Photoacoustic imaging (PA) is an emerging biomedical modality consisting in the emission of laser light, which, when is absorbed by the tissue components, generates ultrasound waves. After reception, the signals PA are used to provide an image by reconstruction algorithm, as the delay-and-sum beamforming. In the vast field of biomedical imaging, this modality is really promising, as it permits to image the tissue optical properties at depths with interesting resolutions and can provide images of the optical absorption with specific molecular contrast which can be enhanced by spectroscopy. In particular, the omnipresence of haemoglobin in living tissues allows the imaging of the microvasculature, which is one of the most important uses of photoacoustic imaging.