<s>
Elastography	B-Algorithm
is	O
any	O
of	O
a	O
class	O
of	O
medical	B-Application
imaging	I-Application
modalities	O
that	O
map	O
the	O
elastic	O
properties	O
and	O
stiffness	B-Algorithm
of	O
soft	O
tissue	O
.	O
</s>
<s>
The	O
most	O
prominent	O
techniques	O
use	O
ultrasound	B-Application
or	O
magnetic	O
resonance	O
imaging	O
(	O
MRI	B-Algorithm
)	O
to	O
make	O
both	O
the	O
stiffness	B-Algorithm
map	O
and	O
an	O
anatomical	O
image	O
for	O
comparison	O
.	O
</s>
<s>
Palpation	O
is	O
the	O
practice	O
of	O
feeling	O
the	O
stiffness	B-Algorithm
of	O
a	O
person	O
's	O
or	O
animal	O
's	O
tissues	O
with	O
the	O
health	O
practitioner	O
's	O
hands	O
.	O
</s>
<s>
Elastography	B-Algorithm
,	O
the	O
measurement	O
of	O
tissue	O
stiffness	B-Algorithm
,	O
seeks	O
to	O
address	O
these	O
challenges	O
.	O
</s>
<s>
Elastographic	O
techniques	O
use	O
ultrasound	B-Application
,	O
magnetic	O
resonance	O
imaging	O
(	O
MRI	B-Algorithm
)	O
and	O
pressure/stress	O
sensors	O
in	O
tactile	B-Algorithm
imaging	I-Algorithm
(	O
TI	O
)	O
using	O
tactile	O
sensor(s )	O
.	O
</s>
<s>
In	O
most	O
cases	O
,	O
the	O
result	O
is	O
displayed	O
to	O
the	O
operator	O
along	O
with	O
a	O
conventional	O
image	O
of	O
the	O
tissue	O
,	O
which	O
shows	O
where	O
in	O
the	O
tissue	O
the	O
different	O
stiffness	B-Algorithm
values	O
occur	O
.	O
</s>
<s>
Once	O
the	O
response	O
has	O
been	O
observed	O
,	O
the	O
stiffness	B-Algorithm
can	O
be	O
calculated	O
from	O
it	O
.	O
</s>
<s>
Most	O
elastography	B-Algorithm
techniques	O
find	O
the	O
stiffness	B-Algorithm
of	O
tissue	O
based	O
on	O
one	O
of	O
two	O
main	O
principles	O
:	O
</s>
<s>
Some	O
techniques	O
will	O
simply	O
display	O
the	O
distortion	O
and/or	O
response	O
,	O
or	O
the	O
wave	O
speed	O
to	O
the	O
operator	O
,	O
while	O
others	O
will	O
compute	O
the	O
stiffness	B-Algorithm
(	O
specifically	O
the	O
Young	O
's	O
modulus	O
or	O
similar	O
shear	O
modulus	O
)	O
and	O
display	O
that	O
instead	O
.	O
</s>
<s>
There	O
are	O
a	O
great	O
many	O
ultrasound	B-Application
elastographic	O
techniques	O
.	O
</s>
<s>
Quasistatic	O
elastography	B-Algorithm
(	O
sometimes	O
called	O
simply	O
'	O
elastography	B-Algorithm
 '	O
for	O
historical	O
reasons	O
)	O
is	O
one	O
of	O
the	O
earliest	O
elastography	B-Algorithm
techniques	O
.	O
</s>
<s>
In	O
this	O
technique	O
,	O
an	O
external	O
compression	O
is	O
applied	O
to	O
tissue	O
,	O
and	O
the	O
ultrasound	B-Application
images	O
before	O
and	O
after	O
the	O
compression	O
are	O
compared	O
.	O
</s>
<s>
From	O
the	O
relative	O
distortion	O
image	O
,	O
however	O
,	O
