Method for locating a magnetic field measuring assembly by a variable magnetic field

Abstract

Method for locating a magnetic field measuring assembly by a variable magnetic field The invention relates to a method for locating a magnetic field measuring assembly comprising at least one magnetoresistive sensor and / or one Hall effect sensor, comprising the steps of: a / generating, by means of an electromagnetic field generating device (1), a magnetic field of variable amplitude and / or shape(s) such that the position of a predetermined value of the amplitude of the magnetic field varies along at least two directions (X, Y) at different frequencies; b / measuring the magnetic field along each of the directions at the frequency corresponding to each direction by means of the magnetic field measuring assembly; c / when the magnetic field measuring assembly detects the predetermined value of the magnetic field along each of the directions, determining the position of the magnetic field measuring assembly.Figure for abstract: Fig. 1.

Description

Title of the invention: Method for locating a magnetic field measurement assembly using a variable magnetic field Technical field

[0001] The present invention relates to the field of electromagnetic localization of an object in space, in particular when direct visualization of this object is impossible.

[0002] The invention relates more particularly to a location method comprising the detection by a magnetic field measuring assembly of an electromagnetic signal coded in space by its amplitude and / or its shape, allowing the three-dimensional location of an object. The measuring assembly may in particular comprise one or more magnetoresistive sensors.

[0003] The main field of application envisaged concerns the localization and / or guidance of a medical device, in particular a catheter during a surgical / endoscopic intervention. The invention applies, however, to any field requiring the localization of an object, including robotics or microrobotics, the positioning of industrial equipment or even indoor positioning systems known as indoor localization systems. Prior art

[0004] It is known to implement guidance of medical devices by radiation imaging, including in particular X-ray tomography and computed tomography. Existing guidance methods make it possible to determine the position of the medical device in space and are currently used for surgical applications. However, the invasive aspect of the emitted radiation greatly limits the use of these methods.

[0005] The use of coding electromagnetic fields and their detection by coils have been proposed. Thus, the company NDI markets a device under the name Aurora allowing the implementation of such a method. This type of method, however, has several limitations. First of all, it is necessary to use detection coils having a ferrous core in order to obtain sufficient sensitivity to electromagnetic fields, which makes it difficult to apply these methods to the location of very small objects. Coils with ferrous cores are in fact difficult to miniaturize. In addition, it is necessary to carry out the detection of electromagnetic fields at their emission frequency.

[0006] Consequently, if the object to be located is connected for example to a cable as is the case with a catheter, the cable contributes to part of the detected signal, inducing noise and uncertainty in the measurement.

[0007] The article "A pilot study on an electromagnetic tracking system using tunneling magnetoresistance (TMR) sensors applicable to a 4F catheter (1.4 mm in diameter)", Nagano, R., Hara, K., Kobayashi, E. et al.. Int J CARS 18, 17-27 (2023) describes a localization method using tunneling magnetoresistance sensors to detect a magnetic field. However, the described device requires direct coupling between the sensors and the excitation system.

[0008] There is therefore a need to improve existing localization methods.

[0009] The aim of the invention is to meet at least part of this need. Statement of the invention

[0010] To do this, the invention relates in one of its aspects to a method of locating within a volume a magnetic field measurement assembly comprising at least one magnetoresistive sensor and / or one Hall effect sensor, comprising the steps consisting of: a / generating in the volume, by means of an electromagnetic field generating device, a magnetic field of variable amplitude and / or shape(s) so that the position of a predetermined value of the amplitude of the magnetic field varies along each of at least a first direction (X) and a second direction (Y), the magnetic field having respectively a first frequency and a second frequency along the first direction and the second direction, the first and second frequencies being different from each other;

[0011] b / measuring the magnetic field in each of the directions at the frequency corresponding to each direction by means of the magnetic field measuring assembly;

[0012] cl when the magnetic field measuring assembly detects the predetermined value of the magnetic field along each of the directions, determining the position of the magnetic field measuring assembly.

[0013] Preferably, a magnetic field of variable amplitude and / or shape is generated such that the position of a predetermined value of the amplitude of the magnetic field varies along each of a first direction (X), a second direction (Y) and a third direction (Z), the magnetic field having respectively a first frequency, a second frequency and a third frequency along the first direction, the second direction and the third direction, the first, second and third frequencies being different from each other.

