WO2010142760A2

WO2010142760A2 - Sensor and magnetic field unit for use in a magnetic resonance tomography system or in a magnetic resonance spectroscopy system

Info

Publication number: WO2010142760A2
Application number: PCT/EP2010/058144
Authority: WO
Inventors: Volker Rasche; Erich Hell; Johannes Ulrici
Original assignee: Sirona Dental Systems Gmbh
Priority date: 2009-06-10
Filing date: 2010-06-10
Publication date: 2010-12-16
Also published as: WO2010142760A3; DE102009026897A1

Abstract

The invention relates to a sensor (1) for use in a magnetic resonance tomography system or in a magnetic resonance spectroscopy system, said sensor comprising at least one gradient coil system (4) for producing a gradient field and at least one receiver coil (3) for measuring a high-frequency field. The at least one receiver coil (3) and the at least one gradient coil system (4) are fastened on a fixture (2), said fixture (2), together with the at least receiver coil (3), being at least partially introducible into an oral cavity (21) in the immediate vicinity of an object (7) to be tested. The invention further relates to a magnetic field unit which comprises the sensor (1) according to the invention and to a permanent magnet for producing a main magnetic field.

Description

description

Sensor and magnetic field unit for use within a magnetic resonance tomography system or a magnetic resonance spectroscopy system

The invention relates to a sensor and a magnetic field unit for use within a magnetic resonance tomography system or a magnetic resonance spectroscopy system for dental applications for the targeted representation of small volumes within the oral cavity, such as one or more teeth.

State of the art

MRI is an imaging technique that can only be used to a limited extent for dental applications in the field of temporomandibular joint diagnosis and for the planning of orthodontic surgery today.

A widened use of MRI for the dental sector fails because of the fact that devices on the market for whole-body tomography and for the representation of soft tissue are designed. Thus, their use for the representation of dental structures on the one hand due to the low signal-to-noise ratio and on the other due to the high purchase, installation and operating costs in general out of the question.

DE 20 2007 008 008 U1 discloses a device for tomography for tissue examinations of body parts, in particular in the mouth area on the basis of mechanical excitations, wherein an arrangement of mechanical exciters is arranged on means for stationary alignment, which are advantageously insertable into the mouth. DE 101 47 743 C1 discloses a high-frequency coil which is adapted as closely as possible to the anatomy of the body part to be examined by means of a device made of a special polymer material. As a result, a higher signal-to-noise ratio can be achieved.

An intraoral receptor coil for dental applications has appeared in the article "In Vivo MRI-Based Dental Impression Using an Intraoral RF Receiver Coil" by PM Jakob et al., In the Concepts in Magnetic Resonance Part B, Magnetic Resonance Engineering, Vol. 244-251, 2008, wherein the intraoral receiving coil is adapted for use within a whole body tomograph.

The object of the present invention is to provide a sensor and a magnetic field unit for use in a magnetic resonance tomography or magnetic resonance spectroscopy system, which are tailored to a dental-specific use and are particularly suitable for improved imaging of one or more teeth.

DESCRIPTION OF THE INVENTION The sensor according to the invention for use within a magnetic resonance tomography system comprises at least one receiving coil for measuring a high-frequency field. The at least one receiving coil and at least one gradient coil system for generating a gradient field are mounted on a holder, which is at least partially insertable together with the at least one receiving coil and the at least one gradient coil system in an oral cavity in the immediate vicinity of an object to be examined. As a result, the receiver coil can be brought as close as possible to an object to be examined and thus a higher signal to-noise ratio in the received signal can be achieved. By arranging the holder on or around the object to be examined, namely one or more teeth, a fixation of the gradient coil system and also the receiving coil with respect to the object to be examined is possible without having to fix the patient. In this way, it is possible to avoid errors caused by a movement of the object relative to the gradient coil system and to the receiving coil, without impairing the well-being of the patient during reception by an external fixation.

Advantageously, the at least one receiving coil and / or at least one coil of the at least one gradient coil system are formed as planar coils and the holder advantageously has plate-shaped elements.

As a result, the dimensions of the sensor can be kept as small as possible, so that it can easily be brought in completely or at least partially into an oral cavity.

Advantageously, the at least one receiving coil and / or at least one coil of the at least one gradient coil system are saddle-shaped and are held in a U- or V-shaped holder, so that the coils extend around the object to be examined on three sides.

As a result, the object to be recorded, that is, for example, a tooth or a plurality of teeth, surrounded by at least two accessible sides of the sensor to obtain the best possible measurement signal. Advantageously, at least two receiver coils and / or at least two coils of the gradient coil system are mounted on the holder and introduced into the oral cavity such that the at least two receiver coils and / or the at least two coils of the gradient coil system respectively on at least two different sides of the object to be examined, for example a tooth or a plurality of teeth are arranged.

