 The purpose of the study is to examine the influence of demographic, clinical and laboratory characteristics on the presence and size of penumbra in acute ischemic stroke patients and to determine those of them which related significantly and independently to the presence and size of Penumbra. The examined factors will include demographic variables such as age, gender, ethnic background, vascular risk factors and medical history, clinical parameters such as time from stroke onset until arrival to the hospital, results of neurological evaluation by NIHSS and imaging findings, laboratory tests such as body temperature, blood pressure, glucose level, renal functions etc. and imaging findings - the presence and the size of collateral blood vessels, the state of carotid arteries by CTA. The possible correlation between all this parameters and the presence and the size of penumbra as detected by CTP will be further examined. 