High-frequency sound focused on a single point acts like an invisible lens gathering sunlight. Inside a tumor, such a lens can raise the temperature to about 72°C in a second, like hot water from a tap, but inside living tissue. Meanwhile, surrounding healthy cells remain almost untouched.
The key trick is the wave's shape. A regular flat wave heats everything in its path, like an iron pressed against tissue. But a spherical wave converging on a point works like a magnifying glass: it barely heats along the way, yet at the focus the temperature soars to 90°C. The boundary between the cooked tumor and living tissue is as sharp as a cookie cutter's imprint.
One second after the pulse, heat begins to dissipate, and within a few seconds the temperature at the boundary drops below 60°C — the threshold at which proteins in cells irreversibly denature. So doctors can be confident: the tumor is destroyed, and neighboring organs are safe.
At 60°C, proteins in cells denature like egg white in a frying pan. So a tumor heated to 72°C can be considered 'cooked'—the cells die irreversibly.