making	O
a	O
quantitative	O
stiffness	B-Algorithm
map	O
is	O
often	O
desired	O
.	O
</s>
<s>
Acoustic	O
radiation	O
force	O
impulse	O
imaging	O
(	O
ARFI	O
)	O
uses	O
ultrasound	B-Application
to	O
create	O
a	O
qualitative	O
2-D	O
map	O
of	O
tissue	O
stiffness	B-Algorithm
.	O
</s>
<s>
It	O
does	O
so	O
by	O
creating	O
a	O
'	O
push	O
 '	O
inside	O
the	O
tissue	O
using	O
the	O
acoustic	O
radiation	O
force	O
from	O
a	O
focused	O
ultrasound	B-Application
beam	O
.	O
</s>
<s>
The	O
amount	O
the	O
tissue	O
along	O
the	O
axis	O
of	O
the	O
beam	O
is	O
pushed	O
down	O
is	O
reflective	O
of	O
tissue	O
stiffness	B-Algorithm
;	O
softer	O
tissue	O
is	O
more	O
easily	O
pushed	O
than	O
stiffer	O
tissue	O
.	O
</s>
<s>
ARFI	O
shows	O
a	O
qualitative	O
stiffness	B-Algorithm
value	O
along	O
the	O
axis	O
of	O
the	O
pushing	O
beam	O
.	O
</s>
<s>
By	O
pushing	O
in	O
many	O
different	O
places	O
,	O
a	O
map	O
of	O
the	O
tissue	O
stiffness	B-Algorithm
is	O
built	O
up	O
.	O
</s>
<s>
By	O
using	O
an	O
image	O
modality	O
like	O
ultrasound	B-Application
or	O
MRI	B-Algorithm
to	O
see	O
how	O
fast	O
the	O
wave	O
gets	O
to	O
different	O
lateral	O
positions	O
,	O
the	O
stiffness	B-Algorithm
of	O
the	O
intervening	O
tissue	O
is	O
inferred	O
.	O
</s>
<s>
Since	O
the	O
terms	O
"	O
elasticity	O
imaging	O
"	O
and	O
"	O
elastography	B-Algorithm
"	O
are	O
synonyms	O
,	O
the	O
original	O
term	O
SWEI	O
denoting	O
the	O
technology	O
for	O
elasticity	O
mapping	O
using	O
shear	O
waves	O
is	O
often	O
replaced	O
by	O
SWE	O
.	O
</s>
<s>
The	O
principal	O
difference	O
between	O
SWEI	O
and	O
ARFI	O
is	O
that	O
SWEI	O
is	O
based	O
on	O
the	O
use	O
of	O
shear	O
waves	O
propagating	O
laterally	O
from	O
the	O
beam	O
axis	O
and	O
creating	O
elasticity	O
map	O
by	O
measuring	O
shear	O
wave	O
propagation	O
parameters	O
whereas	O
ARFI	O
gets	O
elasticity	O
information	O
from	O
the	O
axis	O
of	O
the	O
pushing	O
beam	O
and	O
uses	O
multiple	O
pushes	O
to	O
create	O
a	O
2-D	O
stiffness	B-Algorithm
map	O
.	O
</s>
<s>
Supersonic	O
shear	O
imaging	O
(	O
SSI	O
)	O
gives	O
a	O
quantitative	O
,	O
real-time	O
two-dimensional	O
map	O
of	O
tissue	O
stiffness	B-Algorithm
.	O
</s>
<s>
SSI	O
is	O
based	O
on	O
SWEI	O
:	O
it	O
uses	O
acoustic	O
radiation	O
force	O
to	O
induce	O
a	O
'	O
push	O
 '	O
inside	O
the	O
tissue	O
of	O
interest	O
generating	O
shear	O
waves	O
and	O
the	O
tissue	O
's	O
stiffness	B-Algorithm
is	O
computed	O
from	O
how	O
fast	O
the	O
resulting	O
shear	O
wave	O
travels	O
through	O
the	O
tissue	O
.	O
</s>
<s>
SSI	O
is	O
the	O
first	O
ultrasonic	B-Application
