<s>
Positron	B-Application
emission	I-Application
tomography	I-Application
(	O
PET	O
)	O
is	O
a	O
functional	B-Algorithm
imaging	I-Algorithm
technique	O
that	O
uses	O
radioactive	O
substances	O
known	O
as	O
radiotracers	O
to	O
visualize	O
and	O
measure	O
changes	O
in	O
metabolic	O
processes	O
,	O
and	O
in	O
other	O
physiological	O
activities	O
including	O
blood	O
flow	O
,	O
regional	O
chemical	O
composition	O
,	O
and	O
absorption	O
.	O
</s>
<s>
For	O
example	O
,	O
-FDG	O
is	O
commonly	O
used	O
to	O
detect	O
cancer	O
,	O
NaF	O
is	O
widely	O
used	O
for	O
detecting	O
bone	O
formation	O
,	O
and	O
oxygen-15	O
is	O
sometimes	O
used	O
to	O
measure	O
blood	O
flow	O
.	O
</s>
<s>
PET	O
is	O
a	O
common	O
imaging	B-Application
technique	I-Application
,	O
a	O
medical	O
scintillography	O
technique	O
used	O
in	O
nuclear	O
medicine	O
.	O
</s>
<s>
A	O
radiopharmaceutical	B-Algorithm
—	O
a	O
radioisotope	O
attached	O
to	O
a	O
drug	O
—	O
is	O
injected	O
into	O
the	O
body	O
as	O
a	O
tracer	O
.	O
</s>
<s>
When	O
the	O
radiopharmaceutical	B-Algorithm
undergoes	O
beta	O
plus	O
decay	O
,	O
a	O
positron	O
is	O
emitted	O
,	O
and	O
when	O
the	O
positron	O
collides	O
with	O
an	O
ordinary	O
electron	O
,	O
the	O
two	O
particles	O
annihilate	O
and	O
gamma	O
rays	O
are	O
emitted	O
.	O
</s>
<s>
These	O
gamma	O
rays	O
are	O
detected	O
by	O
gamma	O
cameras	O
to	O
form	O
a	O
three-dimensional	O
image	O
,	O
in	O
a	O
similar	O
way	O
that	O
an	O
X-ray	B-Library
image	O
is	O
captured	O
.	O
</s>
<s>
PET	B-Application
scanners	I-Application
can	O
incorporate	O
a	O
CT	O
scanner	O
and	O
are	O
known	O
as	O
PET-CT	O
scanners	O
.	O
</s>
<s>
PET	B-Application
scan	I-Application
images	O
can	O
be	O
reconstructed	O
using	O
a	O
CT	O
scan	O
performed	O
using	O
one	O
scanner	O
during	O
the	O
same	O
session	O
.	O
</s>
<s>
One	O
of	O
the	O
disadvantages	O
of	O
a	O
PET	B-Application
scanner	I-Application
is	O
its	O
high	O
initial	O
cost	O
and	O
ongoing	O
operating	O
costs	O
.	O
</s>
<s>
Regional	O
tracer	O
uptake	O
in	O
various	O
anatomic	O
structures	O
can	O
be	O
visualized	O
and	O
relatively	O
quantified	O
in	O
terms	O
of	O
injected	O
positron	O
emitter	O
within	O
a	O
PET	B-Application
scan	I-Application
.	O
</s>
<s>
PET	B-Application
imaging	I-Application
is	O
best	O
performed	O
using	O
a	O
dedicated	O
PET	B-Application
scanner	I-Application
.	O
</s>
<s>
The	O
quality	O
of	O
gamma-camera	O
PET	B-Application
imaging	I-Application
is	O
lower	O
,	O
and	O
the	O
scans	O
take	O
longer	O
to	O
acquire	O
.	O
</s>
<s>
Alternative	O
methods	O
of	O
medical	B-Application
imaging	I-Application
include	O
single-photon	O
emission	O
computed	O
tomography	B-Algorithm
(	O
SPECT	O
)	O
,	O
x-ray	B-Library
computed	O
tomography	B-Algorithm
(	O
CT	O
)	O
,	O
magnetic	O
resonance	O
imaging	O
(	O
MRI	O
)	O
and	O
functional	B-Algorithm
magnetic	I-Algorithm
resonance	I-Algorithm
imaging	I-Algorithm
(	O
fMRI	B-Algorithm
)	O
,	O
and	O
ultrasound	B-Application
.	O
</s>
<s>
SPECT	O
is	O
an	O
imaging	B-Application
technique	I-Application
similar	O
to	O
PET	O
that	O
uses	O
radioligands	O
to	O
detect	O
molecules	O
in	O
the	O
body	O
.	O
</s>
<s>
PET	O
scanning	O
with	O
the	O
tracer	O
18F-FDG	B-Application
is	O
widely	O
used	O
in	O
clinical	O
oncology	O
.	O
</s>
<s>
FDG	B-Application
is	O
a	O
glucose	O
analog	O
that	O
is	O
taken	O
up	O
by	O
glucose-using	O
cells	O
and	O
phosphorylated	O
by	O
hexokinase	O
(	O
whose	O
mitochondrial	O
