Journal of Mechanics in Medicine and Biology

Accelerometers have become increasingly integrated in the biomedical field, as they are highly portable and capable of objectively and reliably quantifying motion. Two specific applications for accelerometers are the quantification of gait and movement disorders, such as Parkinson's disease and essential tremor. The evolution of accelerometers to their present status is discussed. Accelerometry is contrasted with more traditional means for accessing gait and movement disorders. Advances in the research validation of accelerometers for the characterization of gait and movement disorders, such as essential tremor and Parkinson's disease, are addressed. The review concludes with the advancement of three-dimensional (3D) wireless accelerometers and pertinent future implications.

Cellular biomechanics is an area of study that is receiving more attention as time progresses. The response of cells to their mechanical environment, including biomechanical stimuli, has far-reaching ramifications for the area of tissue engineering, especially for tissues designed to withstand mechanical loading (e.g. bone, cartilage, tendons and ligaments, and arteries). The effects of mechanical stimuli on cells are only recently being examined, and the potential role of mechanical stimuli in tissue engineering is still one that is largely ignored in the design of tissue engineering scaffolds. The relationship of mechanical properties of scaffolds or of mechanical stimuli to cell behavior is complex, but vital to the development of the field. Also, understanding the complex interplay of form and environment on cells involves an increase in our knowledge of how cells react to their total environment including mechanical stimuli and material properties. In order to improve tissue engineering outcomes, a nexus must be developed between the mechanical, biochemical, and biological studies of cellular behavior, in the context of extremely complex systems.

Finite element (FE) simulations can be utilized to predict contact pressures at the bone/implant interface as well as to identify the position and shape of the contact region. However, the accuracy and reliability of FE models of the bone/implant interface reconstructed from tomographic images may be affected by a number of factors such as the presence of image artifacts, the magnitude of geometric errors made in the reconstruction process, the type of boundary and loading conditions hypothesized in the model, the nonlinear solver utilized for computing the contact pressure distribution, and the element type. This paper attempts to estimate the global effect of the aforementioned factors. For this purpose, a cylindrical contact problem — pin/muff — portraying a simplified model of the bone/implant interface is considered. The accuracy of numerical predictions is estimated by comparing contact pressures predicted by an FE model reconstructed from computed tomography (CT) scan images and by an "ideal", experimentally validated FE model. Two different couplings, i.e. chromium-cobalt alloy and titanium implants, are considered. In the former case, image artifacts complicate the reconstruction process of model geometry and lead to less accurate predictions on contact pressure distribution; conversely, the limited streaking effects occurring in the titanium pin case allow us to precisely reconstruct coupling geometry. Finally, a rather clear correlation between errors on contact pressure and geometric errors made in the reconstruction process is found only for the titanium pin.

Recent in vitro studies have provided evidence of the propagation of two different longitudinal wave modes at ultrasonic frequencies in cancellous bone. The genesis of these two plane waves in fluid-saturated porous media is predicted by the poroelastic approach to wave propagation originally developed by Biot. However, wave velocity is usually analyzed as a function of bone mass density only; therefore, the influence of the cancellous bone microstructure over the wave velocity is not taken into account. In the present study, a descriptor of the microstructure is considered in Biot's theory. This model is used to evaluate the large experimental variability of both fast and slow wave velocities measured on randomly oriented human and bovine cancellous bone samples. The role of the anisotropic solid structure and fluid in the behavior of fast and slow wave velocities is examined. Experimental and theoretically predicted velocities are found in close agreement when analyzed as a function of both porosity and structural index. This model has the potential to be used to determine an acoustically derived structural index in cancellous bone.

