<s>
Neuroimaging	B-Algorithm
is	O
the	O
use	O
of	O
quantitative	O
(	O
computational	O
)	O
techniques	O
to	O
study	O
the	O
structure	O
and	O
function	O
of	O
the	O
central	O
nervous	O
system	O
,	O
developed	O
as	O
an	O
objective	O
way	O
of	O
scientifically	O
studying	O
the	O
healthy	O
human	O
brain	O
in	O
a	O
non-invasive	O
manner	O
.	O
</s>
<s>
Neuroimaging	B-Algorithm
is	O
a	O
highly	O
multidisciplinary	O
research	O
field	O
and	O
is	O
not	O
a	O
medical	O
specialty	O
(	O
however	O
post-residency	O
fellowships	O
in	O
Neuro-Radiology	O
do	O
exist	O
)	O
.	O
</s>
<s>
Neuroimaging	B-Algorithm
differs	O
from	O
neuroradiology	B-Algorithm
which	O
is	O
a	O
medical	O
specialty	O
and	O
uses	O
brain	B-Algorithm
imaging	I-Algorithm
in	O
a	O
clinical	O
setting	O
.	O
</s>
<s>
Neuroradiology	B-Algorithm
is	O
practiced	O
by	O
radiologists	O
who	O
are	O
medical	O
practitioners	O
.	O
</s>
<s>
Neuroradiology	B-Algorithm
primarily	O
focuses	O
on	O
identifying	O
brain	O
lesions	O
,	O
such	O
as	O
vascular	O
disease	O
,	O
strokes	O
,	O
tumors	O
and	O
inflammatory	O
disease	O
.	O
</s>
<s>
In	O
contrast	O
to	O
neuroimaging	B-Algorithm
,	O
neuroradiology	B-Algorithm
is	O
qualitative	O
(	O
based	O
on	O
subjective	O
impressions	O
and	O
extensive	O
clinical	O
training	O
)	O
but	O
sometimes	O
uses	O
basic	O
quantitative	O
methods	O
.	O
</s>
<s>
Functional	O
brain	B-Algorithm
imaging	I-Algorithm
techniques	O
,	O
such	O
as	O
functional	B-Algorithm
magnetic	I-Algorithm
resonance	I-Algorithm
imaging	I-Algorithm
(	O
fMRI	B-Algorithm
)	O
,	O
are	O
common	O
in	O
neuroimaging	B-Algorithm
but	O
rarely	O
used	O
in	O
neuroradiology	B-Algorithm
.	O
</s>
<s>
Neuroimaging	B-Algorithm
falls	O
into	O
two	O
broad	O
categories	O
:	O
</s>
<s>
Structural	O
imaging	O
,	O
which	O
is	O
used	O
to	O
quantify	O
brain	O
structure	O
using	O
e	O
,	O
g	O
,	O
voxel	B-Algorithm
based	I-Algorithm
morphometry	I-Algorithm
.	O
</s>
<s>
Functional	B-Algorithm
imaging	I-Algorithm
,	O
which	O
is	O
used	O
to	O
study	O
brain	O
function	O
,	O
often	O
using	O
fMRI	B-Algorithm
and	O
other	O
techniques	O
such	O
as	O
PET	O
and	O
MEG	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
The	O
first	O
chapter	O
of	O
the	O
history	O
of	O
neuroimaging	B-Algorithm
traces	O
back	O
to	O
the	O
Italian	O
neuroscientist	O
Angelo	O
Mosso	O
who	O
invented	O
the	O
'	O
human	O
circulation	O
balance	O
 '	O
,	O
which	O
could	O
non-invasively	O
measure	O
the	O
redistribution	O
of	O
blood	O
during	O
emotional	O
and	O
intellectual	O
activity	O
.	O
</s>
<s>
X-ray	B-Library
images	O
of	O
the	O
ventricular	O
system	O
within	O
the	O
brain	O
were	O
obtained	O
by	O
injection	O
of	O
filtered	O
air	O
directly	O
into	O
one	O
or	O
both	O
lateral	O
ventricles	O
of	O
the	O
brain	O
.	O
</s>
<s>
Soon	O
after	O
the	O
introduction	O
of	O
CAT	O
in	O
the	O
early	O
1980s	O
,	O
