SNR-dependent coherence-based adaptive imaging for high-frame-rate ultrasonic and photoacoustic imaging.

This paper introduces the SNR-dependent coherence factor (CF), which can be used for adaptive side lobe suppression in ultrasound (US) and photoacoustic (PA) imaging. Previous methods employed the minimum-variance distortionless response (MVDR)-based CF to achieve remarkable resolution improvement (by MVDR) and to suppress side lobes (by CF). However, the SNR is often low when using an unfocused acoustic beam (e.g., high-frame-rate imaging) and in PA imaging (limited laser energy), giving such an approach suboptimal performance in these applications because noise also lowers the coherence and thus affects the effectiveness of the side lobe suppression by these CF-based methods. To overcome this problem, the proposed method takes into account the local SNR in the CF formulation so that the contrast can be restored even when the SNR is low. We tested this method with both high-frame-rate US imaging and PA imaging. Simulations show that the proposed method performs well even when the SNR is as low as -10 dB. Compared with the conventional CF, the contrast (CR) and contrast-to-noise ratio (CNR) in clinical US imaging can be improved by an average of 27.2% in CR and 11.1% in CNR with the proposed method, whereas in PA imaging, the lateral resolution could be restored and the image contrast was elevated by 17 dB.