Electrical Impedance Tomography (EIT) research was performed while studying for my PhD in the Department of Physics and Astronomy at the University of Southampton. A brief introduction to imaging with EIT, its applications, my research, and some clinical images are available together with links to other EIT pages.
Introduction To EIT
EIT measures the distribution of impedance in a cross-section of the body. This is possible because the electrical resistivities of different body tissues varies widely from 0.65 ohm m for cerebrospinal fluid to 150 ohm m for bone. Before data can be recorded a series of electrodes are attached to a subject in a transverse plane. These are linked to a data acquisition unit which outputs data to a PC. By applying a series of small currents to the body a set of potential difference measurements can be made from non-current carrying pairs of electrodes. Since electric currents applied to the body take the paths of least impedance, where the currents flow depends on the subject's conductivity distribution, the image reconstruction process is a non-linear problem. Therefore images can be reconstructed from the data using a variety a methods.
Possible Clinical Applications
EIT does not use ionising Electro-Magnetic radiation and is safe enough for use as a long term monitor. Eventually EIT could replace some imaging techniques, since it is both safer and more pleasant for the patient. The most promising clinical use of EIT is in the measurement of gastric emptying. Images of the stomach can be produced and by monitoring a region of interest for the stomach position, gastric emptying curves can be plotted to determine the half time for stomach emptying. Respiratory measurements have also been well investigated. The volume of air in the lungs is proportional to the resistivity change measured. This allows images of lung ventilation to be produced and ventilation disorders to be investigated.
Other applications being investigated include : the measurement of pharyngeal transit times, diagnosis of swallowing disorders, detection of gastric motility - the 3 cpm activity of the stomach wall, respiratory screening to look for emphysema and pulmonary emboli, the measurement of cardiac output, and investigations of the brain to locate the focus of an epileptic seizure.
My research included investigating possible improvements to and the clinical validation of EIT. Work focused on incorporated a priori knowledge into the reconstruction process (1), investigating limitations of data acquisition in the clinical environment (2), post processing of spectral expansion images to reduce artefact images and reduce noise contributions (3), the development of a full iterative non-linear solution to the inverse problem of generating tomographic images from patient data (4), and reducing the sensitivity of the reconstruction process to the electrode positions (5). Examples of clinical image sequences with reduced sensitivity to the electrode positions are available on page 2. All work is detailed in my PhD thesis (6).
1. Meeson S, Killingback ALT, Blott BH. The dependence of EIT images on the assumed initial conductivity distribution : a study of pelvic imaging.Phys. Med. Biol. 1995;40:643-657. Abstract
2. Meeson S, Blott BH, Killingback ALT. EIT data noise evaluation in the clinical environment.Physiol. Meas. 1996;17:A33-A38. Abstract
3. Meeson S, Killingback ALT, Blott BH, Mitchell C, Evans DF, Milla PJ. Optimal filtering of EIT data in spectral expansion analysis.Physiol. Meas. 1996;17:A85-A90. Abstract
4. Blott BH, Daniell GJ, Meeson S. Non-linear reconstruction constrained by image properties in Electrical Impedance Tomography.Phys. Med. Biol. 1998;43:1215-1224. Abstract
5. Blott BH, Daniell GJ, Meeson S. Electrical Impedance Tomography with compensation for electrode positioning variations.Phys. Med. Biol. 1998;43:1731-1739. Abstract
6. Meeson S. An investigation of optimal performance criteria in Electrical Impedance Tomography. PhD Thesis, University of Southampton, 1997. Abstract
1. EIT system noise performance and optical data filtering
9th International Conference on Electrical Bio-Impedance (ICEBI) and EC Concerted Action On Impedance Tomography (CAIT), University of Heidelberg, September 1995.
2. The state of the art of Electrical Impedance Tomography
Scientific Meeting, Southampton General Hospital, 3rd July 1996.
1. 1st Joint IPSM and BES Annual Scientific Meeting 1994 - University of Keele
Meeson S, Blott BH. Dependence of EIT dynamic images on the assumed initial conductivity distribution: a study of pelvic imaging.
Awarded conference POSTER PRIZE.
2. Postgraduate Poster Day 1996 - University of Southampton
Meeson S. Tomographic imaging from peripheral measurements of electrical impedance.
Last modified 15th March 2003