Electrical Impedance Tomography/Neurophysiology
Electrical Impedance Tomography is a recently developed imaging technique, with which images of the internal impedance of the subject can be rapidly collected with rings of external ECG-type electrodes. It is fast, inexpensive, portable and sensitive to physiological changes which affect electrical impedance properties. For about two decades, satisfactory images have been obtained of changes over time related to gastric emptying and ventilation and cardiac output in the thorax.
The work of our group at UCL has been to pioneer EIT for imaging brain function. It could be used to image in acute stroke or epileptic seizures, when its portability and low cost would give it unique practical advantages over existing methods such as fMRI. It could also provide images of fast neural activity in the brain over milliseconds which would constitute a revolutionary advance in neuroscience technology. Innovations in hardware and image reconstruction algorithms enable accurate images to be collected in tanks and in experimental animals with electrodes on the brain; the next challenge is to see if recent technical improvements allow us to collect clinically useful images in human subjects with scalp electrodes.
- Key advances
- Development of idea that EIT could provide tomographic images of fast electrical activity in the brain and so provide a uniquely new method to test theories in computational neuroscience (Holder, 1987)
- Demonstration that EIT with the Sheffield Mark 1 EIT system could produce reproducible EIT images of stroke (Holder, 1992), epileptic seizures, functional activity (Holder et al, 1996, Oh et al, 2011) and the phenomenon of spreading depression which is thought to underlie migraine (Boone et al, 1994) in anaesthetised experimental animals (rats or rabbits) with a ring of electrodes on exposed brain
- Development of image reconstruction software able to produce accurate EIT images of brain function in 3D with scalp electrodes, using anatomically realistic Finite Element Models of the brain (Bagshaw et al, 2003). Refinements include anatomically realistic Finite Element Model meshes (Vonach et al, 2012, Aristovich et al, 2014), adjustment for anisotropy (Abascal et al, 2008), improved regularization methods (Aristovich et al, 2014), and novel methods for imaging at a single moment in time in acute stroke based of recording with multiple frequencies (Malone et al, 2013, Malone et al, 2014).
- Development of electronic hardware specially tailored for EIT imaging in acute stroke (Yerworth et al, 2003; McEwan et al, 2006, Oh et al, 2007), epileptic seizures (Yerworth et al 2002) and fast neural activity in the brain (Oh et al, 2011).
- First clinical studies in humans of EIT in stroke (Romsauerova et al, 2006), epileptic seizures (Fabrizi et al, 2006) and blood flow related changes over seconds in normal cortical evoked activity (Tidswell et al, 2001).
- A recent breakthrough has been the production of the first tomographic images of fast neural activity during cortical evoked activity in the anaesthetized rat (Aristovich et al, 2014).
- Further reading on EIT of brain function