Position control of medical appliances in the human body by means of phase difference measurement

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.

CROSS REFERENCE TO RELATED APPLICATIONS

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

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.

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.

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.

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

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.

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.

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.

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.

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).

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

First Exemplary Embodiment

FIG. 1shows a first embodiment of an apparatus for controlling a position x,y,z of a medical device10in a workspace A. The workspace A can be a cavity in the inside of a patient, like for instance the stomach, while the medical device10is preferably an endoscopy capsule. The endoscopy capsule10is 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 apparatus80and/or magnetic coil arrangement, as described for instance in DE 102 40 925 B3 and according to the exemplary illustration shown inFIG. 5.

Furthermore, the endoscopy capsule10contains 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.

The signal S is received by one or several of four receiving devices11-14in the first exemplary embodiment. To this end, the receiving devices11-14are provided with an antenna for receiving an electrical and/or a magnetic field. Furthermore, the receiving devices11-14each contain a preamplifier for amplifying the received signal. The signals SE11-SE14received and amplified with the receiving devices11-14are transmitted to a signal processing facility20. The signal processing facility20contains several facilities21-24, with each receive facility11-14being assigned a facility21-24. The facilities21-24each have a first and a second signal input and a signal output, with the received signals SE11-SE14applied in each instance at the second signal input.

Furthermore, a reference signal source60is provided, which generates a reference signal R. The reference signal source60may 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 facilities21-24.

The facilities21-24preferably each contain a mixing device31-34and a phase measurer41-44, with each mixing device31-34having a first and a second signal input in each instance. The first and/or second signal inputs of the facilities21-24correspond to the first and/or second inputs of the mixing devices31-34. The signal outputs of the phase measurer41-44correspond to the signal outputs of the facilities21-24.

The signals applied at the signal inputs of a mixing device31-34are mixed with one another in a known manner. The output signals of the mixing device31-34are each forwarded to a signal input of the phase measurer41-44. The phase measurer41-44determines 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 measurer41-44then correspond in each instance to the phase deviations dφ11,dφ12,dφ13,dφ14between the phases of the signals, which are applied at the first and second signal inputs of the facilities21-24and/or the mixing device31-34. For instance, the signal R is applied at the first signal input of the facility21, while the signal SE11received at the receive facility11is applied at the second signal input of the facility21. The output signal of the facility21then corresponds to the deviation dφ11=φ(SE11)−φ(R) between the phase φ(SE11) of the signal SE11and the phase φ(R) of the reference signal R. The same applies to the input and output signals of the facilities22-24, i.e. the output signals of the facilities21-24correspond to the phase deviations dφ11,dφ12,dφ13,dφ14between the phases φ(SE11), φ(SE12), φ(SE13), φ(SE14) of the signals SE11-SE14received at the receiving devices11-14and the phase φ(R) of the reference signal R generated by the reference signal source60.

Since the frequencies of the reference signal source60and the transmit facility do not generally exactly agree with the endoscopy capsule10, the phase deviations dφ11,dφ12,dφ13,dφ14do are not temporally constant but increase linearly with time. Provided that the endoscopy capsule10is not moved, the difference between the deviations must however be temporally constant. A difference formation apparatus50is therefore provided in the signal processing facility20, into which the deviations dφ11,dφ12,dφ13,dφ14are fed.

In the difference formation apparatus50, phase differences Δφ1, Δφ2, Δφ3are determined. Here any of the phase deviations dφ11,dφ12,dφ13,dφ14is determined as a reference value dφref, for instance dφref=dφ11, and the difference between the remaining phase deviations dφ12,dφ13,dφ14and the reference value dφrefis formed, i.e. Δφ1=dφ12−dφ11, Δφ2=dφ13−dφ11and Δφ3=dφ14−dφ11. The selection of one of the deviations as a reference value dφrefcan take place randomly or for instance as a function of the sum of the deviations dφ11,dφ12,dφ13,dφ14.

The phase differences Δφ1, Δφ2, Δφ3are determined temporally continuously or at intervals.

