Spatiotemporal monitoring of tissue coagulation treated by continuous high-intensity focused ultrasound with...

High-intensity focused ultrasound (HIFU) is a widely used non-invasive modality for tissue ablation. Ultrasound-based monitoring of HIFU therapy is essential but remains challenging due to strong acoustic interference during treatment. This study investigates the integration of pulse inversion (PI) imaging to suppress HIFU-induced artifacts and improve the accuracy of shear wave elastography (SWE) for monitoring tissue thermal responses during treatment. Tissue-mimicking phantom and ex vivo porcine liver experiments demonstrated that PI subtraction under in-phase conditions effectively eliminated HIFU interference, improving shear wave propagation tracking and enabling accurate elasticity reconstruction without requiring synchronization between the imaging and HIFU systems. In phantom experiments, PI processing reduced the HIFU-induced temporal noise in particle velocity maps fourfold (±9.23 mm/s without PI vs. ±2.05 mm/s with PI) and improved elasticity map uniformity (±14.21 kPa without PI vs. ±2.24 kPa with PI). PI-SWE captured stiffness reductions during thermal ablation (from 19.24 ± 0.34  kPa to 12.57 ± 0.18  kPa) and a stabilized change rate of -1.46±0.57 kPa/min. Without PI, reconstruction errors were evident, with greater variability in elasticity change rate (±3.89  kPa/min). Ex vivo experiments showed progressive stiffening caused by tissue coagulation (from 2.53±0.32  kPa to 16.15±1.84  kPa), improved uniformity (±13.55 kPa without PI vs. ±3.65 kPa with PI), and reduced change rate variability (±5.00 kPa/min without PI vs. ±3.56 kPa/min with PI) during HIFU exposure. Compared to B-mode, which showed minimal sensitivity (<1 dB) to ablation effects even with PI processing, PI-SWE provided robust, interference-free monitoring with high sensitivity to tissue mechanical changes during continuous HIFU treatment, highlighting its clinical potential as a precise, quantitative tool for real-time therapy monitoring.