Semiquantitative assessment of optic nerve injury using manganese-enhanced MRI.

Abstract

OBJECTIVE: To evaluate the capability of manganese (Mn(2+))-enhanced MRI (MEMRI) in a continuously semiquantitative assessment of rat optic nerve (ON) injury. METHODS: Forty rats were divided into three groups: (I) a control group that was submitted to MEMRI or to fluorescent labeling of retinal ganglion cells (RGCs) (n&#xa0;=&#xa0;10); (II) an ON injury group that was submitted to MEMRI (n&#xa0;=&#xa0;15); (III) an ON injury group that was submitted to fluorescent labeling of RGCs (n&#xa0;=&#xa0;15). Groups II and III were examined at 3, 7, and 14&#xa0;days post-lesion (dpl), when the contrast-to-noise ratio (CNR) of the retina and ON was measured on MEMRI images and the RGCs were counted by fluorescence microscopy and compared between the groups. RESULTS: In the control group, the intact visual pathway from the retina to the contralateral superior colliculus was visualized by MEMRI. In group II, continuous Mn(2+) enhancement was seen from the retina to the lesion site of the optic nerves at 3, 7, and 14&#xa0;dpl. However, no Mn(2+) enhancement was observed distal to the lesion site at those time points. The observed Mn(2+) enhancement proximal to the ON lesion site declined between 7 and 14&#xa0;dpl. The decrease in Mn(2+)-enhanced signal intensity at these sites at 7 and 14&#xa0;dpl when compared to that at 3&#xa0;dpl was significant (P&#xa0;<&#xa0;0.05). The RGC density dropped by 6.84, 45.31, and 72.36&#xa0;% at 3, 7, and 14&#xa0;dpl, respectively. CONCLUSION: MEMRI can be used to evaluate the structural changes after optic nerve injury.