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

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.

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.

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.

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.

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.