T₁ and T₂ measurements of the neonatal brain at 7 T

To determine the expected range of NMR relaxation times (T₁ and T₂) in the neonatal brain at 7 T.

Data were acquired in a total of 40 examinations on infants in natural sleep. The cohort included 34 unique subjects with postmenstrual age range between 33 and 52 weeks and contained a mix of healthy individuals and those with clinical concerns. Single-slice T₁ and T₂ mapping protocols were used to provide measurements in white matter, cortex, cerebellum, and deep gray matter. Automatic image segmentation of a separate T₂-weighted brain volume was used to define regions of interest for analysis.

Linear regression was used to estimate relaxation times at term equivalent age (40 weeks postmenstrual age). $T_1^{40\mathrm{wk}}$ with 95% confidence intervals was measured to be 2933 [2893, 2972] ms in white matter; 2653 [2604, 2701] ms in cerebellum; and 2486 [2439, 2532] ms in basal ganglia. $T_2^{40\mathrm{wk}}$ was estimated as 119 [116, 121] ms in white matter, 99 [96, 102] ms in cerebellum, and 90 [89, 92] ms in basal ganglia. Most tissue-relaxation times showed a significant negative correlation with postmenstrual age, with the strongest correlation seen in cerebellum.

We describe neonatal brain tissue and age-specific T₁ and T₂ relaxation values at 7 T. The presented values differ substantially from both adult values at 7 T and neonate values measured at lower field strengths, and will be essential for pulse-sequence optimization for neonatal studies.