1,721,039 research outputs found
A surface electrode array-based system for functional electrical stimulation
No full textThe goal of this thesis is to develop an electrode array-based functional electrical stimulation (FES) system for foot drop correction. The thesis reports a series of studies on the design and development of an electrode array, describes how these results informed the design of a practical array and demonstrates methods for using this array in combination with a multi-channel stimulator to appropriately steer the foot. In the first study a finite element model was used to predict the effects of electrode design on the spatial spread of stimulation selectivity in tissue underlying the cathode. The model suggested that the Imm thick hydrogel of 5000m or higher resistivity placed between the electrode array and skin can effectively maintain selectivity, when compared with the no hydrogel case. In recognition of the potential discomfort problems associated with array-based FES, two studies were carried out to investigate the effect of hydrogel properties on discomfort. Finite element modelling was used to predict the effect of hydrogel properties on current density distribution in the skin, a parameter associated with discomfort. Increasing hydrogel resistivity led to an increase in the homogeneity of current density distribution in relevant areas of the skin and a likely decrease in peak current density. A single-blinded randomised study of the effects of hydrogel resistivity on discomfort was also conducted in which the discomfort associated with stimulation through a low impedance electrode was compared with that experienced during stimulation with a high impedance electrode. The high impedance electrode allowed 9% more current to be passed for an equivalent sensation to that experienced with the low impedance electrode. A 28% decrease in discomfort with the use of the high impedance electrode was also reported. The results of the studies on electrode design informed the design of a practical electrode array, consisting of 64 small electrodes, each of which was independently controllable via a purpose-built stimulator. interfaced with the skin through a thin layer of high resistivity hydrogel. Groups of 2x2 adjacent actiYe electrodes were termed Virtual Electrodes (VEs). Two approaches were presented to find the best VE(s) based on foot response to stimulation. In the first approach foot responses during a slowly ramped increase in stimulus current to each of 49 YEs were measured to directly identify suitable VE(s) (slowly ramped stimulation). Secondly, foot responses to various short bursts of stimulation (twitch stimulation) were then used to predict the subsets containing the best VEe s) identified using the first method. 9 of the 10 subj ects required a single VE and one subj ect needed 2 YEs to steer the foot to the target orientation. It was identified that the lowest number of incorrectly identified YEs using twitch stimulation was found with a four pulse stimuli train at maximal current. As the comprehensive slowly ramped stimulation search is too slow to be used in clinical practice, a two stage process, based on an initial search using twitch stimulation, followed by a more focused ramped stimulation search, is suggested as a future approach. The work presented in the thesis was demonstrated on healthy seated subjects and hence further work is required to investigate its application for people with foot drop
The effects of Functional Electrical Stimulation on motor-cognitive interference during gait in people with foot drop following stroke
Full text linkA stroke can impair both motor and cognitive functioning, reducing the automaticity of walking and increasing susceptibility to motor-cognitive interference (MCI). There is also some evidence of an association between susceptibility to MCI and the increased incidence of falls in stroke. Functional Electrical Stimulation (FES) is commonly used for correction of foot drop due to stroke. At the start of the PhD, studies had shown FES increases walking speed. However, questionnaire-based studies found that users rated a reduction in effort and a reduced risk of tripping or falling as the two most important reasons for using FES. In these studies, the term ‘effort’ was not defined, but the results from a qualitative study suggested that the questionnaire respondents may have been referring to both physical and mental components. Based on this evidence the following research question was posed “Does FES reduce motor-cognitive interference during gait in people with foot drop following stroke?”The question was first examined in a questionnaire study which collated FES user opinion from thirty current users. Respondents identified a statistically significant reduction in concentration required when walking with FES compared with walking without the device. Furthermore, the majority noted that walking without thinking about walking was easier with FES.The second study developed and piloted a dual-task based methodology to assess the impact of FES on MCI during gait. Two participants with foot drop following stroke were evaluated over 14 weeks following first use of FES. In one participant, cognitive task performance was maintained at a similar level when walking with FES, compared with seated performance, and reduced without FES. The effects were less clear in the second participant. However, the study demonstrated the feasibility of the proposed methodology and provided the first quantitative evidence that FES can reduce MCI during gait.In the final study of the thesis, a similar methodology was used to study the effects of MCI in a larger cohort of sixteen established FES users. Outcomes suggest that although FES can reduce the motor-cognitive interference experienced during a dual-task situation in some participants, when analysed as a group, the results did not support the existence of this effect
Using magneto-inertial-measurement-units to track upper-limb movement during rehabilitation
