DE102007042622A1 - Method and system for determining the position and / or orientation of an object - Google Patents

Abstract

The invention relates to a method and a system for determining the position and / or orientation of an object in which the electromagnetic field generated by at least one emitter is measured by means of at least one field sensor and / or the object position and / or the measured values. or object orientation is determined in the generated electromagnetic field, characterized in that a reference object (1) with at least two field sensors (2a, 2b, 2c, 2d) is arranged to compensate for disturbances in the generated electromagnetic field, in particular in the environment of the object whose relative spatial desired positions (O1, O2, O3, O4) known to each other, in particular fixed and known, wherein by means of the field sensors (2a, 2b, 2c, 2d) of the reference object (1) the electromagnetic field measured and from the measured value / the measured values faulty actual position (V1, V2, V3, V4) of the field sensors (2a, 2b, 2c, 2d) of the reference object (1) we determined and based on the deviations between the actual and desired positions, a correction is determined by means of which the measured object position (P1 ', P2') and / or object orientation is corrected, in particular in real time.

Description

The The invention relates to a method for determining the position and / or Orientation of an object in which by means of at least one field sensor on / in the object the electromagnetic generated by at least one emitter Field measured and from the measured value / the measured values the object position and / or object orientation in the generated and electromagnetic Field is determined. Emitters of this type are also called transmitters designated.

The The invention further relates to a system for determining the position and / or orientation of an object comprising an object having at least a field sensor, at least one emitter for generating an electromagnetic Feldes and a measuring device with which the position and / or Orientation of the object by measuring the electromagnetic Field can be determined by means of at least one field sensor.

in the It is known in the prior art that the position of a substantially Any object in space, for example by means of a generated electromagnetic Field monitors can be. The principle of this type of position and / or orientation determination of an object is under the name of the so-called electromagnetic Tracking known in the art.

Essential for a Such method or system for carrying out such a method it is that by means of at least one emitter an electromagnetic Field, in particular a spatial extensive electromagnetic field is generated, its field strength and / or Field direction in dependence from the space coordinates is known, so the possibility exists, by means of a field sensor, the local field strength and / or Field direction to determine the location of the field sensor and thus from the Measured value or the measured values determined to the position of the field sensor to deduce within the generated electromagnetic field. there can z. B. by means of a field sensor one after the other, the field measured from several emitter coils and from this the position in space be determined.

Becomes Accordingly, at least one field sensor on an object or in a Arranged object, so hereby the position of the object within the electromagnetic generated by the at least one emitter Field are determined. By temporal succession determination The position can therefore be tracked, with which not only the current position or orientation of the object, but also the time course of a movement can be determined.

in the The prior art is in systems for carrying out such a method Accordingly, provided that at least one emitter, optionally also several emitters for the production of different overlapping ones Fields is provided, as well as an object with at least one field sensor and a measuring device for detecting the measured values of the at least in amount and / or direction measured electromagnetic Field, wherein preferably the measuring device established is, in addition to the acquisition of the measured values, a corresponding evaluation and to carry out a position determination from the evaluation.

in this connection can be the measuring principle with both static electromagnetic fields be performed as well as with temporally varying electromagnetic fields. Depending on the type of electromagnetic selected Field can different sensors are used. For example are preferred for temporally variable electromagnetic fields As field sensors coils are used, in which on the basis of induced currents on the amount and / or direction of the measured electromagnetic Field closed back at the location of the coil can be.

at Static electromagnetic fields, for example, Hall sensors be used. Essential in all known at the outset Procedure is that the local dependence of generated static or temporally variable electromagnetic Feldes at least theoretically known to from the readings on respective location of an object to be considered so on the position to be able to conclude.

there it is in the prior art as a disadvantage of such a method It is known that the generated electromagnetic field can be disturbed by z. B. external influences. External influences can be, for example be given by others, constant in time or especially temporally variable electromagnetic fields as well as metallic Objects in the vicinity of the generated electromagnetic field or within the generated electromagnetic field.

hereby can Field distortions arise, whereby the at least theoretically known produced electromagnetic field is no longer exactly coincident with the practically present generated electromagnetic field, so that Although, due to the measured values obtained a position of the considered Object can be determined, but this due to the interference by one of the aforementioned possibilities is flawed.

