Detecting Diffusion-Weighted Imaging-Negative Strokes in Rat Models of Acute Internal Carotid Artery Occlusion Using Magnetic Resonance Spectroscopy.

Introduction: The aim of this study was to explore the potential of magnetic resonance spectroscopy (MRS) for the early diagnosis of the ischemic brain tissue with negative diffusion-weighted imaging (DWI) results in the model of acute internal carotid artery occlusion (AICAO) in rats.

Methods: Fifteen rats were randomly assigned to three groups: the sham group (SHAM, n = 5), the 2-h ischemia model group (CI2H, n = 5), and the 12-h ischemia model group (CI12H, n = 5). In the experimental group, the method of AICAO was adopted to establish a right cerebral ischemia model. After the successful establishment of the model, DWI and MRS scans were first performed, and then the MRS results were recorded. Immunohistochemical analysis of zonula occludens-1 (ZO-1), neuron-specific enolase, S-100β protein, and cytochrome C (CytC) was conducted on paraffin-embedded brain sections, followed by Spearman correlation analysis between relevant parameters and these proteins.

Results: Lipid (Lip) levels were lower in the SHAM group compared to the CI2H group (p < 0.05), but no significant difference was observed between the SHAM and CI12H groups. Lip was negatively correlated with ZO-1 across all groups (ρ = -0.768, p < 0.001). Lactate (Lac) levels were lower in the SHAM group than in the CI2H and CI12H groups (p < 0.05), and Lac was positively correlated with CytC across all groups (ρ = 0.801, p < 0.001). Apparent diffusion coefficient (ADC) values on the right side of the brain were lower in the CI12H group than in the SHAM group (p < 0.05), with no significant difference compared to the CI2H group. The level of N-acetyl aspartate (NAA) in the CI12H group was lower than that in the SHAM group and the CI2H group (p < 0.05), and there was no statistically significant difference in the level of NAA between the CI2H group and the SHAM group. The Choline (Cho) level in the CI12H group exhibited a statistically significant increase compared to both the SHAM and CI2H groups (p < 0.05), and there was no statistically significant difference in the level of Cho between the CI2H group and the SHAM group.

Conclusion: Brain damage in AICAO rats became evident at 2 h after successful modeling. MRS detected brain damage earlier than DWI, with Lac and Lip as the most sensitive markers, preceding changes in NAA, Cho, and ADC values.