Patent Publication Number: US-2013237805-A1

Title: Magnetic resonance apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of German application No. 10 2011 082 407.3 filed Sep. 9, 2011, which is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The present application relates to a magnetic resonance apparatus having a magnet unit, which includes a main magnet, a gradient coil and a high frequency coil unit, a cylindrical imaging region for imaging a patient, wherein the magnet unit cylindrically surrounds the imaging region, and a housing unit surrounding the magnet unit having a rigid, fixedly installed housing shell unit, which is arranged between the imaging region and the magnet unit. 
     BACKGROUND OF INVENTION 
     During operation, magnetic resonance apparatuses have high noise levels which can cause discomfort for a patient located in an imaging region of the magnetic resonance apparatus for the purposes of an examination. Large vibration amplitudes develop on a surface of a high frequency coil unit, which surrounds the imaging region for the patient, said vibration amplitudes resulting in significant noise radiation for the patient. Acoustic resonances can also develop within the imaging region, said acoustic resonances possibly representing an additional noise load. Conventional magnetic resonance apparatuses comprise a rigid, fixedly installed housing shell unit with a high noise radiation. 
     SUMMARY OF INVENTION 
     The object underlying the present application is to provide a magnetic resonance apparatus, with which an effective noise protection is achieved for a patient in an imaging region. The object is achieved by the features of the independent claims. Embodiments are described in the dependent claims. 
     The application is based on a magnetic resonance apparatus having a magnet unit, which includes a main magnet, a gradient coil and a high frequency coil unit, a cylindrical imaging region for imaging a patient, wherein the magnet unit cylindrically surrounds the imaging region, and a housing unit surrounding the magnet unit with a rigid, fixedly installed housing shell unit which is arranged between the magnet unit and the imaging region. 
     It is proposed that the housing unit comprises at least one noise protection unit, which is arranged at least partially surrounding the magnet unit so as to be removable within the imaging region. A shielding of the high frequency coil unit and of the gradient coil in respect of a noise radiation can be achieved. Furthermore, a noise reduction within the imaging region can be achieved for the patient during a magnetic resonance examination, wherein the noise reduction up to 10 dB can be achieved. The noise protection unit comprises a dampening and/or decoupling of sound waves in a frequency range, in which a noise radiation of the magnetic resonance apparatus takes place. In addition, depending on the requirements for a magnetic resonance examination the noise protection unit can also be arranged on the magnetic resonance apparatus within the imaging region, and/or fastened thereto, and the use of the noise protection unit is thus dispensed with for instance for a magnetic resonance examination in the case of a claustrophobic patient. In this context, a noise protection unit which is arranged so as to be removable is understood to mean a noise protection unit, which, depending on the requirements for a magnetic resonance examination, can be arranged so as to protect the patient from a large noise load within the imaging region on the magnetic resonance apparatus, such as on the rigid, fixedly installed housing shell unit and/or on a patient couch of the magnetic resonance apparatus, by an operator, such as for instance clinical staff attending to the magnetic resonance apparatus, wherein a mode of operation of the noise protection unit and/or the magnetic resonance apparatus is retained during the removal or disassembly of the noise protection unit. The rigid, fixedly installed housing shell unit may be formed for instance by a supporting construction of the high frequency coil unit, such as for instance made of a fiber-reinforced plastic. Alternatively, the rigid, fixedly installed housing shell unit may also be formed by a housing shell unit embodied separately from the high frequency coil unit. 
     Furthermore, it is proposed that the noise protection unit comprises at least one absorption unit, as a result of which an absorption of air-borne sound waves can be achieved. A dampening of air-borne sound waves, such as in a frequency range of up to 1500 Hz, such as up to 1000 Hz, takes place by the absorption unit, wherein the air-borne sound waves propagate along a surface of the rigid, fixedly installed housing shell unit. In this context, an absorption unit is understood to mean a sound-absorbing absorption unit, which is configured to convert sound energy from sound waves into an oscillation energy of inaudible oscillation waves, and accordingly to reduce or prevent a reflection of audible sound waves onto a boundary surface. The sound waves, such as the air-borne sound waves, herewith excite individual particles, such as for instance foam particles, of the absorption unit to oscillate, wherein a generated oscillation energy is converted into thermal energy within the absorption unit. Oscillation energy is taken from the sound waves, such as the air-borne sound waves and the air-borne sound waves are dampened. A layer thickness of the absorption unit may amount here from approximately 5 mm to a few cm. The absorption unit may be formed from all materials appearing meaningful to the person skilled in the art, such as for instance a melamine material and/or a porous material with open pores. 
