Methods of complex impedance measurements in biologic tissue

Bioelectric impedance measurements have been used to monitor a variety of physiologic events. While important insights have been gained and useful techniques developed, there are a number of limitations to the methods usually employed. Among these are the inability to define current pathways in complex systems and the inability to distinguish between volumetric changes and materials property changes. Methods that have been used successfully in materials science can be used to address these limitations: these methods involve measurements of both real and reactive components over a wide frequency range coupled with various plotting and analytic techniques. Accurate measurement of the reactive component is inherently difficult since biologic systems are highly conductive. In addition, safety considerations have generally limited bioelectric impedance measurements in humans to frequencies above 20 kHz. For these reasons the techniques have not been widely applied in vivo; however, the techniques have been used in studies of cell suspensions and biologic tissue. This paper reviews these applications, summarizes the theory from a materials science viewpoint, discusses the instrumentation considerations for extension of the techniques to other studies, and presents more recent applications.     

Numerical considerations for interface reflections in medical ultrasound

The original concept of the echo mechanism in diagnostic medical ultrasound--of step impedance discontinuities--is investigated in terms of the numerical implications of more refined models. The effect of a discontinuity in the attenuation coefficients is found to have as much significance as the impedance discontinuity at low reflection interfaces. An approximate analytical model is developed for spatially varying changes in the impedance. Numerical calculations are presented for reflections from delta-function and Gaussian-envelope RF pulses for two different models: an impedance gradient, and a connective tissue layer. The models used are well documented in acoustics textbooks, but the numerical results for typical tissue parameters show that a wide variety of interface structures may give rise to reflected amplitudes in the same range as that determined by the step impedance model. It is suggested that experimental investigation of interface structures may increase our understanding of the tissue: ultrasound interaction in diagnostic processes.     

A critique of impedance measurements in cardiac tissue

The specific impedance of cardiac tissue cannot be measured directly. Instead, the investigator obtains voltage and current measurements and places them into a model of the tissue's structure to infer the impedances of elements of the model. If the model fails to describe major aspects of the real tissue, the results may be worthless, although possibly self-consistent. In the literature of impedance measurement in cardiac tissue, only rarely is the model explicitly described; more commonly, the tissue model is adopted implicitly when equations giving the impedance in terms of voltage and current measurements are adopted. This paper examines the series of models that have been used in specific impedance measurements of cardiac tissue and shows how the same or similar measurements can accurately describe tissue impedivity or can lead to significant errors when inadequate models such as isotropic and anisotropic monodomains (although a part of work of historical merit) are used.     

Pathology of soft tissue sarcomas. Selected current issues

Soft tissue sarcomas are a heterogeneous group of malignant tumors with a wide range of clinical presentation, morphologic features and biologic behavior. During the past two decades, many acceptable new entities have been proposed, and the diagnosis and classification of these tumors have been modified. This paper reviews several current issues that are considered worthy of note for the histologic diagnosis of soft tissue sarcomas.     

双通道血流容积测量系统的设计与实现

本文介绍了双通道血流容积测量系统的设计与实现.系统包括硬件与软件两个部分.硬件部分主要功能是采用双通道直接式电路阻抗法测量生物体受检部位的基础阻抗Z0和反应血流容积变化的△Z曲线;软件部分是采用定时器中断方式,利用汇编语言与C语言混合编程来控制A/D板的信号实时采集.整个系统采用双通道方式,可以同时测量左右肢体的血流容积变化情况,提高了测量的准确性.     

Effects of Glial Cells on Electrode Impedance Recorded from Neural Prosthetic Devices <Emphasis Type="Italic">In Vitro</Emphasis>

Neural prosthetic devices hold the potential to be used in the treatment of a variety of neurological disorders. However, their long-term clinical success is currently limited by the ability to achieve stable interfaces between devices and the CNS. Immunohistochemical analysis has shown that cellular responses occur in tissue surrounding implanted devices. These cellular responses have been correlated with the impedance measured from device electrodes, leading to the hypothesis that a possible mechanism resulting in inconsistent device performance is the formation of an electrically insulating glial sheath at the implantation site. However, little is known about what cellular and tissue changes affect impedance values and thus contribute to the decreases in electrode performance. We have designed an in vitro system in which cell conditions can be varied within an artificial tissue matrix surrounding a neural prosthetic device. In this study, high-density cultures of glial cells were analyzed by immunohistochemical methods and impedance spectroscopy. Astrocytes and microglia were cultured at various ratios within the matrix surrounding the probes, and were observed over a period of 2 weeks. Cell seeding conditions and confocal images were compared to impedance data to enable the effects of glial cell type on electrode impedance to be determined.     

Ethical issues in molecular pathology: paradigms in flux.

