Figure 4. Cerebral Volume and Surface Area Growth in Preterm Infants.

(A) Values for cerebral volume and cortical surface area for 113 infants imaged serially between 23 and 48 wk gestation (274 scans) displayed on log-log coordinates and related to gestational age at scan, showing linear relationships for both variables.

(B) Scaling of cortical surface area relative to cerebral volume shown as a scatter plot in log-log coordinates of the cortical surface area s against cerebral volume v determined from each of these 274 scans. The linear relationship apparent for volumes greater than about 45 cm³ indicates a power law scaling of the form s = kv^α, where α is the scaling exponent and k is a constant. For a three-dimensional object that maintains its shape with changing size, the exponent α would take the value 2/3 (since area scales as length squared and volume as length cubed). For the data in this plot, in contrast, a good fit (for v > 45 cm³) is obtained with α = 1.29 (95% confidence interval 1.25–1.33).