Abstract
In this study, we attempt to apply adaptive photoacoustic array imaging technique to improve spatial resolution and image contrast in photoacoustic imaging. Due to the diffusive nature of the photoacoustic excitation laser source in biological tissue, the spatial resolution and image contrast of photoacoustic imaging are worse than those of ultrasound imaging. Conventionally, apodization is commonly employed to enhance image contrast while the spatial resolution is sacrificed. To solve such issues, we proposed an adaptive photoacoustic array imaging technique based on a MVDR algorithm along with coherence-factor (CF) weighting. The MVDR algorithm suppresses sidelobe interferences and noises while offering narrower mainlobe width. That is, higher spatial resolution can be obtained. In addition, based on the MVDR algorithm, a MVDR+CFMV weighting technique is derived and applied to further suppress sidelobes; thus higher spatial resolution and better image contrast can be obtained simultaneously. Simulation results showed that the sub-array length of the MVDR algorithm is about one third of full aperture length. In this study, we used a 128-element array transducer, therefore the employed optimal sub-array length is 48. Additionally, we discuss the algorithm limited. Simulation results showed that MVDR+CFMV the Velocity error tolerance is about ±50m/s which is better than other algorithm. CF weighting can work in low SNR environment, but MVDR need high SNR. Experimental results demonstrated that our proposed MVDR+CFMV weighting can suppress sidelobes by 60dB, reduce mainlobe width by 80%, improve contrast resolution by 24dB compared with conventional delay and sum beamforming; showing the efficacy of our proposed method.