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

BACKGROUND AND PURPOSE: Fluid-attenuated inversion-recovery (FLAIR) MR imag ing is widely accepted for brain diagnoses, though to our knowledge no desc ription of the MR FLAIR appearance of the normal infantile brain has been p ublished. The purpose of this study was to investigate the appearance of no rmal infantile brain maturation on FLAIR MR images. METHODS: FLAIR images were obtained in 52 children between the ages of 1 da y and 4 years who had clinically suspected brain disease but no neurologic abnormality or growth retardation. T1- and T2-weighted images were also obt ained in all the children, and these images were compared with the FLAIR se quences for the appearance of brain maturation. A grading system for the di fferences in signal intensity between gray and white matter on FLAIR images was introduced to make detailed profiles of maturation in each brain regio n, including the posterior limb of the internal capsule, the cerebellar ped uncle, 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 ce rebellar peduncle and the posterior limb of the internal capsule, showed hi gh 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 d eep white matter, the occipital deep white matter, and the centrum semioval e, showed low signal intensity at birth. The white matter showed high signa l 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 F LAIR appearance of infantile white matter can be divided into two phases, r eflecting development of the myelination process: the first phase is simila r to that seen on SE T1-weighted images and the second phase is similar to that seen on SE T2-weighted images.