  In case of non-dissipative tissue the inverse problem of thermoacoustic
imaging basically consists of two inverse problems. First, a function $\phi$
depending on the \emph{electromagnetic absorption function}, is estimated from
one of three types of projections (spherical, circular or planar) and secondly,
the \emph{electromagnetic absorption function} is estimated from $\phi$. In
case of dissipative tissue, it is no longer possible to calculate explicitly
the projection of $\phi$ from the respective pressure data (measured by point,
planar or line detectors). The goal of this paper is to derive for each of the
three types of pressure data, an integral equation that allows estimating the
respective projection of $\phi$. The advantage of this approach is that all
known reconstruction formulas for $\phi$ from the respective projection can be
exploited.
