3,182 research outputs found
Artificial Human Balance Control by Calf Muscle Activation Modelling
The natural neuromuscular model has greatly inspired the development of control mechanisms in addressing the uncertainty challenges in robotic systems. Although the underpinning neural reaction of posture control remains unknown, recent studies suggest that muscle activation driven by the nervous system plays a key role in human postural responses to environmental disturbance. Given that the human calf is mainly formed by two muscles, this paper presents an integrated calf control model with the two comprising components representing the activations of the two calf muscles. The contributions of each component towards the artificial control of the calf are determined by their weights, which are carefully designed to simulate the natural biological calf. The proposed calf modelling has also been applied to robotic ankle exoskeleton control. The proposed work was validated and evaluated by both biological and engineering simulation approaches, and the experimental results revealed that the proposed model successfully performed over 92% of the muscle activation naturally made by human participants, and the actions led by the simulated ankle exoskeleton wearers were overall consistent with that by the natural biological response
Control of posture with FES systems
One of the major obstacles in restoration of functional FES supported standing in paraplegia is the lack of knowledge of a suitable control strategy. The main issue is how to integrate the purposeful actions of the non-paralysed upper body when interacting with the environment while standing, and the actions of the artificial FES control system supporting the paralyzed lower extremities. In this paper we provide a review of our approach to solving this question, which focuses on three inter-related areas: investigations of the basic mechanisms of functional postural responses in neurologically intact subjects; re-training of the residual sensory-motor activities of the upper body in paralyzed individuals; and development of closed-loop FES control systems for support of the paralyzed joints
Artificial Intelligence, Mathematical Modeling and Magnetic Resonance Imaging for Precision Medicine in Neurology and Neuroradiology
La tesi affronta la possibilità di utilizzare metodi matematici, tecniche di simulazione, teorie
fisiche riadattate e algoritmi di intelligenza artificiale per soddisfare le esigenze cliniche in
neuroradiologia e neurologia al fine di descrivere e prevedere i patterns e l’evoluzione
temporale di una malattia, nonché di supportare il processo decisionale clinico.
La tesi è suddivisa in tre parti.
La prima parte riguarda lo sviluppo di un workflow radiomico combinato con algoritmi di
Machine Learning al fine di prevedere parametri che favoriscono la descrizione quantitativa
dei cambiamenti anatomici e del coinvolgimento muscolare nei disordini neuromuscolari, con
particolare attenzione alla distrofia facioscapolo-omerale.
Il workflow proposto si basa su sequenze di risonanza magnetica convenzionali disponibili
nella maggior parte dei centri neuromuscolari e, dunque, può essere utilizzato come
strumento non invasivo per monitorare anche i più piccoli cambiamenti nei disturbi
neuromuscolari oltre che per la valutazione della progressione della malattia nel tempo.
La seconda parte riguarda l’utilizzo di un modello cinetico per descrivere la crescita tumorale
basato sugli strumenti della meccanica statistica per sistemi multi-agente e che tiene in
considerazione gli effetti delle incertezze cliniche legate alla variabilità della progressione
tumorale nei diversi pazienti. L'azione dei protocolli terapeutici è modellata come controllo
che agisce a livello microscopico modificando la natura della distribuzione risultante. Viene
mostrato come lo scenario controllato permetta di smorzare le incertezze associate alla
variabilità della dinamica tumorale. Inoltre, sono stati introdotti metodi di simulazione
numerica basati sulla formulazione stochastic Galerkin del modello cinetico sviluppato.
La terza parte si riferisce ad un progetto ancora in corso che tenta di descrivere una
porzione di cervello attraverso la teoria quantistica dei campi e di simularne il
comportamento attraverso l'implementazione di una rete neurale con una funzione di
attivazione costruita ad hoc e che simula la funzione di risposta del modello biologico
neuronale. E’ stato ottenuto che, nelle condizioni studiate, l'attività della porzione di cervello
può essere descritta fino a O(6), i.e, considerando l’interazione fino a sei campi, come un
processo gaussiano. Il framework quantistico definito può essere esteso anche al caso di un
processo non gaussiano, ovvero al caso di una teoria di campo quantistico interagente
utilizzando l’approccio della teoria wilsoniana di campo efficace.The thesis addresses the possibility of using mathematical methods, simulation techniques,
repurposed physical theories and artificial intelligence algorithms to fulfill clinical needs in
neuroradiology and neurology. The aim is to describe and to predict disease patterns and its
evolution over time as well as to support clinical decision-making processes.
The thesis is divided into three parts.
Part 1 is related to the development of a Radiomic workflow combined with Machine
Learning algorithms in order to predict parameters that quantify muscular anatomical
involvement in neuromuscular diseases, with special focus on Facioscapulohumeral
dystrophy. The proposed workflow relies on conventional Magnetic Resonance Imaging
sequences available in most neuromuscular centers and it can be used as a non-invasive
tool to monitor even fine change in neuromuscular disorders and to evaluate longitudinal
diseases’ progression over time.
Part 2 is about the description of a kinetic model for tumor growth by means of classical tools
of statistical mechanics for many-agent systems also taking into account the effects of
clinical uncertainties related to patients’ variability in tumor progression.
The action of therapeutic protocols is modeled as feedback control at the microscopic level.
The controlled scenario allows the dumping of uncertainties associated with the variability in
tumors’ dynamics. Suitable numerical methods, based on Stochastic Galerkin formulation of
the derived kinetic model, are introduced.
