Quantitative comparison of intrabrain diffusion in adults and preterm and term neonates and infants

OBJECTIVE. Quantitative measurements of mean water diffusivity (D-av) were made in human neonates, infants, and adults to assess changes in brain tiss ue that occur with maturation. SUBJECTS AND METHODS. Values of D-av were obtained by calculating the avera ge of the diffusion measurements made with diffusion-sensitizing gradients placed along three orthogonal directions. The mean diffusivity, a rotationa lly invariant determination of apparent diffusion coefficient, was measured in five healthy prematurely born neonates and infants, in 10 healthy term neonates and infants, and in five adults. RESULTS. Values of D-av were found to decrease with maturation in most part s of the brain. In prematurely born neonates and infants with a postmenstru al age (postgestastional age + postnatal age) under 36 weeks, the average v alue of D-av in frontal white matter was 1.90 x 10(-3) mm(2) sec(-1). The c orresponding value was measured as 1.62 x 10(-3) mm(2) sec(-1) in neonates and infants born at term with a postnatal age of no more than 43 days and 0 .79 x 10(-3) mm(2) sec(-1) in the adult brain. CONCLUSION. Values of D-av are known to decrease in neonates and young infa nts in the period immediately after ischemic insult. This decrease and the associated increase in signal intensity seen on diffusion-weighted imaging have been used to monitor ischemic brain injury in neonates and infants. Th erefore, the decrease in D-av that occurs with maturation, which we report in this study, must be considered if quantitative diffusion measurements ar e used to assess ischemic neonatal brain injury.