DE102009026897A1 - Sensor and magnetic field unit for use within a magnetic resonance imaging system or a magnetic resonance spectroscopy system - Google Patents

Abstract

The invention relates to a sensor (1) for use within a magnetic resonance tomography system or a magnetic resonance spectroscopy system, comprising at least one gradient coil system (4) for generating a gradient field and at least one receiving coil (3) for measuring a high-frequency field. The at least one receiving coil (3) and the at least one gradient coil system (4) are mounted on a holder (2), wherein 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 introduced. Furthermore, the invention relates to a magnetic field unit which comprises the sensor (1) according to the invention and a permanent magnet for generating a main magnetic field.

Description

Technical area

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

State of the art

The MRI is an imaging procedure that is used nowadays for dental applications only to a very limited extent in the field of diagnosis of the temporomandibular joint and for planning of oral surgery.

A broadened use of MRI for the dental field fails because of devices on the market for the whole-body tomography and for the presentation are designed by soft tissue. Thus, their commitment comes for the representation of dental structures on the one hand due to the low Signal-to-noise ratio and on the other hand due to the high purchase, Installation and operating costs generally out of the question.

The DE 20 2007 008 008 U1 discloses a device for tomography for tissue examinations of body parts, in particular in the mouth region on the basis of mechanical excitations, wherein an array of mechanical exciters is arranged on means for fixed alignment, which are advantageously insertable into the mouth.

The 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 receiving coil for dental applications is from the article "In Vivo MRI-Based Dental Impression Using an Intraoral RF Receiver Coil" by PM Jakob et al. published in Concepts in Magnetic Resonance Part B, Magnetic Resonance Engineering, Vol. 33B (4) 244-251, 2008 , wherein the intraoral receiving coil is adapted for use within a whole body tomograph.

task The present invention is a sensor and a magnetic field unit for use in a magnetic resonance or magnetic resonance spectroscopy system provide tailored to a dental-specific use are and in particular for the improved illustration of one or more teeth.

Presentation of the invention

Of the Sensor according to the invention for use within a magnetic resonance imaging system comprises at least one Receiver coil for measuring a high-frequency field. The least a receiving coil and at least one gradient coil system for Generation of a gradient field are mounted on a holder which together with the at least one receiving coil and the at least a gradient coil system in an oral cavity in the immediate Neighborhood to an object to be examined at least partially can be introduced.

Thereby the receiver coil as close as possible to be examined Object brought and thus a higher signal-to-noise ratio be achieved in the received signal. By placing the bracket at or around the object to be examined, namely one or multiple teeth, is a fixation of the gradient coil system and also the receiver coil opposite the one to be examined Object possible without having to fix the patient. So mistakes can be avoided by a movement of the object relative to the gradient coil system and to the receiver coil be avoided without the well-being of the Patients during a recording by an external Affect fixation.

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

Thereby The dimensions of the sensor can be as small as possible be held so that it is easily complete or at least partially into an oral cavity can be brought.

advantageously, are the at least one receiving coil and / or at least one Spool of the at least one gradient coil system saddle-shaped trained and are in a U- or V-shaped bracket held so that the coils on three sides around the examined Pass the object around.

Thereby is the object to be recorded, so for example, a tooth or several teeth, from at least two accessible Pages surrounded by the sensor to get the best possible signal to obtain.

advantageously, are at least two receiving coils and / or at least two coils of the Gradient coil system mounted on the bracket and so in the Oral cavity introducible that the at least two receiving 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, one tooth or more teeth arranged are.

Thereby the tooth can be surrounded by the sensor from different sides, to get the best possible measurement signal.

advantageously, the sensor is arranged on a bite rail. This allows the Sensor by biting the patient on the bite rail during be fixed a total recording time.

advantageously, the bite rail has a guide rail and the Sensor is longitudinally displaceable along the guide rail held.

Thereby The position of the sensor on the bite rail can be selected be that the sensor after insertion of the bite rail in the mouth extends over the teeth to be examined.

advantageously, At least two sensors are at least partially in at the same time the oral cavity can be introduced, wherein the at least two sensors either at the same time, in terms of time, or alternating in time can be read out.

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

advantageously, the at least two sensors can be positioned in the oral cavity, that at the same time an object to be examined on the upper jaw and one on the lower jaw can be detected. Thereby can simultaneously or at least after only one positioning step Teeth in the upper jaw and in the lower jaw are measured.

advantageously, the receiving coil is used as a transmitting coil for generating a high-frequency field used. As a result, in the MRI system in which the inventive Sensor is to be used, a transmission coil can be saved.

advantageously, is at least one permanent magnet for generating a main magnetic field provided, via a bracket, the return allows the magnetic flux connected to the holder is, wherein the permanent magnet to the outside of the holder spaced is and remains outside the oral cavity when the holder is positioned inside the oral cavity.

