT) is capable of providing detailed information about the geometry and mineral density of skeletal structures. Such accurate data are of great interest in studying the effects of orthopaedic implants on bone adaptive behaviour in vivo. Metallic implants, however, generate artifacts, typically seen as starburst streaking. These artifacts can degrade the capabilities of CT images to provide accurate information about the geometry and mineral density of bone structures. The aim of this work was to investigate the possibility of developing finite element models (FEM) of the human femur after hip joint arthroplasty using CT images acquired directly after surgery. The capability of modern CT scanners to accurately reconstruct the cross-section geometry of titanium alloy hip joint prosthetic stems was primarily investigated. A new measuring procedure dealing with the geometry of real stems was developed and its accuracy assessed. Secondly, the artifacts generated by a prosthetic stem on the radiological density of the bone were analysed, and their effects on the assessment of FEM material properties were evaluated. Results showed that CT images provide accurate information on metal stem geometry. An average error of 0.45 mm was estimated in the reconstruction of stem cross-section geometry. Concerning bone density estimation around the implant, it was observed that the effect of metal artifacts on tissue density becomes zero at a distance of 2 mm from the implant.

Alloys↗
PubMedDate not supplied

A new method for the automatic mesh generation of bone segments from CT data.

A new procedure for the automatic generation of finite element meshes of bone segments from computed tomography (CT) data sets is described. The new method allows a direct automatic generation from the CT data and produces a very accurate unstructured hexahedral mesh. The accuracy of the method was established using the CT images of an artificial femur showing range of attenuation values comparable to those of a human femur. To establish the optimal values for the parameters controlling the mesh a sensitivity analysis was carried out using mesh-conditioning indicators. Some of the best meshes, with increasing levels of refinement, were used to analyse the stresses induced in the proximal femur by single leg stance posture. The accuracy of the meshes was evaluated using an implicit a posteriori residual-based error estimates. The number of elements with stress residuals larger than 10% of the peak stress was 7.8% using the coarsest mesh and only 1.8% with the finest mesh. The proposed method has been proved able to conjugate full automation with high-quality finite element meshes. The stress predictions obtained using these hexahedral-only meshes have been more accurate than those obtained by any other automatic mesh generation algorithm. Once properly integrated in an easy-to-use application, the described method could finally make feasible many clinical applications of finite element analysis.

Bone and Bones↗
PubMedDate not supplied

Development of a software for the design of custom-made hip prostheses using an open-source rapid application development environment.

The present work describes a technology transfer project called HIPCOM devoted to the re-engineering of the process used by a medical devices manufacturer to design custom-made hip prostheses. Although it started with insufficient support from the end-user management, a very tight scheduling and a moderate budget, the project developed into what is considered by all partners a success story. In particular, the development of the design software, called HIPCOM Interactive Design Environment (HIDE) was completed in a time shorter than any optimistic expectation. The software was quite stable since its first beta version, and once introduced at the user site it fully replaced the original procedure in less than two months. One year after the early adoption, more than 80 custom-made prostheses had been designed with HIDE and the user had reported only two bugs, both cosmetics. The scope of the present work was to report the development experience and to investigate the reasons for these positive results, with particular reference to the development procedure and the software architecture. The choice of TCL/TK as development language and the adoption of well-defined software architecture were found to be the success key factors. Other important determinants were found to be the adoption of an incremental software engineering strategy, well suited for small to medium projects and the presence in the development staff of a technology transfer expert.

Computer-Aided Design↗