In this paper, we present the Nakagami shape parameter m estimated by the statistical analysis of ultrasonic scattered echoes from a soft-tissue-mimicking phantom and a soft tissue heated from room temperature up to 42.0 °C. The ratio change of m values for both phantom and biological tissue specimens clearly show temperature dependence. We show changes in the internal temperature of the biological tissue specimens using two-dimensional hot-scale images indicating absolute values of the ratio change of m values. However, in an in vitro experiment using porcine tissue, no clear change of m values was observed with a smaller region of interest (ROI) owing to the tissue deformation during heating. We could obtain the temperature-dependent ratio change of m values by increasing the ROI size. These results suggest that the selection of a proper ROI size would be significantly important for detecting internal temperature changes by the ratio change of m values because not only the tissue deformation owing to heating but also body motion and pulsating exist under in vivo conditions.

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.

In the present study, the variation of the Nakagami shape parameter m of the probability distribution of amplitudes of ultrasonic echoes from soft tissue due to a temperature increase is shown to exhibit initial m-value dependence. The change of the Nakagami shape parameter m due to the temperature rise increased with increasing the initial m-value. In order to measure the temperature distribution in soft tissue, we propose a parameter that indicates the absolute values of ratio changes of m values with the multiplying factor varying as a function of the initial m-value. In the hot-scale images indicating the absolute values of ratio changes of m values with the consideration of the initial m-value dependence, the temperature distribution in soft tissue was visualized clearly.

Non-invasive monitoring of temperature elevations inside tumor tissue is imperative for the oncological thermotherapy known as hyperthermia. In the present study, two cancer patients, one with a developing right renal cell carcinoma and the other with pseudomyxoma peritonei, underwent hyperthermia. The two patients were irradiated with radiofrequency current for 40 min during hyperthermia. We report the results of our clinical trial study in which the temperature increases inside the tumor tissues of patients with right renal cell carcinoma and pseudomyxoma peritonei induced by radiofrequency current irradiation for 40 min could be detected by statistical analysis of ultrasonic scattered echoes. The Nakagami shape parameter m varies depending on the temperature of the medium. We calculated the Nakagami shape parameter m by statistical analysis of the ultrasonic echoes scattered from the tumor tissues. The temperature elevations inside the tumor tissues were expressed as increases in brightness on 2-D hot-scale maps of the specific parameter a mod , indicating the absolute values of the percentage changes in m values. In the a mod map for each tumor tissue, the brightness clearly increased with treatment time. In quantitative analysis, the mean values of a mod were calculated. The mean value of a mod for the right renal cell carcinoma increased to 1.35 dB with increasing treatment time, and the mean value of a mod for pseudomyxoma peritonei increased to 1.74 with treatment time. The increase in both a mod brightness and the mean value of a mod implied temperature elevations inside the tumor tissues induced by the radiofrequency current; thus, the acoustic method is promising for monitoring temperature elevations inside tumor tissues during hyperthermia.