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Cui Z, Yang P, Li X, Wang H. An alternative excitation method for electrical impedance tomography. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:044710. [PMID: 35489953 DOI: 10.1063/5.0083681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Accepted: 04/03/2022] [Indexed: 06/14/2023]
Abstract
Electrical impedance tomography (EIT) can be utilized to image the conductivity distribution of material under test. The EIT measurements depend on the quality in the current injection and voltage measuring circuits. The current source plays a vital role in the EIT instruments. In most of the research studies, the push-pull current sources were employed for the source and sink signal generation. It usually requires frequent calibration to achieve proper functioning, especially for the sweeping frequency measurements. In this paper, an alternative excitation method has been proposed for simplifying the design of the current source in EIT instruments, which aims to achieve the performance of the push-pull current source by using a single-ended current source. It could offer the following advantages: (1) hardware simplification and (2) reduced requirements on current source calibration. The corrected measurements could be consistent with that using push-pull excitation, as confirmed by the numerical simulations. In addition, the reconstructed images have also been investigated to illustrate the effectiveness of the proposed method.
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Affiliation(s)
- Ziqiang Cui
- School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China
| | - Pengyu Yang
- School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China
| | - Xuan Li
- Department of Mathematics, Tianjin University of Finance and Economics Pearl River College, Tianjin 301811, China
| | - Huaxiang Wang
- School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China
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2
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Analysis, Simulation, and Development of a Low-Cost Fully Active-Electrode Bioimpedance Measurement Module. TECHNOLOGIES 2021. [DOI: 10.3390/technologies9030059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A low-cost 1 kHz–400 kHz operating frequency fully-active electrode bioimpedance measurement module, based on Howland current source, is presented in this paper. It includes a buffered positive feedback Howland current source, implemented with operational amplifiers, as well as an AD8421 instrumentation amplifier, for the differential voltage measurements. Each active electrode module can be connected to others, assembling a wearable active electrode module array. From this array, 2 electrodes can be selected to be driven from a THS413 fully differential amplifier, activating a mirrored Howland current source. This work performs a complete circuit analysis, verified with MATLAB and SPICE simulations of the current source’s transconductance and output impedance over the frequency range between 1 kHz and 1 MHz. Resistors’ tolerances, possible mismatches, and the operational amplifiers’ non-idealities are considered in both the analysis and simulations. A comparison study between four selected operational amplifiers (ADA4622, OPA2210, AD8034, and AD8672) is additionally performed. The module is also hardware-implemented and tested in the lab for all four operational amplifiers and the transconductance is measured for load resistors of 150 Ω, 660 Ω, and 1200 Ω. Measurements showed that, using the AD8034 operational amplifier, the current source’s transconductance remains constant for frequencies up to 400 KHz for a 150 Ω load and 250 kHz for a 1200 Ω load, while lower performance is achieved with the other 3 operational amplifiers. Finally, transient simulations and measurements are performed at the AD8421 output for bipolar measurements on the 3 aforementioned load resistor values.
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Saulnier GJ, Abdelwahab A, Shishvan OR. DSP-based current source for electrical impedance tomography. Physiol Meas 2020; 41:064002. [PMID: 32603311 DOI: 10.1088/1361-6579/ab8f74] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE EIT systems, particularly those that use a parallel, multiple source architecture, require current sources with very high output impedance. To meet this requirement, sources often use complex analog circuits and require manual or electronically-controlled adjustments. The goal is to implement a current source with simple, adjustment-free analog electronics with high effective output impedance even with significant stray impedance at its output. APPROACH The excitation provided to the voltage-to-current converter is adjusted to accommodate the current lost in the finite output and stray impedances. The adaptive algorithm uses the measured voltage and the previously-measured output and stray impedance to determine the needed current adjustment. MAIN RESULTS The structure of the source is presented along with an implementation, and experimental results that show the effectiveness of the approach for frequencies up to 1 MHz. The measured output impedance with and without the adaptive compensation are presented as well as measurements of resistive and complex loads. SIGNIFICANCE The new current source has low analog complexity, operates over a wide range of frequencies, and can compensate for a significant stray shunt impedance. It can be used to implement improved parallel or serial EIT systems.
