1. An imaging system for imaging structures of tissue, comprising: a detector array; an acoustic receiver coupled to said detector array for receiving acoustic signals generated in response to radiant energy delivered to said tissue and detected by said detector array, an image reconstructor coupled to said acoustic receiver for performing a backprojection algorithm to generate a representation of acoustic signals generated at points within the tissue, the representation for a point being based upon signals from plural detectors in said detector array; an ultrasound receiver coupled to said detector array for receiving echoes from an ultrasonic beam delivered into said tissue; and an ultrasound beam steering circuit coupled to said detector array for causing said array to generate said ultrasonic beam.