Feasibility of oscillating and pulsed gradient diffusion MRI to assess neonatal hypoxia-ischemia on clinical systems

Abstract

Diffusion-time- (<i>t_d</i>) dependent diffusion MRI (dMRI) extends our ability to characterize brain microstructure by measuring dMRI signals at varying <i>t_d</i>. The use of oscillating gradient (OG) is essential for accessing short <i>t_d</i> but is technically challenging on clinical MRI systems. This study aims to investigate the clinical feasibility and value of <i>t_d</i>-dependent dMRI in neonatal hypoxic-ischemic encephalopathy (HIE). Eighteen HIE neonates and six normal term-born neonates were scanned on a 3 T scanner, with OG-dMRI at an oscillating frequency of 33 Hz (equivalent <i>t_d</i> ≈ 7.5 ms) and pulsed gradient (PG)-dMRI at a <i>t_d</i> of 82.8 ms and b-value of 700 s/mm². The <i>t_d</i>-dependence, as quantified by the difference in apparent diffusivity coefficients between OG- and PG-dMRI (ΔADC), was observed in the normal neonatal brains, and the ΔADC was higher in the subcortical white matter than the deep grey matter. In HIE neonates with severe and moderate injury, ΔADC significantly increased in the basal ganglia (BG) compared to the controls (23.7% and 10.6%, respectively). In contrast, the conventional PG-ADC showed a 12.6% reduction only in the severe HIE group. White matter edema regions also demonstrated increased ΔADC, where PG-ADC did not show apparent changes. Our result demonstrated that <i>t_d</i>-dependent dMRI provided high sensitivity in detecting moderate-to-severe HIE.