Ultrasonic noninvasive temperature estimation using echoshift gradient maps: Simulation results

Percutaneous ultrasound-image-guidcd radiofrequcncy (rf) ablation is an effective treatment for patients with hepatic malignancies that are excluded from surgical resection due to other complications. However, ablated regions arc not clearly differentiated from normal untreated regions using conventional ultrasound imaging due to similar echogenic tissue properties. In this paper, we investigate the statistics that govern the relationship between temperature elevation and the corresponding temperature map obtained from the gradient of the echoshifts obtained using consecutive ultrasound radiofrequency signals. A relationship derived using experimental data on the sound speed and tissue expansion variations measured on canine liver tissue samples at different elevated temperatures is utilized to generate ultrasound radiofrequency simulated data. The simulated data set is then utilized to statistically estimate the accuracy and precision of the temperature distributions obtained. The results show that temperature increases between 37 and 67 °C can be estimated with standard deviations of ±3 °C. Our results also indicate that the correlation coefficient between consecutive radiofrequency signals should be greater than 0.85 to obtain accurate temperature estimates.