Source density apodisation in 2D all-optical ultrasound imaging

In this work, an all-optical ultrasound imaging system that is capable of synthesising arbitrary source aperture geometries is presented. This capability is achieved by delivering focussed excitation light onto a spatially extended generating surface, where ultrasound is generated photoacoustically. Using a scanning mirror, the position of the resulting acoustical source was continuously varied to scan an aperture. This system exhibited sufficient sensitivity to acquire 2D images of clinically relevant tissue in under a second, as demonstrated on a tissue-mimicking phantom. The flexibility in the source array geometry was demonstrated through the implementation of two source array geometries on the same system, which allowed for the direct comparison of the image quality. It was shown that applying source density apodisation to obtain an aperiodic source array resulted in an improvement of up to 5 dB in image contrast, as compared to using a conventional, periodic array exhibiting the same number of sources and spatial extents.