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Topic: Electrical impedance


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In the News (Thu 18 Apr 19)

  
  Medical Policy MED.00044 | Electrical Impedance Scanning of the Breast
Electrical impedance scanning of the breast involves the transmission of continuous electricity into the body using either an electrical patch attached to the arm or a hand held cylinder.
The majority of patients studied with electrical impedance of the breast were involved in the study presented to the FDA during the approval process for the T-Scan 200 device.
Electrical impedance scanning of the breast involves the transmission of a continuous low level electrical current through the body, using either an electrically charged skin patch attached to the arm or a hand-held cylinder.
medpolicy.bluecrossca.com /policies/MED/electrical_impedance.html   (1620 words)

  
  Electrical impedance - Wikipedia, the free encyclopedia
Electrical impedance or simply impedance is a measure of opposition to a 'sinusoidal' electric current.
A resistor's impedance is R (its resistance) and its reactance is 0.
Impedance is defined by the ratio of two phasors where a phasor is the complex peak amplitude of a sinusoidal function of time.
en.wikipedia.org /wiki/Impedance   (1958 words)

  
 Medical Policy MED.00044 | Electrical Impedance Scanning of the Breast
Electrical impedance scanning of the breast involves the transmission of continuous electricity into the body using either an electrical patch attached to the arm or a hand held cylinder.
The majority of patients studied with electrical impedance of the breast were involved in the study presented to the FDA during the approval process for the T-Scan 200 device.
Electrical impedance scanning of the breast involves the transmission of a continuous low level electrical current through the body, using either an electrically charged skin patch attached to the arm or a hand-held cylinder.
www.healthlink.com /provider/medpolicy/policies/MED/electrical_impedance.html   (1535 words)

  
 United States Patent Application: 0020193957   (Site not responding. Last check: 2007-10-13)
An apparatus comprising: means for applying electrical signals to an array of sensors; means for measuring electrical signals from the array of sensors; means for correcting the measured electrical signals for parasitic current sources errors; and means for deriving measurement data for each of the sensors.
Applying electrical signals to the output electrical conductors and measuring electrical signals at the input electrical conductors, generates sufficient information to correct for parasitic current sources and derive the measured parameter of each sensor using algorithms that include equations for combining electrical impedances.
The electrical conductors and sensors are arranged to form a crosspoint array wherein the rows (horizontal conductors) are formed by the input electrical conductors, the columns (vertical conductors) are formed by the output electrical conductors, and the sensors are connected between the output electrical conductors and the input electrical conductors at each crossing point (nodes).
appft1.uspto.gov /netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=/netahtml/PTO/search-adv.html&r=1&f=G&l=50&d=PG01&S1=20020193957.PGNR.&OS=DN/20020193957&RS=DN/20020193957   (6453 words)

  
 Principles of Bioelectrical Impedance Analysis   (Site not responding. Last check: 2007-10-13)
An ohm is a unit of electrical resistance equal to the resistance of a circuit in which an electromotive force of one volt maintains a current of one ampere.
Electrically determined TBW is equal to the L²/R, multiplied by a coefficient and constant (y intercept).
Electrical impedance prediction equations for assessing TBW and LBM are based on the variables of total body resistance, height and to weight.
www.rjlsystems.com /docs/bia_info/principles   (3813 words)

  
 [No title]   (Site not responding. Last check: 2007-10-13)
impedance of electrical model 10 is dominated by the resistance, and the magnitude of Z is substantially equal to the ESR of the capacitor.
The impedance values were computed by simulating the application of a 1 ampere constant current between the centers of planes 22, varying the frequency of the current, and determining the magnitude of the steady state voltage between the centers of planes 22.
Again, the impedance values were computed by simulating the application of a 1 ampere constant current between the centers of planes 22, varying the frequency of the current, and determining the magnitude of the steady state voltage between the centers of planes 22.
www.wipo.int /cgi-pct/guest/getbykey5?KEY=01/99479.011227&ELEMENT_SET=DECL   (9918 words)

