Photoacoustic imaging - also called optoacoustic imaging - is a new hybrid modality of high tissue contrast which is based on the varying optical properties of tissue. The acoustic signal generated by pulsed laser absorption reports tissue-specific information with high spatial resolution. To increase the intrinsic contrast in tissue, absorbing particles are of great interest for optical imaging because of their considerable capacity to absorb and scatter light at visible and near-infrared wavelengths. The aim of the work presented here is to establish a scalable photoacoustic technology for volume imaging of biological samples down to diffraction limited microscopy. For this purpose a versatile photoacoustic microscopy platform has been developed with unmatched spatial resolution consisting of a microchip laser and a measurement cell with different transducers attached allowing generation and detection of laser-induced ultrasound signals in a frequency range up to 400 MHz. The performance of a versatile photoacoustic microscopy platform was evaluated via 2D optoacoustic images of light absorbing microparticles (5 mum Fe₃O₄ and 1 mum black toner particles) embedded in a polystyrene matrix. High frequency signals in the frequency range of 400 MHz generated by a single 1 mum particle could be recorded with a high signal to noise ratio (SNR) of 34 dB.

Optoacoustic imaging represents a new modality that allows noninvasive in vivo molecular imaging with optical contrast and acoustical resolution. Whereas structural or functional imaging applications such as imaging of vasculature do not require contrast enhancing agents, nanoprobes with defined biochemical binding behavior are needed for molecular imaging tasks. Since the contrast of this modality is based on the local optical absorption coefficient, all particle or molecule types that show significant absorption cross sections in the spectral range of the laser wavelength used for signal generation are suitable contrast agents. Currently, several particle types such as gold nanospheres, nanoshells, nanorods, or polymer particles are used as optoacoustic contrast agents. These particles have specific advantages with respect to their absorption properties, or in terms of biologically relevant features (biodegradability, binding to molecular markers). In the present study, a comparative analysis of the signal generation efficiency of gold nanorods, polymeric particles, and magnetite particles using a 1064 nm Nd:YAG laser for signal generation is described.

For the more efficient application of ultrasound in future therapies, fundamental research is needed on the mode of action of ultrasound on biological systems using therapeutic frequencies. To address this need, a new versatile high-throughput platform for focused ultrasound in vitro application was designed, developed, and characterized. The applicator was aligned with the dimensions of a 96-well plate and frequencies commonly used in the therapeutic ultrasound range (0.5–2.0 MHz). Two different platform configurations were developed: (a) a low-intensity version with 96 individual transducers allowing dry coupling of the well plate; and (b) a high-intensity version with water cooling, supporting parallel sonication of 32 out of 96 wells. The platforms were characterized by performing an analysis of the homogeneity of the sound pressure and intensity, the impact of filled volume per well, the cross-coupling effect between the wells, and the influence of the well plate. The low-intensity design delivers pressure levels up to 605 kPa inside the well with maximum I_SPPA values between 0.78 and 12.38 W/cm². In contrast, the high-intensity system achieves pressures up to 1460 kPa and a maximum I_SPPA of 72 W/cm² inside the wells. The successfully developed high-throughput platform supports parallelized sonication in standard, well-plate formats and is suitable for focused ultrasound applications in vitro.