A magnetic resonance imaging system comprising: a main magnet with an imaging zone, wherein the main magnet is configured for generating a main magnetic field with an average magnetic field strength within the imaging zone; a gradient magnetic field system (110, 112) for generating a spatially dependent gradient magnetic field within the imaging zone; a magnet power supply configured for adjusting the average magnetic field strength within the imaging zone; a current source for supplying RF current between multiple electrodes (122, 122') of the magnetic resonance imaging system, wherein the multiple electrodes comprise a first portion and a second portion, wherein the current source is configured for supplying the RF current between the first portion and the second portion, wherein the multiple electrodes are configured for forming an electrical contact with an exterior surface of a subject; a memory containing machine executable instructions and pulse sequence commands, wherein the pulse sequence commands comprise instructions for controlling the magnetic resonance imaging system for acquiring magnetic resonance data from the imaging zone according to a three-dimensional imaging protocol, wherein the pulse sequence commands comprise readout gradient commands for controlling the gradient magnetic field system; a processor for controlling the magnetic resonance imaging system; wherein execution of the machine executable instructions cause the processor to: set the average magnetic field strength within the imaging zone to a first value by controlling the magnet power supply with the pulse sequence commands; which average magnetic field strength of the first value serves to pre-polarise spins in the imaging zone; set the average magnetic field strength within the imaging zone to a second value by controlling the magnet power supply with the pulse sequence commands, the second value is lower than the first value; control the current source to have a known RF current travel between the first portion of the electrodes and the second portion of the electrodes; acquire the magnetic resonance data from the subject by controlling the magnetic resonance imaging system with the readout gradient commands; reconstruct three-dimensional image data from the magnetic resonance data; and calculate a resistive model of the subject using the three-dimensional image data and the known RF current through the electrodes. a main magnet with an imaging zone, wherein the main magnet is configured for generating a main magnetic field with an average magnetic field strength within the imaging zone; a gradient magnetic field system (110, 112) for generating a spatially dependent gradient magnetic field within the imaging zone; a magnet power supply configured for adjusting the average magnetic field strength within the imaging zone; a current source for supplying RF current between multiple electrodes (122, 122') of the magnetic resonance imaging system, wherein the multiple electrodes comprise a first portion and a second portion, wherein the current source is configured for supplying the RF current between the first portion and the second portion, wherein the multiple electrodes are configured for forming an electrical contact with an exterior surface of a subject; a memory containing machine executable instructions and pulse sequence commands, wherein the pulse sequence commands comprise instructions for controlling the magnetic resonance imaging system for acquiring magnetic resonance data from the imaging zone according to a three-dimensional imaging protocol, wherein the pulse sequence commands comprise readout gradient commands for controlling the gradient magnetic field system; a processor for controlling the magnetic resonance imaging system; wherein execution of the machine executable instructions cause the processor to: set the average magnetic field strength within the imaging zone to a first value by controlling the magnet power supply with the pulse sequence commands; which average magnetic field strength of the first value serves to pre-polarise spins in the imaging zone; set the average magnetic field strength within the imaging zone to a second value by controlling the magnet power supply with the pulse sequence commands, the second value is lower than the first value; control the current source to have a known RF current travel between the first portion of the electrodes and the second portion of the electrodes; acquire the magnetic resonance data from the subject by controlling the magnetic resonance imaging system with the readout gradient commands; reconstruct three-dimensional image data from the magnetic resonance data; and calculate a resistive model of the subject using the three-dimensional image data and the known RF current through the electrodes.