Optoacoustic imaging can noninvasively provide visualization of vasculature structures with optical contrast well below the skin surface. For meaningful biological investigations, high-resolution at mesoscopic penetration depths and therefore thorough adaption of the systematic arrangement to the object of interest is required. A suitable modular optoacoustic tomography system is presented here and its performance is demonstrated in three exemplary studies on imaging agar phantoms, mouse head vasculature and mouse tumor vasculature ex-vivo.