Abstract
A medical electrode with a lead wire connector, the electrode including an electrode body with a skin side having a peripheral skin contact area and a central cavity with a central cavity area, both areas having an electrically conductive surface, the central cavity area being provided with at least one protrusion extending within the cavity only, and an outer side opposite to the skin side.
Claims
1. A medical electrode, comprising: an electrode body including: a skin side; an outer side opposite the skin side; a dome comprising a central cavity and having a height, the central cavity comprising a central cavity area and at least one protrusion extending only within the central cavity; and a rim surrounding the central cavity and having a thickness smaller than the height, the rim having a skin contact area; and a lead wire connector extending outwardly from the body, wherein each of the central cavity area and the skin contact area of the rim are electrically conductive and are located on the skin side.
2. The medical electrode of claim 1, wherein the at least one protrusion comprises a rib arranged within +/10 degrees of a radial direction relatively to a central axis through the central cavity.
3. The medical electrode of claim 1, wherein the at least one protrusion comprises between 3 and 5 ribs, each of the ribs arranged within +/10 degrees of a radial direction relatively to a central axis through the central cavity.
4. The medical electrode of claim 3, wherein the ribs are evenly distributed within the central area.
5. The medical electrode of claim 4, wherein each of the ribs comprises a rib area, wherein the electrode comprises a total active area comprised of the central cavity area, the rib areas, and the skin contact area, and wherein the total active area is in the range of 95 to 130 mm.sup.2.
6. The medical electrode of claim 1, wherein the dome has the shape of a truncated cone with rounded edges.
7. The medical electrode of claim 1, wherein the lead wire connector comprises a depression and at least one wall adjacent to the depression.
8. The medical electrode of claim 7, the depression is sectioned by a step providing a shallow conducting portion and a deep connection portion, the deep connection portion being outward of the shallow conducting portion.
9. The medical electrode of claim 1, wherein the skin contact area of the rim comprises an outer periphery, and wherein the medical electrode further comprises cut-outs extending inwardly from the outer periphery of the rim.
10. The medical electrode of claim 9, wherein the cut-outs comprise between 3 and 5 cut-outs, each of the cut-outs having a radial depth in the range of 0.5-1.5 mm.
11. The medical electrode of claim 1, wherein the body comprises a polymer-based core material with a conductive surface coating of Ag/AgCl.
12. The medical electrode of claim 1, wherein the cavity is prefilled with a conductive gel.
13. The medical electrode of claim 1, wherein the medical electrode is an MR conditional electrode.
14. An electrode array comprising a plurality of the medical electrode of claim 1 and lead wires, each of the lead wires comprising a lead wire conductor with an electrically insulating cladding, and each lead wire connector of the plurality of the medical electrode being electrically conductive, wherein each of the lead wires has a first end and a second end, the first end being physically embedded in and electrically connected to a respective one of the lead wire connectors of the plurality of the medical electrode, and the second end being connected to an electrode connector.
15. The electrode array of claim 14, wherein the lead wire conductor of each of the lead wires is made of an electrically conductive non-magnetic material or materials.
16. The electrode array of claim 14, wherein each lead wire connector of the plurality of the medical electrode is comprised substantially of polymer materials and devoid of metal parts.
17. The electrode array of claim 14, wherein each lead wire connector of the plurality of the medical electrode has a length in the interval of 30 to 50 cm.
18. The electrode array of claim 1, wherein the plurality of the medical electrode are MR conditional.
19. A method of making the electrode array of claim 14, the method comprising, for each of the medical electrodes of the plurality of the medical electrode: positioning the first end of the lead wire in the lead wire connector; applying energy to material of the lead wire connectors to soften or melt the material; and allowing the softened or molten material to set around the lead wire, thereby integrating the lead wire in the lead wire connector of the medical electrode.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The present technology will be described in more detail below with reference to the following figures. The figures illustrate embodiments, variations and examples of the present technology to facilitate the understanding of a person of ordinary skill in the art and are not to be construed as limiting the scope of the claims.
