FIELD: medicine.SUBSTANCE: group of inventions relates to medical equipment, specifically to means for magnetic resonance imaging. Method of operation of a magnetic resonance imaging system based on adjustment of a radio-frequency excitation field B1, applied to analyzed subject to be tomographed, comprises steps of determining at least one position parameter (d), which indicates the position of at least a portion of the analyzed subject with respect to at least one radio frequency transmitting antenna of the magnetic resonance imaging system and is carried out by using proximity detection unit, which includes at least two proximity sensors (D1, D9), determination by means of two proximity sensors (D1, D9) of at least one transverse dimension (wi) of the analyzed subject for a plurality of locations (zi) of at least part of analyzed subject, obtaining data for generating a geometric outline of the analyzed subject with respect to said at least one radio frequency transmitting antenna of the magnetic resonance imaging system from parameters (di) position and transverse dimensions (wi) defined on said plurality of locations (zi), adjustment of at least one radio-frequency power parameter of radio-frequency signal power, to be transmitted to said at least one radio frequency transmitting antenna, depending on at least one of the determined at least one position (d) position and the determined geometric size (w) of the analyzed subject. Magnetic resonance imaging system is configured to obtain magnetic resonance images of at least part of the analyzed subject and comprises a scanning unit providing a test space for accommodating at least a portion of the analyzed subject, wherein the test space has an input region for the analyzed subject to enter the examination space, and the scanning unit further has a main magnet configured to generate a static magnetic field B0 in the surveyed space, a magnetic field gradient coil system configured to generate gradient magnetic fie
