Abstract Body: Purpose: In acute ischemic stroke, the typically employed 620×10^-6mm²/s ADC threshold to automatically delineate the core on diffusion-weighted imaging (DWI) was established by overlaying the manually defined core onto the baseline ADC (ADC₀) in recanalized patients following intravenous thrombolysis. However, recanalization was assessed 3-6hrs after treatment, which may entail substantial core growth, and follow-up imaging was at 90 days, implying infarct underestimation due to atrophy. Other studies typically used day 2-5 follow-up MRI (FU-MRI) but did not correct for vasogenic edema, implying infarct overestimation. We re-evaluated the ADC core threshold in patients with early recanalization following EVT, and applied edema correction on 24h post-EVT MRI.
Methods: From our center’s EVT registry (2012-2021), all consecutive mothership patients with mTICI2c-3 recanalization within 90min after baseline MRI (MRI₀) and who underwent FU-MRI at 24h post-EVT were included. Basilar occlusions and small DWI lesion (<3mL) were excluded. Edema correction was performed by applying non-linear coregistration of FU-MRI onto MRI₀ using the ANTs library. The baseline ischemic lesion was manually delineated on initial DWI (DWI₀), and the final infarct ROI (Infarct_24h) was manually delineated on non-corrected and edema-corrected FU-DWI. The intersection between DWI₀ and Infarct_24h (the manual core) was then overlayed onto the ADC₀, after exclusion of CSF and spurious ADC voxels. A ROC analysis then compared all ‘core’ voxels to ‘non-core’ voxels across patients, and the Youden Index was computed to determine the optimal ADC (OptADC) core threshold.
Results: Across 56 eligible patients (median age: 73yrs; female 52%; median [IQR] NIHSS: 12 [8-19]), the mean ADC within the manual core was 609.8 (± 66.8)×10^-6mm²/s and the OptADC was 584×10^-6mm²/s without edema correction. The corresponding values with edema correction were 598.7 (± 69.1)×10^-6mm²/s and 636×10^-6mm²/s, respectively (both p<0.001 vs. non-corrected data).
Conclusion: We report here the first ADC core threshold values derived from EVT-induced ultra-early complete recanalization using 24h follow-up MRI, with and without edema correction. Our strict selection criteria likely partly explain the substantially lower uncorrected ADC threshold found as compared to the classic 620×10^-6mm²/s threshold. We also document the effect of edema correction on ADC threshold calculation when an early follow-up MRI is used.