Feasibility of detecting change in backscattered energy of acoustic harmonics in locally heated tissues

Abstract

Purpose: A real-time noninvasive thermometry technique is required to estimate the temperature distribution during hyperthermia to monitor and control the treatment. The main objective of this study is to demonstrate the possibility of detecting change in backscatter energy (CBE) of acoustic harmonics in tissue-mimicking gel phantoms and ex vivo bovine muscle tissues in which the temperature was locally increased within the hyperthermia regime. Materials and Methods: A peristaltic pump was used to circulate hot water through a needle inserted inside the samples to locally increase the temperature from 26 C to 46 C. The CBE of acoustic harmonics were used to identify the location of temperature changes in the samples. A conventional echo-shift technique was also implemented for comparison. Data collection was performed for two conditions to investigate the effect of motion on both techniques by: (1) inducing vibration in the sample through the peristatic pump and, (2) subsequently with no sample vibration while the pump was off. Results: Harmonics were able to determine the location of temperature rise in the presence and absence of vibration. In gel phantom, the mean contrast to noise ratio (CNR) in CBE maps reduced by a factor of 0.86 due to vibration whereas in gradient maps the CNR reduced by a factor of 8.3. Conclusions: The findings of this study suggest that the change in backscatter energy of acoustic harmonics can potentially be used to develop a noninvasive ultrasound-based thermometry technique with lower susceptibility to motion artifacts compared to the echo-shift method.

Monitoring Focused Ultrasound Thermal Therapy Using Synthetic Aperture Ultrasound Imaging With Decorrelated Compounding

“…Similarly, the CNR measures the ability to measure differences in pixel intensity between two regions while also considering image noise. CNR can be defined as follows [12]:…”

“…As this method aims to measure shifts in the backscattered RF echoes, tissue motion can mask the temperature dependent RF echo shifts. To combat this shortcoming, this motion susceptibility can be mitigated through the use of motion compensation techniques [12].…”

“…As such, tissue motion can result in the loss of registration between images and appear as a change in energy at a given location. While the CBE method has been demonstrated to be less sensitive to motion compared to the RF echo shift method [12], motion compensation algorithms are frequently used to mitigate the motion sensitivity. Furthermore, CBE thermometry is comparatively simpler employ for in vivo cases, as the RF echo shift method also requires a priori knowledge of the tissue SOS and thermal expansion coefficient.…”

Imaging-based internal body temperature measurements: The journal Temperature toolbox

“…Compared to the echo-shift method, CBE seems to have lower susceptibility to motion artifacts [53]. In thermal strain imaging, Shah et al achieved a lateral spatial temperature resolution of several millimeters and an axial resolution of below one millimeter [54].…”

Feasibility study of MR-guided pancreas ablation using high-intensity focused ultrasound in a healthy swine model

“…Monitoring of target tissue ablation is based on changes in echogenicity and elasticity that are associated with coagulative tissue necrosis [43,[45][46][47]. However, an ultrasound-based method for measuring tissue temperatures above 50 C for the purpose of monitoring the treatment and off-site heating has not yet been reported [48][49][50][51].…”