Front-end architecture for a multi-frequency electrical impedance tomography system

This paper provides a critical review of a number of the primary aspects of EIT system hardware presented in the literature. A thorough analysis of injection and measurement errors is presented to provide clarifying extensions to that provided by previous authors. From this basis, it proposes a novel design for a distributed parallel multi-frequency EIT system. The system described is modular, employs active electrodes to maximise CMRR (common mode rejection ratio) and was designed to employ digitally generated current injection and digital demodulation of the acquired signals.     

Design of an electrical impedance tomography phantom using active elements

The architecture of a novel phantom for electrical impedance tomography (EIT) is proposed. The design employs active elements, which include multiplying digital to analogue converters (MDAC), so that the impedance distribution in the phantom may be varied dynamically using computer control. The phantom is designed to assist in the validation of an EIT system under test. A number of published layouts for passive phantoms are analysed, and the requirements for an active element are specified for the most applicable of these. The use of active elements throughout a phantom imposes significant costs because of the need for each active element to operate independently. This proposal limits the cost and complexity by employing active elements in a restricted region of the phantom. Currently available technology, principally due to the limited analogue bandwidth of the MDAC, precludes the construction of a fully capable phantom from active elements. However, a design is specified that would enable its future development to cover the frequency range from 10kHz to 1 MHz.     

医学EIT复合电极结构参数优化设计

目的探索医学EIT复合电极结构参数变化对系统性能的影响。方法采用笔者建立的EIT电极结构及参数优化设计方法对复合电极进行了仿真研究，研究了位于成像区域不同位置的成像目标，复合电极各结构参数改变对成像质量和系统检测灵敏度影响的规律。结果和结论各结构参数的影响错综复杂，采用多参数仿真实验的方法是一种有效的方法。     

Electrical impedance tomography (EIT) of brain function

Summary Electrical impedance tomography (EIT) is a recently developed technique which enables the internal impedance of an object to be imaged non-invasively. Images are at present reconstructed from measurements made at 51 kHz with a ring of sixteen electrodes placed around the subject. A minimum data set is acquired in 40 msec, and an image can be reconstructed in about 5 sec. The technique is rapid, safe, portable and inexpensive, and so is ideal for non-invasive continuous imaging at the bedside. It cannot be used at present to image changes in the brain with scalp electrodes, as the relative resistance of the skull is too great. It should be possible to use it in the near future with a ring of subdural electrodes to produce images of brain regions undergoing anoxic depolarization in conditions such as epilepsy or stroke. It may be possible to use it in the future to image impedance changes related either to blood flow or depolarization during functional activity. Images of depolarization could be produced with a temporal resolution of milliseconds and would form a substantial advance in neuroscience methodology.     

Effect of skin impedance on image quality and variability in electrical impedance tomography: a model study

A computer simulation is used to investigate the relationship between skin impedance and image artefacts in electrical impedance tomography. Sets of electrode impedance are generated with a pseudo-random distribution and used to introduce errors in boundary voltage measurements. To simplify the analysis, the non-idealities in the current injection circuit are replaced by a fixed common-mode error term. The boundary voltages are reconstructed into images and inspected. Where the simulated skin impedance remains constant between measurements, large impedances (>2kΩ) do not cause significant degradation of the image. Where the skin impedances ‘drift’ between measurements, a drift of 5% from a starting impedance of 100Ω is sufficient to cause significant image distortion. If the skin impedances vary randomly between measurements, they have to be less than 10 Ω to allow satisfactory images. Skin impedances are typically 100–200 Ω at 50 kHz on unprepared skin. These values are sufficient to cause image distortion if they drift over time. It is concluded that the patient's skin should be abraded to reduce impedance, and measurements should be avoided in the first 10 min after electrode placement.     

Simplified electrode array for impedance cardiography

Impedance cardiography has enjoyed widespread interest owing to the promise of noninvasive monitoring of cardiac function. In clinical practice, one factor limiting its use has been the need to use circumferential electrodes. These electrodes can be inconvenient to apply, may interfere with chest tubes or intravenous lines, and can cause additional apprehension in critically ill patients. The paper describes a more convenient electrode array. It uses four disposable electrocardiographic electrodes, two on the base of the neck and two on the lower left, anterolateral surface of the thorax. Simultaneous impedance derivative recordings were made with this ‘spot’ electrode array and with the conventional ‘band’ electrode array, at rest and after exercise on ten normal volunteers. On a given individual, the two signals had shapes which were remarkably similar and relative heights which correlated well, exhibiting correlation coefficients (r′) between 0·77 and 0·98. This new array should facilitate impedance cardiographic measurements in the clinical setting.     

Controlled metallic nanopillars for low impedance biomedical electrode

Radial metallic nanopillar/nanowire structures can be created by a controlled radiofrequency (RF) plasma processing technique on the surface of certain alloy wires, including important biomedical alloys such as MP35N (Co–Ni–Cr–Mo alloy), platinum–iridium and stainless steel. In electrode applications such as pacemakers or neural stimulators, the increase in surface area in elongated MP35N nanopillars allows for decreased surface impedance and greater current density. However, the nanopillar height on MP35N alloy tends to be self-limiting at ∼1–3 μm. The objective of this study was to further elongate the radial nanopillars so as to reduce electrode impedance for biomedical electrode applications. Intelligent experimental design allowed for efficient investigation of processing parameters, including plasma material, process duration, power, pressure and repetition. It was found that multi-step repeated processing in the parameter-controlled RF environment could increase nanopillar height to ∼10 μm, a 400% improvement, while the RF plasma processing with identical total duration but in a single step did not lead to desired nanopillar elongation. Measurement of electrode impedance in phosphate-buffered saline solution showed an associated decrease to one-fifth of the surface impedance of unprocessed wire for signals below 100 Hz. For the purposes of this study, MP35N and Pt–Ir wires were characterized and demonstrated augmented surface impedance properties which, in combination with superior cell integration, enhanced biomedical electrode performance.     

