Purpose <p>Two types of asymmetry index (AI) have been utilized in evaluating cerebral function in ischemic cerebrovascular disease, however, few data exist on the differences between these AI measures. This study aimed to compare the two AIs in assessing PET cerebral metabolism and their correlation with clinical scales, to explore their potential value and applications in clinical settings.</p> Procedures <p>Seventy patients diagnosed with subacute and chronic ischemic stroke were retrospectively analyzed. All patients underwent 2-deoxy- 2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) PET/MR scans and were assessed using the National Institutes of Health Stroke Scale (NIHSS) and the Modified Rankin Scale (mRS). Nineteen patients underwent a repeat [¹⁸F]FDG PET/MR scan one year later. Two voxel-wise AI methods, designated as AI₁ and AI₂, were calculated based on standardized uptake value ratio (SUVR). The hypometabolism on affected side assessed by different AI methods were compared. The correlations between the hypometabolism and the clinical scores were analyzed.</p> Results <p>The volume and percentage of decreased [¹⁸F]FDG metabolism assessed by AI₂ was larger than that obtained from AI₁ (all <i>p</i> &lt; 0.0001). The correlation coefficients between the clinical scores and the decreased metabolism in temporal and parietal lobes assessed by AI₁ method were all higher than those from AI₂. In addition, the improved follow-up patients showed more pronounced metabolic improvement as assessed by AI₁.</p> Conclusions <p>The assessment of cerebral [¹⁸F]FDG metabolism in patients with unilateral internal carotid/middle cerebral artery steno-occlusion to reflect clinical neurological function using the AI₁ method demonstrated superior performance in comparison to the AI₂ method.</p>