Numerical Analysis of Transcranial Phase Aberration Correction Techniques

Wavefront aberration in ultrasound imaging arises when the assumption of constant sound speed in tissues is violated, producing phase errors that distort the acoustic beam and degrade image quality. This problem is particularly severe when imaging through strongly aberrating layers, such as the human skull, where the complex geometry and heterogeneous acoustic properties introduce large, spatially varying distortions. Estimating the underlying tissue sound speed enables more effective aberration correction, and recent advances in reconstructing sound speed maps from ultrasound signals have opened new possibilities for distributed correction strategies. However, different aberration correction approaches involve important trade-offs between accuracy, computational cost, and practical feasibility. In this numerical study, we systematically compared three representative correction methods: Eikonal-based travel time estimation, full-wave simulation, and time reversal. Acoustic property maps were derived from micro-CT scans of ex vivo human skulls. A phased array was simulated to focus at 30 mm through the skull, and corrections were applied using the three approaches. Without the skull, the targeted focal depth was achieved with a lateral full width at half maximum (FWHM) of 1.8 mm, whereas with the skull and no correction, the focus shifted and beam quality degraded. All three correction strategies effectively reduced distortion. Eikonal correction restored the focus efficiently (0.5 seconds) but generated higher side lobes and a wider FWHM of 3.1 mm. Full-wave correction provided improved sharpness (FWHM = 2.5 mm) but required longer computation (2 minutes). Time reversal achieved the best focus (FWHM = 1.7 mm) but required complete waveform modification, limiting its experimental practicality. Overall, the results demonstrate clear trade-offs between computational efficiency and correction performance.