[0026] FIG. 1 is a perspective illustration of an EEG system system including an electrode array, an electrode harness, a connector box and a computer;
[0027] FIG. 2 is an illustration of electrodes as applied to a patient,
[0028] FIG. 3 is a view from below of an embodiment of an electrode;
[0029] FIG. 4 is a top view of the electrode of FIG. 3;
[0030] FIG. 5 is a perspective top view of the electrode of FIG. 3,
[0031] FIG. 6 is a sectional side view of the electrode of FIG. 3;
[0032] FIG. 7A is a detail of FIG. 6 including a lead wire and a tool;
[0033] FIG. 7B corresponds to FIG. 7A with the lead wire integrated;
[0034] FIG. 8 is a perspective view from below of the electrode of FIG. 3,
[0035] FIG. 9 is a sectional side view of the electrode of FIG. 3 as attached to a patient;
[0036] FIG. 10 is a top view of the electrode of FIG. 3 with additional features;
[0037] FIG. 11 is a sectional side view of the electrode of FIG. 10;
[0038] FIG. 12 is a flowchart illustrating a method of making a medical electrode; and
[0039] FIG. 13 is a flowchart illustrating a method of making a medical electrode array.
DETAILED DESCRIPTION
[0040] FIG. 1 illustrates an embodiment of an EEG system 1 including an electrode array 10, a harness 12, a connector box 14 and a processor 16. The electrode array 10 comprises several lead wires 18 each having a first end with an electrode 20 and a second end with an electrode connector 22. The harness 12 similarly has a first end with a harness connector 24 connectable to the electrode connector 22, and a second end with connectors, such as the illustrated harness jacks 26. The harness jacks 26 are in turn adapted to connect to the connector box 14 via sockets 27. The connector box in turn is adapted to connect to the processor 16 as schematically illustrated by an arrow. The connector box 14 and the processor 16 may be separate parts but could, alternatively, be provided as one unit. The processor 16 is adapted to process input from the electrodes 20 and output a signal that can be presented to a physician, such as in a graph on a screen or on print. The array 10 may be magnetic resonance (MR) conditional, meaning that under certain conditions it is safe to include the array 10 in an MR scan without a risk of harm to the patient and with low risk of negatively influencing image quality of the MR scan. For this the array 10 may be disconnected from the harness 12, which may be a reusable, MR unsafe part to lower cost and environmental impact, and in this event the harness 12 should not enter the MR room.
[0041] Electrodes as applied to a patient are illustrated in FIG. 2. The electrodes 20 are attached to the head of the patient, such as the scalp and forehead. Prior to application of the electrodes the skin of the patient is typically prepared to reduce the electrical resistance, such as by abrading the skin of the patient at the positions for electrode application. A gel, paste or adhesive may be used to attach the electrodes to the head of the patient. The gel, paste or adhesive may be electrically conductive, e.g. by containing chloride ions. As an example, Ten20(RM) Conductive Paste, by Weaver and Company, may be used. It is also possible to use the electrodes in dry state, without a gel, or to use e.g. a wet sponge with a saline solution. However, an electrically conductive gel is generally considered advantageous and may improve conduction and reduce skin-electrode interface impedance. Therefore, the gel between the skin and electrode allows for good-quality recording of biopotentials, which is measured in V. Supplementary or alternatively, tape may be used to attach the electrodes to the head of the patient. In some cases, an elastic electrode cap is used. An advantage of the elastic electrode cap is that application of the electrodes to the patient can be done very quickly. A disadvantage of the elastic electrode cap is that it may feel restrictive to the patient as the cap generally needs to be held down with straps anchored around the chin or chest. Further, such caps are generally not for single patient use and must hence be cleaned and dried after each use. Additional individual electrodes come at a lower cost and a versatile application area.
