Ultrasound Simulation of Real-Time Temperature Estimation during Radiofrequency Ablation using Finite Element Models

摘要

Radiofrequency ablation is the most common minimally invasive therapy used in the United States to treat hepatocellular carcinoma and liver metastases. The ability to perform real-time temperature imaging while a patient is undergoing radiofrequency ablation may help reduce the high recurrence rates of hepatocellular carcinoma (～34-55%) or metastases following radiofrequency ablation therapy. In this paper we demonstrate the feasibility of performing real-time temperature imaging of radiofrequency ablation using ultrasound. Ultrasound echo signals undergo a time shift with increasing temperature, which is tracked using 1-D and 2-D correlation-based speckle tracking methods. These time shifts or displacements in the echo signal are then accumulated and the gradient of these time shifts related to changes in the temperature of liver tissue using a calibration curve generated from prior experimental data. A finite element analysis (FEA) simulation of radiofrequency ablation was developed and used in conjunction with an ultrasound array simulation program to demonstrate the effectiveness of ultrasound-based temperature estimation algorithms. Temperature maps obtained from the finite element simulation (gold standard) were compared to those obtained from simulated ultrasound echo signals acquired at 6 second intervals using both 1-D and 2-D cross-correlation methods. Our results demonstrate that 2D cross-correlation provides excellent tracking of the temperature variations when compared to the 1D cross-correlation method. Results obtained using the 1D cross-correlation method diverge from the ideal finite element results after around 5 minutes of ablation and for temperatures greater than 65°C estimated around the tines of the RF electrode.