Lecture 2 Chapter 4: The Origin of Biopotentials · Electroneurogram (ENG) • Measures nerve field...
Transcript of Lecture 2 Chapter 4: The Origin of Biopotentials · Electroneurogram (ENG) • Measures nerve field...
Lectu
re 2
Chapte
r 4: T
he O
rigin
of
Bio
pote
ntials
Dr.
Nitis
h V
. T
hakor
Bio
medic
al In
str
um
enta
tion
JH
U A
pplie
d P
hysic
s L
ab
Intr
od
uction
Biopotentials arise from cells, and more generally from organs. They hold rich
physiological and clinical information. For example, action potentials give
information on fundamental ion channel biophysics and molecular aspects of
any pathology. Biopotentials from the organs of the body are of clinical
diagnostic significance.
Examples:
1.Action Potentials from Cells (and 3 Nobel prizes!)
1.Neuronal action potential (history of Squid axon and Hodgkin-Huxley work)
2.Patch clamp technique and single channel recording (Sakman-Neher)
3.Water channel work of Peter Agre (JHU)
2.Biopotentials from the organ/body
1.Electrocardiogram (ECG) from heart -> use in heart attack, pacemakers
2.Electroencephalogram (EEG) from brain -> use in epilepsy, brain trauma
3.Electromyogram (EMG) from muscle -> use in muscle diseases, prosthesis
4.Others…
Ele
ctr
ical A
ctivity o
f E
xcitable
Ce
lls
•E
xcita
ble
ce
lls
–E
xis
t in
nerv
ous,
muscula
r
and g
land
ula
r tissue
–E
xh
ibit a
resting p
ote
ntial
and a
n a
ction p
ote
ntia
l
–N
ecessary
for
info
rmatio
n
transfe
r (e
.g.
sensory
info
in n
erv
ous s
yste
m o
r
coord
inatio
n o
f blo
od
pum
pin
g in
the h
eart
)
0 m
V
-70
mV
depola
rization:
Na+
influx
repola
rization:
K+
outflu
x
Na+
Ca+
+
K
+
Neuronal action potential
Cardiac action potential
repola
rization:
K+
outflu
x
Resting v
s. A
ctive S
tate
•R
esting S
tate
–S
tea
dy e
lectr
ica
l po
ten
tia
l o
f d
iffe
ren
ce
be
twe
en
in
tern
al a
nd
exte
rna
l e
nvir
on
me
nts
–T
yp
ica
lly b
etw
ee
n -
70
to
-9
0m
V,
rela
tive
to
the
exte
rna
l m
ed
ium
•A
ctive S
tate
–E
lectr
ica
l re
sp
on
se
to
ad
eq
ua
te s
tim
ula
tio
n
–C
on
sis
ts o
f “a
ll-o
r-n
on
e”
actio
n p
ote
ntia
l a
fte
r
the
ce
ll th
resh
old
po
ten
tia
l h
as b
ee
n r
ea
ch
ed
Record
ing o
f A
ction P
ote
ntial
•T
yp
ica
l
reco
rdin
g
syste
m (
top
)
usin
g
mic
roe
lectr
od
e
•R
eco
rdin
g o
f
an
actio
n
po
ten
tia
l in
ne
rve
ce
ll
(bo
tto
m)
Resting M
em
bra
ne P
ote
ntial
•C
ell
pote
ntial is
a f
unctio
n o
f m
em
bra
ne p
erm
eab
ility
and
conce
ntr
ation g
rad
ient to
various m
ole
cu
les (
i.e.
