IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Sep 2009
Atlas-based segmentation of degenerated lumbar intervertebral discs from MR images of the spine.
Intervertebral disc degeneration is an age-associated condition related to chronic back pain, while its consequences are responsible for over 90 % of spine surgical procedures. In clinical practice, MRI is the modality of reference for diagnosing disc degeneration. In this study, we worked toward 2-D semiautomatic segmentation of both normal and degenerated lumbar intervertebral discs from T2-weighted midsagittal MR images of the spine. ⋯ The dice similarity indexes of this method were 91.6 % for normal and 87.2 % for degenerated discs. Research in progress utilizes the proposed approach as part of a computer-aided diagnosis system for quantification and characterization of disc degeneration severity. Moreover, this approach could be exploited in computer-assisted spine surgery.
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IEEE Trans Biomed Eng · Sep 2009
Does the estimation of light attenuation in tissue increase the accuracy of reflectance pulse oximetry at low oxygen saturations in vivo?
A new technique was validated in vivo in reflectance pulse oximetry for measuring low oxygen saturations. Two pairs of light emitter/detector diodes allow for estimation of light attenuation (LA) in tissue, which is assumed to be responsible for the inaccuracy of pulse oximetry at less than 70 % arterial oxygen saturation. For validation, 17 newborn piglets were desaturated stepwise from 21 % to 1.25 % inspiratory oxygen concentration during general anesthesia, and arterial oxygen saturation was measured with the reflectance pulse oximeter adjusted for LA in tissue, with a standard transmission pulse oximeter and a hemoximeter. ⋯ From 2 % to 100 % arterial oxygen saturation, the reflectance pulse oximeter estimated oxyhemoglobin saturation more accurately than a conventional transmission pulse oximeter (p < 0.05). At low oxygen saturations below 70 %, the bias and variability of the reflectance pulse oximeter calibration were closer to the hemoximeter measurements than the transmission pulse oximeter (p < 0.05). The variability of the reflectance pulse oximeter was slightly lower than the traditional oximeter by taking into account the LA in tissue (9 % versus 11 % -15 %, ns), and thus, the quality of the individual calibration lines improved (correlation coefficient, p < 0.05).
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IEEE Trans Biomed Eng · Sep 2009
Biophysical model of an auditory nerve fiber with a novel adaptation component.
Recent data from feline auditory nerve fibers (ANFs) indicate that electrically stimulated fibers can undergo large degrees of rate adaptation to pulse-train stimuli using pulse rates within the range used by clinical auditory prostheses. However, the application of Hodgkin-Huxley-type models does not produce such adaptation, which occurs over time periods on the order of 100 ms. ⋯ This relatively simple and computationally tractable approach produces poststimulus time histograms that are similar to experimental (cat) data. Furthermore, this mechanism could be easily incorporated into other models to produce much more realistic estimates of the neural coding produced by repeated electric stimulation.
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IEEE Trans Biomed Eng · Sep 2009
Muscle stimulation waveform timing patterns for upper and lower leg muscle groups to increase muscular endurance in functional electrical stimulation pedaling using a forward dynamic model.
Functional electrical stimulation (FES) of pedaling provides a means by which individuals with spinal cord injury can obtain cardiorespiratory exercise. However, the early onset of muscle fatigue is a limiting factor in the cardiorespiratory exercise obtained while pedaling an FES ergometer. One objective of this study was to determine muscle excitation timing patterns to increase muscle endurance in FES pedaling for three upper leg muscle groups and to compare these timing patterns to those used in a commercially available FES ergometer. ⋯ The lower leg muscle group did not generate sufficient mechanical energy to reduce the energy contributions of the upper leg muscle groups. The computed stimulation on and off times could prolong FES pedaling, and thereby provide improved cardiorespiratory and muscle training outcomes for individuals with spinal cord injury. Including the lower leg muscle group in FES pedaling could increase cardiorespiratory demand while not affecting the endurance of the muscles involved in the pedaling task.