Medical instrument for use in a magnetic resonance imaging device and method for positioning

Abstract

The invention relates to a medical instrument for use in a magnetic resonance imaging scanner. The medical instrument has a spirit level for determining a spatial position of the medical instrument. The spirit level has a liquid that can be detected by the magnetic resonance imaging scanner, so that the position can be detected with the magnetic resonance imaging scanner. The invention further relates to a method for aligning the medical instrument, in which a trajectory for the medical instrument for a predetermined procedure is determined, an entry point for the medical instrument is identified, and the medical instrument is positioned there. Using a magnetic resonance image of the spirit level, an actual value for a solid angle of the medical instrument is detected, a target value for the solid angle is determined by the magnetic resonance imaging scanner, and information on a deviation is output to a surgeon.The surgeon corrects the alignment based on the information.

Description

[0001] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0002] The invention relates to a medical instrument for use in a magnetic resonance imaging scanner and to a method for positioning a medical instrument according to one of the claims on a patient. The medical instrument has a spirit level for determining the spatial position of the medical instrument, which spirit level contains a liquid detectable by the magnetic resonance imaging scanner.

[0003] A trajectory for the medical instrument for a predetermined procedure is determined, the instrument is positioned on the patient, the alignment of the instrument is determined using a magnetic resonance image of the spirit level, and information on the alignment is output.

[0004] Image-guided minimally invasive procedures are also performed in magnetic resonance imaging (MRI) scanners. The medical instrument is guided under real-time control by the MRI scanner. This requires that the instrument to be inserted be positioned at a predetermined orientation at the insertion point before inserting the patient's abdomen or pelvic region. The success of the procedure(s) during the course of a working day depends on many factors. In particular, the interaction between the surgeon and the individual components ensures lasting success.

[0005] The entry point and angle can be planned using the patient's anatomical magnetic resonance image. Needle advancement is visualized using real-time magnetic resonance imaging.

[0006] The puncture angles in two spatial directions are estimated, sometimes by the interventionalist placing a finger on the puncture point and correcting the orientation of a finger in the MRI image until it is estimated to be in the correct position.

[0007] It is therefore an object of the invention to provide a medical instrument and a method that facilitates and improves alignment.

[0008] The object is achieved by a medical instrument according to claim 1 and a method for positioning according to the invention according to claim 4.

[0009] The medical instrument according to the invention is intended for use in a magnetic resonance imaging scanner, in particular in a region of the scanner that can be captured by magnetic resonance imaging. The term "medical instrument" also refers, in particular, to surgical instruments, such as needles or probes used for biopsy, ablation, or brachytherapy, and intended to be inserted into a patient.

[0010] The medical instrument according to the invention comprises a spirit level. A spirit level refers to all instruments that are designed to detect the alignment of the spirit level, and thus of a medical instrument connected to it in a fixed relative position, with respect to the direction of gravity by means of a liquid under the influence of gravity.

[0011] The spirit level is arranged in a predetermined position and orientation relative to the medical instrument. For example, the spirit level can be connected to the medical instrument in a fixed position. However, it is also conceivable that the alignment of the spirit level can be adjusted to a predetermined value, for example, using one or more swivel joints, and then fixed in the adjusted position.

[0012] For example, a vessel with a concave inner wall filled with a liquid and another fluid of lower density is conceivable, so that the fluid collects, due to buoyancy, at a location on the inner wall of the vessel that is opposite to the direction of gravity. The relative position of the fluid in the vessel indicates the vessel's orientation relative to the direction of gravity. For a permanently installed magnetic resonance imaging scanner with a predetermined position, this also indicates the vessel's orientation or spatial position relative to the magnetic resonance imaging scanner.

[0013] The liquid can be captured by the magnetic resonance imaging scanner in a magnetic resonance image. In other words, the liquid's position and shape can be captured, allowing, for example, the shape of the liquid in the vessel and thus also the position of the fluid within the liquid to be captured. The fluid and the liquid exhibit different properties with respect to the magnetic resonance imaging image, allowing them to be distinguished in the captured image. The liquid can be water, for example, and the fluid can be air or a gas such as oxygen, nitrogen, carbon dioxide, helium, or argon.

[0014] In an advantageous manner, the medical instrument according to the invention enables the position of the instrument in the magnetic resonance imaging scanner to be detected even without direct view of the instrument.

[0015] The method according to the invention is provided for positioning a medical instrument according to the invention on a patient by means of a magnetic resonance imaging scanner, ie using magnetic resonance images.