the	O
development	O
of	O
radioligands	O
allowed	O
single-photon	O
emission	O
computed	O
tomography	O
(	O
SPECT	O
)	O
and	O
positron	B-Application
emission	I-Application
tomography	I-Application
(	O
PET	O
)	O
of	O
the	O
brain	O
.	O
</s>
<s>
More	O
or	O
less	O
concurrently	O
,	O
magnetic	O
resonance	O
imaging	O
(	O
MRI	B-Algorithm
or	O
MR	O
scanning	O
)	O
was	O
developed	O
by	O
researchers	O
including	O
Peter	O
Mansfield	O
and	O
Paul	O
Lauterbur	O
,	O
who	O
were	O
awarded	O
the	O
Nobel	O
Prize	O
for	O
Physiology	O
or	O
Medicine	O
in	O
2003	O
.	O
</s>
<s>
In	O
the	O
early	O
1980s	O
MRI	B-Algorithm
was	O
introduced	O
clinically	O
,	O
and	O
during	O
the	O
1980s	O
a	O
veritable	O
explosion	O
of	O
technical	O
refinements	O
and	O
diagnostic	O
MR	O
applications	O
took	O
place	O
.	O
</s>
<s>
Scientists	O
soon	O
learned	O
that	O
the	O
large	O
blood	O
flow	O
changes	O
measured	O
by	O
PET	O
could	O
also	O
be	O
imaged	O
by	O
the	O
correct	O
type	O
of	O
MRI	B-Algorithm
.	O
</s>
<s>
since	O
the	O
1990s	O
,	O
fMRI	B-Algorithm
has	O
come	O
to	O
dominate	O
the	O
brain	O
mapping	O
field	O
due	O
to	O
its	O
low	O
invasiveness	O
,	O
lack	O
of	O
radiation	O
exposure	O
,	O
and	O
relatively	O
wide	O
availability	O
.	O
</s>
<s>
In	O
the	O
early	O
2000s	O
,	O
the	O
field	O
of	O
neuroimaging	B-Algorithm
reached	O
the	O
stage	O
where	O
limited	O
practical	O
applications	O
of	O
functional	O
brain	B-Algorithm
imaging	I-Algorithm
have	O
become	O
feasible	O
.	O
</s>
<s>
The	O
main	O
application	O
area	O
is	O
crude	O
forms	O
of	O
brain	B-Application
–	I-Application
computer	I-Application
interface	I-Application
.	O
</s>
<s>
The	O
world	O
record	O
for	O
the	O
spatial	O
resolution	O
of	O
a	O
whole-brain	O
MRI	B-Algorithm
image	O
was	O
a	O
100-micrometer	O
volume	O
(	O
image	O
)	O
achieved	O
in	O
2019	O
.	O
</s>
<s>
Neuroradiology	B-Algorithm
often	O
follows	O
a	O
neurological	O
examination	O
in	O
which	O
a	O
physician	O
has	O
found	O
cause	O
to	O
more	O
deeply	O
investigate	O
a	O
patient	O
who	O
has	O
or	O
may	O
have	O
a	O
neurological	O
disorder	O
.	O
</s>
<s>
Common	O
clinical	O
indications	O
for	O
neuroimaging	B-Algorithm
include	O
head	O
trauma	O
,	O
stroke	O
like	O
symptoms	O
eg	O
:	O
sudden	O
weakness/numbness	O
in	O
one	O
half	O
of	O
body	O
,	O
difficulty	O
talking	O
or	O
walking	O
;	O
seizures	O
,	O
sudden	O
onset	O
severe	O
headache	O
,	O
sudden	O
change	O
in	O
level	O
of	O
consciousness	O
for	O
unclear	O
reasons	O
.	O
</s>
<s>
Another	O
indication	O
for	O
neuroradiology	B-Algorithm
is	O
CT-	O
,	O
MRI	B-Algorithm
-	O
and	O
PET-guided	O
stereotactic	O
surgery	O
or	O
radiosurgery	O
for	O
treatment	O
of	O
intracranial	O
tumors	O
,	O
arteriovenous	O
malformations	O
and	O
other	O
surgically	O
treatable	O
conditions	O
.	O
</s>
<s>
Neuroradiology	B-Algorithm
is	O
not	O
indicated	O
for	O
patients	O