form	O
is	O
significantly	O
elevated	O
in	O
rapidly	O
growing	O
malignant	O
tumors	O
)	O
.	O
</s>
<s>
Metabolic	O
trapping	O
of	O
the	O
radioactive	O
glucose	O
molecule	O
allows	O
the	O
PET	B-Application
scan	I-Application
to	O
be	O
utilized	O
.	O
</s>
<s>
The	O
concentrations	O
of	O
imaged	O
FDG	B-Application
tracer	O
indicate	O
tissue	O
metabolic	O
activity	O
as	O
it	O
corresponds	O
to	O
the	O
regional	O
glucose	O
uptake	O
.	O
</s>
<s>
18F-FDG	B-Application
is	O
used	O
to	O
explore	O
the	O
possibility	O
of	O
cancer	O
spreading	O
to	O
other	O
body	O
sites	O
(	O
cancer	O
metastasis	O
)	O
.	O
</s>
<s>
These	O
18F-FDG	B-Application
PET	B-Application
scans	I-Application
for	O
detecting	O
cancer	O
metastasis	O
are	O
the	O
most	O
common	O
in	O
standard	O
medical	O
care	O
(	O
representing	O
90%	O
of	O
current	O
scans	O
)	O
.	O
</s>
<s>
Less	O
often	O
,	O
other	O
radioactive	O
tracers	O
,	O
usually	O
but	O
not	O
always	O
labelled	O
with	O
fluorine-18	O
,	O
are	O
used	O
to	O
image	O
the	O
tissue	O
concentration	O
of	O
different	O
kinds	O
of	O
molecules	O
of	O
interest	O
inside	O
the	O
body	O
.	O
</s>
<s>
A	O
typical	O
dose	O
of	O
FDG	B-Application
used	O
in	O
an	O
oncological	O
scan	O
has	O
an	O
effective	O
radiation	O
dose	O
of	O
7.6mSv	O
.	O
</s>
<s>
Because	O
the	O
hydroxy	O
group	O
that	O
is	O
replaced	O
by	O
fluorine-18	O
to	O
generate	O
FDG	B-Application
is	O
required	O
for	O
the	O
next	O
step	O
in	O
glucose	O
metabolism	O
in	O
all	O
cells	O
,	O
no	O
further	O
reactions	O
occur	O
in	O
FDG	B-Application
.	O
</s>
<s>
This	O
means	O
that	O
FDG	B-Application
is	O
trapped	O
in	O
any	O
cell	O
that	O
takes	O
it	O
up	O
until	O
it	O
decays	O
,	O
since	O
phosphorylated	O
sugars	O
,	O
due	O
to	O
their	O
ionic	O
charge	O
,	O
cannot	O
exit	O
from	O
the	O
cell	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
FDG-PET	B-Application
can	O
be	O
used	O
for	O
diagnosis	O
,	O
staging	O
,	O
and	O
monitoring	O
treatment	O
of	O
cancers	O
,	O
particularly	O
in	O
Hodgkin	O
lymphoma	O
,	O
non-Hodgkin	O
lymphoma	O
,	O
and	O
lung	O
cancer	O
.	O
</s>
<s>
A	O
2020	O
review	O
of	O
research	O
on	O
the	O
use	O
of	O
PET	O
for	O
Hodgkin	O
lymphoma	O
found	O
evidence	O
that	O
negative	O
findings	O
in	O
interim	O
PET	B-Application
scans	I-Application
are	O
linked	O
to	O
higher	O
overall	O
survival	O
and	O
progression-free	O
survival	O
;	O
however	O
,	O
the	O
certainty	O
of	O
the	O
available	O
evidence	O
was	O
moderate	O
for	O
survival	O
,	O
and	O
very	O
low	O
for	O
progression-free	O
survival	O
.	O
</s>
<s>
Also	O
,	O
FDOPA	O
PET/CT	O
(	O
or	O
F-18-DOPA	O
PET/CT	O
)	O
has	O
proven	O
to	O
be	O
a	O
more	O
sensitive	O
alternative	O
to	O
finding	O
and	O
also	O
localizing	O
pheochromocytoma	O
than	O
the	O
MIBG	O
scan	O
.	O
</s>
<s>
PET	B-Application
imaging	I-Application
with	O
oxygen-15	O
indirectly	O
measures	O
blood	O
flow	O
to	O
the	O
brain	O
.	O
</s>
<s>
PET	B-Application
imaging	I-Application
with	O
18F-FDG	B-Application
takes	O
advantage	O
of	O
the	O
fact	O
that	O
the	O
brain	O
is	O
normally	O
a	O
rapid	O
user	O
of	O
glucose	O
.	O
</s>
<s>
Standard	O
18F-FDG	B-Application
PET	O
of	O
the	O
brain	O
measures	O
regional	O
glucose	O
use	O
and	O
can	O
be	O
used	O
in	O
neuropathological	O
diagnosis	O
.	O
</s>
<s>
Therefore	O
18F-FDG	B-Application
PET	O
of	O
the	O
brain	O
may	O
also	O
be	O
used	O
to	O
successfully	O
differentiate	O
Alzheimer	O
's	O
disease	O
from	O
other	O
dementing	O
