Authors - L

Lacy, F.; Kadimanzuji, M.; Malveaux, F.J.; Carter, E.L.
Title   Distinguishing between activated and nonactivated eosinophils
        by AC impedance measurements
Journal IEEE Transactions on Biomedical Engineering
        43
        2
        FEB
Year    1996
Page    218-221
Address F Lacy
        Univ Calif San Diego
        Dept Bioengn
        La Jolla, CA 92093 USA
Serial# 0018-9294
Keys    TISSUE-CULTURE; ELECTRIC-FIELDS; MAMMALIAN-CELLS; BEHAVIOR;
        MONITOR; MOTION
Abs.    A cellular electrical impedance device which can detect the
        activated state of eosinophils has been developed and
        tested. This impedance device consists of a small gold
        electrode (50 mu m x 50 mu m) and a large gold electrode
        (1.5 cm x 0.5 cm) on a glass substrate, and it was
        fabricated by standard photolithographic techniques.
        Eosinophils, which belong to the granulocytic class of
        white blood cells, exhibit different physical properties
        when they change from the nonactivated state to the
        activated state. Hypothetically, these changes should
        correspond to a change in the measured electrical
        impedance. In this paper, data from the measured electrical
        impedance of eosinophils is presented. The measurements
        show that the average impedance of the activated
        eosinophils is 26% lower than the average impedance of the
        nonactivated eosinophils. Statistical analysis of the
        measured data shows that there is a significant difference
        between the measured impedances of activated and
        nonactivated eosinophils.
 

Li, J.H.; Joppek, C.; Faust, U.
Title   Fast EIT data acquisition system with active electrodes and
        its application to cardiac imaging
Journal Physiological Measurement
        17
         Suppl. 4A
        NOV
Year    1996
Page    A25-A32
Address JH Li
        Univ Stuttgart
        Inst Biomed Tech
        Stuttgart, Germany
Serial# 0967-3334
Abs.    A wide-band high-speed data acquisition system for
        electrical impedance tomography (EIT) is described. 32
        active electrodes are used in the system, half of them as
        receive electrodes and the other half as drive electrodes.
        A buffer is mounted on the back of each receive electrode
        and a current source on each drive electrode. A
        multielectrode system with active electrodes was built to
        make it convenient to attach all the electrodes on the
        human thorax. The system is suitable for both dynamic
        imaging and multifrequency electrical impedance tomography
        (MFEIT). Its operating frequency can be chosen between 25
        kHz and 400 kHz. Current is injected sequentially into 16
        adjacent current electrode pairs and the 16 voltages
        between adjacent receive electrodes are measured for each
        current injection. ECG is collected to determine the
        relationship between the reconstructed images and cardiac
        activity. The collection of one frame of data is completed
        within 25 ms. The system has been successfully used for
        imaging the variation of conductivity distribution of the
        human thorax. The beat-by-beat cardiac-related change of
        conductivity distribution has been imaged by our system.
        The quasi-periodic variation of the impedance distribution
        can be seen from the image sequence with breath-holding.
 

Lo, C.M.; Keese, C.R.; Giaever, I.
Title   Impedance analysis of MDCK cells measured by electric cell-
        substrate impedance sensing
Journal Biophysical Journal
        69
        6
        DEC
Year    1995
Page    2800-2807
Address I Giaever
        Rensselaer Polytech Inst
        Sch Sci
        Dept Phys & Biol
        Troy, NY 12180 USA
Serial# 0006-3495
Keys    TISSUE-CULTURE; TIGHT JUNCTION; PARACELLULAR PATHWAYS;
        NECTURUS GALLBLADDER; 2 STRAINS; EPITHELIA; TRANSPORT;
        RESISTANCE; MONOLAYERS; IDENTIFICATION
Abs.    Transepithelial impedance of Madin-Darby canine kidney cell
        layers is measured by a new instrumental method, referred
        to as electric cell-substrate impedance sensing. In this
        method, cells are cultured on small evaporated gold
        electrodes, and the impedance is measured in the frequency
        range 20-50,000 Hz by a small probing current. A model for
        impedance analysis of epithelial cells measured by this
        method is developed. The model considers three different
        pathways for the current flowing from the electrode through
        the cell layer: (1) in through the basal and out through
        the apical membrane, (2) in through the lateral and out
        through the apical membrane, acid (3) between the cells
        through the paracellular space. By comparing model
        calculation with experimental impedance data, several
        morphological and cellular parameters can be determined:
        (1) the resistivity of the cell layer, (2) the average
        distance between the basal cell surface and substratum, and
        (3) the capacitance of apical, basal, and lateral cell
        membranes. This model is used to analyze impedance changes
        on removal of Ca2+ from confluent Mardin-Darby canine
        kidney cell layers. The method shows that reduction of Ca2+
        concentration causes junction resistance between cells to
        drop and the distance between the basal cell surface and
        substratum to increase.
 