with	O
stable	O
headaches	O
which	O
are	O
diagnosed	O
as	O
migraine	O
.	O
</s>
<s>
Computed	O
tomography	O
(	O
CT	O
)	O
or	O
Computed	O
Axial	O
Tomography	O
(	O
CAT	O
)	O
scanning	O
uses	O
a	O
series	O
of	O
x-rays	B-Library
of	O
the	O
head	O
taken	O
from	O
many	O
different	O
directions	O
.	O
</s>
<s>
Typically	O
used	O
for	O
quickly	O
viewing	O
brain	O
injuries	O
,	O
CT	O
scanning	O
uses	O
a	O
computer	O
program	O
that	O
performs	O
a	O
numerical	O
integral	O
calculation	O
(	O
the	O
inverse	B-Algorithm
Radon	I-Algorithm
transform	I-Algorithm
)	O
on	O
the	O
measured	O
x-ray	B-Library
series	O
to	O
estimate	O
how	O
much	O
of	O
an	O
x-ray	B-Library
beam	O
is	O
absorbed	O
in	O
a	O
small	O
volume	O
of	O
the	O
brain	O
.	O
</s>
<s>
Magnetic	O
resonance	O
imaging	O
(	O
MRI	B-Algorithm
)	O
uses	O
magnetic	O
fields	O
and	O
radio	O
waves	O
to	O
produce	O
high	O
quality	O
two	O
-	O
or	O
three-dimensional	O
images	O
of	O
brain	O
structures	O
without	O
the	O
use	O
of	O
ionizing	O
radiation	O
(	O
X-rays	B-Library
)	O
or	O
radioactive	O
tracers	O
.	O
</s>
<s>
Positron	B-Application
emission	I-Application
tomography	I-Application
(	O
PET	O
)	O
and	O
brain	B-Algorithm
positron	I-Algorithm
emission	I-Algorithm
tomography	I-Algorithm
,	O
measure	O
emissions	O
from	O
radioactively	O
labeled	O
metabolically	O
active	O
chemicals	O
that	O
have	O
been	O
injected	O
into	O
the	O
bloodstream	O
.	O
</s>
<s>
Sensors	O
in	O
the	O
PET	B-Application
scanner	I-Application
detect	O
the	O
radioactivity	O
as	O
the	O
compound	O
accumulates	O
in	O
various	O
regions	O
of	O
the	O
brain	O
.	O
</s>
<s>
Especially	O
useful	O
are	O
a	O
wide	O
array	O
of	O
ligands	O
used	O
to	O
map	O
different	O
aspects	O
of	O
neurotransmitter	O
activity	O
,	O
with	O
by	O
far	O
the	O
most	O
commonly	O
used	O
PET	O
tracer	O
being	O
a	O
labeled	O
form	O
of	O
glucose	O
(	O
see	O
Fludeoxyglucose	B-Application
(	O
18F	O
)	O
(	O
FDG	O
)	O
)	O
.	O
</s>
<s>
These	O
measurements	O
reflect	O
the	O
amount	O
of	O
brain	B-Application
activity	I-Application
in	O
the	O
various	O
regions	O
of	O
the	O
brain	O
and	O
allow	O
to	O
learn	O
more	O
about	O
how	O
the	O
brain	O
works	O
.	O
</s>
<s>
PET	B-Application
scans	I-Application
were	O
superior	O
to	O
all	O
other	O
metabolic	O
imaging	O
methods	O
in	O
terms	O
of	O
resolution	O
and	O
speed	O
of	O
completion	O
(	O
as	O
little	O
as	O
30	O
seconds	O
)	O
when	O
they	O
first	O
became	O
available	O
.	O
</s>
<s>
Before	O
fMRI	B-Algorithm
technology	O
came	O
online	O
,	O
PET	O
scanning	O
was	O
the	O
preferred	O
method	O
of	O
functional	O
(	O
as	O
opposed	O
to	O
structural	O
)	O
brain	B-Algorithm
imaging	I-Algorithm
,	O
and	O
it	O
continues	O
to	O
make	O
large	O
contributions	O
to	O
neuroscience	O
.	O
</s>
<s>
PET	O
scanning	O
is	O
also	O
used	O
for	O
diagnosis	O
of	O
brain	O
disease	O
,	O
most	O
