Synopsis
Considering
the extra-environmental associated effects on brain development, it may be unreasonable
to scan preterm infants at term-equivalent GA. To clarify this, we aim to explore
the effects of postnatal days on neonatal WM maturation by DTI. Results
indicate that postnatal days at-scan may be a considerable factor to
investigate the WM maturation: during a close to in-uterine period, the absent
effects of postnatal days may suggest the reasonability of performing neonatal
MR-scans in such period; while as postnatal days increases, observed FA changes
may imply the bias of comparing the preterm neonates at term-equivalent GA to
term ones.Introduction
From
birth, neonatal brain begins to rapidly develop and mature in totally different
ways from the ‘intrauterine protection’ period during gestation
1-3. Particularly,
within first months of life, neonatal brain encounters kinds of extra-uterine
stimulations. It may be the intermingled that cause cerebral intense growth
1,2 and microstructure maturation
4,5. In this regard, part of preterm
neonates (GA<33wk) tend to undergo more external-stimulations from birth to
term-equivalent GA. However, most studies compared preterm neonates at
term-equivalent GA to the term-born neonates for characterizing the
developmental differences. Considering the potential effects of postnatal days,
it may be unreasonable to scan preterm infants at term-equivalent GA. To
clarify such issue, this study aims to explore the effects of variations in
postnatal days on the maturation of neonatal WM characterized by DTI-derived FA
values.
Methods
The Internal Review Board approved this study and all the written informed consents were obtained.
Patients Through presuming a within 18 days after birth as a close to in-uterine period
6, 100 neonates (preterm/term, 45/55; male/female, 58/42; GA range, 30~42 wk) with no evidence abnormality on MRI were included in full-group and scanned by DTI within 28 days after birth; 92 in 100 neonates (preterm/term, 39/53; male/female, 53/38; GA range, 30~42 wk) within 18 days after birth comprised the early-group (Table 1).
MR Protocols All MR examinations were performed using a 3T scanner (GE, Signa HDxt) with an 8-channel head coil. The protocols included sequences: (1) a transverse 3D T1-weighted sequence (TR/TE, 10ms/4.6ms; matrix, 256×256; section-thickness, 1mm; FOV, 240mm); (2) a T2-weighted sequence (TR/TE, 4200ms/120ms; matrix, 256×256; section-thickness, 4mm; FOV, 180mm); (3) DTI (35 directions; b-value, 1000 s/mm
2; TR/TE, 5500ms/95ms; section-thickness, 4mm; FOV, 180mm).
Data and statistical analysis DTI data was processed with the aid of the FMRIB software library (FSL, www.fmrib.ox.au.uk/fsl). The TBSS was used to investigate the effects of postnatal days at-scan on DTI-derived FA values respectively for the full- and early-groups.
Results
There was significant difference in postnatal days at-scan between full- and early- groups, while no differences were observed in terms of maturity (i.e. preterm/term), gender, birth weight, GA and 10min-APGAR (Table 1). As for full-group, the postnatal days at-scan (range 1~28 days) showed statistically significant relation with the increasing FA in regional WM, e.g. centrum semiovale, temporal lobe, brainstem, bilateral CR (corona radiate), PLIC (posterior limb of internal capsule) and PTR (posterior thalamic radiation) (rmax=0.37, p<.001) ( Figure 1).
With respect to early-group, as postnatal days at-scan (range 1~18 days) increased, no statistically significant relations were found with FA values. And no significant relations with FA values were also observed in term or preterm neonates.
Discussion
Previous
study suggested that 5~17 days after birth didn’t affect the WM developments in
neonates6. Through presuming a within 18 days as a close to
in-uterine period, our early-group and subgroups (i.e. term and preterm groups)
showed consistent results. These findings further support the definition of a
close to in-uterine period and suggest future studies to take it as a critical
factor aiming at eliminating its potential effects.
As for
full-group, the postnatal days at-scan (range 1~28 days) showed significant
relation with increasing FA in regional WM, e.g. bilateral CR, PLIC and PTR (p<.001). Such results may hint the
increasing myelination and reduced water contents in regional WM of
corticospinal tract (CST), PTR and auditory radiation that may support the
early motor, visual and hearing functions. However, the myelination of CST, PTR
and auditory radiation often occurs at the term period, rather than preterm
period2. The results about the included preterm neonates appear to
be inconsistent with the above conclusion. The underlying reason may lie in the
fact that besides of GA, WM’s myelination also depends on its functional stimulation 7.
Specifically,
previous studies revealed that artificial opening of rabbit eyes would result
in the accelerated myelination of optic radiation8. Besides,
through DTI-based WM tracing in preterm neonates, FA values in optic radiation
showed statistically relation with vision maturity, but had no relation with GA9.
Taken together, the stimulation induced by extra-environment postpartum on some
nerve fibers would facilitate its maturation and myelination.
Conclusion
The
postnatal days at-scan may be a considerable factor to investigate the neonatal
WM maturation: during a close to in-uterine period, the absent effects of
postnatal days on WM maturation may suggest the reasonability of performing the
neonatal MR-scans in such period; while as postnatal days goes on, the observed
FA changes may imply the bias of comparing the preterm neonates at
term-equivalent GA to term ones.
Acknowledgements
This work is partially supported by the National Natural Science Foundation of China (No.81171317 & 81471631) and the 2011 New Century Excellent Talent Support Plan from Ministry of Education of China (NCET-11-0438).References
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