Abstract:
The invention relates to a brain stimulation electrode line ( 10 ) for electric stimulation of the brain areas with an elongated flexible electrode line body ( 12 ) having on or near its distal end at least one stimulation electrode ( 18 ) designed for delivering electric pulses to surrounding body tissue in the event of use. The brain stimulation electrode line ( 10 ) is characterized in that the electrode line body has on its distal end at least one ultrasonic transducer ( 20 ), which is arranged so that it can detect reflected ultrasound in a detection range aligned distally along the longitudinal direction of the electrode line body ( 12 ).

Description:
This application takes priority from German Patent Application DE 10 2008 015 156.4, filed 20 Mar. 2008, the specification of which is hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a brain stimulation electrode line for stimulating deep areas of the brain. The brain stimulation electrode line has an elongated flexible electrode line body on which at least one stimulation electrode is arranged at or near its distal end. This stimulation electrode serves to deliver electric pulses to surrounding body tissue when it is used. 
     2. Description of the Related Art 
     The stimulation of deep areas of the brain is a medical treatment method for treating symptoms of Parkinson&#39;s disease, for example. Brain stimulation electrodes for deep brain stimulation (DBS) are usually implanted today by means of neuroradiological planning based on computer tomography and/or magnetic resonance imaging data. The brain stimulation electrode lines may currently be advanced only straight ahead with the help of a stereotactic target yoke. The direction of implantation is determined according to the neuroradiological planning in such a way as to prevent possible injury to intercranial blood vessels. 
     One disadvantage of this method is the residual risk of intracranial bleeding because the brain may shift with regard to the planned coordinates during implantation. 
     Another disadvantage of the implantation technique described here is that controllable brain stimulation electrode lines cannot be implanted on the basis thereof because in this case neuroradiological planning cannot be performed in realtime for all implantation feasible pathways with the controllable brain stimulation electrode line. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the invention is to provide a brain stimulation electrode line with which at least some of the disadvantages of the state of the art can be avoided. 
     According to the invention, this object is achieved by a brain stimulation electrode line of the type defined in the introduction, which has in the area of its distal end an ultrasonic transducer that is equipped so that it has a detection area pointing distally in the longitudinal direction of the electrode line body, i.e., looking forward in the longitudinal direction of the brain stimulation electrode line, so to speak. If necessary, multiple ultrasonic transducers, which are arranged so that some of them look straight ahead in the direction of the electrode line and others are directed obliquely, may also be provided. In any case, the brain stimulation electrode line has fewer than fifteen ultrasonic transducers. 
     The ultrasonic transducer(s) is/are preferably Pulse Wave Doppler sensors for detection of moving erythrocytes. 
     The brain stimulation electrode line is preferably connected to its insertion device, which preferably has at least one ultrasonic generator and receiver as well as a demodulator, which trigger the ultrasonic transducer to emit ultrasonic waves and which receive and demodulate the signals generated by the ultrasonic transducers due to the ultrasonic waves that are reflected and received. The demodulator is connected to a control and analyzer unit, which is designed to generate a detection signal from the demodulated ultrasonic signal, indicating whether there is a blood vessel in the detection area of the ultrasonic transducer. 
     The control and analyzer unit may be connected either to an optical display or an acoustic signal generator or to both. 
     The control and analyzer unit is preferably designed in combination with the optical display or the acoustic signal generator or both, so that the signal displayed or reproduced acoustically is different from the signal generated by the respective ultrasonic transducer, depending on the distance from the detected blood vessel. In this context, the optical display is preferably designed so that the distance from a detected blood vessel to the respective ultrasonic transducer is represented by harmless colors. In the case of the acoustic signal generator, the control and analyzer unit is preferably designed in combination with this acoustic signal generator to represent different distances between a detected blood vessel and a respective ultrasonic transducer by different sound levels. 