processes	O
,	O
and	O
also	O
to	O
make	O
early	O
diagnoses	O
of	O
Alzheimer	O
's	O
disease	O
.	O
</s>
<s>
The	O
advantage	O
of	O
18F-FDG	B-Application
PET	O
for	O
these	O
uses	O
is	O
its	O
much	O
wider	O
availability	O
.	O
</s>
<s>
PET	B-Application
imaging	I-Application
with	O
FDG	B-Application
can	O
also	O
be	O
used	O
for	O
localization	O
of	O
seizure	O
focus	O
.	O
</s>
<s>
FDG	B-Application
,	O
and	O
the	O
less	O
common	O
tracers	O
flumazenil	O
and	O
MPPF	O
have	O
been	O
explored	O
for	O
this	O
purpose	O
.	O
</s>
<s>
If	O
the	O
sclerosis	O
is	O
unilateral	O
(	O
right	O
hippocampus	O
or	O
left	O
hippocampus	O
)	O
,	O
18F-FDG	B-Application
uptake	O
can	O
be	O
compared	O
with	O
the	O
healthy	O
side	O
.	O
</s>
<s>
The	O
development	O
of	O
a	O
number	O
of	O
novel	O
probes	O
for	O
noninvasive	O
,	O
in	O
vivo	O
PET	B-Application
imaging	I-Application
of	O
neuroaggregate	O
in	O
human	O
brain	O
has	O
brought	O
amyloid	O
imaging	O
close	O
to	O
clinical	O
use	O
.	O
</s>
<s>
[11C]PMP	O
(	O
N-	O
 [ 11C ] 	O
methylpiperidin-4-yl	O
propionate	O
)	O
is	O
a	O
novel	O
radiopharmaceutical	B-Algorithm
used	O
in	O
PET	B-Application
imaging	I-Application
to	O
determine	O
the	O
activity	O
of	O
the	O
acetylcholinergic	O
neurotransmitter	O
system	O
by	O
acting	O
as	O
a	O
substrate	O
for	O
acetylcholinesterase	O
.	O
</s>
<s>
Avid	O
Radiopharmaceuticals	B-Algorithm
has	O
developed	O
and	O
commercialized	O
a	O
compound	O
called	O
florbetapir	O
that	O
uses	O
the	O
longer-lasting	O
radionuclide	O
fluorine-18	O
to	O
detect	O
amyloid	O
plaques	O
using	O
PET	B-Application
scans	I-Application
.	O
</s>
<s>
Numerous	O
compounds	O
that	O
bind	O
selectively	O
to	O
neuroreceptors	O
of	O
interest	O
in	O
biological	O
psychiatry	O
have	O
been	O
radiolabeled	O
with	O
C-11	O
or	O
F-18	O
.	O
</s>
<s>
Studies	O
have	O
been	O
performed	O
examining	O
the	O
state	O
of	O
these	O
receptors	O
in	O
patients	O
compared	O
to	O
healthy	O
controls	O
in	O
schizophrenia	B-Application
,	O
substance	O
abuse	O
,	O
mood	O
disorders	O
and	O
other	O
psychiatric	O
conditions	O
.	O
</s>
<s>
Cardiology	O
,	O
atherosclerosis	O
and	O
vascular	O
disease	O
study	O
:	O
18F-FDG	B-Application
PET	O
can	O
help	O
in	O
identifying	O
hibernating	O
myocardium	O
.	O
</s>
<s>
18F-FDG	B-Application
PET	B-Application
imaging	I-Application
of	O
atherosclerosis	O
to	O
detect	O
patients	O
at	O
risk	O
of	O
stroke	O
is	O
also	O
feasible	O
.	O
</s>
<s>
Imaging	O
infections	O
with	O
molecular	B-Algorithm
imaging	I-Algorithm
technologies	O
can	O
improve	O
diagnosis	O
and	O
treatment	O
follow-up	O
.	O
</s>
<s>
Clinically	O
,	O
PET	O
has	O
been	O
widely	O
used	O
to	O
image	O
bacterial	O
infections	O
using	O
fluorodeoxyglucose	B-Application
(	O
FDG	B-Application
)	O
to	O
identify	O
the	O
infection-associated	O
inflammatory	O
response	O
.	O
</s>
<s>
PET	B-Application
scanners	I-Application
designed	O
specifically	O
for	O
imaging	O
rodents	O
,	O
often	O
referred	O
to	O
as	O
microPET	O
,	O
as	O
well	O
as	O
scanners	O
for	O
small	O
primates	O
,	O
are	O
marketed	O
for	O
academic	O
and	O
pharmaceutical	O
research	O
.	O
</s>
<s>
In	O
2018	O
the	O
UC	O
Davis	O
School	O
of	O
Veterinary	O
Medicine	O
became	O
the	O
first	O
veterinary	O
center	O
to	O
employ	O
a	O
small	O
clinical	O
PET-scanner	B-Application
as	O
a	O
pet-PET	O
scan	O
for	O
clinical	O
(	O
rather	O
than	O
research	O
)	O
animal	O
diagnosis	O
.	O
</s>
<s>
PET	B-Application
imaging	I-Application
