<s>
Doppler	B-Algorithm
ultrasonography	I-Algorithm
is	O
medical	B-Application
ultrasonography	I-Application
that	O
employs	O
the	O
Doppler	O
effect	O
to	O
perform	O
imaging	B-Application
of	O
the	O
movement	O
of	O
tissues	O
and	O
body	O
fluids	O
(	O
usually	O
blood	O
)	O
,	O
and	O
their	O
relative	O
velocity	O
to	O
the	O
probe	B-Algorithm
.	O
</s>
<s>
Duplex	B-Algorithm
ultrasonography	I-Algorithm
sometimes	O
refers	O
to	O
Doppler	B-Algorithm
ultrasonography	I-Algorithm
or	O
spectral	O
Doppler	B-Algorithm
ultrasonography	I-Algorithm
.	O
</s>
<s>
Doppler	B-Algorithm
ultrasonography	I-Algorithm
consists	O
of	O
two	O
components	O
:	O
brightness	O
mode	O
(	O
B-mode	O
)	O
showing	O
anatomy	O
of	O
the	O
organs	O
,	O
and	O
Doppler	O
mode	O
(	O
showing	O
blood	O
flow	O
)	O
superimposed	O
on	O
the	O
B-mode	O
.	O
</s>
<s>
Meanwhile	O
,	O
spectral	O
Doppler	B-Algorithm
ultrasonography	I-Algorithm
consists	O
of	O
three	O
components	O
:	O
B-mode	O
,	O
Doppler	O
mode	O
,	O
and	O
spectral	O
waveform	O
displayed	O
at	O
the	O
lower	O
half	O
of	O
the	O
image	O
.	O
</s>
<s>
Therefore	O
,	O
"	O
duplex	B-Algorithm
ultrasonography	I-Algorithm
"	O
is	O
a	O
misnomer	O
for	O
spectral	O
Doppler	B-Algorithm
ultrasonography	I-Algorithm
,	O
and	O
more	O
exact	O
name	O
should	O
be	O
"	O
triplex	O
ultrasonography	O
"	O
.	O
</s>
<s>
This	O
is	O
particularly	O
useful	O
in	O
cardiovascular	O
studies	O
(	O
sonography	B-Application
of	O
the	O
vascular	O
system	O
and	O
heart	O
)	O
and	O
essential	O
in	O
many	O
areas	O
such	O
as	O
determining	O
reverse	O
blood	O
flow	O
in	O
the	O
liver	O
vasculature	O
in	O
portal	O
hypertension	O
.	O
</s>
<s>
Any	O
sudden	O
changes	O
in	O
direction	O
of	O
blood	O
flow	O
produces	O
audible	O
sounds	O
on	O
the	O
ultrasound	B-Application
machine	I-Application
.	O
</s>
<s>
Both	O
antegrade	O
or	O
retrograde	O
flow	O
can	O
be	O
either	O
towards	O
or	O
away	O
from	O
the	O
probe	B-Algorithm
transducer	O
,	O
depending	O
on	O
the	O
position	O
of	O
the	O
probe	B-Algorithm
relative	O
to	O
the	O
blood	O
flow	O
.	O
</s>
<s>
Upstream	O
and	O
downstream	O
stenosis	O
refers	O
to	O
the	O
location	O
of	O
the	O
stenotic	O
site	O
relative	O
to	O
the	O
ultrasound	B-Algorithm
probe	I-Algorithm
.	O
</s>
<s>
Upstream	O
stenosis	O
means	O
the	O
location	O
of	O
stenosis	O
is	O
located	O
before	O
the	O
ultrasound	B-Algorithm
probe	I-Algorithm
.	O
</s>
<s>
Meanwhile	O
,	O
downstream	O
stenosis	O
is	O
located	O
after	O
the	O
ultrasound	B-Algorithm
probe	I-Algorithm
.	O
</s>
<s>
Power	B-Algorithm
Doppler	I-Algorithm
is	O
a	O
non	O
directional	O
Doppler	O
.	O
</s>
<s>
All	O
modern	O
ultrasound	B-Application
scanners	I-Application
use	O
pulsed	O
Doppler	O
to	O
measure	O
velocity	O
.	O
</s>
<s>
The	O
disadvantage	O
of	O
pulsed	O
Doppler	O
is	O
that	O
the	O
measurements	O
can	O
suffer	O
from	O
aliasing	B-Error_Name
.	O
</s>
