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This work investigates a forward model associated with intra-lumenal detection of acoustic signal originated from
transient thermal-expansion of the tissue. The work is specific to intra-lumenal thermo-acoustic tomography (TAT)
which detects the contrast of tissue dielectric properties with ultrasonic resolution, but it is also extendable to intralumenal
photo-acoustic tomography (PAT) which detects the contrast of light absorption properties of tissue with
ultrasound resolution. Exact closed-form frequency-domain or time-domain forward model of thermally-induced
acoustic signal have been studied rigorously for planar geometry and two other geometries, including cylindrical and
spherical geometries both of which is specific to external-imaging, i.e. breast or brain imaging using an externally-deployed
applicator. This work extends the existing studies to the specific geometry of internal or intra-lumenal imaging,
i.e., prostate imaging by an endo-rectally deployed applicator. In this intra-lumenal imaging geometry, both the source
that excites the transient thermal-expansion of the tissue and the acoustic transducer that acquires the thermally-induced
acoustic signal are assumed enclosed by the tissue and on the surface of a long cylindrical applicator. The Green's
function of the frequency-domain thermo-acoustic equation in spherical coordinates is expanded to cylindrical
coordinates associated with intra-lumenal geometry. Inverse Fourier transform is then applied to obtain a time-domain
solution of the thermo-acoustic pressure wave for intra-lumenal geometry. Further employment of the boundary
condition to the "convex" applicator-tissue interface would render an exact forward solution toward accurate
reconstruction for intra-lumenal thermally-induced acoustic imaging.
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