[0016] In one step of the method, a trajectory for the medical instrument for a predetermined procedure is determined. This can be done, for example, by controlling the magnetic resonance imaging scanner or a planning system using a magnetic resonance image of the patient and information about the target of the medical instrument during the procedure, which is specified by a user or the planning system. The trajectory is a straight line through an entry point on the patient's surface to the target, avoiding sensitive organs or structures such as nerves and larger blood vessels.

[0017] In a further step, the entry point is identified according to the trajectory relative to the patient, and an orientation of the medical instrument is determined that enables movement of the medical instrument along the trajectory. Identifying means that the entry point of the trajectory, which was determined from the image or model of the patient, is assigned to the real patient and preferably marked. Likewise, a spatial direction is determined, preferably by the control system of the magnetic resonance imaging scanner, which corresponds to the determined trajectory. This can be done, for example, by acquiring a magnetic resonance image of the patient from the magnetic resonance imaging scanner and determining the position of the patient based on contour and / or organs relative to the magnetic resonance imaging scanner.From this position, the controller can determine a coordinate transformation that transforms the model's coordinates to the actual patient position in the MRI scanner when determining the trajectory. Applying this coordinate transformation to the determined entry point and the orientation of the medical instrument results in the entry point and the orientation of the actual patient in the MRI scanner, which can be output by the controller as a graphic representation and / or coordinates.

[0018] In a next step, the user positions the medical instrument at the entry point on the patient. It is conceivable that the magnetic resonance imaging scanner will scan the patient with the medical instrument or a marker on a tip of the instrument facing the patient and provide the user with the position of the determined entry point and the position of the tip, for example, in a graphical representation, as coordinates or coordinate difference, or as an indication of the direction of movement for the instrument to reach the entry point.

[0019] In another step, the magnetic resonance imaging scanner acquires at least one actual value of a first solid angle using a magnetic resonance image of at least one spirit level. The first solid angle and the second solid angle are angles of a polar coordinate system that indicate an orientation in space. The rotation axes of the solid angles do not necessarily have to be perpendicular to each other.

[0020] The fluid's position can be identified by the image of the liquid and its contrast with the fluid. Preferably, the bubble containing the fluid is located at the highest point of the vessel, opposite the direction of gravity. The external shape of the vessel containing the liquid, reflected by the fluid, reveals the vessel's orientation relative to the magnetic resonance image. A marking or scale on the vessel, detectable with an MRI image, would also be conceivable, revealing an angle to the vertical.

[0021] In a further step, the controller determines a target value for the first solid angle. In other words, the controller determines a target value for the first solid angle for which, when measured by the first spirit level with the medical instrument appropriately aligned, the medical instrument is aligned at least in one angular axis parallel to the predetermined trajectory. It is conceivable that the medical instrument is rotated about a longitudinal axis, so that the target angle is determined by a coordinate transformation from the determined trajectory or its polar coordinates. Depending on the selected coordinate system, it is advantageous to first select and set the angle that is linearly independent as the first solid angle, i.e. that does not depend on another or second solid angle.

[0022] For example, the controller can perform a coordinate transformation from a coordinate system related to the patient or the magnetic resonance imaging scanner to a polar coordinate system, whose reference axes or reference planes are defined by a first spirit level and the second spirit level, as explained below in the dependent claims, or, in the case of a 2D spirit level, by its reference point. The coordinate transformation can be performed, for example, by matrix multiplication of a vector from the first solid angle and the second solid angle with a 2x2 transformation matrix.

[0023] The rotation of the medical instrument can be determined, for example, from an orientation of the vessel of the liquid in the magnetic resonance image if the vessel does not have rotational symmetry around the longitudinal axis of the medical instrument.

[0024] It is also conceivable, however, that the vessel of the spirit level is rotationally symmetrical in the form of a lens and arranged perpendicular to the longitudinal axis of the medical instrument, as in the two-dimensional spirit level explained below. The fluid assumes the highest point, and the distance from the center of symmetry is a measure of the inclination of the medical instrument to the vertical, determined by the direction of gravity. The direction of the fluid or bubble relative to a vertical line through the entry point indicates a second solid angle, which is specified below in the dependent claims.