The The object of the invention is to provide a method and a system of the initially mentioned generic type to provide with the opportunity is given, an exact, in particular of any disturbances independent positioning at least one object within a generated and thus at least theoretically known electromagnetic field.

According to the invention this Task by means of a generic method mentioned above solved, that is further developed by the fact that to compensate for disturbances in generated electromagnetic field, especially in the environment of the object, a reference object with at least two field sensors is arranged, their relative spatial desired positions to each other known, in particular fixed and known, wherein by means of the field sensors of the reference object, the electromagnetic field measured and off the measured value / the measured values faulty actual positions of the field sensors of the reference object and based on the deviations between the actual and target position a correction is determined by means of corrects the measured object position and / or object orientation becomes.

Farther solved the object is achieved by a system of the aforementioned generic type, which is characterized according to the invention that for compensation of disorders in the generated electromagnetic field, a reference object with at least has two field sensors whose relative spatial desired position to each other known, in particular fixed and known, wherein by means of the field sensors of the reference object and the measuring device of the electromagnetic Field measurable and erroneous from the measured value / the measured values Actual positions of the field sensors of the reference object can be determined are, wherein the measuring device is further set up on the basis of Deviations between actual and set position of the reference object to determine a correction by means of the measured object position and / or object orientation is correctable.

Of the The essential core idea of the invention is that in particular in real time a possibly present disturbance of the generated electromagnetic Field and from such a rating Correction is determined by means of a faulty position and / or orientation of one in position or in orientation to be determined object can be corrected.

Doing this the invention exploits that in a reference object at least two field sensors are arranged, preferably even more field sensors are arranged as two, their spatial positions fixed and are known and within the scope of this description of the invention as target positions be designated.

Become these known positions of the field sensors of the reference object determined by the method mentioned, the specifically determined positions in the reference object used coming sensors in case of failure of the electromagnetic field do not coincide with the known spatial target positions, because it is a fault of the field to distortions and thus deviations in the local dependence the amount and / or orientation of the generated electromagnetic Field comes.

by virtue of the fact that then the objectively known nominal position of a each field sensor is different from the actual measured and thus faulty actual position of the field sensor, it is possible to to evaluate the determined deviations and from this a correction to determine which can be used to position or the Orientation of the observed object to correct and thus actually correct position or orientation of this object in the disturbed magnetic field to obtain.

The Correction can be formed, for example, such that it is suitable, the measured faulty actual positions the field sensors of the reference object to be converted into the actual known spatial Target positions of the field sensors of the reference object. Will one Such correction formed from the known deviations, so the same correction is also appropriate to the objectively flawed Object position and / or object orientation to correct in the each actually present sizes.

in this connection can it be provided that from the measured actual positions of Field sensors of the reference object and the known target positions an interpolation and / or extrapolation function is formed, by means of a field disturbed Object position and / or object orientation by applying the function is corrected to this position / orientation. That's how it turns out thus, in abstract terms, the corrected position / orientation analytically as F (faulty position / orientation).

Preferably, it is therefore provided that the measuring device used for determining the magnitude and / or the orientation of the measured electromagnetic field is also set up using the deviations between the desired and actual positions of the reference object such a correction, in particular to determine such a function and this determined Function then apply for the determination of the position and / or orientation of the object to be measured within the electromagnetic field. Such a function mentioned above can be nourished, for example, by a polynomial, wherein the approximation can be optimized by a polynomial of the nth degree with the highest possible value for n.

In another version it can also be provided that from the measured actual positions the field sensors of the reference object and the known target positions calculates a theoretical electromagnetic compensation field which is used to correct the real disturbed electromagnetic field is used.

