A Novel Ultrasound Imaging Method for 2D Temperature Monitoring of Thermal Ablation

Accurate temperature monitoring is a crucial task that directly affects the safety and effectiveness of thermal ablation procedures. Compared to MRI, ultrasound-based temperature monitoring systems have many advantages, including higher temporal resolution, low cost, safety, mobility and ease of use. However, conventional ultrasound (US) images have a limited accuracy due to a weak temperature sensitivity. As a result, it is more challenging to fully meet the clinical requirements for assessing the completion of ablation therapy. A novel imaging method for temperature monitoring is proposed based on the injection of virtual US pattern in the US brightness mode (B-mode) image coupled with biophysical simulation of heat propagation. This proposed imaging method does not require any hardware extensions to the conventional US B-mode system. The main principle is to establish a bi-directional US communication between the US imaging machine and an active element inserted within the tissue. A virtual pattern can then directly be created into the US B-mode display during the ablation by controlling the timing and amplitude of the US field generated by the active element. Changes of the injected pattern are related to the change of the ablated tissue temperature through the additional knowledge of a biophysical model of heat propagation in the tissue. Those changes are monitored during ablation, generating accurate spatial and temporal temperature maps. We demonstrated in silico the method feasibility and showed experimentally its applicability on a clinical US scanner using ex vivo data. Promising results are achieved: a mean temperature error smaller than 4 ° C was achieved in all the simulation experiments. The system performance is tested under different configurations of noise in the data. The effect of error in the localization of the RFA probe is also evaluated.