Image-quality enhancement in optoacoustic tomography with flat detectors

In order achieve high signal-to-noise ratio (SNR), optoacoustic imaging
setups often employ acoustic transducers with the maximal size
possible under manufacturing and setup-geometry constraints. In the
case of flat detectors, the finite-detector size may lead to a distorted
sensitivity field, loss of reconstruction resolution, and image artifacts.
The reason for reduced image quality is that inversion algorithms
are based on the assumption of isotropic sensitivity, which losses its
accuracy in finite-size detectors. Specifically, flat detectors exhibit a
higher bandwidth and sensitivity for targets that are positioned in front
of them than for offset targets. In addition, the finite size of the detector
leads to variations in the delay of the optoacoustic signal as compared
to a point detector. These effects cannot be readily corrected for when
using closed-form reconstruction formulae such as those used in
back-projection algorithm.
In this work we study the distortions caused to optoacoustic signals
by the size of flat detectors and the resulting reconstruction errors and
resolution loss in 2D tomographic geometries and demonstrate how
they can be overcome. The analysis is performed using an analytical
solution for the impulse response of a flat detector and our recently
developed interpolated model matrix inversion (IMMI) algorithm. The
spatially dependent impulse response of the detector is integrated into
IMMI using temporal convolution, and can thus be taken into account
in the inversion. We show that when sufficient projections are available,
the reconstru