A calibration method for calibrating a measuring element which is configured to determine an electric current I flowing through a basic-field magnet of a magnetic resonance imaging system, comprising the steps: - performing a measurement with the measuring element, - performing a frequency measurement of the Larmor frequency of protons within a patient or a phantom in the magnetic field of the basic-field magnet with a frequency measuring unit, wherein the measurement of the measuring element and the frequency measurement are corresponding to the same magnetic field of the basic-field magnet, - calculating a calibration factor based on the deviation between the measurement of the measuring element and the frequency measurement, - calibrating the measuring element based on the calibration factor, wherein the calibration of the measuring element is performed by calculating corresponding parameters from the measurement of the measuring element and the frequency measurement, preferably a magnetic field, an electric current I or a frequency f, and determining the calibration factor as an aging factor of the measuring element based on the difference of these corresponding parameters, wherein a measurement of the measuring element is performed at the beginning of a ramping procedure and the frequency measurement is performed before the ramping procedure, wherein the basic-field magnet is a superconducting magnet with a persistent switch and the ramping procedure is performed by opening the persistent switch and determining the electric current I flowing through the basic-field magnet by determining a time resolved current-curve based on the measurement of the measuring element, wherein the electric current I flowing through the basic-field magnet before opening the persistent switch being calculated by reconstructing the current-curve to the point of time of opening the persistent switch. - performing a measurement with the measuring element, - performing a frequency measurement of the Larmor frequency of protons within a patient or a phantom in the magnetic field of the basic-field magnet with a frequency measuring unit, wherein the measurement of the measuring element and the frequency measurement are corresponding to the same magnetic field of the basic-field magnet, - calculating a calibration factor based on the deviation between the measurement of the measuring element and the frequency measurement, - calibrating the measuring element based on the calibration factor, wherein the calibration of the measuring element is performed by calculating corresponding parameters from the measurement of the measuring element and the frequency measurement, preferably a magnetic field, an electric current I or a frequency f, and determining the calibration factor as an aging factor of the measuring element based on the difference of these corresponding parameters, wherein a measurement of the measuring element is performed at the beginning of a ramping procedure and the frequency measurement is performed before the ramping procedure, wherein the basic-field magnet is a superconducting magnet with a persistent switch and the ramping procedure is performed by opening the persistent switch and determining the electric current I flowing through the basic-field magnet by determining a time resolved current-curve based on the measurement of the measuring element, wherein the electric current I flowing through the basic-field magnet before opening the persistent switch being calculated by reconstructing the current-curve to the point of time of opening the persistent switch. <EOS>