Relationship between severity of MR perfusion deficit and DWI lesion evolution

Objective: To assess whether a quantitative analysis of the severity of the early perfusion deficit on MRI in acute ischemic stroke predicts the evolu tion of the perfusion/diffusion mismatch and to determine thresholds of hyp operfusion that can distinguish between critical and noncritical hypoperfus ion. Methods: Patients with acute ischemic stroke were studied in whom perf usion-weighted imaging (PWI) and diffusion-weighted imaging (DWI MRI) were performed within 7 hours of symptom onset and again after 4 to 7 days. Pati ents with early important decreases in points on the NIH Stroke Scale were excluded. Maps of cerebral blood flow (CBF), cerebral blood volume (CBV), a nd mean transit time (MTT) were created. These hemodynamic parameters were correlated with the degree of recruitment of the baseline PWI lesion by the DWI lesion. Results: Twelve patients had an initial PWI > DWI mismatch of > 20%. A linear relationship was observed between the initial MTT and the d egree of recruitment of the baseline PWI lesion by the DWI lesion at follow -up (R-2 = 0.9, p < 0.001). Higher CBV values were associated with higher d egrees of recruitment (p= 0.732, p < 0.007). The volume of MTT of >4 (R-2 = 0.86, p < 0.001) or >6 seconds (R-2 = 0.85, p < 0.001) predicted final inf arct size. Conclusion: Among patients who have had an acute stroke with PWI > DWI, who do not have dramatic early clinical improvement, the degree of expansion of the initial DWI lesion correlates with the severity of the ini tial perfusion deficit as measured by the mean transit time and the cerebra l blood volume.