Code Division Multiplexed Impedance Tomography

Ref: 12694
The invention applies the techniques of code division multiplexing used in mobile telecommunications and global positioning systems to allow simultaneous impedance spectrum measurements on multiple channels.

Key advantages
  • Faster collection of impedance images, or use of many more electrode channels to improve images.
  • Able to collect images at many more frequencies without an increase in imaging time.
  • Uses simpler hardware which reduces costs


Impedance tomography devices are limited by the need to multiplex a four terminal impedance measurement between multiple electrodes (time division multiplexing).

The application of these systems is also limited by the need to acquire an image before and after an event (time difference imaging) to remove errors.

Some recent systems measure impedance over a range of frequencies which provides spectral information to reduce errors as an alternative to time difference imaging.

Some of these systems use simultaneous receivers and multiplex the sources and others use simultaneous sources and receivers but do not measure four terminal impedance.

One recent system uses frequency division multiplexing which allows sources to be used simultaneously, but each electrode channel must be sampled at each frequency to measure a spectrum and the overall image acquisition time can be lengthy for low frequencies.

The invention

This invention assigns a code to each channel so that they may be used simultaneously, speeding up imaging time. This is an implementation of code division multiplexing in impedance measurement.

The codes are received by all detectors at the same time and decoded to determine the response from each source. As the codes are also spread over the desired frequency range this also provides simultaneous spectroscopic information. This provides potential improvements to impedance imaging and widens the range of applications.


Medical imaging, physiological monitoring, intensive care, ambulatory monitors, implanted device monitoring, surgical ablation monitoring, drug discovery, geological surveying, environmental monitoring, process control

Principal inventors