Longbottom, C.; Huysmans, M.C.D.N.J.; Pitts, N.B.; Los, P.;
        Bruce, P.G.
Title   Detection of dental decay and its extent using ac impedance
        spectroscopy
Journal Nature Medicine
        2
        2
        FEB
Year    1996
Page    235-237
Address C Longbottom
        Univ Dundee
        Sch Dent
        Dept Dent Hlth
        Pk Place
        Dundee DD1 4HR, Scotland
Serial# 1078-8956
Keys    CARIES
Abs.    Dental caries (decay), the most prevalent of diseases,
        represents a health problem of immense proportions(1). It
        principally affects posterior (back) teeth on occlusal
        (biting) and approximal (adjacent contacting) surfaces.
        Caries starts as a subsurface demineralization of enamel,
        may progress to the underlying dentine and, eventually, to
        cavitation of the surface. Accurate diagnosis before
        cavitation would permit targeted preventive treatment,
        thereby significantly improving dental health and reducing
        the need for expensive drilling and filling.
        Inaccessibility of caries initiation sites and recent
        changes in lesion morphology contribute to the relatively
        poor accuracy of conventional diagnostic methods(2). Among
        alternative techniques, measurements of electrical
        resistance(3-5) have shown the most promise. Here we
        described new experimental technique that demonstrates an
        outstanding 100% correlation between a.c. impedance
        measurements of whole teeth and the actual extent of
        approximal caries in vitro. Only relatively minor
        modifications should be required to transfer the technique
        to in vivo applications.
 

Lozano, A.; Rosell, J.; Pallasareny, R.
Title   A multifrequency multichannel electrical impedance data
        acquisition system for body fluid shift monitoring
Journal Physiological Measurement
        16
        4
        NOV
Year    1995
Page    227-237
Address A Lozano
        Univ Politecn Catalunya
        Dept Electr Engn
        Barcelona, Spain
Serial# 0967-3334
Keys    bioimpedance; multifrequency; multisegmantal; signal
        synthesis; haemodialysis; body compartments
        HEMODIALYSIS; PLETHYSMOGRAPHY; WATER; LIMBS
Abs.    This paper discusses some important issues for the design
        of electrical impedance measurement systems intended for
        body fluid shift monitoring, in particular during dialysis
        treatments. We have studied two common signal generation
        systems: digital synthesis and carrier recovery. We have
        found that in prolonged measurement applications, digital
        synthesis yields the best performance. On the demodulation
        side, we balance the demodulator errors between the real
        and imaginary parts by rotating the demodulation axes. We
        use segmental multifrequency impedance measurements to
        estimate the values of intracellular and extracellular
        impedance by adjusting the parameters of a Cole-Cole model
        for each segment measured. We stress the need to perform
        segmental measurements in order to accurately measure the
        segments of interest, in particular the trunk during
        dialysis treatments. Our results show that there is a sharp
        disequilibrium between the intracellular and extracellular
        compartments in the very first dialysis period. This fact
        generates the need to continuously measure segmental
        impedance instead of comparing initial and final values.
 

Lu, L.; Brown, B.H.; Barber, D.C.; Leathard, A.D.
Title   A fast parametric modelling algorithm with the Powell method
Journal Physiological Measurement
        16
         Suppl. 3A
        AUG
Year    1995
Page    A39-A47
Address L Lu
        Royal Hallamshire Hosp
        Dept Med Phys & Clin Engn
        Sheffield S10 2JF
        S Yorkshire, England
Serial# 0967-3334
Abs.    This paper presents a model that comprises only two
        parameters (R/S, f(r)) and the application of three
        function minimization algorithms (simplex, Powell and
        modified Powell) to this model to obtain parametric images.
        Comparisons among the three algorithms in terms of
        efficiency and reliability were carried out. It was found
        that, with proper initialization by taking the shape of the
        modelled data into consideration, the minimization function
        can be approximated by a quadratic function near the
        minimum point, therefore the iteration times can be
        minimized in the modified Powell method. The results show
        that with the modified Powell method a substantial
        reduction of computation time can be achieved in the
        parametric imaging. This makes it possible to obtain a 16 x
        16 parametric image in 1 s.
 

Lu, L.; Brown, B.H.; Barber, D.C.; Leathard, A.D.
Title   A fast parametric modelling algorithm with the Powell method
Journal Physiological Measurement
        16
         Suppl. 3A
        AUG
Year    1995
Page    A39-A47
Address L Lu
        Royal Hallamshire Hosp
        Dept Med Phys & Clin Engn
        Sheffield S10 2JF
        S Yorkshire, England
Serial# 0967-3334
Abs.    This paper presents a model that comprises only two
        parameters (R/S, f(r)) and the application of three
        function minimization algorithms (simplex, Powell and
        modified Powell) to this model to obtain parametric images.
        Comparisons among the three algorithms in terms of
        efficiency and reliability were carried out. It was found
        that, with proper initialization by taking the shape of the
        modelled data into consideration, the minimization function
        can be approximated by a quadratic function near the
        minimum point, therefore the iteration times can be
        minimized in the modified Powell method. The results show
        that with the modified Powell method a substantial
        reduction of computation time can be achieved in the
        parametric imaging. This makes it possible to obtain a 16 x
        16 parametric image in 1 s.