notably	O
brain	O
tumors	O
,	O
epilepsy	O
,	O
and	O
neuron-damaging	O
diseases	O
which	O
cause	O
dementia	O
(	O
such	O
as	O
Alzheimer	O
's	O
disease	O
)	O
all	O
cause	O
great	O
changes	O
in	O
brain	O
metabolism	O
,	O
which	O
in	O
turn	O
causes	O
easily	O
detectable	O
changes	O
in	O
PET	B-Application
scans	I-Application
.	O
</s>
<s>
PET	O
is	O
probably	O
most	O
useful	O
in	O
early	O
cases	O
of	O
certain	O
dementias	O
(	O
with	O
classic	O
examples	O
being	O
Alzheimer	O
's	O
disease	O
and	O
Pick	O
's	O
disease	O
)	O
where	O
the	O
early	O
damage	O
is	O
too	O
diffuse	O
and	O
makes	O
too	O
little	O
difference	O
in	O
brain	O
volume	O
and	O
gross	O
structure	O
to	O
change	O
CT	O
and	O
standard	O
MRI	B-Algorithm
images	O
enough	O
to	O
be	O
able	O
to	O
reliably	O
differentiate	O
it	O
from	O
the	O
"	O
normal	O
"	O
range	O
of	O
cortical	O
atrophy	O
which	O
occurs	O
with	O
aging	O
(	O
in	O
many	O
but	O
not	O
all	O
)	O
persons	O
,	O
and	O
which	O
does	O
not	O
cause	O
clinical	O
dementia	O
.	O
</s>
<s>
FDG-PET	B-Application
scanning	O
is	O
also	O
often	O
used	O
in	O
assessment	O
of	O
patients	O
with	O
epilepsy	O
who	O
continue	O
to	O
have	O
seizures	O
despite	O
adequate	O
medical	O
treatment	O
.	O
</s>
<s>
A	O
significant	O
limitation	O
of	O
SPECT	O
is	O
its	O
poor	O
resolution	O
(	O
about	O
1cm	O
)	O
compared	O
to	O
that	O
of	O
MRI	B-Algorithm
.	O
</s>
<s>
Tomographic	B-Algorithm
reconstruction	I-Algorithm
,	O
(	O
mainly	O
used	O
for	O
functional	O
"	O
snapshots	O
"	O
of	O
the	O
brain	O
)	O
requires	O
multiple	O
projections	O
from	O
Detector	O
Heads	O
which	O
rotate	O
around	O
the	O
human	O
skull	O
,	O
so	O
some	O
researchers	O
have	O
developed	O
6	O
and	O
11	O
Detector	O
Head	O
SPECT	O
machines	O
to	O
cut	O
imaging	O
time	O
and	O
give	O
higher	O
resolution	O
.	O
</s>
<s>
Cranial	B-Algorithm
ultrasound	I-Algorithm
is	O
usually	O
only	O
used	O
in	O
babies	O
,	O
whose	O
open	O
fontanelles	O
provide	O
acoustic	O
windows	O
allowing	O
ultrasound	O
imaging	O
of	O
the	O
brain	O
.	O
</s>
<s>
Advantages	O
include	O
the	O
absence	O
of	O
ionising	O
radiation	O
and	O
the	O
possibility	O
of	O
bedside	O
scanning	O
,	O
but	O
the	O
lack	O
of	O
soft-tissue	O
detail	O
means	O
MRI	B-Algorithm
is	O
preferred	O
for	O
some	O
conditions	O
.	O
</s>
<s>
Functional	B-Algorithm
magnetic	I-Algorithm
resonance	I-Algorithm
imaging	I-Algorithm
(	O
fMRI	B-Algorithm
)	O
and	O
arterial	B-Algorithm
spin	I-Algorithm
labeling	I-Algorithm
(	O
ASL	O
)	O
relies	O
on	O
the	O
paramagnetic	O
properties	O
of	O
oxygenated	O
and	O
deoxygenated	O
hemoglobin	O
to	O
see	O
images	O
of	O
changing	O
blood	O
flow	O
in	O
the	O
brain	O
associated	O
with	O
neural	O
activity	O
.	O
</s>
<s>
Most	O
fMRI	B-Algorithm
scanners	O
allow	O
subjects	O
to	O
be	O
presented	O
with	O
different	O
visual	O
images	O
,	O
sounds	O
and	O
touch	O
stimuli	O