Recent advances in molecular pathology and molecular genetics have created new concerns about the use of human biologic materials in research. Since researchers now have the ability to extract and amplify DNA from minuscule archived samples, virtually any human tissue sample can potentially become the template for a test that provides information that may relate to the inherited genes of an individual. Researchers using human biologic materials should follow the 3 basic principles that have been defined for all ethical human subjects research: respect for persons, beneficence, and justice. Institutional Review Boards are responsible for providing review of the risks and benefits of research proposals to safeguard the rights and welfare of human subjects. Currently, there is considerable debate concerning the role of informed consent procedures and the Institutional Review Board oversight process in situations when researchers use human biologic materials that have been anonymized or coded. In 1999, the National Bioethics Advisory Commission is expected to make recommendations to President Clinton and the National Science and Technology Council that are expected to clarify the balance between respect for personal autonomy and the societal need to pursue biomedical research to improve the health and welfare of all individuals.     

Pathology of Soft Tissue Sarcomas

Soft tissue sarcomas are a heterogeneous group of malignant tumors with a wide range of clinical presentation, morphologic features and biologic behavior. During the past two decades, many acceptable new entities have been proposed, and the diagnosis and classification of these tumors have been modified. This paper reviews several current issues that are considered worthy of note for the histologic diagnosis of soft tissue sarcomas. Acta Pathol Jpn 40: 863 870, 1990.     

基于CST的乳腺癌组织介电常数成像探究

目的：研究乳腺癌组织的介电常数成像的可行性及成像效果,并初步确立合适的成像参数。方法：根据已有文献中正常乳房组织与乳腺癌组织介电常数的数据差异,利用CST微波工作室软件建立正常乳房组织、乳腺癌组织及原测量同轴探头仿真模型,通过改变癌变组织半径及在正常乳房组织中的深度这两个参数,得到不同条件下的散射参数,并将其转化为阻抗信息后进行成像,通过分别固定癌变组织半径和深度,对另一参数下得到的不同成像图形进行比较分析,最终确定扫描成像的最优分辨率及深度。结果：在0.5 GHz-9.5 GHz频段,对本文所建立的乳腺癌组织模型进行介电常数成像可以得到清晰的成像图像,其分辨率为1 mm;其中,阻抗值实部的成像效果要明显优于阻抗值虚部的成像效果,在频率为5.89 GHz时,最佳的成像参数为：乳腺癌组织半径r=2 mm,距正常乳房组织表面深度h=1 mm。结论：本文分析了乳房X线照相术与超声检测的优缺点,并对乳腺癌组织仿真模型进行介电常数成像,成像结果具有较高的分辨率,验证了介电常数成像的可行性,为乳腺癌组织检测提供了新的思路。     

Decellularization of tissues and organs

Decellularized tissues and organs have been successfully used in a variety of tissue engineering/regenerative medicine applications, and the decellularization methods used vary as widely as the tissues and organs of interest. The efficiency of cell removal from a tissue is dependent on the origin of the tissue and the specific physical, chemical, and enzymatic methods that are used. Each of these treatments affect the biochemical composition, tissue ultrastructure, and mechanical behavior of the remaining extracellular matrix (ECM) scaffold, which in turn, affect the host response to the material. Herein, the most commonly used decellularization methods are described, and consideration give to the effects of these methods upon the biologic scaffold material.     

Surface fluids effects on the bladder tissue characterisation using electrical impedance spectroscopy

The electrical impedance of the human urinary bladder in both benign and malignant areas can be measured using an electrical impedance spectroscopy system (EIS). Glycine is usually used in the bladder surgery in the theatre to make an insulation medium for electro-surgery and the extension of the mucosa. In addition, a saline solution is usually used to wash the inside of the bladder after bladder surgery and it is used to extend the bladder tissue mucosa. Therefore, the effect of glycine and the saline solution that fills the bladder is important, because it was expected that the application of common surface fluids (air, saline solution and glycine solution) in the bladder epithelium would affect the measured electrical impedance of the urothelium, to differentiate the malignant area from the normal bladder tissue. In this study, bladders were removed from the patients' bodies and then were moved from theatre to the histopathology department immediately after excision. These bladder samples were then opened and pinned to a corkboard to take the impedance readings, using the impedance spectroscopy system. Following this, the bladder and corkboard were completely submerged in a saline solution and readings were taken at about 1cm from the sutures. Subsequently, this procedure was repeated with the bladder submerged in glycine and then air, respectively. According to the statistical work, these fluids were found to have a significant effect on the measured impedance of the bladder tissue in benign and malignant areas. Furthermore, the best fluid between air, glycine and saline, to measure the impedance of the urinary bladder, is air (P<0.0001).     

