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Rehabilitation Engineering, IEEE Transactions on

Issue 2 • Date Jun 1996

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Displaying Results 1 - 7 of 7
  • A system for the analysis of seat support surfaces using surface shape control and simultaneous measurement of applied pressures

    Page(s): 103 - 113
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1488 KB)  

    A system for the design and analysis of seat support and buttock tissue interfaces has been developed. It has the ability to control the seating surface shape while measuring the pressure applied to the buttocks by the surface. Pressures are measured over an 11×12 rectangular array of support elements using silicon pressure sensors mounted in a swiveling head atop each support element. Control of surface shape is mediated by selective linear translation of the support elements along their respective vertical axes. Closed-loop control of the system allows for the dynamic formulation of a support surface on the basis of programmable criteria. The system is intended to function as a research tool to facilitate the study of the relationships between support surface shape and interface pressure, and support surface shape and soft tissue distortion. The purpose of this paper is to present the system instrumentation and the rationale behind its design and development. The paper also presents the results of several tests to evaluate the accuracy and performance of the system. This evaluation included a pilot study on 10 able-bodied subjects. The results of these system evaluations indicate that the system is capable of making repeatable and precise measurements of pressure and surface element position and can formulate support surface shapes that satisfy specified optimization criteria View full abstract»

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  • A PC-based ultrasonic data acquisition system for computer-aided prosthetic socket design

    Page(s): 114 - 119
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    A PC-based ultrasound data acquisition system has been developed which uses compound scanning techniques to image a residual limb in a water tank. From the received ultrasonic echo data, the system produces cross-sectional images and reconstructs a three-dimensional (3-D) model of the limb. A commercial software for computer-aided prosthetic socket design was modified so that it can display both the external shape and cross-sectional image of the limb and allow the prosthetist to perform socket design with the help of a visualization of the limb's internal structure. The image resolution and measurement accuracy of the system were tested using a wire phantom and a contrast tissue mimicking phantom, respectively, preliminary results from amputee patients are presented and the sources of measurement error are discussed View full abstract»

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  • Automated hexahedral mesh generation from biomedical image data: applications in limb prosthetics

    Page(s): 91 - 102
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    A general method to generate hexahedral meshes for finite element analysis of residual limbs and similar biomedical geometries is presented. The method utilizes skeleton-based subdivision of cross-sectional domains to produce simple subdomains in which structured meshes are easily generated. Application to a below-knee residual limb and external prosthetic socket is described. The residual limb was modeled as consisting of bones, soft tissue, and skin. The prosthetic socket model comprised a socket wall with an inner liner. The geometries of these structures were defined using axial cross-sectional contour data from X-ray computed tomography, optical scanning, and mechanical surface digitization. A tubular surface representation, using B-splines to define the directrix and generator, is shown to be convenient for definition of the structure geometries. Conversion of cross-sectional data to the compact tubular surface representation is direct, and the analytical representation simplifies geometric querying and numerical optimization within the mesh generation algorithms. The element meshes remain geometrically accurate since boundary nodes are constrained to lie on the tubular surfaces. Several element meshes of increasing mesh density were generated for two residual limbs and prosthetic sockets, Convergence testing demonstrated that approximately 19 elements are required along a circumference of the residual limb surface for a simple linear elastic model. A model with the fibula absent compared with the same geometry with the fibula present showed differences suggesting higher distal stresses in the absence of the fibula. Automated hexahedral mesh generation algorithms for sliced data represent an advancement in prosthetic stress analysis since they allow rapid modeling of any given residual limb and optimization of mesh parameters View full abstract»

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  • Application of tilt sensors in functional electrical stimulation

    Page(s): 63 - 72
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    Tilt sensors, or inclinometers have been investigated for the control of functional electrical stimulation (FES) to improve the gait of persons who had a stroke or incomplete spinal cord injury (SCI). Different types of tilt sensors were studied for their characteristics and their performance in measuring the angular displacement of leg segments during gait. Signal patterns of the lower leg with inertial tilt sensors were identified with control subjects and subjects with footdrop who are being stimulated during level walking. To minimize acceleration responses when the foot swings or hits the ground, we use low-pass filtering (1.5-2 Hz). A finite state approach allows the sensor fixed on the shank to effectively detect the step intention in a population of stroke and incomplete SCI subjects and to control the FES. When the lower leg tilts backward, the common peroneal nerve is stimulated to bring the foot up and forward. We have designed a miniature footdrop stimulator with a magnetoresistive tilt sensor built in, so no external sensor cables are required. The thresholds to turn the stimulator on and off can be adjusted, as well as the maximum period of stimulation and the minimum interval between periods of stimulation. This device features several important advantages over traditional AFO's or stimulators controlled by foot switches. Initial trials with stroke and SCI subjects have demonstrated substantial gait improvement for some subjects, while most liked the good cosmesis and ease of using the device with a tilt sensor View full abstract»

