1
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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INTRODUCTION
¨ State of The Art ¨ Hypothesis 1�
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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
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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
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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”
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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
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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 :
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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
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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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01 02 03
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 :
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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
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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)
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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�
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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!
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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
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