K+, N
a+,
Cl- ,
and C
a2+)
•E
qu
ilibri
um
pote
ntial is
the m
em
bra
ne p
ote
ntial at
whic
h
a g
ive
n m
ole
cule
has n
o n
et
movem
ent
acro
ss the
mem
bra
ne
–N
ern
stE
quation (
in V
olts a
t 37 o
C):
–n
is the v
ale
nce o
f K
+, [K
] iand [K
] oare
the intr
a-
and e
xtr
acellu
lar
concentr
ations, R
is the u
niv
ers
al gas c
onsta
nt, T is the a
bsolu
te
tem
pera
ture
in K
elv
in, F
is the F
ara
day c
onsta
nt, a
nd EK
is the
equili
brium
pote
ntial
io
io
K
KK
KK
nF
RT
E]
[
][
log
0615
.0
][
][
ln10
==
Resting M
em
bra
ne P
ote
ntial
•E
qu
ilib
riu
m m
em
bra
ne
re
stin
g p
ote
ntia
l w
he
n
ne
t cu
rre
nt
thro
ug
h t
he
me
mb
ran
e is z
ero
–P
is t
he p
erm
eab
ility
coeff
icie
nt
of th
e g
ive
n ion
•F
acto
rs in
flu
en
cin
g io
n f
low
acro
ss the
m
em
bra
ne
–D
iffu
sio
n g
rad
ients
–In
ward
ly-d
irecte
d e
lectr
ic fie
ld
–M
em
bra
ne s
tructu
re
–A
ctive t
ransport
of io
ns a
gain
st
ele
ctr
ochem
ical
gra
die
nt
++
++
=o
Cl
iNa
iK
iCl
oNa
oK
Cl
PNa
PK
P
Cl
PNa
PK
P
FRT
E]
[]
[]
[
][
][
][
ln
Action P
ote
ntial
•S
tim
ula
tio
n o
f e
xcita
ble
ce
lls c
au
se
s “
all-
or-
no
ne
”re
sp
on
se
•A
t th
resho
ld,
the
me
mb
ran
e p
ote
ntia
l ra
pid
ly
de
po
lari
ze
s d
ue
to a
ch
an
ge
in
me
mb
ran
e
pe
rme
ab
ility
–P
Na
sig
nific
antly incre
ases c
ausin
g t
he m
em
bra
ne
pote
ntia
l to
appro
ach E
Na
(+60m
V)
•A
de
laye
d in
cre
ase
in
PK
ca
use
s
hyp
erp
ola
riza
tio
na
nd
a r
etu
rn t
o r
estin
g
po
ten
tia
l
Action P
ote
ntial and
Ionic
Con
du
cta
nce
•g
Na
and g
Kare
the
cond
ucta
nce o
f
Na
+an
d K
+
•v
is the
mem
bra
ne
pote
ntia
l
•A
bso
lute
and
rela
tive
refr
acto
ry
peri
ods
Circuit D
iagra
m o
f M
em
bra
ne
•N
etw
ork
equiv
ale
nt
circuit
of
a s
mall
incre
me
nt
of
mem
bra
ne
•N
ote
critica
l ele
ments
: extr
ace
llula
r-in
tracellu
ar
–M
em
bra
ne c
apacitance, voltage d
ependent io
n c
hannel
conducta
nce, re
vers
e p
ote
ntial fo
r each ion c
hannel (N
a, K
, …
)
Neuro
n S
chem
atic
•C
ond
uctio
n
alo
ng a
nerv
e–
Result o
f depola
rization o
f sm
all
patc
h o
f m
em
bra
ne
–C
onduction
alo
ng a
nerv
e
fiber
(more
genera
lly a
xons
and d
endrite
s)
–S
altato
ryconduction a
long
myelin
ate
dfibers
in
nerv
es, spin
al
cord
Org
aniz
ation o
f P
eri
phe
ral N
erv
ous
Syste
m
•R
efle
x a
rc
–S
ense o
rgan (
e.g
. re
cepto
rs)
–S
ensory
nerv
e (
transfe
rs info
rmation f
rom
recepto
r to
CN
S)
–C
NS
(i.e.
info
rmation p
rocessin
g s
tation)
–M
oto
r nerv
e (
transfe
rs info
rmation f
rom
CN
S t
o
eff
ecto
rorg
an)
–E
ffecto
rO
rgan (
i.e.
