Quantitative Comparison of Intrabrain Diffusion in Adults and Preterm and Term Neonates and Infants

Abstract

OBJECTIVE. Quantitative measurements of mean water diffusivity (D_av) were made in human neonates, infants, and adults to assess changes in brain tissue that occur with maturation. SUBJECTS AND METHODS. Values of D_av were obtained by calculating the average of the diffusion measurements made with diffusion-sensitizing gradients placed along three orthogonal directions. The mean diffusivity, a rotationally 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 parts of the brain. In prematurely born neonates and infants with a postmenstrual age (postgestastional age + postnatal age) under 36 weeks, the average value of D_av in frontal white matter was 1.90 × 10^-3 mm² sec^-1. The corresponding value was measured as 1.62 × 10^-3 mm² sec^-1 in neonates and infants born at term with a postnatal age of no more than 43 days and 0.79 × 10^-3 mm² sec^-1 in the adult brain. CONCLUSION. Values of D_av are known to decrease in neonates and young infants 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. Therefore, the decrease in D_av that occurs with maturation, which we report in this study, must be considered if quantitative diffusion measurements are used to assess ischemic neonatal brain injury.