In the bidomain model, two alternative sets of boundary conditions at the interface between cardiac tissue and a saline bath have been used. It is shown that these boundary conditions are equivalent if the length cons...
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In the bidomain model, two alternative sets of boundary conditions at the interface between cardiac tissue and a saline bath have been used. It is shown that these boundary conditions are equivalent if the length constant of the tissue in the direction transverse to the fibers is much larger than the radius of the individual cardiac cells. If this is not the case, the relative merits of the two boundary conditions are closely related to the question of the applicability of a continuum model, such as the bidomain model, to describe a discrete multicellular tissue.
A model of electromagnetic stimulation predicts the transmembrane potential distribution along a myelinated nerve axon and the volume of stimulated tissue within a limb. Threshold stimulus strength is shown to be inve...
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A model of electromagnetic stimulation predicts the transmembrane potential distribution along a myelinated nerve axon and the volume of stimulated tissue within a limb. Threshold stimulus strength is shown to be inversely proportional to the square of the axon diameter. It is inversely proportional to pulse duration for short pulses and independent of pulse duration for long ones. These results are also predicted by dimensional analysis. Two dimensionless numbers, S(em), the ratio of the induced transmembrane potential to the axon's threshold potential, and T(c)/T, the ratio of the pulse duration to the membrane time constant, summarise the dependence of threshold stimulus strength on pulse duration and axon diameter.
Recent developments in the use of magnetic resonance (MR) to measure and image diffusion and blood microcirculation ("perfusion") are summarized. After a brief description of the effects of diffusion and per...
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Recent developments in the use of magnetic resonance (MR) to measure and image diffusion and blood microcirculation ("perfusion") are summarized. After a brief description of the effects of diffusion and perfusion on the MR signal, the different methods (conventional spin-echo, stimulated-echo, gradient-echo, and echo-planar imaging) that have been proposed and used to image and measure diffusion and perfusion by gradient sensitization are presented, along with their advantages and limitations. The difficulties of diffusion/perfusion imaging related to both hardware and software are then discussed. Special attention is given to specific problems encountered with in vivo studies and data analysis. Finally, the potential biologic and clinical applications are outlined, and some examples are presented.
We have developed a PC based light monitoring system for use during intra-operative photo-dynamic therapy for plueral, intraperitoneal, and bladder malignancies. The system provides for storage and application of two ...
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