Magnetic resonance prediction of outcome after thrombolytic treatment

Treatment of clinical stroke with recombinant tissue plasminogen activator (rt-PA) carries the risk of hemorrhagic complications. Hence, predictors of therapeutic outcome with respect to (a) reperfusion and (b) tissue recover y would be very useful to identify potentially salvageable brain tissue. Ma gnetic resonance (MR) parameters, especially the apparent diffusion coeffic ient of water (ADC), perfusion weighted imaging (PWI) and T-2 relaxometry a re thought to provide this information. We evaluated the prognostic implica tions of ADC, PWI and T-2 relaxometry immediately before initiation of thro mbolytic treatment in a model of clot embolism in rats. Animals (n = 14) we re treated with intraarterial fi-PA (10 mg/kg) at 90 min after embolism. MR imaging was repeatedly performed at 4.7 T before and up to 5.5 h after emb olism. ADC was calculated from diffusion-weighted images (b-values: 30, 765 , 1500 s/mm(2)), arterial spin tagging was used for PWI, and quantitative T -2 relaxometry was performed with a Carr-Purcell-Meiboom-Gill (CPMG) sequen ce. A reperfusion index was calculated to assess the quality of thrombolyti c recanalization. The decline of ADC at the end of the experiment to below 80% of control was defined as unfavorable outcome. The probability of tissu e injury at the end of the experiments increased with the severity of ADC c hanges before the initiation of treatment (probability of unfavorable outco me: 21%, 44%, 65% for ADC values of 80-90%, 70-80% and < 70% of control, re spectively). Pretreatment PWI or T-2 relaxometry also correlated with outco me but-alone or in combination with pretreatment ADC maps-did not improve i njury prediction over that obtained by ADC alone. Outcome was influenced po sitively by successful reperfusion the quality of which, however, could not be predicted by pre-treatment MR characteristics. The data demonstrate tha t ADC mapping performed before the initiation of thrombolytic treatment pro vides reliable risk assessment of impeding brain injury but due to uncertai nties of postischemic reperfusion does not allow precise outcome prediction in individual experiments. (C) 2001 Elsevier Science Inc. All rights reser ved.