MRI assessment of neonatal brain maturation

Nadine J Girard, Philippe Dory-Lautrec, Mériam Koob, Anca Melania Dediu
2012 Imaging in Medicine  
Brain maturation begins in the second trimester and continues progressively to reach an adult-like pattern at approximately 2 years of age. Consequently, different windows of brain vulnerability and different diseases are encountered in infants and neonates compared with older children and adults. Although ultrasonography and CT can show the changes in brain morphology, these techniques are insensitive to myelination, which is one of the most important events occurring during brain maturation.
more » ... brain maturation. MRI is currently the method of choice to evaluate brain maturation. Owing to improvements in neonatal intensive care, indications of brain MRI in neonates have spread widely in the past 10 years. Moreover, highly premature neonates are also receiving brain MRI. However, MRI is most commonly performed at term-equivalent age to look for white matter damage that is not indicated on the ultrasound scan rather than in the first 2-week period after birth for medical decisionmaking. Although an ultrasonography scan is still a rapid imaging method to assess the neonatal brain, MRI provides improved anatomical details and identifies the cortex and subarachnoid spaces that are not affected by calvaria, in contrast to ultrasonography. MRI also provides an accurate depiction of the morphological and signal changes of normal brain development and of its disorders. It gives insight into mechanisms of injury through diffusion-weighted imaging and diffusion tensor imaging (DTI), as well as the microstructure of brain tissue, and biochemical composition through proton MR spectroscopy. MR sequences to assess brain maturation In neonates and young infants, the standard MRI protocol consists of axial and coronal T2-weighted images (WIs), sagittal and axial gradient echo T1-WI, axial diffusion or diffusion tensor images, and proton spectroscopy [1, 2] . T1-WIs are generally acquired using gradient echo images, spin echo images or inversion recovery images. Gradient echo and inversion recovery T1-WIs allow excellent gray-white matter differentiation, especially in infants less than 6 months of age. T2-WIs can be acquired using spin echo, fast-spin echo or turbo-spin echo techniques. Fast-spin echo and turbo-spin echo images show myelin maturation at an earlier age than spin echo images due to increased magnetization-transfer effects [3] , and are obtained in a shorter acquisition time. Heavily T2-weighted sequences are used in infants less than 12 months of age to compensate for the long T1 values due to the increased cerebral water content [4] . Although fluid-attenuated inversion recovery sequences are considered highly efficient in assessing the white matter, these images demonstrate a paradoxical signal pattern through infancy. In neonates the white matter is of low signal intensity as on T1-WI, then of high signal intensity in infants and young children, and reaches the mature aspect of low signal intensity, as on T2-WI at approximately 4-5 years of age. Alternatives for T1 and T2-WIs consist of 3D T1 and T2 images whenever MRI is currently the method of choice to evaluate brain maturation. MRI provides improved anatomical details and accurate depiction of the morphological and signal changes of normal brain development and its disorders. It also gives insight into the microstructure of brain tissue and into mechanisms of injury through diffusion-weighted imaging and diffusion-tensor imaging, and into the brain's biochemical composition through proton MR spectroscopy. Computational automated techniques are emerging that help to generate a 3D fetal atlas by motion-corrected high resolution images, to more precisely identify volumetric brain growth, cortical folding over gestational age and white matter organization. Validations by clinical studies are still needed, especially in applying the computational methods in the different groups of pathology encountered in the pre-and neo-natal periods. KeywoRds: brain n diffusion MRI n fetus n human development n infant n MRI n MR spectroscopy n newborn
doi:10.2217/iim.12.59 fatcat:pd45kjmxrzhwfgfdydxvi7dbaq