[0025] The controller determines a first piece of information based on the actual value of the first solid angle, which enables the predetermined alignment to be achieved. This can, for example, be a representation of the target value, which, together with a representation of the actual value, indicates to the user how to adjust the alignment. Also conceivable is a directional indication, e.g., an arrow or a sound or an instruction that indicates to the user the type of correction required to achieve the alignment according to the target value.

[0026] In another step, the controller provides the first information to the user to correct the alignment of the medical instrument, for example on a display or acoustically, so that the user can make the alignment correction.

[0027] The method according to the invention advantageously allows a medical instrument according to the invention to be precisely aligned in the magnetic resonance imaging scanner without direct view of it.

[0028] Further advantageous embodiments are specified in the subclaims.

[0029] In one possible embodiment, the medical instrument comprises a spirit level comprising a first spirit level and a second spirit level. The spirit levels or their vessels preferably have a longitudinal extension along which the fluid moves when the inclination of the vessel changes in a plane in which the longitudinal extension lies. For example, the first spirit level and the second spirit level can have the shape of a curved tube.

[0030] The second spirit level is arranged at an angle to the first spirit level such that an inclination can be detected in two linearly independent solid angles using the first spirit level and the second spirit level. In other words, the two solid angles span a polar coordinate system in space. This advantageously makes it possible to determine the alignment of the medical instrument using the first and second spirit levels in a polar coordinate system.

[0031] Alternatively, a 2-dimensional spirit level is also conceivable as a spirit level, in which the fluid moves along a curved surface, for example, along the inside of a sphere or a lens filled with the liquid. Preferably, the position of the vessel can be detected in the magnetic resonance image, for example, by a marking detectable with the magnetic resonance imaging scanner on or in the immediate vicinity of the spirit level in a fixed position relative to the spirit level, or by an at least partially asymmetrical shape of the spirit level, such as a corner or protrusion or invagination, so that the liquid within makes the position detectable in the magnetic resonance image through its shape.

[0032] A 2-dimensional spirit level advantageously simplifies the construction and also the representation, especially when the medical instrument is essentially rotationally symmetrical to its longitudinal axis.

[0033] In one possible embodiment of the medical instrument according to the invention, the fluid contains a contrast agent for magnetic resonance imaging. For example, gadolinum or another substance that accelerates the decay of the excitation and thus briefly generates a stronger magnetic resonance signal can be added to the fluid, preferably water. The contrast agents are not limited to those used medically in the body, but can also include substances that are incompatible with humans, if necessary, due to their inclusion in the spirit level.

[0034] Advantageously, accelerated excitation decay enables faster rates of image acquisition with a higher contrast image.

[0035] In a conceivable embodiment of the method according to the invention, the method further comprises the step of detecting at least one actual value of a second solid angle using a magnetic resonance image of at least one spirit level. This can be a second spirit level, which, for example, as already explained, has an elongated shape and is arranged at an angle to the first spirit level, so that the first solid angle and second solid angle detectable by the two spirit levels span a polar coordinate system.

[0036] However, it is also conceivable that the first spirit level, as already explained for the 2-dimensional spirit level, is designed to detect a second solid angle. The two solid angles can then be differentiated, for example, in a 3D magnetic resonance image by a position of the fluid relative to a marking on the spirit level or to a predetermined axis or plane in the image. However, two-dimensional slice images or projection images using the magnetic resonance imaging scanner onto a first plane and a second plane are also conceivable, wherein the planes intersect at an angle. The angle is preferably greater than 5 degrees or 10 degrees and, in a preferred case, is 90 degrees. By means of the 2-dimensional images in intersecting planes, a first solid angle and a second solid angle of an alignment of the spirit level and thus of the medical instrument can be determined, e.g.In the 90-degree arrangement of the planes, this is achieved by a simple representation of the images; however, a coordinate transformation by the control system is also conceivable in order to be able to use a coordinate system preferred by a user, which, for example, corresponds to the usual coordinate axis designations in magnetic resonance imaging.

[0037] Advantageously, capturing the second solid angle with the magnetic resonance imaging scanner enables complete alignment of the medical instrument without visual contact.

[0038] However, it is also conceivable to perform alignment by measuring only one angle, especially if the second angle can be visually determined by looking lengthwise into the tunnel. It may then be sufficient if magnetic resonance imaging only captures a solid angle that corresponds to a tilt along the z-axis and cannot be visually determined by looking through the patient tunnel.

