Multi-frequency static imaging in electrical impedance tomography: Part 1 instrumentation requirements

Static images of the human body using electrical impedance tomography techniques can be obtained by measuring at two or more different frequencies. The frequencies used depend on the application, and their selection depends on the frequency behaviour of the impedance for the target tissue. An analysis using available data and theoretical models for tissue impedance yields the expected impedance and boundary voltage changes, therefore setting the measurement instrument specifications. The instrument errors produced by different sources are analysed, and, from this analysis it is possible to determine the feasibility of building the instrument, the limit values for some parameters (or components) and indications on the most suitable design of critical parts. This analysis also shows what kinds of error can be expected in the reconstructed images. It is concluded that it is possible to build an instrument with limited errors, allowing static images to be obtained. An instrument has been built that meets some of the design requirements and fails in others because of technological problems. In vivo images obtained with this instrument will be presented in Part 2 of this work.     

Microprocessor-based system for measurement of electrical impedances during haemodialysis and in postoperative care

The paper describes an instrument designed for accurate measurement of the mean specific electrical impedance of tissue. Two basic measurements are possible. One implementation called tetrapolar impedance plethysmography is employed for investigation with respect to transcellular fluid shifts during haemodialysis. The other measuring configuration called differential tetrapolar impedance plethysmography, deals with measurement of intrathoracic fluid content, which is important in monitoring treatment and prevention of lung oedema. An alternating current of 1 mA is passed through the tissue at different frequencies. Two measuring channels are available for differential tetrapolar measurement. Only one channel is required for straightforward tetrapolar measurement. Recovery of the impedance signals is achieved by synchronous demodulation. The impedance signal is passed through an analogue-to-digital convertor for digital processing to estimate the specific impedance in case of a differential tetrapolar measurement. Output display is possible via an xy recorder. The design of the instrument is discussed and some results shown.     

Biomechanical and reflex responses to joint perturbations during electrical stimulation of muscle: instrumentation and measurement techniques

A test device is developed to measure ankle joint compliance and muscle activity when the ankle is subjected to perturbations in angular position (or torque) from bias positions achieved volitionally or via electrical stimulation. The ankle measurement system uses a pivoting footplate and is operable with the subject sitting or supine. A companion platform for the knee is developed that uses a rotary arm and attached leg brace and is operable with the subject’s leg in the horizontal or vertical plane. The knee fixture’s pivoting arm can slide to account for the cam-like movement of the knee during rotation. The devices use similar hardware and share common instrumentation and control. Precise torque or position perturbations are delivered by a computer-controlled torque motor to the ankle or knee. Angular displacement, torque, acceleration, knee fixture moment arm and electromyographic data are collected on analogue tape and simultaneously digitised and stored. A special stimulator/recording amplifier permits the recording of electromyographic signals from the stimulated muscle. Experimental data indicate that the ankle and knee devices, operated horizontally, are purely inertial systems. Sample ankle and knee joint responses to perturbations are presented.     

Value of the cumulative sum test for the assessment of a learning curve: Application to the introduction of patient-specific instrumentation for total knee arthroplasty in an academic department

Background

The purpose of the study was to use the cumulative summation (CUSUM) test to assess the learning curve during the introduction of a new surgical technique (patient-specific instrumentation) in total knee arthroplasty (TKA) in an academic department.

PID算法在温控医疗仪器上的应用

在微机应用系统中，使用ＰＩＤ算法实现参数控制，可以取得快速、精确的控制效果。本文通过一种医用温控装置，介绍ＰＩＤ算法在这方面的应用。在硬件上还扼要介绍了晶闸管的温控原理。     

