Thermoacoustic Tomography is a promising hybrid medical imaging technique that has received considerable attention during the last decade. It has been observed that acoustic attenuation limits the quality of the reconstruction and how deep we are able to see inside human tissue, therefore it is important consider it in the modeling of the inverse problem. In the particular case of biological tissue, its acoustically dissipative character is commonly modeled by fractional derivative which motivates the study of attenuations given by integro-differential operators. In this talk, I'll focus in the uniqueness question of whether the ultrasound boundary data uniquely determines the initial source of waves in media with integro-differential attenuation.