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PubMed1987

High-quality MR imaging with flexible transmission line resonators.

A novel type of surface coil suitable for human magnetic resonance (MR) imaging is described. The radio frequency receiving unit consists of a coaxial transmission line resonator (TLR). Its high filling factor and loaded Q-value of about 140 result in a high signal-to-noise ratio and thus a high-quality image. The coaxial Faraday shield eliminates di-electric losses and capacitive detuning of conductive samples. The stabilizing effect of the TLR makes it unnecessary to tune the coil between imaging of patients. The TLR can be immediately adapted to the individual body contours of a patient. Regions of the body traditionally difficult to image (e.g., throat) are easily examined due to the flexibility of the coaxial cables. These advantages coupled with ease of handling and shorter preparation time have made the TLR a proved tool that has been successfully used in many areas of diagnostic MR imaging.

Equipment Design↗
PubMed1989

[Movement profile analysis--automatic registration and evaluation of the movement patterns of small animals].

A method is described, in which small laboratory animals are freely moving in the field of analogous capacitive sensors. The electrical signals induced by animal movements which, according to amplitude and polarity, contain informations on intensity and direction of movements are conveyed to a classification device and classified according to well-defined classes. By measuring during a fixed time (e.g. 10 min) or for a previously determined number of signals (e.g. 2000) a distribution of class frequencies, the movement profile, is obtained. Parameters of movement profile of mice in the orientation phase and factors of influence are reported on. The method allows the continuously automatic registration of movement profiles.

Animals↗
PubMed1989

[The effect of drugs on electronically determined movement profile (movement profile analysis)].

In the movement profile analysis, movements of small laboratory animals, according to both intensity and direction (amplitude and polarity), are electronically measured by means of capacitive sensors. The electrical signals are amplified, classified into 13 classes in a classification device and depicted as frequency distribution. The obtained distribution corresponds to a Gaussian distribution if normal control mice are used (normal movement profile, MP). The normal MP is characteristically changed by drugs. By centrally depressing drugs (droperidol, chlorpromazine, diazepam, medazepam) distribution classes of weak movements are dose-dependently increased while classes of strong movements are decreased. Stimulating drugs (dexphenmetrazine, methamphetamine, caffeine) gave opposite changes of the MP. A certain time after a stimulating drug the change of the MP can turn to the MP of depressing drugs obviously as the result of exhaustion of the animal. After low doses of echinoramine I a MP with the characteristics of a depressing drug was found, after high doses the MP was that of a stimulating drug, perhaps as the result of subtoxic effects. After apomorphine (1, 5, and 10 mg/kg) no clear dose-dependence could be found. The movement profile analysis can be useful in the specified analysis of movements-influencing drugs.

Animals↗
PubMed1993

Transformation of Escherichia coli with foreign DNA by electroporation.

Electroporation has been widely applied in molecular biology in recent years. In this study, successful transformation of plasmid DNA and transfection of phage DNA into E. coli were described by using intense electrical field of exponential decay waveform (electroporation) generated by a Gene Pulsar LN-101 (made in Tianjin, Tianjin Institute of Technology and Nankai University). We have obtained 10(9)-10(10) transformants/micrograms with strain DH5 alpha and plasmid pUC18, by a single voltage pulse at 1.0-2.5 kV (initial electric field strength = 2.8-16 kV/cm) with 5-20 microF capacitor. The efficiency of electroporation depends on various parameters: the electric field strength, capacitance, the pulse length (RC time constant), etc. The frequency of transformation was a linear function of the DNA concentration, as well as the density of recipient cell. The incubation time of before or after electroporation has no significant effect on transformation. The high transfection efficiency was also achieved with strain JM109 and M13mp19RF by electroporation. The method was easier, more time-saving and more efficient than Ca(2+)-dependent transformation (transfection) method. The results obtained by Gene-Pulsar LN-101 was similar to that by the Bio-Rad Gene-Pulsar apparatus.

Calcium↗
PubMed1986

Stable transformation of tobacco by electroporation: evidence for plasmid concatenation.

Electroporation (electric field-mediated DNA transfer) of tobacco protoplasts in the presence of the linearized plasmid pMON200 has led to the formation of transgenic plants. Defined electric shocks were delivered by capacitive discharges with readily available, low-cost electrical components. This transformation procedure is simple and efficient and may suggest a quick method for determining the appropriate electric fields for new cell systems. An optimal transformation frequency of 2.2 X 10(-4) (based on the number of cells subjected to the shock) was obtained with a single 2000-V/cm, 250-microseconds-duration capacitive discharge. Calli transformed to kanamycin resistance have been regenerated into whole plants. Southern blots of DNA from the transgenic plants demonstrate the integration of the selectable marker gene (neomycin phosphotransferase) at single or multiple genomic sites. In some cases, the plasmid appears to be integrated intact; in others, it is rearranged. The blots also provide evidence of plasmid recircularization and/or the formation of head-to-head and head-to-tail concatemers in most of the plants analyzed. Although some plants apparently have multiple integration sites, analysis of progeny obtained by self-fertilization of the transgenic plants indicates that the kanamycin-resistance marker is inherited as a single dominant gene.