[0014] The method according to the invention performs a coding of the space within the volume of interest by a magnetic field whose shape and / or amplitude are variable over time in a known manner. A scan of the volume of interest or at least of a surface contained in the volume of interest is carried out with a predetermined value. The magnetic field measuring assembly can be precisely located by measuring the magnetic field in the volume of interest until this predetermined value is measured.

[0015] Any object can be located by attaching a magnetic field measuring assembly to the object.

[0016] The volume of interest is encoded by generating an electromagnetic field along the three spatial directions X, Y and Z in such a way that the local amplitude of the magnetic field varies over time, preferably at any point in the volume of interest. When the local magnetic field reaches a target value on the measuring assembly, the position of the measuring assembly is recognized because it is linked to the time coding of the magnetic field. The time coding of the magnetic field therefore makes it possible to determine the position of the measuring assembly.

[0017] For example, a magnetic field may be generated along the X direction with an amplitude having a predetermined value, preferably an amplitude maximum or zero, which moves along the X direction over time. When this predetermined value is measured with the magnetic field measuring assembly, the measuring assembly is located at the corresponding X coordinate. The same operation may be performed along each of the Y and Z directions to locate the measuring assembly in space.

[0018] Volume scanning can also be performed in all three directions at the same time.

[0019] The electromagnetic field used to encode the space is applied at three different frequencies according to the three directions X, Y, Z and it is measured at these three frequencies with the measurement assembly to discriminate between the three directions.

[0020] Alternatively, a surface contained in the volume of interest is coded by generating a magnetic field in the volume such that the local amplitude of the magnetic field varies over time in the surface of interest defined by the first and second directions X, Y, preferably at any point of this surface. The surface of interest is advantageously planar. The electromagnetic field used to code the plane is applied at two different frequencies in the first and second directions X, Y. The position in the third direction Z is preferably determined based on the absolute value of the magnetic field in the direction Z.

[0021] The measuring assembly is sensitive to the magnetic field in the three directions X, Y, Z and may comprise one or more magnetic field sensors. A sensor magnetic field sensor may be sensitive to the magnetic field in one or more directions. For example, the measuring assembly may comprise three magnetic field sensors each sensitive in an X, Y or Z direction, or two magnetic field sensors each sensitive in two spatial directions, for example X, Y and Y, Z, or one magnetic field sensor sensitive in one spatial direction and one sensor sensitive in two spatial directions.

[0022] If a magnetic field sensor is sensitive in multiple directions, the same sensor can be used to detect the magnetic field in those directions by demodulating the signal at the excitation frequencies corresponding to those directions.

[0023] The magnetic field sensors may in particular comprise one or more Hall effect sensors and / or one or more magnetoresistive sensors, which may be giant magnetoresistance sensors (GMR sensors), tunneling magnetoresistance sensors (TMR sensors) and / or anisotropic magnetoresistance sensors (AMR sensors). These sensors can advantageously be easily miniaturized, which improves positioning accuracy.

[0024] Advantageously, the magnetoresistance and Hall effect sensors can be powered by a current of frequency fcap, measure a magnetic field of frequency emf and perform in situ modulation, so as to produce a reading current of frequency fcap ± emf for reading. Thus, these sensors make it possible to overcome the noise and uncertainties induced by their cables, as well as direct couplings by the cables.

[0025] Advantageously, a measurement assembly using two GMR or TMR sensors typically allows detection of weak signals, of the order of a few nanoteslas, with good spatial resolution. Preferably, the sensitive surface of each sensor is greater than or equal to 1 pm2, 10 pm2 or 20 pm2 and / or less than or equal to 1000 pm2, 500 pm2, 100 pm2, 50 pm2 or 20 pm2. The length of the active zones of the sensors along their sensitivity directions is preferably less than or equal to 500 pm, 200 pm, 100 pm, 50 pm or 10 pm and / or greater than or equal to 1 pm, 5 pm, 100 pm, 50 pm or 100 pm.

[0026] Preferably, the first, second and third directions are linearly independent, in particular orthogonal two by two.

