Ultrasonic CBE monitoring approach with high contrast for thermal therapy using percutaneous catheter-based ultrasound applicators

Background, Motivation and Objectives: Intraluminal and percutaneous catheter-based ultrasound (CBUS) technology can achieve precise energy control and delivery, and thus treat deep tumors with conforming ablation volumes. However, methods of real-time ultrasound monitoring of CBUS typically have low sensitivity and contrast, with limited ability of temperature estimation. Thus, this study aimed to propose a multi spatial scale change in backscatter energy (MS-CBE) monitoring approach of temperature to improve the detection sensitivity and contrast of energy changes by CBUS. Statement of Contribution/Methods: A directional CBUS applicator with 3 elements (180° active sector, 1.5 mm OD x 10 mm transducers, catheter OD = 2.4 mm, fc ≈ 7.6 MHz) was used for thermal ablation within ex vivo muscle (burst = 10 s, duration = 10 min, duty = 97%, power = 10 W). Raw radiofrequency data were recorded real-time by Ultrasonix MDP system equipped with a stereotactically aligned BCL9-5 endorectal probe at 11 Hz within a short-time window of 270 ms, in which CBUS power was paused. Multijunction thermocouple probes were used to detect the temperature changes to correlate MS-CBE with temperature. Each point value in MS-CBE is quantified by the average power ratio of the scale parameter of the statistical analysis within 4 increasing volumes from 3×3 to 12×12 wavelengths. MS-CBE maps of positive and absolute components and the corresponding spatial fitting maps were finally reconstructed. Results, Discussion and Conclusions: Detection sensitivity and contrast of the proposed MS-CBE were quantified by the tissue-modification-ratio (TMR). The detailed changes in tissue coagulation during energy delivery from the directional CBUS were clearly monitored by the MS-CBE. The corresponding regional ablation size was also effectively characterized by the fitting MS-CBE. Compared with B mode and conventional CBE, the proposed MS-CBE has the highest TMR with 30 dB improvement. Moreover, the proposed MS-CBE has a high correlation coefficient of 0.99 (p <; 0.001, a norm of residuals = 0.9) with temperature elevation. These results suggest that the proposed CBUS-based MS-CBE method with temperature component could be useful to provide accurate monitoring and evaluation with a high TMR for the CBUS precise thermal therapy.