Chromosome Mapping↗
PubMed2003

Electrical characterization of coupled and uncoupled MEMS ultrasonic transducers.

We report electrical characterization of micromachined polysilicon capacitive diaphragms for use as ultrasonic transducers. Admittance measurements yield insight into the resonant behavior and also the damping resulting from ultrasonic radiation and frictional forces caused by the etch release holes. Unbonded transducers exhibit sharp resonances with Q values that increase with decreasing air pressure. We also report for the first time direct bonding of these transducers to solid surfaces. Transducers survive the bonding process and show distinctly different displacement in response to applied dc bias. Finally, a single-degree-of-freedom model is used to obtain insight into the various contributions to damping.

Acoustic Stimulation↗
PubMed2003

Capacitance and resistance of the bilayer lipid membrane formed of phosphatidylcholine and cholesterol.

Capacity and electric resistance of lipid membranes composed of lecithin and cholesterol were determined. The components were chosen for the study because they were present in biological membranes. Capacitance of the lecithin and cholesterol membranes amounts to 0.38 and 0.61 microF/cm(2), and resistance to 1.44(10(4)and 2.12(10(6)Omega cm(2), respectively. A 1:1 complex appears as a result of lecithin-cholesterol membrane formation. Parameters of the membrane formed of the lecithin-cholesterol complex were determined: surface concentration (Gamma(3)), capacitance (C(3)), and conductance (R;(3)(-1), as well as the stability constant (K) of the complex. The mean values of those magnitudes are as follows: 4.265(10(-6)mol/m(2), 0.54 microF/cm(2), 1.381(10(-6)Omega(-1)cm(-2)and 3.748(10(7), respectively.

Cholesterol↗
PubMedDate not supplied

Thermal energy deposition from a single-loop rf whole-body applicator.

Whole-body hyperthermia at moderate temperatures (40.0 +/- 0.5 degrees C) is currently being investigated to assess its effectiveness as an adjuvant to other cancer therapies. At our institution, the whole-body heating is achieved by a combination of hot air circulation and rf inductive heating at 27.1 MHz. This paper reports the results of a study of the thermal energy deposition pattern associated with the rf applicator. The applicator consists of a single loop of nearly elliptical shape with dimensions 20 x 46 cm. The loop is embedded in a mattress and is fed by lead wires entering the side of the mattress. Temperature mapping in a heated gelatin phantom placed just above the rf loop showed maximum heating near the lead wires and a cool region above the center of the loop. Calculations of the magnetically induced and capacitive contributions to the electric field near the applicator indicate that the heating near the lead wires is largely capacitive in nature. This feature of the rf heating is of interest because capacitive fields result in preferential heating of fatty tissues. Further calculations showed that the capacitive heating contribution falls away much more rapidly than the induced field contribution with increasing distance from the plane of the rf loop.

Diathermy↗
PubMed1988

[Methods for measuring the symptoms of "dry skin"].

"Dry skin" is a sign of many skin diseases and is, on account of its typical aspect, mostly diagnosed only macroscopically in everyday practice. Because the water content of the stratum corneum, according to current opinion, is said to be the most responsible for the appearance of the skin, using physical measuring methods is essential to investigate physiological relations. The more frequently used methods of capacitance measurement, infrared-spectroscopy, electrical resistance measurement, resonance frequency measurement, determination of the transepidermal water loss (TEWL), profilometry and scanning electron microscopy are characterized. Own investigations show correlations between the results of IR-spectroscopy, capacitance measurement and electrical resistance measurement with AC and DC in various depths of the stratum corneum.

Humans↗
PubMed2003

Molecular quantum cellular automata cells. Electric field driven switching of a silicon surface bound array of vertically oriented two-dot molecular quantum cellular automata.

