  This paper surveys inverse problems arising in several coupled-physics
imaging modalities for both medical and geophysical purposes. These include
Photo-acoustic Tomography (PAT), Thermo-acoustic Tomography (TAT),
Electro-Seismic Conversion, Transient Elastrography (TE) and Acousto-Electric
Tomography (AET). These inverse problems typically consists of multiple inverse
steps, each of which corresponds to one of the wave propagations involved. The
review focus on those steps known as the inverse problems with internal data,
in which the complex geometrical optics (CGO) solutions to the underlying
equations turn out to be useful in showing the uniqueness and stability in
determining the desired information.
