Seeing into the body electric.

To look around inside the human body for medical purposes, one must be able to distinguish among tissues.

As it turns out, the electric resistance of animal tissues varies enough that appropriate equipment can use that difference to differentiate organs. Now, Peter Metherall, a physicist at the University of Sheffield in England, and his colleagues have devised a system to generate three-dimensional images of a body's interior based on differences in the electrical properties of its tissues.

Called electrical impedance tomography, or EIT, the technique bears some similarity to magnetic resonance imaging (MRI). In both, a computer infers structure from the body's response to a field and constructs a model from that information.

The EIT procedure uses 64 electrodes placed on the surface of the body. Half of them send current, the other half receive it. The system measures voltage changes, from which the computer generates a color picture.

The technique does not yet have such fine resolution as MRI or computerized tomography, but it has "several distinct advantages over existing medical imaging methods," Metherall's team says in the April 11 Nature. "These include safety, portability, long-term monitoring, cost, and the inherent ability to image physiological function."

Contending that three-dimensional EIT will prove especially useful for lung and brain imaging, the researchers have begun a clinical trial to see how well it detects obstructions in the lungs. "If the trial is successful," they say, "3-D EIT will provide an important alternative to the established radionuclide imaging techniques."