P2H-5 Ultrasound-Based Temperature Imaging for Monitoring Electromagnetic Radiofrequency Ablation - Phantom Results

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 ultrasound-based temperature imaging on a tissue-mimicking phantom undergoing radiofrequency heating. Ultrasound echo signals undergo time shifts with increasing temperature, which may be tracked using 2D correlation-based speckle tracking methods. The time shifts or displacements in the echo signal are accumulated, and the gradient of these time shifts are related to changes in the temperature of the tissue-mimicking phantom material using a calibration curve generated from experimental data. A tissue-mimicking phantom was developed that undergoes repeated radiofrequency heating procedures. The speed of sound change with temperature and the thermal expansion of the tissue-mimicking material were obtained experimentally and used to generate a calibration curve relating temperature to the gradient of the displacement for the tissue-mimicking material. Temperature maps were obtained and specific regions-of-interest on the temperature maps were compared to invasive temperatures obtained using fiber optic temperature probes at the same location. Temperature during a radiofrequency ablation procedure on a tissue-mimicking phantom was successfully tracked using 2D block matching to within plusmn5deg C