has	O
been	O
used	O
for	O
imaging	O
muscles	O
and	O
bones	O
.	O
</s>
<s>
18F-FDG	B-Application
is	O
the	O
most	O
commonly	O
used	O
tracer	O
for	O
imaging	O
muscles	O
,	O
and	O
NaF-F18	O
is	O
the	O
most	O
widely	O
used	O
tracer	O
for	O
imaging	O
bones	O
.	O
</s>
<s>
This	O
is	O
due	O
to	O
the	O
time	O
it	O
takes	O
for	O
FDG	B-Application
to	O
accumulate	O
in	O
the	O
activated	O
muscles	O
.	O
</s>
<s>
Together	O
with	O
NaF-F18	O
,	O
PET	B-Algorithm
for	I-Algorithm
bone	I-Algorithm
imaging	I-Algorithm
has	O
been	O
in	O
use	O
for	O
60	O
years	O
for	O
measuring	O
regional	O
bone	O
metabolism	O
and	O
blood	O
flow	O
using	O
static	O
and	O
dynamic	O
scans	O
.	O
</s>
<s>
Researchers	O
have	O
recently	O
started	O
using	O
NaF-18	O
to	O
study	O
bone	O
metastasis	O
as	O
well	O
.	O
</s>
<s>
18F-FDG	B-Application
,	O
which	O
is	O
now	O
the	O
standard	O
radiotracer	O
used	O
for	O
PET	O
neuroimaging	O
and	O
cancer	O
patient	O
management	O
,	O
has	O
an	O
effective	O
radiation	O
dose	O
of	O
14mSv	O
.	O
</s>
<s>
The	O
amount	O
of	O
radiation	O
in	O
18F-FDG	B-Application
is	O
similar	O
to	O
the	O
effective	O
dose	O
of	O
spending	O
one	O
year	O
in	O
the	O
American	O
city	O
of	O
Denver	O
,	O
Colorado	O
(	O
12.4	O
mSv/year	O
)	O
.	O
</s>
<s>
For	O
comparison	O
,	O
radiation	O
dosage	O
for	O
other	O
medical	O
procedures	O
range	O
from	O
0.02	O
mSv	O
for	O
a	O
chest	O
x-ray	B-Library
and	O
6.5	O
–	O
8	O
mSv	O
for	O
a	O
CT	O
scan	O
of	O
the	O
chest	O
.	O
</s>
<s>
In	O
2020	O
by	O
far	O
the	O
most	O
commonly	O
used	O
radiotracer	O
in	O
clinical	O
PET	O
scanning	O
is	O
the	O
carbohydrate	O
derivative	O
fluorodeoxyglucose	B-Application
(	O
18F	O
)	O
(	O
18F-FDG	B-Application
)	O
.	O
</s>
<s>
Due	O
to	O
the	O
short	O
half-lives	O
of	O
most	O
positron-emitting	O
radioisotopes	O
,	O
the	O
radiotracers	O
have	O
traditionally	O
been	O
produced	O
using	O
a	O
cyclotron	O
in	O
close	O
proximity	O
to	O
the	O
PET	B-Application
imaging	I-Application
facility	O
.	O
</s>
<s>
The	O
half-life	O
of	O
fluorine-18	O
is	O
long	O
enough	O
that	O
radiotracers	O
labeled	O
with	O
fluorine-18	O
can	O
be	O
manufactured	O
commercially	O
at	O
offsite	O
locations	O
and	O
shipped	O
to	O
imaging	O
centers	O
.	O
</s>
<s>
Recently	O
rubidium-82	B-Algorithm
generators	O
have	O
become	O
commercially	O
available	O
.	O
</s>
<s>
These	O
contain	O
strontium-82	O
,	O
which	O
decays	O
by	O
electron	O
capture	O
to	O
produce	O
positron-emitting	O
rubidium-82	B-Algorithm
.	O
</s>
<s>
The	O
use	O
of	O
positron-emitting	O
isotopes	O
of	O
metals	O
in	O
PET	B-Application
scans	I-Application
has	O
been	O
reviewed	O
,	O
including	O
elements	O
not	O
listed	O
above	O
,	O
such	O
as	O
lanthanides	O
.	O
</s>
<s>
The	O
isotope	O
89Zr	O
has	O
been	O
applied	O
to	O
the	O
tracking	O
and	O
quantification	O
of	O
molecular	O
antibodies	O
with	O
positron	B-Application
emission	I-Application
tomography	I-Application
(	O
PET	O
)	O
cameras	O
(	O
a	O
method	O
called	O
"	O
immuno-PET	O
"	O
)	O
.	O
</s>
<s>
The	O
molecule	O
most	O
commonly	O
used	O
for	O
this	O
purpose	O
is	O
F-18	O
labeled	O
fluorodeoxyglucose	B-Application
(	O
FDG	B-Application
)	O
,	O
a	O
sugar	O
,	O
for	O
which	O
the	O
waiting	O
period	O
is	O
typically	O
an	O
hour	O
.	O
</s>
<s>
The	O
encounter	O
annihilates	O
both	O
electron	O
and	O
positron	O
,	O
producing	O
a	O
pair	O
of	O
annihilation	O
(	O
gamma	O
)	O
photons	B-Application
moving	O
in	O
approximately	O
opposite	O