[0027] According to an advantageous embodiment, the electromagnetic field generation device comprises three pairs of coils each aligned along one of the first, second and third directions.

[0028] Alternatively, the electromagnetic field generating device comprises a first pair of coils extending in a first plane and configured to generate a first variable magnetic field along the first direction, a second pair of coils extending in a second plane parallel to the first plane and configured to generate a second variable magnetic field along the second direction, and a fifth coil extending in the second plane, arranged between the coils of the second pair of coils and configured to generate a magnetic field along a direction orthogonal to the first and second directions.

[0029] According to an alternative embodiment, the electromagnetic field generating device comprises three pairs of permanent magnets each aligned and movable along one of the first, second and third directions. Preferably, the permanent magnets are each mounted on a movable support. The movement of the permanent magnets makes it possible to create a variable magnetic field.

[0030] Preferably, each coil is supplied with an alternating current of the form ^ij ( ^ ) ~ pjj ( ) cos^27ry*^

[0031] where i = {1, 2} identifies the coils of a pair, j = {X, Y, Z] identifies a pair of coils according to the alignment direction of this pair, t is the time and fj is the frequency of the current in the coil. The frequencies fx, fY and fz are different from each other. Ip which can be positive or negative, represents the maximum amplitude of the current flowing through the coil i, j. This amplitude Ip is preferably constant for a duration allowing the magnetic field measuring assembly to carry out a measurement, typically of the order of a millisecond, but varies over longer durations as a function of a quantity tA which defines the coding of the magnetic field. The values ​​of Ip> ^follow a determined profile, such as the profiles shown in [Fig.5]. These profiles advantageously make it possible to vary the position of the zero of the magnetic field linearly between the coils.

[0032] Thus, the magnetic field Bj (J) generated by the pair of coils j varies according to the value of Ip and therefore varies over time. Since the amplitude of the magnetic field at a given point varies over time, it is possible to vary the position of a predetermined value of the amplitude of the magnetic field.

[0033] Depending on the values ​​of the current flowing through the two coils of a pair, the field Bj can therefore reach a predetermined characteristic value for a precise torque L / t refX IljOref )•

[0034] The detection of this field value, for example Bj — Bmax or Bj = 0, for t = tref makes it possible to identify Iy(tref ), / zj(tref ) and therefore the position of the measurement set x ~ xref-

[0035] According to an advantageous variant, the predetermined value of the magnetic field is a maximum or a zero and this value is detected when the derivative of the value of the magnetic field with respect to time tA 4^ is zero or maximum, respectively. ^A This method of measuring the predetermined value of the magnetic field is more accurate if the predetermined value of the magnetic field is poorly resolved spatially.

[0036] The frequencies fj are typically between 1 kHz and 100 kHz. However, they may be higher if the temporal resolution for the intended application requires it. For example, a temporal resolution of the order of a millisecond is required for a cardiovascular endoscopic monitoring application. The temporal resolution is notably determined by the signal acquisition speed and the current scanning speed for encoding the space.

[0037] According to an advantageous characteristic, the determination of the position of the magnetic field measuring assembly is carried out successively for each direction, the magnetic field being generated so that the position of the predetermined value varies successively along the first direction, along the second direction and then along the third direction.

[0038] Alternatively, the determination of the position of the magnetic field measuring assembly is carried out simultaneously for each direction, the magnetic field being generated so that the position of the predetermined value varies simultaneously along the first, second and third directions.

[0039] Preferably, the electromagnetic field generating device comprises three pairs of coils, each pair being aligned along one of the three directions.

[0040] More preferably, the magnetic field measuring assembly comprises a first magnetoresistive sensor, preferably being a first GMR, TMR or AMR sensor extending in a plane. The plane may in particular be formed by two of the three directions.

[0041] The magnetic field measuring assembly may advantageously comprise a second magnetoresistive sensor, preferably being a second GMR, TMR or AMR sensor extending in a plane orthogonal to the plane in which the first magnetoresistive sensor extends.

[0042] The magnetic field measuring assembly may further comprise a third magnetoresistive sensor, preferably being a third GMR, TMR or AMR sensor extending in a plane orthogonal to the planes in which the first and second magnetoresistive sensors extend.

