Journal of Mechanics in Medicine and Biology

Intra-cardiac blood flow imaging and visualization is challenging due to the processes involved in generating velocity fields of flow within specific chambers of interest. Visual analysis of cardiac flow or wall deformation is crucial for an accurate examination of the heart.

Cardiac chamber boundary encapsulation is one of the key implementations for region definition. To provide intelligible results describing flow within the human heart, cardiac chamber segmentation is a pre-requisite so that fluid motion information can be presented within a region of interest defined by the chamber boundary. A technique that is used to establish contouring along the cardiac wall is described mathematically. This article also sets the practical foundation for flow vector synthesis and visualization in the cardiac discipline. We have outlined conceptual development and the construction of flow field based on a three-dimensional Cartesian grid that can give a greater insight into the blood dynamics within the heart.

We developed a framework that is able to present both anatomical as well as flow information by overlaying velocity fields over medical images and displaying them in cine-mode. By addressing most of the methods involved from the programming perspective, procedural execution and memory efficiency have been considered. Our implemented system can be used to examine abnormal blood motion behaviour or discover flow phenomena in normal or defective hearts.

In this work, the primary and secondary tensile strength components of human femur trabecular bone are qualitatively assessed using planar radiographic images and spectral analysis. Normal and abnormal femur trabecular images (N = 40) were recorded using planar radiography following standard image acquisition protocol. From the images, the tensile strength components of the trabeculae are delineated using image processing procedures and are then subjected to Fourier transform. The zero (DC), First (FMOI), and Second Moments of Inertia (SMOI) are the parameters considered and are correlated with presence and absence of mineralization in the image. Results show that the values of moments correlate well with percentage mineralization in normal images when compared to abnormal images for both primary and secondary tensile strength components. Further, no or poor correlations were found for abnormals in all cases. Among all, the values of second moment showed highest correlation in the secondary tensile region. In this paper the objectives, methodology, significance results and the conclusions are presented.

Ventricular interdependence is an important part of heart function, and hence a key mediator of most pathological consequences of its impairment. It can only be explained by accounting for overall chamber deformation as well as cardiac dimensions and nonlinear material properties. Further, clinically useful interpretation of imaging data about pathological alterations in chamber geometry is hampered by lack of understanding of its significance in cardiac function. A model has been developed which describes the ventricles and septum as portions of ellipsoid shells, allowing structural characterization of diastolic ventricular interaction over arbitrary ranges of chamber pressures and volumes as well as intrathoracic pressures. Chamber configuration is derived as a function of pressure gradients by combining shell element equilibrium equations through static boundary conditions applied at the sulcus. Coupling coefficients between state variables are then calculated by letting the system evolve quasistatically through the solution space. The model is used to simulate a number of cardiac pathologies (constrictive pericarditis, restrictive myocarditis, left/right free wall and septal hypertrophy, left dilatative cardiomyopathy) and quantify their effect on ventricular pressure–pressure coupling as well as diastolic pressure–volume relationships. Results match experimental observations where available. The model can aid in interpreting diagnostic data about chamber geometry in a quantitative manner, and the differential effect of cardiac pathologies with otherwise similar phenomenology on ventricular interaction can serve as a discriminating diagnostic criterion.

The study presented in this paper is concerned with the analysis of the ultrasound Doppler signal of the carotid arteries in the time-frequency domain using the short time Fourier transform (STFT) and the Wigner–Ville distribution (WVD). This study is carried out in order to investigate the behavior of the spectral broadening index (SBI) derived from spectra obtained using these methods. The variations in the shape of the Doppler power spectra as a function of time are presented in the form of sonograms in order to determine the degree of primitive carotid artery stenosis. The obtained results show a qualitative improvement in the appearance of the sonograms generated using the WVD over the STFT. However, despite this qualitative improvement the WVD suffers from some drawbacks: the presence of the cross terms which are primarily due to its quadratic nature. The application of the Choi–Williams distribution (CWD) in this analysis shows a noticeable reduction of these cross terms, improving therefore the quality of the sonograms. From these generated sonograms, the ultrasound frequency envelopes are extracted. The maximum and the mean frequencies in these envelopes are used to determine the SBI. The magnitude of the CWD-SBI is significantly greater than that of the STFT-SBI. In addition, there is a correlation between the SBIs obtained using the STFT and the CWD and the degree of severity of stenosis measured by 2D Doppler imaging.

The burden of proof of any theory aiming to represent a physical or biological reality by demonstrating its unifying properties is applied in the present paper in relation to the Neoclassical growth model and its ability to reproduce Gompertz growth. The Neoclassical growth model derived from first biological and physical principles was shown to capture all qualitative features that were revealed experimentally, including the possibility of a Logarithmic Inflection Point (LIP), the possibility of a LAG, concave as well as convex curves on the phase diagram, the Logistic growth as a special case, growth followed by decay, as well as oscillations. In addition, quantitative validation demonstrated its ability to reproduce experimental data in a few tested cases. This paper demonstrates that the Neoclassical growth model can reproduce a Generalized version of Gompertz growth too.

Biothermomechanics of skin tissue is highly interdisciplinary, involving bioheat transfer, burn damage, biomechanics and physiology. Characterization of the thermomechanical behavior of skin tissue is of great importance and can contribute to a variety of medical applications. However, few studies have attempted to address the influence of heat induced thermal damage on the mechanical properties of skin tissue. This paper presents the compressive behavior of pigskin at different thermal damage levels and discusses the possible mechanisms of thermal damage–dependent compressive behavior of skin. The results demonstrate that skin stiffness decreases with increasing thermal damage degree and there exists strain rate sensitivity at different damage levels, caused mainly by hydration changes.

Typically, active muscle force is calculated by subtracting measured passive force from measured total force for corresponding whole muscle lengths (standard method). From a mechanical point of view, this requires a parallel elastic component (PEC) that is arranged in parallel to both the series elastic component (SEC) and the contractile component (CC). From a morphological point of view, however, the PEC should be rather in parallel to the CC, and both in series to the SEC (model [CC]). In this study, we investigated the differences in active muscle force estimated with these two different approaches and their impact on the interpretation of experiments. We measured passive forces without stimulation and total forces during supramaximal stimulation of six cat soleus muscles in end-held isometric contractions from lengths near active insufficiency to lengths close to inducing stretch damage. The active forces estimated with model [CC] reach about 10% higher maximum isometric forces and reveal about 10% longer optimal lengths of the CC compared to the standard method. Model choice affects the interpretation of the physiological working range and residual force enhancement. The active force-length relationships of the contractile component determined with model [CC] agree better with the theoretical sarcomere force-length relationship.

Nowadays, the biological resource in the prey–predator ecosystem is commercially harvested and sold with the aim of achieving economic interest. Furthermore, the harvest effort is usually influenced by the variation of economic interest of harvesting. In this paper, a differential–algebraic model is proposed, which is utilized to investigate the dynamical behavior of the prey–predator ecosystem due to the variation of economic interest of harvesting. By discussing the local stability of the proposed model around the interior equilibrium, the instability mechanism of harvested prey–predator ecosystem is studied. With the purpose of stabilizing the proposed model around the interior equilibrium and maintaining the economic interest of harvesting at an ideal level, a feedback controller is designed. Finally, numerical simulations are carried out to demonstrate consistency with the theoretical analysis.