<s>
Contrast-to-noise	B-Algorithm
ratio	I-Algorithm
(	O
CNR	B-Algorithm
)	O
is	O
a	O
measure	O
used	O
to	O
determine	O
image	O
quality	O
.	O
</s>
<s>
CNR	B-Algorithm
is	O
similar	O
to	O
the	O
metric	O
signal-to-noise	O
ratio	O
(	O
SNR	O
)	O
,	O
but	O
subtracts	O
a	O
term	O
before	O
taking	O
the	O
ratio	O
.	O
</s>
<s>
Thus	O
this	O
image	O
may	O
have	O
a	O
high	O
SNR	O
metric	O
,	O
but	O
will	O
have	O
a	O
low	O
CNR	B-Algorithm
metric	O
.	O
</s>
<s>
One	O
way	O
to	O
define	O
contrast-to-noise	B-Algorithm
ratio	I-Algorithm
is	O
:	O
</s>
<s>
where	O
SA	O
and	O
SB	O
are	O
signal	O
intensities	O
for	O
signal	O
producing	O
structures	O
A	O
and	O
B	O
in	O
the	O
region	O
of	O
interest	O
and	O
σo	O
is	O
the	O
standard	B-General_Concept
deviation	I-General_Concept
of	O
the	O
pure	O
image	B-Algorithm
noise	I-Algorithm
.	O
</s>
