Patent Publication Number: US-2015084635-A1

Title: Magnetic resonance imaging apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2013-197851, filed on Sep. 25, 2013 and No. 2014-162767, filed on Aug. 8, 2014; the entire contents of which are incorporated herein by reference. 
     FIELD  
     Embodiments described herein relate to a magnetic resonance imaging apparatus. 
     BACKGROUND  
     A magnetic resonance imaging (MRI) apparatus is an apparatus configured to image an inside of a subject by utilizing a magnetic resonance phenomenon. This MRI apparatus includes various devices required for imaging the inside of the subject, such as an external magnet configured to generate a static magnetic field in an imaging area, a gradient magnetic field coil configured to apply a gradient magnetic field to the subject placed in the static magnetic field, and a high frequency coil configured to apply a high frequency pulse to the subject. A superconducting magnet using a superconducting coil is used for the external magnet, and a strong static magnetic field can be generated. 
     In the MRI, a coil (an antenna) configured to receive a nuclear magnetic resonance phenomenon is disposed on a surface of the subject. The coil for reception to be disposed on the surface of the subject corresponds to an imaging site, and the coil corresponding to the imaging site is needed. Further, the coil for reception to be disposed on the surface of the subject applies oppressive feeling to the subject. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a configuration conceptual diagram of a magnetic resonance imaging apparatus of an embodiment; 
         FIG. 2  is a conceptual diagram of a receiving antenna of the embodiment; 
         FIG. 3  is a conceptual diagram of a magnetic resonance imaging apparatus of the embodiment; 
         FIG. 4  is a conceptual diagram of a magnetic resonance imaging apparatus of the embodiment; 
         FIG. 5  is a conceptual diagram of a magnetic resonance imaging apparatus of an embodiment; 
         FIG. 6  is a conceptual diagram of a magnetic resonance imaging apparatus of the embodiment; 
         FIG. 7  is a configuration conceptual diagram of a magnetic resonance imaging apparatus of an embodiment; 
         FIG. 8  is a conceptual diagram of a magnetic resonance imaging apparatus of the embodiment; and 
         FIG. 9  is a conceptual diagram of a magnetic resonance imaging apparatus of an embodiment. 
     
    
    
     DETAILED DESCRIPTION  
     A magnetic resonance imaging apparatus of an embodiment includes a housing, a static magnetic field source having a superconducting coil or a permanent magnet inside the housing, and a superconducting array antenna inside the housing. 
     First Embodiment  
     A magnetic resonance imaging apparatus of a first embodiment has a housing and a superconducting antenna inside the housing as a receiving antenna.  FIG. 1  illustrates a configuration conceptual diagram of the magnetic resonance imaging apparatus of the embodiment. A magnetic resonance imaging apparatus  100  in  FIG. 1  has a static magnetic field source  101 , a gradient magnetic field coil  102 , a transmission coil  103 , a receiving antenna  104 , a cooling device  106 , a receiving unit  107 , a transmission unit  108 , a gradient magnetic field power source  109 , and a controller  110 . A top plate  105  is disposed in an imaging range. It should be noted that a subject of the magnetic resonance imaging apparatus includes animals including human beings, chemical substances, or the like. 
     The static magnetic field source  101 , the gradient magnetic field coil  102 , the transmission coil  103 , and the receiving antenna  104  are provided in the housing of the magnetic resonance imaging apparatus. 
     The magnetic resonance imaging of the embodiment includes nuclear magnetic resonance (NMR), the MRI, and electron spin resonance (ESR). For example, the MRI includes special imaging, such as magnetic resonance angiography (MRA) or magnetic resonance spectroscopy (MRS). 