  
 Electrical Impedance Mismatch
When a "transmitter" emits a wave towards a "receiver", the "impedance" (a measure of the dynamic ohms-law relationship between the current and voltage of a source) of the two must match in order to maximize the power transferred from the transmitter to the receiver.
If the impedance of the receiver does not match the impedance of the transmitter, a portion of the transmitter's energy will be reflected by the receiver and therefore unavailable to it.
Impedance mismatch is when you have a difference in electrical impedance in the interface between an antenna and its base which causes problem with reflected waves.
c2.com /cgi/wiki?ElectricalImpedanceMismatch   (659 words)

  
 Tutorial: impedance   (Site not responding. Last check: 2007-10-13)
With impedance spectroscopy, the permeability for alternating electric current is investigated and the components of the circuit shown in Fig.
The apparent opposition in an electrical circuit composed of ohmic resistors and capacitances to the flow of i (analogous to the electrical resistance to a direct current) is called electrical impedance (Z).
The transcellular impedance is the sum of the impedances of apical and basolateral cell membranes.
www.medizin.fu-berlin.de /klinphys/themen_ahg/impedance_e.htm   (720 words)

  
 Peavey.com :: Impedance in Audio Technology
Audio electrical signals are electrical analogues or representations of the positive and negative fluctuations of air pressure that have been converted to positive and negative fluctuations of voltage.
This fluctuating electrical signal that represents the vibrations of air or sound is by its very nature Alternating Current or AC (i.e., the direction of current flow changes directly with the number of audio cycles per second being reproduced).
Third is the impedance of the air or the acoustic impedance that the combination loudspeaker/enclosure encounters.
www.peavey.com /support/technotes/concepts/impedance_2.cfm   (2696 words)

  
 electrical impedance - HighBeam Encyclopedia
Reactance is an additional opposition to the movement of electric charge that arises from the changing electric and magnetic fields in circuits carrying alternating current.
Impedance in circuits carrying steady direct currents is simply resistance.
The magnitude of the impedance of a circuit is equal to the maximum value of the potential difference, or voltage, across the circuit, divided by the maximum value of the current through the circuit, or simply = /.
www.encyclopedia.com /doc/1B1-363535.html   (323 words)

  
 Mirabel Medical - Breast Cancer Detection by Electrical Impedance Scanning (EIS) - T-Scan™ 2000ED
Based on Electrical Impedance Scanning (EIS), the T-Scan™ 2000ED is used in conjunction with CBE in an age group for which other screening methods are less effective or limited.
Electrical Impedance Scanning involves the measurement of capacitance and conductivity levels of breast tissue, producing a real-time grey-scale image of differences in impedance measured over a wide range of frequencies.
Differences in electrical impedance properties between normal/benign and malignant tissue were identified in the 1920's.
www.transscan.co.il /physicians.asp   (996 words)

  
 [No title]   (Site not responding. Last check: 2007-10-13)
In characterizing semiconductors and in the field of electrochemistry, conventional impedance spectroscopy cannot be used for many dynamic processes such as the in situ observation of rapid etching processes or the relaxation of electrochemical systems after voltage jumps since the necessary time resolution is impossible in the required bandwidths.
The impedance data may be displayed using a color from a color scale in a two-dimensional layout that corresponds to the relative position of each channel of data within a test matrix.
Impedance data prior to the making of this invention was displayed graphically as either a numerical value or a point on an x-y graph, or as a bar graph, which was cumbersome to analyze.
www.wipo.int /cgi-pct/guest/getbykey5?KEY=03/73089.030904&ELEMENT_SET=DECL   (6756 words)

  
 Electrical Impedance Scanning of the Breast
Electrical impedance studies are used as an adjunct to mammography to improve patient selection for biopsy in patients with equivocal indications, i.e., those designated as a Bi-RADS™ category 3 or 4.
Electrical impedance scanning in breast cancer imaging: correlation with mammographic and histologic diagnosis.
Electrical impedance scanning for the early detection of breast cancer in young women: preliminary results of a multicenter prospective clinical trial.
www.regence.com /trgmedpol/medicine/med110.html   (2170 words)