Thereby can in addition to the Gradientespulensystem and the receiving coil a another component of the MRI system in which the inventive Sensor is used, attached directly to the sensor. Farther may be high costs for an external Main magnet can be saved.

advantageously, is the at least one spaced apart from the outside of the holder Permanent magnet removably attached to the bracket. Thereby the permanent magnet is exchangeable. It is therefore possible different permanent magnets be available and one each adapted to the patient and the study objective permanent magnet select and attach to the bracket.

advantageously, The bracket is detachably attached to the bracket. This makes it possible to use different stirrups. Thus, one can adapt to the anatomy of the patient and the location of the object to be examined, for example, a molar tooth or an incisor, selected and used.

advantageously, a holding device is provided on the head of the patient can be arranged and at the at least one to the outside the holder spaced permanent magnet is attachable. Thereby Can the weight of the permanent magnet through the bracket on the head be worn and not from the patient with the teeth being held.

When Another object of the invention comprises a magnetic field unit for use within an MRI system, the at least one permanent magnet for generating a main magnetic field, at least one gradient coil system for Generation of a gradient field and at least one receiving coil for generating a high frequency field and the sensor according to the invention used, wherein the at least one permanent magnet on the holder is arranged or the holder partially or completely replaced.

The integration of a permanent magnet in the sensor according to the invention makes it possible, a very small, inexpensive largely intra To provide a magnetic field unit to be used orally in an MRI system 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, Both poles of the at least one permanent magnet are formed so that the homogeneous portion of the main magnetic field over the object to be examined, for example one or more teeth, extends. This allows one or more teeth without having to move the device in between.

advantageously, is a means for temperature stabilization of the at least one Permanent magnets provided.

Nice slight temperature changes of the permanent magnets can change the main magnetic field generated by them. A means for temperature stabilization it allows the temperature of the permanent magnet and thus the magnetic field generated by it to keep constant.

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

advantageously, is the means for temperature stabilization a liquid or gaseous heat carrier, which in an inner space between the poles of the at least one permanent magnet is filled. This is a relatively large Volume for the liquid or gaseous Heat carrier available, creating a efficient temperature stabilization is possible.

advantageously, are at least two led out of the oral cavity Hoses provided over which the liquid or gaseous heat transfer medium exchangeable is. Due to the heat transfer medium, the temperature 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.

Thereby The temperature of the permanent magnet can be stabilized and regulated without, for example, the entire interior space between the permanent magnet with a liquid or gaseous Heat transfer medium must be filled.

advantageously, is a means of measuring the magnetic field strength of at least provided a permanent magnet. This allows the magnetic field strength of the main magnetic field during a recording of measurement signals the magnetic field unit is measured and optionally recorded, occurring fluctuations in an evaluation of the measurement signals to take into account or appropriate corrections of the main magnetic field make. The measurement of the magnetic field strength is, for example without the provision of an additional measuring apparatus Measuring the resonance frequency possible.

advantageously, is at least one to the outside of the holder spaced and outside the oral cavity arranged permanent magnet over a strap, which is the return of the Magnetic flux allows, with at least one of the Holding the bracket or the bracket partially or completely replacing permanent magnets within the oral cavity, wherein the permanent magnet remains outside the oral cavity, when the holder is positioned inside the oral cavity is.

This allows part of generating the main magnetic field necessary permanent magnets do not provide on the holder and thereby the size of the recoverable into the oral cavity Part of the magnetic field unit to keep as low as possible.

advantageously, the bracket is removable on the held on the bracket or partially or completely replacing the holder Permanent magnets attached. This allows different To use bracket. So can each one to the anatomy the patient and the location of the object to be examined, for example a molar tooth or an incisor, selected and used become.

When Another object of the invention comprises a magnetic field unit a magnetic resonance spectroscopy system (MRS system) accordingly the magnetic field unit according to the invention, however without gradient coil system.

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, although no spatially resolved measurement of the object to be examined longer possible, but a spectroscopic examination of the object in the homogeneous region of the magnetic field. Such a structure to be used in an MRS system can be used, for example be used to test a tooth for specific components of tooth decay.

