<s>
An	O
MRI	B-Algorithm
sequence	I-Algorithm
in	O
magnetic	O
resonance	O
imaging	O
(	O
MRI	O
)	O
is	O
a	O
particular	O
setting	O
of	O
pulse	O
sequences	O
and	O
pulsed	O
field	O
gradients	O
,	O
resulting	O
in	O
a	O
particular	O
image	O
appearance	O
.	O
</s>
<s>
A	O
multiparametric	B-Algorithm
MRI	I-Algorithm
is	O
a	O
combination	O
of	O
two	O
or	O
more	O
sequences	O
,	O
and/or	O
including	O
other	O
specialized	O
MRI	O
configurations	O
such	O
as	O
spectroscopy	B-Algorithm
.	O
</s>
<s>
Each	O
tissue	O
returns	O
to	O
its	O
equilibrium	O
state	O
after	O
excitation	O
by	O
the	O
independent	O
relaxation	O
processes	O
of	O
T1	B-Algorithm
(	O
spin-lattice	B-Algorithm
;	O
that	O
is	O
,	O
magnetization	O
in	O
the	O
same	O
direction	O
as	O
the	O
static	O
magnetic	O
field	O
)	O
and	O
T2	O
(	O
spin-spin	B-Algorithm
;	O
transverse	O
to	O
the	O
static	O
magnetic	O
field	O
)	O
.	O
</s>
<s>
To	O
create	O
a	O
T1-weighted	O
image	O
,	O
magnetization	O
is	O
allowed	O
to	O
recover	O
before	O
measuring	O
the	O
MR	O
signal	O
by	O
changing	O
the	O
repetition	O
time	O
(	O
TR	O
)	O
.	O
</s>
<s>
This	O
image	O
weighting	O
is	O
useful	O
for	O
assessing	O
the	O
cerebral	O
cortex	O
,	O
identifying	O
fatty	O
tissue	O
,	O
characterizing	O
focal	O
liver	O
lesions	O
,	O
and	O
in	O
general	O
,	O
obtaining	O
morphological	O
information	O
,	O
as	O
well	O
as	O
for	O
post-contrast	B-Algorithm
imaging	O
.	O
</s>
<s>
This	O
image	O
weighting	O
is	O
useful	O
for	O
detecting	O
edema	O
and	O
inflammation	O
,	O
revealing	O
white	B-Algorithm
matter	I-Algorithm
lesions	I-Algorithm
,	O
and	O
assessing	O
zonal	O
anatomy	O
in	O
the	O
prostate	O
and	O
uterus	O
.	O
</s>
<s>
The	O
standard	O
display	O
of	O
MRI	O
images	O
is	O
to	O
represent	O
fluid	O
characteristics	O
in	O
black	B-Application
and	I-Application
white	I-Application
images	O
,	O
where	O
different	O
tissues	O
turn	O
out	O
as	O
follows	O
:	O
</s>
<s>
Proton	B-Application
density	O
(	O
PD	O
)	O
-	O
weighted	O
images	O
are	O
created	O
by	O
having	O
a	O
long	O
repetition	O
time	O
(	O
TR	O
)	O
and	O
a	O
short	O
echo	O
time	O
(	O
TE	O
)	O
.	O
</s>
<s>
On	O
images	O
of	O
the	O
brain	O
,	O
this	O
sequence	O
has	O
a	O
more	O
pronounced	O
distinction	O
between	O
gray	B-Device
matter	I-Device
(	O
bright	O
)	O
and	O
white	O
matter	O
(	O
darker	O
gray	O
)	O
,	O
but	O
with	O
little	O
contrast	O
between	O
brain	O
and	O
CSF	O
.	O
</s>
<s>
There	O
are	O
three	O
main	O
methods	O
of	O
manipulating	O
contrast	O
at	O
this	O
stage	O
,	O
namely	O
steady-state	O
free-precession	O
(	O
SSFP	O
)	O
that	O
does	O
not	O
spoil	O
the	O
remaining	O
transverse	O
magnetisation	O
,	O
but	O
attempts	O
to	O
recover	O
them	O
(	O
thus	O
producing	O
T2-weighted	O
images	O
)	O
;	O
