Figure 1.

(a) Sketch of the high-frequency spherical matrix detection array having an effective detection bandwidth beyond 25 MHz. Distribution of the 510 sensing elements is shown along 7 segments, which are bent to form a hemispherical surface. (b) Optoacoustic micro-tomography (OMT) set-up. Optoacoustic responses are excited by illuminating optical absorbers with a short-pulsed laser beam guided through a central cavity of the spherical matrix array. Simultaneous signal detection by all array elements and subsequent tomographic reconstruction render three-dimensional images in real time with isotropic spatial resolution of ~35 µm across an effective field of view >50 mm³. The array can be further raster-scanned to render larger image volumes at the expense of temporal imaging resolution. DAQ – Data acquisition system. (c) Influence of the radial and lateral errors in the position accuracy of the reconstructed images. (d) Calibration of the radial position with pulse-echo time-of-flight measurements using a steel sphere with a radius of 13 mm. (e) Time-of-flight calibration using optoacoustic signals generated by a ~20 μm polyethylene microsphere located at the center of the spherical array geometry.