directions	O
.	O
</s>
<s>
The	O
technique	O
depends	O
on	O
simultaneous	O
or	O
coincident	O
detection	O
of	O
the	O
pair	O
of	O
photons	B-Application
moving	O
in	O
approximately	O
opposite	O
directions	O
(	O
they	O
would	O
be	O
exactly	O
opposite	O
in	O
their	O
center	O
of	O
mass	O
frame	O
,	O
but	O
the	O
scanner	O
has	O
no	O
way	O
to	O
know	O
this	O
,	O
and	O
so	O
has	O
a	O
built-in	O
slight	O
direction-error	O
tolerance	O
)	O
.	O
</s>
<s>
Photons	B-Application
that	O
do	O
not	O
arrive	O
in	O
temporal	O
"	O
pairs	O
"	O
(	O
i.e.	O
</s>
<s>
The	O
most	O
significant	O
fraction	O
of	O
electron	O
–	O
positron	O
annihilations	O
results	O
in	O
two	O
511	O
keV	O
gamma	O
photons	B-Application
being	O
emitted	O
at	O
almost	O
180	O
degrees	O
to	O
each	O
other	O
;	O
hence	O
,	O
it	O
is	O
possible	O
to	O
localize	O
their	O
source	O
along	O
a	O
straight	O
line	O
of	O
coincidence	O
(	O
also	O
called	O
the	O
line	O
of	O
response	O
,	O
or	O
LOR	O
)	O
.	O
</s>
<s>
In	O
practice	O
,	O
the	O
LOR	O
has	O
a	O
non-zero	O
width	O
as	O
the	O
emitted	O
photons	B-Application
are	O
not	O
exactly	O
180	O
degrees	O
apart	O
.	O
</s>
<s>
The	O
raw	O
data	O
collected	O
by	O
a	O
PET	B-Application
scanner	I-Application
are	O
a	O
list	O
of	O
'	O
coincidence	O
events	O
 '	O
representing	O
near-simultaneous	O
detection	O
(	O
typically	O
,	O
within	O
a	O
window	O
of	O
6	O
to	O
12	O
nanoseconds	O
of	O
each	O
other	O
)	O
of	O
annihilation	O
photons	B-Application
by	O
a	O
pair	O
of	O
detectors	O
.	O
</s>
<s>
Analytical	O
techniques	O
,	O
much	O
like	O
the	O
reconstruction	O
of	O
computed	O
tomography	B-Algorithm
(	O
CT	O
)	O
and	O
single-photon	O
emission	O
computed	O
tomography	B-Algorithm
(	O
SPECT	O
)	O
data	O
,	O
are	O
commonly	O
used	O
,	O
although	O
the	O
data	B-General_Concept
set	I-General_Concept
collected	O
in	O
PET	O
is	O
much	O
poorer	O
than	O
CT	O
,	O
so	O
reconstruction	O
techniques	O
are	O
more	O
difficult	O
.	O
</s>
<s>
Coincidence	O
events	O
can	O
be	O
grouped	O
into	O
projection	O
images	O
,	O
called	O
sinograms	B-Algorithm
.	O
</s>
<s>
The	O
sinograms	B-Algorithm
are	O
sorted	O
by	O
the	O
angle	O
of	O
each	O
view	O
and	O
tilt	O
(	O
for	O
3D	O
images	O
)	O
.	O
</s>
<s>
The	O
sinogram	O
images	O
are	O
analogous	O
to	O
the	O
projections	O
captured	O
by	O
computed	O
tomography	B-Algorithm
(	O
CT	O
)	O
scanners	O
,	O
and	O
can	O
be	O
reconstructed	O
in	O
a	O
similar	O
way	O
.	O
</s>
<s>
The	O
statistics	O
of	O
data	O
thereby	O
obtained	O
are	O
much	O
worse	O
than	O
those	O
obtained	O
through	O
transmission	O
tomography	B-Algorithm
.	O
</s>
<s>
A	O
normal	O
PET	O
data	B-General_Concept
set	I-General_Concept
has	O
millions	O
of	O
counts	O
for	O
the	O
whole	O
acquisition	O
,	O
while	O
the	O
CT	O
can	O
reach	O
a	O
few	O
billion	O
counts	O
.	O
</s>
<s>
This	O
contributes	O
to	O
PET	O
images	O
appearing	O
"	O
noisier	O
"	O
than	O
CT	O
.	O
Two	O
major	O
sources	O
of	O
noise	O
in	O
PET	O
are	O
scatter	O
(	O
a	O
detected	O
pair	O
of	O
photons	B-Application
,	O
at	O
least	O
one	O
of	O
which	O
was	O
deflected	O
from	O
its	O
original	O
path	O
by	O
interaction	O
with	O
matter	O
in	O
the	O
field	O
of	O
view	O
,	O
leading	O
to	O
the	O
pair	O
being	O
assigned	O
to	O
an	O
incorrect	O
LOR	O
)	O
and	O
random	O
events	O
(	O
photons	B-Application
originating	O
from	O
two	O
different	O
annihilation	O
events	O
but	O
incorrectly	O
recorded	O
as	O
a	O
coincidence	O
pair	O
because	O
their	O
arrival	O
