Abstract:
A cable for enhancing biopotential measurements, including a core, the core including a first conductive line, a first shield that surrounds the first conductive line, and a first insulator that surrounds the first shield. The cable further includes a control section located outside the core, which includes a second conductive line, a second shield that surrounds the conductive line, and a second insulator that surrounds the second shield.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a cable for enhancing biopotential measurements. 
       BACKGROUND OF THE INVENTION 
       [0002]    A typical biopotential amplifier system includes an amplifier module connected to a patient headbox with a multi-conductor cable. Patient electrodes are connected between a patient and the headbox. A typical amplifier has multiple electrode inputs or channels, for example, 8, 16, 32, or 64 channels. 
         [0003]    Common mode rejection ratio (CMRR) is one measurement of an amplifier&#39;s performance. CMRR indicates the ability of an amplifier to reject common mode interference, typically 50 or 60 Hz, depending upon the power source, e.g., AC power. Common mode voltage can be reduced by driving an inverted version of the patient common-mode signal back into the patient in a negative feedback loop, commonly called the right leg drive (RLD). In this way right leg drive effectively increase the CMRR of a biopotential amplifier system. 
         [0004]      FIG. 1  shows a conventional cable  100  for use with a patient headbox for acquiring biopotential measurements having a bundle of wires surrounded by a shield  110 , which is itself surrounded by an outer jacket  120 . This bundle includes the multiple channel (e.g., patient) electrode wires  130 , a reference electrode wire  140 , and a right leg drive (RLD) electrode wire  150 . 
         [0005]    This conventional configuration has drawbacks in that the achievable CMRR is lower then possible. This aforementioned low CMRR results from capacitance, e.g., parasitic capacitance, between the RLD wire  150  and the channel electrode wires  140  due to the close proximity between them in the cable  100 . Moreover, this capacitance allows coupling of the RLD signal to the channel wires  130  bypassing the patient. Unbalance of this parasitic capacitance works in conjunction with the patient electrode impedances to reduce the CMRR of the amplifier system. The higher the patient electrode impedance the larger the potential difference between the patient and the channel wires. 
         [0006]    Accordingly, there is a need and desire to provide a cable with reduced coupling between the RLD and channel wires for enhancing biopotential measurements and increasing the CMRR of a biopotential amplifier system. 
       SUMMARY OF THE INVENTION 
       [0007]    Embodiments of the present invention advantageously provide a cable for enhancing biopotential measurements. 
         [0008]    An embodiment of the invention includes a cable for enhancing biopotential measurements which includes a feedback core including a first conductive line which includes a central feedback line, a first shield that surrounds the central feedback line, and a first insulator that surrounds the first shield. The cable further includes a second conductive line located radially outside the feedback core, a second shield that surrounds the second conductive line and the feedback core, and a second insulator that surrounds the second shield. 
         [0009]    Another embodiment includes a cable for enhancing biopotential measurements which includes a feedback core having a first conductive line comprising a central feedback line, a first shield that surrounds the central feedback line, and a first insulator that surrounds the first shield. The cable further includes a control section having a plurality of conductive control lines located radially outside the feedback core, a second shield that surrounds the plurality of conductive control lines and the feedback core, a second insulator that surrounds the second shield, and a sensing section including a plurality of conductive sensing lines radially located outside the control section, a third shield that surrounds the plurality of conductive sensing lines and the control section, and a third insulator that surrounds the third shield. 
         [0010]    Another embodiment includes cable for enhancing biopotential measurements which includes a feedback means having a first means for conducting comprising a central feedback means, a first means for shielding that surrounds the central feedback means, and a first means for insulating that surrounds the first means for shielding. The cable further includes a second means for conducting located radially outside the feedback means, a second means for shielding that surrounds the second means for conducting and the feedback means, and a second means for insulating that surrounds the second means for shielding. 
         [0011]    A cable for enhancing biopotential measurements, including a core, the core including a first conductive line, a first shield that surrounds the first conductive line, and a first insulator that surrounds the first shield. The cable further includes a control section located outside the core, which includes a second conductive line, a second shield that surrounds the conductive line, and a second insulator that surrounds the second shield. 
         [0012]    There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
         [0013]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
         [0014]    As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become more apparent and the disclosure itself will be better understood by reference to the following description of various embodiments of the disclosure taken in conjunction with the accompanying figures, wherein: 
           [0016]      FIG. 1  is a cross-sectional view of a conventional cable. 
           [0017]      FIG. 2  is a cross-sectional view of a cable in accordance with an embodiment of the present invention. 
           [0018]      FIG. 3  is a top view of the  FIG. 2  cable in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    In the following detailed description, reference is made to the accompanying drawings, which form a part hereof and show by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that other embodiments may be utilized, and that structural, logical, processing, and electrical changes may be made. It should be appreciated that any list of materials or arrangements of elements is for example purposes only and is by no means intended to be exhaustive. The progression of processing steps described is an example; however, the sequence of steps is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps necessarily occurring in a certain order. 