,	O
and	O
to	O
make	O
different	O
actions	O
such	O
as	O
pressing	O
a	O
button	O
or	O
moving	O
a	O
joystick	O
.	O
</s>
<s>
Consequently	O
,	O
fMRI	B-Algorithm
can	O
be	O
used	O
to	O
reveal	O
brain	O
structures	O
and	O
processes	O
associated	O
with	O
perception	O
,	O
thought	O
and	O
action	O
.	O
</s>
<s>
The	O
resolution	O
of	O
fMRI	B-Algorithm
is	O
about	O
2-3	O
millimeters	O
at	O
present	O
,	O
limited	O
by	O
the	O
spatial	O
spread	O
of	O
the	O
hemodynamic	O
response	O
to	O
neural	O
activity	O
.	O
</s>
<s>
There	O
is	O
also	O
significant	O
concern	O
regarding	O
the	O
validity	O
of	O
some	O
of	O
the	O
statistics	O
used	O
in	O
fMRI	B-Algorithm
analyses	O
;	O
hence	O
,	O
the	O
validity	O
of	O
conclusions	O
drawn	O
from	O
many	O
fMRI	B-Algorithm
studies	O
.	O
</s>
<s>
With	O
between	O
72%	O
and	O
90%	O
accuracy	O
where	O
chance	O
would	O
achieve	O
0.8	O
%	O
,	O
fMRI	B-Algorithm
techniques	O
can	O
decide	O
which	O
of	O
a	O
set	O
of	O
known	O
images	O
the	O
subject	O
is	O
viewing	O
.	O
</s>
<s>
Recent	O
studies	O
on	O
machine	O
learning	O
in	O
psychiatry	O
have	O
used	O
fMRI	B-Algorithm
to	O
build	O
machine	O
learning	O
models	O
that	O
can	O
discriminate	O
between	O
individuals	O
with	O
or	O
without	O
suicidal	O
behaviour	O
.	O
</s>
<s>
Imaging	B-Application
studies	I-Application
in	O
conjunction	O
with	O
machine	O
learning	O
algorithms	O
may	O
help	O
identify	O
new	O
markers	O
in	O
neuroimaging	B-Algorithm
that	O
could	O
allow	O
stratification	O
based	O
on	O
patients	O
 '	O
suicide	O
risk	O
and	O
help	O
develop	O
the	O
best	O
therapies	O
and	O
treatments	O
for	O
individual	O
patients	O
.	O
</s>
<s>
Diffuse	B-Algorithm
optical	I-Algorithm
imaging	I-Algorithm
(	O
DOI	O
)	O
or	O
diffuse	B-Algorithm
optical	I-Algorithm
tomography	I-Algorithm
(	O
DOT	O
)	O
is	O
a	O
medical	B-Application
imaging	I-Application
modality	O
which	O
uses	O
near	O
infrared	O
light	O
to	O
generate	O
images	O
of	O
the	O
body	O
.	O
</s>
<s>
High-density	O
diffuse	B-Algorithm
optical	I-Algorithm
tomography	I-Algorithm
(	O
HD-DOT	O
)	O
has	O
been	O
compared	O
directly	O
to	O
fMRI	B-Algorithm
using	O
response	O
to	O
visual	O
stimulation	O
in	O
subjects	O
studied	O
with	O
both	O
techniques	O
,	O
with	O
reassuringly	O
similar	O
results	O
.	O
</s>
<s>
HD-DOT	O
has	O
also	O
been	O
compared	O
to	O
fMRI	B-Algorithm
in	O
terms	O
of	O
language	O
tasks	O
and	O
resting	O
state	O
functional	O
connectivity	O
.	O
</s>
<s>
Event-related	B-Algorithm
optical	I-Algorithm
signal	I-Algorithm
(	O
EROS	O
)	O
is	O
a	O
brain-scanning	O
technique	O
which	O
uses	O
infrared	O
light	O
through	O
optical	O
fibers	O
to	O
measure	O
changes	O
in	O
optical	O
properties	O
of	O
active	O
areas	O
of	O
the	O
cerebral	O
cortex	O
.	O
</s>
<s>
Whereas	O
techniques	O
such	O
as	O
diffuse	B-Algorithm
optical	I-Algorithm
imaging	I-Algorithm
(	O
