Abstract:
An electrode belt for impedance tomography shall be improved such that it has a simple design and makes possible good contacting of the electrodes ( 2 ) with the body of the test subject to be examined. The electrode belt ( 1 ) has at least 16 electrodes ( 2 ) on an electrode holder or belt material ( 3 ), which is elastic at least in some sections. The belt formed of one or more belt material sections completely surrounds a test subject to be examined on the circumference of the body. Electrode feed lines ( 63 ) extend along the electrode holder ( 3 ). The electrode feed lines and are connected to a feed line ( 6 ) at least at one feed point ( 4 ) on the electrode holder ( 3 ).

Description:
FIELD OF THE INVENTION 
     The present invention pertains to an electrode belt for electrical impedance tomography. 
     BACKGROUND OF THE INVENTION 
     Electrical impedance tomography (EIT) is a method in which a weak alternating electric current is introduced into the human body in order to measure the surface potentials at different points of the body. By rotating the sites at which the current is introduced around the body while measuring the surface potentials at the same time, a two-dimensional tomogram of the electrical impedance distribution in the body being examined can be determined by means of suitable mathematical reconstruction algorithms. A tomogram of the impedance distribution of the human body is of interest in medicine because the electrical impedance changes with both the content of air and the extracellular fluid content in the tissue. The ventilation of the lungs and the shifts in the blood and serum can thus be imaged and monitored in a regionally resolved manner. 
     To make it possible to carry out the measurement, the electrodes must be able to be arranged on the test subject&#39;s body in a simple manner. It is known that the electrodes may be arranged on a belt that can be placed around the test subject&#39;s body. 
     Such a belt, hereinafter called an electrode belt, has become known from EP 1 000 580 A1. An electrode holder with typically 16 electrodes is arranged on a test subject such that it fully encloses the circumference of the body. The electrode belt is connected via a feed line to an evaluating unit, in which the tomogram for the body section being examined is calculated. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide an electrode belt which has a simple design and makes possible the good contacting of the electrodes with the body of the test subject to be examined. 
     According to the invention, an electrode belt for electrical impedance tomography is provided with numerous electrodes (e.g, 16 or more). The electrodes are on a belt material, which is elastic at least in some sections and which fully surrounds a test subject to be examined over the circumference of the body. Electrode feed lines are provided, which extend along the belt material and are connected to a feed line (primary connection line) at least at one feed point (primary connection site). 
     The advantage of the present invention is essentially that at least some sections or even all of the electrode belt consist/consists of an elastic material and as a result, the electrode belt fits the body circumferences to be examined especially well. The suitable elastic materials are elastomers or also elastic fabrics, as they are known from bandages. Due to the elasticity of the belt material, the electrode belt is in contact with the test subject&#39;s upper body under a certain pretension, as a result of which a radial force component acts as a pressing force on the electrodes. The elastic belt material also makes possible a good adaptation to the respiratory movements of the test subject. Furthermore, it is advantageous that the electrode feed lines are integrated within the material of the belt, so that these can be united at a central point in order to establish the connection to an external feed line. In the event the electrode belt consists of an elastomer, the electrode feed lines may be incorporated in the elastomer material by vulcanization. The electrode feed lines are woven into the fabric material in the case of the elastic fabric. 
     According to an advantageous embodiment, two adjacent electrodes have shaped elements as a padding in the area of indentation of the body, e.g., in the chest area or in the area of the vertebral column, and a sufficient pressing pressure is achieved for the electrodes located there due to these shaped elements. The shaped elements may be structures made of an elastic material, which are integrated in the belt and model the shape of the concave indentations of the body and thus adapt themselves to the contour of the body especially well. It is also possible to fasten the shaped elements to the material of the belt on the outside in the area of the adjacent electrodes, so that the electrodes are pressed on by the shaped elements with the test subject in the recumbent position. The contact surfaces of the electrodes are designed such, e.g., in the form of a convex structure, that the pressing pressure does not lead to local skin damage as a consequence of the action of strong forces in a punctiform pattern. 
