MR quantitation of volume and diffusion changes in the developing brain

Abstract

Background and purpose: Brain volume and diffusion change during maturation. Quantitation of these changes may be helpful in understanding normal brain development. We used diffusion-weighted imaging to characterize the volumetric and diffusion changes in vivo.

Methods: We recruited 30 pediatric volunteers (aged 1 month-17 years; 14 male, 16 female). Diffusion was measured in three orthogonal directions with a b value of 1000 s/mm2. The diffusion parameters from the entire brain were calculated and fitted to a triple gaussian model. In addition, region-of-interest measurements were made in caudate, thalamus, genu and splenium of the corpus callosum, and periventricular white matter (PVWM). The brain volume was measured by counting pixels and by using the model.

Results: Water diffusion of the whole brain, caudate, thalamus, genu and splenium of the corpus callosum, and PVWM decreased during maturation, with the most significant change within the first 2 years. Robust negative correlations were found between age and the measured average diffusion constant (Dav) values in each of the measured locations (P <.005). Volumes of different cerebral compartments and the total intracranial volume (ICV) increased rapidly during the first 2 years of life and then had a slower growth process through adolescence. Age was correlated with the ICV and the volume of each brain compartment (P <.005).

Conclusion: Brain diffusion decreases and brain volume increases during maturation, with the most significant changes occurring within the first 2 years of life. The brain model used in this study provides a good estimate of the increasing brain volume.

Fig 1.

Representative diffusion distribution histogram in a 3.5-year-old girl with triple gaussian fit. BD_av = 0.839 10⁻⁵cm²/s, σ = 0.183 10⁻⁵cm²/s.

Fig 2.

Locations of ROIs in a 2-year-old boy. Round ROIs were placed on D_av maps to measure the diffusion constants of the PVWM, caudate, thalamus, and genu and splenium of the corpus callosum in all subjects.

Fig 3.

Biexponential curves of D_av versus age. A, Caudate and splenium of the corpus callosum. B, Thalamus, PVWM, and whole brain (BD_av). C, Data for the genu are fitted by using a single exponential curve. Brain diffusion decreases fastest in the first 2 years, with slower changes afterward.

Fig 4.

Age dependence of brain volume. The most significant volume changes occur within the first 2 postnatal years. Lines are the logarithmic fit.

Fig 5.

ICV measured by using the pixel count and the brain model. Correlation was excellent (R = 0.999).