the	O
sequence	O
with	O
spoiler	O
gradient	O
that	O
averages	O
the	O
transverse	O
magnetisations	O
(	O
thus	O
producing	O
mixed	O
T1	B-Algorithm
and	O
T2-weighted	O
images	O
)	O
,	O
and	O
RF	O
spoiler	O
that	O
vary	O
the	O
phases	O
of	O
RF	O
pulse	O
to	O
eliminates	O
the	O
transverse	O
magnetisation	O
,	O
thus	O
producing	O
pure	O
T1-weighted	O
images	O
.	O
</s>
<s>
Inversion	O
recovery	O
is	O
an	O
MRI	B-Algorithm
sequence	I-Algorithm
that	O
provides	O
high	O
contrast	O
between	O
tissue	O
and	O
lesion	O
.	O
</s>
<s>
It	O
can	O
be	O
used	O
to	O
provide	O
high	O
T1	B-Algorithm
weighted	O
image	O
,	O
high	O
T2	O
weighted	O
image	O
,	O
and	O
to	O
suppress	O
the	O
signals	O
from	O
fat	O
,	O
blood	O
,	O
or	O
cerebrospinal	O
fluid	O
(	O
CSF	O
)	O
.	O
</s>
<s>
Diffusion	B-Algorithm
MRI	I-Algorithm
measures	O
the	O
diffusion	O
of	O
water	O
molecules	O
in	O
biological	O
tissues	O
.	O
</s>
<s>
Clinically	O
,	O
diffusion	B-Algorithm
MRI	I-Algorithm
is	O
useful	O
for	O
the	O
diagnoses	O
of	O
conditions	O
(	O
e.g.	O
,	O
stroke	O
)	O
or	O
neurological	O
disorders	O
(	O
e.g.	O
,	O
multiple	O
sclerosis	O
)	O
,	O
and	O
helps	O
better	O
understand	O
the	O
connectivity	O
of	O
white	O
matter	O
axons	B-Algorithm
in	O
the	O
central	O
nervous	O
system	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
molecule	O
inside	O
the	O
axon	B-Algorithm
of	O
a	O
neuron	O
has	O
a	O
low	O
probability	O
of	O
crossing	O
the	O
myelin	O
membrane	O
.	O
</s>
<s>
If	O
it	O
is	O
known	O
that	O
molecules	O
in	O
a	O
particular	O
voxel	B-Algorithm
diffuse	O
principally	O
in	O
one	O
direction	O
,	O
the	O
assumption	O
can	O
be	O
made	O
that	O
the	O
majority	O
of	O
the	O
fibers	O
in	O
this	O
area	O
are	O
parallel	O
to	O
that	O
direction	O
.	O
</s>
<s>
The	O
recent	O
development	O
of	O
diffusion	B-Algorithm
tensor	I-Algorithm
imaging	I-Algorithm
(	O
DTI	O
)	O
enables	O
diffusion	O
to	O
be	O
measured	O
in	O
multiple	O
directions	O
,	O
and	O
the	O
fractional	O
anisotropy	O
in	O
each	O
direction	O
to	O
be	O
calculated	O
for	O
each	O
voxel	B-Algorithm
.	O
</s>
<s>
This	O
enables	O
researchers	O
to	O
make	O
brain	O
maps	O
of	O
fiber	O
directions	O
to	O
examine	O
the	O
connectivity	O
of	O
different	O
regions	O
in	O
the	O
brain	O
(	O
using	O
tractography	B-Algorithm
)	O
or	O
to	O
examine	O
areas	O
of	O
neural	O
degeneration	O
and	O
demyelination	O
in	O
diseases	O
like	O
multiple	O
sclerosis	O
.	O
</s>
<s>
Another	O
application	O
of	O
diffusion	B-Algorithm
MRI	I-Algorithm
is	O
diffusion-weighted	O
imaging	O
(	O
DWI	O
)	O
.	O
</s>
<s>
Dynamic	O
contrast	O
enhanced	O
(	O
DCE	O
)	O
:	O
Measuring	O
shortening	O
of	O
the	O
spin	B-Algorithm
–	I-Algorithm
lattice	I-Algorithm
relaxation	I-Algorithm
(	O
T1	B-Algorithm
