The Thesis “The impact of early imaging and reperfusion therapy tactics on radiological and clinical outcome in acute ischemic stroke” addresses one of the most topical current problems – diagnostics and active treatment of acute ischemic stroke. Acute ischemic stroke is one of the major causes of mortality and long-term disability in the world, having a significant social impact. The aim of the Thesis was to evaluate the relationship between multimodal computed tomography (CT) diagnostic and active treatment tactics for acute ischemic stroke with radiological and clinical outcome. The study included 288 patients with acute ischemic stroke with major cerebral vascular occlusion. The Thesis deals with less researched problems to date of active treatment of acute ischemic stroke in patients with large cerebral artery occlusion: use of isolated endovascular thrombectomy compared to the bridging therapy (intravenous thrombolysis with subsequent endovascular thrombectomy) and thrombolysis alone, also recanalization efficiency in the posterior circulation area. The Thesis provides evaluation of treatment complications and thrombectomy procedure parameters, for instance, number of attempts before recanalization and the duration of the procedure. As a result of endovascular treatment, it is possible to reach a high degree of recanalization, which may not correlate with satisfactory clinical outcome; therefore, patient selection is vitally important, which can be improved using modern radiological examination, radiological evaluation. The Thesis evaluates such radiological criteria upon the choice of the treatment tactics and prognostication of the outcome as collaterals, stroke volume on ASPECTS scale, occlusion site, etc. The study revealed statistically significantly better results in patients with endovascular treatment compared to patients undergoing isolated intravenous thrombolysis with occlusion of the large cerebral arteries. The results indicated that the clinical outcome of the bridging therapy (intravenous thrombolysis with subsequent endovascular thrombectomy) is similar to that of isolated endovascular thrombectomy, moreover without a significant increase in the number of complications. As a result of endovascular thrombectomy, patients with large cerebral artery occlusion in most cases reached a higher recanalization rate; furthermore, the risk of complications turned out to be low. Early multimodal CT diagnostics is vitally important is patient selection for active treatment to obtain good late clinical outcome. Radiological parameters such as good collaterals and pre-defined infarct volume in CT perfusion on the ASPECTS scale ? 6 statistically significantly correlated with a better clinical and functional outcome, which has been affected by various factors, especially with successful recanalization and reperfusion. The study includes recommendations in active treatment of acute ischemic stroke and screening of patients with known large cerebral artery occlusion and definition of the action algorithm.