Hyperoxygenation Differentiates Vascular Lesions From Parenchymal Lesions Using Susceptibility Weighted MRI In Mice With Experimental Autoimmune Encephalomyelitis (P1.166)

OBJECTIVE: To determine whether using hyperoxygenation can differentiate between vascular lesions and parenchymal white matter lesions in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS) with susceptibility weighted imaging (SWI). BACKGROUND: SWI detects lesions in MS patients not seen with conventional magnetic resonance imaging (MRI) methods. Previously in the EAE model (Nathoo et al., Multiple Sclerosis J 19:721, 2013), we observed two types of lesions using SWI: 1) vascular lesions, due to deoxyhemoglobin and 2) parenchymal white matter lesions, due to iron deposition and demyelination. We aimed to determine if these two lesion types could be differentiated by increasing the inspired oxygen, hypothesizing that vascular lesions would alter in appearance with high oxygen in SWI, whereas parenchymal lesions would not. DESIGN/METHODS: Lumbar spinal cords of control and EAE mice were imaged at 9.4T for SWI with 30% O2/70% N2 then 100% O2. A subset of mice were imaged with these gases and then after perfusion (to remove blood). Lesions (hypointensities, or dark spots) were counted and compared between control and EAE mice, and the number of hypointensities seen with 30% O2 was compared with the number unchanged with 100% O2. RESULTS: Most hypointensities seen with 30% O2 (control: 8.6±0.8, peak EAE: 13.4±1.3; mean±SEM) altered in appearance with 100% O2 (control: 7.1±0.9, p<0.001; EAE: 8±1.7, p<0.01). Hypointensities changing in appearance with 100% O2 disappeared after perfusion, supporting that they are due to deoxyhemoglobin. Parenchymal lesions did not change in appearance with hyperoxygenation. CONCLUSIONS: Using hyperoxygenation with SWI differentiates between vascular and parenchymal lesions in EAE in vivo. This method can be applied in MS, paving the way to investigate the pathophysiology of venous hypoxia and iron deposition in MS. Study Supported by: CIHR, NSERC, Alberta Innovates - Health Solutions, MS Society of Canada, and the Alberta endMS Regional Research and Training Centre of the endMS Research and Training Network. Disclosure: Dr. Nathoo has nothing to disclose. Dr. Rogers has nothing to disclose. Dr. Yong has received personal compensation for activities with Teva Neuroscience as a speaker. Dr. Yong has received research support from Teva Neuroscience and Novartis. Dr. Dunn has nothing to disclose.