)	O
induced	O
by	O
a	O
gadolinium	O
contrast	O
bolus	O
.	O
</s>
<s>
Arterial	B-Algorithm
spin	I-Algorithm
labelling	I-Algorithm
(	O
ASL	O
)	O
:	O
Magnetic	O
labeling	O
of	O
arterial	O
blood	O
below	O
the	O
imaging	O
slab	O
,	O
without	O
the	O
need	O
of	O
gadolinium	O
contrast	O
.	O
</s>
<s>
Another	O
MRI	B-Algorithm
sequence	I-Algorithm
,	O
diffusion-weighted	B-Algorithm
MRI	I-Algorithm
,	O
estimates	O
the	O
amount	O
of	O
tissue	O
that	O
is	O
already	O
necrotic	O
,	O
and	O
the	O
combination	O
of	O
those	O
sequences	O
can	O
therefore	O
be	O
used	O
to	O
estimate	O
the	O
amount	O
of	O
brain	O
tissue	O
that	O
is	O
salvageable	O
by	O
thrombolysis	O
and/or	O
thrombectomy	O
.	O
</s>
<s>
Functional	B-Algorithm
MRI	I-Algorithm
(	O
fMRI	B-Algorithm
)	O
measures	O
signal	O
changes	O
in	O
the	O
brain	O
that	O
are	O
due	O
to	O
changing	O
neural	O
activity	O
.	O
</s>
<s>
Increases	O
in	O
neural	O
activity	O
cause	O
changes	O
in	O
the	O
MR	O
signal	O
via	O
T	O
changes	O
;	O
this	O
mechanism	O
is	O
referred	O
to	O
as	O
the	O
BOLD	O
(	O
blood-oxygen-level	B-Algorithm
dependent	I-Algorithm
)	O
effect	O
.	O
</s>
<s>
The	O
precise	O
nature	O
of	O
the	O
relationship	O
between	O
neural	O
activity	O
and	O
the	O
BOLD	B-Algorithm
signal	I-Algorithm
is	O
a	O
subject	O
of	O
current	O
research	O
.	O
</s>
<s>
While	O
BOLD	B-Algorithm
signal	I-Algorithm
analysis	O
is	O
the	O
most	O
common	O
method	O
employed	O
for	O
neuroscience	O
studies	O
in	O
human	O
subjects	O
,	O
the	O
flexible	O
nature	O
of	O
MR	O
imaging	O
provides	O
means	O
to	O
sensitize	O
the	O
signal	O
to	O
other	O
aspects	O
of	O
the	O
blood	O
supply	O
.	O
</s>
<s>
Alternative	O
techniques	O
employ	O
arterial	B-Algorithm
spin	I-Algorithm
labeling	I-Algorithm
(	O
ASL	O
)	O
or	O
weighting	O
the	O
MRI	O
signal	O
by	O
cerebral	O
blood	O
flow	O
(	O
CBF	O
)	O
and	O
cerebral	O
blood	O
volume	O
(	O
CBV	O
)	O
.	O
</s>
<s>
The	O
CBV	O
method	O
requires	O
injection	O
of	O
a	O
class	O
of	O
MRI	B-Algorithm
contrast	I-Algorithm
agents	I-Algorithm
that	O
are	O
now	O
in	O
human	O
clinical	O
trials	O
.	O
</s>
<s>
Because	O
this	O
method	O
has	O
been	O
shown	O
to	O
be	O
far	O
more	O
sensitive	O
than	O
the	O
BOLD	O
technique	O
in	O
preclinical	O
studies	O
,	O
it	O
may	O
potentially	O
expand	O
the	O
role	O
of	O
fMRI	B-Algorithm
in	O
clinical	O
applications	O
.	O
</s>
<s>
The	O
CBF	O
method	O
provides	O
more	O
quantitative	O
information	O
than	O
the	O
BOLD	B-Algorithm
signal	I-Algorithm
,	O
albeit	O
at	O
a	O
significant	O
loss	O
of	O
detection	O
sensitivity	O
.	O
</s>
<s>
Magnetic	B-Algorithm
resonance	I-Algorithm
angiography	I-Algorithm
(	O
MRA	O
)	O
is	O
a	O
group	O
of	O
techniques	O
based	O
to	O
image	O
blood	O
vessels	O
.	O
</s>
<s>