Brief description of the drawing

Several Embodiments of the invention are in the drawing shown. It shows that

1A , B, C, D a sensor according to the invention, the

2 a magnetic field unit according to the invention, the

3 a magnetic field unit according to the invention for spectral analysis, the

4A , B, C, D Options for temperature stabilization of the permanent magnets of the magnetic field unit 2 , the

5 the holder of the sensor movably mounted on an impression tray 1 or the magnetic field unit 2 , the

6 the impression tray off 4 with two brackets of the sensor arranged on it 1 or the magnetic field unit 2 , the

7A , B the holder of the sensor 1 or the magnetic field unit 2 with a partially inside the oral cavity and partially outside arranged permanent magnets, the

8th a holder for the outside arranged permanent magnet 7A and 7B ,

embodiments

A sensor according to the invention 1 includes a bracket 2 at the at least one receiving coil 3 for receiving a nuclear magnetic resonance tomography signal and at least one gradient coil system 4 consisting of a plurality of coils for generating a gradient field is maintained. The holder may for example be U-shaped, as in 1A . 1B and 1C shown, L-shaped as in 1C shown 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 in 1A shown. In this case, the at least one coil of the gradient coil system 4 in a first level 5 held on the inwardly facing walls of the U-shaped bracket and the at least one receiving coil 3 will be in a second level 6 at the first level 5 held.

Other possible embodiments are in 1B . 1C and 1D shown. In 1B and 1D are two receiving coils 3 and the coils of a gradient coil system 4 in each case on one of the two mutually facing sides of the U-shaped holder 2 arranged by the coils of the gradient coil system 4 in a first level 5 on the side walls of the bracket 2 be held and the receiving coils 3 in a second level 6 at the first level 5 are arranged. In 1C is a receiver coil 3 and a gradient coil system 4 shown, each on a surface of an L-shaped bracket 2 being held.

The U-shaped bracket 2 allows the holder 2 around the object to be examined 7 for example, to put a tooth around so that the one or more receiving coils 3 Surround the object to be examined by two or even three sides. This can improve the quality of the measurement signal. By slipping over, for example, a tooth, the holder on the object to be examined 7 held. This will cause the bracket to move 2 and thus also the at least one receiving coil 3 and in particular the coils of the gradient coil system 4 with the object to be examined 7 With. Thus, errors can be caused by a movement of the object to be examined 7 relative to the gradient field or relative to the receiver coil 3 occur, be avoided.

The L-shaped bracket 2 allows the at least one receiver coil 3 at least from one side close to the object to be examined 7 in bringing. For example, it can be arranged on one or more teeth that the receiving coil 3 and at least partially the gradient coil system 4 holding surface bears laterally against one or more teeth, while the further surface of the holder 2 rests on the occlusal surface of the tooth or teeth and is fixed, for example, by biting the patient.

Of the Sensor can be used within an MRI system, for example a superconducting magnet, one or more resistive electromagnets or one or more permanent magnets for generating a main magnetic field having. The patient is positioned with the one in the oral cavity Bracket positioned in the main magnetic field so that the Holder and the object to be examined, for example several Teeth of the upper and / or lower jaw in the homogeneous area of the main magnetic field.

According to the invention, a magnetic field unit 8th with the bracket 2 be realized, which in addition to the gradient field also generates a necessary for magnetic resonance or magnetic resonance spectroscopy main magnetic field. In addition to the at least one receiver coil 3 and the at least one coil of the gradient coil system 4 also at least one permanent magnet 9 provided, which is also on the bracket 2 is attached and / or the holder 2 partly or completely replaced. For example, two permanent magnets 9 be provided for generating the main magnetic field and as lateral support surfaces of a U-shaped holder 2 serve as in 2 is shown. The two poles of the magnet are designed so that the homogeneous portion of the magnetic field generated over the entire object to be recorded 7 , so for example one or more teeth extends. To return the magnetic field, these two permanent magnets are connected by a bridge 10 connected, which is the third side of the U-shaped bracket 2 forms.

The coils of the gradient coil system 4 then be in a first level 5 on the two side surfaces forming permanent magnet 9 held. The receiver coils 3 are also between the permanent magnets 9 arranged and each in a second level 6 for example, at the first level 5 held.

To generate the high frequency field, either the receiving coil 3 be used or another planar coil as a transmitting coil on the mutually facing sides of the permanent magnet 9 or at the second, the receiving coil 3 containing level 6 to be ordered.

The magnetic field unit according to the invention 8th can also be used for spectral analysis of the object to be examined 7 be used. 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 for this purpose either without a gradient coil system 4 be built up as in 3 or the gradient field can be turned off. The main magnetic field can as described by means of permanent magnets 9 be generated, which also serves as a lateral bracket 2 for the receiver coil 3 serve. The high-frequency field can, as previously described, either by a transmitting coil, which also on the side surfaces of the permanent magnets 9 is arranged, or by the receiving coil 3 be generated. Through spectral analysis, in the examined object 7 For example, components of the caries are detected due to their specific spectroscopic fingerprint.