[0043] The magnetic field measuring assembly may also include a Hall effect sensor extending parallel to the first magnetoresistive sensor.

[0044] Hall effect sensors are sensitive in a direction perpendicular to the plane in which they extend while magnetoresistive sensors are sensitive in the plane in which they extend.

[0045] The invention also relates to a method for tracking an object, in particular a catheter in a human or animal body, comprising the attachment of a set of measuring the magnetic field at the object and locating the magnetic field measuring assembly by the locating method as described above.

[0046] Preferably, the tracking method comprises fixing one or more reference measurement sets in a volume of interest and locating them by the localization method as described above.

[0047] Ultimately, the invention provides numerous advantages, among which we can cite:

[0048] - separation of the components of the magnetic field in the three directions of the X, Y, Z space as a function of the magnetic field frequencies,

[0049] - insensitivity to radio frequency disturbances because the signal is demodulated locally at the object level,

[0050] - insensitivity to static fields possibly creating a measurement shift on the magnetic field measuring assembly when the derivative of the magnetic field is used to detect the predetermined value,

[0051] - use of magnetic fields of variable frequencies depending on the application For example, for catheter guidance in the context of cardiovascular endoscopic monitoring, low frequencies (less than 100 kHz) are advantageously used, which avoid signal distortions in the body or in the presence of metallic objects such as implants or medical instruments and which have no induced effects.

[0052] Other advantages and characteristics of the invention will become more apparent upon reading the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures. Brief description of the drawings

[0053] [Fig.l] [Fig.l] represents an electromagnetic field generation device which can be used within the framework of the invention.

[0054] [Fig.2] [Fig.2] represents a first configuration of coils which can be used to generate a magnetic field as implemented within the framework of the invention.

[0055] [Fig.3] [Fig.3] shows a second coil configuration that can be used to generate a magnetic field.

[0056] [Fig.4] [Fig.4] represents the temporal evolution along the axis of a pair of coils of a magnetic field generated in the context of a method according to the invention.

[0057] [Fig.5] [Fig.5] is a graph showing an example of a profile of the intensity of the currents flowing through a pair of coils so as to generate a magnetic field, the position of the zero of the magnetic field being determined by these currents.

[0058] [Fig.6] [Fig.6] shows a third coil configuration that can be used to generate a magnetic field. Detailed description

[0059] [Fig.l] illustrates a magnetic field generation device 1 adapted to generate a magnetic field as implemented according to the invention. For reasons of clarity, only one pair of coils is shown in this figure.

[0060] The device 1 comprises a computer 2 connected to a frequency generator 3 which generates one or more alternating currents at one or more determined frequencies. Each generated current is transmitted to two amplifiers 4 which amplify it. At the output of each amplifier 4, the amplified current supplies a coil of the pair of coils 5, 6. The two coils 5, 6 are arranged opposite each other. The currents flowing in the coils 5, 6 create a magnetic field whose frequency and amplitude are controlled by the computer 2 by means of the frequency generator 3 and the amplifiers 4.

[0061] A magnetic field measuring assembly 7 is arranged in the volume delimited by the three pairs of coils. The magnetic field measuring assembly 7 is advantageously configured to be fixed to an object in order to allow the latter to be located.

[0062] One or more reference measuring assemblies 8 may also be arranged in the volume delimited by the three pairs of coils. The reference measuring assemblies 8 may in particular be used when the magnetic field measuring assembly 7 is arranged within an object capable of moving. This object is for example a human or animal body, in which case the reference measuring assemblies 8 may advantageously be placed on the skin of the body. The reference measuring assemblies 8 then make it possible to measure any movement of the body during the localization process so that the position of the magnetic field measuring assembly 7 within the body can be tracked precisely, even in the event of movement or deformation of the latter.

[0063] The magnetic field measuring assembly 7 and the reference measuring assemblies 8 are configured to measure a magnetic field along three linearly independent spatial directions, preferably orthogonal in pairs. The reference measuring assemblies 8 may be identical to the magnetic field measuring assembly 7. Their location may be achieved in the same manner.