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Affiliation(s)
- Gary J Saulnier
- Electrical and Computer Engineering, University at Albany, State University of New York, Albany, NY, United States of America
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Abstract
In this paper a number of LT Spice simulations have been carried out on an Electrical Impedance Tomography (EIT) system, which includes the whole analog and digital circuitry as well as the subject to be examined (phantom model). The aim of this study is to show how the analog and digital parts, the electrodes and the subject’s physical properties may impact the measurements and the quality of the reconstructed image. This could provide a useful tool for designing an EIT system. Special attention has been given to the current source’s output impedance and swing, to the noise produced by the circuits and to the Analog to Digital Converters (ADCs) resolution and sampling rate. Furthermore, some 3D phantom subjects have been modeled and simulated as equivalent circuits, merged with the EIT simulated hardware, in order to observe how changes on their properties interact with the whole circuitry and affect the final result. Observations show that mirrored current sources with z o u t > 350 k Ω and sufficiently high ADC acquisition sampling rate ( f s a m p l e ≥ 16 f i n ) can result to accurate impedance measurements and therefore quality image reconstruction within a frequency span of at least 10 to 100 kHz. Moreover, possible hardware failures (electrode disconnections and imbalanced contact impedances) can be detected with a simple examination of the first extracted image and measurement set, so that by direct modification of the reconstruction process, a corrected result can be obtained.
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Takhti M, Odame K. Structured Design Methodology to Achieve a High SNR Electrical Impedance Tomography. IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS 2019; 13:364-375. [PMID: 30668480 DOI: 10.1109/tbcas.2019.2894157] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
In this paper, we present a methodology for designing the main circuit building blocks of an electrical impedance tomography (EIT) system. In particular, we derive equations that map system-level EIT specifications to the performance requirements of each circuit block. We also review the circuit architectures that are best suited for meeting a given set of performance requirements. Our proposed design methodology is focused on maximizing the EIT system's signal-to-noise ratio while minimizing total power consumption.
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Khalighi M, Mikaeili M. A floating wide-band current source for electrical impedance tomography. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:085107. [PMID: 30184672 DOI: 10.1063/1.5028435] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2018] [Accepted: 07/12/2018] [Indexed: 06/08/2023]
Abstract
The quality of reconstructed images in Electrical Impedance Tomography (EIT) depends on two essential factors: first, precision of the EIT hardware in current injection and voltage measurement and second, efficiency of its image reconstruction algorithm. Therefore the current source plays an important and a vital role in EIT instruments. Floating-load current sources constructed using sink and source drivers have better performance and higher output impedance than grounded-load (single-ended) current sources. In addition, a main feature of this kind is that the current source is not connected to the ground potential directly but via a large impedance. In this paper, we first focus on recent studies on designed EIT current sources, and after that, a practical design of a floating-load high output impedance current source-operating over a wide frequency band-will be proposed in detail. Simulation results of the proposed voltage-controlled current source (VCCS), along with some other models, will be shown and compared. At the end, the results of practical tests on the VCCS and a few EIT images, taken using our prototype EIT system coupled with the mentioned VCCS, will be illustrated which proves the quality of the proposed current source.
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Affiliation(s)
- M Khalighi
- Biomedical Engineering Group, Department of Engineering, Shahed University, Tehran, Iran
| | - M Mikaeili
- Biomedical Engineering Group, Department of Engineering, Shahed University, Tehran, Iran
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7
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Zhang F, Teng Z, Zhong H, Yang Y, Li J, Sang J. Wideband mirrored current source design based on differential difference amplifier for electrical bioimpedance spectroscopy. Biomed Phys Eng Express 2018. [DOI: 10.1088/2057-1976/aaa9cd] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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8
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Han B, Xu Y, Dong F. Design of current source for multi-frequency simultaneous electrical impedance tomography. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017; 88:094709. [PMID: 28964244 DOI: 10.1063/1.5004185] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 09/11/2017] [Indexed: 06/07/2023]
Abstract
Multi-frequency electrical impedance tomography has been evolving from the frequency-sweep approach to the multi-frequency simultaneous measurement technique which can reduce measuring time and will be increasingly attractive for time-varying biological applications. The accuracy and stability of the current source are the key factors determining the quality of the image reconstruction. This article presents a field programmable gate array-based current source for a multi-frequency simultaneous electrical impedance tomography system. A novel current source circuit was realized by combining the classic current mirror based on the feedback amplifier AD844 with a differential topology. The optimal phase offsets of harmonic sinusoids were obtained through the crest factor analysis. The output characteristics of this current source were evaluated by simulation and actual measurement. The results include the following: (1) the output impedance was compared with one of the Howland pump circuit in simulation, showing comparable performance at low frequencies. However, the proposed current source makes lower demands for resistor tolerance but performs even better at high frequencies. (2) The output impedance in actual measurement below 200 kHz is above 1.3 MΩ and can reach 250 KΩ up to 1 MHz. (3) An experiment based on a biological RC model has been implemented. The mean error for the demodulated impedance amplitude and phase are 0.192% and 0.139°, respectively. Therefore, the proposed current source is wideband, biocompatible, and high precision, which demonstrates great potential to work as a sub-system in the multi-frequency electrical impedance tomography system.
