<s>
In	O
mathematical	O
optimization	O
,	O
the	O
ordered	B-Algorithm
subset	I-Algorithm
expectation	I-Algorithm
maximization	I-Algorithm
(	O
OSEM	B-Algorithm
)	O
method	O
is	O
an	O
iterative	B-Algorithm
method	I-Algorithm
that	O
is	O
used	O
in	O
computed	O
tomography	O
.	O
</s>
<s>
In	O
applications	O
in	O
medical	B-Application
imaging	I-Application
,	O
the	O
OSEM	B-Algorithm
method	O
is	O
used	O
for	O
positron	B-Application
emission	I-Application
tomography	I-Application
,	O
for	O
single	O
photon	O
emission	O
computed	O
tomography	O
,	O
and	O
for	O
X-ray	O
computed	O
tomography	O
.	O
</s>
<s>
The	O
OSEM	B-Algorithm
method	O
is	O
related	O
to	O
the	O
expectation	B-Algorithm
maximization	I-Algorithm
(	O
EM	O
)	O
method	O
of	O
statistics	O
.	O
</s>
<s>
The	O
OSEM	B-Algorithm
method	O
is	O
also	O
related	O
to	O
methods	O
of	O
filtered	O
back	O
projection	O
.	O
</s>
