Abstract: A method for determining a flow rate and/or a concentration of particles of a fluid flowing in a chamber, which includes the steps of: producing an ultrasound beam of a given frequency with a first transducer such that all fluid components traveling through an intersection region between the ultrasound beam and the chamber are insonated by the first transducer; receiving Doppler-shifted ultrasound signals generated by the fluid components in the insonated region of the chamber with a second transducer; acquiring the ultrasound signals received by the second transducer during an acquisition time; obtaining a Doppler Power Spectrum of the acquired ultrasound signals; and determining the flow rate and/or the concentration of particles of the fluid by adjustment between, on the one hand, the obtained Doppler Power Spectrum and, on the other hand, a model of the Doppler Power Spectrum.