A Brillouin modality can be supplemented by an auxiliary modality, such as an optical imaging modality or a spectroscopy modality. In some embodiments, the auxiliary modality can be used to guide the Brillouin measurement to a desired region of interest, so that acquisition times for the Brillouin measurement can be reduced as compared to interrogating the entire sample. The auxiliary modality may have an acquisition speed faster than that of the Brillouin modality. In some embodiment, the auxiliary modality determines a composition of materials within a voxel in the sample interrogated by the Brillouin modality. Using the information provided by the auxiliary modality, the Brillouin signatures corresponding to the materials within the voxel can be unmixed, thereby providing a more accurate measurement of the sample.