Monitoring focused ultrasound ablation surgery (FUAS) using echo amplitudes of the therapeutic focused transducer

Objective

B-mode sonography is commonly used to monitor focused ultrasound ablation surgery (FUAS), but has limitations in sensitivity. More accurate and reliable prediction of coagulation is required.

Methods

The focused ultrasound (FUS) transducer was adapted for echo reception. Numerical simulations compared the normalized echo amplitudes from the FUS transducer and imaging probe at varying tissue depths and frequencies with a 3 mm necrosis at focus. An ex vivo experiment then evaluated echo changes from the FUS transducer and ultrasound imaging probe under different settings. Finally, coagulation prediction using FUS echo data was compared to sonography in a clinical ex vivo context.

Results

The echo amplitudes from the FUS transducer exhibit a less pronounced decline with increasing tissue penetration depth compared to the ultrasound imaging probe. In ex vivo bovine liver experiments at depths of 2 cm and 4 cm, the FUS transducer detected normalized echo amplitudes that were significantly larger (i.e., 2∼3 folds) than those received by the ultrasound imaging probe. Moreover, multi-layered ex vivo tissue experiments that replicate clinical conditions revealed that coagulation prediction utilizing the FUS transducer's echo amplitudes achieved superior accuracy (91.2% vs. 60.3 %), sensitivity (92.1% vs. 54.5 %), and negative prediction (78.9% vs. 30.6 %), but similar specificity (88.2% vs. 84.6 %) and positive prediction (95.9% vs. 93.8 %) in comparison to sonography.

Conclusion

The echo amplitude of the FUS transducer serves as a sensitive and dependable metric for monitoring the FUAS outcomes. Its utilization may augment the procedure's safety and efficacy.