Myelination process in preterm subjects with periventricular leucomalacia assessed by magnetization transfer ratio

Background: Magnetization transfer imaging assesses the myelination status of the brain. Objectives: To study the progress of myelination in children with periventricular leucomalacia (PVL) by measuring the magnetization transfer ratio (MTR) and to compare the MTR values with normal values. Materials and methods: Brain MTR in 28 PVL subjects (16 males, 12 females, gestational age 30.7 +/- 2.5 weeks, corrected age 3.1 +/- 2.9 years) was measured using a 3D gradient echo sequence (TR/TE 32/8 ms, flip angle 60 degrees, 4 mm/2 mm overlapping sections) without and with magnetization transfer prepulse and compared with normal values for preterm subjects. Results: MTR of white-matter structures followed a monoexponential function model (y=A-B*exp(-x/C)) while the thalamus and caudate nucleus had a poor goodness of fit. MTR of the splenium of the corpus callosum reached a final value lower than normal (0.67 versus 0.70) at a younger age [t(99%) at 10.32 versus 18.90 months; P < 0.05]. MTR of the normal-appearing occipital white matter and of the genu of the corpus callosum reached a normal final MTR but at a younger age than normal preterm infants [t(99%) at 8.51 versus 14.50 months and 12.51 versus 20.85 months, respectively]. Conclusion: In PVL subjects, myelination of the splenium is characterized by early arrest and deficient maturation. Accelerated myelination in unaffected white matter might suggest a compensatory process of reorganization.