Temperature elevation in tissue detected in vivo based on statistical analysis of ultrasonic scattered echoes

It is demanded to monitor temperature in tissue during oncological hyperthermia therapy. In the present study, we non-invasively measured the temperature elevation inside the abdominal cavity and tumour tissue of a living rat induced by capacitive-coupled radiofrequency heating. In the analysis of ultrasound scattered echoes, the Nakagami shape parameter m in each region of interest was estimated at each temperature. The Nakagami shape parameter m has temperature dependence; hence, the temperature increase inside tissue specimens can be detected with the m values. By carrying out in vivo experiments, we visualized the temperature increase inside the abdominal cavity and tumour tissue of living rats using two-dimensional hot-scale images indicating the absolute values of the ratio changes of the m values. In both the abdominal cavity and tumour tissue, the brightness in the hot-scale images clearly increased with increasing temperature. The increases in brightness in the hot-scale images imply the temperature elevations inside the abdominal cavity and tumour tissue of the living rats. The study results prove that the acoustic method we proposed is a promising method for monitoring changes in the internal temperature of the human body under hyperthermia treatment.