Currently, the diagnosis of NAFLD requires biopsy and liver histology results. Liver biopsy is considered the gold standard to detect and stage liver cell injury from NAFLD [23-26]. However, liver biopsy has several disadvantages, one of the biggest being its invasive nature, others including sampling error, inter- and intra- variability, poor patient acceptance, and potential complications including excessive bleeding and death [21-23]. On the other hand, traditional imaging modalities, such as ultrasound, computed tomography [CT], and magnetic resonance [MR] imaging can help to detect the presence of hepatic steatosis; however, none of them can help to distinguish necroinflammation and mild fibrosis from simple steatosis. New noninvasive methods have been in development to distinguish necroinflammation, mild fibrosis and steatosis and have shown promising results, yet further validation is still required [27-29]. Based upon the fact that each biological tissue has distinguishable electrical characteristics, ElectricalImpedancetomography presents a new way of diagnosing the stage of the fatty liver condition by determining the liver's electricalimpedance.
In time difference EIT(tdEIT), we reconstruct the temporal change of the complex conductivity distribution using the time difference between two consecutive measured voltage data sets. tdEIT takes advantage of alleviating modeling errors contained in the voltage data set since the time difference between two consecutive boundary voltage data sets may cancel out boundary geometry errors and electrode positions uncertainty. tdEIT imaging was first proposed by Barber and Brown  using the backprojection method, and Cheney et al.  used the one-step Newton method for tdEIT. tdEIT has been applied to the monitoring of heart function, blood flow, and emptying of the stomach. Most of the published researches on phantom experiments essentially were based on tdEIT techniques since their results used the measured voltage data set corresponding to a homogeneous background instead of using a computed voltage data set for a forward model [15, 25, 28].
Cardiotocogram (CTG) is a standard method for monitoring of fetal heart rate (FHR) and the uterine con- tractions (UC) in the later stage of the pregnancy. By analysis and appropriate interpretation of changes in the CTG obstetrician are able to prevent still birth or as- phyxia. Other available techniques such as external and internal tocography (TOCO) , Ultrasound  and Magnetocardiograpghy  have also been in used for monitoring of vital parameters of the fetus and mother . The growth of the fetus and in understanding of the anatomy and functions of an organ or a physiological process, various invasive and non-invasive imagining techniques are available. All medical modalities rely on ionizing radiation to produce images of structure and function through a variety of mechanism but the main biological risk is cancer when imaging in utero. Ultra- sound is widely used for imaging of the fetus which has some limitations like long term monitoring is not possible and demands well trained experience ultrasonographer for data acquisition.
Electricalimpedancetomography (EIT) is one of the process tomographytechniques to provide an on-line non-invasive imaging for multiphase flow measurement. With EIT measurements, the images of impedance real part, impedance imaginary part, phase angle, and magnitude can be obtained. However, most of the applications of EIT in the process industries rely on the conductivity difference between two phases in fluids to obtain the concentration profiles. It is not common to use the imaginary part or phase angle due to the dominant change in conductivity or complication in the use of other impedance information. In a solid-liquid two phases system involving nano- or submicro-particles, characterisation of particles (e.g. particle size and concentration) have to rely on the measurement of impedance phase angle or imaginary part. Particles in a solution usually have an electrical double layer associated with their surfaces and can form an induced electrical dipole moment due to the polarization of the electrical double layer under the influence of an alternating electric field. Similar to EIT, electricalimpedancespectroscopy (EIS) measurement can record the electricalimpedance data, including impedance real part, imaginary part and phase angle ( ) , which are caused by the polarization of the electrical double layer. These impedance data are related to the particle characteristics e.g. particle size, particle and ionic concentrations in the aqueous medium, therefore EIS method provides a capability for characterising the particles in suspensions. Electricalimpedancetomographybased on EIS measurement or namely, electricalimpedancetomographyspectroscopy (EITS) could image the spatial distribution of particle characteristics. In this paper, a new method, including test set-up and data analysis, for characterisation of particles in suspensions are developed through the experimental approach. The experimental results on tomographic imaging of colloidal particles based on EIS measurement using a sensor of 8 electrodes are reported. Results have demonstrated the potential as well as revealed the challenge in the use of EIS and EITS for characterisation of particle in suspension.
