Phase-aberration-corrected coherence factor beamforming for photoacoustic computed tomography.

Abstract

Significance: Coherence factor (CF) beamforming can suppress sidelobes in photoacoustic computed tomography, but phase aberration can make genuine absorbers appear incoherent and cause conventional CF to downweight real signals.

Aim: We aim to reduce photoacoustic volume tomography phase-aberration-induced loss of true signals in conventional coherence-factor reconstruction and validate the method using phantom and in vivo experiments.

Approach: PAC-CF extends an ellipsoidal two-region time-of-flight correction to the angle-weighted channel contributions used for both coherent backprojection and final conventional energy-ratio CF evaluation. The ROI-optimized effective internal sound speed is selected from multiframe PA receive data by maximizing the mean CF within a fixed region of interest.

Results: Simulations showed that conventional CF at the true source dropped to 0.00794 at a $170m/s$ sound-speed difference and to $\sim 0.00039$ to 0.00042 at larger sound-speed differences, whereas PAC-CF preserved coherence and localization. The four-method phantom ablation showed that combining two-region TOF correction with final CF weighting produced the most concentrated wire responses and strongest background suppression, whereas mouse experiments showed recovery of vascular features suppressed by conventional CF.

Conclusions: By extending two-region time-of-flight correction to the channel contributions evaluated by the final CF weight, PAC-CF reduces the erroneous suppression of true signals caused by propagation-model mismatch and provides a practical PA-only approach for coherence-weighted three-dimensional PACT.