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Affiliation(s)
- Bing Han
- Tianjin Key Laboratory of Process Measurement and Control, School of Electrical and Information Engineering, Tianjin University, Tianjin, People's Republic of China
| | - Yanbin Xu
- Tianjin Key Laboratory of Process Measurement and Control, School of Electrical and Information Engineering, Tianjin University, Tianjin, People's Republic of China
| | - Feng Dong
- Tianjin Key Laboratory of Process Measurement and Control, School of Electrical and Information Engineering, Tianjin University, Tianjin, People's Republic of China
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Yang Y, Wang L, Wang P, Yang X, Zhang F, Wen H, Teng Z. Design of tri-level excitation signals for broadband bioimpedance spectroscopy. Physiol Meas 2015; 36:1995-2007. [PMID: 26261063 DOI: 10.1088/0967-3334/36/9/1995] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Bioimpedance spectroscopy (BIS) measurement methods have been evolving from the traditional frequency-sweep approach to the multi-frequency simultaneous measurement technique which can drastically reduce measuring time and will be increasingly attractive for time-varying biological applications. Multi-frequency mixed (MFM) signals with sparsely distributed spectra are desirable for broadband BIS measurement. This paper proposes a synthesis method to design a series of tri-level MFM signals which contain only three values (+1, 0, -1), and has majority energy distributed on its (2(n))th primary harmonics. Tri-level MFM signals have both high energy efficiency and a low crest factor. An impedance measurement experiment excited by an 8th-order tri-level MFM signal on a RC three-element equivalent model has been performed, and the results on 8 primary harmonic frequencies ranging from 8 to 1024 kHz show a high accuracy with the mean amplitude relative error of 0.41% and mean phase absolute error of 0.18°, which has validated the feasibility of the tri-level MFM signals for broadband BIS measurement.
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Affiliation(s)
- Yuxiang Yang
- Department of Precision and Instrumentation Engineering, Xi'an University of Technology, Xi'an, People's Republic of China
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Dodde RE, Kruger GH, Shih AJ. Design of Bioimpedance Spectroscopy Instrument With Compensation Techniques for Soft Tissue Characterization. J Med Device 2015; 9:0210011-210018. [PMID: 26029317 PMCID: PMC4410770 DOI: 10.1115/1.4029706] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2014] [Revised: 01/22/2015] [Indexed: 11/08/2022] Open
Abstract
Bioimpedance spectroscopy (BIS) has shown significant potential in many areas of medicine to provide new physiologic markers. Several acute and chronic diseases are accompanied by changes in intra- and extracellular fluid within various areas of the human body. The estimation of fluid in various body compartments is therefore a simple and convenient method to monitor certain disease states. In this work, the design and evaluation of a BIS instrument are presented and three key areas of the development process investigated facilitating the BIS measurement of tissue hydration state. First, the benefit of incorporating DC-stabilizing circuitry to the standard modified Howland current pump (MHCP) is investigated to minimize the effect of DC offsets limiting the dynamic range of the system. Second, the influence of the distance between the bioimpedance probe and a high impedance material is investigated using finite element analysis (FEA). Third, an analytic compensation technique is presented to minimize the influence of parasitic capacitance. Finally, the overall experimental setup is evaluated through ex vivo BIS measurements of porcine spleen tissue and compared to published results. The DC-stabilizing circuit demonstrated its ability to maintain DC offsets at less than 650 μV through 100 kHz while maintaining an output impedance of 1 MΩ from 100 Hz to 100 kHz. The proximity of a bioimpedance probe to a high impedance material such as acrylic was shown to increase measured impedance readings by a factor of 4x as the ratio of the distance between the sensing electrodes to the distance between the bioimpedance probe and acrylic reached 1:3. The average parasitic capacitance for the circuit presented was found to be 712 ± 128 pF, and the analytic compensation method was shown to be able to minimize this effect on the BIS measurements. Measurements of porcine spleen tissue showed close correlation with experimental results reported in published articles. This research presents the successful design and evaluation of a BIS instrument. Specifically, robust measurements were obtained by implementing a DC-stabilized current source, investigating probe-material proximity issues and compensating for parasitic capacitance. These strategies were shown to provide tissue measurements comparable with published literature.