         [0020]    The invention will now be described with reference to the drawing figures in which like reference numerals refer to like parts throughout. As depicted in  FIG. 2 , a cable  200  is depicted having a conductive right leg drive (RLD) electrode line  205  at an approximate center surrounded by a right leg drive (RLD) shield  210  and a right leg drive (RLD) insulating jacket  215 . The central conductive RLD electrode line  205  functions to provide an inverted version of a common-mode signal back into a patient in a negative feedback loop. In one embodiment, a low power DC voltage line  220 , a ground line  225 , and digital control lines  230 - 233  may be surrounded by a middle shield  235  and a middle insulating jacket  240 . Conductive patient sensing electrode lines  250  may be arranged around the above-described middle jacket  240 . In one embodiment, each conductive line  205 ,  220 ,  225 ,  230 - 233 , and  250  may be constructed from a conducting material  255  surrounded by an insulating sheath  260 . The conducting material  255  may be, for example, a single conducting wire or braided strands of a conductor, e.g., copper. An outer shield  265  and an outer insulating jacket  270  may surround the patient electrode lines  250 . 
         [0021]    The centrally-located RLD line  205  has advantages at least in that the dedicated RLD shield  210  and RLD insulating jacket  215  protect it from parasitic capacitances and interference from the other conductive lines and outside interference sources, thus raising the CMRR of the cable  200 . It should be appreciated that the number of digital control lines and patient electrode lines and the order in which the lines are arranged may be adjusted based on the particular application, so long as the RLD line  205  is approximately in the center of the cable  200  surrounded by its dedicated RLD shield  210  and RLD jacket  215 . In addition, any or all of the low power DC voltage line  220 , ground line  225 , and digital control lines  230 - 233  may be located among the patient sensing electrode lines  250  with no middle shield  235  or middle insulating jacket  240  employed. Either or both of the middle shield  235  and middle jacket  240  may be omitted altogether, depending on the intended use of the cable  200 . 
         [0022]    Additional shields may be added, for example, to provide more safety protection for lines intended to convey electrical power, e.g., the low power DC voltage line  220 . Also, additional material may be added to impart desired properties of mechanical structural strength and/or flexibility to the finished cable assembly. Each shield may be, for example, braided strands of copper, (or other metal), a non-braided spiral winding of copper tape, or a layer of conducting polymer, mylar, aluminum, or copper. The shields may be constructed to have specific dielectric properties, such as to impart a particular desired characteristic impedance to the signals with which they interface. Each jacket  215 ,  240 ,  270  may be formed of an insulating material, e.g., PVC or polypropylene. 
         [0023]    Embodiments of the present invention may also include an insulation (not shown) outside the outer jacket  270  and a drain line  280  for providing another ground voltage for additional safety and/or to further increase CMRR. An additional shield and jacket (not shown) may be positioned outside the drain line, although the drain line  280  may be placed between the outer shield  265  and the outer jacket  270  or between the outer shield and an additional shield (not shown), with the outer jacket  270  surrounding all of the inner parts. In one embodiment, the drain line  280  is in contact with the additional shield or outer shield  265  so all parts of the shield may be at the same ground voltage. A filler material  285  may be deposited in spaces between any of the materials to displace air and make the cable  200  mechanically more robust and enhance its appearance. 
         [0024]    The coupling of the RLD signal in the cable is thus reduced as a result of the above-described cable design and arrangement. Also, an added construction benefit is a closer matching of the capacitance from the patient sensing electrode wires  250  to the middle and outer shield  235 ,  265  as compared with conventional cables, e.g., cable  100 , which further improves the common mode rejection ratio (CMRR). In addition, the DC voltage line  220  may be protected from contact with patient electrode wires by the additional middle shield  235  and a middle jacket  240 . 
         [0025]      FIG. 3  shows a top view of the cable  200 . It should be noted that the  FIG. 2  cross section is taken along the line A-A′ of  FIG. 3 . The outer shield  270  is shown as stretched between two connectors  310 ,  320 . The connectors  310 ,  320  may be configured to connect between a patient headbox (not shown) and an amplifier module (not shown). In the illustrated example, the connectors are both female connectors having attached connecting fastener  330 , e.g., a jackscrew, for ensuring a tight and persistent connection. Each connecting fastener  330  may be configured to be removable manually or with a tool, e.g., a screwdriver. The connectors  310 ,  320  may be custom-made for the application, or may be an off-the-shelf connector. The connectors may have pinouts  340  being respectively connected to each of the above-described conductive lines. It should be appreciated that it is not necessary for each pinout  340  to be connected to a conductive line, and any may be a floating pinouts, as desired. 
         [0026]    In one embodiment, a D-subminiature DD-50 connector may be used having fifty (50) connections for up to fifty total conductive lines. For example, there may be one RLD line (e.g., RLD line  205 ), one power line (e.g., low power DC voltage line  220 ), one ground line (e.g., ground line  225 ), four control lines (e.g., digital control lines  230 - 233 ), and forty-three (43) sensing line (e.g., patient electrode lines  250 ). Another embodiment may use a Small Computer System Interface (SCSI) connector. The connectors  310 ,  320  may be male or female, as appropriate for the intended connection. 
         [0027]    Embodiments of the present invention could be manufactured in accordance with the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment Regulations of the European Union (RoHS Regulations). Embodiments also include the feedback core being off-center and/or outside the rest of the cables and/or cable package. The central line is not limited to an RLD use or feedback use, but may be used for any purpose that requires increasing CMRR. 
         [0028]    The processes and devices in the above description and drawings illustrate examples of only some of the methods and devices that could be used and produced to achieve the objects, features, and advantages of embodiments described herein. Thus, they are not to be seen as limited by the foregoing description of the embodiments, but only limited by the appended claims. Any claim or feature may be combined with any other claim or feature within the scope of the invention. 
         [0029]    The many features and advantages of the invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention.