Aikaterini D. Koutsou

Review of Hybrid Exoskeletons to Restore Gait Following Spinal Cord Injury

Different approaches are available to compensate gait in persons with spinal cord injury, including passive orthoses, functional electrical stimulation (FES), and robotic exoskeletons. However, several drawbacks arise from each specific approach. Orthotic gait is energy-demanding for the user and functionally ineffective. FES uses the muscles as natural actuators to generate gait, providing not only functional but also psychological benefits to the users. However, disadvantages are also related to the early appearance of muscle fatigue and the control of joint trajectories. Robotic exoskeletons that provide joint moment compensation or substitution to the body during walking have been developed in recent years. Significant advances have been achieved, but the technology itself is not mature yet because of many limitations related to both physical and cognitive interaction as well as portability and energy-management issues. Meanwhile, the combination of FES technology and exoskeletons has emerged as a promising approach to both gait compensation and rehabilitation, bringing together technologies, methods, and rehabilitation principles that can overcome the drawbacks of each individual approach. This article presents an overview of hybrid lower-limb exoskeletons, related technologies, and advances in actuation and control systems. Also, we highlight the functional assessment of individuals with spinal cord injury.

Preliminary Localization Results With An RFID Based Indoor Guiding System

This paper reports preliminary work with an RFID based local positioning system (LPS) designed for location and guidance of people and autonomous vehicles in indoor environments. The system consists of an RF reader carried by the mobile user, and a number of active RFID tags, disseminated at known positions in the displacement region, which regularly emit RF signals with an identification code. Upon reception of a signal, the range of the user to the corresponding tag is estimated indirectly from the received signal strength (RSSI), using a previously obtained statistical model. A computationally efficient Bayesian localization method (particle filter) is used to process the measurements and produce an estimation of the users position. The RFID-LPS is tested empirically in a displacement region comprised of three adjacent rooms, with a total area of 250 m2, in which there are placed 21 tags. Our first results show a typical mean positioning error of 3.25 m, which compares favorably with other systems reported in the literature.

Customizable field airborne ultrasonic transducers based on electromechanical film

In this work we empirically show that the Emfit film can be stuck on a curved surface without influencing its original electromechanical performance. This characteristic along with the previously reported piston-like response of the film at frequencies below 150 kHz, opens up the possibility to fabricate ultrasonic transducers of complex developable substrate and subsequently, customizable acoustic field. As a first step to complex acoustic directivity patterns, a quasi-spherical substrate is proposed in order to customize an omnidirectional radiation field. Numerical simulations were used in order to show that such an omnidirectional radiation directivity pattern can be approximated by an Emfit based transducer stuck on a quasi-spherical substrate. This works shows preliminary efforts directing to build an omnidirectional, spherical ultrasonic transducer, based on Emfit film.

Advances in selective activation of muscles for non-invasive motor neuroprostheses

Non-invasive neuroprosthetic (NP) technologies for movement compensation and rehabilitation remain with challenges for their clinical application. Two of those major challenges are selective activation of muscles and fatigue management. This review discusses how electrode arrays improve the efficiency and selectivity of functional electrical stimulation (FES) applied via transcutaneous electrodes. In this paper we review the principles and achievements during the last decade on techniques for artificial motor unit recruitment to improve the selective activation of muscles. We review the key factors affecting the outcome of muscle force production via multi-pad transcutaneous electrical stimulation and discuss how stimulation parameters can be set to optimize external activation of body segments. A detailed review of existing electrode array systems proposed by different research teams is also provided. Furthermore, a review of the targeted applications of existing electrode arrays for control of upper and lower limb NPs is provided. Eventually, last section demonstrates the potential of electrode arrays to overcome the major challenges of NPs for compensation and rehabilitation of patient-specific impairments.

