We are working on project of searching for areas with primary signs of a brain stroke. This work based on analyzing of multispiral computed tomography (MSCT) images of the human brain. As part of these investigations, there is a need for initial filtering of original data for contrast identification of potential abnormal areas. We perform a formula to represent brain tissue from original medical data. Also we offer sequence of actions to change pixel values for improvement of primary signs of a brain stroke presentation. The algorithm of data pre-preparation within the framework of the studied problem is presented.