imaging	I-Application
technology	O
able	O
to	O
reach	O
more	O
than	O
10,000	O
frames	O
per	O
second	O
of	O
deep-seated	O
organs	O
.	O
</s>
<s>
A	O
large	O
multi-center	O
breast	O
imaging	O
study	O
has	O
demonstrated	O
both	O
reproducibility	O
and	O
significant	O
improvement	O
in	O
the	O
classification	O
of	O
breast	O
lesions	O
when	O
shear	O
wave	O
elastography	B-Algorithm
images	O
are	O
added	O
to	O
the	O
interpretation	O
of	O
standard	O
B-mode	O
and	O
Color	O
mode	O
ultrasound	B-Application
images	O
.	O
</s>
<s>
Transient	O
elastography	B-Algorithm
was	O
initially	O
called	O
time-resolved	O
pulse	O
elastography	B-Algorithm
when	O
it	O
was	O
introduced	O
in	O
the	O
late	O
1990s	O
.	O
</s>
<s>
The	O
propagation	O
of	O
the	O
shear	O
wave	O
is	O
tracked	O
using	O
ultrasound	B-Application
in	O
order	O
to	O
assess	O
the	O
shear	O
wave	O
speed	O
from	O
which	O
the	O
Young	O
's	O
modulus	O
is	O
deduced	O
under	O
hypothesis	O
of	O
homogeneity	O
,	O
isotropy	O
and	O
pure	O
elasticity	O
(	O
E	O
=	O
3ρV²	O
)	O
.	O
</s>
<s>
An	O
important	O
advantage	O
of	O
transient	O
elastography	B-Algorithm
compared	O
to	O
harmonic	O
elastography	B-Algorithm
techniques	O
is	O
the	O
separation	O
of	O
shear	O
waves	O
and	O
compression	O
waves	O
.	O
</s>
<s>
The	O
technique	O
can	O
be	O
implemented	O
in	O
1D	O
and	O
2D	O
which	O
required	O
the	O
development	O
of	O
an	O
ultrafast	O
ultrasound	B-Application
scanner	I-Application
.	O
</s>
<s>
Transient	O
elastography	B-Algorithm
gives	O
a	O
quantitative	O
one-dimensional	O
(	O
i.e.	O
</s>
<s>
a	O
line	O
)	O
image	O
of	O
"	O
tissue	O
"	O
stiffness	B-Algorithm
.	O
</s>
<s>
It	O
functions	O
by	O
vibrating	O
the	O
skin	O
with	O
a	O
motor	O
to	O
create	O
a	O
passing	O
distortion	O
in	O
the	O
tissue	O
(	O
a	O
shear	O
wave	O
)	O
,	O
and	O
imaging	O
the	O
motion	O
of	O
that	O
distortion	O
as	O
it	O
passes	O
deeper	O
into	O
the	O
body	O
using	O
a	O
1D	O
ultrasound	B-Application
beam	O
.	O
</s>
<s>
It	O
then	O
displays	O
a	O
quantitative	O
line	O
of	O
tissue	O
stiffness	B-Algorithm
data	O
(	O
the	O
Young	O
's	O
modulus	O
)	O
.	O
</s>
<s>
This	O
technique	O
is	O
used	O
mainly	O
by	O
the	O
Fibroscan	B-Algorithm
system	O
,	O
which	O
is	O
used	O
for	O
liver	O
assessment	O
,	O
for	O
example	O
,	O
to	O
diagnose	O
cirrhosis.A	O
specific	O
implementation	O
of	O
1D	O
transient	O
elastography	B-Algorithm
called	O
VCTE	O
has	O
been	O
developed	O
to	O
assess	O
average	O
liver	O
stiffness	B-Algorithm
which	O
correlates	O
to	O
liver	O
fibrosis	O
assessed	O
by	O
liver	O
biopsy	O
.	O
</s>
<s>
Magnetic	O