Mandibular symphyseal distraction osteogenesis is a clinical procedure utilized in orthodontics for solving problems of dental overcrowding on the mandibular arch. A critical issue is to evaluate the optimal duration of the latency period between the osteotomy and the first aperture of distraction device. In fact, the latency period should change with the patient's age. To this end, a computational mechanobiological model has been developed in order to find optimal durations of latency period for young, adult, and elder patients. The model is implemented in a finite element framework simulating the process of tissue differentiation in the bone callus formed after osteotomy. The biophysical stimulus regulating the tissue differentiation process is hypothesized to be a function of the octahedral shear strain and interstitial fluid flow velocity. The resulting spatial distribution of stiffness properties in the callus region is analyzed in order to assess the risk of premature bone union of osteotomy edges. The three-dimensional (3D) finite element model (FEM) of human mandible is reconstructed from computed tomography (CT) scans and also includes a tooth-borne device. Under unilateral occlusion, the mandible is submitted to full mastication loading or to mastication forces reduced by 70%. The results show that optimal durations of the latency period for preventing premature bone union are about 5–6 days for the young patient, 7–8 days for the adult patient, and 9–10 days for the elder patient. These durations seem rather insensitive to the magnitude of mastication forces. Finally, distraction force values predicted by the present mechanobiological model are in good agreement with data reported in the literature.

It is important to deliver radiation to treatment targets with accuracy. Typically, patients are positioned using marks on the surface of the skin. However, without imaging procedures, there is no information about the location of mobile internal organs and targets. The use of implanted radiopaque markers can help localize internal target organs using imaging modalities. Quality assurance procedures have been performed on commercially available spiral gold markers to determine their location and image quality. The results obtained from different, least essential imaging modalities employed in radiation therapy showed that these markers are not as clearly visible on radiographs as compared to the modalities with electronic output formats. The image quality was also poorer on megavoltage as compared to kilovoltage X-ray imaging modalities.

Imaging devices aid clinicians in disease staging and treatment planning procedures for cancer patients. In this technical report, the basic physics of positron emission tomography (PET) are briefly discussed. The integration of PET images into radiation therapy computerized treatment planning systems (TPS) for PET and computed tomography (CT) image fusion via portable storage media and Web-based PET image manipulation software is described. The PET images were obtained from a mobile dual PET/CT scanner (Discovery ST, GE Medical Systems) located two miles away from our radiation therapy center, and were fused with CT images from an independent stand-alone CT scanner (Siemens Somatom Emotion). Quality assurance for treatment planning PET images as well as radiation safety issues related to PET are also briefly discussed.

The QT interval is the electrocardiographic representation of the duration of ventricular depolarization and repolarization. In this paper, we have developed a new real-time QT interval detection algorithm for automatically locating the onset of QRS and the end of the T wave. The algorithm consists of several steps: signal-to-noise enhancement, QRS detection, QRS onset, and T-wave end definition. The detection algorithm is tested on electrocardiogram (ECG) signals from the universal MIT-BIH Arrhythmia Database. The resulting QRS detection algorithm has a sensitivity of 99.79% and a specificity of 99.72%. The QRS onset and T-wave detection algorithm is tested using several data records from the MIT/BIH Arrhythmia Database. The results obtained are shown to be highly satisfactory.

The present paper is concerned with the study of a mathematical model for the flow of blood through a multi-stenosed artery. Blood is considered here to consist of a peripheral plasma layer which is free from red cells, and a core region which is represented by a Casson fluid. A suitable generalized geometry of multiple stenoses existing in the arterial segment under consideration is taken for the study. A thorough quantitative analysis has been made through numerical computations of the variables involved in the analysis that are of special interest in the study. The computational results are presented graphically.

In orthopedics, a currently developed technique for large graft hybrid implants consists of using porous and biocompatible scaffolds seeded with a patient's bone cells. Successful culture in such large implants remains a challenge for biologists, and requires strict control of the physicochemical and mechanical environments achieved by perfusion within a bioreactor for several weeks. This perfusion, with a nutritive fluid carrying solute ingredients, is necessary for the active cells to grow, proliferate, differentiate, and produce extracellular matrices. An understanding and control of these processes, which lead to substrate degradation and extracellular matrix remodeling during the in vitro culture phase, depend widely on the success in the realization of new orthopedic biomaterials. Within this context, the analysis of the interactions between convective phenomena of hydrodynamic origin and chemical reactions of biological order which are associated to these processes is a fundamental challenge in the framework of bone tissue engineering. In order to better account for the different intricate processes taking place in such a sample and to design a relevant experimental protocol leading to the definition of an optimal tissue implant, we propose one- and two-dimensional theoretical models based on transport phenomena in porous active media.