As a result, the tooth can be surrounded by the sensor from different sides in order to obtain the best possible measuring signal.

Advantageously, the sensor is fixedly or removably mounted on a bite rail. As a result, the sensor can be fixed by biting the patient on the bite rail during a total recording time.

Advantageously, the bite rail has a guide rail and the sensor is held longitudinally displaceable along the guide rail.

Thereby, the position of the sensor on the bite rail can be chosen so that the sensor extends after insertion of the bite rail in the mouth on the teeth to be examined.

Advantageously, at least two sensors can be introduced at least partially into the oral cavity at the same time, wherein the at least two sensors can be read out alternately either simultaneously, temporally or in terms of time.

This makes it possible to position the device only once in the oral cavity of a patient in order to measure several areas. A simultaneous measurement of several areas can be made possible, the two Sensors can be read, for example, during a common time window. The two sensors can also be read in each case during a time window, wherein these time windows can overlap in time or follow each other in time without overlapping.

Advantageously, the at least two sensors can be positioned in the oral cavity so that at the same time an object to be examined can be detected on the upper jaw and one on the lower jaw. As a result, teeth in the upper jaw and in the lower jaw can be measured simultaneously or at least after only one positioning step.

Advantageously, the receiving coil is used as a transmitting coil for generating a high-frequency field. As a result, a transmission coil can be saved in the MRT system in which the sensor according to the invention is to be used.

Advantageously, a transmitting coil for generating a high-frequency field is arranged on the holder of the sensor.

If, for example, the receiving coil can not be used as a transmitting coil, or if this is undesirable for any reason, then the transmitting coil of the MR system in which the sensor according to the invention is to be used can be designed as an additional coil and be arranged on the holder of the sensor , Advantageously, at least one permanent magnet is provided for generating a main magnetic field, which is connected via a bracket, which allows the return of the magnetic flux with the holder, wherein the permanent magnet to the outside of the holder is spaced and remains outside the oral cavity when the holder within the oral cavity is positioned. As a result, in addition to the gradient coil system and the receiving coil, a further component of the MRT system in which the sensor according to the invention is used can be attached directly to the sensor. Furthermore, possibly high costs for an external main magnet can be saved.

Advantageously, the at least one spaced apart from the outside of the holder permanent magnet is removably attached to the bracket. As a result, the permanent magnet is replaceable. It is therefore possible to provide various permanent magnets and in each case to select a permanent magnet adapted to the patient and the examination objective and to fasten it to the bracket.

Advantageously, the bracket is removably attached to the bracket. This makes it possible to use different brackets. Thus, in each case one can be selected and used on the anatomy of the patient and on the position of the object to be examined, for example a molar or an incisor.

Advantageously, a holding device is provided which can be arranged on the head of the patient and to which the at least one spaced apart from the outside of the holder permanent magnet is attachable. As a result, the weight of the permanent magnet can be carried by the holder on the head and does not have to be held by the patient with the teeth.

As a further subject matter, the invention comprises a magnetic field unit for use within an MR system which comprises at least one permanent magnet for generating a main magnetic field, at least one gradient coil system for generating a gradient field and at least one receiver coil for generating a high-frequency field and uses the sensor according to the invention, wherein the at least one permanent magnet is arranged on the holder or partially or completely replaces the holder.

The integration of a permanent magnet into the sensor according to the invention makes it possible to provide a very small, cost-effective, largely intraoral magnetic field unit of an MRI system, which is tailored to dental applications. The magnetic field unit according to the invention, which comprises all system components of a magnetic resonance tomograph, thus represents an intra-oral magnetic resonance tomograph.

Advantageously, a transmitting coil is provided which can be positioned at a distance from the magnetic field unit. The MRI system in which the magnetic field unit is to be used usually has a transmitting coil for excitation. If this is arranged at a distance from the magnetic field unit, for example outside the oral cavity, the size of the parts to be arranged in the patient's mouth during a recording, in particular the magnetic field unit, can be minimized, which is more pleasant for the patient.

Advantageously, both poles of the at least one permanent magnet are formed such that the homogeneous portion of the main magnetic field extends over the object to be examined, for example one or more teeth. This makes it possible to take one or more teeth without having to move the device in between.

Advantageously, a means for temperature stabilization of the at least one permanent magnet is provided.

Even slight temperature changes of the permanent magnets can change the main magnetic field generated by them. A means of temperature stabilization allows the Temperature of the permanent magnet and thus to keep the magnetic field generated by them constant. A temperature stabilization can take place, for example, by means of cooling by means of a Peltier element or by heating by means of a heating wire, a heating coil or another heating element.