[0064] The device 1 also comprises an acquisition system 9 preferably comprising an acquisition card connected to the magnetic field measuring assembly 7 as well as to the reference measuring assemblies 8. The acquisition system 9 transmits the collected data to the computer 2 which carries out the data processing.

[0065] The device 1 is shown in [Fig.l] with a single pair of coils 5, 6. A pair of coils makes it possible to locate the magnetic field measuring assembly according to a direction of space. Thus, to achieve the localization of a measurement set in the three directions of space, three pairs of coils 5, 6, 15, 16, 25, 26 are used. Each pair of coils is arranged along an axis orthogonal to the other two.

[0066] Preferably, the frequency generator 3 generates a signal for each of the three pairs of coils, the generation of these signals being multiplexed. The frequency generator 3 is preferably a synchronous multi-channel frequency generator controllable in amplitude and phase. However, each pair of coils can also be associated with a natural frequency generator.

[0067] More preferably, each coil is associated with its own amplifier 4.

[0068] Preferably, the amplifiers 4 generate currents of intensity greater than or equal to 5 A, 10 A or 20 A and / or less than or equal to 20 A or 10 A, and of frequency greater than or equal to 1 kHz, 2 kHz or 5 kHz and / or less than or equal to 200 kHz, 100 kHz or 50 kHz.

[0069] The magnetic field measuring assembly 7 and / or the reference measuring assemblies 8 may comprise one or more magnetoresistive and / or Hall effect sensors, each sensor making it possible to measure the magnetic field in one or two directions in space.

[0070] The device 1 may also comprise, if necessary, a power supply configured to supply the magnetic field measuring assembly 7 and / or the reference measuring assemblies 8. The device 1 may also comprise electronic means for processing the signal from the sensors 7 and 8, such as an amplifier, a filter and a demodulation means, before acquisition by the acquisition card.

[0071] The acquisition card of the acquisition system 9 is preferably adapted to acquire data at a frequency greater than or equal to twice the highest frequency of the currents supplying the coils. The acquisition card advantageously has as many acquisition channels as there are magnetoresistive and / or Hall effect sensors in the magnetic field measuring assembly 7 and the reference measuring assemblies 8 and six additional channels intended to sample the currents flowing in the coils.

[0072] [Fig. 2] represents a possible configuration of three pairs of coils 5, 6, 15, 16, 25, 26 adapted to generate a magnetic field allowing the location of sensors in the three directions of space. The coils of the same pair face each other and are aligned on the same axis, the axes of the three pairs of coils being orthogonal to each other.

[0073] In the example of [Fig.2], the coils are circular in shape in a plane orthogonal to the axis of their pair of coils.

[0074] [Fig. 3] shows an alternative configuration of the three pairs of coils 5, 6, 15, 16, 25, 26, the coils having a rectangular shape with rounded corners. Such a configuration is particularly suitable for the case of locating a magnetic field measuring assembly inside a human or animal body.

[0075] [Fig.4] represents the evolution of the magnetic field between two coils 5, 6 as a function of the evolution over time of the current flowing through these two coils.

[0076] Ii(t) and I2(t) respectively represent the intensity of the current flowing through the coil 5 and that of the current flowing through coil 6. The curves Bb B2, ..., BN each represent the amplitude between the two coils 5, 6 of the magnetic field generated by the currents h and I2 at times tb t2, ..., tN respectively. The acquisition of the magnetic field measurements is carried out at the frequency of the currents supplying coils 5, 6. The points Xb X2, ..., XN represent the points on the axis of the pair of coils where the value of the magnetic field is equal to 0 at times tb t2, ..., tN respectively.

[0077] As illustrated in [Fig.4], the evolution of the currents supplying the coils modifies the profile of the magnetic field generated between these coils.

[0078] Preferably, the evolution profile of the currents supplying the coils is chosen so that the amplitude of the generated magnetic field has a linear profile in the axis of the corresponding pair of coils, as shown in [Fig.4].

[0079] The predetermined value of the magnetic field which makes it possible to locate the magnetic field measuring assembly is preferably chosen to be equal to 0 or to be equal to the maximum or minimum of the amplitude of the magnetic field.

[0080] [Fig.5] shows an example of a profile of the amplitudes of the currents Ib I2 making it possible to obtain a linear profile of variation of the amplitude of the magnetic field.

