Abstract:
A system measures a change in position of a medical appliance, such as an endoscopy capsule. A device uses this measurement in order to influence the position of the medical appliance. The medical appliance sends a signal that is received by a multiplicity of spatially separate receiving devices. The time profile of the phase differences between the received signals and a reference signal provides an indication of whether the medical appliance has moved. In the event of a movement being detected, a maneuvering device can be regulated by a regulating means in such a way that the maneuvering device generates forces and/or torques and applies them to the medical appliance to counteract the detected movement.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and hereby claims priority to PCT Application No. PCT/EP2008/066988 filed on Dec. 8, 2008 and DE Application No. 10 2008 003 005.8 filed on Jan. 2, 2008, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a system for measuring a change in position of a medical device, such as an endoscopy capsule, and to an appliance which utilizes this measurement in order to influence the position of the medical device. 
         [0003]    Endoscopy capsules are used increasingly in medicine to diagnose or treat the inside of a patient. An endoscopy capsule can contain inter alia medical instruments for instance for biopsy or for introducing medicines into the body and/or image systems such as cameras. Furthermore, a permanent magnet can be integrated in the capsule, which affords the capsule a magnetic dipole moment, so that that it can be maneuvered at will with the aid of a magnetic coil arrangement as described in DE 103 40 925 B3 for instance. 
         [0004]    With examinations inside the body using a medical device such as an endoscopy capsule, the position of the device is generally monitored and if necessary influenced. For instance, with an examination of the stomach, this is half filled with water and the endoscopy capsules floats on the water surface. When recording images of the inside of the stomach, the problem arises that the capsule and with it the camera are moved as a result of the water movement which cannot be avoided, so that only unclear, blurred images can be recorded. In the event that a series of images of a certain region is to be recorded, it is necessary for the capsule to be stationary. 
         [0005]    For position determination purposes, electromagnetic measuring methods mostly use low-frequency magnetic alternating fields, which penetrate the human body in an almost uninfluenced fashion, thereby rendering an absolute position determination possible. A system of this type is described in WO 2005/120345 A2. Nevertheless, known systems on the one hand are disadvantageous in terms of a limited measuring accuracy. On the other hand, as a result of a poor signal-to-noise ratio and the necessary long integration time associated therewith, the temporal resolution is relatively minimal and the measuring value delay is comparatively great. Alternatively, phase difference measurements on high-frequency electromagnetic waves were proposed for the absolute position measurement of medical devices in the inside of the body. Account was not taken here of the fact that the wave propagation through body tissue with a different dielectric constant and conductivity results in a considerable deformation of the spherical wave front in the free space. Nevertheless, to enable an absolute position determination, complex correction methods are needed. 
       SUMMARY 
       [0006]    One potential object is therefore to specify an apparatus and a method, with which a change in position of a medical device can be detected and can counteract a change of this type. 
         [0007]    The inventors proposals assume that the absolute position of the device is not needed to control the position of a medical device inside the body and for a possible position correction but that only changes in position have to be detected in accordance with their direction and at least roughly in accordance with their size. When determining a deviation of the medical device from a target position or more generally if the medical device implements an unwanted movement, a controller can be used, which counteracts the deviation and/or the movement. It is accordingly sufficient only to implement a relative position determination. 
         [0008]    To this end, the medical device sends high-frequency electromagnetic signals continuously or at intervals, the electromagnetic signals being received by several spatially distributed receiving devices. The temporal behavior of the phase differences between the signals received at the receiving devices and a reference signal is monitored in order to detect a movement of the medical device. The reference signal can originate here from a separate reference signal source or from one of the receiving devices. In the event that one or several of the phase differences of the receiving devices change, it is assumed that the medical device has moved, so that if necessary corresponding countermeasures can be taken to counteract the movement. 
         [0009]    The countermeasures are triggered by a control facility as a function of the detected phase differences. The control facility controls a maneuvering apparatus for influencing the position of the medical device, with it being possible for the maneuvering apparatus to be a magnetic coil arrangement, as described in DE 103 40 925 B3. 
         [0010]    The method is advantageous in that only one relative position measurement is implemented, such that as a result of the high signal-to-noise ratio, a rapid measurement and thus a short reaction time ensue. Deviations in the medical device from a target position are thus rapidly detected and can be correspondingly corrected at short notice before the sum of the position changes becomes too great. Furthermore, contrary to the absolute position measurements, no knowledge is advantageously needed relating to the body tissue located between the medical device and/or the transmit facility and the receiving devices (e.g. dielectric constant, conductivity). 
