Correlation of apparent diffusion coefficient and fractional anisotropy values in the developing infant brain.

Objective: The purpose of our study was to correlate decrease in apparent diffusion coefficient (ADC) and increase in fractional anisotropy (FA) in various white matter (WM) regions using diffusion tenor imaging (DTI) within the first year of life.

Materials And Methods: We performed DTI on 53 infants and measured FA and ADC within 10 WM regions important in brain development. For each region, we calculated the slope of ADC as a function of FA, the correlation coefficient (r) and correlation of determination (r(2)). We performed a group analysis of r values and r(2)values for six WM regions primarily composed of crossing fibers and four regions primarily having parallel fibers. Upon finding that a strong correlation of FA with age existed, we adjusted for age and calculated partial correlation coefficients.

Results: Slopes of FA versus ADC ranged from -1.00711 to -1.67592 (p < 0.05); r values ranged from -0.81 to -0.50 and r(2) values from 0.25 to 0.66. The four greatest r(2) values were within WM regions having large numbers of crossing fibers and the three lowest r(2) values were in regions having predominantly parallel fibers. After adjusting for age, slopes ranged from -1.08095 to 0.09612 (p < 0.05 in five cases); partial correlation coefficients ranged from -0.49 to 0.03 and r(2) values from 0.31 to 0.79. The highest partial correlation coefficients were then relatively equally distributed between the two types of WM regions.

Conclusion: In various regions, FA and ADC evolved with differing degrees of correlation. We found a strong influence of age on the relationship between FA and ADC.