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  • A portable digital speech-rate converter for hearing impairment

    Page(s): 73 - 83
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    A real-time hand-sized portable device that slows speech speed without changing the pitch is proposed for hearing impairment. By using this device, people can listen to fast speech at a comfortable speed. A combination of solid-state memory recording and real-time digital signal processing with a single chip processor enables this unique function. A simplified pitch-synchronous, time-scale-modification algorithm is proposed to minimize the complexity of the DSP operation. Unlike the traditional algorithm, this dynamic-processing algorithm reduces distortion even when the expansion rate is only just above 1. Seven out of 10 elderly hearing-impaired listeners showed improvement in a sentence recognition test when using speech-rate conversion with the largest expansion rate, although no improvement was observed in a word recognition test. Some subjects who showed large improvement had limited auditory temporal resolution, but the correlation was not significant. The results suggest that, unlike conventional hearing aids, this device can be used to overcome the deterioration of auditory ability by improving the transfer of information from short-term (echoic) memory into a more stable memory trace in the human auditory system View full abstract»

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  • Quantification of recruitment properties of multiple contact cuff electrodes

    Page(s): 49 - 62
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    Nerve-based stimulating electrodes provide the technology for advancing the function of motor system neural prostheses. The goal of this work was to measure and quantify the recruitment properties of a 12 contact spiral nerve cuff electrode. The cuff was implanted on the cat sciatic nerve trunk, which consists of at least four distinct motor fascicles, and the torque generated at the ankle joint by selective stimulation of the nerve was recorded in nine acute experiments. Comparisons of torques generated with the cuff to torques generated by selective stimulation of individual nerve branches indicated that the cuff allowed selective activation of individual nerve fascicles. Selectivity was dependent on the relative location of the electrode contacts and the nerve fascicles, as well as the size and relative spacing of neighboring fascicles. Selective stimulation of individual nerve fascicles allowed independent and graded control of dorsiflexion and plantarflexion torques in all nine experiments. Field steering currents improved selectivity as reflected by significant increases in the maximum torques that could be generated before spillover to other fascicles, significant increases in the difference between the current amplitude at spillover and the current amplitude at threshold, and significant increases in the slope of the current distance relationship View full abstract»

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  • Objective method to determine the contribution of the great toe to standing balance and preliminary observations of age-related effects

    Page(s): 84 - 90
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    The purpose of this study was to examine the relationship between toe pressure and tactile sensitivity in the great toe and to describe two newly developed measurements of postural stability. The subjects of the study were 21 healthy volunteers. The subjects were divided into two age groups, the young group (mean 21.0±1.6 years, 7 males and 6 females), and the elderly group (mean 71.4±2.8 years, 4 males and 4 females). The methods and materials used for the first experiment (balance test): The instrument for measuring standing balance was a force plate. Data were analyzed to provide two main variables: (1) body sway index (SI: mm) and (2) toe pressure (%BW/cm2). The subjects were asked to stand in a relaxed posture for 20 s. The variables of body sway were measured in four conditions: normal surface with eyes open or closed, and soft surface with eyes open or closed. Second experiment (tactile sense test): This experiment utilized a new system which was developed for measuring the tactile sensation. The tactile threshold value was measured with the subject seated in a chair, the back supported, and the hips and knees flexed at 90 degrees. The contactor pulled and pushed the toe longitudinally along its axis at a constant velocity of 1 mm/s. There were significant differences between the young and elderly groups in the tactile sense of the great toe (p<.001). No significant difference between age groups was found for postural sway while the subjects stood on the normal surface with eyes open; however, when they stood on the soft surface with their eyes open and closed, the elderly showed significantly more sway (p<0.01) than the young. Moreover, the maximal great toe pressure in the elderly group was significantly greater than that in the young group. The results suggest that the reduced tactile sense, deprivation of visual information, and toe pressure weakness are all important factors associated with postural instability View full abstract»

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Aims & Scope

This Transaction ceased publication in 2000. The current retitled publication is IEEE Transactions on Neural Systems and Rehabiliation Engineering.

Full Aims & Scope