In the 3 Not only can the magnetic field unit shown be part of a magnetic resonance spectroscopy system, it can of course 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 in such a way that the gradient field in the region of the object to be examined, for example a plurality of teeth of the patient, has the desired course.

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

For temperature stabilization of the at least one permanent magnet 9 For example, a liquid or gaseous heat carrier 12 serve in the space between the permanent magnets 9 is provided. A necessary sealing device 13 can be made of a flexible material such as rubber and as in 4A represented to the object to be examined 7 around to the permanent magnets 9 pass.

The sealing device 13 still has two hoses 14 on, over which the liquid or gaseous heat carrier 12 can be added and removed. For this purpose, a circuit may be provided, the turmessung example, according to the temperature, for example, on the wall of the permanent magnet 9 attached temperature sensor 15 is controlled. 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 one in the permanent magnets 9 integrated cooling devices. These can be channels, for example 16 for a liquid or gaseous heat carrier 12 or temperature regulating elements 17 be like her in 4B . 4C and 4D are shown.

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 in 5 shown, the holder can 2 the sensor according to the invention 1 out 1 or the magnetic field unit according to the invention 8th out 2 for stable positioning in the oral cavity 21 , on a bite rail 18 to be assembled. The Bissschien 18 may for example have the shape of an impression tray. It can also be a guide rail 19 be provided on the the holder 2 is held longitudinally displaceable, so that the sensor 1 or the magnetic field unit can be positioned at any position along the row of teeth in the mouth. By biting the patient on the bite rail 18 becomes the sensor 1 or the magnetic field unit 8th opposite the object to be examined 7 fixed.

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

In 7 is an embodiment of the inventive magnetic field unit 8th shown, for generating the main magnetic field at least one permanent magnet 20 having, after insertion of the holder 2 into the oral cavity 21 remains outside. This is the permanent magnet 20 via a correspondingly shaped bracket 22 with bracket 2 or the permanent magnet mounted on the bracket 9 connected. The 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 arranged outside the oral cavity and laterally next to the holder when the holder is positioned on the one or more molars to be measured. In 7B The structure is so changed that it is suitable for measuring the anterior teeth. For this, the hanger is straight and rather short.

So you do not need two completely separate structures to different regions within the oral cavity 21 to gauge, accordingly, differently shaped straps 22 and further permanent magnets 20 be provided, which is interchangeable with the holder 2 or on the bracket 2 attached permanent magnets 9 can be connected. It can also different shaped and / or different sized bracket 22 and permanent magnets 20 be provided to adapt the structure of the anatomical conditions of the patient P.

In 8th is a possible bracket 23 represented, which can be arranged on the head of the patient P and at the at least one for mounting 2 spaced permanent magnet 20 can be held. Also cables for connecting the magnetic field unit 8th with the control unit 11 For example, on the bracket 23 being held.

Disturbances in the magnetic resonance signal to be measured can, as usual in the context of magnetic resonance tomography, be avoided by shielding the entire measurement volume from external high-frequency fields. If possible, a shield should be designed so that it encloses the entire patient. It can also be shielded corresponding to an entire room in which the sensor according to the invention 1 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.

1

sensor

2

bracket

3

receiving coil

4

gradient coil

5

first level

6

second level

7

to examining object, for example tooth

8th

magnetic unit

9

permanent magnet

10

bridge

11

Tax- and control unit

12

liquid or gaseous heat carrier

13

sealing

14

tube

15

temperature sensor

16

channel

17

Temperature control elements

18

oral appliance

19

guide rail

20

permanent magnet

21

oral cavity

22

hanger

23

holder

P

patient

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 202007008008 U1 [0004]
• - DE 10147743 C1 [0005]

Cited non-patent literature

• - "In Vivo MRI-Based Dental Impression Using an Intraoral RF Receiver Coil" by PM Jakob et al. published in Concepts in Magnetic Resonance Part B, Magnetic Resonance Engineering, Vol. 33B (4) 244-251, 2008 [0006]

Claims (25)