[0042] An embodiment of the electrode 20 is shown in FIGS. 3 to 9. The electrode body 28 has a skin side 34, illustrated in FIG. 3, adapted to face the skin of a patient, and an outer side 36, illustrated in FIG. 4, opposite the skin side. Turning first to a view from the skin side, the illustrated electrode 20 has an electrode body 28 with a periphery 30 and a lead wire connector portion 32. As shown, the periphery 30 is circular. The periphery 30 also comprise arcs of a circle separated by cut-outs, as shown in FIG. 10, or other shapes such as oval. The lead wire connector portion 32 is adapted to connect to the lead wire 18, as will be discussed in more detail below with reference to FIGS. 7A and 7B. The lead wire connector portion 32 may double as a mini-handle for the health care professional to ease handling and positioning of the electrode 20.
[0043] The electrode body 18 comprises a dome 37 and a rim 39 extending radially outwardly from the dome 37 and surrounding a central cavity 40 formed by the dome 37. Most of the dome is comprised by a wall that forms the central cavity 40, which therefore also has the shape of the dome 37. Therefore, as used herein, the term dome refers to a central portion that extends outwardly from the rim without regard for its shape. The rim 39 has a peripheral skin contact area 38 extending between a rim inner edge 39a and a rim outer edge 39b of the rim 39. The central cavity 40 extends longitudinally outwardly from the skin contact area 38 such that a height of the central cavity 40 is greater than a thickness of the rim 39. The central cavity 40 has the approximate shape of a dome or truncated cone (see for example FIGS. 6 and 8). The central cavity 40 may, as illustrated, have an opening 42. The opening 42 allows for needle insertion and escape of air or surplus gel, if any. As an example, the opening may have a diameter in the interval of 1.5 to 2 mm. A central axis 43 intersects the opening 42 and extends through the central cavity 40, as also indicated on FIG. 6. Protrusions 44, here in the shape of ribs, extend inwardly from an inner surface of the dome 37 inside the central cavity 40 (see FIGS. 3, 6 and 8). The protrusions, or ribs, 44 may be arranged in radial planes 45. The ribs 44 increase the surface area of the central cavity's interior, and further may assist in holding any gel or paste in the central cavity 40. The central cavity 40 of the electrode 20 may be prefilled with a gel or paste, thereby providing a ready-to-use electrode. Alternatively, the electrode 20 may be supplied without gel or paste, which may be added to the electrode at a later stage, such as the time of application to the patient. The skin contact area 38 and the dome 37 have electrically conductive surfaces. The electrode may or may not be made of, or comprise, a conductive material, whereas the surfaces should be conductive. The conductive surface may be provided as a coating, a lamination, or a layer of the body, for example. The lamination layer or the coating may be applied in a mold so that they bond with the polymer that forms the body. The lamination layer or the coating may be applied to the body post-molding. The layer of the body may be injection-molded in a two-material or two-step process. The electrically conductive surface may comprise silver/silver chloride (Ag/AgCl), which is found to provide consistent and superior signal quality. Increasing the surface area improves signal quality and enables longer working periods of the electrodes. The ribs/protrusions are sized and positioned so that they are contained inside the interior of the central cavity 40. As the ribs do not extend outside of the interior of the central cavity, the ribs do touch the skin of the patient and hence do not negatively influence the patient's comfort.
[0044] For optimum patient comfort the peripheral skin contact area 38 preferably has curvatures having radius of at least 0.3 mm, such as at least 0.5 mm, at the transition from the skin contact area 38 to the interior cavity 40 at the inner periphery, e.g. from the inner rim edge 39a, and similarly at the outer periphery of the skin contact area 38, e.g. from the outer rim edge 39b. This is primarily of relevance for electrodes positioned on a patient's head, where there is a risk that the electrode will be squeezed between the patient and a substrate. A height h.sub.e (shown in FIG. 6) of the electrode in the interval of 2.5 to 3.5 mm, such as 2.8 to 3.2, or such as 3 mm is found to provide a reasonable compromise between patient comfort and signal quality.
[0045] Referring now to FIG. 4, two fixation wings 33 are provided on the electrode body 28 for easier positioning (see also FIG. 5). The diameter of the electrode body in this embodiment is 10 mm, which is found to provide a reasonable compromise between size of the electrode and signal quality. If the electrode body has a much larger diameter it may be difficult to place electrodes correctly, especially when applied to children, whereas if the electrode is much smaller signal quality may become poor, and small electrodes may be difficult to handle for a health care professional.