[0081] In the case of a pair of circular coils of diameter d separated by a distance 2a, the magnetic field generated along the axis of the pair of coils is given by l^2 for the first coil and vj^2 for the "1 “ H—7—T - _ n—7—r 4^44^)2 4^ / -44^+^ second coil, where x is the position along the axis with x = 0 at the midpoint between the coils, and po is the magnetic permeability of the vacuum.

[0082] At position x = 0, the field is zero when h = I2. For any position x, the magnetic field is zero when

[0083] i , . T* >f rsssss; — (J 4^F+4 <r- <a ^d^a^x+aÿ

[0084] et donc lorsque

[0085] ^d^+^x-a')2 2      \^d"+4*(x+a^

[0086] ainsi, il est possible de générer un champ magnétique dont l’amplitude nulle à point arbitraire tout le long l’axe la paire bobines entre les deux bobines, jusqu’à position des elles-mêmes.

[0087] les courants permettant d’obtenir une variation temporelle linéaire du zéro (c’est-à-dire x où t temps v vitesse zéro) sont déterminés par

[0088]

[0089] la plus grande résolution obtenue maximaux. on fixe préférence h="Imax" négatif i2 positif, imax l’intensité maximale courant alimentant bobines.

[0090] pour 1 m diamètre séparées distance m, on obtient profils l représentés [fig.5]. l’abscisse graphique [fig.5] indique pour chaque (ib i2).

[0091] [fig.6] représente troisième configuration pouvant être utilisée magnétique. une première 30, 31 s’étend dans premier plan. adjacentes. deuxième 32, 33 plan parallèle au de préférence, adjacente direction verticale z disposée en-dessous cinquième bobine 34

[0092] configurée volume d’intérêt.

[0093] alimentées électriquement en phase configurées variable orthogonale verticale, exemple x. ce s’annule centre d’intérêt identiques.

[0094] celles champs générés bobine, y.

[0095] représentée permet ou forme varie x-y ajustant d’alimentation paires il ainsi déterminer l’ensemble mesure recherchant valeur prédéterminée

[0096] le n’est pas ajustable z. estimation cette peut partir d’une absolue direction.

[0097] manière avantageuse, compacte positionner sans occuper l’espace toutes directions autour telle particulièrement avantageuse l’on cherche patient. peuvent notamment disposées sous table sur laquelle patient doit s’allonger. exemples

[0098] dans mode réalisation particulier, procédé selon l’invention mis œuvre réaliser suivi cardiovasculaire endoscopique personne.

[0099] cet exemple, dispositif génération électromagnétique comporte trois chacune orientée d’un axe orthogonal aux autres axes. personne laissant suffisamment d’espace permettre l’accès ont longueur typique l’ordre mètre comprennent 100 1000 tours fils cuivre.

[0100] l’ensemble capteurs type gmr disposés sorte pouvoir mesurer axes sensibilité nt.hz 2, inférieure égale 10 supérieure 0,5 -1

[0101] fixé cathéter. l’intérieur

[0102] zones actives pm. cette limite localisation choisie fonction l’application visée.

[0103] fréquences distinctes, supérieures égales khz inférieures khz.

[0104] l’amplitude parcourant +1 -i profil bien choisi tel que celui représenté [fig.5], i courant, typiquement a. cela faire varier 0 lequel déplacé mx m.

[0105] fait alors x, y, l’une après l’autre afin détecter

[0106] acquièrent pendant durée d’environ 20 ms. l’analyse niveau analyse comporter transformée fourier réalisée signal fréquence (fem - fc ap) fem ap capteur qui

[0107] ensuite, même 7 acquiert signal, toujours ms, autre ta. différents rapport acquisition également différente. nouveau déterminée.

[0108] processus se répète faisant modifier prédéterminée.

[0109] x

[0110] optimise choix amplitudes ip>ijj currents to accelerate the determination of the position of the measuring assembly. For example, the magnetic field value can first be measured at a limited number of points distributed between two coils, for example five points. From these measurements, the approximate position of the predetermined magnetic field value is estimated, for example by means of linear regression. The magnetic field value is then measured in a restricted interval around this estimated position. If necessary, the process can be repeated. Typically, two or three iterations are sufficient to obtain maximum positioning accuracy of the measuring assembly, i.e. a position whose accuracy is limited by the signal-to-noise ratio of the measuring assembly.