Advantageously, a temperature sensor is arranged in the vicinity of the at least one permanent magnet for controlling the means for temperature stabilization. As a result, the temperature of the permanent magnet can be measured and the temperature stabilization can be controlled accordingly.

Advantageously, the means for temperature stabilization is a liquid or gaseous heat carrier, which is filled into an interior space between the poles of the at least one permanent magnet. As a result, a relatively large volume is available for the liquid or gaseous heat carrier, as a result of which efficient temperature stabilization is possible.

Advantageously, at least two tubes led out of the oral cavity are provided, via which the liquid or gaseous heat carrier is exchangeable. By the heat transfer medium, the temperature of the permanent magnet can be stabilized in a simple manner.

Advantageously, the at least one permanent magnet has channels for a liquid or gaseous heat carrier or for temperature regulating elements.

As a result, the temperature of the permanent magnet can be stabilized and regulated without, for example, the entire interior space between the permanent magnets having to be filled with a liquid or gaseous heat carrier. Advantageously, a means for measuring the magnetic field strength of the at least one permanent magnet is provided. As a result, the magnetic field strength of the main magnetic field can be measured during recording of measurement signals of the magnetic field unit and recorded, if necessary, in order to take account of fluctuations in an evaluation of the measurement signals or to make corresponding corrections of the main magnetic field. The measurement of the magnetic field strength is possible, for example, without the provision of an additional measuring apparatus by measuring the resonance frequency.

Advantageously, at least one compensating coil is provided, with which changes in the main magnetic field can be compensated and which is arranged on the at least one permanent magnet, on which at least one gradient coil system or on the at least one receiving coil of the magnetic field unit.

This makes it possible to compensate for disturbances of the main magnetic field. In this case, the compensation coil is arranged as close as possible to the field to be compensated, since in this way the smallest possible currents are necessary in order to produce a desired field strength for the compensation of local field inhomogeneities. The closer the coil is arranged to the main magnetic field, the lower the current required to produce a necessary correction field strength.

Advantageously, to compensate for changes in the main magnetic field, at least one compensating permanent magnet can be movably positioned on the magnetic field unit.

This eliminates the need for a further amplifier, which would be necessary for a corresponding coil. The heat development, which has a resistive coil, does not occur. However, the attachment of the at least one compensating permanent magnet may be formed on the magnetic field unit so that the compensating permanent magnet can be moved relative to the magnetic field unit. The Ausgleichspermanentmagnet can be kept for example on rails or on a sliding bracket. This makes it possible to follow the permanent magnets in order to correct the correction field strength over the distance of the magnet to the main magnetic field and to match it to the inhomogeneity of the main magnetic field to be compensated. Advantageously, at least one permanent magnet arranged at a distance from the holder and arranged outside the oral cavity is connected to the at least one permanent magnet inside the oral cavity held on the holder or partially or completely replacing the holder via a bracket which enables the magnetic flux to be returned, the permanent magnet remains outside the oral cavity when the holder is positioned within the oral cavity.

This makes it possible not to provide part of the permanent magnets necessary for generating the main magnetic field on the holder and thereby to minimize the dimensions of the part of the magnetic field unit that can be introduced into the oral cavity.

Advantageously, the bracket is detachably attached to the holder held on the holder or the holder partially or completely replacing the permanent magnet. This makes it possible to use different brackets. Thus, in each case one can be selected and used on the anatomy of the patient and on the position of the object to be examined, for example a molar or an incisor.

As a further object, the invention comprises a magnetic field unit of a magnetic resonance spectroscopy system (MRS system) according to the magnetic field unit according to the invention, but without Gradientenspulensystem.

By using a magnetic field unit which does not provide a gradient coil system but otherwise has all the features of the magnetic field unit according to the invention, no spatially resolved measurement of the object to be examined is possible, but a spectroscopic examination of the object in the homogeneous region of the magnetic field. Such a construction to be used in an MRS system can be used, for example, to test a tooth for specific components of caries.

The invention further relates to a method for generating magnetic resonance tomography images by means of a magnetic resonance tomography system with a sensor at least partially insertable into an oral cavity in the immediate vicinity of an object to be examined with at least one gradient coil system for generating a gradient field. In a recording step, a magnetic resonance tomography image is generated, wherein during a time interval required for the recording step, the gradient coil system is subjected to a recording current which changes in time according to a predetermined current profile. Before generating a first magnetic resonance tomography image, a preparation current is applied to the at least one gradient coil system in a preparation step.

Typically, it is above all the gradient coils or the coils of a gradient coil system of a magnetic resonance tomography system which heat it up during operation by means of waste heat. By applying the gradient coil system with a preparation current, the coils of the gradient coil system and thus the entire te system already heated before the production of the actual recording. As a result, for example, already a stable temperature of the entire system can be achieved, which does not change much during a recording or a temperature profile can be achieved, which corresponds to the temperature profile set for the calibration of the sensor.

By using the gradient coil system for heating the gradient coil system itself and, if appropriate, the surrounding components, it is not necessary to provide further heating means.

Advantageously, the preparation current corresponds to the course of one or more current waveforms during the generation of a magnetic resonance tomography image. A variant of heating the sensor by means of the gradient coil system is to select the time course of the preparation current according to the current flow of the recording current during a recording cycle or even during several recording cycles. For example, this could cause the system to reach an equilibrium-like state that does not change much in the following shot.

Advantageously, the preparation current corresponds at most to a maximum current value of the current waveform predetermined for a magnetic resonance tomography recording and the at least one gradient coil system is energized continuously or pulsed during a time interval that is less than or equal to the time interval required for a magnetic resonance tomography recording. Another variant is a constant or arbitrarily varying current value less than or equal to the maximum Current value to select and apply the gradient coil system continuously or pulsed with this current. Thus, a desired operating temperature can be achieved as quickly and easily. Advantageously, the sensor is arranged in the oral cavity during the execution of the preparation and the recording step. As a result, temperature changes due to the elevated temperature in the oral cavity compared to the ambient temperature can already be set during the first step. Thus, a disturbing corresponding temperature change during the actual recording can be avoided.

Advantageously, the sensor is arranged in a receiving position within the oral cavity during the execution of the preparation and the recording step. As a result, the receiving step can be directly connected to the preparation step, without a change in position of the sensor is necessary. Further temperature changes occurring during a positioning process can thus be avoided.

Advantageously, a temperature sensor is arranged on the sensor and the temperature of the sensor is controlled by means of the temperature sensor, wherein during the preparation step when a predetermined maximum temperature is exceeded, the current impinging on the at least one gradient coil system is cut off, the preparation step is ended and in the acquisition step the magnetic resonance tomography acquisition is carried out.

On the one hand, a temperature sensor makes it possible to monitor or quickly determine the attainment of a desired temperature. On the other hand, the control of the temperature is possible to the extent that an exceeding of an ner permissible maximum temperature of the system can be monitored.

Brief description of the drawing

Several embodiments of the invention are illustrated in the drawing. It shows that

Fig.l A, B, C, D a sensor according to the invention, the

Fig. 2 A, B, C a magnetic field unit according to the invention, the

FIG. 3 shows a magnetic field unit according to the invention for spectral analysis, FIGS. 4 A, B, C, D possibilities for temperature stabilization of the permanent magnets of the magnetic field unit from FIG

FIG. 5 shows the mounting of the sensor from FIG. 1 or the magnetic field unit of FIG. 2A movably mounted on an impression tray. FIG

FIG. 6 shows the impression tray from FIG. 5 with two holders of the sensor of FIG. 1 arranged thereon or the magnetic field unit from FIG. 2A, FIGS. 7A, B the holder of the sensor from FIG. 1 or the magnetic field unit from FIG with a partially inside the oral cavity and partially outside arranged permanent magnets, Fig. 8 shows a holder for the outside arranged permanent magnet of Fig. 7A and 7B, the

9 shows an exemplary current profile of a preparation current. embodiments

A sensor 1 according to the invention comprises a holder 2 on which at least one receiver coil 3 for receiving a nuclear spin resonance tomography signal and at least one gradient coil system 4 consisting of several coils for generating a gradient field is held. The holder may for example be U-shaped, as shown in Fig. IA, IB and IC, L-shaped as shown in Fig. IC or V-shaped. The receiver coils 3 and the coils of the gradient coil system 4 are preferably formed as a planar coil system and can, for example saddle-shaped over all three or at least two sides of a U-shaped holder 2 extend, as shown in Fig. IA. In this case, the at least one coil of the gradient coil system 4 is held in a first plane 5 on the inwardly facing walls of the U-shaped holder and the at least one receiving coil 3 is held in a second plane 6 at the first level 5. Further possible embodiments are shown in FIG. 1B, IC and ID. In FIG. 1B and ID, two receiving coils 3 and the coils of a gradient coil system 4 are respectively arranged on one of the two mutually facing sides of the U-shaped holder 2, by the coils of the gradient coil system 4 in a first plane 5 on the side walls of the holder 2 are held and the receiving coils 3 are arranged in a second plane 6 at the first level 5. In Fig. IC, a receiving coil 3 and a gradient coil system 4 are shown, which are each held on a surface of an L-shaped holder 2.