  
 Quantum Electrical Metrology Division: National Electrical Standards, Farad and Impedance Metrology   (Site not responding. Last check: 2007-10-13)
This work also forms the foundation of NIST's measurement services for electrical impedance, ensuring the sound metrological basis for all impedance measurements, both nationally and internationally, and ensuring that the claims of measurement accuracy by U.S. industries are recognized and accepted worldwide.
The primary facility for tying the U.S. legal system of electrical units to the international system of units is the NIST calculable capacitor, with which the measurement of capacitance is effectively achieved through a measurement of length.
Electricity Division staff have recently completed a detailed characterization of the transfer of the farad unit from the calculable capacitor to calibration laboratory reference standards at a frequency of 1 kHz (previously only done at 1592 Hz).
www.eeel.nist.gov /817/817g/FaradandImpedance.html   (1786 words)

  
 Signal Integrity, Impedance and Electrical Models > The Bottom Line   (Site not responding. Last check: 2007-10-13)
Though impedance has the same definition in the time and frequency domains, the description is simpler and easier to generalize for C and L components in the frequency domain.
The impedance of an ideal R is constant with frequency.
The impedance of an ideal capacitor varies as 1/ωC and the impedance of an ideal inductor varies as ωL. is a very powerful tool to simulate the impedance of any circuit or the voltage and current waveforms expected in both the time and frequency domains.
www.informit.com /articles/article.asp?p=102225&seqNum=11   (455 words)

  
 Collaborations - NIH Center for Integrative Biomedical Computing at the Scientific Computing and Imaging Institute - ...
Electrical impedance imaging systems apply patterns of electrical currents to electrodes placed on a portion of the surface of a body.
From this electrical data they reconstruct and display an approximation of the electrical conductivity and permittivity inside a portion of the body surrounded by or near the surface electrodes.
In fact, a non-tomographic electrical impedance device, the T-Scan 2000, has been reported to be useful as an adjunct to X-ray mammogram imaging and has received FDA approval for this purpose.
www.sci.utah.edu /cibc/collab/isaacson.html   (524 words)

  
 Electrical impedance measurement of plastically deforming halite rocks at 125°C and 50 MPa
Electrical impedance measurements have been performed on deforming fine-grained (∼300 μm) synthetic halite rocks containing small quantities of water in order to study the evolution of fluid distribution.
The measured impedance shows that an interconnected network of water is formed even in the dry sample and that the connectivity in bulk is attained through the very thin (1–10 nm) elements of fluid.
For further understanding of mechanical and electrical properties of halite rocks it is essential to clarify properties of thin water films.
www.agu.org /pubs/crossref/2002/2001JB000204.shtml   (411 words)

  
 BioMedical Engineering OnLine | Full text | Comparison of human uterine cervical electrical impedance measurements ...
We sought to compare uterine cervical electrical impedance spectroscopy measurements employing two probes of different sizes, and to employ a finite element model to predict and compare the fraction of electrical current derived from subepithelial stromal tissue.
The electrical properties of biological tissues are a function of the electrical frequency applied, and the resistive and charge storage (capacitive) properties of cellular and non-cellular components of tissues.
Most recently, we have described cervical impedance using a 9 mm probe in a cohort of non-pregnant and pregnant women at various gestations, and noted an increase in resistivity in the third trimester perhaps resulting from changes in the collagen content and cervical cellular infiltration preparatory to prelabour ripening [8].
www.biomedical-engineering-online.com /content/5/1/62   (3577 words)

