<s>
Dual-energy	B-Algorithm
X-ray	I-Algorithm
absorptiometry	I-Algorithm
(	O
DXA	B-Algorithm
,	O
or	O
DEXA	B-Algorithm
)	O
is	O
a	O
means	O
of	O
measuring	O
bone	O
mineral	O
density	O
(	O
BMD	O
)	O
using	O
spectral	O
imaging	O
.	O
</s>
<s>
Two	O
X-ray	B-Library
beams	O
,	O
with	O
different	O
energy	O
levels	O
,	O
are	O
aimed	O
at	O
the	O
patient	O
's	O
bones	O
.	O
</s>
<s>
Dual-energy	B-Algorithm
X-ray	I-Algorithm
absorptiometry	I-Algorithm
is	O
the	O
most	O
widely	O
used	O
and	O
most	O
thoroughly	O
studied	O
bone	O
density	O
measurement	O
technology	O
.	O
</s>
<s>
The	O
DXA	B-Algorithm
scan	I-Algorithm
is	O
typically	O
used	O
to	O
diagnose	O
and	O
follow	O
osteoporosis	O
,	O
as	O
contrasted	O
to	O
the	O
nuclear	O
bone	O
scan	O
,	O
which	O
is	O
sensitive	O
to	O
certain	O
metabolic	O
diseases	O
of	O
bones	O
in	O
which	O
bones	O
are	O
attempting	O
to	O
heal	O
from	O
infections	O
,	O
fractures	O
,	O
or	O
tumors	O
.	O
</s>
<s>
Soft	O
tissue	O
and	O
bone	O
have	O
different	O
attenuation	O
coefficients	O
to	O
X-rays	B-Library
.	O
</s>
<s>
A	O
single	O
X-ray	B-Library
beam	O
passing	O
through	O
the	O
body	O
will	O
be	O
attenuated	O
by	O
both	O
soft	O
tissue	O
and	O
bone	O
,	O
and	O
it	O
is	O
not	O
possible	O
to	O
determine	O
,	O
from	O
a	O
single	O
beam	O
,	O
how	O
much	O
attenuation	O
was	O
attributable	O
to	O
the	O
bone	O
.	O
</s>
<s>
However	O
,	O
the	O
attenuation	O
coefficients	O
vary	O
with	O
the	O
energy	O
of	O
the	O
X-rays	B-Library
,	O
and	O
,	O
crucially	O
,	O
the	O
ratio	O
of	O
the	O
attenuation	O
coefficients	O
also	O
varies	O
.	O
</s>
<s>
DXA	B-Algorithm
uses	O
two	O
energies	O
of	O
X-ray	B-Library
.	O
</s>
<s>
One	O
type	O
of	O
DXA	B-Algorithm
scanner	O
uses	O
a	O
cerium	O
filter	O
with	O
a	O
tube	O
voltage	O
of	O
80	O
kV	O
,	O
resulting	O
in	O
effective	O
photon	O
energies	O
of	O
about	O
40	O
and	O
70	O
keV	O
.	O
</s>
<s>
There	O
is	O
also	O
a	O
DXA	B-Algorithm
scanner	O
type	O
using	O
a	O
samarium	O
filter	O
with	O
a	O
tube	O
voltage	O
of	O
100	O
kV	O
,	O
resulting	O
in	O
effective	O
energies	O
of	O
47	O
and	O
80	O
keV	O
.	O
</s>
<s>
The	O
combination	O
of	O
dual	B-Algorithm
X-ray	I-Algorithm
absorptiometry	I-Algorithm
and	I-Algorithm
laser	I-Algorithm
uses	O
the	O
laser	O
to	O
measure	O
the	O
thickness	O
of	O
the	O
region	O
scanned	O
,	O
allowing	O
for	O
varying	O
proportions	O
of	O
lean	O
soft	O
tissue	O
and	O
adipose	O
tissue	O
within	O
the	O
soft	O
tissue	O
to	O
be	O
controlled	O
for	O
and	O
improving	O
the	O
accuracy	O
