The invention relates to a device and an according method for multispectral optoacoustic imaging of an object, the device comprising: an irradiation unit configured to irradiate the object with electromagnetic radiation at two or more different irradiation wavelengths (λ), said electromagnetic radiation having a time-varying intensity； a detection unit configured to detect acoustic waves generated in the object upon irradiating the object with the electromagnetic radiation at the different irradiation wavelengths (λ)； and a processing unit configured to reconstruct images of the object based on the detected acoustic waves generated in the object at each of the irradiation wavelengths (λ) and to determine a spatial distribution of at least one first concentration value, which relates to a concentration of at least one electromagnetic radiation absorber in the object, wherein the determination of the spatial distribution of the at least one first concentration value is based on the reconstructed images at the different irradiation wavelengths (λ), on at least one wavelength-dependent extinction coefficient of the at least one electromagnetic radiation absorber in the object, and on a linear combination of at least two model spectra representing wavelength-dependent basis functions of a radiation fluence or of a function of a radiation fluence, in particular a normalized radiation fluence, in the object.
