The purpose of this project was to calculate the ROI of the middle cerebral artery (MCA) in patients with acute stroke to establish if this measurement could be used as another primary sign of infarction even if other established primary signs of infarction are absent. CT brain scans of 465 patients, who presented in the emergency room in the first six hours after the onset of symptoms, were studied retrospectively. Two polygonal ROIs were drawn on the M1 segments of both middle cerebral arteries and three parameters were calculated automatically: HU density, volume and surface of the corresponding artery segment. The age and gender of each patient were also recorded, as well as the CT findings (including the hyperdense appearance of MCA and the insular ribbon sign) and the neurological findings. The range of calculated ROIs was between 9 HU and 134 HU. A statistically significant difference was reported in ROI measurement between the right and left MCA in patients with left (or right) hemiparesis respectively. A significant difference was also reported between the ROIs of the right and left MCA in patients with acute ischemic stroke in the region of the brain supplied by the left (or right) MCA respectively. ROI measurement of MCA is easy to apply and interpret during the CT scan and might serve as an additional primary sign of infarction.