Biomedical subjects

Denis Rancourt

Publications and source records attributed to Denis Rancourt.

6 recordsLinked to original sources

PubMed2005

Influence of advanced electromyogram (EMG) amplitude processors on EMG-to-torque estimation during constant-posture, force-varying contractions.

Numerous studies have investigated the relationship between surface electromyogram (EMG) and torque exerted about a joint. Most studies have used conventional EMG amplitude (EMGamp) processing, such as rectification followed by low-pass filtering, to pre-process the EMG before relating it to torque. Recently, advanced EMGamp processors that incorporate signal whitening and multiple-channel combination have been shown to significantly improve EMGamp processing. In this study, we compared the performance of EMGamp-torque estimators with and without these advanced EMGamp processors. Fifteen subjects produced constant-posture, non-fatiguing, force-varying contractions about the elbow while torque and biceps/triceps EMG were recorded. EMGamp was related to torque using a linear FIR model. Both whitening and multiple-channel combination reduced EMG-torque errors and their combination provided an additive benefit. Using a 15th-order linear FIR model, EMG-torque errors with a four-channel, whitened processor averaged 7.3% of maximum voluntary contraction (MVC) (or 78% of variance accounted for). By comparison, the equivalent single-channel, unwhitened (conventional) processor produced an average error of 9.9% of MVC (variance accounted for of 55%). In addition, the study describes the occurrence of spurious peaks in estimated torque when the torque model is created from data with a sampling rate well above the bandwidth of the torque. This problem occurs when the torque data are sampled at the same rate as the EMG data. The problem is corrected by decimating the EMGamp prior to relating it to joint torque, in our case to an effective sampling rate of 40.96 Hz.

Adult↗

PubMed2005

Experimental investigation of the intrinsic properties of the optical coupling between axisymmetric Gaussian beams.

Continuing a previous analytical and numerical work, an experimental investigation of seven intrinsic properties of the optical coupling between axisymmetric Gaussian beams is presented. In this study, two single-mode fibers are used as the receiver and the emitter and a five-axis nanopositioning system is used to investigate optical coupling properties by moving one fiber relative to the other. Experiments demonstrate the existence of sufficiently accurate hyperbolic, parabolic, and linear trends for the optical coupling phenomenon, which can be useful for developing model-based alignment algorithms.

Journal Article↗

PubMed2004

Modelling liver tissue properties using a non-linear visco-elastic model for surgery simulation.

In this work, we introduce an extension of the linear elastic tensor-mass method allowing fast computation of non-linear and visco-elastic mechanical forces and deformations for the simulation of biological soft tissue. We aim at developing a simulation tool for the planning of cryogenic surgical treatment of liver cancer. Percutaneous surgery simulation requires accurate modelling of the mechanical behaviour of soft tissue, and previous experimental characterizations have shown that linear elasticity is only a coarse approximation of the real properties of biological tissues. We first show that our model can simulate different types of non-linear and visco-elastic mechanical behaviours at speeds which are compatible with real-time applications. Then an experimental setup is presented which was used to characterize the mechanical properties of deer liver tissue under perforation by a biopsy needle. Experimental results demonstrate that a linear model is not suitable for simulating this application, while the proposed model succeeds in accurately modelling the axial load measured on the needle.

Animals↗

PubMed2004

Intrinsic properties of the optical coupling between axisymmetric Gaussian beams.

On the basis of the overlap integral method, an approximate analytical model is derived to estimate the coupled optical power between axisymmetric Gaussian beams when transverse, axial, and angular misalignments simultaneously exist in three dimensions. Seven optical properties are derived from a detailed analysis of the model. Because the model is an approximate analytical solution to the overlap integral method, the existence of each property is also investigated by a numerical solution. Results show that all seven properties are intrinsic to the optical coupling phenomenon between Gaussian beams. Because numerous single-mode device-to-fiber coupling systems can be well described by use of Gaussian beams, the seven properties provide a solid basis to develop model-based algorithms for single-mode device-to-fiber alignment automation.

Journal Article↗

PubMed2004

Cross-sectional profiles and volume reconstructions of soft tissues using laser beam measurements.

Precise geometric reconstruction is a valuable tool in the study of soft tissues biomechanics. Optical methods have been developed to determine the tissue cross section without mechanical contact with the specimen. An adaptation of the laser micrometer developed by Lee and Woo [ASME J. Biomech. Eng., 110 (2), pp. 110-114]. is proposed in which the laser-collimated beam rotates around and moves along a fixed specimen to reconstruct its cross sections and volume. Beam motion is computer controlled to accelerate data acquisition and improve beam positioning accuracy. It minimizes time-dependent shape modifications and increases global reconstruction precision. The technique is also competent for the measurement of immersed collagen matrices.

Algorithms↗

PubMedDate not supplied

Tissue reorganization in response to mechanical load increases functionality.

In the rapidly growing field of tissue engineering, the functional properties of tissue substitutes are recognized as being of the utmost importance. The present study was designed to evaluate the effects of static mechanical forces on the functionality of the produced tissue constructs. Living tissue sheets reconstructed by the self-assembly approach from human cells, without the addition of synthetic material or extracellular matrix (ECM), were subjected to mechanical load to induce cell and ECM alignment. In addition, the effects of alignment on the function of substitutes reconstructed from these living tissue sheets were evaluated. Our results show that tissue constructs made from living tissue sheets, in which fibroblasts and ECM were aligned, presented higher mechanical resistance. This was assessed by the modulus of elasticity and ultimate strength as compared with tissue constructs in which components were randomly oriented. Moreover, tissue-engineered vascular media made from a prealigned living tissue sheet, produced with smooth muscle cells, possessed greater contractile capacity compared with those produced from living tissue sheets that were not prealigned. These results show that the mechanical force generated by cells during tissue organization is an asset for tissue component alignment. Therefore, this work demonstrates a means to improve the functionality (mechanical and vasocontractile properties) of tissues reconstructed by tissue engineering by taking advantage of the biomechanical forces generated by cells under static strain.

Biocompatible Materials↗