     The brain stimulation electrode line preferably comprises not just one transducer but multiple transducers, e.g., five ultrasonic transducers, one of which has a detection range aligned exactly along the extended longitudinal axis of the electrode line body, while four other ultrasonic transducers are aligned so that they each detect different sectors directed obliquely at the side. 
     In this case, the insertion device preferably includes a channel switch with the help of which the ultrasonic generator and receiver as well as the demodulator may optionally be connected to one of the various ultrasonic transducers. The output signals of the various ultrasonic transducers are then processed in alternation according to a type of time-multiplex method by switching the channel switch. Alternatively, each ultrasonic transducer may also be connected to a suitable ultrasonic generator and receiver. However, this would unnecessarily increase the complexity. In the case of a plurality of ultrasonic transducers and one channel switch, the control and analyzer unit is preferably connected to the channel switch and causes the connection to be switched between one ultrasonic generator and receiver and multiple ultrasonic transducers. 
     In the case of a plurality of ultrasonic transducers, the control and analyzer unit is also designed not only to display a signal on the optical display indicating the proximity of a blood vessel in a color-coded display but instead it additionally shows the position of a detected blood vessel relative to the lengthened longitudinal axis of the distal end of the electrode line body. For example, the optical display may be constructed so that it is subdivided into at least five display sectors, a central sector of which is surrounded by four peripheral sectors. In the central sector, a display signal obtained from the output signals of the central ultrasonic transducer is reproduced. The four other display sectors are assigned to one or more of the peripheral ultrasonic transducers. According to this latter variant of the embodiment, on insertion of the inventive brain stimulation electrode line, not only is the distance from a blood vessel taken into account but also the relative lateral position of a detected blood vessel is taken into account. This allows controlled yielding on insertion of the brain stimulation catheter and thus makes it possible to avoid intracranial; bleeding in an even more secure manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be explained in greater detail on the basis of an exemplary embodiment with reference to the figures, in which: 
         FIG. 1 : shows a schematic longitudinal section through a distal end of an inventive brain stimulation electrode line; 
         FIGS. 2   a  and  2   b : show a schematic longitudinal section through a distal end of an alternative variant of an exemplary embodiment of a brain stimulation electrode line; 
         FIGS. 3   a  and  3   b : show details of a variant of the embodiment of a brain stimulation electrode line having a plurality of ultrasonic transducers in a schematic diagram; 
         FIG. 4 : shows a basic diagram of an insertion device for a brain stimulation electrode line  10  according to the invention; and 
         FIGS. 5   a  and  5   b : show a diagram of an optical display for the insertion device according to  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows schematically a distal end of a brain stimulation electrode line  10  in a partially cut-away diagram. The brain stimulation electrode line  10  has an electrode line body  12 , which is formed by an outer helical coil  14  made of metal and a sheathing  16  of a biocompatible plastic that surrounds the metallic helical coil  14  over most of the length of the brain stimulation electrode line  10 . A ring electrode  18 , which is arranged in the vicinity of the distal end of the brain stimulation electrode line  10  is not surrounded by the sheathing  16  and has an electrically conducting outside surface, which is attached to the metallic helical coil  14 , so that it conducts electricity and serves to deliver stimulation pulses. 
     In the interior of the brain stimulation electrode line  10 , an ultrasonic transducer  20  is arranged all the way at its distal end and is connected by at least one signal line  22  to a connection of the brain stimulation electrode line not shown in  FIG. 1 . 
     The ultrasonic transducer  20  is embedded in a closing body  24 , which seals the brain stimulation electrode line  10  and/or its electrode line body  12  on their distal end(s). The closing body  24  is made of a biocompatible material that allows input and output coupling for transmission of ultrasonic waves with low damping. The shape of the closing body is adapted to the shape of the ultrasonic transducer  20 , so the ultrasonic transducer  20  and the closing body  24  are in contact over a large area. 