.	O
</s>
<s>
The	O
U.S.	O
Preventive	O
Services	O
Task	O
Force	O
recommends	O
that	O
women	O
over	O
the	O
age	O
of	O
65	O
should	O
get	O
a	O
DXA	B-Algorithm
scan	I-Algorithm
.	O
</s>
<s>
Special	O
considerations	O
are	O
involved	O
in	O
the	O
use	O
of	O
DXA	B-Algorithm
to	O
assess	O
bone	O
mass	O
in	O
children	O
.	O
</s>
<s>
Also	O
,	O
there	O
are	O
other	O
variables	O
in	O
addition	O
to	O
age	O
that	O
are	O
suggested	O
to	O
confound	O
the	O
interpretation	O
of	O
BMD	O
as	O
measured	O
by	O
DXA	B-Algorithm
.	O
</s>
<s>
DXA	B-Algorithm
has	O
been	O
shown	O
to	O
overestimate	O
the	O
bone	O
mineral	O
density	O
of	O
taller	O
subjects	O
and	O
underestimate	O
the	O
bone	O
mineral	O
density	O
of	O
smaller	O
subjects	O
.	O
</s>
<s>
This	O
error	O
is	O
due	O
to	O
the	O
way	O
by	O
which	O
DXA	B-Algorithm
calculates	O
BMD	O
.	O
</s>
<s>
In	O
DXA	B-Algorithm
,	O
bone	O
mineral	O
content	O
(	O
measured	O
as	O
the	O
attenuation	O
of	O
the	O
X-ray	B-Library
by	O
the	O
bones	O
being	O
scanned	O
)	O
is	O
divided	O
by	O
the	O
area	O
(	O
also	O
measured	O
by	O
the	O
machine	O
)	O
of	O
the	O
site	O
being	O
scanned	O
.	O
</s>
<s>
Because	O
DXA	B-Algorithm
calculates	O
BMD	O
using	O
area	O
(	O
aBMD	O
:	O
areal	O
Bone	O
Mineral	O
Density	O
)	O
,	O
it	O
is	O
not	O
an	O
accurate	O
measurement	O
of	O
true	O
bone	O
mineral	O
density	O
,	O
which	O
is	O
mass	O
divided	O
by	O
a	O
volume	O
.	O
</s>
<s>
In	O
order	O
to	O
distinguish	O
DXA	B-Algorithm
BMD	O
from	O
volumetric	O
bone-mineral	O
density	O
,	O
researchers	O
sometimes	O
refer	O
to	O
DXA	B-Algorithm
BMD	O
as	O
an	O
areal	O
bone	O
mineral	O
density	O
(	O
aBMD	O
)	O
.	O
</s>
<s>
Despite	O
DXA	B-Algorithm
technology	O
's	O
problems	O
with	O
estimating	O
volume	O
,	O
it	O
is	O
still	O
a	O
fairly	O
accurate	O
measure	O
of	O
bone	O
mineral	O
content	O
.	O
</s>
<s>
Methods	O
to	O
correct	O
for	O
this	O
shortcoming	O
include	O
the	O
calculation	O
of	O
a	O
volume	O
that	O
is	O
approximated	O
from	O
the	O
projected	O
area	O
measure	O
by	O
DXA	B-Algorithm
.	O
</s>
<s>
DXA	B-Algorithm
BMD	O
results	O
adjusted	O
in	O
this	O
manner	O
are	O
referred	O
to	O
as	O
the	O
bone	O
mineral	O
apparent	O
density	O
(	O
BMAD	O
)	O
and	O
are	O
a	O
ratio	O
of	O
the	O
bone	O
mineral	O
content	O
versus	O
a	O
cuboidal	O
estimation	O
of	O
the	O
volume	O
of	O
bone	O
.	O
</s>
<s>
Other	O
imaging	O
technologies	O
such	O
as	O
quantitative	O
computed	O
tomography	O
(	O
QCT	O
)	O
are	O
capable	O
of	O
measuring	O
the	O
bone	O
's	O
volume	O
,	O
and	O