     The electrodes are expediently arranged at equally spaced locations from one another. Sixteen or 32 electrodes are present in a preferred embodiment, and a reference electrode, which is fastened at a predetermined distance from the other electrodes on the test subject&#39;s body, may also be present separately from the electrode belt. 
     In the case of certain image reconstruction algorithms, the image quality of the tomograms is markedly improved by the fact that the electrodes have an equidistant distribution at least in some sections. 
     The material of the belt advantageously consists of silicone, so that good intrinsic elasticity or stretchability is guaranteed by the material. Moreover, silicone is insensitive to the detergents and disinfectants usually used, so that the electrode belt has an especially long service life. 
     In a preferred embodiment, the electrode belt comprises individual belt segments, which are connected to one another by means of belt closures. The belt segments are designed such that they have an equal number of electrodes. There are 8 electrodes per segment in the case of a total of 16 electrodes and two belt segments. 
     In another preferred embodiment, the electrode belt comprises four belt segments with four electrodes each per segment. The splitting of the electrode belt into individual belt segments has the advantage that the number of electrode feed lines to be led in parallel per belt segment is reduced. 
     The belt closures are used to mechanically connect the individual belt segments. However, they may also establish an electrical contact with the adjacent belt segment, besides the mechanical connection. The feed line, which connects the electrode feed lines of the electrode belt with an evaluating unit, may be connected to the electrode belt in different ways. If the electrode belt comprises individual belt segments with the corresponding belt closures, individual feed lines may lead directly to the belt closures. However, it is also possible to separate the mechanical connection and the electrical connection from each other by laying the electrode feed lines of one belt segment in the direction of the center of the belt segment and connecting them to the feed line there. If the belt segment contains eight electrodes and the feed is in the middle of the belt segment, four electrodes each must be contacted starting from the feed point. 
     The advantage of an electrode belt split into belt segments with corresponding belt closures is that this design can be mounted easily and rapidly in unconscious patients. It is sufficient to turn the test subject on one side and then to place two belt segments connected with a belt closure, hanging down around the chest and the back, below the arm on the other side of the test subject. The test subject is then turned back on his back and the belt segments are connected with a second belt closure. By splitting the electrode belt into individual belt segments, the electrode belt can also be opened quickly in case of an emergency, e.g., in the case of imminent defibrillation. For example, the upper belt segment can be easily removed, e.g., by opening a belt closure, while the belt segment located under it remains under the test subject. 
     In another preferred embodiment, the shaped elements contain cavities, which are hermetically sealed against the environment and are filled with a medium, e.g., air, a liquid or a gel. This embodiment has the advantage that the force of gravity of the body being supported is distributed uniformly through the filled cavities and a more uniform pressing pressure of the different electrodes is achieved. An additional spring effect, which presses the electrodes better on the body, is achieved in the case of a gas filling due to the compressibility of the gas. 
     In another preferred embodiment, the shaped elements contain stabilizing inserts of a greater hardness, e.g., metal inserts, such as performed brass or aluminum plates. These inserts are integrated and cast in the electrode holder. The shaped elements are mechanically stabilized as a result of this, and, on the other hand, the inserts can act as spring elements, e.g., as a leaf spring, if designed accordingly, and are thus able to absorb forces and additionally press on the electrodes. It is also possible to preform the metal inserts such that they adapt themselves especially well to the indentations of the body in the region of the chest and the back. 
     The electrode belt advantageously comprises at least three strands (tubes), which extend in parallel and are connected section by section via cross struts (tube mounting piece), the electrodes being arranged directly at the cross struts. One of the strands is hollow from the inside and is designed to accommodate the electrode feed lines. If the shaped elements located under the electrodes are designed as cavities in the area of the cross struts, they can be put under pressure via the hollow strand, and a membrane, which is located on the top side of the cavities, bulges outwardly together with the electrodes in order to generate the necessary pressing pressure on the test subject&#39;s body. The pressure may be generated automatically with a pressure regulator or manually with bellows. 
     The electrode feed lines are advantageously folded in a zigzag-shaped or meandering pattern within the hollow strand in order to compensate the stretching of the electrode material. The electrode feed lines may be cast in an elastomer within the hollow strand. 