Full text linkFunctional Electrical Stimulation (FES) can be used to support upper-limb rehabilitation after a stroke. A key aspect of FES control and also patient monitoring is the automatic tracking of upper-limb motion during intensive and functional practise of upper-limb tasks. To achieve this in a home environment, simple on-body sensors are required. A promising approach is to use Magnetic and Inertial Measurement Units (MIMUs), but they provide body-segment orientations rather than anatomical joint angles, the latter being more meaningful. To solve this problem the sensor orientation data must be interpreted anatomically, which requires that for each body-segment the orientation of its sensor coordinate frame is known with respect to its anatomical coordinate frame. Therefore, appropriate calibration must be performed to obtain the relationship between each sensor frame and its corresponding body-segment anatomical frame.While many papers have been published on anatomical calibration methods for MIMUs, there has been no comprehensive comparison of the alternative approaches to establish their relative merits. For FES supported upper-limb therapy, the need is for simple and fast donning and calibration, whilst achieving acceptable accuracy and repeatability with regards to the calculated joint kinematics. Therefore, the main objective of the PhD research was to undertake such a comparison and make recommendations for donning and calibration for the purposes of upper-limb FES.To address this problem the PhD work included:1. Undertaking a comprehensive and critical comparison of alternative anatomical calibration methods for MIMUs in terms of accuracy, speed, and simplicity.2. Finding the most appropriate anatomical calibration methods for use in upper-limb FES applications with stroke patients.3. Determining the best methods for processing MIMU outputs to provide anatomically meaningful upper-limb kinematic data.4. Experimentally assessing these methods against a gold standard (a VICON optical motion capture system).The results demonstrate that there is considerable variation between the alternative sensor defined anatomical frames and, hence, confirm the need for comprehensive comparisons. The comparisons reported in this thesis have led to tentative recommendations. Nevertheless, the methods reported are a sound foundation for future work to provide stronger recommendations, with more formal measures of confidence
Proceedings of the 1st annual conference of the UK and Republic of Ireland chapter of the International FunctionalElectrical Stimulation Society
Full text linkEvaluation of the effect of breast implants on the accuracy of the CT attenuation Correction (CTAC) map for SPECT/CT myocardial perfusion imaging: a phantom study
Full text linkBackground: Myocardial perfusion imaging (MPI) using single photon emission computedtomography (SPECT) imaging can assess myocardial viability and perfusion. However,overlying thoracic structures, such as ribs or breast tissue lead to gamma ray attenuation. Thisattenuation does not occur equally for all body regions. Photons emitted from deeper structureswill undergo more attenuation than superficial structures, causing artefacts within the imagethat can mimic pathology - such as ischaemia. Such artefacts can be removed or minimised byusing attenuation correction (AC) maps generated using computed tomography (CT). Breastimplants that have density higher than normal breast tissue, could affect the accuracy of the CTnumbers used for AC.Methods: Imaging protocols were compared with and without three sizes of breast implant, ina phantom study. The first experiment used a diagnostic CT scanner to design the method. Thesecond experiment was carried out in a clinical centre using the CT components of a SPECT/CTscanner to assess the impact of three different breast implants on CT number accuracy whenthe CTAC is applied in SPECT/CT MPI. The last experiment used a clinical SPECT/CTscanner and 99mTC as a radiotracer to mimic the clinical MPI scan.Results: The first and second experiments found that large breast implants led to a greaterdifference in CT HU and CT numbers compared to baseline, than the small or medium implants,but the differences were within the tolerance range (±5HUs). This suggested that even largebreast implants did not impact in a clinically significant way on the accuracy of CT HUs andCT numbers. However, the third experiment found that large breast implants resulted in a moresignificant difference in corrected counts and thus more overcorrection than small or mediumbreast implants.Conclusion: The study illustrates that large breast implants resulted in a greater differences inCT HUs, CT number and corrected counts than small or medium implants. Increasing the tubecurrent (mA) improves the CT HU accuracy without significant impact, apart from an increasein the radiation dose to the patient
The effect of socket design on the reliability of EMG signal transduction in trans-radial myoelectric prostheses
No full textBackground: The majority of trans-radial myoelectric prosthesis users experience some level of difficulty and disruption in the control of their prosthesis everyday (1). Previous studies by Head (1) and Chadwell et al. (2) have suggested that the fit and/or design of the socket could be a contributing factor in the disruption of prosthesis control by introducing uncertainty and motion artefacts into the control system. However, there is currently no definitive prescription criterion that determines the effect that trans-radial socket design has on myoelectric control. Aims: To investigate the effect of socket design on:the reliability of voluntary-initiated prosthetic prehensor activation and The avoidance of unwanted prosthetic prehensor activationMethods: Six participants with a trans-radial limb absence and previous experience of using a myoelectric prosthesis were recruited for the study. The user performance of three different trans-radial socket types, the UK Hybrid, Longitudinal Compression and Münster socket, were evaluated against a baseline no-socket ‘ideal’ condition (in which the electrodes are held firmly against the skin). The participants ability to control myoelectric prosthesis activation was assessed via the use of a reaction time test with the forearm in 2 orientations, each being 45° either side of the horizontal, as described by Chadwell et al (2). The frequency of unplanned activations caused by motion artefacts during these movements was determined by a goniometer situated on the prosthetic forefinger that measured the aperture of the hand, and recorded any unwanted activation. Each participant also completed a questionnaire which evaluated each socket via the following: comfort; ease of control; and overall preference. Results: The UK Hybrid had the least impact on voluntary activation of the hand for the Open Function (Difference in Spread= 15.83 (Standard Deviation of Reaction Time Socket – Standard Deviation of Reaction Time No Socket)), and also had a considerably lower standard deviation in reaction times than the no-socket condition in the close function. All three sockets caused unwanted prehensor activations in at least 65% of trials, in comparison to 30.56% of ‘ideal’ no-socket condition trials, in the functional movement tasks. Summary: The socket that produced experimental data closest to that of the ‘ideal’ was the UK Hybrid. The results suggest that the fit of the socket, rather than the specific design, is more important when creating a reliable electrode-socket interface. All participants cited the most comfortable socket as their overall preference, although this finding should be interpreted with caution