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Affiliation(s)
- Robert E Dodde
- Stryker Corporation , 4100 E. Milham Avenue, Kalamazoo, MI 49001 e-mail:
| | - Grant H Kruger
- Mechanical Engineering, University of Michigan , 1031 H.H. Dow Building, 2350 Hayward Street, Ann Arbor, MI 48109 e-mail:
| | - Albert J Shih
- Mechanical Engineering, University of Michigan , 3001E EECS, 1301 Beal, Ann Arbor, MI 48109 e-mail:
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11
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Yang Y, Zhang F, Tao K, Wang L, Wen H, Teng Z. Multi-frequency simultaneous measurement of bioimpedance spectroscopy based on a low crest factor multisine excitation. Physiol Meas 2015; 36:489-501. [PMID: 25679488 DOI: 10.1088/0967-3334/36/3/489] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Bioimpedance spectroscopy (BIS) is becoming a powerful diagnostic tool for a wide variety of medical applications, and the multi-frequency simultaneous (MFS) measurement of BIS can greatly reduce measurement time and record the transient physiological status of a living body compared with traditional frequency-sweep measurement technology. This paper adopts the Van der Ouderaa's multisine, which has 31 equidistant and flat amplitude spectra and a low crest factor of 1.405 as the broadband excitation, and realizes the MFS measurement of BIS by means of spectral analysis using the fast Fourier transform algorithm. The approach to implement the multisine based on a field-programmable gate array and a digital to analog converter is described in detail, and impedance measurement experiments are performed on three resistance-capitance three-element phantoms. Experimental results show a commendable accuracy with a mean relative error of 0.55% for the impedance amplitudes, and a mean absolute error of 0.20° for the impedance phases on the 31 frequencies ranging linearly from 32 to 992 kHz. This paper validates the feasibility of the MFS technology for BIS measurement based on the multisine excitation.
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Affiliation(s)
- Yuxiang Yang
- Department of Precision Instrumentation Engineering, Xi'an University of Technology, Xi'an, People's Republic of China
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12
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Chen J, Cai J, Hu H, Huang X, Yi T, Wang K, Pan S. A dielectric loss angle based portable biosensor system for bacterial concentration detection. RSC Adv 2015. [DOI: 10.1039/c5ra13055g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A new type of portable sensor is proposed to detect bacterial concentration based on the change in dielectric loss angleδ.
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Affiliation(s)
- Jingyao Chen
- College of Food Science and Technology
- Huazhong Agricultural University
- Wuhan 430070
- China
| | - Jie Cai
- College of Food Science and Engineering
- Wuhan Polytechnic University
- Wuhan 430023
- China
| | - Hao Hu
- College of Food Science and Technology
- Huazhong Agricultural University
- Wuhan 430070
- China
| | - Xingjian Huang
- College of Food Science and Technology
- Huazhong Agricultural University
- Wuhan 430070
- China
| | - Tian Yi
- Hubei Academy of Agricultural Sciences
- Wuhan 430064
- China
| | - Kexing Wang
- College of Food Science and Technology
- Huazhong Agricultural University
- Wuhan 430070
- China
| | - Siyi Pan
- College of Food Science and Technology
- Huazhong Agricultural University
- Wuhan 430070
- China
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13
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Development of a stair-step multifrequency synchronized excitation signal for fast bioimpedance spectroscopy. BIOMED RESEARCH INTERNATIONAL 2014; 2014:143461. [PMID: 24701563 PMCID: PMC3950401 DOI: 10.1155/2014/143461] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 01/08/2014] [Accepted: 01/08/2014] [Indexed: 12/04/2022]
Abstract
Wideband excitation signal with finite prominent harmonic components is desirable for fast bioimpedance spectroscopy (BIS) measurements. This work introduces a simple method to synthesize and realize a type of periodical stair-step multifrequency synchronized (MFS) signal. The Fourier series analysis shows that the p-order MFS signal f(p, t) has constant 81.06% energy distributed equally on its p 2nth primary harmonics. The synthesis principle is described firstly and then two examples of the 4-order and 5-order MFS signals, f(4, t) and f(5, t), are synthesized. The method to implement the MFS waveform based on a field-programmable gate array (FPGA) and a digital to analog converter (DAC) is also presented. Both the number and the frequencies of the expected primary harmonics can be adjusted as needed. An impedance measurement experiment on a RC three-element equivalent model is performed, and results show acceptable precision, which validates the feasibility of the MFS excitation.
