Microwave based devices differ on a fundamental level when compared to other imaging diagnostics tools. While x-rays pass straight through the investigated matter and ultrasound uses the reflection of a sound wave, microwaves scatter in the matter.
Microwave based devices use a setup of antennas that surround the investigated body part, such as the brain. One antenna at a time sends a signal that scatters in the investigated matter while all the other antennas are receiving. The received signals are mathematically processed to generate a diagram or a picture.
The individual components needed to build a microwave based instrument are simpler than for other imaging techniques, while the demands on the mathematics in the signal processing steps are higher. The development of smart algorithms and continued computer development now make microwave based diagnostic tools possible.