Emg article summary

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 METHODOLOGIE
S
RESULTS CONCLUSIONS
1 2 3 4
2

INTRODUCTION
¨  State of The Art
¨  Hypothesis
1
3

I N T R O D U C T I O N
State 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
4

State 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
5

Hypothesis
“ 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”
6

METHODOLOGIES
¨  Simulation Models
¨  Simulated Scenarios
¨  Types of Spatial Filters
¨  Indexes of Selectivity
2
7

M E T H O D O L O G I E S
Simulation 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
8

01 02 03
Simulation Models (2)
BONE - MUSCLE BONE – MUSCLE - FAT BONE – MUSCLE – FAT - SKIN
Three simulation models are adopted :
9

Simulated 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
Types of Spatial Filters
LONGITUDINAL
DOUBLE DIFFERENTIAL
LONGITUDINAL
SINGLE DIFFERENTIAL
NORMAL DOUBLE
DIFFERENTIAL
Three types of spatial filters are compared :

01 02 03
Selectivity 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
transversally 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
3

R E S U L T S
Case 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 1Anatomy 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 S
Case 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
✓  In bone-muscle-fat-highly
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
Superficial Depth (1 mm)
Master TIS | TIS04 Course

R E S U L T S
Case 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)
Propagating Components on
Superficial Depth – SL = 50 mm

R E S U L T S
Case 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
Propagating Components
Fiber Semi-Length = 50 mm

R E S U L T S
Case 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 always shows longer
potentials than LDD & NDD
anatomies
Superficial Depth (1 mm)

CONCLUSIONS
¨  Brief Summary
¨  Recommendations
4

C O N C L U S I O N S
Brief 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 S
Recommendations
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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