A ns-μs duration, millitesla, exponential decay pulsed magnetic fields generator for tumor treatment

In order to research a new tumor treatment method using exponential decay pulsed magnetic fields (EDPMF), we developed a EDPMF generator by means of the integration of pulsed power technology and modern power electronics technology. After charging a capacitor with a high voltage dc power supply, EDPMF was generated inside the Helmholtz coils by means of discharging the capacitor through a switch to the discharge resistor. After a brief introduction of basic principle of EDPMF generator, steep pulse formation circuit and Helmholtz coils, two main parts of EDPMF generator, were discussed in detail, especially on design techniques. A height-adjustable platform was designed inside the Helmholtz coils. Cell solution and little animals could be treated on this platform. The peak value, width and repeat rate of the output EDPMF waveform could be adjusted independently in the range of 0 - 1 mT, 160 ns-55 μs and 1 Hz-1 kHz, respectively. The rise time of the output EDPMF waveform was shortened to 70-220 ns by means of choosing quickly operating switch and reducing circuit stray inductance. Magnetic field distribution uniformity was improved via designing better geometrical structure of Helmholtz coils. This was proved by finite element simulation and measurement. Cell experiment in vitro was performed by exposing human liver cancer cells (Hep-G2) to pulsed magnetic field (0.8 mT, 55 μs, 15 Hz) using this generator and the result showed that proliferation of cancer cells in treated group was significantly (P<;0.01) inhibited. This suggests possible clinical application using this kind of EDPMF for local tumor treatment.