阿托伐他汀对快速起搏兔房颤模型心房电重构的影响

 目的: 观察阿托伐他汀(ATO)对快速起搏兔房颤模型心房电重构、心房肌离子通道蛋白及心脏功能的影响,探讨阿托伐他汀防治心房颤动的电生理机制。方法: 30只新西兰大白兔开胸植入心房起搏和测试电极,采用特制动物心脏起搏器快速起搏心房的方法建立兔房颤模型,将其分为对照组、起搏组和药物组。药物组预先给予阿托伐汀钙片2 mg·kg^-1·d^-1灌胃7 d,起搏组和药物组快速起搏心房48 h,期间药物组持续给药处理,分别于0 h、8 h、16 h、24 h、32 h、40 h、48 h测量心房有效不应期,计算心房频率适应性,观察心脏大小及心功能的变化,比较各组心房肌细胞离子通道蛋白CaLα1和Kv4.3的表达差异。结果: 与对照组相比,药物组和起搏组心房有效不应期缩短,频率适应性下降,心房肌细胞离子通道蛋白CaLα1及Kv4.3表达水平降低(P<0.05),其中以起搏组变化最为明显。快速起搏心房48 h后,起搏组和药物组左房较对照组增大(P<0.05),而左心室大小及射血分数起搏前后均无明显差异。结论: 短期快速心房起搏可引起心房有效不应期缩短,导致心房频率适应性不良,阿托伐他汀预处理可有效改善快速起搏诱导的兔心房电重构,而对心脏结构影响不大。进一步研究发现阿托伐他汀可在一定程度上抑制心房肌钾、钙离子通道蛋白水平降低,这可能是其改善电重构的机制之一。     

Characterization and control of muscle response to electrical stimulation

The maintenance of upright posture in neurologically intact human subjects is mediated by two major nervous pathways. The first, leading from the cerebral cortex through the spinal cord to motor neurons, activates muscles which produce postural movements. The second, leading from various sensory organs to higher centers, provides sensory feedback regarding the postural state. The path through the spinal cord is no longer intact in victims of spinal cord injury and loss of normal control of muscle activity results. Functional neuromuscular stimulation (FNS) has been shown as a feasible method for obtaining muscle contraction in paraplegic and has been proposed as a means for control of antero-posterior sway to make upright posture possible for these individuals. Before muscle can be controlled through the use of FNS, the response of muscle to electrical stimulation must be understood. In past studies, linear control theory has been applied to the analysis of this response and to the testing of various controllers. The aim of this study was to demonstrate some control issues in FNS using linear control theory, as it applies to electrical stimulation of muscle for stabilization of posture. The linearity of the muscle response was improved through closed-loop control using pole compensation techniques. The excess phase shift of the system due to the time delay in the muscle response, however, limits the ability to increase the open-loop gain in order to obtain improved performance. A suggestion for further study is the application of this methodology for uses in posture control.     

Design of affordable and ruggedized biomedical devices using virtual instrumentation

Abstract

This paper presents the designs of four low-cost and ruggedized biomedical devices, including a blood pressure monitor, thermometer, weighing scale and spirometer, designed for the East African context. The design constraints included a mass-production price point of $10, accuracy and precision comparable to commercial devices and ruggedness to function effectively in the harsh environment of East Africa. The blood pressure device, thermometer and weighing scale were field-tested in Kenya and each recorded data within 6% error of the measurements from commercial devices and withstood the adverse climate and rough handling. The spirometer functioned according to specifications, but a re-design is needed to improve operability and usability by patients. This article demonstrates the feasibility of designing and commercializing virtual instrumentation-based biomedical devices in resource-constrained environments through context-driven design. The next steps for the devices include designing them such that they can be more easily manufactured, use standardized materials, are easily calibrated in the field and have more user-friendly software programs that can be updated remotely.     

Modified cell proliferation due to electrical currents

In view of the evidence that electrical currents may enhance healing of chronic wounds and retard tumour growth it is suggested that these currents normalise cell proliferation. Additional support to this contention is given by two reports: one on healing of pressure sores in man and one on tumour growth retardation in mice. The effect of an ionic environment on the cell cycle is analysed. Finally a hypothesis attempting to explain the normalising effect of electrical currents on cell proliferation is proposed. It is known that non-dividing cells, e.g. mature neurons, have high transmembrane potential (TMP) whereas fast-dividing cells, e.g. cancerous cells, have low TMP. When a cell is exposed to an electrical field, one side of the cell becomes hyperpolarised while the opposite side is depolarised. Assuming a nonlinear relationship between TMP and the transmembrane ionic currents, it can be shown that in non-dividing cells their high TMP is lowered; whereas in cells with a high division rate, their low TMP is raised due to cell exposure to the external electrical field. These alterations in transmembrane potential could contribute to the normalisation of abnormal cell proliferation.     

