<s>
Fast	B-Algorithm
low	I-Algorithm
angle	I-Algorithm
shot	I-Algorithm
magnetic	I-Algorithm
resonance	I-Algorithm
imaging	I-Algorithm
(	O
FLASH	B-Algorithm
MRI	I-Algorithm
)	O
is	O
a	O
particular	O
sequence	B-Algorithm
of	O
magnetic	O
resonance	O
imaging	O
.	O
</s>
<s>
It	O
is	O
a	O
gradient	O
echo	O
sequence	B-Algorithm
which	O
combines	O
a	O
low-flip	O
angle	O
radio-frequency	O
excitation	O
of	O
the	O
nuclear	O
magnetic	O
resonance	O
signal	O
(	O
recorded	O
as	O
a	O
spatially	O
encoded	O
gradient	O
echo	O
)	O
with	O
a	O
short	O
repetition	O
time	O
.	O
</s>
<s>
It	O
is	O
the	O
generic	O
form	O
of	O
steady-state	B-Algorithm
free	I-Algorithm
precession	I-Algorithm
imaging	I-Algorithm
.	O
</s>
<s>
Siemens	O
uses	O
the	O
name	O
FLASH	O
,	O
General	O
Electric	O
used	O
the	O
name	O
SPGR	O
(	O
Spoiled	O
Gradient	O
Echo	O
)	O
,	O
and	O
Philips	O
uses	O
the	O
name	O
CE-FFE-T1	O
(	O
Contrast-Enhanced	O
Fast	B-Algorithm
Field	I-Algorithm
Echo	I-Algorithm
)	O
or	O
T1-FFE	O
.	O
</s>
<s>
Depending	O
on	O
the	O
desired	O
contrast	O
,	O
the	O
generic	O
FLASH	O
technique	O
provides	O
spoiled	O
versions	O
that	O
destroy	O
transverse	O
coherences	O
and	O
yield	O
T1	B-Algorithm
contrast	O
as	O
well	O
as	O
refocused	O
versions	O
(	O
constant	O
phase	O
per	O
repetition	O
)	O
and	O
fully	O
balanced	O
versions	O
(	O
zero	O
phase	O
per	O
repetition	O
)	O
that	O
incorporate	O
transverse	O
coherences	O
into	O
the	O
steady-state	O
signal	O
and	O
offer	O
T1/T2	O
contrast	O
.	O
</s>
<s>
dynamic	O
acquisitions	O
synchronized	O
to	O
the	O
electrocardiogram	B-Application
generate	O
movies	O
of	O
the	O
beating	O
heart	O
,	O
</s>
<s>
sequential	O
acquisitions	O
monitor	O
physiological	O
processes	O
such	O
as	O
the	O
differential	O
uptake	O
of	O
contrast	B-Algorithm
media	I-Algorithm
into	O
body	O
tissues	O
,	O
</s>
<s>
Magnetic	B-Algorithm
resonance	I-Algorithm
angiography	I-Algorithm
(	O
MRA	O
)	O
yields	O
three-dimensional	O
representations	O
of	O
the	O
vasculature	O
.	O
</s>
<s>
The	O
physical	B-Algorithm
basis	I-Algorithm
of	I-Algorithm
MRI	I-Algorithm
is	O
the	O
spatial	O
encoding	O
of	O
the	O
nuclear	O
magnetic	O
resonance	O
(	O
NMR	O
)	O
signal	O
obtainable	O
from	O
water	O
protons	O
(	O
i.e.	O
</s>
<s>
The	O
generic	O
FLASH	O
technique	O
emerges	O
as	O
a	O
gradient	O
echo	O
sequence	B-Algorithm
which	O
combines	O
a	O
low-flip	O
angle	O
radio-frequency	O
excitation	O
of	O
the	O
NMR	O
signal	O
(	O
recorded	O
as	O
a	O
spatially	O
encoded	O
gradient	O
echo	O
)	O
with	O
a	O
rapid	O
repetition	O
of	O
the	O
basic	O
sequence	B-Algorithm
.	O
</s>
<s>
The	O
repetition	O
time	O
is	O
usually	O
much	O
shorter	O
than	O
the	O
typical	O
T1	B-Algorithm
relaxation	I-Algorithm
time	O
of	O
the	O
protons	O
in	O
biologic	O
tissue	O
.	O
</s>
<s>
Only	O
the	O
combination	O
of	O
(	O
i	O
