Provided herein are genetically engineered gas vesicle expression systems (GVES) that are configured to express gas vesicles (GVs) in a mammalian cell, related gas vesicle polynucleotide constructs, gas vesicle reporting genetic circuits, vectors, genetically engineered mammalian cells, non-human mammalian hosts, compositions, methods and systems, which in several embodiments can be used together with contrast-enhanced imaging techniques to detect and report biological events in an imaging target site comprising a mammalian cell and/or organism.