In vivo T₁ mapping of neonatal brain tissue at 64 mT

Ultralow-field (ULF) point-of-care MRI systems allow image acquisition without interrupting medical provision, with neonatal clinical care being an important potential application. The ability to measure neonatal brain tissue T₁ is a key enabling technology for subsequent structural image contrast optimization, as well as being a potential biomarker for brain development. Here we describe an optimized strategy for neonatal T₁ mapping at ULF.

Examinations were performed on a 64-mT portable MRI system. A phantom validation experiment was performed, and a total of 33 in vivo exams were acquired from 28 neonates with postmenstrual age ranging from 31⁺⁴ to 49⁺⁰  weeks. Multiple inversion-recovery turbo spin-echo sequences were acquired with differing inversion and repetition times. An analysis pipeline incorporating inter-sequence motion correction generated proton density and T₁ maps. Regions of interest were placed in the cerebral deep gray matter, frontal white matter, and cerebellum. Weighted linear regression was used to predict T₁ as a function of postmenstrual age.

Reduction of T₁ with postmenstrual age is observed in all measured brain tissue; the change in T₁ per week and 95% confidence intervals is given by dT₁  = -21 ms/week [-25, -16] (cerebellum), dT₁  = -14 ms/week [-18, -10] (deep gray matter), and dT₁  = -35 ms/week [-45, -25] (white matter).

Neonatal T₁ values at ULF are shorter than those previously described at standard clinical field strengths, but longer than those of adults at ULF. T₁ reduces with postmenstrual age and is therefore a candidate biomarker for perinatal brain development.