CT Perfusion Does Not Modify the Effect of Reperfusion in Patients with Acute Ischemic Stroke Undergoing Endovascular Treatment in the ESCAPE-NA1 Trial.

BACKGROUND AND PURPOSE: Although reperfusion is associated with improved outcomes in patients with acute ischemic stroke undergoing endovascular treatment, many patients still do poorly. We investigated whether CTP modifies the effect of near-complete reperfusion on clinical outcomes, ie, whether poor clinical outcomes despite near-complete reperfusion can be partly or fully explained by CTP findings. MATERIALS AND METHODS: Data are from the Safety and Efficacy of Nerinetide in Subjects Undergoing Endovascular Thrombectomy for Stroke (ESCAPE-NA1) trial. Admission CTP was processed using RAPID software, generating relative CBF and CBV volume maps at standard thresholds. CTP lesion volumes were compared in patients with-versus-without near-complete reperfusion. Associations between each CTP metric and clinical outcome (90-day mRS) were tested using multivariable logistic regression, adjusted for baseline imaging and clinical variables. Treatment-effect modification was assessed by introducing CTP lesion volume × reperfusion interaction terms in the models. RESULTS: CTP lesion volumes and reperfusion status were available in 410/1105 patients. CTP lesion volumes were overall larger in patients without near-complete reperfusion, albeit not always statistically significant. Increased CBF <34%, CBV <34%, CBV <38%, and CBV <42% lesion volumes were associated with worse clinical outcome (ordinal mRS) at 90 days. CTP core lesion volumes did not modify the treatment effect of near-complete recanalization on clinical outcome. CONCLUSIONS: CTP did not modify the effect of near-complete reperfusion on clinical outcomes. Thus, CTP cannot explain why some patients with near-complete reperfusion have poor clinical outcomes.

Fresnel filtering in lasing emission from scarred modes of wave-chaotic optical resonators.

We study lasing emission from asymmetric resonant cavity GaN microlasers. By comparing far-field intensity patterns with images of the microlaser we find that the lasing modes are concentrated on three-bounce unstable periodic ray orbits; i.e., the modes are scarred. The high-intensity emission directions of these scarred modes are completely different from those predicted by applying Snell's law to the ray orbit. This effect is due to the process of "Fresnel filtering" which occurs when a beam of finite angular spread is incident at the critical angle for total internal reflection.