muscle
s)
•S
imp
lest e
xa
mp
le
–K
ne
e r
eflex
Reflex A
rc
Org
aniz
ation o
f P
eri
phe
ral N
erv
ous
Syste
m
•Ju
nctio
na
lT
ran
sm
issio
n
–C
om
mun
ication lin
ks b
etw
een
•N
euro
ns a
nd n
euro
n c
onnte
ctions: calle
d synapses
•N
euro
ns a
nd e
ffecto
rorg
ans, calle
d end-plate region
–E
lectr
oche
mic
al tr
ansm
issio
n v
ia n
euro
transm
itte
rs:
(Inhib
itory
and E
xcitato
ry;
chem
ical, g
aseo
us)
•A
cety
lcholin
e
•G
AB
A
•G
luta
mate
•D
opam
ine
•N
itric o
xid
e Pre
synaptic r
ele
ase o
f
neuro
transm
itte
r
Posts
ynaptic c
hannel
openin
g a
nd m
em
bra
ne
depola
rization
Tra
nsm
issio
n o
f action
pote
ntial
Ele
ctr
oneuro
gra
m(E
NG
)
•M
easure
s n
erv
e f
ield
pote
ntia
ls
•U
se o
f nee
dle
ele
ctr
odes
•S
tim
ula
te the p
eri
ph
era
y
and m
easu
re t
he
cond
uctio
n v
elo
city
•U
se
d in a
ssessin
g
neuro
muscula
r dis
ord
ers
:
peri
ph
era
l nerv
e inju
ry,
muscula
r dystr
ophy
Ele
ctr
om
yogra
m(E
MG
)
•M
easure
s m
uscle
activity
•R
ecord
in
tram
uscu
larl
y
thro
ugh n
eed
le
ele
ctr
odes
•R
ecord
surf
ace
EM
G u
sin
g
ele
ctr
odes o
n
bic
eps,
tric
eps…
•U
se in m
uscula
r dis
ord
ers
, m
uscle
base
d p
rosth
esis
–pro
sth
etic a
rm, le
g
Anato
my o
f th
e H
eart
http://info
.med.y
ale
.edu/intm
ed/c
ard
io/e
cho_atlas/r
efe
rences/g
raphic
s/h
eart
_anato
my.g
if
Ele
ctr
ical B
ehavio
r of th
e H
eart
•C
ond
uctio
n
syste
m
•O
rigin
in t
he
sin
us n
od
e:
pacemaker
•A
tria
l-ve
ntr
icula
r cond
uctio
n
•C
om
ple
te E
CG
•D
isord
ers
of
pacemaker,
conduction, ion
channel
abnormalities
Taken fro
m h
ttp://m
ed.m
c.n
tu.e
du.tw
/~chenhs/c
vd/
Ele
ctr
ocard
iogra
m (
EC
G)
•M
easure
s a
ctivity o
f th
e h
eart
•S
ourc
e o
f card
iac a
ctivity: dip
ole
mode
l
–E
lectr
ical circuit r
epre
senta
tion: equiv
ale
nt genera
tor
•M
easure
ments
on b
ody s
urf
ace o
r in
tracard
iac
–P
ut ele
ctr
odes o
n the tors
o, arm
s, le
gs; cath
ete
r in
sid
e the h
eart
Card
iac v
ecto
r
-has m
agnitude
and d
irection
=>
Dip
ole
(ele
ctr
ical vecto
r
with m
agnitude
and d
irection to
the s
ourc
e)
+
-
Dip
ole
Model
•D
ipo
le r
ep
rese
nts
ele
ctr
ic a
ctivity o
f th
e h
ea
rt
•C
ha
ng
es in
th
e d
ipo
le m
ag
nitu
de
an
d o
rie
nta
tio
n
ca
use
de
tecta
ble
ch
an
ge
s in
th
e e
lectr
ic f
ield
Vecto
r A
lgebra
•D
ot
pro
duct of vecto
rs, w
here
va1
is a
scala
r voltag
e:
•W
hen t
he v
ecto
r is
perp
en
dic
ula
r to
M, v
a1
is z
ero
θcos
11
Ma
M=
⋅=
av
Ein
thoven’s
Triangle
•T
hre
e v
ecto
rs
use
d t
o fu
lly
ide
ntify
the
e
lectr
ica
l a
ctivity
–V
ecto
r show
n in
fronta
l pla
ne o
f th
e b
ody
•K
irch
ho
ff’s
law
is
use
d f
or
the
th
ree
le
ad
s
I –
II +
III
= 0
Ele
ctr
ode P
lacem
ent
Thre
e A
ugm
ente
d L
imb L
ea
ds
Tra
nsvers
e P
lane E
CG
•C
hest
lead
s u
sed t
o o
bta
in t
he E
CG
in t
he tra
nsvers
e
pla
ne
•O
bta
ins E
CG
fro