     The noise protection unit comprises at least one spring-mass unit, as a result of which a radiation of sound waves from the rigid, fixedly installed housing shell unit into the imaging region can be reduced. A reduction in the noise radiation on account of the spring mass unit takes place here with an increased frequency of the sound waves. In this context, a spring-mass unit is understood to mean a unit of the noise protection unit, which has at least one elastic spring element and at least one heavy mass element, so that on account of a high mass inertia and an absorption of oscillation energy from sound waves, a dampening and/or decoupling of sound waves is achieved. The heavy mass element comprises a surface density of at least 3 kg/m 2  or at least of 5 kg/m 2  auf. The at least one elastic spring element and the at least one heavy mass element may herewith be embodied in one piece. 
     In a development of the application, it is proposed that the noise protection unit has at least one facing shell unit. A radiation of sound waves into the imaging region can be reduced by a reflection of sound waves taking place at least partially on the facing shell unit. The facing shell may simultaneously be the unit of the housing unit which is visible to the patient and fulfill such sterility requirements which are needed for a clinical measuring operation. The facing unit may also be integrated within the spring mass unit as a heavy mass element. 
     It is further proposed that the noise protection unit is arranged at least partially at a distance from the rigid, fixedly installed housing shell unit, as a result of which an effective absorption of air-borne sound can be achieved on account of reducing sound pressure. In addition, the distance between the noise protection unit and the rigid, fixedly installed housing shell unit achieves a softness of an acoustic spring in the spring mass unit and in such a way a dampening property is achieved in respect of a radiation of sound waves into the imaging region. 
     A compact housing unit can be achieved if the noise protection unit is arranged in an arched manner on the rigid, fixedly installed housing shell unit. The noise protection unit which can additionally be introduced into the imaging region can be minimized in a spatial context so that a large region is available to the patient within the imaging region. The arched noise protection unit may herewith cover a region in respect of a noise radiation of the rigid, fixedly installed housing shell unit, which is arranged within a region which is enclosed by a couch surface of the patient couch and the rigid housing shell unit. 
     In an alternative embodiment of the application, the noise protection unit may also comprise a cylindrical shape, as a result of which a region of the imaging region, which is not occupied by the patient, can be filled by the noise protection unit. A cross-section of the imaging region can herewith be filled by the noise protection unit without in the process negatively affecting the patient in a spatial context and the patient thus being protected from a high noise load. 
     Furthermore, it is proposed that the housing unit comprises at least one fastening unit for fastening the noise protection unit to the rigid, fixedly installed housing shell unit, as a result of which a direct fastening can be achieved within the imaging region on the housing shell unit. The fastening unit is provided for a detachable fastening of the noise protection unit, so that the noise protection unit can be disassembled from the housing shell unit in a structurally simple manner at any time without negatively affecting its mode of operation. The fastening unit may for instance include clamping elements, such as flexible clamping elements, which provide for a secure hold of the noise protection unit on the housing shell unit. 
     It is also proposed that the housing unit comprises at least one fastening unit for fastening the noise protection unit on a patient couch of the magnetic resonance apparatus, as a result of which an unused sub region of the imaging region can be occupied with the noise protection unit when positioning the patient within the imaging region. The fastening unit may be arranged here for instance on a front side, which is firstly inserted into the imaging region, of the patient couch. Alternatively, the noise protection unit can also be positioned manually by an operator directly within the imaging region. 
     The noise protection unit is embodied to be compatible in terms of magnetic resonance. An embodiment which is compatible in terms of magnetic resonance is understood here to mean that the noise protection unit is formed from a non-magnetizable material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and details of the application result from the embodiments described below as well as with the aid of the drawings, in which: 
         FIG. 1  shows a disclosed magnetic resonance apparatus in a schematic representation, 
         FIG. 2  shows a sub region of the magnetic resonance apparatus having a first embodiment of a noise protection unit and 
         FIG. 3  shows a sub region of the magnetic resonance apparatus having a second embodiment of a noise protection unit. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows a schematic representation of a disclosed magnetic resonance apparatus  10 . The magnetic resonance apparatus  10  includes a magnet unit  11  with a main magnet  12  to generate a strong and constant main magnetic field  13 . In addition, the magnetic resonance apparatus  10  comprises a cylindrical imaging region  14  for imaging a patient  15 , wherein the imaging region  14  is surrounded by the magnet unit  11  in a circumferential direction. The patient  15  can be introduced into the imaging region  14  by a patient couch  16  of the magnetic resonance apparatus  10 . The patient couch  16  is to this end arranged so as to be moveable within the magnetic resonance apparatus  10 . Furthermore, the magnetic resonance apparatus  10  comprises a housing unit  30  surrounding the magnet unit  11 . 
