<s>
Steady-state	O
free	O
precession	O
(	O
SSFP	O
)	O
imaging	O
is	O
a	O
magnetic	O
resonance	O
imaging	O
(	O
MRI	B-Algorithm
)	O
sequence	B-Algorithm
which	O
uses	O
steady	O
states	O
of	O
magnetizations	O
.	O
</s>
<s>
In	O
general	O
,	O
SSFP	O
MRI	B-Algorithm
sequences	I-Algorithm
are	O
based	O
on	O
a	O
(	O
low	O
flip	O
angle	O
)	O
gradient	O
echo	O
MRI	B-Algorithm
sequence	I-Algorithm
with	O
a	O
short	O
repetition	O
time	O
which	O
in	O
its	O
generic	O
form	O
has	O
been	O
described	O
as	O
the	O
FLASH	B-Algorithm
MRI	I-Algorithm
technique	O
.	O
</s>
<s>
Fully	O
balanced	O
SSFP	O
MRI	B-Algorithm
sequences	I-Algorithm
achieve	O
a	O
phase	O
of	O
zero	O
by	O
refocusing	O
all	O
imaging	O
gradients	O
.	O
</s>
<s>
If	O
,	O
within	O
one	O
TR	O
,	O
either	O
one	O
of	O
the	O
gradient	O
moments	O
of	O
magnetic	O
gradients	O
along	O
three	O
logical	O
directions	O
,	O
including	O
slice	O
selection	O
direction	O
(	O
Gss	O
)	O
,	O
phase	O
encoding	O
(	O
Gpe	O
)	O
and	O
readout	O
(	O
Gro	O
)	O
,	O
is	O
not	O
zero	O
,	O
then	O
spins	O
along	O
such	O
direction	O
obtain	O
different	O
phases	O
,	O
making	O
the	O
signal	O
intensity	O
(	O
SI	O
)	O
of	O
a	O
single	O
voxel	B-Algorithm
the	O
vector	O
sum	O
of	O
magnetizations	O
therein	O
.	O
</s>
<s>
gradients	O
of	O
opposite	O
polarities	O
cancel	O
out	O
,	O
then	O
there	O
are	O
no	O
additional	O
effects	O
on	O
the	O
phase	O
from	O
gradients	O
;	O
that	O
is	O
to	O
say	O
,	O
SI	O
of	O
each	O
voxels	B-Algorithm
is	O
the	O
contributions	O
of	O
a	O
series	O
of	O
RF	O
pulses	O
and	O
relaxation	O
phenomena	O
.	O
</s>
<s>
bSSFP	B-Algorithm
sequences	O
demand	O
a	O
very	O
high	O
level	O
of	O
magnetic	O
field	O
homogeneity	O
and	O
control	O
over	O
gradient	O
switching	O
and	O
shaping	O
.	O
</s>
<s>
During	O
the	O
last	O
decade	O
modern	O
scanners	O
have	O
overcome	O
these	O
limitations	O
making	O
bSSFP	B-Algorithm
a	O
viable	O
and	O
useful	O
sequence	B-Algorithm
on	O
most	O
mid	O
-	O
and	O
high-field	O
systems	O
.	O
</s>
<s>
Thus	O
,	O
bSSFP	B-Algorithm
sequences	O
behave	O
more	O
like	O
spin	O
echo	O
than	O
gradient	O
echo	O
sequences	O
in	O
that	O
they	O
do	O
not	O
have	O
T2*	O
-dependence	O
.	O
</s>
<s>
SSFP	O
is	O
beneficial	O
as	O
a	O
localizer	O
sequence	B-Algorithm
,	O
such	O
as	O
for	O
initial	O
images	O
of	O
the	O
anal	O
canal	O
in	O
order	O
to	O
align	O
the	O
planes	O
of	O
subsequent	O
T2-weighted	O
images	O
to	O
be	O
cross-sections	O
and	O
longitudinal	O
sections	O
of	O
the	O
canal	O
.	O
</s>
<s>
A	O
particular	O
SSFP	O
used	O
for	O
this	O
purpose	O
is	O
one	O
termed	O
TRUE	B-Algorithm
FISP	I-Algorithm
by	O
Siemens	O
,	O
FIESTA	O
by	O
GE	O
,	O
and	O
balanced	O
FFE	O
by	O
Philips	O
.	O
</s>
<s>
SSFP	O
protocols	O
have	O
different	O
names	O
among	O
different	O
MRI	B-Algorithm
manufacturers	O
.	O
</s>