       FIGS. 2   a  and  2   b  show a preferred variant of the embodiment in which the ultrasonic transducer  20 ′ and the signal line  22 ′ are guided in a lumen of the electrode line body  12  so that they are movable longitudinally. The signal line  22 ′ is therefore designed as a removable mandrel.  FIG. 2   a  shows the ultrasonic transducer  20 ′ and the signal line  22 ′ in the state in which they are completely inserted into the lumen of the electric line body  12 ′, with at least one front surface of the ultrasonic transducer  20 ′ being in flush contact with an inside surface of the closing body  24 ′.  FIG. 2   b  shows how the ultrasonic transducer  20 ′ can be removed from the lumen of the electrode line body  12 ′ together with the signal line  22 ′. The signal line  22 ′ is therefore embedded in the mandrel, which is labeled with the same reference numeral  22 ′. This mandrel  22 ′ may even contain multiple signal lines and may therefore also be referred to as a signal line body. 
     All these embodiments have in common the fact that the brain stimulation electrode line for deep brain stimulation and one or more ultrasonic transducers are arranged either in surface contact or on a hemisphere in the probe body of the brain stimulation electrode line itself or at the tip of a guide catheter, such that the detection ranges of the ultrasonic transducers are directed in the distal direction of the brain stimulation electrode line. 
       FIGS. 3   a  and  3   b  show one possible arrangement of five ultrasonic transducer crystals  20  as ultrasonic transducers, which are arranged on a convex carrier  27  in the tip of a brain stimulation electrode line  10 , so that it is possible to look to the right and obliquely forward from the respective ultrasonic transducers  20 . 1  and  20 . 2 . 
       FIG. 3   a  here shows the distal end of a preferred variant of an embodiment of such a signal line body  26  with signal lines  22 ′ which are embedded therein and are connected at their respective distal ends to a respective ultrasonic transducer  20 . 1  or  20 . 2 . The ultrasonic transducers  20 . 1 ,  20 . 2  are embedded in an end face of the signal line body  26 , so that they form a central ultrasonic transducer  20 . 1  in a view of the end face ( FIG. 3   b ) as well as forming four peripheral ultrasonic transducers  20 . 2  distributed uniformly around it. 
     As shown in  FIG. 3   a , the central ultrasonic transducer  20 . 1  is oriented so that the detection range  28 . 1  is aligned concentrically with the lengthened longitudinal axis of the signal line body  26 , while the peripheral ultrasonic transducers  20 . 2  are arranged so that their detection ranges  28 . 2  are each aligned obliquely forward. 
     The signal line body  26  with a total of five ultrasonic transducers  20 . 1  and  20 . 2  may be inserted into the lumen of an electrode line body  12 ′, as illustrated in  FIGS. 2   a  and  2   b , in such a way that the convex end face of the signal line body  26  is in flush contact with a corresponding concave inside surface of a correspondingly shaped closing body. This forms a brain stimulation electrode line having five ultrasonic detection channels. In one or more embodiments, the elongated flexible electrode line body has a maximum outside diameter of 1 mm on a length of the elongated flexible electrode line body that is intended for implantation 
     The ultrasonic transducers  20  are each Pulse Wave Doppler sensors, which are designed to detect moving erythrocytes according to the Doppler principle, which is already known per se. In this way, blood vessels in the detection area of a respective ultrasonic transducer  20  can be detected with the help of the ultrasonic transducers  20 . 
     This allows detection of blood vessels upstream from the distal end of the brain stimulation electrode line  10  when the latter is to be inserted up to a respective stimulation site. 
     To do so, the ultrasonic transducers  20  of the brain stimulation electrode line  10  are connected to an insertion device, which is diagrammed schematically in  FIG. 4  and has a signal processing unit  30  next to the brain stimulation electrode line  10 . First it includes a channel switch  32  to optionally send the signals originating from the respective ultrasonic transducer  20  to an ultrasonic generator and receiver as well as a demodulator  34 , whose output values are in turn sent to a control and analyzer unit  36 . This control and analyzer unit  36  also controls the channel switch  32 . Furthermore, the control and analyzer unit  36  is connected to a graphic display  38  and to an acoustic signal generator  40 . 