[0046] FIGS. 5 and 6 illustrate features of the lead wire connector 32. The perspective top view of FIG. 5 illustrates the electrode 20 and specifically them second, or outer, side 36 thereof with the wings 33, the opening 42 and the lead wire connector 32. FIG. 6 is a sectioned side view of the electrode 20. The lead wire connector 32 comprises a depression 46 comprising a step 48 as also illustrated in FIG. 6. The depression is bordered at two sides by walls 50. The step 48 sections the depression 46 into a shallow conducting portion 46a and a deep connection portion 46b. As used herein, deep and shallow refer to the depth of the recess relative to an outer edge of the wall 50. The height h.sub.e of the electrode 20, described above, is also shown. Further, FIG. 6 illustrates that the ribs 44 may be positioned at the same radial position as the wings 33 and the lead wire connector 32. Superimposing the positions may be facilitate molding of the electrode 20 in view of flow of material in the mold. By superimposing it is meant that a radial plane traverses a rib or protrusion 44 and a wing 33, or a rib or protrusion 44 and the lead wire connector 32.
[0047] The lead wire connector 32 serves as a handle which the medical practitioner can use to place the electrode. In the magnetic field in the MR scanner the lead wire will act as an antenna and take up energy. The connection between the lead wire and the lead wire connector is achieved by e.g. ultrasonic welding, where material of the electrode will flow and surround the lead wire. The body has an electrically conducting surface coating and further may comprise material (polymer) with conductivity agents e.g. particles. The electrical connection between body and the lead wire will be a weld zone with a mixture of conducting surface coating and polymer material with conducting particles/conductivity agents. The resulting electrical connection may have some electrical resistance greater than the electrical resistance of the lead wire. The electrical connection may generate heat, due to the electrical resistance, beneficially in a part of the electrode that does not contact the patient. The lead wire connector 32 has some distance to the skin, and further a portion of the lead wire connector 32 (mainly the wire connection/weld zone) may be covered by a heat shrink tube to provide mechanical strength and thermal protection for the skin of the patient in the case the patient undergoes an MRI scan.
[0048] FIGS. 7A and 7B are sectional views of the lead wire connector 32 in a process to connect a lead wire to the lead wire connector 32 of the electrode. FIG. 7A schematically illustrates a lead wire 18 with a lead wire conductor 52 having an insulating cladding 54. A portion of the lead wire 18 is stripped and the bare lead wire conductor 52 positioned in the conducting portion 46a of the depression 46 and with an unstripped portion of the lead wire positioned in the connection portion 46b with an end 56 of the insulating cladding positioned against the step 48. On top of the wall a tool 58 may be applied, such as an ultrasonic horn or a heat staking tool, to at least partially soften or melt the walls 50. As shown, the wall 50 comprises an optional peak 50a, which may aid in focusing the energy of the tool 58. The material of the walls redistribute as embedding material 60 to embed the lead wire in the lead wire connector 32 and electrically connect the lead wire conductor 52 to the electrode. This allows for automation and provides a secure connection without adding material. Other ways to connect the lead wire to the electrode are conceivable, such as using a crimp bushing or by soldering, which are simple and well known ways of connecting wires. However, these alternatives are less advantageous as they have some drawbacks. For example, the use of crimp bushings may result in faulty connection if the parts are not carefully arranged prior to application. Further, the electrical contact is not always optimum. Finally, such bushings are generally made of metal, which should be avoided for MR conditional electrodes. In case of soldering, cold solder joints may occur, creating an incorrect joint. Cold solder joints are not always easy to detect and may result in faulty electrodes. Further, the use of solder adds metal to the electrode, which should be avoided for MR conditional electrodes.
[0049] FIG. 8 provides a view of the skin, or first, side of the electrode showing the interior cavity 40, the opening 42 and the ribs 44. The lead wire connector 32 advantageously has a rounded free end 62 to limit any potential discomfort for a patient should the lead wire connector 32 get in contact with the skin of the patient. Similarly, the outer edge 64 of the electrode 20 preferably has a rounded profile to minimize any potential discomfort for the patient.