Sensor ( 1 ) for use within a magnetic resonance imaging (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 generating a gradient field on a holder ( 2 ) are fastened, wherein 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. 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. 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 formed saddle-shaped and the holder is U- or V-shaped, so that the receiving coil ( 3 ) and the at least one coil of the gradient coil system ( 4 ) on three sides around the object to be examined ( 7 ) pass around. 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 ) on the bracket ( 2 ) are attached and so into the oral cavity ( 21 ) can be introduced, that the at least two receiving coils ( 3 ) and / or the at least two coils of the gradient coil system ( 4 ) on at least two different sides of the object to be examined ( 7 ), For example, one or more teeth are arranged. Sensor ( 1 ) according to one of claims 1 to 4, characterized in that the sensor ( 1 ) on a bite rail ( 18 ) is arranged. Sensor ( 1 ) according to one of claims 1 to 4, characterized in that the bite rail ( 18 ) a guide rail ( 19 ) and that the sensor ( 1 ) along the guide rail ( 19 ) is held longitudinally displaceable. Sensor ( 1 ) according to one of claims 1 to 4, characterized in that at least two sensors ( 1 ) at least partially into the oral cavity ( 21 ) and that the at least two sensors ( 1 ) can be read out either simultaneously, temporally or alternatively in terms of time. Sensor ( 1 ) according to claim 7, characterized in that the at least two sensors ( 1 ) so in the oral cavity ( 21 ) are positioned so that at the same time an object to be examined on the upper jaw and one on the lower jaw is detected. 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. Sensor ( 1 ) according to one of claims 1 to 9, characterized in that for generating a main magnetic field at least one permanent magnet ( 20 ) provided by a bracket ( 22 ), which allows a return of a magnetic flux, with the holder ( 2 ), wherein the permanent magnet ( 20 ) is spaced to the outside of the holder and outside the oral cavity ( 21 ) is arranged when the holder within the oral cavity ( 21 ) is positioned. Sensor ( 1 ) according to claim 10, characterized in that the at least one for mounting ( 2 ) spaced permanent magnet ( 20 ) removable on the bracket ( 22 ) is attached. Sensor ( 1 ) according to claim 10 or 11, characterized in that the bracket ( 22 ) detachable on the holder ( 2 ) is attached. Sensor ( 1 ) according to one of claims 10 to 12, characterized in that a holding device ( 23 ) is provided, which can be arranged on a head of the patient (P) and at which the at least one for mounting ( 2 ) spaced permanent magnet ( 20 ) is attachable. Magnetic field unit ( 8th ) 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 coil ( 3 ) for a high-frequency field, characterized in that a sensor ( 1 ) according to one of claims 1 to 13, wherein the at least one permanent magnet ( 9 ) on the bracket ( 2 ) is arranged or the holder ( 2 ) partially or completely replaced. Magnetic field unit ( 8th ) according to claim 14, 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 more teeth, he stretches. Magnetic field unit ( 8th ) according to claim 14 or 15, characterized in that a means for temperature stabilization of the at least one permanent magnet ( 9 ) is provided. Magnetic field unit ( 8th ) according to claim 16, characterized in that for controlling the means for temperature stabilization a temperature sensor ( 15 ) is arranged in the vicinity of the at least one permanent magnet. Magnetic field unit ( 8th ) according to claim 16 or 17, characterized in that the means for temperature stabilization a liquid or gaseous heat carrier ( 12 ), which is filled in an inner space between the poles of the at least one permanent magnet. Magnetic field unit ( 8th ) according to claim 18, characterized in that at least two from the oral cavity ( 21 ) lead out hoses ( 14 ) are provided, via which the liquid or gaseous heat carrier ( 12 ) is interchangeable. Magnetic field unit ( 8th ) according to one of claims 14 to 19, 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 ) having. Magnetic field unit ( 8th ) according to one of claims 14 to 20, characterized in that a means for measuring the magnetic field strength of the at least one permanent magnet ( 9 ) is provided. Magnetic field unit ( 8th ) according to claim 21, characterized in that at least one further coil is provided, with the changes of the main magnetic field can be compensated. Magnetic field unit ( 8th ) according to any one of claims 14 to 22, characterized in that the at least one for mounting ( 2 ) spaced and outside the oral cavity ( 21 ) arranged permanent magnet ( 20 ) via a bracket ( 22 ), which allows a return of a magnetic flux, with at least one of the holder ( 2 ) or the holder ( 2 ) partially or completely replacing permanent magnets ( 9 ) within the oral cavity ( 21 ), the permanent magnet remaining outside the oral cavity when the holder is positioned within the oral cavity. Magnetic field unit ( 8th ) according to claim 23, characterized in that the bracket ( 22 ) detachable to the on the bracket ( 2 ) or the holder ( 2 ) partially or completely replacing permanent magnets ( 9 ) is attached. Magnetic field unit of a magnetic resonance spectroscopy system corresponding to the magnetic field unit ( 8th ) according to any one of claims 14 to 24, but without a gradient coil system ( 4 ).