[0039] In another step, the control system of the magnetic resonance imaging scanner determines a target value for the second solid angle. For example, the control system can perform a coordinate transformation from a coordinate system related to the patient or the magnetic resonance imaging scanner to a polar coordinate system whose reference axes or reference planes are defined by the first spirit level and the second spirit level, or in the case of a 2D spirit level, by its reference point. The coordinate transformation can be performed, for example, by matrix multiplication of a vector from the first solid angle and the second solid angle with a 2x2 transformation matrix. The target value of the second solid angle can depend, in particular, on the first solid angle, in particular, on its actual value or its target value.

[0040] In a further step, a second piece of information is determined for achieving the predetermined alignment based on the actual value of the second solid angle. In most cases, this information also depends on the actual value of the first solid angle. Furthermore, the same applies as already explained for the first piece of information, particularly regarding the type of information.

[0041] In another step, the second information is output to the user to correct the orientation of the medical instrument, in particular to correct the actual value for the second solid angle.

[0042] Advantageously, the method also allows a correction in two solid angles and thus a complete alignment parallel to the trajectory

[0043] In a preferred embodiment of the method according to the invention, the user then corrects the orientation of the medical instrument based on the first piece of information and / or the second piece of information. In other words, the user moves the medical instrument based on the information in such a way that the deviation of the actual value from the target value of the first solid angle and / or the second solid angle becomes smaller. The information can specify the direction, or it can represent the target and actual values ​​for the user, so that the user can intuitively determine the direction for the correction, particularly in the iterative process described below.

[0044] In a preferred embodiment of the method according to the invention, the steps of detecting an actual value, determining information, outputting the information and correcting the alignment for the first and / or second solid angle are repeated.

[0045] In an advantageous way, the user can track the success of his correction and, especially when the angle corrections are dependent on each other, the user is guided to the desired result more safely and quickly.

[0046] In one possible embodiment, the control system of the magnetic resonance imaging scanner determines a deviation between the target value and the actual value, for example, using a square sum of the differences. The control system compares the deviation with a predetermined threshold, and if the deviation falls below the threshold, the system sends a message to the user. This can be done, for example, with an audible signal or information on a display. It is then conceivable that the control system automatically aborts a repetition of the previously explained steps because the goal has been reached through the iteration. However, it is also possible that this only occurs after a user input for confirmation.

[0047] Advantageously, the method informs the user when the alignment has been achieved with sufficient accuracy and the procedure can begin.

[0048] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0049] They show: Fig. 1 a schematic representation of an embodiment of a magnetic resonance imaging device according to the invention for carrying out the method according to the invention; Fig. 2 an embodiment of a medical instrument according to the invention; Fig. 3 shows a further embodiment of a medical instrument according to the invention; Fig. 4 a schematic flow chart of a method according to the invention.

[0050] Fig. 1 shows a schematic representation of an embodiment of a magnetic resonance imaging device 1 for carrying out the method according to the invention with the medical instrument 70 according to the invention.

[0051] The magnet unit 10 has a field magnet 11 that generates a static magnetic field B0 for aligning nuclear spins of samples or the patient 100 in a recording area. The recording area is characterized by an extremely homogeneous static magnetic field B0, with the homogeneity particularly affecting the magnetic field strength or magnitude. The recording area is nearly spherical and arranged in a patient tunnel 16 that extends in a longitudinal direction 2 through the magnet unit 10.

[0052] A patient bed 30 is movable in the patient tunnel 16 by the movement unit 36.

[0053] Typically, the field magnet 11 is a superconducting magnet capable of generating magnetic fields with a magnetic flux density of up to 3T, and even higher in the latest devices. However, permanent magnets or electromagnets with normally conducting coils can also be used for lower field strengths.

[0054] Furthermore, the magnet unit 10 has gradient coils 12, which are configured to superimpose variable magnetic fields in three spatial directions on the magnetic field B0 for spatial differentiation of the acquired imaging regions in the examination volume. The gradient coils 12 are typically coils made of normally conducting wires that can generate mutually orthogonal fields in the examination volume.

[0055] The magnet unit 10 also has a body coil 14, which is configured to transmit a radio-frequency signal supplied via a signal line into the examination volume and to receive resonance signals emitted by the patient 100 and transmit them via a signal line. In the following, the term transmitting antenna refers to an antenna via which the radio-frequency signal is transmitted to excite the nuclear spins. This can be the body coil 14, but also a local coil 50 with a transmitting function.

[0056] A control unit 20 supplies the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14 and evaluates the received signals.