The U-shaped holder 2 makes it possible to mount the holder 2 around the object 7 to be examined, for example To put a tooth around so that the one or more receiving coils 3 surround the object to be examined from two or even three sides. This can improve the quality of the measurement signal. By slipping over, for example, a tooth, the holder is held on the object 7 to be examined. As a result, the holder 2 and thus also the at least one receiving coil 3 and in particular the coils of the gradient coil system 4 moves with the object 7 to be examined. Thus, errors that occur by a movement of the object to be examined 7 relative to the gradient field or relative to the receiving coil 3, can be avoided.

The L-shaped holder 2 makes it possible to bring the at least one receiving coil 3 at least from one side close to the object 7 to be examined. For example, it can be arranged on one or more teeth such that the receiving coil 3 and at least partially the gradient coil 4 holding surface laterally abuts one or more teeth, while the other surface of the holder 2 rests on the occlusal surface of the tooth or teeth and fixed, for example, by the biting of the patient.

The sensor may be used within an MRI system that includes, for example, a superconducting magnet, one or more resistive electromagnets, or one or more permanent magnets for generating a main magnetic field. With the holder positioned in the oral cavity, the patient is positioned in the main magnetic field such that the holder and the object to be examined, for example several teeth of the upper and / or lower jaw, are located in the homogeneous region of the main magnetic field. According to the invention, a magnetic field unit 8 with the holder 2 can be realized, which, in addition to the gradient field, also generates a main magnetic field necessary for magnetic resonance tomography or magnetic resonance spectroscopy. For this purpose, in addition to the at least one receiving coil 3 and the at least one coil of the gradient coil system 4, at least one permanent magnet 9 is also provided, which is likewise fastened to the holder 2 and / or partially or completely replaces the holder 2. For example, two permanent magnets 9 for generating the

Main magnetic field can be provided and serve as lateral support surfaces of a U-shaped holder 2, as shown in Fig. 2A. The two poles of the magnet are designed so that the homogeneous portion of the generated magnetic field extends over the entire object to be recorded 7, that is, for example, one or more teeth. To return the magnetic field, these two permanent magnets are connected by a bridge 10, which forms the third side of the U-shaped holder 2. The coils of the gradient coil system 4 are then held in a first plane 5 on the two permanent magnets 9 forming the side surfaces. The receiving coils 3 are likewise arranged between the permanent magnets 9 and held in each case in a second plane 6, for example on the first plane 5.

To generate the high-frequency field, either the receiving coil 3 can be used or a further planar coil can be arranged as a transmitting coil on the mutually facing sides of the permanent magnet 9 or on the second level 6 containing the receiving coil 3.

To compensate for changes or disturbances of the main magnetic field, which in particular disturb its homogeneity, Furthermore, at least one compensation coil 24 can be provided. Such a compensating coil 24 can be arranged, for example, on the plane 6 containing the receiving coils. In order to avoid interference between the coils as much as possible, the compensation coil 24 can also be arranged in a further plane 24 'between the permanent magnet 9 and the plane 5 holding the at least one coil of the gradient coil system 4, to which the plane 6 with the at least one Reception coil 3 connects, as shown in Fig. 2B.

However, it would also be possible to arrange the compensation coil 24 between the plane 5 holding the at least one coil of the gradient coil system 4 and the plane 6 holding the at least one receiving coil 3.

The compensation coil can also be kept in a suitable plane.

Instead of using a compensating coil 24 for compensating for inhomogeneities of the main magnetic field, at least one compensating permanent magnet 25 may also be provided, which is disposed at a suitable location on the magnetic field unit 8. Compensating permanent magnets 25 may, for example, be arranged on the plane 6 containing the receiving coils. The compensating permanent magnet 25 can also be arranged in a further plane 25 'between the permanent magnet 9 and the plane 5 holding the at least one coil of the gradient coil system 4 in order to avoid mutual interference corresponding to the compensating coils 24, as shown in FIG. 2C. It is also possible, of course, to arrange the compensating permanent magnet 25 between the planes 5 and 6, ie between the at least one coil of the gradient coil system 4 and the receiver coil 3. The magnetic field unit 8 according to the invention can also be used for the spectral analysis of the object 7 to be examined. Advantageously, only a main magnetic field, a high-frequency field and no gradient field are used. Although this makes it impossible to measure spatially resolved, the signal to noise ratio improves. The magnetic field unit according to the invention can either be constructed without a gradient coil system 4, as shown in FIG. 3, or the gradient field can be switched off. The main magnetic field can be generated as described by means of permanent magnets 9, which also serve as a lateral support 2 for the receiving coil 3. The high-frequency field can be generated as previously described either by a transmitting coil, which is also arranged on the side surfaces of the permanent magnet 9, or by the receiving coil 3. By means of spectral analysis, components of caries, for example, can be detected in the examined object 7 on the basis of their specific spectroscopic fingerprint.