at	O
their	O
respective	O
detectors	O
occurred	O
within	O
a	O
coincidence	O
timing	O
window	O
)	O
.	O
</s>
<s>
In	O
practice	O
,	O
considerable	O
pre-processing	O
of	O
the	O
data	O
is	O
required	O
—	O
correction	O
for	O
random	O
coincidences	O
,	O
estimation	O
and	O
subtraction	O
of	O
scattered	O
photons	B-Application
,	O
detector	O
dead-time	O
correction	O
(	O
after	O
the	O
detection	O
of	O
a	O
photon	B-Application
,	O
the	O
detector	O
must	O
"	O
cool	O
down	O
"	O
again	O
)	O
and	O
detector-sensitivity	O
correction	O
(	O
for	O
both	O
inherent	O
detector	O
sensitivity	O
and	O
changes	O
in	O
sensitivity	O
due	O
to	O
angle	O
of	O
incidence	O
)	O
.	O
</s>
<s>
A	O
further	O
advantage	O
of	O
statistical	O
image	O
reconstruction	O
techniques	O
is	O
that	O
the	O
physical	O
effects	O
that	O
would	O
need	O
to	O
be	O
pre-corrected	O
for	O
when	O
using	O
an	O
analytical	O
reconstruction	O
algorithm	O
,	O
such	O
as	O
scattered	O
photons	B-Application
,	O
random	O
coincidences	O
,	O
attenuation	O
and	O
detector	O
dead-time	O
,	O
can	O
be	O
incorporated	O
into	O
the	O
likelihood	O
model	O
being	O
used	O
in	O
the	O
reconstruction	O
,	O
allowing	O
for	O
additional	O
noise	O
reduction	O
.	O
</s>
<s>
Good	O
's	O
roughness	O
method	O
may	O
yield	O
superior	O
performance	O
to	O
expectation-maximization-based	O
methods	O
which	O
involve	O
a	O
Poisson	O
likelihood	O
function	O
but	O
do	O
not	O
involve	O
such	O
a	O
prior	O
.	O
</s>
<s>
Attenuation	O
correction	O
:	O
Quantitative	O
PET	B-Application
Imaging	I-Application
requires	O
attenuation	O
correction	O
.	O
</s>
<s>
Attenuation	O
occurs	O
when	O
photons	B-Application
emitted	O
by	O
the	O
radiotracer	O
inside	O
the	O
body	O
are	O
absorbed	O
by	O
intervening	O
tissue	O
between	O
the	O
detector	O
and	O
the	O
emission	O
of	O
the	O
photon	B-Application
.	O
</s>
<s>
As	O
different	O
LORs	O
must	O
traverse	O
different	O
thicknesses	O
of	O
tissue	O
,	O
the	O
photons	B-Application
are	O
attenuated	O
differentially	O
.	O
</s>
<s>
Contemporary	O
scanners	O
can	O
estimate	O
attenuation	O
using	O
integrated	O
x-ray	B-Library
CT	O
equipment	O
,	O
in	O
place	O
of	O
earlier	O
equipment	O
that	O
offered	O
a	O
crude	O
form	O
of	O
CT	O
using	O
a	O
gamma	O
ray	O
(	O
positron	O
emitting	O
)	O
source	O
and	O
the	O
PET	O
detectors	O
.	O
</s>
<s>
2D/3D	O
reconstruction	O
:	O
Early	O
PET	B-Application
scanners	I-Application
had	O
only	O
a	O
single	O
ring	O
of	O
detectors	O
,	O
hence	O
the	O
acquisition	O
of	O
data	O
and	O
subsequent	O
reconstruction	O
was	O
restricted	O
to	O
a	O
single	O
transverse	O
plane	O
.	O
</s>
<s>
Time-of-flight	O
PET	O
makes	O
use	O
of	O
very	O
fast	O
gamma-ray	O
detectors	O
and	O
data	O
processing	O
system	O
which	O
can	O
more	O
precisely	O
decide	O
the	O
difference	O
in	O
time	O
between	O
the	O
detection	O
of	O
the	O
two	O
photons	B-Application
.	O
</s>
<s>
PET	B-Application
scans	I-Application
are	O
increasingly	O
read	O
alongside	O
CT	O
or	O
magnetic	O
resonance	O
imaging	O
(	O
MRI	O
)	O
scans	O
,	O
with	O
the	O
combination	O
(	O
called	O
"	B-Algorithm
co-registration	I-Algorithm
"	I-Algorithm
)	O
giving	O
both	O
anatomic	O
and	O
metabolic	O
information	O
(	O
i.e.	O
,	O
what	O
the	O
structure	O
is	O
,	O
and	O
what	O
it	O
is	O
doing	O
biochemically	O
)	O
.	O
</s>
<s>
Because	O
PET	B-Application
imaging	I-Application
is	O
most	O
useful	O
in	O
combination	O
with	O
anatomical	O
imaging	O
,	O
such	O
as	O
CT	O
,	O
modern	O
