Magnetic resonance signal intensity ratio of gray/white matter in children. Quantitative assessment in developing brain

Myelination progression in language-correlated regions in brain of normal children determined by quantitative MRI assessment

OBJECTIVE

To investigate the myelination progression course in language-correlated regions of children with normal brain development by quantitative magnetic resonance imaging (MRI) analysis compared with histological studies.

METHODS

The subjects were 241 neurologically intact neonates, infants and young children (128 boys and 113 girls) who underwent MRI between 2001 and 2007 at the University of Tokyo Hospital, ranging in age from 0 to 429 weeks corrected by postnatal age. To compare their data with adult values, 25 adolescents and adults (14 men and 11 women, aged from 14 to 83 years) were examined as controls. Axial T2-weighted images were obtained using spin-echo sequences at 1.5 T. Subjects with a history of prematurity, birth asphyxia, low Apgar score, seizures, active systemic disease, congenital anomaly, delayed development, infarcts, hemorrhages, brain lesions, or central nervous system malformation were excluded from the analysis. Seven regions of interest in language-correlated areas, namely Broca's area, Wernicke's area, the arcuate fasciculus, and the angular gyrus, as well as their right hemisphere homologous regions, and the auditory cortex, the motor cortex, and the visual cortex were examined. Signal intensity obtained by a region-of-interest methodology progresses from hyper- to hypointensity during myelination. We chose the inferior cerebellar peduncle as the internal standard of maturation.

RESULTS

Myelination in all these seven language-correlated regions examined in this study shared the same curve pattern: no myelination was observed at birth, it reached maturation at about 1.5 years of age, and it continued to progress slowly thereafter into adult life. On the basis of scatter plot results, we put these areas into three groups: Group A, which included the motor cortex, the auditory cortex, and the visual cortex, myelinated faster than Group B, which included Broca's area, Wernicke's area, and the angular gyrus before 1.5 years old; Group C, consisting of the arcuate fasciculus, has similar degree of myelination as Group B before 1.5 years but then myelinated more slowly after 3 years of age. No gender or left-right differences between homologous regions were found.

CONCLUSIONS

In this study, we determined the sequence of myelination of language-correlated regions in infants and children by quantitative MRI assessment. The higher cortical areas matured later than the primary cortical areas, and the arcuate fasciculus matured last. The observation that myelination reaches maturity after 18 months suggests that myelination may be a reason for the acceleration in vocabulary acquisition observed in children from that age. The slow pace of myelination also suggested the possibility of language development's continuation into early adult life. Myelination assessed by MRI was at least 1 month behind that assessed by histological staining. No gender or left-right hemisphere differences in myelination were noted.

Manganese-enhanced magnetic resonance imaging (MEMRI) of mouse brain development

Given the importance of genetically modified mice in studies of mammalian brain development and human congenital brain diseases, MRI has the potential to provide an efficient in vivo approach for analyzing mutant phenotypes in the early postnatal mouse brain. The combination of reduced tissue contrast at the high magnetic fields required for mice, and the changing cellular composition of the developing mouse brain make it difficult to optimize MRI contrast in neonatal mouse imaging. We have explored an easily implemented approach for contrast-enhanced imaging, using systemically administered manganese (Mn) to reveal fine anatomical detail in T1-weighted MR images of neonatal mouse brains. In particular, we demonstrate the utility of this Mn-enhanced MRI (MEMRI) method for analyzing early postnatal patterning of the mouse cerebellum. Through comparisons with matched histological sections, we further show that MEMRI enhancement correlates qualitatively with granule cell density in the developing cerebellum, suggesting that the cerebellar enhancement is due to uptake of Mn in the granule neurons. Finally, variable cerebellar defects in mice with a conditional mutation in the Gbx2 gene were analyzed with MEMRI to demonstrate the utility of this method for mutant mouse phenotyping. Taken together, our results indicate that MEMRI provides an efficient and powerful in vivo method for analyzing neonatal brain development in normal and genetically engineered mice.

Quantitative Signal Intensity Measures on Magnetic Resonance Imaging in Attention-Deficit Hyperactivity Disorder

OBJECTIVE

The aim of this study was to investigate possible abnormalities of cerebral myelination in subjects with attention-deficit hyperactivity disorder (ADHD).