resonance	O
elastography	B-Algorithm
(	O
MRE	O
)	O
was	O
introduced	O
in	O
the	O
mid-1990s	O
,	O
and	O
multiple	O
clinical	O
applications	O
have	O
been	O
investigated	O
.	O
</s>
<s>
An	O
imaging	O
acquisition	O
sequence	O
that	O
measures	O
the	O
velocity	O
of	O
the	O
waves	O
is	O
used	O
,	O
and	O
this	O
is	O
used	O
to	O
infer	O
the	O
tissue	O
's	O
stiffness	B-Algorithm
(	O
the	O
shear	O
modulus	O
)	O
.	O
</s>
<s>
The	O
result	O
of	O
an	O
MRE	O
scan	O
is	O
a	O
quantitative	O
3-D	O
map	O
of	O
the	O
tissue	O
stiffness	B-Algorithm
,	O
as	O
well	O
as	O
a	O
conventional	O
3-D	O
MRI	B-Algorithm
image	O
.	O
</s>
<s>
Because	O
MRI	B-Algorithm
is	O
not	O
limited	O
by	O
air	O
or	O
bone	O
,	O
it	O
can	O
access	O
some	O
tissues	O
ultrasound	B-Application
cannot	O
,	O
notably	O
the	O
brain	O
.	O
</s>
<s>
It	O
also	O
has	O
the	O
advantage	O
of	O
being	O
more	O
uniform	O
across	O
operators	O
and	O
less	O
dependent	O
on	O
operator	O
skill	O
than	O
most	O
methods	O
of	O
ultrasound	B-Algorithm
elastography	I-Algorithm
.	O
</s>
<s>
MR	O
elastography	B-Algorithm
has	O
made	O
significant	O
advances	O
over	O
the	O
past	O
few	O
years	O
with	O
acquisition	O
times	O
down	O
to	O
a	O
minute	O
or	O
less	O
and	O
has	O
been	O
used	O
in	O
a	O
variety	O
of	O
medical	O
applications	O
including	O
cardiology	O
research	O
on	O
living	O
human	O
hearts	O
.	O
</s>
<s>
MR	O
elastography	B-Algorithm
's	O
short	O
acquisition	O
time	O
also	O
makes	O
it	O
competitive	O
with	O
other	O
elastography	B-Algorithm
techniques	O
.	O
</s>
<s>
Elastography	B-Algorithm
is	O
used	O
for	O
the	O
investigation	O
of	O
many	O
disease	O
conditions	O
in	O
many	O
organs	O
.	O
</s>
<s>
Biopsies	O
are	O
invasive	O
and	O
painful	O
,	O
presenting	O
a	O
risk	O
of	O
hemorrhage	O
or	O
infection	O
,	O
whereas	O
elastography	B-Algorithm
is	O
completely	O
noninvasive	O
.	O
</s>
<s>
Elastography	B-Algorithm
is	O
used	O
to	O
investigate	O
disease	O
in	O
the	O
liver	O
.	O
</s>
<s>
Liver	O
stiffness	B-Algorithm
is	O
usually	O
indicative	O
of	O
fibrosis	O
or	O
steatosis	O
(	O
fatty	O
liver	O
disease	O
)	O
,	O
which	O
are	O
in	O
turn	O
indicative	O
of	O
numerous	O
disease	O
conditions	O
,	O
including	O
cirrhosis	O
and	O
hepatitis	O
.	O
</s>
<s>
Elastography	B-Algorithm
is	O
particularly	O
advantageous	O
in	O
this	O
case	O
because	O
when	O
fibrosis	O
is	O
diffuse	O
(	O
spread	O
around	O
in	O
clumps	O
rather	O
than	O
continuous	O
scarring	O
)	O
,	O
a	O
biopsy	O
can	O
easily	O
miss	O
sampling	O
the	O
diseased	O
tissue	O
,	O
which	O
results	O
in	O
a	O
false	O
negative	O
misdiagnosis	O
