Noninvasive ultrasound temperature imaging with fusion algorithm

There is a great demand for a noninvasive temperature imaging to commercialize the US guided HIFU system. Echo shift is currently the most technologically developed method, but it cannot give an exact temperature over roughly 43°C since the relation between temperature and speed of sound is irregular depending on the temperature range and tissue type. CBE (Change in Backscattered Energy) has wider temperature range but has the severe artifact that appears behind heated region on ultrasound beam pathway. The object of this paper was to develop a temperature imaging method over the full temperature range by remedying these shortcomings. We present analysis for characteristics of echo shift and CBE up to 60°C through experiments and a fusion approach probabilistically combining echo shift and CBE for more exact temperature imaging over wider temperature range. They can be modeled based on the previous fusion temperature images and the current temperature images by each method. Then the current fusion temperature image can be obtained by combining the two temperature images with optimal weights calculated from the two error covariance maps. The possibility of this method was verified through in-vitro experiments.