[0111] The same steps are then carried out with the pairs of coils aligned along the second Y direction and the third Z direction to determine the position of the magnetic field measuring assembly in space.

[0112] If reference measuring assemblies 8 are used, the same localization method is then implemented to determine their positions. Tracking the position of the reference measuring assemblies makes it possible to correct for any movement of an object in which the magnetic field measuring assembly 7 is arranged.

[0113] The computer 2 is configured to control the device 1 and to reconstruct the position of the measuring assembly, for example in relation to a previously acquired anatomical image of the body.

[0114] Other variants and improvements may be provided without departing from the scope of the invention.

Claims

Claims

1. A method for locating within a volume a magnetic field measuring assembly (7) comprising at least one magnetoresistive sensor and / or a Hall effect sensor, comprising the steps of: a / generating in the volume, by means of an electromagnetic field generating device (1), a magnetic field of variable amplitude and / or shape(s) such that the position of a predetermined value of the amplitude of the magnetic field varies along each of at least a first direction (X) and a second direction (Y), the magnetic field having respectively a first frequency and a second frequency along the first direction and the second direction, the first and second frequencies being different from each other; b / measuring the magnetic field along each of the directions at the frequency corresponding to each direction by means of the magnetic field measuring assembly;c / when the magnetic field measuring assembly detects the predetermined value of the magnetic field along each of the directions, determining the position of the magnetic field measuring assembly.;

2. A location method according to claim 1, wherein the magnetic field generated in step a / is of variable amplitude and / or shape such that the position of a predetermined value of the amplitude of the magnetic field also varies along a third direction (Z), the magnetic field having a third frequency along the third direction, the first, second and third frequencies being different from each other.

3. A location method according to claim 2, the determination of the position of the magnetic field measuring assembly being carried out successively for each direction, the magnetic field being generated so that the position of the predetermined value varies successively along the first direction, along the second direction and then along the third direction.

4. A location method according to claim 2, the determination of the position of the magnetic field measuring assembly being carried out simultaneously for each direction, the magnetic field being generated so that the position of the predetermined value varies simultaneously along the first, second and third directions.

5. A method of locating according to one of the preceding claims, the electromagnetic field generating device comprising three pairs of coils (5, 6, 15, 16, 25, 26), each pair being aligned along one of the three directions.

6. The locating method of claim 1, the electromagnetic field generating device comprising a first pair of coils (30, 31) extending in a first plane and configured to generate a first variable magnetic field along the first direction, a second pair of coils (32, 33) extending in a second plane parallel to the first plane and configured to generate a second variable magnetic field along the second direction, and a fifth coil (34) extending in the second plane, arranged between the coils of the second pair of coils and configured to generate a magnetic field along a direction orthogonal to the first and second directions.

7. Location method according to one of the preceding claims, the magnetic field measuring assembly comprising a first magnetoresistive sensor, preferably being a first GMR, TMR or AMR sensor extending in a plane.

8. Location method according to the preceding claim, the magnetic field measuring assembly comprising a second magnetoresistive sensor, preferably being a second GMR, TMR or AMR sensor extending in a plane orthogonal to the plane in which the first magnetoresistive sensor extends.

9. Location method according to the preceding claim, the magnetic field measuring assembly comprising a third magnetoresistive sensor, preferably being a third GMR, TMR or AMR sensor extending in a plane orthogonal to the planes in which the first and second magnetoresistive sensors extend.

10. A locating method according to claim 7, the magnetic field measuring assembly comprising a Hall effect sensor extending parallel to the first magnetoresistive sensor.

11. Method for tracking an object, in particular a catheter in a human or animal body, comprising the attachment of a measuring assembly

12. magnetic field to the object and locating the magnetic field measuring assembly by the locating method according to one of the preceding claims. Tracking method according to the preceding claim, comprising fixing one or more reference measurement sets (8) in a volume of interest and locating them by the locating method according to one of claims 1 to 10.

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