The amine functionality of the linker on the dinuclear complex [trans-Ru(dppm)(2)(Ctbd1;CFc)(NCCH(2)CH(2)NH(2))][PF(6)] reacts with Si-Cl bonds of a chlorinated, highly B doped Si (111) surface to yield Si-N surface-complex bonds. The surface bound complex is constrained to a near vertical orientation by the chain length of the linker as confirmed by variable angle XPS. Oxidation of the dinuclear complex with ferrocenium ion or electrochemically generates a stable, biased Fe(III)-Ru(II) mixed-valence complex on the surface. Characterization of the array of surface bound complexes with spectroscopic as well as electrochemical techniques confirms the presence of strongly bound, chemically robust, mixed-valence complexes. Capping the flat array of complexes with a minimally perturbing mercury electrode permits the equalization of the Fe and Ru energy wells by an applied electric field. The differential capacitance of oxidized and unoxidized bound complexes is compared as a function of voltage applied between the Hg gate and the Si. The results show that electron exchange between the Fe and Ru sites of the array of dinuclear mixed-valence complexes at energy equalization generates a fluctuating dipole that produces a maximum in the capacitance versus voltage curve for each complex-counterion combination present. Passage through the capacitance maximum corresponds to switching of the molecular quantum cellular automata (QCA) cell array by the electric field from the Fe(III)-Ru(II) configuration to the Fe(II)-Ru(III) configuration, thereby confirming that molecules possess an essential property necessary for their use as elements of a QCA device.

Journal Article↗
PubMed2002

Anomalous capacitive sheath with deep radio-frequency electric-field penetration.

A novel nonlinear effect of anomalously deep penetration of an external radio-frequency electric field into a plasma is described. A self-consistent kinetic treatment reveals a transition region between the sheath and the plasma. Because of the electron velocity modulation in the sheath, bunches in the energetic electron density are formed in the transition region adjacent to the sheath. The width of the region is of order V(T)/omega, where V(T) is the electron thermal velocity, and omega is the frequency of the electric field. The presence of the electric field in the transition region results in a collisionless cooling of the energetic electrons and an additional heating of the cold electrons.

Journal Article↗
PubMed2003

Electrical impedance scanning: a new approach to skin cancer diagnosis.

BACKGROUND/AIMS: Skin cancer diagnosis depends, to a great extent, on visual inspection and histopathological examination of excised tissues. The aim of this study is to evaluate the ability of electrical impedance scanning to differentiate between benign and malignant skin lesions. METHODS: A preclinical study was conducted on 40 nude mice injected subcutaneously with a human melanoma strain. Impedance measurements were recorded every week to correlate electrical changes with tumor growth and histological findings. A clinical study was also performed on 178 human suspicious skin lesions before excision. The impedance measurements were correlated to the histopathological results. RESULTS: Normalized conductivity and capacitance, recorded on growing skin tumors in nude mice, were shown to change relative to lesion size. Necrosis, present in most of the larger lesions, was associated with a decrease in the electrical conductivity. Similar electrical parameters were used to classify human melanoma lesions with 92% sensitivity and 67% specificity. In addition, four out of five BCC lesions were correctly diagnosed. Moreover, dysplastic lesions were diagnosed with 91% sensitivity and 59% specificity. For comparison, physicians diagnosed melanoma lesions with 75% sensitivity and 87% specificity and dysplastic lesions with 46% sensitivity and 80% specificity. CONCLUSIONS: The animal study showed that electrical impedance measurements reflect morphological changes related to the growth of a cancerous skin lesion. These findings are in agreement with a preliminary clinical study. Electrical Impedance Scanning can therefore be considered as an objective and non-invasive tool for differentiation between benign and malignant skin lesions.

Animals↗
PubMedDate not supplied

An enhanced electrical impedance imaging algorithm for hyperthermia applications.

Electrical impedance imaging is a technique which is under investigation as a noninvasive method of tracking subsurface temperature distributions and/or associated cellular response during hyperthermia. In previous work, a finite element image reconstruction algorithm for converting surface potential distributions recorded at discrete electrode positions into spatial maps of conductivity values was developed. This paper reports on a series of significant improvements in the basic image reconstruction approach. Specifically, the ability to recover both the resistive and capacitive components of tissue electrical impedance have been incorporated. In addition, the image enhancement schemes of (1) total variation minimization, (2) dual meshing, and (3) spatial low-pass filtering, have been added. Through a series of simulation studies involving both phantom-like and clinically-relevant geometries having discrete regions and continuously-varying electrical property profiles, a significantly improved ability to recover spatial images of electrical properties in the impedance imaging context is demonstrated. The results show that the new algorithm is much more tolerant of measurement noise with levels up to 1% causing relatively modest degradations in image quality (compared to 0.1% which was needed previously in order to produce high quality images). The recovered electrical properties, themselves, both resistive and capacitive, are also found to be quantitative in value with errors in the 10-20% range occurring in the majority of cases, although deviations can reach 40% or more when noise levels as high as 10% are used. Temperature estimation simulations show that maximum temperature errors are significantly reduced (to approximately 2 degrees C relative to more than 10 degrees C in previous thermal simulations) with the new algorithm; however, temperature accuracies of better than 0.5 degree C on average are still found to be difficult to achieve with electrical impedance imaging even when the enhanced image reconstruction approach is used.

