A magnetic resonance based apparatus capable of measuring, without using time-of-flight measurements, flow regimes of multi-phase fluids in a pipe, comprises a magnetic resonance module through which the fluid phases flow, wherein the magnetic resonance module includes a radiofrequency coil for transmitting and detecting a signal and means for generating inside the module a homogenous constant magnetic field Bx that is thermally compensated and a transverse magnetic field gradient Gx that is superposed on Bx; and at least one pre-polarization module through which the fluid phases flow before entering the magnetic resonance module.