         [0011]    To enable a more precise and rapid absolute position measurement, it is conceivable for the method and/or apparatus to be combined with other, e.g. low-frequency measuring methods for absolute position measurement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
           [0013]      FIG. 1  shows a first exemplary embodiment of the proposed apparatus, 
           [0014]      FIG. 2  shows a second exemplary embodiment of the proposed apparatus, 
           [0015]      FIG. 3  shows an arrangement of a plurality of receiving devices and a medical device on a patient, 
           [0016]      FIG. 4  shows an overview of the changes in phase difference occurring during a movement of a medical device according to  FIG. 3   
           [0017]      FIG. 5  shows a maneuvering apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       First Exemplary Embodiment 
       [0019]      FIG. 1  shows a first embodiment of an apparatus for controlling a position x,y,z of a medical device  10  in a workspace A. The workspace A can be a cavity in the inside of a patient, like for instance the stomach, while the medical device  10  is preferably an endoscopy capsule. The endoscopy capsule  10  is equipped with a permanent magnet and therefore has a magnetic dipole moment, so that it can be maneuvered magnetically and in a contact-free fashion with the aid of a maneuvering apparatus  80  and/or magnetic coil arrangement, as described for instance in DE 102 40 925 B3 and according to the exemplary illustration shown in  FIG. 5 . 
         [0020]    Furthermore, the endoscopy capsule  10  contains a transmit facility. This sends a modulated or non-modulated signal S continuously or at intervals, for instance a high frequency signal S with a frequency of 435 MHz. 
         [0021]    The signal S is received by one or several of four receiving devices  11 - 14  in the first exemplary embodiment. To this end, the receiving devices  11 - 14  are provided with an antenna for receiving an electrical and/or a magnetic field. Furthermore, the receiving devices  11 - 14  each contain a preamplifier for amplifying the received signal. The signals SE 11 -SE 14  received and amplified with the receiving devices  11 - 14  are transmitted to a signal processing facility  20 . The signal processing facility  20  contains several facilities  21 - 24 , with each receive facility  11 - 14  being assigned a facility  21 - 24 . The facilities  21 - 24  each have a first and a second signal input and a signal output, with the received signals SE 11 -SE 14  applied in each instance at the second signal input. 
         [0022]    Furthermore, a reference signal source  60  is provided, which generates a reference signal R. The reference signal source  60  may be a reference oscillator, the frequency of which preferably only deviates marginally from the frequency of the signal S. The reference signal R is applied at each first signal input of the facilities  21 - 24 . 
         [0023]    The facilities  21 - 24  preferably each contain a mixing device  31 - 34  and a phase measurer  41 - 44 , with each mixing device  31 - 34  having a first and a second signal input in each instance. The first and/or second signal inputs of the facilities  21 - 24  correspond to the first and/or second inputs of the mixing devices  31 - 34 . The signal outputs of the phase measurer  41 - 44  correspond to the signal outputs of the facilities  21 - 24 . 
         [0024]    The signals applied at the signal inputs of a mixing device  31 - 34  are mixed with one another in a known manner. The output signals of the mixing device  31 - 34  are each forwarded to a signal input of the phase measurer  41 - 44 . The phase measurer  41 - 44  determines the phase position of the signal applied at its input, with, for instance, the signal initially being amplified such that a rectangular signal almost arises and the zero passage of the rectangular signal is then determined. The output signals of the phase measurer  41 - 44  then correspond in each instance to the phase deviations dφ 11 ,dφ 12 ,dφ 13 ,dφ 14  between the phases of the signals, which are applied at the first and second signal inputs of the facilities  21 - 24  and/or the mixing device  31 - 34 . For instance, the signal R is applied at the first signal input of the facility  21 , while the signal SE 11  received at the receive facility  11  is applied at the second signal input of the facility  21 . The output signal of the facility  21  then corresponds to the deviation dφ 11 =φ(SE 11 )−φ(R) between the phase φ(SE 11 ) of the signal SE 11  and the phase φ(R) of the reference signal R. The same applies to the input and output signals of the facilities  22 - 24 , i.e. the output signals of the facilities  21 - 24  correspond to the phase deviations dφ 11 ,dφ 12 ,dφ 13 ,dφ 14  between the phases φ(SE 11 ), φ(SE 12 ), φ(SE 13 ), φ(SE 14 ) of the signals SE 11 -SE 14  received at the receiving devices  11 - 14  and the phase φ(R) of the reference signal R generated by the reference signal source  60 . 
