Analysis of negatively focused detectors in optoacoustic imaging

In optoacoustic tomography, negatively focused detectors may be used for
improving the tangential image resolution while preserving a high signalto-noise ratio (SNR). Commonly, image reconstruction in such scenarios
is facilitated by the use of the virtual-detector approach. Although the
validity of this approach has been experimentally verified, it is based on an
approximation whose effects on the optoacoustic reconstruction have not
yet been studied.
In this work, we analyze analytically the response of negatively focused
acoustic detectors in both time and frequency domains . Based on this
analysis, simple tradeoffs between the detector size, curvature, and
sensitivity are formulated. In addition, our analysis reveals the geometrical
underpinning of the virtual-detector approximation and quantifies its
deviation from the exact solution. The effect of the error involved in
the virtual-detector approximation is studied in image reconstruction
simulations and its effect on image quality is shown.
Our analysis reveals that negatively focused detectors are, in many cases,
superior to flat detectors in terms of image resolution and SNR. While
tangential resolution of images obtained with large flat detectors may be
improved by the use of deblurring algorithms, this procedure often comes
at the expense of SNR. The theoretical tools developed in this work give
valuable insight into the mechanisim of negatively focused detection and
may be used in the design of new optoacoustic detection geometries as well
as for improved image reconstruction.