Algorithms↗
PubMedDate not supplied

Distributed self-capacitance of magnetic resonance imaging birdcage coils.

Presented is a theoretical description of the self-capacitance of a low-pass birdcage coil. The problem considered is that the modification of the distributed self-capacitance produced by the electric interaction between the coil and a cylindrical Faraday screen and illustrates the phenomenon of coil self-capacitance as well as the influence of Faraday screens. Changes in coil self-capacitance produced by the presence of the screens are shown to be consistent with measured shifts in coil resonant frequencies.

Magnetic Resonance Imaging↗
PubMed1974

Interfacial photoreactions and chemical capacitance in lipid bilayers.

The electrical response of a pigmented lipid bilayer to a short laser pulse is measured by a tunable voltage clamp method. In this method, a variable access impedance permits "tuning" of the observed relaxations for optimal measurements. Analysis of the data so obtained leads to an equivalent circuit that contains a novel chemical capacitance charged by the specific photoreaction across a single membrane-water interface. This chemical capacitance is distinct from the ordinary membrane capacitance. The intrinsic chemical rate constant obtained from the equivalent circuit analysis is shown to be the pseudo-first-order rate constant of the reverse dark reaction of the reduced acceptor and the oxidized pigment. The tunable voltage clamp method of measurement and analysis allows unambiguous separation of this rate constant into resistive and capacitative elements, which are interpreted in molecular terms.

Cell Membrane↗
PubMed2000

A few comments on electrostatic interactions in cell physiology.

The role of fixed charges present at the surface of biological membranes is usually described by the Gouy-Chapman-Grahame theory of the electric double-layer where the Grahame equation is applied independently on each side of the membrane and where the capacitive charges (linked to the transmembrane ionic currents) are disregarded. In this article, we generalize the Gouy-Chapman-Grahame theory by taking into account both intrinsic charges (resulting from the dissociation of membrane constituents) and capacitive charges, in the density value of the membrane surface charges. In the first part, we show that capacitive charges couple electrostatic potentials present on both sides of the membrane. The intensity of this coupling depends both on the value of the membrane specific capacitance and the transmembrane electric potential difference. In the second part, we suggest some physiological implications of membrane electric double-layers.

Ion Channels↗
PubMed1999

Membrane capacitance techniques to monitor granule exocytosis in neutrophils.

Cell membranes behave like electrical capacitors and changes in cell capacitance therefore reflect changes in the cell area. Monitoring capacitance can thus be used to study dynamic cellular phenomenon involving rapid changes in cell surface, such as exo- and/or endocytosis. In this review focus is on the use of capacitance techniques to study exocytosis in human neutrophils. We compare the whole-cell and the cell-attached capacitance techniques, and we review the complete literature dealing with capacitance measurements in human neutrophils.

Animals↗
PubMed2001

Patch-clamp analysis of voltage-activated and chemically activated currents in the vomeronasal organ of Sternotherus odoratus (stinkpot/musk turtle).

The electrophysiological basis of chemical communication in the specialized olfactory division of the vomeronasal (VN) organ is poorly understood. In total, 198 patch-clamp recordings were made from 42 animals (Sternotherus odoratus, the stinkpot/musk turtle) to study the electrically and chemically activated properties of VN neurons. The introduction of tetramethylrhodamine-conjugated dextran into the VN orifice permitted good visualization of the vomeronasal neural epithelium prior to dissociating it into single neurons. Basic electrical properties of the neurons were measured (resting potential, -54.5 +/- 2.7 mV, N=11; input resistance, 6.7 +/- 1.4 G Omega, N=25; capacitance, 4.2 +/- 0.3 pF, N=22; means +/- S.E.M.). The voltage-gated K(+) current inactivation rate was significantly slower in VN neurons from males than in those from females, and K(+) currents in males were less sensitive (greater K(i)) to tetraethylammonium. Vomeronasal neurons were held at a holding potential of -60 mV and tested for their response to five natural chemicals, female urine, male urine, female musk, male musk and catfish extract. Of the 90 VN neurons tested, 33 (34 %) responded to at least one of the five compounds. The peak amplitude of chemically evoked currents ranged from 4 to 180 pA, with two-thirds of responses less than 25 pA. Urine-evoked currents were of either polarity, whereas musk and catfish extract always elicited only inward currents. Urine applied to neurons harvested from female animals evoked currents that were 2-3 times larger than those elicited from male neurons. Musk-evoked inward currents were three times the magnitude of urine- or catfish-extract-evoked inward currents. The calculated breadth of responsiveness for neurons presented with this array of five chemicals indicated that the mean response spectrum of the VN neurons is narrow (H metric 0.11). This patch-clamp study indicates that VN neurons exhibit sexual dimorphism in function and specificity in response to complex natural chemicals.iol

Animals↗