are	O
,	O
therefore	O
,	O
not	O
susceptible	O
to	O
the	O
confounding	O
effect	O
of	O
bone-size	O
in	O
the	O
way	O
that	O
DXA	B-Algorithm
results	O
are	O
susceptible	O
.	O
</s>
<s>
DXA	B-Algorithm
results	O
need	O
to	O
be	O
adjusted	O
if	O
the	O
patient	O
is	O
taking	O
strontium	O
supplements	O
.	O
</s>
<s>
DXA	B-Algorithm
can	O
also	O
used	O
to	O
measure	O
trabecular	O
bone	O
score	O
.	O
</s>
<s>
DXA	B-Algorithm
is	O
,	O
by	O
far	O
,	O
the	O
most	O
widely	O
used	O
technique	O
for	O
bone	O
mineral	O
density	O
measurements	O
,	O
since	O
it	O
is	O
considered	O
to	O
be	O
cheap	O
,	O
accessible	O
,	O
easy	O
to	O
use	O
,	O
and	O
able	O
to	O
provide	O
an	O
accurate	O
estimation	O
of	O
bone	O
mineral	O
density	O
in	O
adults	O
.	O
</s>
<s>
T-scores	O
are	O
prohibited	O
with	O
children	O
and	O
should	O
not	O
even	O
appear	O
on	O
DXA	B-Algorithm
reports	O
.	O
</s>
<s>
Some	O
clinics	O
may	O
routinely	O
carry	O
out	O
DXA	B-Algorithm
scans	I-Algorithm
on	O
pediatric	O
patients	O
with	O
conditions	O
such	O
as	O
nutritional	O
rickets	O
,	O
lupus	O
,	O
and	O
Turner	O
syndrome	O
.	O
</s>
<s>
DXA	B-Algorithm
has	O
been	O
demonstrated	O
to	O
measure	O
skeletal	O
maturity	O
and	O
body	O
fat	O
composition	O
and	O
has	O
been	O
used	O
to	O
evaluate	O
the	O
effects	O
of	O
pharmaceutical	O
therapy	O
.	O
</s>
<s>
However	O
,	O
it	O
seems	O
that	O
DXA	B-Algorithm
is	O
still	O
in	O
its	O
early	O
days	O
in	O
pediatrics	O
,	O
and	O
there	O
are	O
widely	O
acknowledged	O
limitations	O
and	O
disadvantages	O
with	O
DXA	B-Algorithm
.	O
</s>
<s>
A	O
view	O
exists	O
that	O
DXA	B-Algorithm
scans	I-Algorithm
for	O
diagnostic	O
purposes	O
should	O
not	O
even	O
be	O
performed	O
outside	O
specialist	O
centers	O
,	O
and	O
,	O
if	O
a	O
scan	O
is	O
done	O
outside	O
one	O
of	O
these	O
centers	O
,	O
it	O
should	O
not	O
be	O
interpreted	O
without	O
consultation	O
with	O
an	O
expert	O
in	O
the	O
field	O
.	O
</s>
<s>
Whole-body	O
calcium	O
measured	O
by	O
DXA	B-Algorithm
has	O
been	O
validated	O
in	O
adults	O
using	O
in-vivo	O
neutron	O
activation	O
of	O
total	O
body	O
calcium	O
but	O
this	O
is	O
not	O
suitable	O
for	O
paediatric	O
subjects	O
and	O
studies	O
have	O
been	O
carried	O
out	O
on	O
paediatric-sized	O
animals	O
.	O
</s>
<s>
DXA	B-Algorithm
scans	I-Algorithm
can	O
also	O
be	O
used	O
to	O
measure	O
total	O
body	O
composition	O
and	O
fat	O
content	O
with	O
a	O
high	O
degree	O
of	O
accuracy	O
comparable	O
to	O
hydrostatic	O
weighing	O
with	O
a	O
few	O
important	O
caveats	O
.	O