     The static magnetic field source  101  is an external magnet configured to generate a static magnetic field in an imaging area, in which a subject is placed. The external magnet is a magnet of a horizontal magnetic field type. For example, the static magnetic field source  101  has a vacuum chamber, a refrigerant chamber, and a superconducting coil. A power source (not illustrated) for causing a current to flow to the superconducting coil is connected with the static magnetic field source  101 . The superconducting coil is cooled by a cooling refrigerant (freezing mixture) including liquid helium, liquid nitrogen, or the like. Here, in order to keep an object to be cooled at a low temperature, the object to be cooled is thermally insulated by vacuum insulation using the vacuum chamber. The vacuum chamber is formed in a substantially cylindrical shape, and an inside of a cylindrical wall is kept in a vacuum state. A space formed inside this vacuum chamber becomes the imaging area, in which the subject is placed. A refrigerant chamber (first refrigerant chamber) is formed in a substantially cylindrical shape and is accommodated within the cylindrical wall of the vacuum chamber. It should be noted that, as a general example, the refrigerant chamber contains liquid helium within the cylindrical wall as the refrigerant to keep an inside of the chamber in a sufficiently low temperature state. The superconducting coil is disposed within the cylindrical wall of the refrigerant chamber and is immersed in the liquid helium. This superconducting coil generates the static magnetic field in the imaging area provided inside the vacuum chamber. It is preferable that at least a part of the vacuum chamber be covered with a refrigerant chamber (second refrigerant chamber) containing a cooling refrigerant including liquid helium, liquid nitrogen, or the like and that heat be relieved from the outside. Moreover, a correction magnet for making a magnetic field uniform may be further provided. The cooling device  106  is, for example, a device configured to liquefy a vaporized cooling refrigerant, and it is preferable that the device  106  be provided in the magnetic resonance imaging apparatus. It is preferable that, even during a time when the magnetic resonance imaging apparatus is not operated, this cooling device  106  be continuously operated regularly in such a manner that the static magnetic field source  101  is always held in a superconducting state. 
     The gradient magnetic field coil  102  is formed in a substantially cylindrical shape and disposed inside the static magnetic field source  101  within the housing. The gradient magnetic field coil  102  controls an imaging direction. The gradient magnetic field coil  102  in an x axis direction, a y axis direction, and a z axis direction is disposed. This gradient magnetic field coil  102  generates a gradient magnetic field in the x axis direction, the y axis direction, and the z axis direction set in the imaging area according to the corkscrew rule by a current supplied from the gradient magnetic field power source  109 . A pulse current is repeatedly supplied to this gradient magnetic field coil  102  during execution of the imaging. 
     The transmission coil  103  is disposed within the housing. Specifically, the transmission coil  103  is disposed inside the gradient magnetic field coil  102  within the housing. This transmission coil  103  irradiates the subject placed in the imaging area with a high frequency pulse transmitted from the transmission unit  108 . The transmission coil  103  generates a rotating magnetic field so as to be rotated within a surface vertical to the static magnetic field. In a case where a nuclear magnetic resonance phenomenon is utilized, a nucleus can be inverted from a ground state to an excited state or from the excited state to the ground state by the high frequency pulse. A frequency of the high frequency pulse is a precession frequency of the nucleus. Similarly, in a case where electron spin resonance is utilized, a precession frequency of an electron is utilized. The subject may be irradiated with the high frequency pulse by using an antenna having a configuration similar to that of the receiving antenna  104 . 
     The receiving antenna  104  is disposed within the housing. Specifically, the receiving antenna  104  is disposed inside the gradient magnetic field coil  102  inside the static magnetic field source  101 . The receiving antenna  104  receives an electromagnetic wave generated from the subject by the pulse irradiated from the transmission coil  103 . A received signal is transmitted to the receiving unit  107  through optical wiring or conductive wiring. In the embodiment, instead of using an external receiving antenna optimized for an imaging site of the subject, the receiving antenna  104  in a form built in the housing is used. The receiving antenna  104  may have one row or plural rows as in  FIG. 1 . The plural rows of receiving antennas  104  are preferable from a viewpoint of shortening an imaging time and obtaining an imaged image with high resolution. It is also preferable that efficiency of image processing be improved by increasing the number of antennas. With an increase in the number of antennas, directivity of the antenna can be high. Due to the high directivity, a direction of a radio wave received by one antenna is narrower, and reception sensitivity of the antenna is improved. Since the number of antennas is increased, it is preferable that the signal received by the antenna be sent to the controller  110  or an external device through the optical wiring. Due to the high sensitivity of the receiving antenna, it is preferable that a slice thickness be thinned and that the slice can be arranged in many rows. 
     It should be noted that, other than the above-described method, there is a method in which the receiving antenna  104  can have a function of the transmission coil. It is possible to have a configuration in which an antenna is shared during transmission and reception and which has an antenna, a transmission/reception circuit, and a transmission/reception switching unit. Regarding the receiving antenna  104 , a bandpass filter or a low noise signal amplifier configured to process the signal received by the receiving antenna  104  may be disposed within the housing, such as within the receiving antenna  104 . Since a superconducting filter can be used for the bandpass filter, the bandpass filter can be turned into a superconducting state by cooling the antenna or the superconducting magnet. The low noise signal amplifier can amplify a signal with lower noise under a low temperature environment. In this case, the transmission coil  103  is omitted. 
