Besides x-ray imaging, sonography is the most common method for breast cancer screening. The intention of our work is to develop optoacoustical imaging as an add-on to a conventional
system. While ultrasound imaging reveals acoustical properties of tissue, optoacoustics generates an image of the distribution of optical absorption. Hence, it can be a valuable addition to sonography, because acoustical properties of different tissues show only a slight variation whereas the optical properties may differ strongly. Additionally, optoacoustics gives
access to physiological parameters, like oxygen saturation of blood.
For the presented work, we combine a conventional ultrasound system to a 100 Hz laser. The
laser system consists of a Nd:YAG-laser at a wavelength of 532 nm with 7 ns pulse duration,
coupled to a tunable Optical Parametric Oscillator (OPO) with a tuning rage from 680 nm to
2500 nm. The tunable laser source allows the selection of wavelengths which compromising
high spectral information content with high skin transmission. The laser pulse is delivered
fiber-optically to the ultrasound transducer and coupled into the acoustical field of view.
Homogeneous illumination is crucial in order to achieve unblurred images. Furthermore the
maximum allowed pulse intensities in accordance with standards for medical equipment have
to be met to achieve a high signal to noise ration. The ultrasound instrument generates the
trigger signal which controls the laser pulsing in order to apply ultrasound instrument's
imaging procedures without major modifications to generate an optoacoustic image. Detection
of the optoacoustic signal as well as of the classical ultrasound signal is carried out by the
standard medical ultrasound transducer.
The characterization of the system, including quantitative measurements, performed on tissue
phantoms, is presented. These phantoms have been specially designed regarding their acoustical as well as their optical properties.