     The magnet unit  11  further comprises a gradient coil  17  for generating magnetic field gradients, which is used for spatial encoding during an imaging process. The gradient coil  17  is controlled by a gradient control unit  18 . Furthermore, the magnet unit  11  comprises a cylindrical high frequency coil unit  19  and a high frequency control unit  20  for exciting a polarization, which develops in the main magnetic field  13  generated by the main magnet  12 . The high frequency coil unit  19  is controlled by the high frequency control unit  20  and radiates high frequency magnetic resonance sequences into an examination room, which is formed by the imaging region  14 . The magnetization is herewith deflected from its position of equilibrium. Furthermore, magnetic resonance signals are received by the high frequency coil unit  19 . 
     The magnetic resonance apparatus  10  comprises a control unit  21  formed from a computing unit in order to control the main magnet  12 , the gradient control unit  18  and to control the high frequency control unit  20 . The computing unit controls the magnetic resonance apparatus  10  centrally, such as for instance implementing a predetermined imaging gradient echo sequence. Control information such as for instance imaging parameters, and reconstructed magnetic resonance images can be displayed on a display unit  22 , for instance on at least one monitor, of the magnetic resonance apparatus  10  for an operator. The magnetic resonance apparatus  10  also comprises an input unit  23 , by which information and/or parameters during a measuring process can be input by an operator. 
     The magnetic resonance apparatus  10  shown can naturally include further components, which magnetic resonance apparatuses  10  usually comprise. A general functionality of a magnetic resonance apparatus  10  is also known to the person skilled in the art, so that a detailed description of the general components is omitted. 
       FIG. 2  shows the housing unit  30  in closer detail. The housing unit  30  comprises a rigid, fixedly installed housing shell unit  31 , which, in the present embodiment is formed of a support unit, which is formed for instance of a glass fiber-reinforced plastic, of the high frequency coil unit  19 . The rigid, fixedly-installed housing shell unit  31  is in this way formed of a side of the support unit facing the imaging region  14  and is provided for instance with a lacquer. 
     Moreover, the housing unit  30  comprises a noise protection unit  32 , which, in the present embodiment, comprises an arched cross-sectional surface and is arranged on a side  33  of the housing shell unit  31  facing the imaging region  14 . The noise protection unit  32  is herewith arranged hereupon at a distance  34  from the housing shell unit  31 . A maximum distance  34  of the noise protection unit  32  from the housing shell unit  31  may amount here to 5 cm, however, the maximum distance  34  is arranged between 2 cm and 3 cm. To this end, the housing unit  30  comprises spacing elements (not shown), which are arranged between the housing shell unit  31  and the noise protection unit  32 . Alternatively, it is also possible for the noise protection unit  32  to be arranged directly, such as without a spacing, on the side  33  of the housing shell unit  31  facing the imaging region  14 . 
     In the present embodiment, the noise protection unit  32  includes three different noise reduction units. A first noise reduction unit is formed by an absorption unit  35 , which is formed from a sound-absorbing material, such as for instance a melamine material and/or a porous material. A layer thickness  36  of the absorption unit  35  can amount here to be between 5 mm and a maximum of 5 cm, however a maximum of 3 cm. The absorption unit  35  is arranged on a side of the noise protection unit  32  facing the housing shell unit  31 , so that a dampening of air-borne sound waves, which, during operation of the magnetic resonance apparatus  10 , propagate along the housing shell unit  31 , takes place. 
     A second noise reduction unit of the noise protection unit  32  is formed by a spring-mass unit  37 , which includes an elastic spring element as an acoustic spring and a heavy mass element as an acoustic mass. The spring-mass unit  37  is arranged on a side of the absorption unit  35  facing the imaging region  14 . During operation of the magnetic resonance apparatus  10 , sound waves radiated by the housing shell unit  31  are dampened by the spring-mass unit  37 . 
     A third noise reduction unit of the noise protection unit  32  is formed by a facing shell unit  38 , which is arranged on a side of the spring-mass unit  37  facing the imaging region  14 . The facing shell unit  38  can be formed rigidly in this way with a high mass and/or high density, so that a reflection of sound waves, which are radiated from the housing shell unit  31  in the direction of the imaging region  14 , is achieved. Moreover, the facing shell unit  38  can also be formed by a flexible layer, such as for instance a soft mass layer, such as an artificial leather layer and/or a washable material layer, and be included in the spring-mass unit  37 . A surface density of the facing shell unit  38  may amount to at least 3 kg/m 2  or to at least 5 kg/m 2 . 
