Abstract
One of the most important advances in biomedical engineering has been the ability to inspect inside the body without opening it. In this sense, rheoencephalography (REG) is an electromedical technique used to assess the cerebral blood flow (CBF) by noninvasive electrical impedance methods, using electrodes attached to the scalp surface. This technique was first proposed by Polzer and Schuhfried (1950), and emerged as an extrapolation of impedance plethysmography applied to the head. An electric current flowing through a biological tissue causes a potential difference between any pair of electrodes that can be measured. This potential difference depends on the amplitude of the injected current, the shape of the conductor, the arrangement of the electrodes, and the electrical characteristics of the tissue. For instance, the electrical conductivity of the lung tissue is much lower than that of the cerebrospinal fluid (CSF), since alveolar sacs are nonconductive. Furthermore, the electrical conductivity depends on the frequency of the electric current, the orientation of the tissue fibers relative to the current flow, and the amount of extracellular fluid that surrounds the cells. For example, electrical conductivity is higher in the blood than in most tissues, since plasma acts as a truehighway for ions (Malmivuo & Plonsey, 1995).
Key Terms in this Chapter
Tetrapolar Rheoencephalogram (REG II): Pulsatile impedance changes of the head, related to the cardiac cycle that is measured by injecting a small current between two electrodes attached to the scalp surface, and reading the electric potential difference between another pair of electrodes.
Finite Element Method: Mathematical technique to solve complex problems in which a physical domain is spatially discretized (meshed) and solved by numerical methods.
Electrical Impedance: Measure of the opposition to the flow of a sinusoidal alternating electric current.
Bipolar Rheoencephalogram (REG I): Pulsatile impedance changes of the head, related to the cardiac cycle that is measured by injecting a small current between two electrodes attached to the scalp surface, and reading the electric potential difference generated between them.
Electrical Conductivity: Measure of the ability of a material or substance to conduct an electric current.
Engineering Model: Simplification of the reality to address a complex problem by simple rules that can be described by means of equations.
Rheoencephalography: Electromedical technique used to assess the cerebral blood flow (CBF) by noninvasive electrical impedance methods using electrodes attached to the scalp surface.