DOT	O
)	O
and	O
near-infrared	O
spectroscopy	O
(	O
NIRS	O
)	O
measure	O
optical	O
absorption	O
of	O
haemoglobin	O
,	O
and	O
thus	O
are	O
based	O
on	O
blood	O
flow	O
,	O
EROS	O
takes	O
advantage	O
of	O
the	O
scattering	O
properties	O
of	O
the	O
neurons	O
themselves	O
and	O
thus	O
provides	O
a	O
much	O
more	O
direct	O
measure	O
of	O
cellular	O
activity	O
.	O
</s>
<s>
It	O
was	O
developed	O
at	O
the	O
University	O
of	O
Illinois	O
at	O
Urbana-Champaign	O
where	O
it	O
is	O
now	O
used	O
in	O
the	O
Cognitive	O
Neuroimaging	B-Algorithm
Laboratory	O
of	O
Dr.	O
Gabriele	O
Gratton	O
and	O
Dr.	O
Monica	O
Fabiani	O
.	O
</s>
<s>
Magnetoencephalography	B-Algorithm
(	O
MEG	O
)	O
is	O
an	O
imaging	O
technique	O
used	O
to	O
measure	O
the	O
magnetic	O
fields	O
produced	O
by	O
electrical	O
activity	O
in	O
the	O
brain	O
via	O
extremely	O
sensitive	O
devices	O
such	O
as	O
superconducting	B-Protocol
quantum	I-Protocol
interference	I-Protocol
devices	I-Protocol
(	O
SQUIDs	B-Protocol
)	O
or	O
spin	O
exchange	O
relaxation-free	O
(	O
SERF	O
)	O
magnetometers	O
.	O
</s>
<s>
MEG	O
offers	O
a	O
very	O
direct	O
measurement	O
of	O
neural	O
electrical	O
activity	O
(	O
compared	O
to	O
fMRI	B-Algorithm
for	O
example	O
)	O
with	O
very	O
high	O
temporal	O
resolution	O
but	O
relatively	O
low	O
spatial	O
resolution	O
.	O
</s>
<s>
The	O
advantage	O
of	O
measuring	O
the	O
magnetic	O
fields	O
produced	O
by	O
neural	O
activity	O
is	O
that	O
they	O
are	O
likely	O
to	O
be	O
less	O
distorted	O
by	O
surrounding	O
tissue	O
(	O
particularly	O
the	O
skull	O
and	O
scalp	O
)	O
compared	O
to	O
the	O
electric	O
fields	O
measured	O
by	O
electroencephalography	B-Application
(	O
EEG	B-Application
)	O
.	O
</s>
<s>
While	O
skull	O
anisotropy	O
has	O
a	O
negligible	O
effect	O
on	O
MEG	O
(	O
unlike	O
EEG	B-Application
)	O
,	O
white	O
matter	O
anisotropy	O
strongly	O
affects	O
MEG	O
measurements	O
for	O
radial	O
and	O
deep	O
sources	O
.	O
</s>
<s>
This	O
makes	O
it	O
likely	O
that	O
MEG	O
is	O
also	O
affected	O
by	O
the	O
skull	O
anisotropy	O
,	O
although	O
probably	O
not	O
to	O
the	O
same	O
degree	O
as	O
EEG	B-Application
.	O
</s>
<s>
Functional	B-Algorithm
ultrasound	I-Algorithm
imaging	I-Algorithm
(	O
fUS	O
)	O
is	O
a	O
medical	O
ultrasound	O
imaging	O
technique	O
of	O
detecting	O
or	O
measuring	O
changes	O
in	O
neural	O
activities	O
or	O
metabolism	O
,	O
for	O
example	O
,	O
the	O
loci	O
of	O
brain	B-Application
activity	I-Application
,	O
typically	O
through	O
measuring	O
blood	O
flow	O
or	O
hemodynamic	O
changes	O
.	O
</s>
<s>
fMRI	B-Algorithm
is	O
commonly	O
classified	O
as	O
a	O
minimally-to-moderate	O
risk	O
due	O
to	O
its	O
non-invasiveness	O
compared	O
to	O
other	O
imaging	O
methods	O
.	O
</s>
<s>
fMRI	B-Algorithm
uses	O
blood	O
oxygenation	O
level	O
dependent	O
(	O
BOLD	B-Algorithm
)	O
-contrast	O
in	O
order	O
