A method acquires RF magnetic field information (B1 magnetic field information) in response to generated radio frequency (RF) pulses in a magnetic resonance imaging (MRI) system. An RF excitation pulse sequence is generated, and the generated RF excitation pulse sequence includes a plurality of RF excitation pulses individually having different flip angles. The generated RF excitation pulse sequence is transmitted to a target object. RF echo response signals are received from the target object corresponding to the plurality of RF excitation pulses and B1 information is acquired by processing the received RF echo response signals.