Harmonic motion imaging in abdominal tumor detection and HIFU ablation monitoring: A feasibility study in a transgenic mouse model of pancreatic cancer

Harmonic motion imaging (HMI) is a radiation force-based elasticity imaging technique that tracks tissue harmonic displacements induced by periodic ultrasonic radiation force to assess tissue stiffness. The objective of this study was to evaluate the feasibility of HMI in pancreatic tumor detection and high-intensity focused ultrasound (HIFU) treatment monitoring. The HMI system consisted of a focused ultrasound transducer (FUS), which generated periodic radiation force to induce harmonic tissue motion at 50 Hz, and a diagnostic ultrasound transducer, which detected the axial tissue displacement within the targeted region using 1D cross-correlation of acquired radiofrequency signals of ultrasound echoes. For pancreatic tumor detection, HMI displacement images were generated for pancreatic tumors in transgenic mice and healthy pancreases of wild-type mice. For pancreatic tumor ablation monitoring, FUS was used to induce HIFU thermal ablation and tissue motion at the same time, allowing HMI monitoring without interrupting tumor ablation. All pancreases were excised immediately after sonication for histological evaluation. The obtained HMI displacement images showed a high contrast between normal and malignant tissue. The HMI monitoring of HIFU ablation displayed consistent pancreatic stiffening after 2 min ablation, and the formation of thermal lesions was confirmed by the histological analysis. This study demonstrated for the first time the feasibility of HMI in pancreatic tumor detection and HIFU ablation monitoring. It was also the first application of a radiation-force based imaging technique in abdominal tumor HIFU treatment monitoring.