The purpose of electrical impedance tomography is to obtain the electrical impedance distribution in the domain of interest by injecting the currents or applying voltages and measuring voltages or currents via a number of electrodes that are mounted on the boundary of the domain. We investigated the influence of various alternating current injection methods on conductivity allocation recovery in biological tissues. We used 16 electrodes allocated uniformly on a circle perimeter. The research technique includes the mathematical modeling by finite element method with 576 nodes. The current injection was performed through two electrodes located nearby (dipole assignment), opposite (polar assignment) or with a shift by 3 electrodes (a quarter of circle). We registered the potential differences between other electrodes for calculation of the internal conductivity allocation by the finite element method. The study revealed that dipole current injection impoved the sensitivity of the method, and polar injection refined the resolution capability. We used the absolute and difference calculation methods implemented in the programming package of potentials allocation and image reconstruction EIDORS (Electrical Impedance and Diffuse Optical Tomography Reconstruction Software). EIDORS is an open source software system for image reconstruction in the electrical impedance tomography and diffuse optical tomography, designed to facilitate collaboration, testing and new research in these fields. Several numerical examples with inclusion of various convex and non-convex smooth shapes (e.g. circular, elliptic, square-shaped) and sizes are presented and thoroughly investigated. The experiments revealed phantoms at round form discontinuities of conductivity. As an accuracy criterion, we selected mean-square and maximum deviation values of the reconstructed image from the true conductivity allocation. The study showed the advantages, lacks and application fields of dipole, polar and other methods of the current injection. The experiments demonstrated the optimal parameters for reconstruction of internal conductivities at various methods of stimulation. The model with polar electrodes showed the best results by the criterion of maximum deviation. The model with electrodes shifted on a circle quarter revealed the best results by mean-square error criterion.

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In this paper we investigated a pulse oximetry-based method for mobile devices. This method obtains bio-signals related to blood pulsation in transparent parts of body. The most widely accepted field for use of this method is hospital care. In these cases a pulse oximeter is the best solution for the monitoring of emergency patients. A promising field for pulse oximetry is physical exercise. It only requires simple clips such as ear-clips, finger-clips, headbands etc. However this method presents some difficulties: weak signal, noise ratio, motion artefacts, low perfusion. We used a MAX30100 Oximeter and Heart Rate Sensor integrated circuit to obtain signals of blood pulse waves from red and infrared light emission diodes (LED). This device measures the oxygen saturation of a person’s blood by placing an LED and a photodetector against the thin skin of a person’s body, such as a fingertip, wrist or earlobe. The MAX30100 is a 14-pin surface mount integrated circuit that contains sensors for measuring a person’s heart rate. It can also indirectly determine the oxygen saturation of a person’s blood. The MAX30100 provides a complete pulse oximetry and heart rate measurement solution for medical monitors and wearable fitness devices. As each LED emits light into a person’s finger, the integrated photodetector measures variations in light caused by changes in blood volume. An integrated 16-bit analog to digital converter (ADC) with programmable sample rate converts the photodetector output to a digital value. The MAX30100 filters out ambient light that can interfere with an accurate reading. Data are read through a serial I2C interface to computer for further processing. The LED current can be programmed from 0 to 50 mA with proper supply voltage. The LED pulse width can be programmed from 200 µs to 1.6 ms to optimize measurement accuracy and power consumption based on use cases. The SpO2 algorithm is relatively insensitive to the wavelength of the infrared LED, but the red LED’s wavelength is critical to correct interpretation of the data. The temperature sensor data can be used to compensate errors with ambient temperature changes. During the experiments we registered oxygen concentration values under different conditions. With low muscular activity we observed high stability and repeatability of measuring values under various exterior conditions. However, with high muscular activity there were various artefacts in the gauged signals that led to contortion of effects. We identified the boundaries of the validity of measuring and propose the use of an adapted filter in order to distinguish pulse waves from optical signals more reliably. These devices can be applied in fitness training , medical monitoring and used as wearable devices.

Photoplethysmography has recently become more widespread among non-invasive methods for obtaining information on the state of physiological systems of the human body. Serial photoplethysmographs are intended for use in clinics and require special care, therefore, interest in portable media developed on the basis of modern sensors and microcontrollers is growing, which would not only make this method available for individual use, but also expand its capabilities through the use of light of various spectral ranges. Such devices require modified signal processing techniques that allow them to be used in mobile applications. The aim of the work is to develop methods for processing signals from a modern two-beam sensor operating in the red and infrared ranges for the analysis of photoplethysmography on a mobile device (smartphone or tablet). A device using the microcontroller and radio module in the Bluetooth standard allows you to continuously record pulse waves, determine the level of oxygen in the blood, calculate peak-peak intervals and heart rate. The use of the two-beam sensor for registration and the implementation of the developed signal processing methods in the Android operation system application increase the accuracy of setting the maximums on pulse curve and provide a relative error in determining the heart rate and pulse-to-pulse intervals relative to the certified electrocardiograph at 9.2% and 9.6% respectively, with an average level of interference and an average activity. An Android operation system mobile device (tablet, smartphone) allows you to visualize the measurement results, store data in the internal memory, and transfer them to the server for further processing.