Photoacoustic Delay-and-Sum Beamforming with Spatiotemporal Coherence Factor

Photoacoustic imaging (PAI) is a hybrid imaging modality involving the use of optical excitation to generate acoustic waves thus, performing optical imaging at ultrasonic spatial and temporal resolution. Delay-and-sum (DAS) beamforming has been typically used to perform photoacoustic (PA) image reconstruction from the received acoustic signals. But non-adaptive DAS performs poorly in artifact rejection (e.g. off-axis signals and resolution degradation). Therefore, adaptive beamforming methods such as coherence factor (CF) weighting has been applied to DAS to improve image quality. In this paper, we report on a spatiotemporal coherence (STCF) weighting factor where spatial and temporal aperture data are used for coherence calculation to weight DAS results (DAS-STCF). Numerical simulation study shows significant signal-to-noise ratio (SNR) improvement with STCF when compared to DAS and CF weighting (DAS-CF). For an absorber located at the depth of 20 mm, DAS-STCF improved SNR over DAS and DAS-CF by 114.89% and 40.44% respectively. STCF weighted DAS had better quality in vivo cardiac PA images which is attributed to improved contrast between myocardial wall and blood in the left ventricular (LV) chamber. These results suggest that STCF weighting has the potential to improve DAS PAI reconstruction quality using temporal data.