[0057] Thus, the control unit 20 has a gradient control 21 which is configured to supply the gradient coils 12 with variable currents via supply lines, which provide the desired gradient fields in the examination volume in a time-coordinated manner.

[0058] Furthermore, the control unit 20 has a radio-frequency unit 22 configured to generate a radio-frequency pulse with a predetermined temporal profile, amplitude, and spectral power distribution for exciting magnetic resonance of the nuclear spins in the patient 100. Pulse powers in the kilowatt range can be achieved. The excitation signals can be transmitted into the patient 100 via the body coil 14 or via a local transmitting antenna.

[0059] A controller 23 communicates via a signal bus 25 with the gradient controller 21 and the high-frequency unit 22.

[0060] A local coil 50 is arranged on the patient 100 and is connected to the radio-frequency unit 22 and its receiver via a connecting line 33. However, it is also conceivable that the body coil 14 is a receiving antenna within the meaning of the invention.

[0061] According to the application, the medical instrument 70 is placed by a surgeon on the patient 100 in the patient tunnel 16 within the detection range of the magnetic resonance imaging scanner. The medical instrument 70 can be, for example, a biopsy needle, a brachytherapy instrument, or another instrument that is to be inserted into the patient's body during an interventional procedure. For this purpose, the medical instrument is placed at a predetermined entry point on the surface or skin of the patient and aligned according to a predetermined inclination along a trajectory to a target location in the patient's body.

[0062] A spirit level 80 is arranged on the medical instrument 70, which is explained in more detail in the next figures.

[0063] In Fig. 2 shows an embodiment of the medical instrument 70 according to the invention. The medical instrument 70 has a longitudinal extension 71 at a distal end, which, in the correct position, faces away from the patient 100, and a spirit level 80. The spirit level 80 has a first spirit level 81 and a second spirit level 82. The first spirit level 81 is arranged in a first plane 84, and the second spirit level 82 in a second plane 85. The two planes 84, 85 are preferably aligned parallel to the longitudinal axis 71 of the medical instrument 70 and enclose an angle that preferably corresponds to 90 degrees. However, it is also conceivable for the planes 84, 85 to be aligned differently, as long as they are not parallel to one another. However, additional coordinate transformations are then required in the subsequent process when aligning the medical instrument 70.

[0064] The first spirit level 81 can, for example, comprise a curved tube that extends in at least one partial circle in the first plane 84. The tube is filled with a liquid detectable by the magnetic resonance imaging scanner in a magnetic resonance image, except for a spirit level or bubble made of a fluid with a lower density than the liquid. Under the effect of gravity on the liquid, the spirit level always positions itself at the highest point of the tube, opposite the direction of gravity or the vertical 72. In conjunction with the position of the tube, which is represented by the liquid or other markers visible in a magnetic resonance image with a predetermined relative position to the tube, an alignment angle of the tube, thus of the first spirit level 81 and the associated medical instrument, in the first plane 84 to the vertical 72 can be determined.

[0065] Preferably, the second spirit level 82 is substantially identical to the first spirit level 81, it is merely arranged in the second plane 85, which is arranged at an angle to the first plane, preferably greater than 10 degrees, 30 degrees or 45 degrees or equal to 90 degrees, so that the angles to the vertical detected by the two spirit levels 81, 82 in the two planes 84, 85 respectively span a polar coordinate system, so that with knowledge of the position of the planes an alignment of the medical instrument can be determined.

[0066] Fig. Figure 3 shows another embodiment of the medical instrument 70 according to the invention, which differs in the type of spirit level 80. While in Fig. 2 a first spirit level 81 and a second spirit level 82 separately measure two solid angles in the first plane 84 and in the second plane 85, the spirit level 80 is in the Fig. 3 a two-dimensional spirit level 86, also referred to as a circular level. However, the two-dimensional spirit level 86 is not designed as a flat lens, but rather has a greater height, for example, as a hemisphere or sphere. As a result, the two-dimensional spirit level is capable of detecting larger angles and thus larger angular deviations of the alignment of the longitudinal axis 71 to the vertical 72 compared to the circular level.

[0067] Preferably, a marking 87 is arranged on the spirit level 80 or the medical instrument 70, which can be captured in an image using the magnetic resonance imaging system 1. This allows the orientation of the medical instrument around the longitudinal axis 71 to be captured, which cannot be captured via the liquid due to the rotational symmetry of the spirit level 80.

[0068] Fig. 4 shows a schematic flow chart of an embodiment of the method according to the invention for positioning a medical instrument with a magnetic resonance imaging device.

[0069] First, in step S10, a trajectory for the medical instrument for a predetermined procedure is determined. This can be done using a planning program that, on a controller 23 of the magnetic resonance imaging scanner 1, uses a magnetic resonance image of the patient 100 to determine a path of the medical instrument 70 from an entry point on the patient 100 to a target area on or in an organ, which path is referred to as a trajectory.

[0070] In a further step S20, an entry point on the patient 100 and an orientation of the medical instrument 70 are determined, which enable movement of the medical instrument along the trajectory. The orientation is preferably defined using two angles, which can be detected using the spirit level 80 and a magnetic resonance image. However, only one angle is also conceivable, which preferably extends with its plane in which it lies in the longitudinal direction or z-axis, since this angle is difficult for a surgeon to visually detect. The other angle, preferably in a plane perpendicular to the z-axis, is then visually detected by the surgeon.

[0071] In the design of the Fig. 2, two angle values ​​to be set for the first spirit level 81 and the second spirit level 82 can be determined by means of coordinate transformation from a coordinate system related to the magnetic resonance tomograph 1 or the patient 100, e.g., with the angles of inclination to the vertical 72 and a rotation angle about the vertical 72 with respect to the z-axis 2 or the longitudinal extent of the patient tunnel. It is conceivable that a predetermined alignment of the first plane 84 with the first spirit level 81 and the second plane 85 with the second spirit level 82 is assumed, e.g., the first plane 84 parallel to the z-axis and the second plane 85 perpendicular to the z-axis, which the surgeon must assume with the medical instrument 70 in the subsequent step S30.Or, in step S30, the alignment of the first spirit level 81 and the second spirit level 82 is detected by means of a magnetic resonance image and only then, in step S20, the two target angles for the first spirit level 81 and the second spirit level 82 are determined.

[0072] In the design of the Fig. 3, however, due to the rotational symmetry of the two-dimensional spirit level 86, only the inclination relative to the vertical 72 can be determined via the position of the spirit level 83 with respect to the two-dimensional spirit level 86. The relative position of the spirit level 83 to the entry point or the patient 100 or a marking 87 on the medical instrument 70 detectable with the magnetic resonance imaging, preferably at the tip at the entry point, provides a second angular coordinate.

[0073] In a further step S30, the user or the surgeon positions the medical instrument 70 at the entry point on the patient 100. To do so, the user moves the tip of the medical instrument 70 to the entry point, which was marked, for example, with a finger or a magnetic resonance-active substance in a previous step under real-time imaging with the magnetic resonance tomograph 1.

[0074] In another step S40, an actual value of a first solid angle is acquired. For this purpose, a magnetic resonance image of the spirit level 80 or the first spirit level 81 and / or the second spirit level 82 or the two-dimensional spirit level 86 is acquired. The fluid of the bubble level 83 is thereby lifted from the liquid in the spirit level 80 and thus indicates at least an angle to the inclination through its position in the spirit level 80.

[0075] In a further step S50, the controller 23 of the magnetic resonance imaging scanner 1 determines a target value for the first solid angle. It is conceivable that the target value for the first solid angle depends on the actual value if the coordinate system of the medical instrument 70 is tilted relative to the coordinate system of the magnetic resonance imaging scanner 1. The target value can be determined, for example, by a coordinate transformation of the trajectory orientation.

[0076] In another step S60, the controller 23 determines a first piece of information for achieving the predetermined orientation based on the actual value of the first solid angle. For example, a directional arrow on a display can indicate a direction in which the medical instrument is to be tilted or the tilt is to be changed in order to reach or approach the target value.

[0077] In a further step S70, the controller outputs the first information to the user. This can be an output or representation on a display, graphically, or as an instruction. An acoustic output is also possible, such as a tone, a sequence of tones, or as a voice output.

[0078] The user can then use the information provided to correct the alignment of the medical instrument 70 or to approximate it to the target value.

[0079] In a possible embodiment of the method, it is also conceivable that the method further comprises step S45 of detecting an actual value of a second solid angle by means of a magnetic resonance image of at least one spirit level. This can be an angle in a second sectional plane for the two-dimensional spirit level 80, or for the spirit level of the Fig. 2 a deflection angle of the second spirit level 82 in the second plane 85.