         [0025]    Since the frequencies of the reference signal source  60  and the transmit facility do not generally exactly agree with the endoscopy capsule  10 , the phase deviations dφ 11 ,dφ 12 ,dφ 13 ,dφ 14  do are not temporally constant but increase linearly with time. Provided that the endoscopy capsule  10  is not moved, the difference between the deviations must however be temporally constant. A difference formation apparatus  50  is therefore provided in the signal processing facility  20 , into which the deviations dφ 11 ,dφ 12 ,dφ 13 ,dφ 14  are fed. 
         [0026]    In the difference formation apparatus  50 , phase differences Δφ 1 , Δφ 2 , Δφ 3  are determined. Here any of the phase deviations dφ 11 ,dφ 12 ,dφ 13 ,dφ 14  is determined as a reference value dφ ref , for instance dφ ref =dφ 11 , and the difference between the remaining phase deviations dφ 12 ,dφ 13 ,dφ 14  and the reference value dφ ref  is formed, i.e. Δφ 1 =dφ 12 −dφ 11 , Δφ 2 =dφ 13 −dφ 11  and Δφ 3 =dφ 14 −dφ 11 . The selection of one of the deviations as a reference value dφ ref  can take place randomly or for instance as a function of the sum of the deviations dφ 11 ,dφ 12 ,dφ 13 ,dφ 14 . 
         [0027]    The phase differences Δφ 1 , Δφ 2 , Δφ 3  are determined temporally continuously or at intervals. 
         [0028]    The phase differences Δφ 1 , Δφ 2 , Δφ 3  are fed to a control facility  70 . The control facility  70  is connected to a maneuvering apparatus  80  for influencing the position x, y, z of the endoscopy capsule  10  and uses the phase differences Δφ 1 , Δφ 2 , Δφ 3  to control the maneuvering apparatus  80 . Here x, y, z defines the position of the center of gravity of the endoscopy capsule  10  in a Cartesian coordinate system, which can be predetetermined for instance by the geometry of the maneuvering apparatus  80 . 
       Second Exemplary Embodiment 
       [0029]    In a second, preferred exemplary embodiment, which is shown in  FIG. 2 , the medical device  10 , as in the first exemplary embodiment, sends a modulated or non-modulated signal S with the aid of a transmit facility continuously or at intervals. The signal S is received by the receiving devices  11 - 14 , with one of the receiving devices  11 - 14  subsequently being referred to as the first receive facility  14  and the remaining receiving devices being referred to as second receiving devices  11 - 13 . The receiving devices  11 - 14  each include an antenna for receiving an electrical and/or a magnetic field and a preamplifier for amplifying the received signal. 
         [0030]    The signals SE 11 -SE 14  received and amplified with the receiving devices  11 - 14  are transmitted to a signal processing facility  20 . In the signal processing facility  20 , phase differences Δφ 1 , Δφ 2 , Δφ 3  are determined between the signals SE 11 -SE 13  received at the second receiving devices  11 - 13  and the signal SE 14  received at the first receive facility  14 , i.e. Δφ 1 =φ(SE 11 )−φ(SE 14 ) Δφ 2 =φ(SE 12 )−φ(SE 14 ), Δφ 3 =φ(SE 13 )−φ(SE 14 ), with φ(X) symbolizing the phase of a signal X. The received signal SE 14  of the first receive facility  14  is used correspondingly as a reference signal R within the meaning of the first exemplary embodiment. 
         [0031]    Facilities  21 - 23 , for instance phase detectors  21 - 23 , are provided for determining the phase differences Δφ 1 , Δφ 2 , Δφ 3 , with the number of phase detectors  21 - 23  corresponding at least to the number of the second receiving devices  11 - 13 . 
         [0032]    Each phase detector  21 - 23  has a first and a second signal input and a signal output. In this way the first receive facility  14  for transmitting the received signal SE 14  is connected to the first signal input of each phase detector  21 - 23 . The second receiving devices  11 - 13  are each connected to the second signal input of the phase detectors  21 - 23 , while the signal outputs for transmitting the determined phase differences Δφ 1 , Δφ 2 , Δφ 3  are connected to a control facility  70 . 
         [0033]    Since the frequencies of the received signals SE 11 -SE 14  are identical, it is possible to determine the phase differences in the second exemplary embodiment directly, contrary to the first exemplary embodiment. 
         [0034]    The phase differences Δφ 1 , Δφ 2 , Δφ 3  are fed to the control facility  70  as in the first exemplary embodiment. As in the first exemplary embodiment, the control facility  70  is connected to a maneuvering apparatus  80  for influencing the position x, y, z of the endoscopy capsule  10  and uses the phase differences Δφ 1 , Δφ 2 , Δφ 3  to control the maneuvering apparatus  80 . 