CO can also be determined from an ultrasound device placed in the esophagus in two different ways. First, in transesophageal echocardiography, CO is assessed from blood flow in the heart measured via Doppler ultrasound (across a cardiac valve or in a ventricular outflow tract) and the cross-sectional area of the measurement site. This approach is limited to intermittent measurements which are – in addition – time consuming and operator dependent as they re- quire a high level of skills and knowledge. Although unsuitable for routine CO monitoring, this technique allows for a fast diagnosis of heart function in critical hemodynamic situations . Second, in transesophageal aortic Doppler ultrasound, the blood flow through the descending aorta is measured and combined with the aortic cross-sectional area. CO values further need to be scaled with a constant factor to correct for the not-measurable portion of flow from the arteries branching of more proximal to the heart (e.g. coronary and brachiocephalic arteries). While this technique provides continuous CO measurements, its correct operation also re- quires a lot of experience and training . Both of the aforementioned ultrasound-basedtechniques are limited by their operator dependency  and mainly restricted to the use in intra-operative and intensive care scenarios .
Research groups publish their main results in international magazines that deal with electricalimpedancetomography. The main ones are: Physics in Medicine and Biology, Physiological Measurement, Measurement Science and Technology, Electronics Letters, IEEE Transactions in Biomedical Engineering, IEEE Transactions in Medical Imaging, Medical and Biological Engineering and Computing, SIAM Journal of Applied Mathematics, British Medical Journal, The Lancet, New England Journal of Medicine, Journal of Physiology, Biomedical electronics, Bulletin of the Russian Research Center of Radiology, Medical Radiology and Radiation Safety, New Scientist, Scientific American, Inverse Problems in Science and Engineering, Progress In Electromagnetics Research, Journal of Electromagnetic Waves and Applications.
ElectricalImpedanceTomography is an imaging technique which images the resistivity distribution of the body. An alternating current is injected through the contact electrodes placed on the surface and resulting potentials are measured to image the current density distribution which is solved as Inverse Problem. The EIDORS (ElectricalImpedance and Diffused Optical Reconstruction Software) is an open source software suite used for the reconstruction of ElectricalImpedanceTomography (EIT) and Diffused Optical Tomography (DOT). This paper describes the EIT experiments conducted on a circular box phantom. Here a low magnitude current is applied in a neighboring current pattern and the boundary potentials are measured and the resistivity images are reconstructed using EIDORS for circular inhomogeneities used inside the phantom.
Typical hardware of an EIT microscopic system has three major parts, which are EIT electrodes, electrical instruments, and a PC with reconstruction algorithm software. Electrodes are used to transmit the current inside the phantom / system from one to another. They also collect the observable signals that will be transferred to a measurement device. Electrical instruments are devices that are used to transmit and receive the measurement from the electrodes. Therefore, a current source circuit has been designed and built to transmit current through the electrodes. At the same time, a receiver circuit is designed to collect the voltage measurement and then the data is transferred serially to the PC for analysis and image reconstruction. Finally, the received analogue signals will be converted to digital via data conversion (ADC) to measure the boundary voltage potential. This basic block diagram as shown in Fig. 1.
A low diagram outlining the key steps for EIT imag- ing of plant roots is shown in Fig. 8. he alternating cur- rent I(A) is introduced via opposite pairs of electrodes and voltage (V) measured at a second pair of electrodes. his is repeated for all electrode combinations. A matrix (‘Jacobian’) representing the voltage sensitivity inside the vessel in response to the injected current is calculated. A theoretical model of the expected conductivity within the pot is created and compared with the experimental values. Initially, the deviation between the theoretical and actual values is large, so values within the Jacobian matrix are adjusted until the deviation is minimised. At this point an acceptable solution has been obtained. his generates a 3-dimensional image reconstruction that describes the impedance of the VOI. One of the promi- nent efects in the image reconstruction around the elec- trode locations is ‘ringing’ , that is an oscillatory error in the reconstruction due to the step-wise change in the actual conductivity between the electrode material and the medium being measured. Ringing can reduce the resolving power of regions with step-wise conductivity
Various attempts have been made to improve the diagnostic efficiency of conventional breast imaging methods by introducing new techniques. The aim of screening is to apply early breast cancer diagnosis and to determine which female patients should be subjected to expensive examinations. The radiation-free EIT meets this requirement. This kind of imaging method detects early symptoms of the human breast pathology using the abnormality in breast impedance distribution which is based on the structural parameters of human breast tissue or metabolic processes in the tissues of interest and in the surrounding tissues. Hence this study is important to know the range of EIT S n for breast cancer screening.
Electricalimpedancetomography (EIT) reconstructs the internal impedance distribution of the body from electrical measurements on body surface. The algorithm research is one of the main problems of the EIT. This paper presents the MPSO-MNR Algorithm, which is formed by combining the Modified Particle Swarm Optimization (MPSO) with Modified Newton-Raphson algorithm (MNR), gives the reconstruction results of certain configurations and analyzes the influence of the noise on the MPSO-MNR algorithm in the EIT. The numerical results show that the MPSO-MNR algo- rithm can reconstruct the resistivity distribution within the certain iterations. With the moving of the target to the centre of 2-D solution domain and the increase of noise, the border of the reconstruction objects becomes vague, and the fit- ness value and the total error increase gradually.