Magnetic	B-Algorithm
resonance	I-Algorithm
angiography	I-Algorithm
is	O
used	O
to	O
generate	O
images	O
of	O
arteries	O
(	O
and	O
less	O
commonly	O
veins	O
)	O
in	O
order	O
to	O
evaluate	O
them	O
for	O
stenosis	O
(	O
abnormal	O
narrowing	O
)	O
,	O
occlusions	O
,	O
aneurysms	O
(	O
vessel	O
wall	O
dilatations	O
,	O
at	O
risk	O
of	O
rupture	O
)	O
or	O
other	O
abnormalities	O
.	O
</s>
<s>
Susceptibility-weighted	O
imaging	O
(	O
SWI	O
)	O
is	O
a	O
new	O
type	O
of	O
contrast	O
in	O
MRI	O
different	O
from	O
spin	O
density	O
,	O
T1	B-Algorithm
,	O
or	O
T2	O
imaging	O
.	O
</s>
<s>
Bound	O
protons	B-Application
are	O
associated	O
with	O
proteins	O
and	O
as	O
they	O
have	O
a	O
very	O
short	O
T2	O
decay	O
they	O
do	O
not	O
normally	O
contribute	O
to	O
image	O
contrast	O
.	O
</s>
<s>
However	O
,	O
because	O
these	O
protons	B-Application
have	O
a	O
broad	O
resonance	O
peak	O
they	O
can	O
be	O
excited	O
by	O
a	O
radiofrequency	O
pulse	O
that	O
has	O
no	O
effect	O
on	O
free	O
protons	B-Application
.	O
</s>
<s>
The	O
most	O
common	O
use	O
of	O
this	O
technique	O
is	O
for	O
suppression	O
of	O
background	O
signal	O
in	O
time	O
of	O
flight	O
MR	B-Algorithm
angiography	I-Algorithm
.	O
</s>
<s>
There	O
are	O
also	O
applications	O
in	O
neuroimaging	O
particularly	O
in	O
the	O
characterization	O
of	O
white	B-Algorithm
matter	I-Algorithm
lesions	I-Algorithm
in	O
multiple	O
sclerosis	O
.	O
</s>
<s>
It	O
is	O
used	O
to	O
detect	O
the	O
atrophy	O
of	O
these	O
nuclei	O
in	O
Parkinson	O
's	O
disease	O
and	O
other	O
parkinsonisms	O
,	O
and	O
also	O
detects	O
signal	O
intensity	O
changes	O
in	O
major	O
depressive	O
disorder	O
and	O
schizophrenia	B-Application
.	O
</s>
<s>
T1	B-Algorithm
rho	O
(	O
T1ρ	O
)	O
is	O
an	O
experimental	O
MRI	B-Algorithm
sequence	I-Algorithm
that	O
may	O
be	O
used	O
in	O
musculoskeletal	O
imaging	O
.	O
</s>
<s>
This	O
type	O
of	O
decay	O
,	O
occurring	O
under	O
the	O
influence	O
of	O
RF	O
,	O
is	O
known	O
as	O
T1ρ	O
.	O
</s>
<s>
It	O
is	O
similar	O
to	O
T2	O
decay	O
but	O
with	O
some	O
slower	O
dipolar	O
interactions	O
refocused	O
,	O
as	O
well	O
as	O
static	O
interactions	O
,	O
hence	O
T1ρ≥T2	O
.	O
</s>
<s>
Saturation	O
recovery	O
sequences	O
are	O
rarely	O
used	O
,	O
but	O
can	O
measure	O
spin-lattice	B-Algorithm
relaxation	I-Algorithm
time	I-Algorithm
(	O
T1	B-Algorithm
)	O
more	O
quickly	O
than	O
an	O
inversion	O
recovery	O
pulse	O
sequence	O
.	O
</s>
<s>
Double-oscillating-diffusion-encoding	O
(	O
DODE	O
)	O
and	O
double	O
diffusion	O
encoding	O
(	O
DDE	O
)	O
imaging	O
are	O
specific	O
forms	O
of	O
MRI	O
diffusion	B-Algorithm
imaging	I-Algorithm
,	O
which	O
can	O
be	O
used	O
to	O
measure	O
diameters	O
and	O
lengths	O
of	O
axon	B-Algorithm
pores	O
.	O
</s>