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14
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Sanchez B, Louarroudi E, Bragos R, Pintelon R. Harmonic impedance spectra identification from time-varying bioimpedance: theory and validation. Physiol Meas 2013; 34:1217-38. [DOI: 10.1088/0967-3334/34/10/1217] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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15
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Pliquett U, Schönfeldt M, Barthel A, Frense D, Nacke T, Beckmann D. Front end with offset-free symmetrical current source optimized for time domain impedance spectroscopy. Physiol Meas 2011; 32:927-44. [PMID: 21646715 DOI: 10.1088/0967-3334/32/7/s15] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Fast impedance measurements are often performed in time domain utilizing broad bandwidth excitation signals. Other than in frequency domain measurements harmonic distortion cannot be compensated which requires careful design of the analog front end. In order to minimize the influence of electrode polarization and noise, especially in low-frequency measurements, current injection shows several advantages compared to voltage application. Here, we show an active front end based on a voltage-controlled current source for a wide range of impedances. Using proper feedback, the majority of the parasitic capacitances are compensated. The bandwidth ranges from dc to 20 MHz for impedance magnitude below 5 kΩ. The output is a symmetric signal without dc-offset which is accomplished by combination of a current conveyor and a voltage inverter. An independent feedback loop compensates the offset arising from asymmetries within the circuitry. We focused especially on the stability of the current source for usage with small metal electrodes in aqueous solutions. At the monitor side two identical, high input impedance difference amplifiers convert the net current through the object and the voltage dropping across into a 50 Ω symmetric output. The entire circuitry is optimized for step response making it suitable for fast time domain measurements.
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Affiliation(s)
- Uwe Pliquett
- Institut für Bioprozess- und Analysenmesstechnik eV, Rosenhof D-37308 Heilbad Heiligenstadt, Germany.
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16
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17
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Rafiei-Naeini M, McCann H. Low-noise current excitation sub-system for medical EIT. Physiol Meas 2008; 29:S173-84. [DOI: 10.1088/0967-3334/29/6/s15] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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18
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Murthy OVSN, Venkataraman V. Construction and calibration of a 12 T pulsed magnet integrated with a 4 K closed-cycle refrigerator. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2007; 78:113905. [PMID: 18052486 DOI: 10.1063/1.2813884] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A low cost 12 T pulsed magnet system has been integrated with a closed-cycle helium refrigerator for performing magnetotransport measurements. Minimal delay between pulses and ac current excitation with software lock-in to reduce noise enables quick but accurate measurements to be performed at temperatures of 4-300 K up to 12 T. An additional pulsed magnet operating with a liquid nitrogen cryostat extends the range up to 19 T. The instrument has been calibrated against a commercial superconducting magnet by comparing quantum Hall effect data in a p-channel SiGe/Si heterostructure, and common issues arising out of pulsed magnet usage have been addressed. The versatility of the system is demonstrated through magnetotransport measurements in a variety of samples such as heterostructures, narrow gap semiconductors, and those exhibiting giant magnetoresistance.
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Affiliation(s)
- O V S N Murthy
- Department of Physics, Indian Institute of Science, Bangalore 560012, India.