     Regarding the external receiving antenna, an antenna corresponding to the imaging site of the subject to efficiently receive a weak electromagnetic wave from the subject is disposed in close contact with the subject or in a vicinity of a surface of the subject. When this antenna is disposed within the housing of the magnetic resonance imaging apparatus, a distance between the receiving antenna and the subject is too far, and the measurable electromagnetic wave cannot be received. 
     In the embodiment, it is preferable that the superconducting antenna be used for the receiving antenna  104 . It is more preferable that a superconducting array antenna obtained by laminating the superconducting antennas be used as the receiving antenna  104 . Even when an antenna pattern of the superconducting array antenna is minute, loss thereof is small and the antenna can be micronized. Since the loss is small, gain of the antenna is high. Further, the gain and directivity of the antenna is improved by the lamination. A shape of the antenna pattern of the superconducting antenna includes a monopole type, a dipole type, a crank type, a spiral type, such as a rectangle, a circle, and an ellipse, an L-type, an inverted-F type, and the like. Further, an antenna constituted with a CPW type having ground and a signal line on the same surface and with a length of integral multiple of a quarter wavelength, or a slot type antenna where a slot is provided in a part of ground can be included. In order to correspond to various imaging methods, it is more preferable that the receiving antenna  104  be a phased array antenna capable of performing beam scanning. 
     It is preferable that the superconducting array antenna of the embodiment have an array antenna obtained by laminating the antenna formed of a superconducting material and a planar antenna having a ground pattern, on a dielectric substrate having low loss in a shortwave band to a millimeter wave band. 
       FIG. 2  illustrates a conceptual diagram of the receiving antenna  104  of the embodiment. The receiving antenna  104  has a first superconducting antenna layer  201 , a first substrate  202 , a second superconducting antenna layer  203 , a second substrate  204 , a third superconducting antenna layer  205 , a third substrate  206 , a superconducting ground layer  207 , an infrared reflective film  208 , a cold head  209 , and a cooling medium  210 . 
     As illustrated in the conceptual diagram of  FIG. 2 , the array antenna (the receiving antenna  104 ) of the embodiment is formed by laminating the first superconducting antenna layer  201 , the first substrate  202 , the second superconducting antenna layer  203 , the second substrate  204 , the third superconducting antenna layer  205 , the third substrate  206 , and the superconducting ground layer  207  in this order. A feeding path (not illustrated) is provided on the antenna layer. The feeding path is connected with the receiving unit  107  (not illustrated in  FIG. 2 ). Further, each superconducting antenna layer connects the feeding path and the ground layer. The superconducting antenna layer has an antenna pattern, in which an oxide superconductor thin film containing one or more elements, such as Y, Ba, Cu, La, Ta, Bi, Sr, Ca, and Pb, has been processed into a desired shape, the feeding path, and a ground pattern. 
     The infrared reflective film  208  is a film configured to prevent infrared, which heats the antenna, from being incident on the antenna. The infrared reflective film  208  is provided on a surface of the antenna (the first superconducting antenna layer  201 ) and prevents incidence of the infrared, which heats the superconducting antenna layer. The infrared reflective film  208  is, for example, a multilayer film formed of a metal oxide. The infrared reflective film  208  can be omitted in case of no infrared source or the like. 
     The cold head  209  is a member having high thermal conductivity and configured to hold and cool the array antenna. The cold head  209  is cooled by thermally connecting with the cooling medium  210 . A cooling temperature is different depending on a superconducting oxide thin film of the array antenna and is, for example, 77 K or lower. 
     The cooling medium  210  is a member configured to cool the cold head  209 , which cools the array antenna. The cooling medium  210  may be cooled by a cooler for an array antenna, or may be made common with a cooling member, such as the cooling refrigerant used for cooling the superconducting coil of the static magnetic field source  101  and including liquid helium or liquid nitrogen. 