     The ultrasonic generator  34  generates ultrasonic pulses whose frequency and ultrasonic energy are adapted for intracerebral use, such that a blood vessel running at a distance of 0-50 mm upstream from the distal end of the brain stimulation electrode line  10  can be evaluated there. 
     The control and analyzer unit  36  is designed in connection with the optical display  38  and/or the acoustic signal generator  40 , so that the respective signal displayed and/or reproduced acoustically is different, depending on the distance between the detected blood vessel and the respective ultrasonic transducer  20 . The loudness of the signal reproduced acoustically may depend on distance, for example. Even better, the acoustic signals depends on distance with regard to the tone pitch, such that high tones characterize a short distance and low-frequency tones characterize a greater distance. No acoustic signal at all is an indication that there are no blood vessels in the detection area of the ultrasonic transducer or transducers. 
     When the signal processing unit  30  detects a blood vessel in the forward direction of an ultrasonic transducer, the control and analyzer unit  36  determines the distance from this blood vessel and initiates an optical signal and an acoustic signal with which the user is notified of the distance from the detected blood vessel. The optical display  38  also supplies in addition to the distance information, information about the direction in which a blood vessel has been detected by the fact that a separate optical display element, e.g., in the form of a sector of the optical display  38  (see further below) for each ultrasonic transducer  20 . For example, this display element may be green, according to the distance (no blood vessel ahead), yellow (blood vessel ahead at a distance of a-b mm) or red (blood vessel immediately ahead). 
     Similarly, the acoustic signal generator  40  may also be controlled in such a way that it receives information about the direction in which a blood vessel has been detected. The repetition frequency of an interrupted acoustic signal is increased in inverse proportion to the distance from the blood vessel. If the blood vessel is directly ahead, then a continuous tone is delivered. 
     The user can individually define the ranges for the various warning levels (green, yellow, red) in the analyzer unit  36 . 
     The optical display  38  is preferably constructed as shown in  FIG. 5 . It has a central sector  42 , which is assigned to the central transducer  20 . 1  and a total of four peripheral sectors  44 , each being assigned to one of the peripheral transducers  20 . 2 . The sectors are each divided into subsectors and the optical display  38  is designed in conjunction with the control and analyzer unit  36 , so that the number of subsectors controlled is greater, the closer a respective detected blood vessel is to the respective transducer. A blood vessel entering the detection range of the central ultrasonic transducer  20 . 1  results in only a central subsector of the central sector  42  being controlled, i.e., being shown in black, for example. More subsectors of the central sector  42  are controlled as the detected blood vessel is closer to the central ultrasonic transducer  20 . 1 . 
     Accordingly, the control and analyzer unit  36  is designed in conjunction with the optical display  38  and the subsectors of the peripheral sectors  44  are also to be triggered as a function of the distance between a blood vessel and the respective ultrasonic transducer to be detected. If the detected blood vessel is still at a great distance from the respective ultrasonic transducer  20 . 2 , then only the internal subsector of the respective peripheral sector  44  is triggered. With increasing proximity, additional subsectors of the peripheral sector  44  are activated gradually from the inside to the outside, e.g., they are shown as being dark in the illustration in  FIG. 5   b  as an example. Such a display allows an intuitive estimation of the respective situation prevailing upstream from the distal end of the brain stimulation electrode line. 
       FIG. 5   b  shows the possible display of the distance information with the optical display  38  having five sectors (four quadrants=obliquely forward, one center=forward right) according to  FIG. 5   a . Each sector is divided into subsectors and indicates the distance from a blood vessel directly ahead in the direction of the ultrasonic transducer assigned to the respective sector  42  or  44  of the display  38  using the colors white=no Doppler signal, green=weak signal, yellow=medium signal, red=strong signal.