An apparatus and method is presented for controlling the quality of a mass density measurement of a multiphase fluid mixture including a plurality of fluid fractions and a plurality of constituting elements. The method includes the steps of: submitting a measuring pipe to a flux of high energy photons and measuring count rates; determining a mass density of the multiphase fluid mixture based on count rate measurements in a first and second energy windows; determining an electronic density of the multiphase fluid mixture based on count rate measurements in a third energy window; and comparing the electronic density to the mass density of the multiphase fluid mixture.