         [0035]    The signal processing facility  20  is configured such that instead of the received signal SE 14  of the first receive facility  14 , a signal SE 11 -SE 13  received at any of the other receiving devices  11 - 13  can be used as a reference signal R, i.e. for instance the signal SE 12  of the receive facility  12 . Accordingly, the phase differences Δφ 1 , Δφ 2 , Δφ 3  would be calculated according to Δφ 1 =φ(SE 11 )−φ(SE 12 ) Δφ 2 =φ(SE 13 )−φ(SE 12 ), Δφ 3 =φ(SE 14 )−φ(SE 12 ). The receive facility  12  then assumes the role of the first receive facility, while the receiving devices  11 ,  13 ,  14  form the group of the second receiving devices. A realization with the aid of a first and a second multiplexer would be conceivable, with the first multiplexer selecting one signal from the signals SE 11 -SE 14 , e.g. SE 14  and outputting this to the first signal inputs of the phase detectors  21 - 23 , while the second multiplexer selects the remaining three signals from the signals SE 11 -SE 14 , in the example SE 11 , SE 12  and SE 13  and forwards these to the second signal inputs in each case. Alternatively, other possibilities of defining any of the receiving devices  11 - 14  in a circuit-specific fashion as a first receive facility and conveying the signals SE 11 -SE 14  accordingly to the first and second signal inputs of the phase detectors are also conceivable. 
         [0036]    More than four receiving devices are advantageously used to increase the measuring accuracy.  FIG. 3  shows a system comprising an endoscopy capsule  10  and eight receiving devices  11 - 18 , which are attached in the region of a workspace A. In a concrete application, the workspace A can be the inside of a patient, with it being possible for the endoscopy capsule to be located in the stomach of the patient for instance. In addition to the receiving devices  11 - 18  shown in  FIG. 3 , further receiving devices can be provided in planes in front of and behind the image plane shown. The receiving devices are advantageously arranged such that the whole region to be examined with the endoscopy capsule  10  is surrounded by a network of receiving devices. 
       Functionality 
       [0037]    The first and second exemplary embodiment differ in terms of providing the reference signal R. While a separate reference signal source  60  provides the reference signal R in the first exemplary embodiment, any of the receiving devices  11 - 14  in the second exemplary embodiment is used as a source of the reference signal R. The basic methods performed in the control facility  70  for controlling the position x,y,z of the endoscopy capsule  10  based on the determined phase differences Δφ 1 , Δφ 2 , Δφ 3  are identical for both exemplary embodiments. 
         [0038]    With the system shown in  FIG. 3 , seven phase differences Δφ 1  to Δφ 7  are determined and fed to the control facility  70 . In the event that the endoscopy capsule  10  is not moved, i.e. is stationary relative to the receiving devices  11 - 18 , the phase differences Δφ 1  to Δφ 7  are temporally constant. 
         [0039]    If the capsule  10  is moved, at least some of the phase differences Δφ 1  to Δφ 7  change during the movement. It can generally be assumed here that a large change in a phase difference accompanies a large movement of the capsule  10  in the direction of the connecting line between the capsule  10  and that of the corresponding receive facility. 
         [0040]    The control facility  70  evaluates the determined phase differences Δφ 1  to Δφ 7  by the temporal behavior Δφ 1 (t) to Δφ 7 (t) of the phase differences Δφ 1  to Δφ 7  fed thereto being monitored. The momentary, i.e. phase differences Δφ 1 (t 2 ) to Δφ 7 (t 2 ) determined at a time instant t 2 , are compared here with the phase differences Δφ 1 (t 1 ) to Δφ 7 (t 1 ) determined immediately beforehand at a time instant t 1  (t 1 &lt;t 2 ). 
         [0041]    Alternatively, the current phase differences Δφ 1 (t 1 ) to Δφ 7 (t 1 ) can be stored as reference values at a first arbitrary time instant t 1 . For instance, if an operator of the system has moved the endoscopy capsule  10  into a target position x(t 1 ), y(t 1 ), z(t 1 ), in which a series of images of a certain region of the inside of the stomach is to be recorded, it is necessary for the capsule  10  to be stationary. At this time instant t 1 , the current phase differences Δφ 1 (t 1 ) to Δφ 7 (t 1 ) determined are stored by the operator pushing a button for instance. The subsequent phase differences Δφ 1 (t) to Δφ 7 (t) determined at second time instants t are continuously compared in the control facility  70  with the stored reference values Δφ 1 (t 1 ) to Δφ 7 (t 1 ). 