     According to an advantageous embodiment of an electrode belt comprising three strands extending in parallel, the shaped element is designed as a gel pad, which is clamped in between the two outer strands and the strand located in the middle. When the electrode belt is put in place, the gel pad is pressed by the two outer strands against the middle strand, as a result of which the contacting of the electrode is improved. The electrodes are located at the middle strand here. A gel pad is especially suitable on the back when the patient is in the recumbent position, because it adapts itself well to the body surface and prevents pressure sores from forming. 
     The electrode belt advantageously has a coding means, which is designed to generate a release signal for the signals transmitted via the feed line. The coding means may be designed as a plug-type connection on the feed line, a magnetic strip, a bar code strip or a transponder. If the coding means is designed as a plug type connection, the release signal is generated during plugging in. Individual contacts at the feed site of the electrode belt can be connected to one another for this purpose through wire bridges such hat a certain coding is recognized by the evaluating unit during the plugging in with the feed line. In the case of a magnetic strip, a bar code or a transponder, the evaluating unit contains a reader, with which the code can be detected and evaluated. It is also possible to integrate an EEPROM or a digital or analog electronic unit in the electrode belt. It can be recognized by evaluating the coding whether the correct electrode belt has been placed on the test subject and whether there is compatibility with the evaluating unit. The coding may advantageously contain manufacturer&#39;s data, the number of electrodes, the type of the belt and the size of the belt. 
     The feed line is advantageously designed for wireless communication between the electrode belt and the evaluating unit. A transmitter or a transmitter-receiver is located for this purpose in the vicinity of the electrode belt, or it is an integral part of the electrode belt, and a receiver or transmitter-receiver of a corresponding design is provided at the evaluating unit. 
     Exemplary embodiments of the present invention are shown in the drawings and will be explained in greater detail below. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an electrode belt with an evaluating unit; 
         FIG. 2  is a schematic view of the electrode belt according to  FIG. 1  with two feed lines arranged symmetrically; 
         FIG. 3  is a schematic view of an electrode belt with two belt closures and symmetrical connection of the feed lines in the area of the belt closures; 
         FIG. 4  is a schematic view of the electrode belt according to  FIG. 2  with a second belt closure; 
         FIG. 5  is a schematic view of an electrode belt with electrodes bulging forward in the area of a depression of the body; 
         FIG. 6  is a schematic view of an electrode belt with shaped elements at two electrodes arranged adjacent to each other; 
         FIG. 7  is a top view of an electrode belt with two belt segments; 
         FIG. 8  is detail “E” from  FIG. 7  with a belt closure; 
         FIG. 9  is a sectional view along the section line A-A, corresponding to  FIG. 8 ; 
         FIG. 10  is a perspective view of a detail of an electrode belt with three strands (tubes). 
         FIG. 11  is a top view of the electrode belt according to  FIG. 10 ; 
         FIG. 12  is a sectional view along the section line B-B of the electrode belt according to  FIG. 11 ; 
         FIG. 13  is a view showing examples of folded electrode feed lines; 
         FIG. 14  is a top view of a belt segment of an electrode belt; 
         FIG. 15  is a side view of the belt segment according to  FIG. 14  in the direction of view C; 
         FIG. 16  is a schematic view of an alternative embodiment of the electrode belt according to  FIG. 11  with a gel pad; 
         FIG. 17  is a side view of the electrode belt according to  FIG. 16 ; and 
         FIG. 18  is a schematic diagram showing an electrode belt and an evaluating unit with wireless communication. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular,  FIG. 1  schematically shows an electrode belt  1  for electrical impedance tomography with 16 electrodes  2  on an elastic electrode holder  3  made of silicone. For the sake of greater clarity, the 16 electrodes  2  are designated by the numbers 1-16. Electrode feed lines extend within the electrode holder  3 . The electrode feed lines are not specifically shown in  FIG. 1 . The electrode feed lines are connected to a feed line (primary connection line)  6  at a feed point (primary connection site)  4 , at which a belt closure  5  is located. Via a connection plug  7  with a connection cable  8  and a device plug  9 , the feed line  6  is connected to an evaluating unit  10 , in which all the calculations necessary for the impedance tomography are performed. The electrode belt  1  is placed around the upper body of a test subject, not specifically shown in  FIG. 1 . The electrode belt  1  can be opened at the belt closure  5 . The belt closure  5  establishes both a mechanical connection and an electrical connection, because eight electrode feed lines each, indicated by arrows  11 ,  12 , extend to the electrodes  2 , starting from the belt closure  5 . The electrodes are arranged at equal distance from each other. A reference electrode  13 , which is likewise fastened to the test subject&#39;s body at the distance D relative to the electrode belt  1 , is located above the electrode belt  1 . 
       FIG. 2  shows an alternative embodiment of an electrode belt  101 , which has, unlike the electrode belt  1  according to  FIG. 1 , two feed lines  61 ,  62 , which are connected separately by a belt closure  51  with an electrode holder  31 . Starting from the feed points  41 ,  42  of the feed lines  61 ,  62 , up to four electrode feed lines extend to the electrodes  2  along the arrows  14 ,  15 . Identical components are designated by the same reference numbers as in  FIG. 1 . 
     Unlike in the embodiment according to  FIG. 2 , the feed lines  61 ,  62  are connected with a belt closure  52 ,  53  each in the electrode belt  102  according to  FIG. 3 . Because of the two belt closures  52 ,  53 , the electrode belt  102  comprises a first belt segment  33  and a second belt segment  34 , each with an equal number of electrodes  2 . 
     The electrode belt  103  according to  FIG. 4  differs from the electrode belt  101  according to  FIG. 2  by an additional belt closure  54 , by which two belt segments  35 ,  36  with equal numbers of electrodes  2  are formed. 
       FIG. 5  schematically shows an electrode belt  104  lying on the sternal depression  70  of a test subject  71 . To cover the sternal depression  70 , two electrodes  21 ,  22  are provided, which are arranged adjacent to each other, bulge forward and lead to a radial force component when the electrode belt  104  is put in place. 
       FIG. 6  illustrates the coverage of the spinal depression  72  of the test subject  71  with an electrode belt  105 , in which shaped elements incorporated in the belt  105  in the form of bead-like projections  73 ,  74  are used as a padding for the electrodes  2 . 
       FIG. 7  shows a top view of the electrode belt  103  according to  FIG. 4  with the belt segments  35 ,  36  and the belt closures  51 ,  54 . The feed lines  61 ,  62  lead directly to the electrode feed lines  63 , which, starting from the feed points  41 ,  42 , extend directly to the electrodes  2 . 
       FIG. 8  shows an enlarged detail E of the electrode belt  103  according to  FIG. 7  with the belt closure  51 . The belt closure  51  comprises two straps  55 ,  56 , which can be displaced in relation to one another, wherein a first strap  55  has two tapering elongated holes  57 , and a second strap  56  has rivets  58 . The diameter of the rivets  58  is selected to be such that the rivets can be introduced into the elongated holes at the point where the elongated holes have the greatest internal diameter. 
       FIG. 9  shows a sectional view of the electrode belt  103  in the area of the belt closure  51  along the section line A-A. 
       FIG. 10  shows a perspective view of an electrode belt  106 , which comprises three strands (tubes)  75 ,  76 ,  77 , which extend in parallel and are connected to one another section by section via cross struts (tube mounting piece)  78 . The electrodes  2  are located in the middle on the cross struts  78 . The two outer strands  75 ,  77  are made of an elastic solid material, whereas the middle strand  76 , though also elastic, is hollow on the inside, so that it can accommodate electrode feed lines  63 . The direction of stretching of the electrode belt  106  is illustrated by the double arrow  16 . 
       FIG. 11  shows a top view of the electrode belt  106  with cross struts  78 , which are located next to each other and are arranged at equal distances from each other. 
       FIG. 12  shows a sectional view of the electrode belt  106  according to  FIG. 11  along a section line B-B. The electrode  2  is fastened to an elastic membrane  79  according to this embodiment. The elastic membrane  79  closes off a cavity  80 . The individual cavities  80  can be put under pressure centrally via the middle strand  76 , and the membranes  79  bulge outwardly. The pressing pressure of the electrodes  2  on the test subject&#39;s body can be affected by changing the pressure. 