So It is necessary, as mentioned at the beginning, that the location dependency the amount and / or the orientation of the generated electromagnetic field is known to use the measured values measured on the position of an object close can. Thus, according to the invention, there is the possibility that real disturbed To detect electromagnetic field, this may be real disturbed electromagnetic Field of calculation of the position and / or orientation of the object be based on what the corresponding information, for example, within the measuring device can be stored.

For example Accordingly, it may be provided that by computer-aided superimposition of the Compensation field with the assumed undisturbed generated electromagnetic Field a simulated, real disturbed Electromagnetic field is calculated, which then the position and / or Orientation determination of the object can be based. It can be assumed that the determination of the compensation field is all the more more precisely, the more field sensors within the reference object be used.

When Field sensors are in a preferred embodiment, for example coils used, it can be provided that at least two Coils the reference object to each other a different orientation exhibit.

In another embodiment it can be provided that the field sensors are formed as coils are at least one coil arranged outside a plane is in which two more coils lie. Such an arrangement therefore has at least three field sensors, resulting in another increase the accuracy of the correction leads.

At the Use of the method or a device according to the invention or a Systems to carry of the method may be provided in a preferred variant be that the measurements of several field sensors by means of a temporal multiplexing over a Measuring line of a measuring device be recorded.

This opens the possibility, if applicable, already existing measuring instruments for carrying out the known in the prior art method for the inventive method use. So can the measured values of a plurality of field sensors by means of such Device are detected, although the device provided for this purpose does not have a correspondingly high number of test leads or input channels for Capturing the measured values. To make the temporal multiplexing, for example, a be provided external device, which an input channel of a meter is upstream or the meter itself can already internally provide appropriate electronics for multiplexing.

All in all It will be provided here that the measurement of the measured values for the Determining the object position or the object orientation with a higher Frequency takes place as the acquisition of the measured values of the field sensors of the reference object. This is based on the fact that the reference object is preferred stationary or only with a low or low speed as the object to be measured within the electromagnetic Field is moved. So it is enough, the position of the field sensors of the reference object to be detected at a lower sampling rate as the position of the object, since thus the underlying Correction with a larger time constant changes than the position of the object.

In a particularly preferred application of the method or the inventive system It can be provided that an object whose position and / or Orientation is determined by a medical instrument is formed. In such an object, it may, for. B. a needle or a catheter, so that with the inventive method the current position or the movement trajectory of such medical instrument can be accurately tracked, even if z. B. metallic objects are within the influence of the generated electromagnetic field, such as B. other instruments or an operating table.

The disturbances caused thereby, such as field distortions, can be determined on the basis of the reference object and a correction can be formed from this in order to thus precisely determine the position and orientation of the object. For such a medical application, it may be provided that a reference object in in the vicinity of an intervention area or around an intervention area on a patient.

For example if such an area can be a puncture site, at which a needle or a catheter is to be applied. Just for one such application may preferably be provided that a reference object frame-shaped, in particular annular is formed and within the frame / ring, the at least two Field sensors are arranged. So such a ring can be the intervention area, especially the puncture site, surrounded, so that in the position or orientation determining object, such as the needle or a catheter through which the frame / ring passes and thus a particularly accurate position determination is possible, there the disorder of the electromagnetic field immediately in the vicinity of the is determined. It can be done in such a context at least two field sensors, especially on different ones Be arranged levels and possibly. Also have different orientations.

at For example, it may continue to be provided for such an application be that the position of the reference object relative to a patient is detected or determined by a radiological recording of the Reference object together with a patient. It can do this be provided that a reference object has radiopaque markers or other markings which can be recorded radiologically, so the opportunity exists, the position of the reference object in an X-ray image, z. B. an image of a computer tomograph or even a magnetic resonance tomograph to locate.

Just for medical Applications can also do this in this way be opened, the detected position of the object in one simultaneously display a radiographic image of the patient and so the track of the movement or the location of the movement time-dependent to capture.

