Fig 3.

The signal-to-noise ratio of diffusion-tensor imaging decreases with brain maturation.

A, Noise in the diffusion-weighted images is age-independent. In 20 participants, the noise is calculated as the SD of pixel values in an air-filled region of interest outside the brain in the b = 337.5 s/mm² diffusion-weighted images (see Methods). The postconceptional age of each participant is the estimated gestational age added to the postnatal age. The data are fit with linear regression. The Pearson correlation coefficient of the noise with postconceptional age is 0.23, which is not statistically significant (P > .3).

B, SNR in diffusion-weighted imaging declines steeply during the first 2 years of postnatal life in the white matter of the posterior limb of the internal capsule. SNR is the quotient of signal intensity divided by noise. The signal intensity is obtained from regions of interest within the brain on b = 337.5 s/mm² diffusion-weighted images. The data are fit with a function (equation 8 in Methods) that defines the theoretical relationship between SNR and participant age. Vertical dashed line indicates the age of normal term birth: 40 gestational weeks.

C, SNR in diffusion-weighted imaging declines steeply during the first 2 years of postnatal life in the gray matter of the lentiform nucleus. Vertical dashed line indicates the age of normal term birth: 40 gestational weeks.