.	O
</s>
<s>
Naturally	O
,	O
elastography	B-Algorithm
sees	O
use	O
for	O
organs	O
and	O
diseases	O
where	O
manual	O
palpation	O
was	O
already	O
widespread	O
.	O
</s>
<s>
Elastography	B-Algorithm
is	O
used	O
for	O
detection	O
and	O
diagnosis	O
of	O
breast	O
,	O
thyroid	O
,	O
and	O
prostate	O
cancers	O
.	O
</s>
<s>
Certain	O
types	O
of	O
elastography	B-Algorithm
are	O
also	O
suitable	O
for	O
musculoskeletal	O
imaging	O
,	O
and	O
they	O
can	O
determine	O
the	O
mechanical	O
properties	O
and	O
state	O
of	O
muscles	O
and	O
tendons	O
.	O
</s>
<s>
Because	O
elastography	B-Algorithm
does	O
not	O
have	O
the	O
same	O
limitations	O
as	O
manual	O
palpation	O
,	O
it	O
is	O
being	O
investigated	O
in	O
some	O
areas	O
for	O
which	O
there	O
is	O
no	O
history	O
of	O
diagnosis	O
with	O
manual	O
palpation	O
.	O
</s>
<s>
For	O
example	O
,	O
magnetic	O
resonance	O
elastography	B-Algorithm
is	O
capable	O
of	O
assessing	O
the	O
stiffness	B-Algorithm
of	O
the	O
brain	O
,	O
and	O
there	O
is	O
a	O
growing	O
body	O
of	O
scientific	O
literature	O
on	O
elastography	B-Algorithm
in	O
healthy	O
and	O
diseased	O
brains	O
.	O
</s>
<s>
In	O
2015	O
,	O
preliminary	O
reports	O
on	O
elastography	B-Algorithm
used	O
on	O
transplanted	O
kidneys	O
to	O
evaluate	O
cortical	O
fibrosis	O
have	O
been	O
published	O
showing	O
promising	O
results	O
.	O
</s>
<s>
In	O
Bristol	O
University	O
's	O
study	O
Children	O
of	O
the	O
90s	O
,	O
2.5	O
%	O
of	O
4,000	O
people	O
born	O
in	O
1991	O
and	O
1992	O
were	O
found	O
by	O
ultrasound	B-Application
scanning	I-Application
at	O
the	O
age	O
of	O
18	O
to	O
have	O
non-alcoholic	O
fatty	O
liver	O
disease	O
;	O
five	O
years	O
later	O
transient	O
elastography	B-Algorithm
found	O
over	O
20%	O
to	O
have	O
the	O
fatty	O
deposits	O
on	O
the	O
liver	O
of	O
steatosis	O
,	O
indicating	O
non-alcoholic	O
fatty	O
liver	O
disease	O
;	O
half	O
of	O
those	O
were	O
classified	O
as	O
severe	O
.	O
</s>
<s>
Other	O
techniques	O
include	O
elastography	B-Algorithm
with	O
optical	B-Application
coherence	I-Application
tomography	I-Application
(	O
i.e.	O
</s>
<s>
Tactile	B-Algorithm
imaging	I-Algorithm
involves	O
translating	O
the	O
results	O
of	O
a	O
digital	O
"	O
touch	O
"	O
into	O
an	O
image	O
.	O
</s>
<s>
Many	O
physical	O
principles	O
have	O
been	O
explored	O
for	O
the	O
realization	O
of	O
tactile	B-Algorithm
sensors	I-Algorithm
:	O
resistive	O
,	O
inductive	O
,	O
capacitive	O
,	O
optoelectric	O
,	O
magnetic	O
,	O
piezoelectric	O
,	O
and	O
electroacoustic	O
principles	O
,	O
in	O
a	O
variety	O
of	O
configurations	O
.	O
</s>