One embodiment The invention is explained in more detail with reference to the following figures. It demonstrate

1 The image of an annular reference object with four field sensors and a needle whose position is to be determined

2 a schematic representation of the measuring principle

3 a flow chart of the method according to the invention

The 1 shows in an overview representation of a ring here shown reference object 1 in which within the ring here total four field sensors 2 are arranged. In this case, the field sensors may have different orientations and / or planes and be formed, for example, as coils, the orientation resulting from the longitudinal orientation of the coil axis. In this illustration it can be seen that the coils 2d and 2c have a different orientation as the two coils 2a and 2 B who are the same.

On the medical instrument shown here as a needle 3 is at least in one place, z. B. at a lower end, preferably at several points a not shown here field sensor arranged to use this field sensor, the position of the needle 3 in the electromagnetic field, not shown here to be able to determine.

According to the invention, it is provided in a medical application, the ring shown here 1 so on an intervention area, z. B. Puncture area to position a patient that this area remains accessible through the interior of the ring or is.

The measured position of the needle 3 Accordingly, in an optionally disturbed electromagnetic field, as described above, the measured values of the individual coils recorded by the reference object can be used 2a - 2d Getting corrected.

The 2 shows the procedure in the overview. It can be seen on the right side in the figure that, assuming a disturbance of the generated electromagnetic field, the positions of the four field coils are determined as actual position V1, V2, V3 and V4, as well as two positions P1 'and P2' of the needle 3 with reference to the illustration in the 1 , where two field sensors are assumed here at the needle.

The each determined positions of both the needle and the Reference objects are distorted or error-prone, as the basis electromagnetic field has a corresponding disorder.

However, the respectively mechanically defined position O1, O2, O3 and O4 of the field coils is known here 2a - 2d according to the left-hand representation in the 2 , z. B. relative to radiopaque markers M1, M2 and M3 defined coordinate system. It is therefore possible to determine a correction, for example, computationally within ei ner appropriately designed for measuring device to convert the distorted measured positions V1, V2, V3 and V4 in the correct positions O1, O2, O3 and O4, z. B. by a coordinate transformation based on a function.

the same Correction is then also appropriate to the measured distorted Positions of the needle P1 'and P2 'in the undistorted actual To transfer positions P1 and P2. The measured positions thus be converted into the distortion-free coordinate system.

The 3 shows the schematic sequence of the method according to the invention. Here, it is provided that both the measured values of the reference object and the known positions of the field sensors of the reference object are based on a calculation that can be implemented, for example, in the measuring device. By way of example, such a calculation can be used to determine a compensation field or also a function which is suitable for correcting an equally performed position measurement of the object to be measured. For this purpose, the faulty position is first determined and then the correction determined from the calculation is applied to the faulty position, resulting in an error-free position of the medical instrument.

The so determined trouble-free Position can therefore in a particularly preferred application a medical Intervention are based. Other applications are also given in virtual reality position determinations.

Regarding all versions It should be noted that those mentioned in connection with an execution technical features not only used in the specific execution can be but also in the other versions. All disclosed technical Features of this invention description are essential to the invention be classified and combined with each other or in isolation used.

Claims (14)