     In an alternative embodiment of the noise protection unit  32 , the absorption unit  35  can be embodied as an acoustic spring of the spring-mass unit  37 . Moreover, it is also conceivable that the noise protection unit  32  comprises only one or two of the three noise reduction units for an effective noise reduction and at least one of the noise reduction units is dispensed with in an embodiment of the noise protection unit  32 . 
     The noise protection unit  32  is also embodied to be compatible in terms of magnetic resonance. 
     The housing unit  30  comprises a fastening unit  39  for arranging the noise protection unit  32  within the imaging region  14 . The fastening unit  39  is herewith provided for a detachable fastening of the noise protection unit  32 , so that the noise protection unit  32  can be arranged and/or fastened by an operator at any time within the imaging region  14  on the housing shell unit  31  or can be removed from the housing shell unit  31 . The housing shell unit  31  can be fastened here without the need for tools. 
     For fastening purposes, the fastening unit  39  in the present embodiment comprises clamping elements (not shown in more detail) which are arranged on the noise reduction unit  32  and/or on the housing shell unit  31 . The noise reduction unit  32  can be arranged and/or fastened to the housing shell unit  31  by the clamping elements in a rapid fashion and if necessary, such as with a claustrophic patient for instance, can be disassembled from the housing shell unit  31  and removed from the imaging region  14  quickly, without herewith negatively affecting the mode of operation of the noise reduction unit  32 . 
     Alternatively, further fastening units which appear meaningful to the person skilled in the art, which enable a detachable fastening of the noise protection unit  32  to the housing shell unit  31 , are conceivable at any time, such as for instance a pulling tool with a cable and/or clamping of the noise reduction unit  32  with the housing shell unit  31 , wherein a clamping force between the noise reduction unit  32  and the housing shell unit  31  can be produced on account of a clamped form of the noise reduction unit  32 . 
     A cladding of the housing shell unit  31  with the noise protection unit  32  brings about a shielding of the high frequency coil unit  19  and of the gradient coil  17  in respect of noise radiation in the direction of the imaging region  14  during operation of the magnetic resonance apparatus. In this way a noise reduction of up to 10 dB for the patient is achieved within the imaging region  14 . 
       FIG. 3  shows an alternative embodiment of the housing unit  50 . Components, features and functions which remain the same are basically numbered with the same reference characters. The description below is restricted to the differences from the embodiment in  FIGS. 1 and 2 , wherein with respect to the components, features and functions which remain the same, reference is made to the description of the embodiment in  FIGS. 1 and 2 . 
       FIG. 3  shows an alternative embodiment of the housing unit  50 . The housing unit  50  comprises a housing shell unit  31 , which is embodied in a similar manner to the embodiment in  FIG. 2 . Moreover, the housing unit  50  comprises a noise protection unit  51 , which is embodied cylindrically in the present embodiment, so that a cross-section of the imaging region  14  of the magnetic resonance apparatus  10  is filled by the noise protection unit  14  within the sub region of the imaging region  14  which is not required by the patient  15 . The noise protection unit  51  is however arranged at a distance  52  of approx. 2 cm to 3 cm from the housing shell unit  31  so that a free air flow channel  53  is provided. Moreover, the noise protection unit  51  for a patient monitoring can be formed at least partially from optically transparent materials. 
     The noise protection unit  51  herewith likewise includes an absorption unit  54 , a spring-mass unit  55  and a facing shell unit  56 . The facing shell unit  56  is herewith arranged on a side of the noise protection unit  51  facing the patient  15 . 
     To fasten the noise protection unit  51 , the housing unit  50  comprises a fastening unit  57 , which enables the noise protection unit  51  to be fastened on a patient couch  16  of the magnetic resonance apparatus  10 . The noise protection unit  51  is herewith fastened on an end region of the patient couch  16  in a removable manner, wherein the end region is firstly inserted into the imaging region  14  upon insertion of the patient couch  16  into the imaging region  14 . The fastening unit  57  to this end comprises fastening elements (not shown), which may include conventional, detachable fastening elements, such as for instance latching elements and/or clamping elements. It is also conceivable for the noise protection unit  51  to be positioned and arranged within the imaging region  14  by a transport unit in order to transport the patient couch  16 . 
     Alternatively, it is to this end also conceivable for the noise protection unit  51  to be fastened on the housing shell unit  31  within the imaging region  14 , such as for instance by a clamping unit. It is moreover also conceivable for the same to be easily inserted into the imaging region  14  by an operator of the magnetic resonance apparatus  10  for an arrangement of the noise protection unit  51  within the imaging region  14 .