m the p
oste
rior
sid
e o
f th
e h
eart
Abnorm
al R
hyth
ms o
f th
e H
eart
•N
orm
al sin
us r
hyth
m
•C
ond
uctio
n
abn
orm
alit
ies
•A
tria
larr
hyth
mia
s
•R
ole
of
dia
gnostic/
thera
pe
utic d
evic
es
–P
acem
akers
, exte
rnal
vs. im
pla
nte
d
–P
acem
akers
:
stim
ula
te, corr
ect
conduction
abnorm
alit
ies
Abnorm
al R
hyth
ms o
f th
e H
eart
•P
VC
sare
pre
mon
itory
V
entr
icu
lar
•V
entr
icu
lar
arr
hyth
mia
s a
re
more
leth
al
•R
ole
of
dia
gnostic
monitori
ng in C
CU
•R
ole
of
thera
pe
utic
devic
es
(im
pla
nta
ble
card
iovert
er)
Atr
ial ta
chyca
rdia
Ventr
icula
r ta
ch
ycard
ia
Abnorm
al R
hyth
ms o
f th
e H
eart
•V
entr
icu
lar
Fib
rilla
tio
n is life
thre
ath
en
ing
–R
ole
of
defibrilla
tor:
exte
rnal and
impla
nte
d
•Is
chem
ic h
eart
die
ases
–R
ole
of
monitoring h
eart
dis
ease
Ele
ctr
ore
tinogra
m(E
RG
)
•B
iopote
ntia
lof th
e
eye (
retina)
•In
dic
ato
r of
retinal
dis
eases s
uch a
s
retina
l deg
enra
tio
n,
macula
r
deg
ern
atio
n
•In
vasiv
e r
ecord
ing
•R
etina
l pro
sth
esis
?
Ele
ctr
oencephalo
gra
m (
EE
G)
•A
vera
ged e
lectr
ica
l activity o
f th
e b
rain
cells
(100 b
illio
n!)
•S
yna
ptic
pote
ntia
ls:
pyra
mid
al neuro
n
str
uctu
re f
orm
s a
dip
ole
•R
ecord
ing f
rom
the
scalp
, fr
om
the
cort
ex s
urf
ace
(epile
psy),
intr
a-
cort
ex (
researc
h)
dip
ole
Avera
ged a
ctivity o
f
10e8 n
euro
ns
is v
ery
com
ple
x: in
dic
ative o
f
-sle
ep s
tage
-epile
psy
-event
rela
ted
changes
-b
rain
-com
pute
r
inte
rface???
Cere
bra
l A
nato
my Neurophysiology
of brain/cortex
-G
ross
org
an
izatio
n:
left
/rig
ht,
diffe
rent
lobs
-F
iner:
gyri a
nd
sulc
i (f
issure
s)
-La
yer
str
uctu
re (
6
layers
of
diffe
rent
types o
f ne
uro
ns
-H
om
uncu
lus:
rough o
rgan
iza
tion
of
sensory
are
as
alo
ng t
he s
ensory
-
moto
r cort
ex
Rhyth
ms o
f th
e B
rain
Different brain waves: divided by spectral
differences: 0—4 (delta), 4-8 (theta), 8-12
(alpha), 12 up (beta): delta/theta in infants,
disease; alpha: sleep; beta: awake, eyes
open
EEG in brain diesease and disorders:
Epilepsy –different types and forms
Brain injury –definition of death?
EE
G E
lectr
od
e R
ecord
ing S
yste
m
•E
EG
record
ing is
don
e u
sin
g a
sta
ndard
le
ad
syste
m c
alle
d 1
0-
20 s
yste
m
•R
ecall
dip
ole
conce
pt to
id
entify
sourc
e o
f bra
in a
ctivity
•In
tere
st in
m
app
ing s
leep
sta
ges,
site o
f seiz
ure
, and
cort
ical fu
nction
Pro
gre
ssio
n o
f E
EG
duri
ng S
leep
Clinical uses of EEG
-Sleep staging: note
different features
-e.g. REM (rapid eye
movement stage)
-Monitoring in
neurocritical care
-e.g. live/dead, coma
status
-Intraoperative monitoring
for depth of anesthesia
-e.g. changes with
anesthesia and depth
status
Refe
rence
•W
ebste
r, J
G (
1998).
M
edic
al
Instr
um
enta
tion. J
ohn W
iley &
Sons, In
c.,
New
York
, N
Y. C
hapte
r 4.
