A magnetic resonance imaging, MRI, system comprising: a primary magnet system adapted to generate a static magnetic field; a gradient system adapted to spatially encode a spin ensemble in an imaging subject in the static magnetic field, the spin ensemble defining a state space comprising a plurality of angular momentum subspaces; a cavity defining a cavity mode that couples with spin states of the spin ensemble; a control system and a resonator, the control system being adapted to provide a voltage to the resonator such as to generate an interaction between the cavity and the spin ensemble that increases polarization of the spin ensemble, by applying a time-varying magnetic drive field to the spin ensemble, wherein the time-varying magnetic drive field is adapted to couple the spin states of the spin ensemble with the cavity mode of the cavity, and the interaction between the cavity and the spin ensemble is generated as a result of the coupling between the spin states and the cavity mode acting independently on each of the plurality of angular momentum subspaces of the spin ensemble, wherein the time-varying magnetic drive field is tuned to a spin-resonance frequency ( ω s ) of the spin ensemble, the cavity mode corresponds to a cavity-resonance frequency ( ω c ), the cavity-resonance frequency ( ω c ) is detuned from the spin-resonance frequency ( ω s ) by an amount δω = ω c - ω s , the time-varying magnetic drive field generates Rabi oscillations at a Rabi frequency (Ω R ), and the difference between the detuning ( δω ) and the Rabi frequency (Ω R ) is small compared to the detuning ( δω ); a thermal barrier that thermally insulates the cavity from the imaging subject, the cavity being at a first temperature, the imaging subject being at a second different temperature; and the control system being operable to acquire a magnetic resonance signal from the spin ensemble. a primary magnet system adapted to generate a static magnetic field; a gradient system adapted to spatially encode a spin ensemble in an imaging subject in the static magnetic field, the spin ensemble defining a state space comprising a plurality of angular momentum subspaces; a cavity defining a cavity mode that couples with spin states of the spin ensemble; a control system and a resonator, the control system being adapted to provide a voltage to the resonator such as to generate an interaction between the cavity and the spin ensemble that increases polarization of the spin ensemble, by applying a time-varying magnetic drive field to the spin ensemble, wherein the time-varying magnetic drive field is adapted to couple the spin states of the spin ensemble with the cavity mode of the cavity, and the interaction between the cavity and the spin ensemble is generated as a result of the coupling between the spin states and the cavity mode acting independently on each of the plurality of angular momentum subspaces of the spin ensemble, wherein the time-varying magnetic drive field is tuned to a spin-resonance frequency ( ω s ) of the spin ensemble, the cavity mode corresponds to a cavity-resonance frequency ( ω c ), the cavity-resonance frequency ( ω c ) is detuned from the spin-resonance frequency ( ω s ) by an amount δω = ω c - ω s , the time-varying magnetic drive field generates Rabi oscillations at a Rabi frequency (Ω R ), and the difference between the detuning ( δω ) and the Rabi frequency (Ω R ) is small compared to the detuning ( δω ); a thermal barrier that thermally insulates the cavity from the imaging subject, the cavity being at a first temperature, the imaging subject being at a second different temperature; and the control system being operable to acquire a magnetic resonance signal from the spin ensemble. <EOS>