Magnetization transfer and diffusion imaging of acute axonal damage in the cerebral peduncle following hypoxia-ischemia in neonatal rats

BACKGROUND: Magnetic resonance imaging (MRI) of axonal degenerative changes in the cerebral peduncle of the corticospinal tract following cerebral hypoxic-ischemic damage might distinguish infants most appropriate for receiving prompt treatment. The optimal MRI sequence for very early diagnosis of axonal degenerative changes is unknown. We hypothesized that magnetization transfer ratio (MTR) imaging would be more sensitive than traditional MRI, e.g., T-2 or diffusion weighted imaging. METHODS: Transient unilateral cerebral hypoxia-ischemia was produced in the neonatal rat followed by MRI of changes in T-2, the apparent diffusion coefficient (ADC) of water, and MTR, with a focus on the parietal cortex (an ischemic damaged region) and the cerebral peduncle (remote within the corticospinal tract). Rats were imaged at 2 h, 1 d, or 1 wk postinsult. RESULTS: In the cerebral peduncle, MTR and T-2 responded similarly, with alterations occurring ipsilaterally at 1 d postinsult. ADC was most sensitive for detecting changes as early as 2 h postinsult, and this corresponded to a reduced staining of axonal filaments ipsilaterally. CONCLUSION: MTR and T-2 imaging have comparable sensitivity for distinguishing early axonal damage in the cerebral peduncle. ADC imaging is highly sensitive for detecting early disruption of corticospinal axons, supporting its potential hyperacute diagnostic use clinically.