Variations inin vivo electrical impedance tomography images due to inaccuracy in boundary representation

A comparison of in vivo image results is performed for five image-reconstruction programs, featuring an increase in accuracy of boundary modelling from a simple 2-D disk to a true boundary shape with each current drive field individually calculated. Variations are found both in the positions of imaged features and their appearance, but reasonable consistency in reconstructed impedance changes is obtained for both phantom and in vivo data. In terms of quantitative measurements, the programs based on the simpler boundary assumptions generally perform more reliably than the more complex versions. It is concluded that the quantitative use of EIT with simple boundary assumptions is not compromised by body contour variations between patients, provided that the appropriate regions of interest can be correctly identified.     

An electrical analogue of a variable compliance

An electrical circuit which simulates a variable compliance is introduced and analysed. The circuit is simple, accurate and inexpensive. It can be used to demonstrate or study the physics of a nonlinear or time-variable compliance. Total arterial compliance is used as an example. Because of its simple structure, the circuit is also ideally suited to be implemented as a building block in a larger electrical model of the cardiovascular system.     

脊柱结核一期病灶清除植骨内固定术的疗效观察

目的探讨不同节段脊柱结核外科治疗的手术策略及内固定方法的选择。方法回顾性分析2004年10月～2006年12月期间接受病灶清除、植骨融合及内固定手术治疗并获得随访的60例脊柱结核患者的临床资料,观察术后患者结核中毒症状和神经功能的改善情况,以及脊柱稳定情况及植骨成活率。结果所有患者术后结核中毒症状明显缓解或消失,神经功能明显改善,脊柱稳定性及植骨成活率显著提高,平均5个月时植骨融合,无内固定物松动、断裂,椎体高度无丢失,脊往后凸畸形改善,平均矫正角度10°。结论脊柱结核一期病灶清除植骨内固定术是安全、有效的,手术策略的制定和内固定的选择应根据病变节段、脓肿大小、范围等综合判断。     

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.     

术中直接皮层电刺激判断大脑功能区在胶质瘤切除术中的应用

目的:试用术中直接电刺激判断大脑功能区的位置和范围的方法,以求术中最大程度切除肿瘤,减少神经系统损伤。方法:对唤醒麻醉下手术切除优势半球语言区胶质瘤患者26例以及邻近或累及脑运动功能区胶质瘤患者26例,在术中直接行皮层刺激,判断功能区的位置和肿瘤的关系。结果:患者在唤醒麻醉下,利用直接皮质电刺激可以准确定位初级运动皮质区和语言功能区,术后患者Karnofsky生活状态(KPS)评分结果较术前提高。结论:在唤醒麻醉下,可检测到患者的运动和语言的脑功能区,并可判断与肿瘤位置的关系。术中采用直接皮质电刺激可定位脑重要功能区,能最大限度地切除病变,最大限度地保护脑功能区。     

电刺激效应在血管新生中的作用

人体生命活动的不断延续,往往伴随着生物电现象的产生,一旦这种电生理环境发生改变,机体易于陷入疾病状态。那么基于这种电生理环境的改变以及电刺激技术的发展,借助电刺激技术改变疾病状态。从而修复机体结构和功能的治疗手段得到大量研究者的证实。血管新生是一个多因素参与、多步骤演变的过程。多种病变情况下如创伤愈合、组织再生修复和肿瘤生长、转移均牵涉到血管的新生,同时也伴随着生物电现象的变化。就近年来电刺激技术作用于血管新生的研究进展作一综述。     

Failure to detect infectious hepatitis b virus using high dose safety test for hepatitis b vaccine

One hundred milliliters of an inactivated hepatitis B vaccine (20 /m?g/ml) were inoculated intravenously into two colony-born infant chimpanzees. Immediately thereafter each received hepatitis B virus from a documented infectious inoculum intravenously at a separate site. Neither chimpanzee developed elevation of aminotransferase levels, hepatitis B surface antigen (HBsAg), or antibody to hepatitis B core antigen during six months of evaluation, the duration of the currently recommended safety test. Both chimpanzees developed antibody to HBsAg beginning 8 and 9 weeks, respectively, after inoculation. The administration of a large intravenous quantity of vaccine antigen thus appeared capable of masking or preventing infection by simultaneously administered hepatitis B virus. This study suggests that a chimpanzee safety test for hepatitis B vaccine should not employ large quantities of vaccine antigen, since such a safety test may fail to detect small amounts of residual infectious hepatitis B virus.