PET	B-Application
scanners	I-Application
are	O
now	O
available	O
with	O
integrated	O
high-end	O
multi-detector-row	O
CT	O
scanners	O
(	O
so-called	O
"	O
PET-CT	O
"	O
)	O
.	O
</s>
<s>
Because	O
the	O
two	O
scans	O
can	O
be	O
performed	O
in	O
immediate	O
sequence	O
during	O
the	O
same	O
session	O
,	O
with	O
the	O
patient	O
not	O
changing	O
position	O
between	O
the	O
two	O
types	O
of	O
scans	O
,	O
the	O
two	O
sets	O
of	O
images	O
are	O
more	O
precisely	O
registered	B-Algorithm
,	O
so	O
that	O
areas	O
of	O
abnormality	O
on	O
the	O
PET	B-Application
imaging	I-Application
can	O
be	O
more	O
perfectly	O
correlated	O
with	O
anatomy	O
on	O
the	O
CT	O
images	O
.	O
</s>
<s>
At	O
the	O
Jülich	O
Institute	O
of	O
Neurosciences	O
and	O
Biophysics	O
,	O
the	O
world	O
's	O
largest	O
PET-MRI	O
device	O
began	O
operation	O
in	O
April	O
2009	O
:	O
a	O
9.4-tesla	O
magnetic	O
resonance	O
tomograph	B-Algorithm
(	O
MRT	O
)	O
combined	O
with	O
a	O
positron	B-Application
emission	I-Application
tomograph	I-Application
(	O
PET	O
)	O
.	O
</s>
<s>
For	O
brain	O
imaging	O
,	O
registration	O
of	O
CT	O
,	O
MRI	O
and	O
PET	B-Application
scans	I-Application
may	O
be	O
accomplished	O
without	O
the	O
need	O
for	O
an	O
integrated	O
PET-CT	O
or	O
PET-MRI	O
scanner	O
by	O
using	O
a	O
device	O
known	O
as	O
the	O
N-localizer	O
.	O
</s>
<s>
Limitations	O
to	O
the	O
widespread	O
use	O
of	O
PET	O
arise	O
from	O
the	O
high	O
costs	O
of	O
cyclotrons	O
needed	O
to	O
produce	O
the	O
short-lived	O
radionuclides	O
for	O
PET	O
scanning	O
and	O
the	O
need	O
for	O
specially	O
adapted	O
on-site	O
chemical	O
synthesis	O
apparatus	O
to	O
produce	O
the	O
radiopharmaceuticals	B-Algorithm
after	O
radioisotope	O
preparation	O
.	O
</s>
<s>
Instead	O
,	O
the	O
isotope	O
must	O
be	O
prepared	O
first	O
,	O
then	O
afterward	O
,	O
the	O
chemistry	O
to	O
prepare	O
any	O
organic	O
radiotracer	O
(	O
such	O
as	O
FDG	B-Application
)	O
accomplished	O
very	O
quickly	O
,	O
in	O
the	O
short	O
time	O
before	O
the	O
isotope	O
decays	O
.	O
</s>
<s>
This	O
limitation	O
restricts	O
clinical	O
PET	O
primarily	O
to	O
the	O
use	O
of	O
tracers	O
labelled	O
with	O
fluorine-18	O
,	O
which	O
has	O
a	O
half-life	O
of	O
110	O
minutes	O
and	O
can	O
be	O
transported	O
a	O
reasonable	O
distance	O
before	O
use	O
,	O
or	O
to	O
rubidium-82	B-Algorithm
(	O
used	O
as	O
rubidium-82	B-Algorithm
chloride	O
)	O
with	O
a	O
half-life	O
of	O
1.27	O
minutes	O
,	O
which	O
is	O
created	O
in	O
a	O
portable	O
generator	O
and	O
is	O
used	O
for	O
myocardial	O
perfusion	O
studies	O
.	O
</s>
<s>
In	O
recent	O
years	O
the	O
shortage	O
of	O
PET	B-Application
scans	I-Application
has	O
been	O
alleviated	O
in	O
the	O
US	O
,	O
as	O
rollout	O
of	O
radiopharmacies	O
to	O
supply	O
radioisotopes	O
has	O
grown	O
30%	O
/year	O
.	O
</s>
<s>
Because	O
the	O
half-life	O
of	O
fluorine-18	O
is	O
about	O
two	O
hours	O
,	O
the	O
prepared	O
dose	O
of	O
a	O
radiopharmaceutical	B-Algorithm
bearing	O
this	O
radionuclide	O
will	O
undergo	O
multiple	O
half-lives	O
of	O
decay	O
during	O
the	O
working	O
day	O
.	O
</s>
<s>
The	O
concept	O
of	O
emission	O
and	O
transmission	O
tomography	B-Algorithm
was	O
introduced	O
by	O
David	O
E	O
.	O
Kuhl	O
,	O
Luke	O
Chapman	O
and	O
Roy	O
Edwards	O
in	O
the	O
late	O
1950s	O
.	O
</s>
<s>
Their	O
work	O
later	O
led	O
to	O
the	O
design	O
and	O
construction	O
of	O
several	O
tomographic	B-Algorithm
instruments	O
at	O
the	O
University	O
of	O
Pennsylvania	O
