RF Transmitter: Power Deposition and Local Heating

RF Transmitter · Safety

The transmit chain is limited by the power it deposits in tissue, and by the fact that the limit that matters is local rather than averaged.

Body outline with an implant lead and a hot spot at its tip — The limit that matters is local: at the tip of an implant lead the electric field, and the heating, concentrate.

Implant prototype and lead placed in a gel phantom — An implant prototype with its lead in a gel phantom, prepared for a heating experiment.

The question

Radiofrequency power deposited in the body is quantified as specific absorption rate. A whole-body average is easy to monitor and is not what injures anyone. The local peak is what matters, it occurs where the electric field concentrates, and it cannot be measured in a patient. It therefore has to be predicted by simulation, and the simulation has to be trusted. Making it trustworthy is the work.

What we work on

Electromagnetic models validated against measurement. A model used for a safety limit has to be shown to match the coil it represents, not merely to look like it.
Direct electric field measurement with probes, which is how a model earns that trust.
Conductive implants, where a lead or a wire concentrates the field and the relevant quantity is the temperature at its tip rather than any average over the body.
Transmit arrays, where the field is shaped per channel and the deposition pattern changes with the shaping, so the safety question has to be answered for the whole operating space rather than for one setting.