The magnetic field unit shown in FIG. 3 can not only be part of a magnetic resonance spectroscopy system, but of course it can also be used within an MRI system, wherein a gradient field necessary for magnetic resonance tomography can be generated by means of an external gradient coil system known from the prior art. The coils of the gradient coil system are positioned in the vicinity of the fixed patient so that the gradient field in the area of the object to be examined, ie For example, several teeth of the patient, the desired course.

For power supply, for controlling and / or reading out the at least one gradient coil system 4 and the at least one receiving coil 3 lines are provided, which are guided after introduction of the holder into the oral cavity of a patient P from the oral cavity to a control and monitoring unit 11.

For temperature stabilization of the at least one permanent magnet 9, for example, a liquid or gaseous heat carrier 12 can be used, which is provided in the intermediate space between the permanent magnets 9. A necessary sealing device 13 may be made of a flexible material such as rubber and, as shown in FIG. 4A, extend around the object 7 to be examined up to the permanent magnet 9.

The sealing device 13 also has two tubes 14, via which the liquid or gaseous heat carrier 12 can be supplied and removed. For this purpose, a circuit may be provided which is controlled, for example, in accordance with the temperature measurement of a temperature sensor 15 attached, for example, to the wall of the permanent magnet 9. The temperature measurement can for example be made optically by a light guide. Another possibility for temperature stabilization of the permanent magnets 9 would be integrated into the permanent magnet 9 cooling devices. These may be, for example, channels 16 for a liquid or gaseous heat carrier 12 or temperature regulating elements 17, as shown in FIGS. 4B, 4C and 4D. By a temperature stabilization of the at least one permanent magnet 9, the generated main magnetic field can be kept constant. However, it is also possible to take into account deviations that occur, for example, due to temperature changes in the evaluation of the measured data. For this purpose, a means for measuring the main magnetic field can be provided, for example, via the resonance frequency.

As shown in FIG. 5, the holder 2 of the sensor 1 according to the invention from FIG. 1 or the magnetic field unit 8 from FIG. 2A for stable positioning in the oral cavity 21 can be mounted on a bite rail 18. The bite bar 18 may for example have the shape of an impression tray. Furthermore, a guide rail 19 can be provided, on which the holder 2 is held longitudinally displaceable, so that the sensor 1 or the magnetic field unit can be positioned in the mouth at any position along the row of teeth. By biting the patient onto the bite rail 18, the sensor 1 or the magnetic field unit 8 is fixed relative to the object 7 to be examined.

By providing and simultaneously using two sensors 1 or two magnetic field units 8, which are mounted in opposite orientation on the same bite rail 18, as shown in Fig. 6, an object to be examined in the upper jaw and one in the lower jaw can be measured simultaneously.

FIG. 7 shows a variant embodiment of the magnetic field unit 8 according to the invention, which has at least one permanent magnet 20 for generating the main magnetic field, which remains outside after insertion of the holder 2 into the oral cavity 21. For this purpose, the permanent magnet 20 via a correspondingly shaped bracket 22 with bracket 2 or attached to the holder permanent magnet 9 is connected. Fig. 7A shows a corresponding structure for the measurement of molars, wherein the bracket is correspondingly long and U-shaped, so that the permanent magnet 20 is located outside the oral cavity and laterally adjacent to the holder when the holder on the one or more molars to be measured is positioned. In Fig. 7B, the structure is changed so that it is suitable for measuring the anterior teeth. For this, the bar is straight and rather short.

So that you do not need two completely separate structures to measure different regions within the oral cavity 21, correspondingly shaped bracket 22 and other permanent magnets 20 may be provided, which can be exchangeably connected to the holder 2 or mounted on the holder 2 permanent magnet 9 , It is also possible to provide differently shaped and / or differently sized brackets 22 and permanent magnets 20 in order to adapt the structure to the anatomical conditions of the patient P.

In Fig. 8, a possible holder 23 is shown, which can be arranged at the head of the patient P and at which the at least one spaced apart from the holder 2 permanent magnet 20 can be held. Cables for connecting the magnetic field unit 8 to the control and monitoring unit 11 can also be held on the holder 23, for example.

According to the invention, the receiving step is preceded by a preparatory step which provides for the gradient coil system 4 to be charged with a preparation current I _v . The course of this preparation current I _v , for example, follow exactly the course of a recording current or this traversing several times in succession, so that the duration of the preparation step corresponds to a time interval T ₁ for a magnetic resonance imaging or a multiple of this time interval Ti. Another variant is the application of the at least one coil of the gradient coil system 4 with a preparation current I _v , which has a value less than or equal to the maximum current value I _ma χ the recording current and continuously or pulsed for a time interval T ₂ , which is less than or equal to the recording necessary time interval Ti is present. An example of such a preparation current I _v is shown as a function of current I and time t in FIG. 9.

