  Photoacoustic computed tomography (PACT) is an emerging computed imaging
modality that exploits optical contrast and ultrasonic detection principles to
form images of the absorbed optical energy density within tissue. When the
imaging system employs conventional piezoelectric ultrasonic transducers, the
ideal photoacoustic (PA) signals are degraded by the transducers'
acousto-electric impulse responses (EIRs) during the measurement process. If
unaccounted for, this can degrade the accuracy of the reconstructed image. In
principle, the effect of the EIRs on the measured PA signals can be ameliorated
via deconvolution; images can be reconstructed subsequently by application of a
reconstruction method that assumes an idealized EIR. Alternatively, the effect
of the EIR can be incorporated into an imaging model and implicitly compensated
for during reconstruction. In either case, the efficacy of the correction can
be limited by errors in the assumed EIRs. In this work, a joint optimization
approach to PACT image reconstruction is proposed for mitigating errors in
reconstructed images that are caused by use of an inaccurate EIR. The method
exploits the bi-linear nature of the imaging model and seeks to refine the
measured EIR during the process of reconstructing the sought-after absorbed
optical energy density. Computer-simulation and experimental studies are
conducted to investigate the numerical properties of the method and demonstrate
its value for mitigating image distortions and enhancing the visibility of fine
structures.
