Normal MRI

PROGRESSION OF MYELINATION  
Proximal pathways before distal (e.g., brainstem before supratentorial brain) 
Sensory (visual and auditory) before motor  
Central white matter before peripheral  
Posterior before anterior  

MYELINATED REGIONS AT BIRTH (OR SHORTLY AFTER BIRTH)  
Dorsal brainstem 
Inferior, superior cerebellar peduncles 
Perirolandic region 
Corticospinal tract 
Central portion of centrum semiovale
Posterior limb of internal capsule to cerebral peduncle
Ventrolateral thalamus 
Optic nerve, chiasm, tract 

• During the first 6 months of life, T1-weighted images are most useful for evaluating the progression of myelination . Inversion recovery images also provide improved T1-weighted contrast differences between tissues. The inherent tissue contrast depends on the inversion time selected. In the first year of life, inversion recovery images using an inversion time of 700 to 800 ms with a repetition time (TR) of 2,000 to 2,500 ms and an echo time (TE) of 15 ms can be substituted for the T1-weighted images. Myelinated regions will appear hyperintense to gray matter on these inversion recovery images. 
• After 6 months of age, most cerebral white matter appears high in signal intensity on the T1-weighted images, and beyond this time the T2-weighted images are generally relied on to further evaluate myelin progression . 
• By 24 months of age, the process of myelination is essentially complete except for the terminal zones of myelination found in the occipital-parietal periventricular white matter. These regions appear as subtle ill-defined areas of hyperintensity on the long TR images and should not be confused with periventricular leukomalacia  and may persist into the fourth decade.