Emg article summary

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EDST - UL Ecole Doctorale des Sciences

et de Technologie Université Libanaise

“Comparison of spatial filter selectivity in surface

myoelectric signal detection: influence of the

volume conductor model”

Submitted to Dr. Sofiane Boudaoud January 28th, 2016

Sarah Hussein | Mahdi Khodor Master TIS | TIS04 Course

Summary of the Article:

D. Farina, L. Mesin, S. Martinaand, R. Merletti - Vol. 42

O U T L I N E S

State of the Art Hypothesis

Simulation Models Simulated Scenarios

Types of Spatial Filters Indexes of Selectivity

Simulation Results: Five Cases

Brief Summary Recommendations

INTRODUCTION METHODOLOGIES

RESULTS CONCLUSIONS

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2 Sarah Hussein | Mahdi Khodor Master TIS | TIS04 Course

INTRODUCTION

¨  State of The Art ¨  Hypothesis 1�


I N T R O D U C T I O NState of The Art

q  Electromyography (EMG) signal is an electrical recording of muscle activity

during voluntary contractions

q  Electrical activity of the active motor units is detected by electrode placed on

the surface of skin

q  Multiple signals from motor units produce an interfered EMG signal

q  Conductor volume act as a spatial low pass filter that blur the detected signal

q  High Selectivity Resolution (HSR) - EMG acts as a spatial high pass filter to

counteract the blurring effect


I N T R O D U C T I O NState of The Art

q  The performance of a spatial filter is measured in terms of selectivity

q  Selectivity is measured with respect to the propagation and non propagation

components of signal

q  Propagation signal components are generated by the intra-cellular action

potential (IAP) travelling along the muscle fiber

q  Non Propagation signal components are due to the generation or extinction of

IAP at the end plates and tendon junctions

q  Adding subcutaneous layers to the muscle tissue in a model cause a larger

spread of the surface potential distribution


I N T R O D U C T I O NHypothesis

“ Adding subcutaneous layers to the volume conductor may lead to different conclusions on the comparison of selectivity of spatial filters to both propagating and non-

propagating signal components”


METHODOLOGIES

¨  Simulation Models ¨  Simulated Scenarios ¨  Types of Spatial Filters ¨  Indexes of Selectivity

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M E T H O D O L O G I E SSimulation Models (1)

q  The signal generation is considered as it is from a limb and a sphincter muscle

q  The geometric model used for volume conductor is a multi-layered cylinder q  The simulated model is of a finite-length of 250 mm and a width of 100 mm


01 02 03

M E T H O D O L O G I E SSimulation Models (2)

BONE - MUSCLE BONE – MUSCLE - FAT BONE – MUSCLE – FAT - SKIN

Three simulation models are adopted :


M E T H O D O L O G I E SSimulated Scenarios

Bone (isotropic)

Muscle (anisotropic) Fat layer (isotropic) Skin Layer (isotropic)

VC model C, S/m Radius, mm C, S/m

Thickness, mm C, S/m

Thickness, mm C, S/m

Thickness, mm

1 0.02 20 0.1; 0.5 30 0.05 NP NP NP

2 0.02 20 0.1; 0.5 29 0.05 1 NP NP

3 0.02 20 0.1; 0.5 28 0.05 1 1 1

4 0.02 20 0.1; 0.5 28 0.05 1 0.5 1

5 0.02 20 0.1; 0.5 28 0.05 1 0.1 1

6 0.02 20 0.1; 0.5 27 0.05 3 NP NP

7 0.02 20 0.1; 0.5 26 0.05 3 1 1

8 0.02 20 0.1; 0.5 26 0.05 3 0.5 1

9 0.02 20 0.1; 0.5 26 0.05 3 0.1 1

10 0.02 20 0.1; 0.5 25 0.05 5 NP NP

11 0.02 20 0.1; 0.5 24 0.05 5 1 1

12 0.02 20 0.1; 0.5 24 0.05 5 0.5 1

13 0.02 20 0.1; 0.5 24 0.05 5 0.1 1


01 02 03

M E T H O D O L O G I E STypes of Spatial Filters

LONGITUDINAL DOUBLE DIFFERENTIAL

LONGITUDINAL SINGLE DIFFERENTIAL

NORMAL DOUBLE DIFFERENTIAL

Three types of spatial filters are compared :


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M E T H O D O L O G I E SSelectivity Indexes

DEPTH SELECTIVITY (DS)

TRANSVERSE SELECTIVITY (TS)

LONGITUDINAL SELECTIVITY (BT)