</s>
<s>
From	O
the	O
DXA	B-Algorithm
scans	I-Algorithm
,	O
a	O
low	O
resolution	O
"	O
fat	O
shadow	O
"	O
image	O
can	O
also	O
be	O
generated	O
,	O
which	O
gives	O
an	O
overall	O
impression	O
of	O
fat	O
distribution	O
throughout	O
the	O
body	O
It	O
has	O
been	O
suggested	O
that	O
,	O
while	O
very	O
accurately	O
measuring	O
minerals	O
and	O
lean	O
soft	O
tissue	O
(	O
LST	O
)	O
,	O
DXA	B-Algorithm
may	O
provide	O
skewed	O
results	O
due	O
to	O
its	O
method	O
of	O
indirectly	O
calculating	O
fat	O
mass	O
by	O
subtracting	O
it	O
from	O
the	O
LST	O
and/or	O
body	O
cell	O
mass	O
(	O
BCM	O
)	O
that	O
DXA	B-Algorithm
actually	O
measures	O
.	O
</s>
<s>
DXA	B-Algorithm
scans	I-Algorithm
have	O
been	O
suggested	O
as	O
useful	O
tools	O
to	O
diagnose	O
conditions	O
with	O
an	O
abnormal	O
fat	O
distribution	O
,	O
such	O
as	O
familial	O
partial	O
lipodystrophy	O
.	O
</s>
<s>
DXA	B-Algorithm
uses	O
X-rays	B-Library
to	O
measure	O
bone	O
mineral	O
density	O
.	O
</s>
<s>
The	O
radiation	O
dose	O
of	O
current	O
DEXA	B-Algorithm
systems	O
is	O
small	O
,	O
as	O
low	O
as	O
0.001	O
mSv	O
,	O
much	O
less	O
than	O
a	O
standard	O
chest	O
or	O
dental	O
x-ray	B-Library
.	O
</s>
<s>
However	O
,	O
the	O
dose	O
delivered	O
by	O
older	O
DEXA	B-Algorithm
radiation	O
sources	O
(	O
that	O
used	O
radioisotopes	O
rather	O
than	O
x-ray	B-Library
generators	O
)	O
could	O
be	O
as	O
high	O
as	O
35	O
mGy	O
,	O
considered	O
a	O
significant	O
dose	O
by	O
radiological	O
health	O
standards	O
.	O
</s>
<s>
The	O
quality	O
of	O
DXA	B-Algorithm
operators	O
varies	O
widely	O
.	O
</s>
<s>
DXA	B-Algorithm
is	O
not	O
regulated	O
like	O
other	O
radiation-based	O
imaging	O
techniques	O
because	O
of	O
its	O
low	O
dosage	O
.	O
</s>
<s>
Each	O
US	O
state	O
has	O
a	O
different	O
policy	O
as	O
to	O
what	O
certifications	O
are	O
needed	O
to	O
operate	O
a	O
DXA	B-Algorithm
machine	O
.	O
</s>
<s>
California	O
,	O
for	O
example	O
,	O
requires	O
coursework	O
and	O
a	O
state-run	O
test	O
,	O
whereas	O
Maryland	O
has	O
no	O
requirements	O
for	O
DXA	B-Algorithm
technicians	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
Victoria	O
,	O
an	O
individual	O
performing	O
DXA	B-Algorithm
scans	I-Algorithm
is	O
required	O
to	O
completed	O
a	O
recognised	O
course	O
in	O
safe	O
use	O
of	O
bone	O
mineral	O
densitometers	O
.	O
</s>
<s>
In	O
NSW	O
and	O
QLD	O
a	O
DXA	B-Algorithm
technician	O
only	O
requires	O
prior	O
study	O
in	O
science	O
,	O
nursing	O
or	O
other	O
related	O
undergraduate	O
study	O
.	O
</s>
