Is there an apparent diffusion coefficient threshold in predicting tissue viability in hyperacute stroke?

Background and Purpose-Rapid and precise identification of the penumbra is important for decision-making in acute stroke. We sought to determine wheth er an early and moderate decrease in the apparent diffusion coefficient (AD C) may help to identify, within the diffusion/perfusion (DWI/PWI) mismatch, those areas that will eventually evolve toward infarction. Methods-We reviewed 48 patients not treated by thrombolytics who had a DWI/ PWI within 6 hours after onset, with infarct evolution documented by follow -up magnetic resonance on days 2 to 4. We calculated absolute values for AD C and the ADC ratio (ADCr) in (1) the initial DWI hypersignal; (2) the fina l volume of the infarct, ie, the follow-up fluid-attenuated inversion recov ery abnormalities; (3) the infarct growth (IGR) area; and (4) the oligemic area (OLI) that remained viable despite initial hemodynamic disturbance. We tested the value of the ADC to predict tissue outcome by using discriminan t analysis. Results-ADC values were marginally but significantly decreased in the IGR a rea (ADC 782 +/- 82X 10(-6) mm(2)/s, ADCr 0.94 +/-0.08) compared with mirro r values (P=0.01) and with OLI (ADC 823 +/- 41X10(-6) mm(2)/s, ADCr 0.99 +/ -0.07; P=0.001). Of all quantitative DWI and PWI parameters, the ADCr best discriminated between IGR and OLI (F-1.50= 13.6, cutoff=0.97, 64% sensitivi ty, 92% specificity) and between the final volume of infarct and OU (F-1.83 =219, cutoff=0.91, 91% sensitivity, 100% specificity). Conclusions-A simple approach based on ADC alone may allow the identificati on of tissue at risk of infarction in acute-stroke patients.