to	O
produce	O
its	O
form	O
of	O
imaging	O
.	O
</s>
<s>
BOLD-contrast	O
is	O
a	O
naturally	O
occurring	O
process	O
in	O
the	O
body	O
so	O
fMRI	B-Algorithm
is	O
often	O
preferred	O
over	O
imaging	O
methods	O
that	O
require	O
radioactive	O
markers	O
to	O
produce	O
similar	O
imaging	O
.	O
</s>
<s>
A	O
concern	O
in	O
the	O
use	O
of	O
fMRI	B-Algorithm
is	O
its	O
use	O
in	O
individuals	O
with	O
medical	O
implants	O
or	O
devices	O
and	O
metallic	O
items	O
in	O
the	O
body	O
.	O
</s>
<s>
CT	O
scans	O
can	O
expose	O
patients	O
to	O
levels	O
of	O
radiation	O
100-500	O
times	O
higher	O
than	O
traditional	O
x-rays	B-Library
,	O
with	O
higher	O
radiation	O
doses	O
producing	O
better	O
resolution	O
imaging	O
.	O
</s>
<s>
In	O
PET	B-Application
scans	I-Application
,	O
imaging	O
does	O
not	O
rely	O
on	O
intrinsic	O
biological	O
processes	O
,	O
but	O
relies	O
on	O
a	O
foreign	O
substance	O
injected	O
into	O
the	O
bloodstream	O
traveling	O
to	O
the	O
brain	O
.	O
</s>
<s>
Patients	O
are	O
injected	O
with	O
radioisotopes	O
that	O
are	O
metabolized	O
in	O
the	O
brain	O
and	O
emit	O
positrons	O
to	O
produce	O
a	O
visualization	O
of	O
brain	B-Application
activity	I-Application
.	O
</s>
<s>
The	O
amount	O
of	O
radiation	O
a	O
patient	O
is	O
exposed	O
to	O
in	O
a	O
PET	B-Application
scan	I-Application
is	O
relatively	O
small	O
,	O
comparable	O
to	O
the	O
amount	O
of	O
environmental	O
radiation	O
an	O
individual	O
is	O
exposed	O
to	O
across	O
a	O
year	O
.	O
</s>
<s>
Currently	O
,	O
fMRI	B-Algorithm
is	O
a	O
preferred	O
method	O
of	O
imaging	O
brain	B-Application
activity	I-Application
compared	O
to	O
PET	O
,	O
since	O
it	O
does	O
not	O
involve	O
radiation	O
,	O
has	O
a	O
higher	O
temporal	O
resolution	O
than	O
PET	O
,	O
and	O
is	O
more	O
readily	O
available	O
in	O
most	O
medical	O
settings	O
.	O
</s>
<s>
The	O
high	O
temporal	O
resolution	O
of	O
MEG	O
and	O
EEG	B-Application
allow	O
these	O
methods	O
to	O
measure	O
brain	B-Application
activity	I-Application
down	O
to	O
the	O
millisecond	O
.	O
</s>
<s>
Both	O
MEG	O
and	O
EEG	B-Application
do	O
not	O
require	O
exposure	O
of	O
the	O
patient	O
to	O
radiation	O
to	O
function	O
.	O
</s>
<s>
EEG	B-Application
electrodes	O
detect	O
electrical	O
signals	O
produced	O
by	O
neurons	O
to	O
measure	O
brain	B-Application
activity	I-Application
and	O
MEG	O
uses	O
oscillations	O
in	O
the	O
magnetic	O
field	O
produced	O
by	O
these	O
electrical	O
currents	O
to	O
measure	O
activity	O
.	O
</s>
<s>
EEG	B-Application
is	O
a	O
much	O
more	O
widely	O
used	O
method	O
to	O
achieve	O
such	O
temporal	O
resolution	O
as	O
EEG	B-Application
systems	O
cost	O
much	O
less	O
than	O
MEG	O
systems	O
.	O
</s>
<s>
A	O
disadvantage	O
of	O
EEG	B-Application
and	O
MEG	O
is	O
that	O
both	O
methods	O
have	O
poor	O
spatial	O
resolution	O
when	O
compared	O
to	O
fMRI	B-Algorithm
.	O
</s>