BACKGROUND

Anatomic and functional neuroimaging studies of subjects with ADHD demonstrated a right frontostriatal deficit and abnormal cerebral asymmetries. Some also reported white matter abnormalities, such as smaller white matter volumes in the right anterior-superior frontal region, and the smaller bilateral retrocallosal region. Smaller volumes in specific areas of the corpus callosum have also been reported. We hypothesized that white matter signal intensities may also show differences indicating abnormal cerebral myelination.

METHOD

We analyzed T2-weighted magnetic resonance images of 11 adolescents with ADHD and 20 controls. Regions of interest were set in both the white and gray matter in frontal and parieto-occipital associative regions.

RESULTS

The ADHD group showed a higher signal intensity ratio, probably reflecting a higher degree of myelination. Significant interhemispheric differences emerged only in the posterior region in the ADHD group.

CONCLUSIONS

The higher degree of myelination in the right frontal region of ADHD may be due to a compensatory mechanism for the right frontostriatal dysfunction.

The effect of intracranial pressure on myelination and the relationship with neurodevelopment in infantile hydrocephalus

The effect of raised intracranial pressure (ICP), due to infantile hydrocephalus, on the process of myelination has been suggested in the literature. In this study 19 hydrocephalic infants were followed-up with anterior fontanelle pressure (AFP) measurement (assessment of ICP), MRI (assessment of the myelination process and the CSF volume), and neurodevelopmental testing (NDT). There was a high correlation (r = 0.80) between the myelination and NDT scores. The size of the CSF volume showed a poor correlation with the mean AFP, the degree of myelination and the NDT scores. There was, however, a significant correlation between the mean AFP and the degree of myelination (r = 0.67) and also between the mean AFP and the NDT scores (r = 0.70). Longer-term follow-up (mean = 27 months) showed a significant correlation between the early progress of myelination and later developmental level (r = 0.78). Most of the children with a severely delayed myelination, preoperatively, showed a recovery of myelination following CSF drainage. It was concluded that: (1) raised ICP is related to developmental outcome, through the process of myelination; (2) the delay in myelination can be (partially) reversible; and (3) CSF volume is of minor importance regarding neurodevelopment.

Infratentorial brain maturation: a comparison of MRI at 0.5 and 1.5T

Our purpose was to establish parameters for normal infratentorial brain maturation at 0.5 and 1.5 T and to evaluate the field strength criteria for the assessment of infratentorial brain maturation with MRI. We examined 27 children with normal psychomotor development (3 days to 24 months) with a 1.5 T system and 22 (4 days to 29 months) with a 0.5 T system; standard T2-weighted spin-echo sequences (TR/TE 2500/90 ms at 1.5 T and TR/TE 2200/90 ms at 0.5 T) were obtained. The signal intensity of infratentorial anatomical structures compared to their surroundings was classified as high, isointense or low by three neuroradiologists. For anatomical structures with age-related contrast changes, the time of these changes was determined statistically for the 0.5 T and 1.5 T system independently. The delineation of the structures without age-related contrast changes at the two field strengths was compared using a chi 2 test. Age-related contrast changed were found in the same anatomical structures ("marker sites") at 0.5 and 1.5 T. Generally, these changes were apparent in larger structures (pons, middle cerebellar peduncles, medulla, cerebellar folia, red nuclei, cerebral peduncles), with only slight field-strength-dependent differences in the time of the contrast changes. Contrast changes from high to isointense signal were observed slightly earlier at 0.5 T and changes from isointense to low signal slightly later at 0.5 T. The delineation of the smaller anatomical structures was significantly better at 1.5 T but these structures did not show age-related contrast changes. The differences in the assessment of infratentorial brain maturation between 0.5 and 1.5 T can be attributed to a lower signal-to-noise ratio at lower magnetic field strengths. These differences do not complicate temporal classification of the stage of infratentorial brain maturation using the same "marker sites" and the same temporal criteria at 0.5 or 1.5 T. However, higher field strengths are preferable for the assessment of smaller structures with physiological signal differences; this may imply better detection of small lesions at higher field strengths.