[0080] Finally, in step S55, the controller 23 determines a target value for the second solid angle. The target value for the second angle can be dependent on the actual value of the first solid angle, and the determination can be dependent on the actual value(s) of the first solid angle and / or the second solid angle.

[0081] In a step S65, the controller determines, corresponding to step S60, a second piece of information for achieving the predetermined alignment as a function of the actual value of the second solid angle and / or first solid angle and outputs this information to the user in a step S75, as set out in step S70, for correcting the alignment of the medical instrument.

[0082] In one embodiment of the method according to the invention, the alignment is preferably performed iteratively. This means that the steps of detecting an actual value S40, S45, determining a target value S50, S55, determining information S60, S65, outputting the information S70, and correcting the alignment for the first and / or second solid angle are repeated until the medical instrument 70 has reached the determined alignment along the trajectory. For this purpose, it is conceivable that the controller 23 of the magnetic resonance imaging system 1 determines a deviation between the target value and the actual value in a step S90 and signals to the user when the deviation between the alignment of the longitudinal axis 71 of the medical instrument 70 and the determined trajectory falls below a predetermined threshold.The deviation can be measured, for example, by the square sum of the differences for the actual value and the target value of the first solid angle and the second solid angle.

[0083] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

[1] Medical instrument for use in a magnetic resonance tomograph (1), wherein the medical instrument (70) has a spirit level (80) for determining a spatial position of the medical instrument (70), wherein the spirit level (80) is arranged in a predetermined relative position and position to the medical instrument (80) and has a liquid that can be detected by the magnetic resonance tomograph (1). [2] Medical instrument according to claim 1, wherein the medical instrument (70) comprises a first spirit level (81) and a second spirit level (82) arranged at an angle to the first spirit level (81) such that a first inclination is detected by means of the first spirit level (81), a second inclination is detected by means of the second spirit level (82), and the solid angle of the first inclination and the solid angle of the second inclination span a polar coordinate system in space. [3] A medical instrument according to claim 1 or 2, wherein the liquid comprises a contrast agent for magnetic resonance imaging. [4] Method for positioning a medical instrument (70) according to one of claims 1 to 3 on a patient by means of a magnetic resonance imaging device (1), the method comprising the steps of: - determining a trajectory (S10) for the medical instrument (70) for a predetermined intervention; - identifying an entry point (S20) on the patient (100) and an orientation of the medical instrument (70) that enable movement of the medical instrument (70) along the trajectory; - positioning (S30) the medical instrument (70) at the entry point by a user; - detecting at least one actual value of a first solid angle (S40) by means of a magnetic resonance image of the spirit level (80); - determining a target value (S50) for the first solid angle by a controller (23) of the magnetic resonance imaging device (1); - determining first information (S60) for achieving the predetermined orientation as a function of the actual value of the first solid angle; - Outputting the first information (S70) to the user to correct the alignment of the medical instrument (70). [5] The method of claim 4, wherein the method further comprises the steps of: - detecting at least one actual value of a second solid angle (S45) by means of a magnetic resonance image of the spirit level (80); - determining a target value for the second solid angle (S55) by a controller (23) of the magnetic resonance imaging device (1); - determining second information (S65) for achieving the predetermined orientation as a function of the actual value of the second solid angle; - Outputting the second information (75) to the user to correct the alignment of the medical instrument (70). [6] Method according to one of claims 4 or 5, wherein in a step (S80) the user corrects an orientation of the medical instrument (70) according to the first information and / or second information. [7] Method according to claim 6, wherein the steps of detecting an actual value (S40, S45), determining a target value (S50, S55), determining information (S60, S65), outputting the information (S70) and correcting the alignment for the first and / or second solid angle (S80) are repeated. [8] Method according to claim 7, wherein the controller (23) of the magnetic resonance imaging device (1) determines a deviation between the target value and the actual value (S90) and signals to the user that the deviation falls below a predetermined threshold value. [9] Magnetic resonance imaging device for positioning a medical instrument according to one of claims 1 to 3, wherein the magnetic resonance imaging device 1 is designed to detect at least one actual value of a first solid angle (S40) of the medical instrument (70) positioned at an entry point on a patient (100) by means of a magnetic resonance image of the spirit level (80), to record a target value (S50) for the first solid angle by a control (23) of the magnetic resonance imaging device (1), to determine information (S60) for achieving the predetermined orientation as a function of the actual value of the first solid angle and output the first information (S70) to the user for correcting the alignment of the medical instrument (70).

Images