[0050] FIG. 9 schematically illustrates the electrode's position on the skin 65 of a patient. Here a conductive gel 66 is applied to the electrode to attach the electrode to the skin 65, and to lower the skin-electrode interface impedance.
[0051] Additional features, which are optional, of the electrode 20, here denoted as electrode 20, are illustrated in FIGS. 10 and 11. The electrode 20 shares many features of the electrode 20, such as the dome 37 and the rim 39, but it also has some differences, which will be discussed in the following. When comparing FIG. 10 and FIG. 4, it can be seen that the electrode 20 comprises cut-outs 68 in its periphery. The cut-outs 68 minimize the potential formation of eddy currents in the electrode 20 when subjected to a changing magnetic field, such in an MR scanner. Eddy currents could potentially lead to artifacts on the MR image, so with the cut-outs 68 an electrode 20 is provided with reduced risk of artifacts in MR imaging. The diameter of the electrode 20 could be around 10 mm. The risk of eddy current formation and artifacts increases with increasing diameter, so the beneficial effect of providing the cut-outs 68 will be more pronounced for larger electrodes. Here, a total of four cut-outs are provided, but one cut-out 68 could in some cases be enough, e.g. for electrodes having a small diameter, or if there is no specific need for artifact-free images. If more than one cut-out is provided, the cut-outs should preferably be equidistant from each other in a radial direction to provide the shortest possible unbroken section of the periphery. Having more than five cut-outs is generally not recommended for the electrodes as the active area of the electrode is considered to be reduced too much, and further provision of cut-outs complicates molding. The illustrated cut-outs are rounded but could alternatively be slots or V-shaped cut-outs. Rounded cut-outs are, however, presently preferred to limit the risk of sharp edges, which could give rise to discomfort for the patient. The peripheral cut-outs 68 can also be provided in the electrode 20 shown in FIGS. 3 to 7B. The cut-outs 68 may extend past the rim outer edge 39b into the rim 39.
[0052] Another difference relates to the lead wire connector, which can be seen when comparing the sectional view of FIGS. 6 and 11. The lead wire connector 32 of the electrode 20 comprises a simplified wall 50 having a straight upper edge without a peak, making the electrode slightly simpler to produce. A lead wire (not shown) may be positioned in the depression 46 and embedded in material in a similar way as exemplified above. As shown, the step 48 is omitted. In another example of the electrode 20, the step 48 is provided. Further, the lead wire connector 32 can be provided in the embodiment of the electrode 20 shown in FIGS. 3 to 7B.
[0053] Another aspect of the present technology relates to a method of making a medical electrode as discussed above, which will now be described with reference to a flowchart 100 in FIG. 12. In an embodiment of the method of making medical electrodes, the method comprises: at 102, providing a mold with protrusion forming recesses; at 104, injecting a polymer into the mold; at 106, ejecting the electrode blank from the mold; and at 108 coating the electrode blank with an electrically conductive surface layer, such as Ag/AgCl. The polymer may for example be polycarbonate (PC) or Acrylonitrile Butadiene Styrene (ABS) or a mixture of PC and ABS, potentially with reinforcing fibers, such as carbon fibers.
[0054] A further aspect of the present technology relates to a method of making an electrode array as discussed above, which will now be described with reference to a flowchart 200 in FIG. 13. In an embodiment of the method of making medical electrodes, the method comprises: at 202, providing an electrode body with a lead wire connector; at 204, positioning a lead wire in the lead wire connector; at 206, applying energy to material of the lead wire connector to soften or melt the material; at 208, allowing the softened or molten material to set around the lead wire, thereby integrating the lead wire in the lead wire connector of the medical electrode.
