<s>
Diffuse	B-Algorithm
optical	I-Algorithm
mammography	I-Algorithm
,	O
or	O
simply	O
optical	B-Algorithm
mammography	I-Algorithm
,	O
is	O
an	O
emerging	O
imaging	B-Algorithm
technique	I-Algorithm
that	O
enables	O
the	O
investigation	O
of	O
the	O
breast	O
composition	O
through	O
spectral	O
analysis	O
.	O
</s>
<s>
It	O
is	O
an	O
application	O
of	O
diffuse	B-Algorithm
optics	I-Algorithm
,	O
which	O
studies	O
light	O
propagation	O
in	O
strongly	O
diffusive	O
media	O
,	O
such	O
as	O
biological	O
tissues	O
,	O
working	O
in	O
the	O
red	O
and	O
near-infrared	O
spectral	O
range	O
,	O
between	O
600	O
and	O
1100nm	O
.	O
</s>
<s>
Currently	O
,	O
the	O
most	O
common	O
breast	B-Algorithm
imaging	I-Algorithm
techniques	I-Algorithm
are	O
X-ray	B-Library
mammography	O
,	O
ultrasounds	B-Application
,	O
MRI	B-Algorithm
and	O
PET	B-Application
.	O
</s>
<s>
X-ray	B-Library
mammography	O
is	O
widely	O
spread	O
for	O
breast	O
screening	O
,	O
thanks	O
to	O
its	O
high	O
spatial	O
resolution	O
and	O
the	O
short	O
measurement	O
time	O
.	O
</s>
<s>
Ultrasounds	B-Application
are	O
non-invasive	O
and	O
they	O
are	O
used	O
especially	O
on	O
young	O
women	O
,	O
who	O
are	O
usually	O
characterized	O
by	O
dense	O
breasts	O
,	O
but	O
the	O
images	O
interpretation	O
depends	O
on	O
the	O
operator	O
's	O
experience	O
.	O
</s>
<s>
MRI	B-Algorithm
shows	O
a	O
good	O
correlation	O
with	O
the	O
tumour	O
dimensions	O
and	O
is	O
claimed	O
to	O
be	O
the	O
best	O
method	O
for	O
the	O
identification	O
and	O
characterization	O
of	O
lesions	O
.	O
</s>
<s>
Even	O
though	O
there	O
is	O
no	O
verified	O
long-term	O
health	O
risk	O
from	O
the	O
magnetic	O
fields	O
employed	O
during	O
an	O
MRI	B-Algorithm
,	O
it	O
is	O
not	O
used	O
as	O
first	O
investigative	O
tool	O
because	O
of	O
the	O
high	O
costs	O
and	O
the	O
elevated	O
duration	O
of	O
the	O
exam	O
.	O
</s>
<s>
Finally	O
,	O
PET	B-Application
allows	O
the	O
early	O
evaluation	O
of	O
the	O
metabolic	O
changes	O
of	O
the	O
tumour	O
,	O
but	O
it	O
is	O
very	O
expensive	O
and	O
requires	O
the	O
administration	O
of	O
a	O
radioactive	B-Algorithm
tracer	I-Algorithm
.	O
</s>
<s>
On	O
the	O
contrary	O
,	O
optical	B-Algorithm
mammography	I-Algorithm
is	O
cheap	O
,	O
efficient	O
also	O
on	O
dense	O
breasts	O
,	O
and	O
devoid	O
of	O
any	O
side	O
effect	O
,	O
so	O
that	O
it	O
can	O
be	O
used	O
to	O
track	O
the	O
evolution	O
of	O
the	O
patient	O
's	O
condition	O
on	O
a	O
daily	O
basis	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
a	O
"	O
multimodal	O
approach	O
"	O
is	O
suggested	O
,	O
where	O
optical	B-Algorithm
mammography	I-Algorithm
is	O
complementary	O
to	O
another	O
conventional	O
technique	O
,	O
so	O
that	O
also	O
the	O
diagnostic	O
efficacy	O
is	O
improved	O
.	O
</s>
<s>
The	O
former	O
is	O
related	O
to	O
the	O
chemical	O
composition	O
of	O
the	O
medium	O
and	O
induces	O
photon	B-Application
annihilation	O
,	O
whereas	O
the	O
latter	O
depends	O
on	O
the	O
microscopic	O
inhomogeneities	O
of	O
its	O
refractive	O
index	O
and	O
determines	O
deviations	O
in	O
photon	B-Application
's	O
trajectory	O
.	O
</s>
<s>
Light	O
propagation	O
through	O
highly	O
diffusive	O
media	O
is	O
typically	O
described	O
through	O
the	O
heuristic	O
approach	O
of	O
the	O
radiative	O
transport	O
theory	O
,	O
sided	O
by	O
the	O
so-called	O
“	O
diffusion	B-Algorithm
approximation	I-Algorithm
”	O
:	O
scattering	O
