Apparent diffusion coefficient thresholds do not predict the response to acute stroke thrombolysis

Background and Purpose - Apparent diffusion coefficient (ADC) thresholds for tissue infarction have been identified in acute stroke. IV tissue plasminogen activator (tPA) is associated with tissue salvage. We hypothesized that tPA would lower the ADC threshold for infarction. Methods - ADC and mean transit time (MTT) maps were generated for 26 patients imaged within 6 hours of stroke onset (12 tPA and 14 conservatively managed controls). MTT maps and day-90 T2-weighted images were coregistered to ADC maps. Relative ADC (rADC) values were calculated for initial diffusion-weighted imaging (DWI) lesions, infarct growth regions ( final infarct volume - the acute DWI lesion volume), and hypoperfused salvaged regions (HS; MTT map abnormality - the final infarct volume). When relevant, the DWI lesion was subdivided into DWI reversal and DWI infarct regions. Results - Mean DWI lesion rADC was 0.79 in tPA and 0.74 in untreated patients (P = 0.097). Mean rADC in HS and infarct growth regions were similar in tPA patients (0.950 and 0.946) and untreated patients (0.957, P = 0.76; 0.970, P = 0.08, respectively). The rADC in HS tissue was directly correlated with the time to treatment with tPA (r = 0.685; P = 0.029). DWI reversal was seen in 67% of tPA-treated patients and in 36% of those conservatively managed (Fisher exact test; P = 0.238). In the 13 patients with DWI reversal, the mean rADC in these regions (0.81 +/- 0.07) was significantly higher than in the acute DWI region that infarcted (0.74 +/- 0.07; P = 0.02), although no absolute thresholds could be identified. Conclusions - The peri-DWI lesion region contains tissue with intermediate ADC values. The fate of this tissue is variable and cannot be predicted based on the ADC alone. DWI expansion occurs in bioenergetically normal tissue, and this is attenuated by tPA in a time-dependent fashion.