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Background: Identifying a last known well (LKW) time surrogate for acute stroke is vital to increase stroke treatment. Previous research have used an MRI DWI vs. FLAIR mismatch to estimate LKW time to within 6 hours. DWI signal intensity initially increases from onset of stroke, but mapping a reliable time course to the signal intensity has not been demonstrated.Methods: We retrospectively reviewed stroke code patients between 1/2016 and 6/2017 from the prospective, IRB approved UCSD Stroke Registry. Patients who had MRI brain from onset, with or without intervention, are included. All ischemic strokes were confirmed with ADC correlation and timing from onset to MRI was calculated. Raw DWI intensity was measured in grays (Gy) using IMPAX software and compared to contralateral side for control, for a relative DWI intensity (rDWI). LKW and MRI time were collected by chart review. Correlation was assessed using Pearson correlation coefficient between DWI intensity, rDWI, and time to MRI imaging. 1.5T, 3T, and combined modalities were examined.Results: 97 patients were included in this analysis. Overall, there is a good correlation (0.39, p<0.001) for minutes from onset to MRI and DWI intensity. There was good correlation with the 1.5T group (0.39, p=0.001) and very good correlation with the 3T group (0.60, p=0.001). There were no significant differences in demographic or time interval between the two MRI types.Conclusions: There is good correlation between DWI intensity and minutes from onset to MRI. This suggests a time-dependent DWI intensity response and supports the potential use of DWI intensity measurements to extrapolate a LKW time in unknown cases. Further studies in a larger dataset within the hyperacute period are being pursued to increase both experience and generalizability.