Part 3 refers to a still-on going project that attempts to describe a brain portion through a
quantum field theory and to simulate its behavior through the implementation of a neural
network with an ad-hoc activation function mimicking the biological neuron model response
function. Under considered conditions, the brain portion activity can be expressed up to
O(6), i.e., up to six fields interaction, as a Gaussian Process. The defined quantum field
framework may also be extended to the case of a Non-Gaussian Process behavior, or rather
to an interacting quantum field theory in a Wilsonian Effective Field theory approach
Estimation of Absolute States of Human Skeletal Muscle via Standard B-Mode Ultrasound Imaging and Deep Convolutional Neural Networks
Objective: To test automated in vivo estimation of active and passive skeletal muscle states using ultrasonic imaging. Background: Current technology (electromyography, dynamometry, shear wave imaging) provides no general, non-invasive method for online estimation of skeletal muscle states. Ultrasound (US) allows non-invasive imaging of muscle, yet current computational approaches have never achieved simultaneous extraction nor generalisation of independently varying, active and passive states. We use deep learning to investigate the generalizable content of 2D US muscle images. Method: US data synchronized with electromyography of the calf muscles, with measures of joint moment/angle were recorded from 32 healthy participants (7 female, ages: 27.5, 19-65). We extracted a region of interest of medial gastrocnemius and soleus using our prior developed accurate segmentation algorithm. From the segmented images, a deep convolutional neural network was trained to predict three absolute, driftfree, components of the neurobiomechanical state (activity, joint angle, joint moment) during experimentally designed, simultaneous, independent variation of passive (joint angle) and active (electromyography) inputs. Results: For all 32 held-out participants (16-fold cross-validation) the ankle joint angle, electromyography, and joint moment were estimated to accuracy 55±8%, 57±11%, and 46±9% respectively. Significance: With 2D US imaging, deep neural networks can encode in generalizable form, the activitylength-tension state relationship of these muscles. Observation only, low power, 2D US imaging can provide a new category of technology for non-invasive estimation of neural output, length and tension in skeletal muscle. This proof of principle has value for personalised muscle assessment in pain, injury, neurological conditions, neuropathies, myopathies and ageing
Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 145
This bibliography lists 301 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1975
Analysis of Venous Blood Flow and Deformation in the Calf under External Compression
Deep vein thrombosis (DVT) is a common post-operative complication, and a serious
threat to the patient’s general recovery. In recent years, there has been increasing
awareness of the risk of DVT in healthy individuals after prolonged immobility, such
as people taking long-period flights or sitting at a computer.
Mechanical methods of DVT prophylaxis, such as compression stockings, have
gained widespread acceptance, but the haemodynamic mechanism of their action is
still not well understood. In this study, computational modelling approaches based on
magnetic resonance (MR) images are used to (i) predict the deformation of calf and
deep veins under external compression, (ii) determine blood flow and wall shear
stress in the deep veins of the calf, and (iii) quantify the effect of external
compression on flow and wall shear stress in the deep veins.
As a first step, MR images of the calf obtained with and without external compression
were analysed, which indicated different levels of compressibility for different calf
muscle compartments. A 2D finite element model (FEM) with specifically tailored
boundary conditions for different muscle components was developed to simulate the
deformation of the calf under compression. The calf tissues were described by a linear
elastic model. The simulation results showed a good qualitative agreement with the
measurements in terms of deep vein deformation, but the area reduction predicted by
the FEM was much larger than that obtained from the MR images.
In an attempt to improve the 2D FEM, a hyperelastic material model was employed
and a finite element based non-rigid registration algorithm was developed to calculate
the bulk modulus of the calf tissues. Using subject-specific bulk modulus derived with
this method together with a hyperelastic material model, the numerical results showed
better quantitative agreement with MR measured deformations of deep veins and calf
tissues.
In order to understand the effect of external compression on flow in the deep veins,
MR imaging and real-time flow mapping were performed on 10 healthy volunteers
before and after compression. Computational fluid dynamics was then employed to
calculate the haemodynamic wall shear stress (WSS), based on the measured changes
in vessel geometry and flow waveforms. The overall results indicated that application
of the compression stocking led to a reduction in both blood flow rate and cross
sectional area of the peroneal veins in the calf, which resulted in an increase in WSS,
but the individual effects were highly variable.
Finally, a 3D fluid-structure interactions (FSI) model was developed for a segment of
the calf with realistic geometry for the calf muscle and bones but idealised geometry
for the deep vein. The hyperelastic material properties evaluated previously were
employed to describe the solid behaviours. Some predictive ability of the FSI model
was demonstrated, but further improvement and validation are still needed
Modelling human musculoskeletal functional movements using ultrasound imaging
<p>Abstract</p> <p>Background</p> <p>A widespread and fundamental assumption in the health sciences is that muscle functions are related to a wide variety of conditions, for example pain, ischemic and neurological disorder, exercise and injury. It is therefore highly desirable to study musculoskeletal contributions in clinical applications such as the treatment of muscle injuries, post-surgery evaluations, monitoring of progressive degeneration in neuromuscular disorders, and so on.</p> <p>The spatial image resolution in ultrasound systems has improved tremendously in the last few years and nowadays provides detailed information about tissue characteristics. It is now possible to study skeletal muscles in real-time during activity.</p> <p>Methods</p> <p>The ultrasound images are transformed to be congruent and are effectively compressed and stacked in order to be analysed with multivariate techniques. The method is applied to a relevant clinical orthopaedic research field, namely to describe the dynamics in the Achilles tendon and the calf during real-time movements.</p> <p>Results</p> <p>This study introduces a novel method to medical applications that can be used to examine ultrasound image sequences and to detect, visualise and quantify skeletal muscle dynamics and functions.</p> <p>Conclusions</p> <p>This new objective method is a powerful tool to use when visualising tissue activity and dynamics of musculoskeletal ultrasound registrations.</p
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