Pro
ble
ms a
nd s
elf-s
tudy
1 A
) H
odgkin
and H
uxle
y r
ece
ived a
No
bel pri
ze f
or
their w
ork
with S
quid
axo
n
to d
ecip
her
the
role
of
ion c
ha
nnels
and f
orm
ation o
f action p
ote
ntia
l.
Researc
h o
rig
inal pa
pers
an
d a
) pre
sent
gra
phic
s o
f th
eir r
ecord
ing t
echn
ique,
b)
describ
e t
he
voltage c
lam
p m
eth
od a
nd its
use,
c)
option
ally
:re
searc
h a
nd
pre
sent/
descri
be t
he v
oltag
e c
lam
p c
ircu
it
B)
Bert
Sakm
an
and E
rwin
Neher
rece
ived a
Nobe
l prize f
or
their d
eve
lopm
ent
of
a p
atc
h p
ipe
tte e
lectr
ode r
ecord
ing t
echniq
ue f
or
measure
ment
of
ion
chann
el activity.
Sho
w t
he s
chem
atic o
f a p
atc
h p
ipett
e a
ttached t
o a
) cell
and
b)
mem
bra
ne.
In e
ach c
ase,
wh
at
is t
he s
ou
rce o
f th
e c
urr
ent
bein
g
measure
d? O
ptionally
desig
n t
he p
atc
h c
lam
p c
ircuit.
C)
Dra
w t
he d
iffe
rent
ion c
ha
nnels
an
d c
urr
ents
active d
urin
g a
card
iac a
ction
pote
ntia
l. R
ese
arc
h h
ow
pace
maker
pote
ntia
l arizes (
rep
ola
rization o
f th
e
action p
ote
ntial)
, and h
ow
isch
em
ia m
ight
alte
r th
e a
ction p
ote
ntials
Atrial
signal
Ventricular
signal
3. A) You are asked to develop an experimental set up to record from rat brain cells
using microelectrodes. What precautions would you take to minimize the electrical
interference in your recording set up?
3. B) You are asked to record magnetic field from the brain. Now, brain’s magnetic field
is 10e-15 Tesla as opposed to earth’s field which is 10e-7 Tesla. What kind of sensor
would you use to record brain’s magnetic field (now, I realize that this is a long shot –
but just may be, you could figure this out)? What precautions would you take to
record this very small magnetic field from the brain in presenceof other interference?
Also, show the
pacing pulse at the
appropriate time
instant in theAtrial
and Ventricular
signals on the left.
2. A) The goal of the pacemaker is to provide an electrical pacing pulse when the
appropriate chamber of the heart is not spontaneously or sequentially not beating.
2. B) For the following recording situation, identify where you would put a
“sensing”electrode, a “pacing”electrode and what the timing of the pacing pulse
would be. That is, show the electrode (catheter) in a schematicof the heart.
4. A) What does the 12-lead ECG system comprise of (sketch the different leads)?
Is it superior or inferior to an orthogonal system (X, Y, and Z leads)? the different
leads)? Is it superior or inferior to an orthogonal system (X, Y, and Z leads)?
B) The ECG signal generating from the heart can be 6.2A) What does the 12-
lead ECG system comprise of (sketch modeled quite simply as a dipole. If a cardiac
dipole has a magnitude of 1 mV and orientation of –45owith respect to Lead I, then
calculate, using theEinthoventriangle, the magnitude of the signal in Lead I, II, and III.
Show the geometric presentation as well as the trigonometric calculations.
5. A) Imagine it is the beginning of the 20thcentury. Cardiac activity is suspected as
an electrical source inside the torso. Let us say that you were a contemporary of Prof.
Einthoven. Prof.Einthovenrecommends that to record ECG from the torso using a
triangular formulation with what you now know at three leads, I,II, and III (respectively
LA-RA, RA-LL, and LA-LL). However, you claim have a different theory of better
presenting the cardiac vector on a different lead system (for example, you prefer not
to use 3 leads arranged in the form of a triangle). Demonstrate superiority of your lead
idea. B) After Einthoven’soriginal idea, a number of solutions were suggested. One of
these was to put 6 leads (V1-V6) around the left ventricle. a) why around left
ventricle? b) for the 6 differential amplifiers, each with one input being V1..V6 what is
the other “neutral”input source?
