Reducing lesion aberration by dual-frequency focused ultrasound ablations

Evaluation of Dual-Frequency Switching HIFU for Optimizing Superficial Ablation

OBJECTIVE

Dual-frequency high-intensity focused ultrasound (HIFU) thermal ablation is an exceptionally promising technique for treating tumors due to its precision and effectiveness. However, there are still a few studies on improving the accuracy and efficiency of HIFU in superficial ablation applications. This study proposes a method utilizing dual frequency switching ultrasound (DFSU) to enhance the efficiency and precision of superficial treatments.

METHODS

A dual-frequency HIFU transducer operating at 4.5 MHz and 13.7 MHz was designed, and a dual-frequency impedance matching network was designed to optimize electro-acoustic conversion efficiency. Phantom and ex vivo tests were conducted to measure and compare thermal lesion areas and temperature rises caused by single-frequency ultrasound (SFU) and DFSU.

RESULTS

In both phantom and ex vivo tests, the utilization of DFSU resulted in larger lesion areas compared to SFU. Moreover, DFSU provided improved control and versatility, enabling precise and efficient ablation.

CONCLUSION

DFSU exhibits the ability to generate larger ablation areas in superficial tissue compared to SFU, and DFSU allows flexible control over the ablation area and temperature rise rate. The acoustic power deposition of HIFU can be optimized to achieve precise ablation.

Numerical investigation of the inertial cavitation threshold by dual-frequency excitation in the fluid and tissue

Inertial cavitation thresholds, which are defined as bubble growth by 2-fold from the equilibrium radius, by two types of ultrasonic excitation (at the classical single-frequency mode and dual-frequency mode) were calculated. The effect of the dual-frequency excitation on the inertial cavitation threshold in the different surrounding media (fluid and tissue) was studied, and the paramount parameters (driving frequency, amplitude ratio, phase difference, and frequency ratio) were also optimized to maximize the inertial cavitation. The numerical prediction confirms the previous experimental results that the dual-frequency excitation is capable of reducing the inertial cavitation threshold in comparison to the single-frequency one at the same output power. The dual-frequency excitation at the high frequency (i.e., 3.1 + 3.5 MHz vs. 1.1 + 1.3 MHz) is preferred in this study. The simulation results suggest that the same amplitudes of individual components, zero phase difference, and large frequency difference are beneficial for enhancing the bubble cavitation. Overall, this work may provide a theoretical model for further investigation of dual-frequency excitation and guidance of its applications for a better outcome.

The effect of high-intensity focused ultrasound treatment on immune function in patients with uterine fibroids

PURPOSE

The aim of this study was to investigate the effect of high-intensity focused ultrasound (HIFU) on immune function in patients with uterine fibroids, in a randomised comparison to conventional myomectomy.

METHODS

The patients were assigned (1:1) to the HIFU group or the myomectomy (MY) group. Venous blood samples were collected 24 h before and 24 h and 72 h after operation. The percentages of CD4(+) and CD8(+) T cells and natural killer (NK) cells were quantified by flow cytometry (FCM). Serum levels of interleukin-2 (IL-2), IL-6 and IL-10 were determined using enzyme-linked immunosorbent assay.

RESULTS

HIFU was associated with early ambulation, fewer post-operative complications, and shorter hospital stay (p < 0.001). The percentages of CD4(+) and CD8(+) T cells and NK cells in the HIFU group were not significantly altered after treatment compared with before treatment. In contrast, the numbers of these cells in the MY group decreased significantly 24 h after conventional myomectomy (p < 0.001). The CD4(+)/CD8(+) T cell ratios were also decreased significantly 24 h and 72 h after conventional myomectomy (p < 0.001). Serum levels of IL-6 and IL-10 increased after treatment in both groups. Peak IL-6 and IL-10 levels were significantly lower in the HIFU group than in the MY group (p < 0.001). In contrast, IL-2 level decreased significantly in the MY group compared to the HIFU group at 24 h post-operation (p < 0.001).

CONCLUSIONS

Short-term post-operative immune function is better preserved after HIFU treatment. Better preserved immune function may reflect a reduction in tissue trauma after HIFU treatment and contribute to reduced post-operative complications.

High intensity focused ultrasound treatment for patients with advanced pancreatic cancer: a preliminary dosimetric analysis

OBJECTIVE

To analyse the clinical dosimetry of high intensity focused ultrasound (HIFU) for the treatment of inoperable pancreatic cancer in humans.

METHODS

136 patients with advanced pancreatic cancer were treated with HIFU, including 89 male and 47 female patients. The median targeted volume (V(t)) was 31.1 cm(3) (range: 9.8-102.1). The median of the average ultrasound power (P(avg)) was 225 W (range: 117-399), and the median energy of the ultrasound (E(total)) was 278.3 kJ (range: 70.5-1195.2). Spearman rank correlation analysis for HIFU dosimetric analysis was conducted.

RESULTS

There was a significant correlation between greyscale changes after HIFU ablation and HIFU dose intensity (DI), P(avg), and unit time (T(u)). However, no correlation was found between greyscale changes after HIFU ablation and gender, age, pancreatic cancer position, or depth of tumour.

CONCLUSIONS

We preliminarily deem that dose intensity and sound power can act as good reference points for HIFU dosimetry in the treatment of pancreatic tumours using the Chongqing system. If there was no obvious change in the ultrasound-monitored image following HIFU treatment for pancreatic cancer, the P(avg) and DI should be no less than 260 W and 11 kJ/cm(3), respectively.