How to build better fall detection technology : a search for characteristics unique to falls and methods to robustly evaluate performance
Full text linkFalls can have severe consequences for older adults, such as bone fractures and long periods unable to get up from the ground, known as a long-lie. The capability to automatically detect falls would reduce long-lies through ensuring prompt arrival of assistance and would be valuable in fall risk assessment and fall prevention research. This research aimed to identify why existing wearable fall detection technology has not achieved acceptable performance and where further development should focus. There have been a plethora of attempts at fall detection; real-world testing is in an embryonic stage, nevertheless, it is clear performance has been poor. The focus has been on the testing of complete system performance, most commonly with acted falls, and it has been unclear how to improve performance. A new framework for the development of fall detection is proposed which promotes targeted investigation of how real-world performance can be improved. An improved method to quantify real-world performance is also proposed based on a systematic review of previous approaches. To prepare for the analysis of a real-world dataset, a pilot study was conducted which focused on the development and testing of posture classification algorithms. One of the world's largest datasets of real-world falls and activities of daily living was collected over 2 years in collaboration with 17 care homes across Scotland and the north of England. Twenty fall signals were extracted from 1,919 days of thigh-worn accelerometer recordings collected with 42 participants. Analysis of the data focused on falls from an upright to a sedentary (sitting or lying) posture, 16 falls met this criterion and were included in the analysis. To allow the data to be thoroughly checked for quality, the dataset was reduced to 104 days, from which 4,293 upright to sedentary transitions were extracted (including the 16 falls). This study was the first to: discern that falls may be too diverse to classify as a single group and focus on a subtype of fall, use posture transitions to select events for analysis, assess the importance of peak jerk and vertical velocity for fall detection, and investigate the occurrence of multiple impacts during falls. The results demonstrated that the core features used previously do not yield sufficient separation of the falls to allow detection without high rates of false positives. For the first time, it was shown that (1) a rapid increase in deceleration may be more indicative of a fall than the peak deceleration, and (2) multiple impacts occur frequently in falls but not other movements
Exploring factors associated with upper-limb prosthesis embodiment : a mixed-methods approach
Full text linkCurrent rejection rates among upper-limb prosthesis users are particularly high. A significant psychological factor associated with prosthesis use is the extent to which users feel their prosthesis is a natural part of them (termed Prosthesis Embodiment [PE]). Many researchers and clinicians suggest that encouraging PE should be an aim of rehabilitation. However, the factors influencing PE, how PE changes over the user’s lifetime, and the potential clinical consequences of PE, are currently unclear. In Study 1, in-depth qualitative email interviews were conducted with 10 upper-limb prosthesis users to explore both factors influencing and resulting from PE, via a qualitative Directed Content Analysis. Participants reported an unexpectedly wide range of both influences (e.g. type of prosthesis) and outcomes (e.g. better prosthesis proficiency). Temporary changes to PE were more noticeable to the user than a gradual change over time. These findings were then used to design a quantitative online questionnaire survey for upper-limb prosthesis users (Study 2) in order to follow-up findings in a larger sample (N = 34). In addition to statistically confirming most of the expected relationships, potential motivational and social aspects for PE emerged from the analysis. Further key findings are that PE is on a continuum rather than being dichotomous, and that satisfaction with aspects of the prosthesis (e.g., functionality) is also a major factor. An Immersive Virtual Reality (IVR) study was conducted with 31 anatomically-intact participants to explore experimentally how the prosthesis control method influences PE (Study 3). Body ownership techniques were utilised in a virtual-hand illusion paradigm, combined with motion tracking of a myoelectric prosthesis. This tested the relative impact of electromyographic (EMG) control (via muscle flexes) on virtual PE compared to anatomical-hand control. Results indicated the feeling of agency and skin conductance response to a virtual threat to the prosthesis were similar between the conditions. However, the feeling of ownership was significantly reduced with EMG control of the prosthesis, suggesting the influence of control method on PE, and may be a key factor for rejection. The results indicate there are a much greater range of influences and outcomes of PE than previously expected or explored, and that IVR prosthetic simulations may provide a method to test specific factors in a controlled setting. Understanding such factors could potentially inform prosthetic design, and ultimately aid in rehabilitation
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