High-intensity focused ultrasound monitoring using harmonic motion imaging for focused ultrasound (HMIFU) under boiling or slow denaturation conditions

Abstract

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a recently developed High-Intensity Focused Ultrasound (HIFU) treatment monitoring method that utilizes an amplitude-modulated therapeutic ultrasound beam to induce an oscillatory radiation force at the HIFU focus and estimates the focal tissue displacement to monitor the HIFU thermal treatment. In this study, the performance of HMIFU under acoustic, thermal and mechanical effects were investigated. The performance of HMIFU was assessed in ex vivo canine liver specimens (n=13) under slow denaturation or boiling regimes. Passive Cavitation Detector (PCD) was used to assess the acoustic cavitation activity while a bare-wire thermocouple was used to monitor the focal temperature change. During lesioning with slow denaturation, high quality displacements (correlation coefficient above 0.97) were observed under minimum cavitation noise, indicating tissue the initial-softening-then-stiffening property change. During HIFU with boiling, HMIFU monitored a consistent change in lesion-to-background displacement contrast (0.46±0.37) despite the presence of strong cavitation noise due to boiling during lesion formation. Therefore, HMIFU effectively monitored softening-then-stiffening during lesioning under slow denaturation, and detected lesioning under boiling with a distinct change in displacement contrast under boiling in the presence of cavitation. In conclusion, HMIFU was shown effective in HIFU monitoring and lesioning identification without being significantly affected by cavitation noise.

Harmonic motion imaging for abdominal tumor detection and high-intensity focused ultrasound ablation monitoring: an in vivo feasibility study in a transgenic mouse model of pancreatic cancer

“…Furthermore, relative low-energy HIFU with long exposure time was used in the present study to induce slow tissue denaturation. Our group has demonstrated the feasibility of HMI in monitoring high-energy HIFU treatment with tissue boiling in ex vivo tissue [37][28]. Future studies will explore the feasibility of in vivo HMI monitoring for HIFU treatment with boiling.…”

“…A brief description of these two systems is as follows. For more details, please refer to our group's previous publications [28][29]. …”

“…Prior to HIFU ablation, a standard B-mode image of the targeted region was acquired using the HMI imaging probe. Then, HIFU with an acoustic power output of 7.56 W in water was applied for 120 s. Previous studies by our group demonstrated that same HIFU treatment protocol consistently generated thermal lesions by slow denaturation without producing extensive boiling effects in ex vivo canine livers and HMI detected significant decreases in HMI displacement amplitudes before and after HIFU ablation [28]. Because HMI did not interrupt HIFU ablation, HIFU sonication was operated with a duty cycle of 100%.…”

Fast lesion mapping during HIFU treatment using harmonic motion imaging guided focused ultrasound (HMIgFUS)in vitroandin vivo

“…Another limitation of this study lies in the fact that only slow denaturation induced ablation was included in the study. However, previous work (Hou et al 2015) from our group has shown that HMIgFUS is robust under faster treatments such as boiling in monitoring the lesion formation in the presence of strong cavitation events with good displacement contrast across the entire treatment window. The present study may have the potential to be applied on cavitation induced HIFU treatment in the future.…”

“…Furthermore, the increase in attenuation can occur during thermal lesioning (Zderic et al 2004), resulting in increased absorption therefore increased radiation force within the stiffer lesioning area. However, it has been shown that the decrease in displacement amplitude occurs approximately after reaching 60°C due to the combined effect of viscoelasticity changes and lesion growth overpowering the effect of attenuation (Suomi et al 2016, Hou et al 2015). The increased radiation force during ablation may generate an opposite lesion-to-background contrast by generating higher HMI displacement inside the lesion, which was not observed in this study.…”