In an embodiment, a system and method are provided for determining position and orientation of an optical delivery unit relative to an acoustic receiving unit, in the field of opto-acoustic imaging, wherein the optical delivery unit comprises a first fiducial marker site configured to emit acoustic responses and a second fiducial marker site configured to emit acoustic responses. A plurality of acoustic signals from a volume of a subject are sampled and recorded, each of the plurality of acoustic signals being collected at a different data collection position relative to a coordinate reference frame. The system is configured to identify in each of the plurality of acoustic signals a response of a first fiducial marker and a response of a second fiducial marker. Each identified response indicates a separation between a fiducial marker site and a data collection position of an acoustic signal. The system determines the position and orientation of the optical delivery unit in the coordinate reference frame by using the identified responses of the first fiducial marker and the identified responses of the second fiducial marker.