Medical & biological engineering & computing
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Med Biol Eng Comput · Jul 2011
EditorialEffectiveness of medical equipment donations to improve health systems: how much medical equipment is broken in the developing world?
It is often said that most of the medical equipment in the developing world is broken with estimates ranging up to 96% out of service. But there is little documented evidence to support these statements. We wanted to quantify the amount of medical equipment that was out of service in resource poor health settings and identify possible causes. ⋯ An average of 38.3% (42,925, range across countries: 0.83-47%) in developing countries was out of service. The three main causes were lack of training, health technology management, and infrastructure. We hope that the findings will help biomedical engineers with their efforts toward effective designs for the developing world and NGO's with efforts to design effective healthcare interventions.
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Med Biol Eng Comput · Apr 2011
Spinal cord direct current stimulation: finite element analysis of the electric field and current density.
Applied low-intensity direct current (DC) stimulates and directs axonal growth in models of spinal cord injury (SCI) and may have therapeutic value in humans. Using higher electric strengths will probably increase the beneficial effects, but this faces the risk of tissue damage by electricity or toxic reactions at the electrode-tissue interface. To inform the optimisation of DC-based therapeutics, we developed a finite element model (FEM) of the human cervical spine and calculated the electric fields (EFs) and current densities produced by electrodes of different size, geometry and location. ⋯ Uniformly distributed EFs were obtained with five disc electrodes placed around the dura mater, but not with a paddle-type electrode placed in the dorsal epidural space. Replacing the five disc electrodes by a single, large band electrode yielded EFs > 5 mV/mm with relatively low current density (2.5 μA/mm(2)) applied. With further optimisation, epidural, single-band electrodes might enhance the effectiveness of spinal cord DC stimulation.
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Med Biol Eng Comput · Apr 2011
Estimating nerve excitation thresholds to cutaneous electrical stimulation by finite element modeling combined with a stochastic branching nerve fiber model.
Electrical stimulation of cutaneous tissue through surface electrodes is an often used method for evoking experimental pain. However, at painful intensities both non-nociceptive Aβ-fibers and nociceptive Aδ- and C-fibers may be activated by the electrical stimulation. This study proposes a finite element (FE) model of the extracellular potential and stochastic branching fiber model of the afferent fiber excitation thresholds. ⋯ The excitation thresholds of the Aδ-fibers were lower than the excitation thresholds of Aβ-fibers when current was applied through small, but not large electrodes. The experimentally assessed perception threshold followed the lowest excitation threshold of the modeled fibers. The model confirms that preferential excitation of Aδ-fibers may be achieved by small electrode stimulation due to higher current density in the dermoepidermal junction.
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Med Biol Eng Comput · Feb 2011
Conduction block of whole nerve without onset firing using combined high frequency and direct current.
This study investigates a novel technique for blocking a nerve using a combination of direct and high frequency alternating currents (HFAC). HFAC can produce a fast acting and reversible conduction block, but cause intense firing at the onset of current delivery. We hypothesized that a direct current (DC) block could be used for a very brief period in combination with HFAC to block the onset firing, and thus establish a nerve conduction block which does not transmit onset response firing to an end organ. ⋯ Ramped DC waveforms allowed for conduction block without nerve activation; however, down ramps were more reliable than up ramps. The degree of nerve activity was found to have a non-monotonic relationship with up ramp time. Block of the onset response resulting from 40 kHz current using DC was achieved in each of the six animals in which it was attempted; however, DC was found to produce a prolonged conduction failure that likely resulted from nerve damage.
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Med Biol Eng Comput · Feb 2011
Three-dimensional reconstruction of cranial defect using active contour model and image registration.
In neurosurgery, cranial incisions during craniotomy can be recovered by cranioplasty--a surgical operation using cranial implants to repair skull defects. However, surgeons often encounter difficulties when grafting prefabricated cranial plates into defective areas, since a perfect match to the cranial incision is difficult to achieve. Previous studies using mirroring technique, surface interpolation, or deformed template had limitations in skull reconstruction to match the patient's original appearance. ⋯ Finally, mesh smoothing refined the three-dimensional model of the cranial defect. Simulation results indicate that the reconstruction was 93.94% accurate for a 20% skull material removal, and 97.76% accurate for 40% skull material removal. Experimental results demonstrate that the proposed algorithm effectively creates a customized implant, which can readily be used in cranioplasty.