Acute respiratory distress syndrome (ARDS) is a clinical entity that acutely affects the lung parenchyma, and is characterized by diffuse alveolar damage and increased pulmonary vascular permeability. Currently, computed tomography (CT) is commonly used for classifying and prognosticating ARDS. However, performing this examination in critically ill patients is complex, due to the need to transfer these patients to the CT room. Fortunately, new technologies have been developed that allow the monitoring of patients at the bedside. Electricalimpedancetomography (EIT) is a monitoring tool that allows one to evaluate at the bedside the distribution of pulmonary ventilation continuously, in real time, and which has proven to be useful in optimizing mechanical ventilation parameters in critically ill patients. Several clinical applications of EIT have been developed during the last years and the technique has been generating increasing interest among researchers. However, among clinicians, there is still a lack of knowledge regarding the technical principles of EIT and potential applications in ARDS patients. The aim of this review is to present the characteristics, technical concepts, and clinical applications of EIT, which may allow better monitoring of lung function during ARDS.
The inverse problem in EIT is to find an approximation to the correct conductivity distribution based on the experimentally acquired current-to-voltage map. It is ill-posed (reviewed e.g. in Borcea, 2002), which means that small changes in the measurements can lead to large changes in the reconstructed image. This makes the inverse problem very unstable in the presence of noise. Furthermore, it has only been proven to have a unique solution for isotropic conductivities and a full knowledge of the boundary (Sylvester and Uhlmann, 1987; Kohn and Vogelius, 1985). In practice, the application of current and measurement of voltages are restricted to a finite set of electrodes and human tissues are sometimes strongly anisotropic (i.e. their conductivity depends on the direction of the current). Therefore, it is not possible to precisely reconstruct the conductivities and instead the aim is to find an approximate solution using a stabilised reconstruction method. The reconstruction is commonly turned into a well-posed problem by introducing prior information through regularisation. Linear reconstruction methods can be used for time-difference and frequency-difference measurements of small, localised changes. For larger changes and absolute imaging, non-linear algorithms have to be used. This review of inversion methods draws from course notes of Arridge (2015).
The level-set technique is chosen to describe changing shapes since this method is able to easily model topolog- ical changes of the boundaries. In the shape reconstruc- tion approach, it is assumed that the approximate values of background parameters and parameters inside the inclusions are known, but that the number, topology and shapes of the inclusions are unknown and have to be recovered from the data. Compared to the more typical pixel/voxel-based reconstruction schemes, the shape reconstruction approach has the advantage that the prior information about the high contrast of the inclusions is incorporated explicitly in the modelling of the problem. In a pixel/ voxel-based reconstruction scheme the approx- imate locations of the unknown inclusions are found dur- ing the early iterations, but it typically takes a large number of additional iterations to achieve accurate infor- mation concerning the precise shapes of these objects. Figure 2 schematically shows a moving boundary and a narrowband at the interface. Here, the equation describ- ing the moving fronts is
The poor performance of method 2a on the Cardiff phantom and saline tank compared with humans may be attributed to the behavior of RE with phase offset for the different noise con- ditions. On phantoms and saline tanks, errors due to electrode impedance are small. RE is small for these cases, and did not vary greatly over a large range of phase offsets. Accurate mini- mization of RE with phase offset is difficult because this func- tion is almost constant with phase and becomes prone to noise. On humans, the mismatch in channel component values due to high and variable skin-contact impedance resulted in a smooth and more minimizable function of RE so that individual reci- procity optimization, unlike in tanks, performed no worse than other methods.
Another important part of the system hardware is the volt- meter. In SUT-1 a synchronous differential demodulator is used. This method is a common method for demodula- tion in EIT. The noise cancellation capability is one of the important features of this circuit. The circuit diagram of this demodulator is illustrated in figure 5. It is a "Sample and Hold" type of demodulator . An AD-625 instru- mentation amplifier is used as the "heart" of the measure- ment system . The output signal of the demodulator is fed into an I/O card by a controlled gain buffer ampli- fier block, which uses CA-3130 at the final stage. In the APT mode of operation, the offset and gain error of this stage is of less importance, so, for a better Signal to Noise Ratio, the gain could be increased to a maximum reason- able value. The time duration in which the voltage meas- urement is performed, is an essential parameter in the overall system speed. This is also dependent upon the multiplexing switching time between different channels. In order to decrease the data reading time, it is possible to use, fast analogue to digital converters, a separate demod- ulator for each channel and/or a decrease in multiplexing time by means of faster digital switches. For example, in APT mode, 16 electrodes can be directly connected to the 16-bit I/O card for voltage measuring and in this way mul- tiplexing time can be saved and hence errors are reduced. We have surveyed different methods namely cross and opposite for data acquisition and their effects on the dis- tinguishability of objects. An example of such methods is shown in Figure 6 in which the variation of measured voltage verses measurement number for a current injector is illustrated.