6. A) Explain the origin of EEG signal in terms of its sources in the brain. Describe
briefly the neural generator and the electrical field/vector representation that
explains how an internal source produces an external EEG.
B) What are the advantages and disadvantages of putting EEG electrodes on the
scalp versus directly on the brain? Under what clinical condition is either
procedure recommended? What kinds of electrodes are used for direct cortical
recording? What are the design considerations? How does a neurologist identify
an epileptic spike or seizure? How does a surgeon determine where to “cut”the
brain to remove the focus?
C) What kind of a lead system would you use to record EEG from the scalp and for
localizing the source of epileptic seizure? Sketch it. Now, putting electrodes on
the scalp may not help localize the seizure focus better. Surgeons now put
electrodes directly on brain. Research direct cortical recordingof seizure and
describe/Illustrate the technology.
D) i) What instrument is used to measure the magnetic field fromthe brain?
ii) What are the possible advantages and disadvantages of the magnetic versus
electrical measurement? iii) To your knowledge, what breakthroughs in the
scientific world that have are occurred (or ought to occur?) that would make
magnetic field measurement more feasible and affordable? iv) If you had a cheap
magnetic field sensor (with a relatively lower sensitivity) available what other
biomedical application would you think of (other thanbiopotentialmeasurements).
7. A) We would like to record ECG of a fetus while in the womb.The main problem
here is that when electrodes are placed on the mother’s stomach to capture the fetal
ECG, a large maternal ECG signal pulse is also picked up. A) Draw a schematic of the
mother and her heart dipole/vector and fetus and its heart dipole/vector. Now, show
how mother’s ECG might corrupt the fetal ECG. B) How would you eliminate the
maternal ECG artifact from the stomach recording? C) Someone suggests that at the
most critical moment in labor, as the head of the fetus presentsitself first , attach the
ECG electrode to fetal scalp. Would you succeed or not in getting fetal ECG from an
electrode placed on the scalp and why/why not? D) During the time of the late stage
labor, what would be more likely to succeed –electrodes on the mother’s stomach or
an electrode on fetus’s head?
B) Show (draw) the possible current distribution between anelectrosurgicalelectrode,
body and the return ground electrode. What would be the desirable properties of the
ground reference electrode?
C) Students in the past have proposed two methods for monitoringeye movements as
a way to provide a command/control signal for a quadriplegic (e.g. eye movement
command may be used to move a cursor on the computer screen). What might be two
such methods (Hint: one is optical and other is based on biopotentials)?
Body P
ow
er!
!!
•P
ow
er
for
an
im
pla
nte
d s
tim
ula
tor
(BIO
N)
–B
att
ery
, in
duction (
rad
io f
requency)
–H
eat, c
hem
ica
l, f
low
, m
echan
ica
l, …
•W
ha
t is
yo
ur
en
erg
y t
ran
sd
uctio
n p
rin
cip
le–
What
sensor/
actu
ato
r w
ould
you u
se
–W
hat
circuit p
rincip
le?
E.g
. pie
zo->
ele
ctr
icity to p
ow
er
the s
tim
ula
tor
–W
hat
physic
al/chem
ical/ e
lectr
ochem
/optica
l princip
le?
–W
hat’s w
rong/b
ad a
bo
ut th
is (
e.g
. efflu
ent,
gas,
…)
–W
hat
kin
d o
f energ
y d
ensity y
ou c
an o
bta
in? W
hat
is
the c
onvers
ion e
ffic
iency o
f each o
f th
ese?
•R
ea
l w
orl
d e
xa
mp
les,
pa
tents
, p
rod
ucts
More
questions
•H
ow
ma
ny e
lectr
od
es/le
ad
in
a 1
2 le
ad
syste
m?
•W
ha
t a
re th
e s
ou
rce
s o
f in
terf
ere
nce
in
bio
po
ten
tia
lre
co
rdin
g?
•H
ow
do
yo
u in
cre
ase
th
e lik
elih
oo
d o
f re
co
rdin
g
eve
nt-
rela
ted
po
ten
tia
l? H
ow
do
yo
u in
cre
ase
the
sig
na
l-to
-no
ise
ra
tio
? (
ave
rag
ing
)
•R
ese
arc
h a
nd
de
scri
be
ne
uro
ch
em
ica
lse
nso
r
tech
no
log
ies