The phase differences Δφ1, Δφ2, Δφ3are fed to a control facility70. The control facility70is connected to a maneuvering apparatus80for influencing the position x, y, z of the endoscopy capsule10and uses the phase differences Δφ1, Δφ2, Δφ3to control the maneuvering apparatus80. Here x, y, z defines the position of the center of gravity of the endoscopy capsule10in a Cartesian coordinate system, which can be predetetermined for instance by the geometry of the maneuvering apparatus80.

Second Exemplary Embodiment

In a second, preferred exemplary embodiment, which is shown inFIG. 2, the medical device10, 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 devices11-14, with one of the receiving devices11-14subsequently being referred to as the first receive facility14and the remaining receiving devices being referred to as second receiving devices11-13. The receiving devices11-14each include an antenna for receiving an electrical and/or a magnetic field and a preamplifier for amplifying the received signal.

The signals SE11-SE14received and amplified with the receiving devices11-14are transmitted to a signal processing facility20. In the signal processing facility20, phase differences Δφ1, Δφ2, Δφ3are determined between the signals SE11-SE13received at the second receiving devices11-13and the signal SE14received at the first receive facility14, i.e. Δφ1=φ(SE11)−φ(SE14) Δφ2=φ(SE12)−φ(SE14), Δφ3=φ(SE13)−φ(SE14), with φ(X) symbolizing the phase of a signal X. The received signal SE14of the first receive facility14is used correspondingly as a reference signal R within the meaning of the first exemplary embodiment.

Facilities21-23, for instance phase detectors21-23, are provided for determining the phase differences Δφ1, Δφ2, Δφ3, with the number of phase detectors21-23corresponding at least to the number of the second receiving devices11-13.

Each phase detector21-23has a first and a second signal input and a signal output. In this way the first receive facility14for transmitting the received signal SE14is connected to the first signal input of each phase detector21-23. The second receiving devices11-13are each connected to the second signal input of the phase detectors21-23, while the signal outputs for transmitting the determined phase differences Δφ1, Δφ2, Δφ3are connected to a control facility70.

Since the frequencies of the received signals SE11-SE14are identical, it is possible to determine the phase differences in the second exemplary embodiment directly, contrary to the first exemplary embodiment.

The phase differences Δφ1, Δφ2, Δφ3are fed to the control facility70as in the first exemplary embodiment. As in the first exemplary embodiment, the control facility70is connected to a maneuvering apparatus80for influencing the position x, y, z of the endoscopy capsule10and uses the phase differences Δφ1, Δφ2, Δφ3to control the maneuvering apparatus80.

The signal processing facility20is configured such that instead of the received signal SE14of the first receive facility14, a signal SE11-SE13received at any of the other receiving devices11-13can be used as a reference signal R, i.e. for instance the signal SE12of the receive facility12. Accordingly, the phase differences Δφ1, Δφ2, Δφ3would be calculated according to Δφ1=φ(SE11)−φ(SE12) Δφ2=φ(SE13)−φ(SE12), Δφ3=φ(SE14)−φ(SE12). The receive facility12then assumes the role of the first receive facility, while the receiving devices11,13,14form 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 SE11-SE14, e.g. SE14and outputting this to the first signal inputs of the phase detectors21-23, while the second multiplexer selects the remaining three signals from the signals SE11-SE14, in the example SE11, SE12and SE13and forwards these to the second signal inputs in each case. Alternatively, other possibilities of defining any of the receiving devices11-14in a circuit-specific fashion as a first receive facility and conveying the signals SE11-SE14accordingly to the first and second signal inputs of the phase detectors are also conceivable.

More than four receiving devices are advantageously used to increase the measuring accuracy.FIG. 3shows a system comprising an endoscopy capsule10and eight receiving devices11-18, 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 devices11-18shown inFIG. 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 capsule10is surrounded by a network of receiving devices.

Functionality

The first and second exemplary embodiment differ in terms of providing the reference signal R. While a separate reference signal source60provides the reference signal R in the first exemplary embodiment, any of the receiving devices11-14in the second exemplary embodiment is used as a source of the reference signal R. The basic methods performed in the control facility70for controlling the position x,y,z of the endoscopy capsule10based on the determined phase differences Δφ1, Δφ2, Δφ3are identical for both exemplary embodiments.