[0055] The following items are examples of various embodiments disclosed above: [0056] 1. A medical electrode, comprising: a lead wire connector, and an electrode body including: a skin side; an outer side opposite the skin side; a central cavity having a height; and a rim surrounding the central cavity and having a thickness smaller than the height, the rim having a peripheral skin contact area and the central cavity having a central cavity area, each of the areas being on the skin side and having an electrically conductive surface, the central cavity area comprising at least one protrusion extending within the central cavity only. [0057] 2. Medical electrode of item 1, wherein the at least one protrusion is at least one rib arranged substantially radially, such as radial direction +/10 deg, relatively to a central axis through the central cavity. [0058] 3. Medical electrode of any one of the items above, wherein the number of protrusions is below 10, such as in the range 2-8, for instance 3-5. [0059] 4. Medical electrode of any one of the items above, wherein the electrode has a total active area in the range of 95 to 130 mm.sup.2, such as 100 to 110 mm.sup.2, for example 102 to 105 mm.sup.2. [0060] 5. Medical electrode of any one of the items above, wherein the central cavity approximately has the shape of a dome or truncated cone. [0061] 6. Medical electrode of any one of the items above, wherein the lead wire connector comprises a depression and at least one wall adjacent the depression. [0062] 7. Medical electrode of item 6, the depression is sectioned by a step providing a shallow conducting portion and a deeper connection portion. [0063] 8. Medical electrode of any one of the items above, wherein the peripheral skin contact area comprises cut-outs in periphery (clover), such as four cut-outs, each having a depth in the range of 0.5-1.5 mm, such as 1 mm. [0064] 9. Medical electrode of any one of the items above, wherein the body comprises a polymer-based core material with a conductive surface coating of Ag/AgCl. [0065] 10. Medical electrode of any of the items above, wherein the cavity is prefilled with a conductive gel. [0066] 11. Electrode array comprising a plurality of medical electrodes of item 1 and a plurality of lead wires each comprising a lead wire conductor with an electrically insulating cladding, where each lead wire has a first end physically embedded in the lead wire connector and electrically connected to the electrically conducting surface of the electrode, and a second end connected to an electrode connector. [0067] 12. Electrode array of item 11, wherein the lead wire conductor of each lead wire is made of an electrically conductive non-magnetic material, such as carbon or copper. [0068] 13. Electrode array of item 11 or 12, wherein each lead wire has a length in the interval of 30 to 50 cm, such as 35 to 45 cm, such as approximately 40 cm. [0069] 14. A method of making an electrode array, the method comprising: providing an electrode body with a lead wire connector; positioning a lead wire in the lead wire connector; applying energy to material of the lead wire connector to soften or melt the material; allowing the softened or molten material to set around the lead wire, thereby integrating the lead wire in the lead wire connector of the medical electrode.
[0070] The use of the terms first, second, third, fourth, primary, secondary, tertiary etc. does not imply any particular order or importance. These labels are included to identify individual elements. Furthermore, the labelling of a first element does not imply the presence of a second element and vice versa.
PARTS LIST
[0071] 1 EEG system [0072] 10 EEG array [0073] 12 harness [0074] 14 connector box [0075] 16 processor [0076] 18 lead wire [0077] 20, 20 electrode [0078] 22 electrode connector [0079] 24 harness connector [0080] 26 jack [0081] 27 socket [0082] 28 electrode body [0083] 30 periphery [0084] 32 lead wire connector [0085] 33 fixation wing [0086] 34 skin side [0087] 36 outer side [0088] 37 dome [0089] 38 skin contact area [0090] 39 rim [0091] 39a rim inner edge [0092] 39b rim outer edge [0093] 40 central cavity [0094] 42 opening [0095] 43 central axis [0096] 44 rib [0097] 45 radial plane [0098] 46 depression [0099] 46a conducting portion [0100] 46b connection portion [0101] 48 step [0102] 50 wall [0103] 52 lead wire conductor [0104] 54 insulating cladding [0105] 56 end [0106] 58 tool [0107] 60 embedding material [0108] 62 rounded end [0109] 64 outer edge [0110] 65 skin [0111] 66 gel [0112] 68 cut-out [0113] 100 flowchart [0114] 200 flow-chart [0115] h.sub.e electrode height
