Appearance of normal brain maturation on fluid-attenuated inversion-recovery (FLAIR) MR images.

BACKGROUND AND PURPOSE Fluid-attenuated inversion-recovery (FLAIR) MR imaging is widely accepted for brain diagnoses, though to our knowledge no description of the MR FLAIR appearance of the normal infantile brain has been published. The purpose of this study was to investigate the appearance of normal infantile brain maturation on FLAIR MR images. METHODS FLAIR images were obtained in 52 children between the ages of 1 day and 4 years who had clinically suspected brain disease but no neurologic abnormality or growth retardation. T1- and T2-weighted images were also obtained in all the children, and these images were compared with the FLAIR sequences for the appearance of brain maturation. A grading system for the differences in signal intensity between gray and white matter on FLAIR images was introduced to make detailed profiles of maturation in each brain region, including the posterior limb of the internal capsule, the cerebellar peduncle, the frontal deep white matter, the occipital deep white matter, and the centrum semiovale. These grades were plotted against patients' ages. RESULTS On the FLAIR images, the myelinated white matter, including the cerebellar peduncle and the posterior limb of the internal capsule, showed high signal intensity relative to gray matter at birth. Thereafter, the white matter lost signal intensity with time and showed low signal intensity at 50 weeks and beyond. The unmyelinated white matter, including the frontal deep white matter, the occipital deep white matter, and the centrum semiovale, showed low signal intensity at birth. The white matter showed high signal intensity at 20 to 30 weeks, and low signal intensity again at 100 to 160 weeks and after. CONCLUSION The dynamics of brain myelination can be accurately delineated and evaluated on FLAIR images without other spin-echo (SE) sequences. The FLAIR appearance of infantile white matter can be divided into two phases, reflecting development of the myelination process: the first phase is similar to that seen on SE T1-weighted images and the second phase is similar to that seen on SE T2-weighted images.