A hyperpolarized liquid contrast agent is for use in a MRT device. The liquid contrast agent passes through a conduit of a MW resonator in the magnetic field of the MRT device. A microwave with a frequency of at least 40 GHz couples into the MW resonator for polarizing the liquid contrast agent upon passage through the conduit in the MW resonator using DNP. The contrast agent is polarized in a continuous passage in the MW resonator and administered immediately. A MW mode is formed in the MW resonator which has an antinode in the magnetic field strength and a node in the electric field strength. The power of the introduced microwave and coupling of the microwave into the resonator are adjusted such that in the area of the line, an amplitude of the MW magnetic field strength B1>；=1.5·10-2 Ts 1/T1,e results, wherein T1,e is the relaxation time of the DNP-active electrons.