% of pk-to-pk signal amplitude between superficial and deeper source

% of pk-to-pk signal a m p l i t u d e f r o m a transversal ly distant source with respect to a source located under the detection system

The temporal support of the simulated potential: the normalized 2nd order central moment of the square of recorded signal

Three indexes of selectivity are assessed :


RESULTS

¨  Case 1 ¨  Case 2 ¨  Case 3 ¨  Case 4 ¨  Case 5

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R E S U L T SCase 1: Potential signals for NDD & LDD at different transverse distances

with fiber semi-length of 50 mm & depth of l mm within muscle for 2 anatomies

Anatomy 1 Anatomy 1 : Bone-Muscle

✓  Inverse polarity of NDD signals ✓  High signal attenuation with

distance for both NDD and LDD

Anatomy 2: Bone-Muscle-Fat-Skin

✓  No inverse polarity of NDD signals

✓  Low signal attenuation with

distance for NDD & much lower for LDD


R E S U L T SCase 2: Relative weight of propagating and non-propagating signal components (PNP) for the 3 filters on a fiber with semi-length 30 mm of among 13 anatomies and for 2 different

transverse distances for superficial and deeper depth of fiber within the muscle

Anatomy 1

✓  I n bone-musc le - fa t -h igh ly conductive skin, LSD is worst than LDD (PNP 160% Vs. 280%)

✓  With bone-muscle model, LSD is

worse than LDD & NDD

Deeper Depth (5 mm)

anatomies

anatomies

✓  In bone-muscle-thicker fat-low conductive skin, LDD & NDD have same performance higher than LSD (PNP 300% Vs. 150%)

✓  Same conclusion of LSD for

bone-muscle model

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Superficial Depth (1 mm)

Master TIS | TIS04 Course

R E S U L T SCase 3: Selectivity in depth direction (DS) for the 3 filters among 13 anatomies and for 2

different transverse distances for propagating components on superficial and non-propagating components on different fiber semi-lengths deeper depth of fiber within the

muscle and for 2 fiber semi-lengths Anatomy 1

✓  General decrease in selectivity when isotropic layers are added

✓  The performance of 3 filters not affected by the anatomy

Non-Propagating Components on Deeper Depth – SL =30 mm

anatomies

anatomies

✓  NDD is less selective w.r.t. these components than LDD and LSD

✓  LSD selectivity w.r.t. LDD depend on the description of the VC ( anatomies 5, 7 and 11)

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Propagating Components on Superficial Depth – SL = 50 mm

R E S U L T SCase 4: Selectivity in Transverse direction (TS) (0° and 10°) for the 3 filters on a fiber of 1 mm depth within muscle among 13 anatomies and for 2 different transverse distances for fibers of

2 different semi-lengths

Anatomy 1

✓  The 3 filter’s performance is the same with some anatomies (ex.1)

✓  Their performance is different for

other anatomies (ex. 11)

Non-Propagating Components Fiber Semi-Length = 30 mm

anatomies

✓  LSD, LDD and NDD show similar p e r f o r m a n c e w i t h s o m e anatomies (ex.1)

✓  Their performance is different for other anatomies (ex. 11)

anatomies

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Propagating Components Fiber Semi-Length = 50 mm

R E S U L T SCase 5: Selectivity in Longitudinal direction (BT) for the 3 filters on a fiber with semi-length of

50 mm among 13 anatomies and for 2 different transverse distances for superficial and deeper depth of fiber within the muscle

Anatomy 1

✓  For the bone-muscle model, LDD potentials have longer duration than NDD and LSD

✓  LSD has longer potentials than

LDD & NDD for other volume conductor descriptions

Deeper Depth (5 mm)

anatomies

✓  The duration of the potentials increases

✓  LSD a lways shows longer potentials than LDD & NDD

anatomies

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Superficial Depth (1 mm)

CONCLUSIONS

¨  Brief Summary ¨  Recommendations 4�


C O N C L U S I O N SBrief Summary

q  The Selectivity of filter differ from an anatomy to another

q  A spatial filter is more or less selective depending on the conductor volume and

the different conductivity of layers

q  Adding subcutaneous layers to the volume conductor lead to different

conclusions on the comparison of selectivity of spatial filters to both propagating

and non- propagating signal components à Hypothesis proved!


C O N C L U S I O N SRecommendations

q  The volume of conductor is not the same among people

q  The EMG signal modeling is very crucial and complicated

q  Filter designs should be accompanied by experimental validations and

simulation-based test of performance


THANK YOU

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Engineering

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