Introduction: Ischemic stroke is caused by cellular injury to the neurovascular unit. During the early stages of stroke onset, MR diffusion-weighted Imaging (DWI) provides sensitive detection of cytotoxic injury. However, measurement of free-water with quantitative R2 (qR2) relaxometry is generally ignored.
Hypothesis: Inclusion of qR2 with DWI will better characterize the heterogeneity of acute ischemia and infarct growth.
Methods: 36 ischemic stroke patients (age; 72 ± 17) were imaged acutely (baseline) and at 24h on a 3 T MR scanner. Apparent diffusion coefficient (ADC) and qR2 maps were calculated from DWI and multi-echo T2 data sets using ANTONIA software. Volumetric segmentation of qR2 lesions were performed using a threshold -12.5% of the mean contra lateral side value. ADC lesions were segmented using a threshold of 630x10^-6mm^2/s. Lesion overlap of qR2 and ADC segmented volumes was also calculated using DICE coefficient.
Results: Time from stroke onset to MRI was 4:5 ± 0.16h, and recanalization was confirmed (10 ± 1.3h) in the acute period. Treatment was provided with tPA in 27/36 (75%) or endovascular therapy in 15/36 (41.7%) or both in 9/36 (25%). Ischemic lesions were identified in 31/36 (86%) patients based on ADC. ADC lesions were identified in 23/31 (74%) at baseline and 27/31 (87%) at 24h, QR2 lesions were observed in 14/27 (52 %) at baseline and 15/27 (56%) at 24h. The Figure shows ADC and qR2 volume changes over time. QR2 and ADC volume overlap was 10.7% at baseline and 19.9% at 24h. The percentage change in qR2 lesion was 189.2%, compared to ADC lesion growth of 90.50%. Lesion growth was more frequently demonstrated by qR2 than ADC (Fishers exact p<0.05).
Conclusion: Acute ischemic lesion growth size was more frequently demonstrated by qR2 than by ADC. Acquisition of ADC alone underestimates severity of acute ischemia and infarct growth. Combining quantitative MRI using ADC and qR2 provide improved characterization of acute infarct evolution.