conducting preoperative examination of the patient for detecting cerebral blood vessels affected by atherosclerotic lesions;

providing a microcatheter device comprising at least a first channel and a second channel, a plurality of microcatheters of gradually reducing diameters for coaxial insertion one into another through the first channel, a light-guiding optical-fiber device connected to a high-power laser source and insertable into the innermost of said plurality of microcatheters, and a source of a washing liquid for supply into the area being treated through the second channel;

puncturing and catheterizing the common femoral artery of the patient for installing an introducer;

inserting a first microcatheter of said plurality of microcatheters into the introducer;

coaxially inserting and moving forward a second microcatheter of said plurality of micorcatheters into the first microcatheter;

coaxially inserting and moving forward a third microcatheter of said plurality of micorcatheters into the second microcatheter;

if necessary, sequentially inserting and moving forward other microcatheters of said plurality of microcatheters into the preceding microcatheter until reaching the affected zone of the microcirculation bloodstream in the patient's brain;

inserting the light-guiding optical-fiber device coaxially into the innermost catheter of said plurality of microcatheters;

guiding the light-guiding optical-fiber device to the zone of the blood vessel occluded by the atherosclerotic lesion;

shifting the catheter device to the descending arch of the aorta or the proximal part of the common carotid artery;

adjusting the distance from the tissue affected by atherosclerotic lesion to the distal end face of the optical fiber device that provides the optimal angle of divergence of the laser beam for covering the tissue affected by atherosclerotic lesions while preventing damage to healthy blood vessel walls; and

restoring the circulation and bloodstream through the treated cerebral blood vessel by conducting laser treatment of the affected tissue, the aforementioned microcatheters being made from a radio-opaque material and said laser treatment being carried out under X-ray TV observation.