Robust regression applied to ultrasound location systems

Local positioning systems (LPS), specially those using ultrasound, are able to accurately estimate the location of persons or objects indoors. However, under certain circumstances, its accuracy can be strongly deteriorated by outlying noise. This paper analyzes and compares several strategies for robust trilateration, such as high-breakdown-point robust methodologies, as well as the parity space outlier detection procedure, which is commonly used in GPS. This analysis is performed by simulation in a typical ultrasound location system scenario based on the actual location of nodes in the 3D-LOCUS system [1]. It is shown how the traditional parity space outlier detection method overcomes robust methodologies when only one ranging error is present, whereas it is not able to detect two simultaneous faults. It is proposed a modification of the LTS robust estimation methodology that offers a good performance even when several range measurements are erroneous, due to multipath and occlusions effects. The complexity of the robust algorithms studied is low enough for being implemented in the 3D-LOCUS system without affecting its current 10 Hz update rate.

Knee Muscle Fatigue Estimation during Isometric Artificially Elicited Contractions in Incomplete Spinal Cord Injured Subjects

Muscle fatigue due to functional electrical stimulation still prevents its widespread use as a gait rehabilitation tool for Spinal Cord Injured subjects. Although there is an active research towards optimization of pulse parameters to delay muscle fatigue, changes in stimulated muscle’s performance during repeated contractions due to fatigue have not been yet determined. A study of muscle fatigue of knee extensors and flexors of incomplete SCI during isometric contractions is presented. The outcome of this study is the proposal of objective criteria for detecting muscle fatigue from initial changes has been extracted. Also a comparison between flexors and extensors knee muscle fatigue models is given.

Design and validation of a neuroprosthesis for the treatment of upper limb tremor

Pathological tremor is the most prevalent movement disorder. In spite of the existence of various treatments for it, tremor poses a functional problem to a large proportion of patients. This paper presents the design and implementation of a novel neuroprosthesis for tremor management. The paper starts by reviewing a series of design criteria that were established after analyzing users needs and the expected functionality of the system. Then, it summarizes the design of the neuroprosthesis, which was built to meet the criteria defined previously. Experimental results with a representative group of 12 patients show that the neuroprosthesis provided significant (p <; 0.001) and systematic tremor attenuation (in average 52.33 ± 25.48 %), and encourage its functional evaluation as a potential new treatment for tremor in a large cohort of patients.

Upper Limb Neuroprostheses: Recent Advances and Future Directions

This review covers the main issues related to the various therapeutic modalities that aim to immediately recover the lost/diminished motor function or resulting carryover effects in patients after a central nervous system lesion caused by injury or disease. The presentation concentrates on upper extremities; yet, most therapeutic modalities are appropriate and applicable for the lower extremities. We critically present the state-of-the-art of methods used for indirect and direct stimulation of the central nervous system, stimulation of peripheral sensory-motor systems, the use of exoskeleton and other robotic platforms for rehabilitation, and the combination of robotic and stimulation systems. The review summarizes who could benefit from the new technologies and what the limitations of the neuroprostheses available today are. We illustrate the methodology by 2 examples: a patient after spinal cord injury and a patient suffering from tremors. These examples were selected to show that the current development of technologies and improved knowledge from the life sciences open new horizons. The message to take home is that an improved therapy that applies the appropriate therapy at the right time after the injury has the chance to improve the quality of life of many humans that become victims due to accidents, lifestyle, and many other reasons. The other message that must be the motto of clinicians and researchers is: Get a smile and a happy face back to the patient.

The Rehabot-Knee Project Approach for Recovery of Neuromuscular Control of the Knee With Controllable Braces

OBJECTIVE The Rehabot-Knee Project investigates the application of muscular estimulation to provide strength to the knee with computer-controlled braces. Such approach has been focused to the application of different types of electrical pulses to produce automated isometric contraction. The Rehabot-Knee Project develops robotic knee braces that in real-time analyze the kinetic, kinematic and neuromuscular variables that relate to the unilateral knee stability, and apply surface electrical stimulation to the muscles.

Does Anode Position and Electrode Impedance Affect Muscle Selectivity in Upper Limb sFES

Muscle selectivity during sFES in upper limb is an issue because of the presence of the “overflow” phenomenon. Surface electrodes array can augment muscle selectivity by generating an irregular electric field under their surface. A study on a) the influence of the anode electrode position factor and b) the impedance of the hydrogel membrane of the electrode array factor to muscle selectivity was made. A platform consisted of a garment with incorporated kinematic sensors and a multi-channel sFES system with an electrode array was used. We concluded that muscle selectivity is correlated to the anode position and the impedance of the hydrogel membrane.