     Next,  FIG. 3  illustrates a conceptual cross-sectional diagram of the magnetic resonance imaging apparatus of the embodiment having the receiving antenna  104  inside the housing. The magnetic resonance imaging apparatus in the conceptual diagram of  FIG. 3  has, within a housing  111 , the static magnetic field source  101 , the receiving antenna  104 , the cold head  209 , and the receiving unit  107 . The top plate  105 , on which the subject is placed, is disposed in the imaging area during the imaging. Illustration of the gradient magnetic field coil  102 , the transmission coil  103 , and the like is omitted. The receiving antenna  104  is disposed inside the static magnetic field source  101 . An output (not illustrated) of each receiving antenna  104  and the receiver  107  are connected through the wiring, and the signal received by the receiving antenna  104  is transmitted to the receiver  107  through the wiring. In  FIG. 3 , the  20  receiving antennas  104  are formed. The receiver  107  and the like may be provided inside the housing  111 . By using superconductivity, the receiving antenna  104  is microminiaturized, and many antennas can be disposed within the housing  111 . Since the number of receiving antennas  104  which can be disposed in the housing  111  is changed by a receiving frequency, the number of antennas illustrated is one example. In case of the magnetic resonance imaging apparatus, in which a diameter of a hollow opening part (subject region) of the housing  111  is 70 cm and external magnetic field intensity is 1.5 T, for example, the 50 receiving antennas  104  are disposed inside the superconducting coil, and tens of rows thereof can be further disposed. Since imaging can be performed by using the great many receiving antennas  104 , it is possible to perform imaging with high resolution, which cannot be realized by the external receiving antenna. In the conventional receiving coil, it is difficult to reduce a size thereof due to the large loss, and it is necessary to bring nearly in contact with the subject to increase the sensitivity. Accordingly, the antennas cannot be placed within the housing inside the superconducting coil due to the limitation on the size and characteristics. Alternatively, if they are placed, the number of antennas is limited to about ten. In the embodiment, the receiving antenna  104  itself is small, and sensitivity of the plurality of small superconducting antennas is improved by arraying. Accordingly, characteristics can be obtained even when the antennas are separated from the subject, and the tens of antennas can be disposed inside the superconducting coil because of the small size. Therefore, compared with the conventional receiving coil, measurement can be performed with high sensitivity. 
     A center part C of the housing  111  is a region X of a central part of the housing. It is preferable that the receiving antenna  104  be disposed in such a manner that directivity is oriented in a center part C 1  (e.g., (x 1 , y 1 , z 1 )). In a case where plural rows of the receiving antennas  104  are provided, it is preferable that the receiving antenna  104  of each row be disposed in such a manner that the directivity is oriented in a center part Ca (e.g., (x 1 , y 1 , z a )) deviated only in a z-axis direction. The receiving antennas  104  are oriented in a direction of the center part C. The receiving antennas  104  are disposed on a (virtual) circumference so as to draw a circumference on an inner circumferential side of the static magnetic field source  101 . It is preferable that the receiving antennas  104  are disposed at equal distances from the center part from a viewpoint of reducing characteristic differences among the respective antennas. It is preferable that a plurality of the receiving antennas  104  be disposed at equal intervals. It is preferable that the receiving antennas  104  be disposed so as to be surrounded by the static magnetic field source  101 . 
     Next,  FIG. 4  illustrates a conceptual cross-sectional diagram of a magnetic resonance imaging apparatus of the embodiment having the receiving antenna  104  inside the housing. The superconducting coil in the static magnetic field source  101  and the superconducting antenna  104  are cooled by a common cooling refrigerant. A difference between the magnetic resonance imaging apparatuses in the conceptual diagrams of  FIGS. 3 and 4  is that the cold head  209  connects a low temperature area of the static magnetic field source  101  and the receiving antenna  104 . Since it is necessary to cool the superconducting coil of the static magnetic field source  101  to be in a superconducting state, the superconducting antenna  104  can be also cooled. For the apparatus in this form, it is not necessary to separately provide a cooler for cooling the receiving antenna  104 , and the apparatus can be configured efficiently. 
     A superconducting material is used for the receiving antenna  104 , which is cooled until the superconducting material is turned into a superconducting state. It is preferable that a circuit formed of the superconducting material and configured to process a signal received by the receiving antenna  104  be provided within the receiving antenna  104 . A superconducting filter is used as the circuit formed of the superconducting material. An electromagnetic wave received by the superconducting antenna includes noise other than a target frequency, and it is preferable that this be removed before amplifying a signal. The superconducting filter functions as a bandpass filter with low loss. 
