Abstract
High-intensity focused ultrasound (HIFU) has been emerging as an effective and noninvasive modality in cancer treatment with very promising clinical results. However, a small vessel in the focal region could be ruptured, which is an important concern for the safety of HIFU ablation. In this study, lesion formation in the polyacrylamide gel phantom embedded with different tubing (inner diameters of 0.76 mm and 3 mm) at varied flow speeds (17–339 cm/s) by HIFU ablation was photographically recorded. Produced lesions have decreased length (~30%) but slightly increased width (~6%) in comparison to that without the embedded tubing. Meanwhile, bubble activities during the exposures were measured by passive cavitation detection (PCD) at the varied pulse repetition frequency (PRF, 10–30 Hz) and duty cycle (DC, 10%-20%) of the HIFU bursts. High DC and low flow speed were found to produce stronger bubble cavitation whereas no significant influence of the PRF. In addition, high-speed photography illustrated that the rupture of tubing was produced consistently after the first HIFU burst within 20 ms and then multiple bubbles would penetrate into the intraluminal space of tubing through the rupture site by the acoustic radiation force. Alignment of HIFU focus to the anterior surface, middle, and posterior surface of tubing led to different characteristics of vessel rupture and bubble introduction. In summary, HIFU-induced vessel rupture is possible as shown in this phantom study; produced lesion sizes and shapes are dependent on the focus alignment to the tubing, flow speed, and tubing properties; and bubble cavitation and the formation liquid jet may be one of the major mechanisms of tubing rupture as shown in the high-speed photography.
Highlights
High-intensity focused ultrasound (HIFU) has become more popular in clinics in the treatment of cancers, such as uteroid fibroids and breast, liver, pancreas, prostate, kidney, prostate, and bone cancers, with very promising results since the middle of the 1990s [1]
Most of the cancer and solid tumors are hypervascular so that whether HIFU ablation is hazardous to blood vessels in or close to the focal region is a critical concern for the safety of this novel technology
The average flow speed in the tubing 2 is within the range of reported blood flow in the human body [14] while that in the tubing 1 is higher
Summary
High-intensity focused ultrasound (HIFU) has become more popular in clinics in the treatment of cancers, such as uteroid fibroids and breast, liver, pancreas, prostate, kidney, prostate, and bone cancers, with very promising results since the middle of the 1990s [1]. No major blood vessel injury was observed in any subjects after 23.8±17.2 mo follow-up. In another investigation of 164 patients, enhanced MRI, color Doppler ultrasound imaging, dynamic radionuclide scanning, digital subtraction angiography, and histologic study were performed to monitor the response of tumor vessels [3]. An abrupt blood interruption was found followed by the cessation of blood flow within the tumor vessels after HIFU treatment. Tumor hemorrhage or rupture of large blood vessels has never been detected after HIFU treatment, which is thought to be because of the heat transfer by the blood flow or its great robustness to damage [6]
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