With the system shown inFIG. 3, seven phase differences Δφ1to Δφ7are determined and fed to the control facility70. In the event that the endoscopy capsule10is not moved, i.e. is stationary relative to the receiving devices11-18, the phase differences Δφ1to Δφ7are temporally constant.

If the capsule10is moved, at least some of the phase differences Δφ1to Δφ7change during the movement. It can generally be assumed here that a large change in a phase difference accompanies a large movement of the capsule10in the direction of the connecting line between the capsule10and that of the corresponding receive facility.

The control facility70evaluates the determined phase differences Δφ1to Δφ7by the temporal behavior Δφ1(t) to Δφ7(t) of the phase differences Δφ1to Δφ7fed thereto being monitored. The momentary, i.e. phase differences Δφ1(t2) to Δφ7(t2) determined at a time instant t2, are compared here with the phase differences Δφ1(t1) to Δφ7(t1) determined immediately beforehand at a time instant t1(t1<t2).

Alternatively, the current phase differences Δφ1(t1) to Δφ7(t1) can be stored as reference values at a first arbitrary time instant t1. For instance, if an operator of the system has moved the endoscopy capsule10into a target position x(t1), y(t1), z(t1), 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 capsule10to be stationary. At this time instant t1, the current phase differences Δφ1(t1) to Δφ7(t1) determined are stored by the operator pushing a button for instance. The subsequent phase differences Δφ1(t) to Δφ7(t) determined at second time instants t are continuously compared in the control facility70with the stored reference values Δφ1(t1) to Δφ7(t1).

With a change in one or several of the phase differences Δφ1to Δφ, a control of the maneuvering apparatus80is initiated by the control facility70. In the two exemplary embodiments, the maneuvering apparatus80is preferably an arrangement with several individual coils for the contactless guidance of the endoscopy capsule10, as is described for instance as a “magnetic coil arrangement” in DE 103 40 925 B3. The maneuvering apparatus80generates, by a correspondingly targeted current feed of the individual coils, one or several magnetic field components, Bx, By, Bzand/or one or several gradient fields Gi,j=∂Bi/∂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 capsule10can exert torques and/or forces on the capsule10. The targeted current feed of the individual coils and consequently thereof the gradient fields Gi,jand/or the magnetic field components Bx, By, Bzare developed as a function of the control predetermined by the control facility70.

The control takes place in this way in that with a change in the position x, y, z of the endoscopy capsule10, which is connected to a change in one or several phase differences as described above, the gradient fields Gi,jand/or the magnetic field components Bx, By, Bzare adjusted so that the generated forces and torques counteract the detected movement of the capsule.

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 apparatus80. The maneuvering apparatus80of 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.

The result of the control of the maneuvering apparatus80by the control facility70is correspondingly such that the phase differences Δφ1(t) to Δφ7(t) remain temporally constant or the currently determined phase differences Δφ1(t) to Δφ7(t) correspond to the stored reference values Δφ1(t1) to Δφ7(t1). Unwanted movements of the endoscopy capsule or deviations in the position x, y, z of the capsule10from a target position x(t1), y(t1), z (t1) can be counteracted.

Further Embodiments

The movement of the capsule10in the x-direction, which is indicated by the arrow inFIG. 3, is reflected in a comparatively large change in the phase differences Δφ2, Δφ6determined in respect of the receiving devices12,16. The phase differences Δφ4, Δφ6determined in respect of the receiving devices14,18are by contrast not changed or only changed minimally.FIG. 4shows a diagram, in which, for the receiving devices11-18, the changes in the phase differences Δφ1, Δφ7, are plotted in any units, which can result during a movement of the capsule10in the x-direction according toFIG. 3.

During the evaluation of the phase differences in the control facility70, only a limited number of phase differences, in particular only the largest phase differences Δφ1, Δφ2, Δφ3, Δφ5, Δφ6, Δφ7are preferably taken into account, while the remaining Δφ4is disregarded. A weighting can alternatively take place in accordance with the sums of the phase differences.

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.

The receiving devices can be attached directly to the patient, for instance by adhesion to the skin, or on the maneuvering apparatus80. For practical reasons, the receiving devices inside the cylindrical maneuvering apparatus80are attached to the inner cylinder wall in the case of a maneuvering apparatus80and/or magnetic coil arrangement as described in DE 103 40 925 B3 for instance.