.	O
</s>
<s>
In	O
1975	O
tomographic	B-Algorithm
imaging	I-Algorithm
techniques	O
were	O
further	O
developed	O
by	O
Michel	O
Ter-Pogossian	O
,	O
Michael	O
E	O
.	O
Phelps	O
,	O
Edward	O
J	O
.	O
Hoffman	O
and	O
others	O
at	O
Washington	O
University	O
School	O
of	O
Medicine	O
.	O
</s>
<s>
Work	O
by	O
Gordon	O
Brownell	O
,	O
Charles	O
Burnham	O
and	O
their	O
associates	O
at	O
the	O
Massachusetts	O
General	O
Hospital	O
beginning	O
in	O
the	O
1950s	O
contributed	O
significantly	O
to	O
the	O
development	O
of	O
PET	O
technology	O
and	O
included	O
the	O
first	O
demonstration	O
of	O
annihilation	O
radiation	O
for	O
medical	B-Application
imaging	I-Application
.	O
</s>
<s>
Their	O
innovations	O
,	O
including	O
the	O
use	O
of	O
light	O
pipes	O
and	O
volumetric	O
analysis	O
,	O
have	O
been	O
important	O
in	O
the	O
deployment	O
of	O
PET	B-Application
imaging	I-Application
.	O
</s>
<s>
In	O
1961	O
,	O
James	O
Robertson	O
and	O
his	O
associates	O
at	O
Brookhaven	O
National	O
Laboratory	O
built	O
the	O
first	O
single-plane	O
PET	B-Application
scan	I-Application
,	O
nicknamed	O
the	O
"	O
head-shrinker.	O
"	O
</s>
<s>
One	O
of	O
the	O
factors	O
most	O
responsible	O
for	O
the	O
acceptance	O
of	O
positron	O
imaging	O
was	O
the	O
development	O
of	O
radiopharmaceuticals	B-Algorithm
.	O
</s>
<s>
In	O
particular	O
,	O
the	O
development	O
of	O
labeled	O
2-fluorodeoxy-D-glucose	O
(	O
2FDG	O
)	O
by	O
the	O
Brookhaven	O
group	O
under	O
the	O
direction	O
of	O
Al	O
Wolf	O
and	O
Joanna	O
Fowler	O
was	O
a	O
major	O
factor	O
in	O
expanding	O
the	O
scope	O
of	O
PET	B-Application
imaging	I-Application
.	O
</s>
<s>
Brain	O
images	O
obtained	O
with	O
an	O
ordinary	O
(	O
non-PET	O
)	O
nuclear	O
scanner	O
demonstrated	O
the	O
concentration	O
of	O
FDG	B-Application
in	O
that	O
organ	O
.	O
</s>
<s>
Later	O
,	O
the	O
substance	O
was	O
used	O
in	O
dedicated	O
positron	O
tomographic	B-Algorithm
scanners	O
,	O
to	O
yield	O
the	O
modern	O
procedure	O
.	O
</s>
<s>
The	O
first	O
applications	O
of	O
PC-I	O
in	O
tomographic	B-Algorithm
mode	O
as	O
distinguished	O
from	O
the	O
computed	O
tomographic	B-Algorithm
mode	O
were	O
reported	O
in	O
1970	O
.	O
</s>
<s>
As	O
of	O
August	O
2008	O
,	O
Cancer	O
Care	O
Ontario	O
reports	O
that	O
the	O
current	O
average	O
incremental	O
cost	O
to	O
perform	O
a	O
PET	B-Application
scan	I-Application
in	O
the	O
province	O
is	O
Can$	O
1,000	O
–	O
1,200	O
per	O
scan	O
.	O
</s>
<s>
This	O
includes	O
the	O
cost	O
of	O
the	O
radiopharmaceutical	B-Algorithm
and	O
a	O
stipend	O
for	O
the	O
physician	O
reading	O
the	O
scan	O
.	O
</s>
<s>
In	O
the	O
United	O
States	O
,	O
a	O
PET	B-Application
scan	I-Application
is	O
estimated	O
to	O
be	O
~	O
$5	O
,	O
000	O
,	O
and	O
most	O
insurance	O
companies	O
do	O
n't	O
pay	O
for	O
routine	O
PET	B-Application
scans	I-Application
after	O
cancer	O
treatment	O
due	O
to	O
the	O
fact	O
that	O
these	O
scans	O
are	O
often	O
unnecessary	O
and	O
present	O
potentially	O
more	O
risks	O
than	O
benefits	O
.	O
</s>
<s>
In	O
England	O
,	O
the	O
National	O
Health	O
Service	O
reference	O
cost	O
(	O
2015	O
–	O
2016	O
)	O
for	O
an	O
adult	O
outpatient	O
PET	B-Application
scan	I-Application
is	O
£798	O
.	O
</s>
<s>
In	O
Australia	O
,	O
as	O
of	O
July	O
2018	O
,	O
the	O
Medicare	O
Benefits	O
Schedule	O
Fee	O
for	O
whole	O
body	O
FDG	B-Application
PET	O
ranges	O
from	O
A$953	O
to	O
A$999	O
,	O
depending	O
on	O
the	O
indication	O
for	O
the	O
scan	O
.	O
</s>