Disturbances in the magnetic resonance signal to be measured can, as usual in the context of magnetic resonance tomography, be avoided or at least reduced by shielding the entire measuring volume from external high-frequency fields. If possible, a shield should be designed so that it encloses the entire patient. It can also be adequately shielded an entire room in which the sensor 1 according to the invention or the magnetic field unit is operated within an MRI system. Alternatively, the patient may be grounded to minimize the effect of the body as an antenna.

LIST OF REFERENCE NUMBERS

1 sensor

2 bracket

3 receiver coil

5 4 gradient coil system

5 first level

6 second level

7 object to be examined, for example tooth

8 magnetic field unit 10 9 permanent magnet

10 bridge

11 control unit

12 liquid or gaseous heat carrier

13 sealing device 15 14 hose

15 temperature sensor

16 channel

17 temperature control elements

18 bite rail

20 19 guide rail

20 permanent magnet

21 oral cavity

22 stirrups

23 holding device 25 24 compensation coil 24 'further level

25 compensating permanent magnet

25 'further level

I current I _v current profile of the preparation current

I _max Maximum current value of the recording current profile

P patient t time

Ti time interval for a magnetic resonance imaging

T ₂ time interval for admission with preparation current

Claims

claims

1. Sensor (1) for use within a magnetic resonance tomography (MRI) system, comprising at least one receiving coil (3) for measuring a high frequency field, characterized in that the at least one receiving coil (3) and at least one gradient coil system (4) for The holder (2) with the at least one receiving coil (3) and the at least one gradient coil system (4) into an oral cavity (21) in the immediate vicinity of an object to be examined (7) is at least partially recoverable.

2. Sensor (1) according to claim 1, characterized in that the at least one receiving coil (3) and / or at least one coil of the at least one gradient coil system (4) are formed as planar coils and the holder (2) has plate-shaped elements.

3. Sensor (1) according to claim 1 or 2, characterized in that the at least one receiving coil (3) and / or at least one coil of the at least one gradient coil system (4) are saddle-shaped and the holder U- or V-shaped is formed in that the receiving coil (3) and the at least one coil of the gradient coil system (4) extend around the object (7) to be examined on three sides.

4. Sensor (1) according to one of claims 1 to 3, characterized in that at least two receiving coils

(3) and / or at least two coils of the gradient coil system (4) are mounted on the holder (2) and in the oral cavity (21) are introduced, that the at least two receiving coils (3) and / or the at least two coils of the gradient coil system (4) respectively on at least two different sides of the object to be examined (7), for example one or more teeth , are arranged.

5. Sensor (1) according to one of claims 1 to 4, characterized in that the sensor (1) on a bite rail (18) is arranged fixed or removable.

6. Sensor (1) according to claim 5, characterized in that the bite rail (18) has a guide rail (19) and that the sensor (1) along the guide rail (19) is held longitudinally displaceable.

7. Sensor (1) according to any one of claims 1 to 6, characterized in that at least two sensors (1) at least partially in the oral cavity (21) can be introduced and that the at least two sensors (1) either simultaneously, temporally nachielliell o - Which can be read out alternately in time.

8. Sensor (1) according to claim 7, characterized in that the at least two sensors (1) are positionable in the oral cavity (21), that at the same time an object to be examined on the upper jaw and one on the lower jaw is detected.

9. sensor (1) according to one of claims 1 to 8, characterized in that the receiving coil (3) is used as a transmitting coil for generating a high-frequency field.

10. Sensor (1) according to one of claims 1 to 8, characterized in that a transmitting coil for generating a nes high-frequency field on the holder (2) of the sensor (1) is arranged.

11. Sensor (1) according to one of claims 1 to 10, characterized in that for generating a main magnetic

At least one permanent magnet (20) is provided, which is connected to the holder (2) via a bracket (22), which allows a return of a magnetic flux, wherein the permanent magnet (20) is spaced from the outside of the holder and is located outside of the oral cavity (21) when the holder is positioned within the oral cavity (21).

12. sensor (1) according to claim 11, characterized in that the at least one to the holder (2) beabstande- te permanent magnet (20) removably on the bracket (22)

15 is attached.

13. Sensor (1) according to claim 11 or 12, characterized in that the bracket (22) is removably attached to the holder (2).

14. Sensor (1) according to one of claims 11 to 13, characterized in that a holding device (23) is provided which can be arranged on a head of the patient (P) and on which the at least one holder (2) spaced permanent magnet (20) is attachable.

25 15. Magnetic field unit (8) for use within an MRI system, comprising at least one permanent magnet (9) for generating a main magnetic field, at least one gradient coil system (4) for generating a gradient field and at least one receiving

30 coil (3) for a high-frequency field, characterized in that a sensor (1) according to one of the claims Chen 1 to 13 is used, wherein the at least one permanent magnet (9) on the holder (2) is arranged or the holder (2) partially or completely replaced.

