Age-dependent changes in magnetization transfer contrast of white matter in the pediatric brain

BACKGROUND AND PURPOSE: It is unknown to what extent magnetization transfer contrast (MTC) in white matter of the brain changes during myelination. Th e goal of this study was to measure the age-dependent changes of MTC in dif ferent regions of the pediatric brain and to evaluate their relation to T2 relaxation times. METHODS: Seventy children aged 1 week to 80 months without evidence of orga nic brain disease underwent MR imaging of the brain. A double-echo spin-ech o (SE) sequence and an SE sequence,vith and without an off-resonance pulse were performed in the axial orientation. Using paired images, we calculated MTC ratios in 13 predefined regions of the brain and compared them with th e T2 relaxation times measured in the same areas. Regression analysis was p erformed for both parameters to evaluate age dependency. RESULTS: MTC in white matter increased during myelination from a range of 1 3% to 19% to a range of 34% to 37%. At the same time, T2 relaxation times d ecreased from a range of 115 to 160 milliseconds to a range of 60 to 70 mil liseconds after myelination. For both MTC and T2 relaxation times, age depe ndency could be expressed by a monoexponential function. CONCLUSION: A strong positive correlation exists between MTC ratios and the degree of myelination in the pediatric brain, and an inverse correlation e xists between MTC and T2 relaxation times. Fast proton relaxation within ma cromolecules in the myelinated white matter and subsequent MT may be the mo st important reason for the decreasing T2 relaxation time of white matter d uring brain myelination.