Impedance cardiography (ICG) offers a safe, noninvasive, and inexpensive method to track stroke volume estimates over long periods of time. Several modified ICG measurement configurations have been suggested where for convenience or improved performance the standard band electrodes are replaced with electrocardiogram electrodes. This report assesses the sensitivity of the conventional and three modified ICG methods in detecting regional conductivity changes in the simulated human thorax. The theoretical analyses of the measurement sensitivity employ the reciprocity theorem and the lead field theory with a highly detailed, anatomically accurate, three-dimensional computer thorax model. This model is based on the finite-difference element method and the U.S. National Library of Medicine's Visible Human Man anatomy data. The results obtained indicate that the conventional four-band ICG is not specifically sensitive to detect conductivity changes in the region of the heart, aortas, and lungs. Analyzed modified electrode configurations do not reproduce exactly the measurement sensitivity distribution of the conventional four-band ICG. Thus, although the signals measured with modified spot arrangements may appear similar to the four-band configuration, the distribution of the signal origin may not be the same. Changing from band to spot electrodes does not overcome the methodological problems associated with ICG.

Textile sensors, when embedded into clothing, can provide new ways of monitoring physiological signals, and improve the usability and comfort of such monitoring systems in the areas of medical, occupational health and sports. However, good electrical and mechanical contact between the electrode and the skin is very important, as it often determines the quality of the signal. This paper introduces a study where the properties of dry textile electrodes, textile electrodes moistened with water, and textile electrodes covered with hydrogel were studied with five different electrode sizes. The aim was to study how the electrode size and preparation of the electrode (dry electrode / wet electrode / electrode covered with hydrogel membrane) affect the measurement noise, and the skin-electrode impedance. The measurement noise and skinelectrode impedance were determined from surface biopotential measurements. These preliminary results indicate that noise level increases as the electrode size decreases. The noise level is high in dry textile electrodes, as expected. Yet, the noise level of wet textile electrodes is quite low and similar to that of textile electrodes covered with hydrogel. Hydrogel does not seem to improve noise properties, however it may have effects on movement artifacts. Thus, it is feasible to use textile embedded sensors in physiological monitoring applications when moistening or hydrogel is applied.

Abstract-Electric properties of tissues depend on many factors, including measurement frequency and temperature. Properties differ also in vivo and in vitro situations. We have collected conductivity values from several studies and compared the values measured from living tissue and tissue samples. The results show that the resistivity ratio of grey and white matter increases 36% after death, and the resistivity values increase over 100%. Keywords -Conductivity, brain tissue, source location I. INTRODUCTIONThe electric properties of tissues have a very important role in biomedical engineering. These properties determine the electrical current pathways through human body. If these properties are known, electrical models can be constructed, for example, to represent the electrical activation of the heart or the conduction of the brain activity to the scalp surface.With resistive model of the head, the information given by electroencephalography (EEG) can be effectively processed [1], [2], [3]. Models can be applied to the simulation of electric fields inside the head. For example, an electric source (dipole or set of dipoles) can be inserted inside the model and thereafter the electric field distribution can be computed. Further, the measured EEG signal can be used for obtaining the source location in the volume conductor. For example, epileptic loci can be located. In principal, accuracy of these computations is dependent on the accuracy of the volume conductor i.e. the number of compartments and their conductivities [4]. In [5] the results indicated that a 10% decrease in tissue resisitivity cause 3.0 -4.1% differences in the sensitivity distributions of the selected 3 EEG leads. In modeling the important factor is the ratio between various conductivities. The ratio of skull and brain resistivites is 15:1 rather than the commonly used ratio of 80:1 [6]. In [7] the estimated resistivity ratio of skull and brain is 14:1.There have been recent advances in source localization techniques. The amount of electrodes in EEG studies has been increased. Instead of the traditional 21 electrode 10-20 system, 64 or more electrodes are usually used. In some studies even 512 electrodes are utilized. This improves the spatial accuracy, thus giving more information about brain functions. However, most researchers continue to take conductivity parameters from standard references [8], [9]. The standard reference values are usually measured from tissue samples. An increase in tissue resistivity with time after death has been reported in [8], [10]. Literature values are also measured at much higher frequencies than EEG frequencies. II. METHODOLOGYPreviously we have made in vivo resistivity measurements with needle electrode from 9 patients with brain tumors [11]. Due to the location of tumors and selected surgical paths, it was not possible to measure both grey and white matters with every patient. The number of measurements ranged from 1 to 13 for each tissue measured.In addition to our own in vivo measurements [11], resistivity val...

A head cap made of fabric for measuring EOG and facial EMG signals is presented. Reusable and easy to use electrodes, embroidered of silver coated thread, are integrated into the cap. A two-way wireless data transmission link operating at license free 2.4 GHz frequency band is used for transferring the 16-bit measurement data, sampled with 1 kHz frequency from six channels at maximum, to the receiver device connected to a PC. Tailored PC software is used for displaying the signals and controlling the measurement parameters. The measurement system is intended for recording facial expressions during human emotion studies but it can also be utilized in computer user interface control. The paper shows preliminary results from EOG and facial EMG measurements.

Neurobiological concepts based on state-of-the art technology have so far lacked the complexity of actual high-level neurobiological systems. Two key advances are needed to improve our understanding of such systems: in vitro 3D-neuronal cell culture and 3D MEA systems for measuring such 3D-cultures. These requirements call for smart multilayer and packaging technology. The material Green Tape TM from DuPont Nemours is chosen for the presented works, because its compatibility and those of available metallisation with cell cultures is already proven. An LTCC multilayer circuit with gold electrodes is the base of the 3D MEA. The layout of the 3D MEA is designed to fit the MEA2100-System for in vitro recording from Multi Channel Systems and enable thus a comparable data processing to established 2D MEAs Slots. The surface topography of the thick film electrodes and the surface state is investigated with laser scanning microscopy, SEM, XPS and measurements of the wetting angle of contact. The impedance of the screen printed electrodes is discussed taking these data into account. Their impedance amounts to 24 kΩ and are falls thus below the impedance of commercially available electroplated gold electrodes of 30 kΩ. First promising results have been achieved using 3D MEAs for 2D culture of human pluripotent stem cell derived neural cells.