Ch 05 Biopotential Electrodes From J G Webster

Ch 05 Biopotential Electrodes © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

5. 5 The Electrode–Skin Interface and Motion Artifact © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Cross-sectional view Conductive gel (containing Cl – as the principal anion) Electrode Gel 角質層 粒層 生長層 (Cl–) 表皮 微血管 真皮層 汗管 汗腺 皮下層 Figure 5. 7 Magnified section of skin, showing the various layers (Copyright © 1977 by The Institute of Electrical and Electronics Engineers. Reprinted with permission, from IEEE Trans. Biomed. Eng. , March 1977, vol. BME-24, no. 2, pp. 134 -139. ) © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Equivalent circuit Ehe Electrode Cd Rd Gel Sweat glands and ducts Rs Ese Semipermeable to ions Why ? EP Epidermis Ce Dermis and subcutaneous layer Re CP RP Ru Figure 5. 8 A body-surface electrode is placed against skin, showing the total electrical equivalent circuit obtained in this situation. Each circuit element on the right is at approximately the same level at which the physical process that it represents would be in the left-hand diagram. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Stratum corneum Methods to reducing the effect of the stratum corneum (To stabilize the electrode) 1. Rubbing (磨擦) with a pad soaked in acetone (丙酮) 2. Abrading (擦掉、磨損) with sandpaper 3. Puncturing (making a hole) © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Motion artifact: — Genesis: Polarizable electrodes moves with respect to the electrolyte — Spectrum: low frequency — can be minimized by using nonpolarizable electrodes — The motion artifact associated with Cse can be significantly reduced by abrading the stratum corneum角質層. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Motion artifact, example of Ag (polarizable electrode) Ag-Ag. Cl (nonpolariza ble electrode) Resistor © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Effect of motion artifact on various biopotentials Motion artifact Figure 6. 16 Voltage and frequency ranges of some common biopotential signals; dc potentials include intracellular voltages as well as voltages measured from several points on the body. EOG is the electrooculogram, EEG is the elctroencephalogram, ECG is the electrocardiogram, EMG is the electromyogram, and AAP is the axon action potential. (From J. M. R. Delgado, “Electrodes from Extracellular Recording and Stimulation, ” in Physical Techniques in Biological Research, edited by W. L. Nastuk, New York: Academic Press, 1964. ) © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Motion artifact can be removed from the signal with HPF. Motion artifact EMG Frequency Motion artifact can NOT be removed from the signal with filtering. A HPF can eliminate the motion artifact, but it also will deform the original ECG waveform. Motion artifact ECG Frequency © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

5. 6 Body-surface Recording Electrodes © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Metal-plate eletrodes Figure 5. 9 Body-surface biopotential electrodes (a) Metal-plate electrode used for application to limbs. (b) Metal-disk electrode applied with surgical tape. (c) Disposable foam-pad electrodes, often used with electrocardiograph monitoring apparatus. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

© From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

© From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Suction eletcrodes Figure 5. 10 A metallic suction electrode is often used as a precordial electrode on clinical electrocardiographs. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Floating electrodes To stabilize the interface Insulating package Double-sided Adhesive-tape ring Metal disk Electrolyte gel in recess (a) (b) Snap coated with Ag-Ag. Cl Plastic cup External snap Gel-coated sponge Plastic disk Dead cellular material Foam pad Tack Capillary loops Germinating layer (c) Figure 5. 11 Examples of floating metal body-surface electrodes (a) Recessed electrode with top-hat structure. (b) Cross-sectional view of the electrode in (a). (c) Cross-sectional view of a disposable recessed electrode of the same general structure shown in Figure 5. 9(c). The recess in this electrode is formed from an open foam disk, saturated with electrolyte gel and placed over the metal electrode. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Flexible electrodes To comform to the change in the body-surface topography Carbon-filled silicone rubber 1 μm, x-ray transparent neonatal 初生的 Figure 5. 12 Flexible body-surface electrodes (a) Carbon-filled silicone rubber electrode. (b) Flexible thin-film neonatal electrode (after Neuman, 1973). (c) Cross-sectional view of the thin-film electrode in (b). [Parts (b) and (c) are from International Federation for Medical and Biological Engineering. Digest of the 10 th ICMBE, 1973. ] © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

