Doctors have been actively attempting to replace existing surgical operations using various ultrasonic effects with non-invasive characteristics. “Pressure-modulated shockwave histotripsy” is a technology that can physically destroy surrounding biological tissues like cutting them with a knife using powerful bubbles “cavitation” generated in a short time of about 1/100 seconds from the focus of ultrasound. This method has the advantage of being able to monitor the treatment process through real-time cavitation analysis and shorter treatment time than the High-Intensity Focused Ultrasound (HIFU) technique, which burns tissue with conventional heat.
Dr. Park Ki-joo of the Bionic Research Center of the Korea Institute of Science and Technology has developed a new ultrasound technology that can more precisely and finely crush biological tissue using variable pressure focused ultrasound.
In the existing focused ultrasound biological tissue crushing technology, Dr. Park discovered for the first time in the academic world the principle of shock wave scattering effect in which secondary microbubbles occur simultaneously not only in the ultrasound focus area but also around it. Existing focused ultrasound surgical techniques are difficult to apply when tissues or tumors closely located in major organs and blood vessels need to be removed because of the shock wave scattering effect.
To overcome these limitations, Dr. Park devised a method of changing the acoustic pressure intensity at the ultrasonic focus. He thought that changing the focal acoustic pressure intensity immediately after the occurrence of air bubbles at the ultrasonic focal point could control the mobility of the air bubbles without the shock wave scattering effect, thereby more precisely crushing the biological tissue. He verified its feasibility through acoustic simulation, high-speed camera-based simulation of human tissue, and animal experiments.
As a result, he confirmed that by adjusting the focal acoustic pressure intensity, water vapor bubbles with a size of tens to hundreds of microns can be generated at the ultrasonic focus without the impact wave scattering effect, and that the bubbles can be controlled and adjusted sustainably for a certain period of time. It was observed during the animal experiment stage that biological tissue can be finely crushed in units of tens to hundreds of μm, which is much more precise than conventional focused ultrasound technology, at the ultrasonic focus.
According to Dr. Park, the newly developed ultrasonic technique is a new technology that can precisely crush tissues by controlling the size and duration of bubbles. This technology complemented the low precision of existing techniques. It is also expected to contribute to the field of decellularization-based cell transplantation research.
Figure: Illustration of the proposed pressure-modulated shockwave histotripsy pulsing protocol to control the extent and lifetime of a boiling bubble without inducing the shock scattering effect. P1,+ and P1,− are the peak positive and negative pressures in shockwaves at the HIFU focus. P2,+ and P2,− are those in the subsequent HIFU waves within a single pressure-modulated shockwave histotripsy pulse.