         [0042]    With a change in one or several of the phase differences Δφ 1  to Δφ, a control of the maneuvering apparatus  80  is initiated by the control facility  70 . In the two exemplary embodiments, the maneuvering apparatus  80  is preferably an arrangement with several individual coils for the contactless guidance of the endoscopy capsule  10 , as is described for instance as a “magnetic coil arrangement” in DE 103 40 925 B3. The maneuvering apparatus  80  generates, by a correspondingly targeted current feed of the individual coils, one or several magnetic field components, B x , B y , B x  and/or one or several gradient fields G i,j =∂B i /∂j with i,j=x, y, z, as a result of which the interaction with the magnetic dipole moment of the permanent magnet of the capsule  10  can exert torques and/or forces on the capsule  10 . The targeted current feed of the individual coils and consequently thereof the gradient fields G i,j  and/or the magnetic field components B x , B y , B z  are developed as a function of the control predetermined by the control facility  70 . 
         [0043]    The control takes place in this way in that with a change in the position x, y, z of the endoscopy capsule  10 , which is connected to a change in one or several phase differences as described above, the gradient fields G i,j  and/or the magnetic field components B x , B y , B z  are adjusted so that the generated forces and torques counteract the detected movement of the capsule. 
         [0044]    As the relationships between the current feed of one or several of the individual coils and the torques and forces thus generatable are known in respect of amount and direction, the movement of the endoscopy capsule which is detected by monitoring the phase differences can be selectively counteracted by the corresponding individual coils having current applied in accordance with the detected movement direction and if necessary amplitude. Reference is made to DE 103 40 925 B3 for the basic functionality of the maneuvering apparatus  80 . The maneuvering apparatus  80  of the apparatus operates comparably, but is not defined in terms of design of the “magnetic coil arrangement” in DE 103 40 925 B3 but can instead also include more or fewer individual coils and be embodied in order to generate another number of magnetic degrees of freedom than the maneuvering apparatus or “magnetic coil arrangement” in DE 103 40 925 B3. 
         [0045]    The result of the control of the maneuvering apparatus  80  by the control facility  70  is correspondingly such that the phase differences Δφ 1 (t) to Δφ 7 (t) remain temporally constant or the currently determined phase differences Δφ 1 (t) to Δφ 7 (t) correspond to the stored reference values Δφ 1 (t 1 ) to Δφ 7 (t 1 ). Unwanted movements of the endoscopy capsule or deviations in the position x, y, z of the capsule  10  from a target position x(t 1 ), y(t 1 ), z (t 1 ) can be counteracted. 
       Further Embodiments 
       [0046]    The movement of the capsule  10  in the x-direction, which is indicated by the arrow in  FIG. 3 , is reflected in a comparatively large change in the phase differences Δφ 2 , Δφ 6  determined in respect of the receiving devices  12 ,  16 . The phase differences Δφ 4 , Δφ 6  determined in respect of the receiving devices  14 ,  18  are by contrast not changed or only changed minimally.  FIG. 4  shows a diagram, in which, for the receiving devices  11 - 18 , the changes in the phase differences Δφ 1 , Δφ 7 , are plotted in any units, which can result during a movement of the capsule  10  in the x-direction according to  FIG. 3 . 
         [0047]    During the evaluation of the phase differences in the control facility  70 , only a limited number of phase differences, in particular only the largest phase differences Δφ 1 , Δφ 2 , Δφ 3 , Δφ 5 , Δφ 6 , Δφ 7  are preferably taken into account, while the remaining Δφ 4  is disregarded. A weighting can alternatively take place in accordance with the sums of the phase differences. 
         [0048]    In the event that the endoscopy capsule is equipped with an imaging system such as a camera and transmits a video signal, the transmitter available for this purpose in the capsule can also be used to transmit the signal S, with a carrier frequency of 433 MHz typically being used. It is then possible to dispense with a separate transmit facility or other additional equipment in the capsule for transmitting the signal S for position control purposes. The transmit program of the capsule must possibly be changed such that the image transmission is interrupted at predetermined intervals and a non-modulated signal is sent for the position measurement for a few microsecs. 
         [0049]    The receiving devices can be attached directly to the patient, for instance by adhesion to the skin, or on the maneuvering apparatus  80 . For practical reasons, the receiving devices inside the cylindrical maneuvering apparatus  80  are attached to the inner cylinder wall in the case of a maneuvering apparatus  80  and/or magnetic coil arrangement as described in DE 103 40 925 B3 for instance. 
         [0050]    The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).