Method for determining the position and / or orientation of an object, in which the electromagnetic field generated by at least one emitter is measured by means of at least one field sensor and the object position and / or object orientation in the generated electromagnetic field is determined from the measured value (s) , characterized in that to compensate for disturbances in the generated electromagnetic field, in particular in the environment of the object, a reference object ( 1 ) with at least two field sensors ( 2a . 2 B . 2c . 2d ) whose relative desired spatial positions (O1, O2, O3, O4) are known to each other, in particular fixed and known, wherein by means of the field sensors ( 2a . 2 B . 2c . 2d ) of the reference object ( 1 ) measures the electromagnetic field and from the measured value / the measured values faulty actual position (V1, V2, V3, V4) of the field sensors ( 2a . 2 B . 2c . 2d ) of the reference object ( 1 ) and a correction is determined on the basis of the deviations between actual and desired positions, by means of which the measured object position (P1 ', P2') and / or object orientation is corrected, in particular in real time. Method according to claim 1, characterized in that the field sensors ( 2a . 2 B . 2c . 2d ) are formed as coils, wherein at least two coils of the reference object ( 1 ) have a different orientation to each other. Method according to claim 1 or 2, characterized in that the field sensors ( 2a . 2 B . 2c . 2d ) are formed as coils, wherein at least one coil is arranged outside a plane in which lie at least two further coils. Method according to one of the preceding claims, characterized in that the measured values of a plurality of field sensors ( 2a . 2 B . 2c . 2d ) are detected by means of a temporal multiplexing via a measuring line of a measuring device. Method according to one of the preceding claims, characterized in that from the measured actual positions (V1, V2, V3, V4) of the field sensors ( 2a . 2 B . 2c . 2d ) of the reference object ( 1 ) and the known desired positions (O1, O2, O3, O4) an interpolation and / or extrapolation function is formed by means of a field-faulted object position (P1 ', P2') and / or object orientation by applying the function to this position / Orientation is corrected. Method according to claim 5, characterized in that that the function is approximated by a polynomial. Method according to one of the preceding claims, characterized in that from the measured actual positions (V1, V2, V3, V4) of the field sensors ( 2a . 2 B . 2c . 2d ) of the reference object ( 1 ) and the known desired positions (O1, O2, O3, O4) a theoretical electromagnetic compensation field is calculated, which is used to correct the real disturbed electromagnetic field, in particular by computer-aided superimposition of the compensation field with the generated as undisturbed generated electromagnetic field, whereby a simulated real disturbed electromagnetic field results, that of the Positi ons and / or orientation determination of the object is based. Method according to one of the preceding claims, characterized in that an object whose position and / or orientation is to be determined by a medical instrument ( 3 ), in particular needle or catheter is formed. Method according to claim 8, characterized in that a reference object ( 1 ) in the spatial environment of an intervention area, in particular around an intervention area around a patient. Method according to one of the preceding claims, characterized in that the position (O1, O2, O3, O4) of a reference object ( 1 ) is detected relative to a patient by radiological detection of the reference object ( 1 ) together with a patient, in particular for which a reference object has radiopaque markings (M1, M2, M3). Method according to one of the preceding claims, characterized in that the desired position (O1, O2, O3, O4) of the at least one field sensor ( 2a . 2 B . 2c . 2d ) is known due to a mechanically fixed connection of the reference object ( 1 ) to a field generator. Method according to one of the preceding claims, characterized characterized in that the reference object comprises several parts, which in each case at least one marker and at least one field sensor include, where the spatial Assignment of several parts by an imaging, in particular Radiological detection takes place. Method according to claim 12, characterized in that that the multipart reference object comprises a plurality of radiopaque spheres, in whose center at least one coil is positioned in each case, the position of the ball and thus also the at least one Coil as a DESIRED position determined by the imaging acquisition. System for determining the position and / or orientation of an object comprising an object with at least one field sensor, at least one emitter for generating an electromagnetic field and a measuring device with which the position and / or orientation of the object by measuring the electromagnetic field by means of the at least one field sensor is determinable, characterized in that it is for compensating for disturbances in the generated electromagnetic field, a reference object ( 1 ) with at least two field sensors ( 2a . 2 B . 2c . 2d ) whose relative spatial desired positions (O1, O2, O3, O4) are known to each other, in particular fixed and known, whereby by means of the field sensors ( 2a . 2 B . 2c . 2d ) of the reference object ( 1 ) and the measuring device, the electromagnetic field measurable and from the measured value / the measured values faulty actual position (V1, V2, V3, V4) of the field sensors ( 2a . 2 B . 2c . 2d ) of the reference object ( 1 ) can be determined, wherein the measuring device is further established, based on the deviations between actual and desired positions of the reference object ( 1 ) to determine a correction by means of which the measured object position (P1 ', P2') and / or object orientation can be corrected.