     Besides the circuit formed of the superconducting material, it is preferable that the receiving antenna  104  have a circuit device preferably operated at a low temperature. A low noise amplifier configured to amplify a received signal is used as this circuit device. The signal can be amplified under a lower temperature environment where the receiving antenna  104  is operated and under a condition of no or very little thermal fluctuation. Besides the low noise amplifier, an amplitude limiter of the received signal for protecting the circuit may be provided within the receiving antenna  104 . 
     Further, a phased array antenna may be used for the receiving antenna  104  so as to arbitrarily change a direction where the receiving antenna  104  is oriented. In this case, a phase shifter is provided within or outside the receiving antenna  104 . 
     The top plate  105  is supported by a bed (not illustrated). Further, the subject is placed on the top plate  105  during the imaging, and the top plate  105  is moved into the imaging area with the subject. 
     The receiving unit  107  detects a magnetic resonance signal received by the receiving antenna  104 , and generates raw data by performing, as needed, any one or more of analog processing, digitization processing (conversion of an analog signal to a digital signal), and digital processing to the detected magnetic resonance signal. Then, the receiving unit  107  transmits the generated raw data to the controller  110 . 
     The transmission unit  108  transmits a high frequency pulse to the transmission coil  103  based on an instruction from the controller  110 . This transmission unit  108  has a high frequency power source for generating a high frequency pulse to be transmitted to the transmission coil  103 . 
     The gradient magnetic field power source  109  supplies a current to the gradient magnetic field coil  102  based on an instruction from the controller  110 . 
     The controller  110  images the subject by respectively driving the gradient magnetic field power source  109 , the transmission unit  108 , and the receiving unit  107 . Then, when the raw data is transmitted from the receiving unit  107  as a result of the imaging, the controller  110  calculates the raw data and outputs the data as image data or transmits the data to an external device or internal device for processing or storing data. 
     When the subject is examined, it is possible that a partial scan is first performed to position the subject, position information is obtained by analyzing the data, and then the data is acquired by optimizing imaging conditions. Alternatively, the imaging may be performed without performing pre-scan. The magnetic resonance imaging apparatus can be used as a diagnostic apparatus during surgery. Since it is not necessary to attach coils to a patient at this time, the apparatus can be used as an apparatus for performing a prompt and hygienic diagnosis in the same way as CT (computed tomography). 
     Second Embodiment  
       FIG. 5  illustrates a conceptual cross-sectional diagram of a magnetic resonance imaging apparatus of an embodiment having a receiving antenna  104  inside a housing. The magnetic resonance imaging apparatus in the conceptual diagram of  FIG. 5  has, within a housing  111 , a static magnetic field source  101 , a receiving antenna  104 , a receiving unit  107 , a cold head  209 , and a second refrigerant chamber  300 . A top plate  105 , on which a subject is placed, is disposed in an imaging area during imaging. Other than the second refrigerant chamber  300 , a configuration of the magnetic resonance imaging apparatus in  FIG. 5  is in common with that of the magnetic resonance imaging apparatus in  FIG. 3 . In the second embodiment, description of things in common with the aforementioned embodiment is omitted. 
     In the second embodiment, cooling of the receiving antenna  104  in the magnetic resonance imaging apparatus in an embodied form will be described. A superconducting coil of the static magnetic field source  101  is cooled by a cooling refrigerant, such as liquid helium. In order to prevent an influence of heat on the liquid helium, it is preferable that at least a part or a whole of a vacuum chamber having a first refrigerant chamber containing the liquid helium be covered with the second refrigerant chamber  300  containing a cooling refrigerant (freezing mixture) including liquid helium or liquid nitrogen. In the present embodiment, the second refrigerant chamber  300  containing this cooling refrigerant is effectively utilized thermally and spatially. At least a superconducting array antenna of the receiving antenna  104  is cooled by this cooling refrigerant (mainly liquid nitrogen from the viewpoint of cost) and is cooled to a superconducting state. Therefore, it is preferable that a superconducting member used for the receiving antenna  104  be a so-called high temperature superconductor. Since the receiving antenna  104  is disposed within the refrigerant chamber for liquid nitrogen also used in the magnetic resonance imaging apparatus in the form requiring a conventional external receiving antenna, there is no or little reduction in the imaging area (an opening diameter). 