Abstract– ElectricalImpedanceTomography (EIT), is one of the safest medical imaging technologies and can be used in industrial process monitoring. In this method, image of electrical conductivity (or electricalimpedance) distribution of the inner part of a conductive subject can be reconstructed. The image reconstruction process is done by injecting an accurate current into the boundary of a volume conductor (Ω), measuring voltages around the boundary (∂Ω) and transmitting them to a computer, and processing on acquired data with software (e.g. MATLAB). The image would be reconstructed from the measured peripheral data by using an iterative algorithm. A precise instrumentation (EIT hardware) plays a very important and vital role in the quality of reconstructed images. In this paper, we have proposed a practical design of a low-cost precise EIT hardware including, a high output impedance VCCS (Voltage-Controlled Current Source) with pulse generation part, precise voltage demodulator and measuring parts, a high performance multiplexer module, and a control unit. All the parts have been practically and accurately tested with successful results, and finally the proposed design was assembled on PCB. The quality of experimental results at the end of this paper, (reconstructed images by using the implemented system), confirms the accuracy of the proposed EIT hardware.
ABSTRACT: Current Drivers are suitable for bioimpedance measurements applications.The CMOS current driver circuits are portable for high resolution, high frequency image system.Current driver are require accurate output current value.This current driver circuits are introduced based on a transconductance and provide accurate current output.This circuit design uses multithreshold CMOS technology (MTCMOS) and negative feedback.The circuit was fabricated in a 0.22µm MTCMOS process technology.It operates at 5v power supply and it can deliver the output current 5mA.
2.3.1. Model and phantom. A cylindrical mesh of diameter 19 cm and height 10 cm, with a ring of 32 electrodes around the centre, was designed, while the boundary voltages were simulated using a mesh with 62784 elements. The ground point was fixed at the centre of the base of the mesh. A current of peak amplitude 133 A , injected though polar electrodes, was simulated, and the voltage differences on all adjacent pairs of electrodes not involved in delivering the current were obtained. The electrodes were described with the complete electrode model, and the electrode impedance was set to 1k ohm. To evaluate the noise performance of the TV algorithms, boundary voltages were simulated with Signal to Noise Ratio (SNR) of 60dB, 40dB and 30dB, generated by adding Gaussian white noise. The conductivity of the background was 0.4 Sm -1 , to simulate that of the NaCl solution. A cylindrical perturbation with conductivity of 0.36 Sm -1 , diameter 4 cm and height 10 cm was placed at a point with coordinates (x: 5 cm y: 0 cm z: 0 cm), with reference to the centre of the mesh (figure 1).
Electronic instrumentation comprised an ultra low noise programmable constant current source which could pro- duce a sinusoidal waveform from 1 Hz to 1 kHz with an amplitude of 0.1–100 uA, the ‘UCL-CS1’. This was con- structed from a FPGA (EP1K50, Altera, USA), pro- grammed as a main controller and digital waveform generator. It received commands from a PC and produced timing and control signals to the acquisition system. The sine waveform was digitally generated in a ROM which contained 2,000 samples of sine waveform data which were read by the FPGA and able to generate frequencies from 125 to 825 Hz. The DC component and high frequency clock noise were rejected by a band pass filter (10 Hz– 10 kHz). There were two independent current sources to supply 0.1–10 l A or 10–100 l A. These comprised a floating Howland current source which contained digitally controlled potentiometers (DS1267-010 and DS1267-050, Dallas, USA) to equal provide equal resistance ratios. Power was supplied from batteries. The output impedance was over 1 M X . Voltages were recorded with a 1 channel Neurolog pre-amplifier (NL106, Digitimer, UK), filter unit (NL125, Digitimer, UK), with a gain of 50 and bandpass of DC to 10 kHz. Data were sampled at 160 kHz by a National instruments 16 bit data acquisition system set to oversample and so provide 18 bit resolution (NI USB 6259, National Instruments, USA). The system was optically isolated and controlled by a Windows PC. The current source and voltage measurement unit operated synchro- nously. A control signal generated from UCL-CS1 was passed to the NI data acquisition system which in turn produced a timing control signal for nerve stimulation using a driven buffer (NL510) and isolated stimulator (NL800A, Digitimer, UK) which was a battery powered and opto-coupled. All systems operated with the same clock (Fig. 3).