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Characterization of white matter alterations in phenylketonuria by magnetic resonance relaxometry and diffusion tensor imaging.
[classical phenylketonuria]
A
multimodal
MR
study
including
relaxometry
,
diffusion
tensor
imaging
(
DTI
)
,
and
MR
spectroscopy
was
performed
on
patients
with
classical
phenylketonuria
(
PKU
)
and
matched
controls
,
to
improve
our
understanding
of
white
matter
(
WM
)
lesions
.
Relaxometry
yields
information
on
myelin
loss
or
malformation
and
may
substantiate
results
from
DTI
attributed
to
myelin
changes
.
Relaxometry
was
used
to
determine
four
brain
compartments
in
normal-appearing
brain
tissue
(
NABT
)
and
in
lesions
:
water
in
myelin
bilayers
(
myelin
water
,
MW
)
,
water
in
gray
matter
(
GM
)
,
water
in
WM
,
and
water
with
long
relaxation
times
(
cerebrospinal
fluid
[
CSF
]
-
like
signals
)
.
DTI
yielded
apparent
diffusion
coefficients
(
ADCs
)
and
fractional
anisotropies
.
MW
and
WM
content
were
reduced
in
NABT
and
in
lesions
of
PKU
patients
,
while
CSF-like
signals
were
significantly
increased
.
ADC
values
were
reduced
in
PKU
lesions
,
but
also
in
the
corpus
callosum
.
Diffusion
anisotropy
was
reduced
in
lesions
because
of
a
stronger
decrease
in
the
longitudinal
than
in
the
transverse
diffusion
.
WM
content
and
CSF-like
components
in
lesions
correlated
with
anisotropy
and
ADC
.
ADC
values
in
lesions
and
in
the
corpus
callosum
correlated
negatively
with
blood
and
brain
phenylalanine
(
Phe
)
concentrations
.
Intramyelinic
edema
combined
with
vacuolization
is
a
likely
cause
of
the
WM
alterations
.
Correlations
between
diffusivity
and
Phe
concentrations
confirm
vulnerability
of
WM
to
high
Phe
concentrations
.