Monitoring cryoablation lesions with quantitative ultrasound elastography: A feasibility study

Percutaneous cryoablation (CA) is a minimally invasive approach where pathological areas are ablated by freezing them with a needle-shaped instrument inserted through the skin of the patient. CA requires image guidance to correctly reach the target lesion since the operator cannot directly see the area of intervention. Ultrasound (US) guidance is commonly used in percutaneous needle based procedures but the image quality is lower compared to other modalities and is user-dependent. On the other hand, US provides inexpensive, portable and real-time images and is harmless for the patient and operator. Unfortunately, in the case of CA the strong reflections and shadows in the US images caused by the ice-ball make the monitoring of the full coverage of the pathological area very difficult. One of the more promising developments in the US imaging is elastography, that could be used to improve the monitoring of the ablation area. US elastography has been already successfully applied to monitor other type of percutaneous ablation based on heat sources. The quality of US data during CA treatment makes very difficult to use elastography. In this work we show results of an ex-vivo animal experiment that proves the feasibility of using US elastography to monitor the frozen zone after the complete thawing of the tissue.