is	O
assumed	O
to	O
be	O
isotropic	O
and	O
strongly	O
dominant	O
over	O
absorption	O
.	O
</s>
<s>
This	O
is	O
the	O
reason	O
why	O
photon	B-Application
migration	O
in	O
biological	O
tissues	O
is	O
known	O
also	O
as	O
"	O
diffuse	B-Algorithm
optics	I-Algorithm
"	O
.	O
</s>
<s>
Diffuse	B-Algorithm
optical	I-Algorithm
mammography	I-Algorithm
can	O
be	O
implemented	O
exploiting	O
three	O
different	O
approaches	O
:	O
time	O
domain	O
,	O
frequency	O
domain	O
and	O
continuous	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
The	O
woman	O
is	O
usually	O
prone	O
or	O
bent	O
forward	O
and	O
places	O
the	O
breast	O
on	O
a	O
support	O
provided	O
with	O
a	O
hole	O
where	O
sources	O
and	O
detectors	B-Application
are	O
located	O
.	O
</s>
<s>
Whatever	O
the	O
chosen	O
approach	O
is	O
,	O
any	O
optical	O
mammograph	O
must	O
comprehend	O
some	O
essential	O
elements	O
:	O
laser	O
sources	O
,	O
a	O
detector	B-Application
,	O
a	O
signal	O
processor	O
.	O
</s>
<s>
Detectors	B-Application
are	O
usually	O
photomultiplier	B-Algorithm
tubes	I-Algorithm
or	O
avalanche	O
photodiodes	O
.	O
</s>
<s>
Finally	O
,	O
the	O
signal	O
processor	O
could	O
be	O
a	O
device	O
for	O
Time-correlated	O
single	O
photon	B-Application
counting	O
in	O
the	O
case	O
of	O
a	O
time-resolved	O
optical	O
mammograph	O
,	O
or	O
a	O
filter	O
for	O
frequency	O
modulation	O
in	O
the	O
case	O
of	O
frequency-domain	B-Algorithm
ones	O
.	O
</s>
<s>
Based	O
on	O
the	O
number	O
and	O
position	O
of	O
sources	O
and	O
detectors	B-Application
,	O
an	O
optical	O
mammograph	O
can	O
produce	O
bidimensional	O
or	O
three-dimensional	B-Algorithm
breast	O
constituents	O
 '	O
maps	O
.	O
</s>
<s>
In	O
time-domain	B-Algorithm
measurements	O
,	O
short	O
light	O
pulses	O
of	O
the	O
order	O
of	O
hundreds	O
of	O
picoseconds	O
are	O
delivered	O
to	O
the	O
breast	O
and	O
its	O
optical	O
properties	O
are	O
retrieved	O
from	O
the	O
features	O
of	O
the	O
re-emitted	O
pulses	O
,	O
which	O
have	O
undergone	O
delay	O
,	O
broadening	O
and	O
attenuation	O
.	O
</s>
<s>
Time-correlated	O
single	O
photon	B-Application
counting	O
is	O
fundamental	O
to	O
cope	O
with	O
the	O
low-level	O
output	O
signal	O
.	O
</s>
<s>
In	O
frequency-domain	B-Algorithm
measurements	O
,	O
an	O
intensity-modulated	O
signal	O
is	O
injected	O
into	O
the	O
breast	O
and	O
its	O
optical	O
properties	O
are	O
deduced	O
from	O
the	O
dephasement	O
and	O
the	O
demodulation	O
of	O
the	O
output	O
signal	O
with	O
respect	O
to	O
the	O
input	O
one	O
.	O
</s>
<s>
In	O
continuous	B-Algorithm
wave	I-Algorithm
(	O
CW	O
)	O
measurements	O
,	O
the	O
light	O
source	O
is	O
a	O
continuous	B-Algorithm
wave	I-Algorithm
laser	O
,	O
which	O
hinders	O
the	O
separation	O
of	O
the	O
absorption	O
and	O
scattering	O
contributions	O
with	O
a	O
single	O
measurement	O
.	O
</s>
<s>
The	O
main	O
constituents	O
of	O
a	O
fibrous	O
tissue	O
are	O
water	O
,	O
collagen	O
and	O
hemoglobin	O
and	O
optical	B-Algorithm
mammography	I-Algorithm
is	O
able	O
to	O
discriminate	O
and	O
quantify	O
tissues	O
 '	O
components	O
.	O
</s>
<s>
Therefore	O
,	O
by	O
measuring	O
breast	O
constituents	O
 '	O
concentrations	O
,	O
optical	B-Algorithm
mammography	I-Algorithm
could	O
assess	O
breast	O
cancer	O
risk	O
.	O
</s>
<s>
Such	O
distinctions	O
suggest	O
that	O
optical	B-Algorithm
mammography	I-Algorithm
could	O
characterize	O
breast	O
lesions	O
.	O
</s>
