Thermal ablation monitoring using radiation force-induced steady-state tissue motion

Abstract

High-intensity focused ultrasound (HIFU) increases temperature in tissue and also induces local tissue movement during HIFU ablation. Such induced motion can be exploited to detect changes in tissue stiffness to monitor HIFU treatment. To implement real-time HIFU treatment monitoring, a HIFU duration is segmented into a sequence of on and off periods. The off periods are required for unaffected interrogation and are sufficiently short to minimize interruption to the intended thermal treatment. It is demonstrated that the displacements generated during the relatively long on period reach steady state and undergo recovery during the next off period. Our study focuses on the investigation of the steady-state displacement and its recovery to detect changes in tissue elasticity without additional push pulses during an HIFU treatment exposure. An integrated model and finite difference algorithm are developed to study how the dynamic displacements are related to HIFU characteristics and tissue properties. Our experiments utilized an ultrasound imaging system. The induced displacement and its recovery are estimated from the acquired backscattered signals using a cross-correlation algorithm. Optimal HIFU on and off periods are investigated. Our results indicate that the steady-state displacements characterize the changes in tissue elasticity accompanying lesion formation during HIFU ablation.