<s>
The	O
terms	O
Doppler	B-Algorithm
ultrasound	I-Algorithm
and	O
Doppler	B-Algorithm
sonography	I-Algorithm
have	O
been	O
accepted	O
to	O
apply	O
to	O
both	O
pulsed	O
and	O
continuous	O
Doppler	O
systems	O
,	O
despite	O
the	O
different	O
mechanisms	O
by	O
which	O
the	O
velocity	O
is	O
measured	O
.	O
</s>
<s>
There	O
are	O
no	O
standards	O
for	O
displaying	O
color	B-Algorithm
Doppler	I-Algorithm
.	O
</s>
<s>
Because	O
of	O
this	O
confusion	O
and	O
lack	O
of	O
standards	O
,	O
the	O
sonographer	O
must	O
understand	O
the	O
underlying	O
physics	O
of	O
color	B-Algorithm
Doppler	I-Algorithm
and	O
the	O
physiology	O
of	O
normal	O
and	O
abnormal	O
blood	O
flow	O
in	O
the	O
human	O
body	O
(	O
see	O
Red	O
shift	O
)	O
.	O
</s>
<s>
These	O
modes	O
of	O
medical	B-Application
imaging	I-Application
conduct	O
a	O
spectral	O
analysis	O
of	O
the	O
acoustic	O
signals	O
they	O
receive	O
and	O
can	O
therefore	O
be	O
classified	O
as	O
methods	O
of	O
active	O
acoustocerebrography	O
.	O
</s>
<s>
The	O
tests	O
are	O
often	O
used	O
in	O
conjunction	O
with	O
other	O
tests	O
such	O
as	O
MRI	O
,	O
MRA	B-Algorithm
,	O
carotid	B-Algorithm
duplex	I-Algorithm
ultrasound	B-Application
and	O
CT	O
scans	O
.	O
</s>
<s>
Ultrasound	B-Application
duplex	O
scanning	O
can	O
provide	O
additional	O
information	O
that	O
may	O
guide	O
therapeutic	O
decisions	O
.	O
</s>
<s>
In	O
addition	O
to	O
visualization	O
,	O
ultrasound	B-Application
can	O
also	O
be	O
used	O
in	O
Doppler	O
auscultation	O
(	O
without	O
visual	O
)	O
,	O
similar	O
to	O
using	O
an	O
ultrasound	B-Application
baby	O
monitor	O
,	O
to	O
locate	O
clots	O
or	O
other	O
vascular	O
obstructions	O
or	O
collapse	O
by	O
tracing	O
a	O
blood	O
vessel	O
until	O
sound	O
is	O
no	O
longer	O
heard	O
.	O
</s>
<s>
Doppler	B-Algorithm
ultrasonography	I-Algorithm
is	O
widely	O
used	O
in	O
renal	B-Algorithm
ultrasonography	I-Algorithm
.	O
</s>
<s>
Renal	O
vessels	O
are	O
easily	O
depicted	O
by	O
the	O
color	B-Algorithm
Doppler	I-Algorithm
technique	O
in	O
order	O
to	O
evaluate	O
perfusion	O
.	O
</s>
<s>
Doppler	O
echocardiography	O
is	O
the	O
use	O
of	O
Doppler	B-Algorithm
ultrasonography	I-Algorithm
to	O
examine	O
the	O
heart	O
.	O
</s>
<s>
One	O
of	O
the	O
limitations	O
is	O
that	O
the	O
ultrasound	B-Application
beam	O
should	O
be	O
as	O
parallel	O
to	O
the	O
blood	O
flow	O
as	O
possible	O
.	O
</s>
<s>
Contrast-enhanced	O
ultrasound	B-Application
using	O
gas-filled	O
microbubble	O
contrast	O
media	O
can	O
be	O
used	O
to	O
improve	O
velocity	O
or	O
other	O
flow-related	O
medical	O
measurements	O
.	O
</s>
<s>
Doppler	B-Algorithm
ultrasonography	I-Algorithm
can	O
help	O
distinguishing	O
benign	O
from	O
malignant	O
soft	O
tissue	O
lumps	O
.	O
</s>
<s>
Power	B-Algorithm
Doppler	I-Algorithm
is	O
useful	O
in	O
assessing	O
tendon	O
and	O
joints	O
inflammation	O
such	O
as	O
paratenonitis	O
.	O
</s>