多频电阻抗成像中的硬件系统

本文回顾了多频电阻抗成像技术的发展历史及现状 ,指出了其研究意义。对现有的多频电阻抗成像的硬件系统主要采用的技术进行了介绍 ,分析了各种技术的优缺点。最后总结了硬件系统可能的研究方向。     

电阻抗成像监护家兔腹内出血的实验研究

目的 为腹腔内出血监护研究建立一种家兔动物模型。通过对家兔腹腔内出血动物模型进行的监护实验，检验一种新研制的腹部出血电阻抗成像监护系统（EIT腹腔内出血监护系统）的成像效果。方法 ①应用专用撞击器对家兔肝外部进行撞击，制作家兔腹内出血动物模型。②用EIT对撞击后的家兔进行监护成像，检验实际成像效果。结果 ①15只家兔被撞击后，均发生了肝出血，出血率为100％，出血量在35—50ml之间，15只家兔均在被撞击后存活3h以上。②EIT腹腔内出血监护系统成像清楚，出血与未出血图像比较反差很大，图像对比度明显，并随出血量的增多图像最小灰度值明显变小。结论 ①家兔腹腔出血动物模型的建立是成功的。②EIT腹腔内出血监护系统成像结果较为清晰，对比明显。     

感应电流电阻抗成像的硬件系统

本文回顾了感应电流电阻抗成像技术的发展历史及现状 ,指出了其研究意义。对感应电流电阻抗成像的硬件系统主要采用的技术进行了介绍 ,并讨论了研究中存在的关键问题。最后总结了今后工作可能的研究方向     

Microcomputer-based respiratory function monitoring system using impedance pneumography

Although information concerned with ventilatory dynamics is indispensable, especially with regard to the care of a critically ill patient, the data available is often very limited, because the currently used methods of ascertaining data are invasive and not tolerable for patients who are still conscious and neither intubated nor tracheotomised. From this viewpoint, a respiratory function monitoring system was developed, using a non-invasive ventilatory volume monitor based on the electrical impedance method as a key component. The system is composed of two ventilatory volume monitors connected to two patients and a central monitor. The central monitor acquires online data transmitted from ventilatory volume monitors and stores then in floppy-disc memory together with off-line data, such as blood gases, blood chemistry and urine volume. These data may be retrieved and displayed on a visual display unit in the form of tables, trend graphs or specially designed graphs. Hard copies can be made on demand. According to the accumulated results obtained from respiratory failure patients, it is now clear that the introduction of the system into medical practice would facilitate more accurate analysis of respiratory and circulatory pathophysiology for the type of patient mentioned. Furthermore, the physical responses to various respiratory and circulatory treatments can be obtained in more detail and the course of these patients' illness can be reviewed more systematically.     

Parametric modelling for electrical impedance spectroscopy system

Three parametric modelling approaches based on the Cole-Cole model are introduced. Comparison between modelling only the real part and modelling both the real and imaginary parts is carried out by simulations, in which random and systematic noise are considered, respectively. The results of modelling the in vitro data collected from sheep are given to reach the conclusions.     

Comparison of a three‐quarter electrode band configuration with a full electrode band configuration for impedance cardiography

Impedance cardiography is a technique commonly used in psychophysiological studies. However, concerns about the utility of full circumferential band electrodes (FB) have been raised. The current study was designed to compare FB with a three‐quarter circumferential band configuration (PB). A total of 47 participants (66% female, mean [SD] age=20.4 [3.0] years) underwent 2 testing sessions, once using FB and once using PB. Session order was randomized and balanced. Each session consisted of 5 min of rest, math task, recovery, and cold pressor test. Average baseline and task pre‐ejection period (PEP), stroke volume (SV), cardiac output (CO), heart rate (HR), blood pressure (BP), and total peripheral resistance (TPR) was calculated from impedance cardiography and blood pressure monitoring. Participants were are asked to rate measures of comfort after each session. There were no significant difference between the mean levels of PEP, SV, CO, HR, and TPR for the PB versus the FB configurations. However, both systolic BP and diastolic BP were higher during the FB session. Intraclass correlations were high (r_icc=.63–.93) between PB and FB. Bland‐Altman analyses revealed a low level of bias (≤5%) between the configurations. Based on limits of agreement between ±30%, there was equivalence in PEP between the 2 configurations, and SV, CO, and TPR were close to reaching equivalence. Participants clearly indicated greater comfort with the PB configuration compared to the FB. The current study provides incremental evidence that suggests a three‐quarter PB configuration may be utilized for standard psychophysiological testing instead of the standard FB configuration. However, further studies are needed to validate the PB configuration against other techniques.     

非接触磁感应脑阻抗断层成像系统设计

针对脑组织电阻抗的研究，本文设计了工作频率在10MHz的单通道硬件电路和试验台，可以分辨电导率介于0．001s/m到6s/m的四种不同浓度的NaCl盐溶液，并对模拟正常人脑组织（0．375s/m）的0．195％NaCl盐溶液目标，给出了初步成像结果。