5. 7 Internal Electrodes (Percutaneous electrodes) Percutaneous needle electrode Percutaneous wire electrodes percutaneous: through the skin © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Circuit Monopolar measurement Circuit Bipolar measurement Metal Insulation, e. g. expozy (樹脂) varnish 漆 hypodermic needle 皮下注射針 barb 倒鉤 Figure 5. 13 Needle and wire electrodes for percutaneous measurement of biopotentials (a) Insulated needle electrode. (b) Coaxial needle electrode. (c) Bipolar coaxial electrode. (d) Fine-wire electrode connected to hypodermic needle, before being inserted. (e) Cross-sectional view of skin and muscle, showing coiled fine-wire electrode in place. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Fetal ECG electrode Fetal ECG is monitored during labor. Amniotic fluid is conductive. So, surface ECG electrode cannot be used. amnion 羊膜 fetus 胎兒 labor 分娩 Source of figure: http: //health. allrefer. com/health/fetal-heart-monitoring-internal-fetal-monitoring. html © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Suction draws the skin surface into the cup. The central electrode pierces the stratum corneum. 50 ~ 700 μV To a pump Negative pressuret air Stainless steel needle helical 螺旋狀的 Figure 5. 14 Electrodes for detecting fetal electrocardiogram during labor, by means of intracutaneous needles (a) Suction electrode. (b) Cross-sectional view of suction electrode in place, showing penetration of probe through epidermis. (c) Helical electrode, which is attached to fetal skin by corkscrew type action. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Don’t use silver, which is toxic. Insulated stainless steel or platinum wire. Implantable electrodes Suture 縫線 body Sutured to the body Telflon insulator Depth electrode Brain suture 縫合 calvaria 頭頂 dura mater 硬膜 varnish 亮光漆 Figure 5. 15 Implantable electrodes for detecting biopotentials (a) Wire-loop electrode. (b) Silver-sphere cortical-surface potential electrode. (c) Multielement depth electrode. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

5. 8 Electrode arrays Disadvantage of the Implantable electrodes in Section 5. 7 1. Time-consuming in fabrication 2. Expensive 3. Lack of consistency © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

1. One-dimensional linear electrode array Microfabrication technology Contacts Ag/Ag. Cl electrodes 40 μm × 40 μm 0. 5 mm wide Insulated leads Base (a) 125 μm thick 10 mm long Application: to measure transmural potential distributions of beating myocardium Property: to be flexible to minimize tissue damage as the muscle contracts and relaxes transmural : through the wall of an organ © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

2. Two-dimensional electrode array Insulated leads Ag/Ag. Cl electrodes (1 -mm diameter) Contacts rigid 不易彎曲的 Base (rigid or flexible) (b) Application: for mapping the electrical potential across a surface region of an organ Figure 5. 16 Examples of microfabricated electrode arrays. (a) One-dimensional plunge electrode array (after Mastrototaro et al. , 1992), (b) Two-dimensional array, and (c) Three-dimensional array (after Campbell et al. , 1991). © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

(This slide is from Section 4. 6) A perfused heart of a person who died from a noncardiac condition Isochronous lines of activation Synchronously excited Direction of propagation: From endocardium toward epicardium Measured with multiple plunge electrode inserted into many sites in the heart Figure 4. 15 Isochronous lines of ventricular activation of the human heart Note the nearly closed activation surface at 30 ms into the QRS complex. (Modified from "The Biophysical Basis for Electrocardiography, " by R. Plonsey, in CRC Critical Reviews in Bioengineering, 1, 1, p. 5, 1971, © The Chemical Rubber Co. , 1971. Used by permission of The Chemical Rubber Co. Based on data by D. Durrer et al. , "Total excitation of the Isolated Human Heart, "1970, Circulation, 41, 899 -912, by permission of the American Heart Association, Inc. ) © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

3. Three-dimensional electrode array Tines, 1. 5 mm, insulated Exposed tip True 3 -d measurement with 1 -d linear electrode arrays Base (c) MEMS (Micro Electro Mechanical System) Figure 5. 16 Examples of microfabricated electrode arrays. (a) One-dimensional plunge electrode array (after Mastrototaro et al. , 1992), (b) Two-dimensional array, and (c) Three-dimensional array (after Campbell et al. , 1991). © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