     For strain relief of the electrode feed lines  63 , the latter are folded within the middle strand  76  in a triangular, loop-like or meandering pattern, as can be determined from  FIG. 13 . 
       FIG. 14  shows an electrode belt  107 , which comprises two belt segments  37  of identical design with eight electrodes  2  each. Only one belt segment  37  is shown in  FIG. 14  for the sake of greater clarity. 
     The belt segment  37  has two outer strands  86 ,  87 , which consist of an elastic solid material, and a middle, hollow strand  88 , which is used to accommodate the electrode feed lines  63 . Plug-in straps  89 ,  90 , which act as feed points and have four plug type connections  91 ,  92  each for contacting four electrodes  2 , are located at the ends of the belt segment  37 . Thus, only a maximum of four electrode feed lines  63  need to be led in parallel within the hollow strand  88 . Two plugs  93 ,  94  with feed lines  64 ,  65  for the electrodes  2  of the belt segment  37  have two rows located in parallel with contact pins  95 ,  96 , which can be connected to the plug type connections  91 ,  92 . The belt segment  37  is connected to the plugs  93 ,  94  both mechanically and electrically with the contact pins  95 ,  96  and the plug type connections  91 ,  92 . A second belt segment  37 , not shown in  FIG. 14 , is connected to the two free contact pins  95 ,  96  of the plugs  93 ,  94 . The complete electrode belt  107  is obtained with two belt segments  37  and the plugs  93 ,  94 . The plugs  93 ,  94 , combined with plug type straps  89 ,  90 , form the belt closures  59 ,  60  of the electrode belt  107 . 
       FIG. 15  shows a side view of the electrode belt  107  in the direction of view C according to  FIG. 14 . Identical components are designated by the same reference numbers as in  FIG. 14 . The electrodes  2  are arranged at equal distances from each other on the belt segment  37 . The electrodes  2  in the area of the middle of the belt have shaped elements  97 ,  98  as a padding in order to achieve good contacting in the chest or back regions. 
       FIG. 16  shows an alternative embodiment of the electrode belt  106  according to  FIG. 11 . The electrodes  2  located adjacent to each other have as the shaped element a gel pad  99 , which is clamped between the outer strands  75 ,  77  and the middle strand  76 .  FIG. 16  shows a top view of the electrode belt  106 , in which the electrodes are concealed. 
       FIG. 17  shows a side view of the electrode belt  106  according to  FIG. 16 , which is in contact with the sternal depression  70  of the test subject  71 . With the electrode belt  106  in place, a radial force is applied to the middle strand  76  by the outer strands  75 ,  77 , as a result of which the electrodes  2  are pressed onto the sternal depression  70 . 
       FIG. 18  shows the concept of the wireless connection of an electrode belt  1  to an evaluating unit  10 . In this embodiment, an analog and digital electronic unit  82  is accommodated together with a transmitter-receiver  83  in a housing  84  located near the test subject. The electronic components accommodated within the housing  84  are supplied with electricity by a separate power supply unit. The analog and digital electronic unit  82  is preferably designed for low energy consumption, as a result of which batteries can be used as the power supply. In an especially preferred embodiment, two sets of batteries are used, which can be removed one by one by means of a suitable mechanical or electromechanical change closure and recharged in an external charging station. It is thus not necessary to interrupt the measuring operation during the battery change. A transmitter-receiver  85 , which receives the measured signals of the electrode belt  1 , is likewise located in front of the evaluating unit  10 . The wireless communication takes place via an infrared transmission link or a radio link with low output. Due to the wireless connection of the electrode belt  1  to the evaluating unit  10 , the evaluating unit  10  can be placed in a site-independent manner from the test subject interface, and long cable connections, which are, moreover, prone to fault, are avoided. The electrode belt  1  has, moreover, a coding means  81  in the form of an EEPROM, which is activated when the feed line  6  is connected. It is thus possible to recognize whether the correct electrode belt  1  is connected to the evaluating unit  10 . 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.