The OPUS (Optoacoustic plus Ultrasound) system is a combination of a medical ultrasound scanner with a highrepetition
rate, wavelength-tunable laser system and a suitable triggering interface to synchronize the laser and the
ultrasound system. The pulsed laser generates an optoacoustic (OA), or photoacoustic (PA), signal which is detected by
the ultrasound system. Alternatively, imaging in conventional ultrasound mode can be performed. Both imaging modes
can be superimposed. The laser light is coupled into the tissue laterally, parallel to the ultrasound transducer, which does
not require for any major modification to the transducer or the ultrasound beam forming. This was a basic requirement
on the instrument, as the intention of the project was to establish the optoacoustic imaging modality as add-on to a
conventional standard ultrasound instrument. We believe that this approach may foster the introduction of OA imaging
as routine tool in medical diagnosis.
Another key aspect of the project was to exploit the capabilities of OA imaging for quantitative analysis. The intention of
the presented work is to summarize all steps necessary to extract the significant information from the PA raw data, which
are required for the quantification of local absorber distributions. We show results of spatially resolved absorption
measurements in scattering samples and a comparison of four different image reconstruction algorithms, regarding their
influence on lateral resolution as well as on the signal to noise ratio for different sample depths and absorption values.
The reconstruction algorithms are based on Fourier transformation, on a generalized 2D Hough transformation, on
circular back-projection and the classical delay-and-sum approach which is implemented in most ultrasound scanners.
Furthermore, we discuss the influence of a newly developed laser source, combining diode and flash lamp pumping.
Compared to all-flash-lamp pumped systems it features a significantly higher pulse-to-pulse stability, which is required
for sensitive and precise quantitative analyses.