In vivo T(1) mapping of neonatal brain tissue at 64 mT

PURPOSE: 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 T(1) 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 T(1) mapping at ULF. METHODS: 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 T(1) maps. Regions of interest were placed in the cerebral deep gray matter, frontal white matter, and cerebellum. Weighted linear regression was used to predict T(1) as a function of postmenstrual age. RESULTS: Reduction of T(1) with postmenstrual age is observed in all measured brain tissue; the change in T(1) per week and 95% confidence intervals is given by dT(1) = −21 ms/week [−25, −16] (cerebellum), dT(1) = −14 ms/week [−18, −10] (deep gray matter), and dT(1) = −35 ms/week [−45, −25] (white matter). CONCLUSION: Neonatal T(1) values at ULF are shorter than those previously described at standard clinical field strengths, but longer than those of adults at ULF. T(1) reduces with postmenstrual age and is therefore a candidate biomarker for perinatal brain development.