The longitudinal tissue impedance of the smooth muscle of guinea-pig taenia coli

1. The absolute value of the tissue impedance of the guinea-pig taenia coli was measured in the longitudinal direction in air at 36 degrees C. The relation between the tissue impedance and the separation of the recording electrodes indicated that the tissue has cable-like properties. The frequency dependence of the impedance, observed at various distances from the current supplying electrode, showed that the tissue has a capacity component in the longitudinal direction.2. The tissue impedance in the longitudinal direction was also measured while the tissue was suspended in a narrow tube at 25-28 degrees C. The tissue impedance was calculated on the basis of the difference between the total impedance in Krebs solution and that in Krebs solution containing half the normal Na concentration, knowing the specific resistance of both solutions.3. The impedance per unit volume of the tissue was 370 Omega cm at 10 c/s and 190 Omega cm at 10 kc/s; at these frequencies the impedance was nearly independent of current frequency. The difference between the impedances (370 - 190 = 180 Omega cm) was taken to be the impedance of the junctions between cells. The possibility of slightly lower values for the actual tissue impedance was discussed. The capacity located at or near the junction was calculated to be 1-3 muF/cm, the time constant of the junctional membrane being about 0.5 msec.4. Ca ions (0-12.5 mM) and adrenaline (2 x 10(-7) g/ml.) had no measurable effect on the longitudinal impedance within 10-15 min. In hyperosmotic solution of twice osmolarity (by adding sucrose), the tissue impedance was increased by about 50%. When the tissue was immersed in sucrose solution containing no ions, the impedance gradually increased up to nearly 10 times in the course of 1 hr.     

The effect of source animal age upon the in vivo remodeling characteristics of an extracellular matrix scaffold

Biologic scaffolds composed of mammalian extracellular matrix (ECM) are routinely used for the repair and reconstruction of injured or missing tissues in a variety of pre-clinical and clinical applications. However, the structural and functional outcomes have varied considerably. An important variable of xenogeneic biologic scaffolds is the age of the animal from which the ECM is derived. The present study compared the in?vivo host response and remodeling outcomes of biologic scaffolds composed of small intestinal submucosa (SIS)-ECM harvested from pigs that differed only in age. Results showed that there are distinct differences in the remodeling characteristics as a consequence of source animal age. Scaffolds derived from younger animals were associated with a more constructive, site appropriate, tissue remodeling response than scaffolds derived from older animals. Furthermore, the constructive remodeling response was associated with a dominant M2 macrophage response.     

E-type prostaglandins and interferons: Yin-yang modulation of macrophage tumoricidal activity

It is proposed that nonimmunologic microenvironmental stimuli such as interferons and E-type prostaglandins (PGE) can modulate macrophage tumoricidal activity in local tissue immunity. These agents act as “local hormones” since they have a high catabolic rate and short biologic half-life in serum. Interferons provide a common pathway for induction of cytotoxic macrophages by diverse agents such as viruses, bacterial lipopolysaccharides, and double-stranded RNA, and PGE act as a biologic “resistor” to control expression of activated macrophage tumor killing. Since both PGE and interferons are secretory products of activated macrophages, it is envisioned that they could act in negative and positive feedback mechanisms to intrinsically modify macrophage functional activity. Finally, tumors may defend themselves from attack by activated tumoricidal macrophages by releasing high levels of PGE that subvert local macrophage activity.     

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.     

The potential of chondroitin sulfate as a therapeutic agent

Chondroitin sulfate (CS) is an omnipresent glycosaminoglycan with significant biologic roles. Chondroitin sulfate has not one structure but its polysaccharide backbone is modified to a smaller or higher degree according to the cell, tissue, species localization, and/or physiopathological stimuli. The potential of chondroitin sulfate for the therapy of osteoarthritis has been under investigation in several clinical trials, which have shown that it is safe and well tolerated. However, there are many issues still unresolved, such as the structure-modifying effects of CS in osteoarthritis, symptom-modifying efficacy in certain groups of patients, structure-activity-pharmacokinetic relationships, knowledge of mechanism of action, and better quality control of the preparations. Furthermore, ongoing basic research on its biologic role will probably show other therapeutic applications.     

The Potential of Chondroitin Sulfate as a Therapeutic Agent

Chondroitin sulfate (CS) is an omnipresent glycosaminoglycan with significant biologic roles. Chondroitin sulfate has not one structure but its polysaccharide backbone is modified to a smaller or higher degree according to the cell, tissue, species localization, and/or physiopathological stimuli. The potential of chondroitin sulfate for the therapy of osteoarthritis has been under investigation in several clinical trials, which have shown that it is safe and well tolerated. However, there are many issues still unresolved, such as the structure-modifying effects of CS in osteoarthritis, symptom-modifying efficacy in certain groups of patients, structure-activity-pharmacokinetic relationships, knowledge of mechanism of action, and better quality control of the preparations. Furthermore, ongoing basic research on its biologic role will probably show other therapeutic applications.     

Well-differentiated extraskeletal osteosarcoma: report of 2 cases, 1 with dedifferentiation

Extraskeletal osteosarcoma (ESOS) is a rare soft tissue sarcoma, typically characterized by high-grade histological features and a grave prognosis. However, 4 cases of well-differentiated ESOS with a better prognosis have been documented in the literature within the last 40 years. We report 2 additional cases, 1 with multicentric presentation and dedifferentiation, and we emphasize the histological features that are useful in distinguishing this lesion from other soft tissue tumors. Well-differentiated ESOS seems to represent a rare but distinct low-grade variant of ESOS. The limited published experience suggests that although the biologic behavior of this tumor is better than that of classical ESOS, there are cases with progression to a higher grade, leading eventually to final demise.