Single-frequency bioelectrical impedance analyzers used to assess body composition are being replaced by multiple-frequency analyzers. At low frequencies, the current flows primarily through extracellular fluids; at high frequencies, it completely penetrates all body tissues. Measures of bioelectrical impedance at multiple frequencies can differentiate total and extracellular fluid compartments in the body. This has considerable value for assessing clinical and nutritional status. Impedance measures at a single frequency contain only a small window of the available impedance spectrum information, which may explain the difficulty in discriminating among individuals. The impedance spectrum and its analysis may provide a much clearer picture of individual differences in body water and body composition. With increasing clinical uses of bioelectrical impedance in individuals and sample populations, the use of multiple-frequency impedance may help to elucidate differences that are not discernible with single-frequency impedance.

Bioelectrical Impedance and Body Composition: Present Status and Future Directions

Biological indexes considered in the derivation of the bioelectrical impedance analysis.

Accurate, Noninvasive Continuous Monitoring of Cardiac Output by Whole-Body Electrical Bioimpedance

Purpose of reviewTo describe recent developments in bioimpedance technique and its application in cardiovascular diseases. Cardiac output determination has been used selectively during recent years because of the need for invasive right heart catheterization. Hence, experience with its application i

Recent developments in cardiac output determination by bioimpedance: comparison with invasive cardiac output and potential cardiovascular applications.

Magnetic resonance electrical impedance tomography (MR-EIT) is an emerging imaging technique that reconstructs conductivity images using magnetic flux density measurements acquired employing MRI together with conventional EIT measurements. In this study, experimental MR-EIT images from phantoms with conducting and insulator objects are presented. The technique is implemented using the 0.15 T Middle East Technical University MRI system. The dc current method used in magnetic resonance current density imaging is adopted. A reconstruction algorithm based on the sensitivity matrix relation between conductivity and only one component of magnetic flux distribution is used. Therefore, the requirement for object rotation is eliminated. Once the relative conductivity distribution is found, it is scaled using the peripheral voltage measurements to obtain the absolute conductivity distribution. Images of several insulator and conductor objects in saline filled phantoms are reconstructed. The L2 norm of relative error in conductivity values is found to be 13%, 17% and 14% for three different conductivity distributions.

/pdf/experimental-results-for-2d-magnetic-resonance-electrical-3nzm9clwyj.pdf

Experimental results for 2D magnetic resonance electrical impedance tomography (MR-EIT) using magnetic flux density in one direction.

A simplified treatment of the electrical impedance of biological tissues is presented, examining the sources of impedance changes and the requirements for recording these changes. The author covers small electrodes, simple models, resistivity of blood, the reactive component in bioimpedance, the use of bioadmittance, the use of the finite-element technique and impedance matching. >

L.E. Baker

Papers

Principles of the impedance technique