<s>
A	O
ventilation/perfusion	B-Algorithm
lung	I-Algorithm
scan	I-Algorithm
,	O
also	O
called	O
a	O
V/Q	O
lung	O
scan	O
,	O
or	O
ventilation/perfusion	B-Algorithm
scintigraphy	I-Algorithm
,	O
is	O
a	O
type	O
of	O
medical	B-Application
imaging	I-Application
using	O
scintigraphy	O
and	O
medical	O
isotopes	O
to	O
evaluate	O
the	O
circulation	O
of	O
air	O
and	O
blood	O
within	O
a	O
patient	O
's	O
lungs	O
,	O
in	O
order	O
to	O
determine	O
the	O
ventilation/perfusion	O
ratio	O
.	O
</s>
<s>
As	O
Q	O
in	O
physiology	O
is	O
the	O
letter	O
used	O
to	O
describe	O
bloodflow	O
the	O
term	O
V/Q	B-Algorithm
scan	I-Algorithm
emerged	O
.	O
</s>
<s>
This	O
test	O
is	O
most	O
commonly	O
done	O
in	O
order	O
to	O
check	O
for	O
the	O
presence	O
of	O
a	O
blood	O
clot	O
or	O
abnormal	O
blood	O
flow	O
inside	O
the	O
lungs	O
(	O
such	O
as	O
a	O
pulmonary	O
embolism	O
(	O
PE	O
)	O
although	O
computed	O
tomography	O
with	O
radiocontrast	B-Application
is	O
now	O
more	O
commonly	O
used	O
for	O
this	O
purpose	O
.	O
</s>
<s>
The	O
V/Q	B-Algorithm
scan	I-Algorithm
may	O
be	O
used	O
in	O
some	O
circumstances	O
where	O
radiocontrast	B-Application
would	O
be	O
inappropriate	O
,	O
as	O
in	O
Allergy	O
to	O
contrast	O
agent	O
or	O
kidney	O
failure	O
.	O
</s>
<s>
Typical	O
effective	O
doses	O
for	O
a	O
V/Q	B-Algorithm
scan	I-Algorithm
range	O
from	O
1-5	O
mSv	O
.	O
</s>
<s>
A	O
CT	B-Algorithm
pulmonary	I-Algorithm
angiogram	I-Algorithm
(	O
CTPA	B-Algorithm
)	O
with	O
radiocontrast	B-Application
can	O
alternatively	O
be	O
performed	O
,	O
although	O
this	O
can	O
result	O
in	O
a	O
greater	O
radiation	O
dose	O
to	O
the	O
patient	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
perform	O
the	O
scan	O
with	O
positron	B-Application
emission	I-Application
tomography	I-Application
(	O
PET	O
)	O
rather	O
than	O
conventional	O
gamma	O
camera	O
scintigraphy	O
.	O
</s>
