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Electrical Impedance Spectroscopy (EIS)

The premise: "Imagine little plastic bags full of stuff floating in interstitial fluid." That's how Alex Hartov, the project leader of the EIS research initiative, describes the cells that make up breast tissue. Interstitial fluid—the fluid between cells—conducts currents, he explains. Cell membranes, however, do not. Therefore, the kind of cells and the number of cells in a given region directly affect tissue conductivity. Different tissue types—normal, fatty, cancerous—have different electrical properties.

The EIS modality (like MIS) is designed to measure those properties throughout the breast and then use that information to create a kind of tissue map, which shows an obvious contrast between normal and cancerous tissue.

One way that Hartov's team is both validating and improving EIS is by taking readings of a tumor in the operating room, before it is removed from a woman's breast, and then taking readings again, after the surgery, when the tumor is in the pathology lab.

"If one were ambitious," says Hartov, "one could imagine that we could conceivably supplant mammography completely [with EIS], which I am sure a lot of women would really like. A more reasonable goal would be to supplement it by being a second-step exam to decide whether or not to do a biopsy. Biopsies are still a pretty big deal in terms of cost, pain, and other annoyances."

The EIS procedure, however, is inexpensive, painless, and relatively quick, he points out.

The procedure: During EIS, the woman lies face down on a table with one of her breasts positioned through an opening. A technician places from one to four rings of electrodes in contact with the breast; the number of rings used depends on the size of the breast. Each ring contains 16 electrodes, and all 16 electrodes on a ring must touch the breast. This can be tricky sometimes, since most breasts are not perfectly round.

Skeins of wires (visible in the lower left photo) power the four rings of electrodes (above) that come into contact with the breast during an EIS exam. Built into a retrofitted breast biopsy table (shown on the bottom right), the EIS system measures electrical properties of normal and abnormal breast tissue.

Using one ring at a time, small currents of varying frequency are then passed through the breast; the current is sent from each electrode in sequence to the other 15 in that ring. As in MIS, the currents are of such low power that the women do not even feel them.


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