5 16. Magnetic field unit (8) according to claim 15, characterized in that a transmitting coil is provided, which is positionable to the magnetic field unit (8) spaced.

17 magnetic field unit (8) according to claim 15 or 16, characterized in that both poles of the at least one permanent magnet (9) are formed so that the homogeneous portion of the main magnetic field on the object to be examined (7), for example a Tooth or several teeth, extending.

15 18. Magnetic field unit (8) according to one of claims 15 to 17, characterized in that a means for temperature stabilization of the at least one permanent magnet (9) is provided.

19. Magnetic field unit (8) according to claim 18, characterized in that a temperature sensor (15) is arranged in the vicinity of the at least one permanent magnet for controlling the means for temperature stabilization.

20 magnetic field unit (8) according to claim 18 or 19, characterized in that the means for temperature stabilization is a liquid or gaseous heat carrier (12) which is filled in an inner space between the poles of the at least one permanent magnet.

30 21. Magnetic field unit (8) according to claim 20, characterized in that at least two of the oral cavity (21) leading out hoses (14) are provided, via which the liquid or gaseous heat transfer medium (12) is interchangeable.

22. magnetic field unit (8) according to one of claims 15 to 21, characterized in that the at least one

Permanent magnet (9) channels (16) for a liquid or gaseous heat carrier (12) or for temperature regulating elements (17).

23. Magnetic field unit (8) according to one of claims 15 to 22, characterized in that a means for measuring the magnetic field strength of the at least one permanent magnet (9) is provided.

24. Magnetic field unit (8) according to one of claims 15 to

23, characterized in that at least one compensating coil (24) is provided, with which changes of the main magnetic field can be compensated, on the holder (2), on the at least one permanent magnet (9), on the at least one gradient coil system (4 ) or at the at least one receiving coil (3) of the magnetic field unit (8) is arranged.

25. Magnetic field unit (8) according to one of claims 15 to

24, characterized in that to compensate for changes in the main magnetic field, at least one compensating permanent magnet (25) is movably positionable on the magnetic field unit.

26. Magnetic field unit (8) according to one of claims 15 to

25, characterized in that the at least one to the holder (2) spaced and outside the oral cavity (21) arranged permanent magnet (20) via a bracket (22), the return of a magnetic flux allows, with the at least one held on the holder (2) or the holder (2) partially or completely replacing permanent magnet (9) within the oral cavity (21) is connected, the permanent magnet outside the oral cavity remains, if the holder inside the oral cavity is positioned.

27 magnetic field unit (8) according to claim 26, characterized in that the bracket (22) removably attached to the holder (2) or the holder (2) partially or completely replacing the permanent magnet (9) is fixed.

28 magnetic field unit of a magnetic resonance spectroscopy system according to the magnetic field unit (8) according to any one of claims 15 to 27, but without gradient coil system (4).

29. A method for generating magnetic resonance tomography images by means of a magnetic resonance tomography system with a sensor (1) at least partially insertable into an oral cavity (21) in the immediate vicinity of an object to be examined (7) with at least one gradient coil system (4) for generating a gradient field, wherein a magnetic resonance tomography image is generated in a recording step, during which the gradient coil system (4) is subjected to a recording current which changes in time according to a predetermined current characteristic during a time interval (T ₁ ) required for the recording step, characterized in that before generating a first magnetic resonance tomography image in a preparatory step, the at least one gradient coil system (4) is subjected to a preparatory current (I _v ).

30. The method according to claim 29, characterized in that the preparation current (I _v ) the course of one or more current waveforms of the recording current during the generation of a magnetic resonance tomography.

5 equivalent.

31. The method according to claim 29, characterized in that the preparation current (I _v ) corresponds at most to a maximum current value of the current waveform predetermined for a magnetic resonance tomography recording, and

10 that the at least one gradient coil system (4) during a time interval (T ₂ ), which is less than or equal to the time interval (Ti) necessary for a magnetic resonance tomography recording, is energized continuously or pulsed pulsed.

32. Method according to claim 29, characterized in that the sensor (1) is arranged in the oral cavity (21) during the execution of the preparation and the receiving step.

33. The method according to claim 32, characterized

20 that the sensor (1) during the preparation of the preparation and the recording step in a receiving position within the oral cavity (21) is arranged.

34. The method according to any one of claims 29 to 33, characterized 25 characterized in that a temperature sensor on the sensor

(1) is arranged and that the temperature of the sensor (1) is controlled by means of the temperature sensor, wherein during the preparation step when exceeding a predetermined maximum temperature of 30 the at least one gradient coil system (4) applied current off and preparatory step is completed and in the recording step, the magnetic resonance imaging is performed.