  
 Electrical Impedance   (Site not responding. Last check: 2007-10-13)
Because of the relatively small number of samples used for the electrical resistivity measurements, it is difficult to distinguish significant trends among formation factor, porosity, density, and permeability.
Using the method 2 resistance for this sample at 20 mHz, a direct measure of the chemical reaction impedance at the 2.54 cm sulfide/brine interface may be inferred.
Even though the electrodes have a capacitance, the measured electrode resistance at 20 mHz is in the range of 7 W. The remainder of the impedance is assumed to be from the sulfide/brine interface.
www-odp.tamu.edu /publications/169_SR/chap_08/c8_4.htm   (1592 words)

  
 Electrical Impedance Tomography
EIT measures the distribution of impedance in a cross-section of the body.
This is possible because the electrical resistivities of different body tissues varies widely from 0.65 ohm m for cerebrospinal fluid to 150 ohm m for bone.
Since electric currents applied to the body take the paths of least impedance, where the currents flow depends on the subject's conductivity distribution, the image reconstruction process is a non-linear problem.
www.geocities.com /CapeCanaveral/9710/html/eit.html   (497 words)

  
 epanorama.net/Speaker impedance
At fundamental resonance, the impedance is purely resistive, its phase angle is 0, and is determined by the effective series combination of the voice coil DC resistance and the reflected mechanical losses of (primarily) the suspension (Re + Res in standard Thiele/Small notation).
The impedance at these frequencies is predominantly resistive in nature and is dominated by the DC resistance of the voice coil.
The impedance of a speaker is only a rough average of the impedance and that the the voice coil dc resistance of most normal cone type dynamic speaker is roughly 75% of its "rated" impedance as the industry rates impedance.
www.epanorama.net /documents/audio/speaker_impedance.html   (1982 words)

  
 Bioelectrical Impedance Analysis (BIA) Phase Angle   (Site not responding. Last check: 2007-10-13)
Impedance analysis is based upon relating the measured electrical values of a subject to their physiologic equivalents as determined when the subject is the only unknown part of a safe and controlled electrical circuit.
There is also disclosed a method for measuring the phase angle due to the impedance of an animal having properties of varying resistance and capacitance due to changes in muscular tension, comprising the steps of passing an alternating current through the animal, and measuring the phase during changes of resistance and capacitance.
These bioelectrical impedance ratios at D0 in both the nonsurviving and surviving patients were 0.84 +/- 0.06 and 0.85 +/- 0.01 (mean +/- SE), respectively, indicating that the initial decrease caused by surgical stress itself was not directly related to the prognosis.
www.rjlsystems.com /docs/phase_angle   (4102 words)

  
 2001 Building Publications - Electrical Impedance Spectra to Monitor Damage During Tensile Loading of Cement Composites.   (Site not responding. Last check: 2007-10-13)
The tensile behavior and impedance behavior of extruded and notched composites with a fiber volume fraction of 0.5% or 3% were examined, with the mechanical load and electrical field applied longitudinally (in the direction of extrusion).
A good correlation between the electrical and mechanical properties was found, in that when a sudden growth in the crack was observed, a dramatic change was also noticed in the impedance values.
Taking advantage of the special frequency-dependent electrical properties of conductive fiber-reinforced composites, impedance values measured during the fracture process were used to distinguish and calculate three different areas at the crack front: uncracked area, bridging area, and open area.
fire.nist.gov /bfrlpubs/build01/art013.html   (281 words)

  
 Regional ventilation by electrical impedance tomography : a comparison with ventilation scintigraphy in pigs - ...   (Site not responding. Last check: 2007-10-13)
Study objective: The validation of electrical impedance tomography (EIT) for measuring regional ventilation distribution by comparing it with single photon emission CT (SPECT) scanning.
Electrical impedance tomography (EIT), which was developed in the early 1980s by Barber and Brown, (1) generates cross-sectional images of the impedance distribution within a measured object.
If surface electrodes are placed around the thorax, changes in the electrical impedance during ventilatory maneuvers parallel to changes of aeration within the lungs can be measured.
findarticles.com /p/articles/mi_m0984/is_1_124/ai_106096394   (891 words)

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