5. 9 Microelectrodes To measure potential differences across the cell membrane Desirable properties: (1) small (2) strong © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Metal microelectrodes * Made by electrolytic etching * Strong metal : stainless steel, platinum-iridium alloy, tungsten, compound tungsten carbide * Insulator: polymeric material or varnish Figure 5. 17 The structure of a metal microelectrode for intracellular recordings. shaft 把手、手柄 shank 小腿、柄 carbide 碳化物 polymeric material 聚合物 varnish 漆 © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Supported-metal microelectrodes Deposited-metal-film microelectrode Metal: silver-solder alloy, platinum and silver alloy, indium, Wood’s metal Figure 5. 18 Structures of two supported metal microelectrodes Glass micropipet or probe, (a) Metal-filled glass micropipet. (b) coated with metal film. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Micropipet electrodes Fabrication: Heating stretching breaking filling sealing 1 um diameter (KCl) Figure 5. 19 A glass micropipet electrode filled with an electrolytic solution (a) Section of fine-bore glass capillary. (b) Capillary narrowed through heating and stretching. (c) Final structure of glass-pipet microelectrode. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Microelectrodes based on microelectronic technology Advantage: reproducibility Bonding pads Si. O 2 insulated Au probes Insulated lead vias Exposed electrodes Si substrate Silicon probe Exposed tips (a) (b) Miniature insulating chamber Hole Lead via Can be put into the cortex Channels Silicon chip Silicon probe (c) Electrode Contact metal film (d) Figure 5. 20 Different types of microelectrodes fabricated using microelectronic technology (a) Beam-lead multiple electrode. (Based on Figure 7 in K. D. Wise, J. B. Angell, and A. Starr, "An Integrated Circuit Approach to Extracellular Microelectrodes. " Reprinted with permission from IEEE Trans. Biomed. Eng. , 1970, BME-17, pp. 238 -246. Copyright (C) 1970 by the institute of Electrical and Electronics Engineers. ) (b) Multielectrode silicon probe after Drake et al. (c) Multiple-chamber electrode after Prohaska et al. (d) Peripheral-nerve electrode based on the design of Edell. © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Equivalent circuit model — Metal electrodes N = Nucleus C = Cytoplasm A Insulation Cell membrane Cd + + +- - +C +++- N + +- - + + (a) Metal rod Tissue fluid Membrane potential + -- + - + - -- + + + B Rs A Cw B Cd 2 Reference electrode Rma Cma Ema Ri Rmb Emb Re Emp (b) Suitable for measuring Cardiac signal? N Brain signal ? Y Muscular signal? Y Cmb Cdi Rma Emp Membrane and action potential (c) A Cma 0 Cd + Cw E Ema - Emb B Figure 5. 21 Equivalent circuit of metal microelectrode (a) Electrode with tip placed within a cell, showing origin of distributed capacitance. (b) Equivalent circuit for the situation in (a). (c) Simplified equivalent circuit. (From L. A. Geddes, Electrodes and the Measurement of Bioelectric Events, Wiley-Interscience, 1972. Used with permission of John Wiley and Sons, New York. ) © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

© From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Equivalent circuit model — Metal electrodes N = Nucleus C = Cytoplasm A Insulation Cell membrane Cd + + +- - +C +++- N + +- - + + (a) Metal rod Tissue fluid Membrane potential + -- + - + - -- + + + B Rs A Cw B Cd 2 Reference electrode Rma Cma Ema Cmb Cdi Ri Emb Re Emp (b) Rmb Rma Emp Membrane and action potential (c) A Cma 0 Cd + Cw E Ema - Emb B Figure 5. 21 Equivalent circuit of metal microelectrode (a) Electrode with tip placed within a cell, showing origin of distributed capacitance. (b) Equivalent circuit for the situation in (a). (c) Simplified equivalent circuit. (From L. A. Geddes, Electrodes and the Measurement of Bioelectric Events, Wiley-Interscience, 1972. Used with permission of John Wiley and Sons, New York. ) © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Equivalent circuit model — Glass electrodes A To amplifier B A Glass Internal electrode Electrolyte in micropipet Rma Cma Ema Stem Environmental fluid Taper Cell Tip membrane + + - N + + +- + (a) Reference Cd electrode + + + - - -+ + Cytoplasm - + N = Nucleus - - + + + Cell membrane B Rt Cmb Cd Ej Emb Et (b) Rmb Ri Emp Re Rt Membrane and action potential (c) 0 Emp Em = Ej + Et + Ema- Emb A Cd = Ct Em B Figure 5. 22 Equivalent circuit of glass micropipet microelectrode (a) Electrode with its tip placed within a cell, showing the origin of distributed capacitance. (b) Equivalent circuit for the situation in (a). (c) Simplified equivalent circuit. (From L. A. Geddes, Electrodes and the Measurement of Bioelectric Events, Wiley-Interscience, 1972. Used with permission of John Wiley and Sons, New York. ) © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

Equivalent circuit model — Glass electrodes A To amplifier B A Glass Internal electrode Electrolyte in micropipet Rma Cma Ema Stem Environmental fluid Taper Cell Tip membrane + + - N + + +- + (a) Reference Cd electrode + + + - - -+ + Cytoplasm - + N = Nucleus - - + + + Cell membrane B Rt Cmb Cd Ej Emb Et (b) Rmb Ri Emp Re Rt Membrane and action potential (c) 0 Emp Em = Ej + Et + Ema- Emb A Cd = Ct Em B Figure 5. 22 Equivalent circuit of glass micropipet microelectrode (a) Electrode with its tip placed within a cell, showing the origin of distributed capacitance. (b) Equivalent circuit for the situation in (a). (c) Simplified equivalent circuit. (From L. A. Geddes, Electrodes and the Measurement of Bioelectric Events, Wiley-Interscience, 1972. Used with permission of John Wiley and Sons, New York. ) © From J. G. Webster (ed. ), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.