Mechanical model of the breast for the prediction of deformation during imaging.

To predict changes in the shape of the breast in different imaging devices, a Coupled Eulerian-Lagrangian (CEL) mechanical model is developed. The CEL method allows for a more adequate representation of the very large deformations experienced by the soft and incompressible tissues of the breast. The mechanical response of the tissues is based on advanced mathematical formulations and experimental data from the literature. Realistic geometries generated from Magnetic Resonance (MR) images are used as study cases. Furthermore, specific boundary conditions are applied to the model to predict the shape of the breast and the location of the internal tissues in a prototype microwave breast imaging system, where an immersion medium is used. The accuracy of the model was assessed by comparing the numerical results with a laser scan of the same subject in the microwave breast imaging system.

A prototype system for measuring microwave frequency reflections from the breast.

Microwave imaging of the breast is of interest for monitoring breast health, and approaches to active microwave imaging include tomography and radar-based methods. While the literature contains a growing body of work related to microwave breast imaging, there are only a few prototype systems that have been used to collect data from humans. In this paper, a prototype system for monostatic radar-based imaging that has been used in an initial study measuring reflections from volunteers is discussed. The performance of the system is explored by examining the mechanical positioning of sensor, as well as microwave measurement sensitivity. To gain insight into the measurement of reflected signals, simulations and measurements of a simple phantom are compared and discussed in relation to system sensitivity. Finally, a successful scan of a volunteer is described.

Modeling assemblies of biological cells exposed to electric fields.

Gap junctions are channels through the cell membrane that electrically connect the interiors of neighboring cells. Most cells are connected by gap junctions, and gaps play an important role in local intercellular communication by allowing for the exchange of certain substances between cells. Gap communication has been observed to change when cells are exposed to electromagnetic (EM) fields. In this work, we examine the behavior of cells connected by gap junctions when exposed to electric fields, in order to better understand the influence of the presence of gap junctions on cell behavior. This may provide insights into the interactions between biological cells and weak, low-frequency EM fields. Specifically, we model gaps in greater detail than is usually the case, and use the finite element method (FEM) to solve the resulting geometrically complex cell models. The responses of gap-connected cell configurations to both dc and time harmonic fields are investigated and compared with those of similarly shaped (equivalent) cells. To further assess the influence of the gap junctions, properties such as gap size, shape, and conductivity are varied. Our findings indicate that simple models, such as equivalent cells, are sufficient for describing the behavior of small gap-connected cell configurations exposed to dc electric fields. With larger configurations, some adjustments to the simple models are necessary to account for the presence of the gaps. The gap junctions complicate the frequency behavior of gap-connected cell assemblies. An equivalent cell exhibits low-pass behavior. Gaps effectively add a bandstop filter in series with the low-pass behavior, thus lowering the relaxation frequency. The characteristics of this bandstop filter change with changes to gap properties. Comparison of the FEM results to those obtained with simple models indicates that more complex models are required to represent gap-connected cells.

A novel equivalent circuit model for gap-connected cells.

Gap junctions connect neighbouring cells, providing the intercellular communication that is essential for cell growth regulation, for example. There is some evidence that gap communication changes upon exposure to electromagnetic (EM) fields. In previous work, we performed detailed finite element method (FEM) modelling of gap junction connected cells exposed to EM fields. For cell configurations, the presence of gap junctions influences the transmembrane potential and its frequency behaviour. The relaxation frequency cannot be accurately predicted by previously developed simplified models. We present a novel equivalent circuit model (ECM) that incorporates more detailed models of the gaps, and compare results obtained with this ECM to finite element and leaky cable (LC) model results. Our ECM provides more accurate estimates of the frequency behaviour of cells than the leaky cable model. Also, our ECM results suggest limitations of the application of simple models to gap-connected cells: with higher gap resistivity, the current flow in the cell interiors becomes increasingly complex and is not well represented by simple models. In this case, techniques such as the finite element method are required to model accurately cell behaviour.

Biological cells with gap junctions in low-frequency electric fields.

Biological effects have been observed from weak, low-frequency magnetic fields. It has been suggested that the observed effects are due to the induced currents and electric fields. The behavior of cells exposed to an electric field is investigated in this paper. The induced transmembrane potential (TMP) is examined in geometrically complex models of various cell configurations. The TMP is evaluated using the finite element method (FEM), a numerical technique that is well suited to complicated geometries. Because displacement currents can be neglected at very low frequencies, a FEM solver that considers only material conductivity is used. Therefore, our results apply only well below the relaxation frequency. Chains and clusters of gap-connected cells of various sizes are modeled. The conductivity and size of the gap junctions in the cell configurations are also varied. The results for small configurations are compared to models of ellipsoidal cells with shapes similar to those of the configurations. FEM estimates of TMP's in long, cylindrical cell chains are compared to the predictions of the leaky cable model. The FEM approach confirms that gap-junction-connected cells can be treated as a single similarly shaped cell. Gaps influence the potential in the interior of cell configurations, and these effects increase with gap size and conductivity. For configurations to which approximations such as the leaky cable model do not apply, the FEM approach can be used to estimate the TMP, if the model is adapted to fit within computational memory limits.

Bone and joint changes in pneumatic drillers.

A clinical and radiological survey of 34 men who were pneumatic drillers employed by the North East Gas Board, was carried out to determine the prevalence of osteoarthrosis. Mild osteoarthrosis of the elbows was found in 2 subjects only. Two drillers had radiological evidence of generalized osteoarthrosis elsewhere, and minor degenerative changes were present in the hands of 15 cases. Our findings do not support the view that pneumatic drillers are particularly prone to develop osteoarthrosis.