Medical researchers are constantly looking for safer, more accurate ways to monitor patients' condition. They hope their machine, which went into clinical testing at the Albany Medical Center in 1993, will eventually offer physicians a powerful but safe diagnostic tool for such illnesses as heart disease, pulmonary edema, and breast cancer. The new technology, known as Electrical Impedance Imaging, works by applying tiny electrical currents through electrodes placed on the skin, measuring the corresponding voltage response, and then deducing the distributions of electrical conductivity and permittivity inside the body. Since different parts of the body have different electrical properties, the computed distributions provide an image of the body's tissues and fluids. Take the lungs, for example.
Air is a notoriously poor conductor of electricity.
As a result, when healthy lungs fill with air, they show up in an impedance image as regions of low conductivity. Because the fluid has high conductivity, the edema appears as an abnormality in an impedance image. Blood, too, has high conductivity, so impedance imaging also has potential for measuring the amount of blood being pumped by the heart. At present, the only reliable ways to measure cardiac output involve passing a catheter through a vein and through the heart, which is a dangerous and expensive procedure. Impedance imaging is one of several medical imaging techniques that rely heavily on mathematics.