)	O
a	O
low-flip	O
angle	O
excitation	O
which	O
leaves	O
unused	O
longitudinal	O
magnetization	O
for	O
an	O
immediate	O
next	O
excitation	O
with	O
(	O
ii	O
)	O
the	O
acquisition	O
of	O
a	O
gradient	O
echo	O
which	O
does	O
not	O
need	O
a	O
further	O
radio-frequency	O
pulse	O
that	O
would	O
affect	O
the	O
residual	O
longitudinal	O
magnetization	O
,	O
allows	O
for	O
the	O
rapid	O
repetition	O
of	O
the	O
basic	O
sequence	B-Algorithm
interval	O
and	O
the	O
resulting	O
speed	O
of	O
the	O
entire	O
image	O
acquisition	O
.	O
</s>
<s>
In	O
fact	O
,	O
the	O
FLASH	O
sequence	B-Algorithm
eliminated	O
all	O
waiting	O
periods	O
previously	O
included	O
to	O
accommodate	O
effects	O
from	O
T1	B-Algorithm
saturation	O
.	O
</s>
<s>
FLASH	O
reduced	O
the	O
typical	O
sequence	B-Algorithm
interval	O
to	O
what	O
is	O
minimally	O
required	O
for	O
imaging	O
:	O
a	O
slice-selective	O
radio-frequency	O
pulse	O
and	O
gradient	O
,	O
a	O
phase-encoding	O
gradient	O
,	O
and	O
a	O
(	O
reversed	O
)	O
frequency-encoding	O
gradient	O
generating	O
the	O
echo	O
for	O
data	O
acquisition	O
.	O
</s>
<s>
Most	O
recently	O
,	O
highly	O
undersampled	O
radial	O
FLASH	B-Algorithm
MRI	I-Algorithm
acquisitions	O
have	O
been	O
combined	O
with	O
an	O
iterative	O
image	O
reconstruction	O
by	O
regularized	O
nonlinear	O
inversion	O
to	O
achieve	O
real-time	B-Algorithm
MRI	I-Algorithm
at	O
a	O
temporal	O
resolution	O
of	O
20	O
to	O
30	O
milliseconds	O
for	O
images	O
with	O
a	O
spatial	O
resolution	O
of	O
1.5	O
to	O
2.0	O
millimeters	O
.	O
</s>
<s>
This	O
method	O
allows	O
for	O
a	O
visualization	O
of	O
the	O
beating	O
heart	O
in	O
real	O
time	O
–	O
without	O
synchronization	O
to	O
the	O
electrocardiogram	B-Application
and	O
during	O
free	O
breathing	O
.	O
</s>
<s>
FLASH	B-Algorithm
MRI	I-Algorithm
was	O
invented	O
in	O
1985	O
by	O
Jens	O
Frahm	O
,	O
Axel	O
Haase	O
,	O
W	O
Hänicke	O
,	O
KD	O
Merboldt	O
,	O
and	O
D	O
Matthaei	O
(	O
German	O
Patent	O
Application	O
P	O
35	O
04	O
734.8	O
,	O
12	O
February	O
1985	O
)	O
at	O
the	O
in	O
Göttingen	O
,	O
Germany	O
.	O
</s>
<s>
The	O
technique	O
is	O
revolutionary	O
in	O
shortening	O
MRI	O
measuring	O
times	O
by	O
up	O
to	O
two	O
orders	B-Device
of	I-Device
magnitude	I-Device
.	O
</s>
<s>
The	O
introduction	O
of	O
FLASH	B-Algorithm
MRI	I-Algorithm
sequences	O
in	O
diagnostic	O
imaging	O
for	O
the	O
first	O
time	O
allowed	O
for	O
a	O
drastic	O
shortening	O
of	O
the	O
measuring	O
times	O
without	O
a	O
substantial	O
loss	O
in	O
image	O
quality	O
.	O
</s>
<s>
In	O
2010	O
,	O
an	O
extended	O
FLASH	O
method	O
with	O
highly	O
undersampled	O
radial	O
data	O
encoding	O
and	O
iterative	O
image	O
reconstruction	O
achieved	O
real-time	B-Algorithm
MRI	I-Algorithm
with	O
a	O
temporal	O
resolution	O
of	O
20	O
milliseconds	O
(	O
1/50th	O
of	O
a	O
second	O
)	O
.	O
</s>
