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

Abstract

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.

Statistical Analysis of Ultrasonic Scattered Echoes Enables the Non-invasive Measurement of Temperature Elevations inside Tumor Tissue during Oncological Hyperthermia

“…6). Our group previously reported similar results, indicating that the mean absolute values of the percentage changes in m values rise precipitously in regions with small temperature changes (Takeuchi et al 2018(Takeuchi et al , 2020. In this study, the upturn in the variation in the mean value of a mod is considered to reflect the slight temperature increase inside the tumor tissue immediately after the RF current was first applied.…”

“…In our previous study, we reported that the spatial gradient in the temperature distribution inside a locally heated soft tissue specimen could be clearly visualized on 2-D a mod maps (Takeuchi et al 2019). Recently, we reported the results of our in vivo studies using SpragueÀDawley rats (Takeuchi et al 2020). In these in vivo studies, the temperature elevation inside the abdominal cavity and tumor tissue of a living rat induced with RF current heating was detected on hot-scale images, indicating the absolute values of the percentage changes in m values, a mod .…”

“…Hence, the application of RF current was paused periodically during acquisition of ultrasonic echo signals. To avoid a substantial drop in temperature inside the tumor tissues from the pause in RF current emission, the application of RF current was resumed in approximately 5 s. In our previous study, the abdominal cavity and tumor tissue of a living SpragueÀDawley rat were heated by RF current as the temperature distribution inside the abdominal cavity and the tumor tissue was measured with invasive-type temperature sensor probes (Takeuchi et al 2020). In the in vivo study, application of RF current was paused for approximately 5 s during acquisition of ultrasonic echo signals as in this study.…”

“…To evaluate the temperature elevation inside the tissue, our research group employed the absolute values of the percentage changes in m values, a mod (Takeuchi et al 2019(Takeuchi et al , 2020. The specific parameter a mod is defined as…”

A study on understanding the physical mechanism of change in ultrasonic envelope statistical property during temperature elevation

“…Our previous studies have indicated that the absolute value of the ratio change in the logarithmic NA parameter visualizes the temperature change inside tissue‐mimicking phantoms and ex vivo and in vivo biological soft tissues 21–23 . Another previous study has also demonstrated that the temperature change is related to variations in the ultrasonic envelope statistical properties 24 .…”