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Yang Y, Wang J, Yu G, Niu F, He P. Design and preliminary evaluation of a portable device for the measurement of bioimpedance spectroscopy. Physiol Meas 2006; 27:1293-310. [PMID: 17135701 DOI: 10.1088/0967-3334/27/12/004] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Portable bioimpedance spectroscopy (BIS) devices are of great value for monitoring the pathological status of biological tissues in clinical and home environments. The two traditional techniques for measuring complex bioimpedance, the bridge method and quadrature demodulation method, are either time-consuming or often associated with high cost, high power consumption, and large board space, and therefore are not ideally suitable for designing a portable device for BIS measurement. This paper describes a novel design of a portable BIS device based on the magnitude-ratio and phase-difference detection method and its implementation using the newest generation of analog electronic products which greatly decrease the complexity of both hardware and software. In order to improve the accuracy of the device, a three-reference calibration algorithm was applied. Experimental sweep-frequency measurements on RC circuits were carried out to preliminarily evaluate the performances of the device. The results obtained by the device were found to be in good agreement with the results measured by a commercial impedance analyzer HP4194, with an overall mean error of 0.014% in magnitude and 0.136 degrees in phase over a frequency range of 20 kHz to 1 MHz.
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Affiliation(s)
- Yuxiang Yang
- Key Laboratory of Biomedical Information Engineering of Education Ministry, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
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20
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Bertemes-Filho P, Brown BH, Wilson AJ. A comparison of modified Howland circuits as current generators with current mirror type circuits. Physiol Meas 2000; 21:1-6. [PMID: 10719993 DOI: 10.1088/0967-3334/21/1/301] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Multi-frequency electrical impedance tomography (EIT) systems require stable voltage controlled current generators that will work over a wide frequency range and with a large variation in load impedance. In this paper we compare the performance of two commonly used designs: the first is a modified Howland circuit whilst the second is based on a current mirror. The output current and the output impedance of both circuits were determined through PSPICE simulation and through measurement. Both circuits were stable over the frequency ranges 1 kHz to 1 MHz. The maximum variation of output current with frequency for the modified Howland circuit was 2.0% and for the circuit based on a current mirror 1.6%. The output impedance for both circuits was greater than 100 kohms for frequencies up to 100 kHz. However, neither circuit achieved this output impedance at 1 MHz. Comparing the results from the two circuits suggests that there is little to choose between them in terms of a practical implementation.
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Affiliation(s)
- P Bertemes-Filho
- Department of Medical Physics and Clinical Engineering, Royal Hallamshire Hospital, University of Sheffield, UK.
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21
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Boone K, Barber D, Brown B. Imaging with electricity: report of the European Concerted Action on Impedance Tomography. J Med Eng Technol 1997; 21:201-32. [PMID: 9429132 DOI: 10.3109/03091909709070013] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- K Boone
- University College, London, UK
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22
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Casas O, Rosell J, Bragós R, Lozano A, Riu PJ. A parallel broadband real-time system for electrical impedance tomography. Physiol Meas 1996; 17 Suppl 4A:A1-6. [PMID: 9001596 DOI: 10.1088/0967-3334/17/4a/002] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
This paper deals with the design, implementation and performance of TIE-4sys, an electrical impedance tomograph. This instrument is a parallel broad-band real-time system. It measures impedance using an array of 16 electrodes and reconstructs the images using a weighted back-projection technique. The objective of this development is to enable multifrequency EIT clinical studies to be undertaken. The system is capable of acquiring 25 frames/s and makes multifrequency cardiac-gated images. The frequency range is from 10 kHz to 250 kHz and the signal to noise ratio for the real component is better than 60 dB.
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Affiliation(s)
- O Casas
- Department d'Enginyeria Electrònica, Universitat Politècnica de Catalunya, Barcelona, Spain
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Boone KG, Holder DS. Current approaches to analogue instrumentation design in electrical impedance tomography. Physiol Meas 1996; 17:229-47. [PMID: 8953622 DOI: 10.1088/0967-3334/17/4/001] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Electrical impedance tomography (EIT) is a novel medical imaging method, which allows reconstructed tomographic images of the internal impedance of a subject to be made with the use of a ring of electrodes. High precision impedance measurements are needed, because the image reconstruction process is ill-conditioned and small errors in measurement can lead to large errors in the final image. In practice, there are formidable instrumentation problems, due to the interaction of finite current drive output impedance, recording amplifier common mode rejection, and unequal skin-electrode impedances. A number of different EIT systems have been constructed or are under development. These employ differing strategies, such as additional electrodes, multiple electrode current injection, or recording at multiple frequencies, to improve image accuracy. This paper reviews the nature of the instrumentation problems and the designs employed by differing groups in attempting to overcome them.
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