New Technology Improves Ultrasonic Tumor Ablation

A novel high-intensity focused ultrasound (HIFU) ultrasound transducer can be used to generate a steady, standing-wave field with a subwavelength-scale focal region and extremely high intensity.

To achieve subwavelength focusing, researchers at Nanjing University the Chinese Academy of Medical Sciences and Chongqing Medical University developed a semi-enclosed, ultrasonic spherical cavity resonator (USCR) with two open ends. The size of the focal region generated by the USCR is 50-70% of the millimeter-scale wavelength, with a pressure amplitude gain over three orders of magnitude, rapidly raising the temperature in focal region to above 65 °C.

In contrast, the size of the focal region generated by a traditional concave spherical transducer is about 10 times the wavelength, and the pressure amplitude gain is generally lower than 200. The researchers suggest that the level of intensity channeled through the tighter focal region of the new transducer may be a significant improvement in HIFU for targeted cancer treatments. The researchers are now planning to build a multiphase lattice Boltzmann method (LBM) model to study bubble dynamics, cavitation, and collapse jetting using the USCR. The study was published in the March 2017 issue of Journal of Applied Physics.

“The size of the focal region generated by conventional spherical concave transducers is restricted by acoustic diffraction to usually the order of the ultrasound wavelength, but this does not meet the needs of more sophisticated treatments,” said Dong Zhang, PhD, of the NJU Institute of Acoustics. “Because it is crucial to reduce the size of the focal region while supplying sufficient ultrasonic energy, we were prompted to design a new kind of ultrasonic transducer.”

HIFU technology is based on nonlinear acoustic mathematical optimization methods to analyze and simulate the propagation of sound in material. The information is then used to enhance the shape of an acoustic lens so that that ultrasound pressure is focused precisely on the location of the tissue to be ablated, while the surrounding tissue retains as little damage as possible.