Real-time ultrasound image-monitored focal changes of the vascular function in rats by pulsed HIFU

It has been shown that B-mode ultrasound can be useful for the real-time visualization of high-intensity focused ultrasound (HIFU) treatment. The aim of this study is to demonstrate the real-time ultrasound observation of functional changes when a vessel is exposed to pulsed-HIFU in the presence of preformed microbubbles. Using in vivo experiments, 12 male Sprague-Dawley rats were sonicated by 1-MHz pulsed-HIFU in the presence of ultrasound contrast agent (UCA) at four doses (0, 150, 300, and 450 μL/kg). The microbubbles passing through the aorta can be discerned with B-mode imaging. The mean peak systolic velocity (PSV) of the blood flow, as measured by Doppler ultrasound imaging, increased in arteries when the low-dose UCA groups (0 and 150 μL/kg) were examined after pulsed-HIFU at 45 W, but decreased when the high-dose UCA groups (300 and 450 μL/ kg) were examined. Additionally, the normalized pulsatility index (PI) changes increased with the injected dose of UCA. The interactions between ultrasound and the microbubbles can be seen to change the tissue permeability of the drug. Thus, monitoring of PSV or PI might be useful as an online method to ensure the correct sonicated position and to indicate when drug delivery has occurred.