       FIG. 6  illustrates a magnetic resonance imaging apparatus in a form where the second refrigerant chamber  300  is provided in the magnetic resonance imaging apparatus of the first embodiment illustrated in  FIG. 4 . The second refrigerant chamber  300  and the cold head  209  are connected with each other. In the present embodiment as well, effects similar to those of the above-described embodiment are obtained by the second refrigerant chamber  300 . 
     Third Embodiment  
     A third embodiment relates to a magnetic resonance imaging apparatus of a vertical magnetic field type.  FIG. 7  illustrates a configuration conceptual diagram of the magnetic resonance imaging apparatus of the third embodiment. The magnetic resonance imaging apparatus in  FIG. 7  has a static magnetic field source  101 , a gradient magnetic field coil  102 , a transmission coil  103 , a receiving antenna  104 , a cooling device  106 , a receiving unit  107 , a transmission unit  108 , a gradient magnetic field power source  109 , and a controller  110  for applying a vertical magnetic field to a subject. A top plate  105  is disposed in an imaging range. In the third embodiment, description of things in common with the aforementioned embodiments is omitted. 
     The static magnetic field source  101  may be a magnet for a superconducting coil or a permanent magnet. In a case where the static magnetic field source  101  is the permanent magnet, the cooling device  106  liquefies vaporized cooling refrigerant configured to cool the receiving antenna  104 . In this case, it is preferable that the cooling refrigerant include liquid nitrogen or liquid helium. 
       FIG. 8  is a conceptual cross-sectional diagram of a magnetic resonance imaging apparatus of the third embodiment as viewed in a different direction. In  FIG. 8 , illustration of several components, such as the cooling device  106 , is omitted. The magnetic resonance imaging apparatus in  FIG. 8  has the static magnetic field source  101 , the gradient magnetic field coil  102 , the transmission coil  103 , the receiving antenna  104 , the receiving unit  107 , the housing  111 , and the cold head  209 . The top plate  105 , on which the subject is placed, is disposed in an imaging area during imaging. 
     In the magnetic resonance imaging apparatus in  FIG. 8 , the receiving antennas  104  cooled within a refrigerant chamber  300 , which contains the cooling refrigerant including liquid helium or liquid nitrogen, are disposed between the static magnetic field sources  101 . The receiving antennas  104  are disposed in an area of supports within the housing  111 . The magnetic resonance imaging apparatus of the vertical magnetic field is called an open type, and it is preferable that an area other than the supports be opened. 
     In the third embodiment, because of the vertical magnetic field type, the static magnetic field source  101  or the like is separated into upper and lower parts of the imaging area. A configuration including the static magnetic field source  101  separated into the upper and lower parts are supported by the supports of the housing  111 . The receiving antennas  104  may be a form disposed at one support. It is preferable that the receiving antennas  104  of the embodiment be disposed within the support so as to include directivity in the imaging area direction. A form of two supports is illustrated. However, the number of supports and a ratio of the support, at which the receiving antenna  104  is disposed, can be changed according to a design of the magnetic resonance imaging apparatus. In  FIG. 8 , the four receiving antennas  104  are disposed in one row. However, since the number of receiving antennas  104  which can be disposed within the housing  111  is changed by a receiving frequency, the number of antennas illustrated is one example. As another example, ten receiving antennas  104  in one row arranged in ten rows, i.e., 100 receiving antennas  104  can be disposed at one support. 
     In this way, as the receiving antenna  104  is disposed within the support needed in the magnetic resonance imaging apparatus of the vertical magnetic field type, the receiving antenna  104  can be disposed within the housing without narrowing or hardly narrowing the opening area or the imaging area. The present embodiment can be employed by the magnetic resonance imaging apparatus using an eternal magnet. 
     Fourth Embodiment  
     A magnetic resonance imaging apparatus of a fourth embodiment is a form where the cooling by liquid nitrogen of the second embodiment is employed by the magnetic resonance imaging apparatus of the third embodiment.  FIG. 9  illustrates a conceptual diagram of the magnetic resonance imaging apparatus of the fourth embodiment. The magnetic resonance imaging apparatus in  FIG. 9  has a static magnetic field source  101 , a gradient magnetic field coil  102 , a transmission coil  103 , a receiving antenna  104 , a receiving unit  107 , a housing  111 , a cold head  209 , and a second refrigerant chamber  300  containing a cooling refrigerant, such as liquid nitrogen. In the present embodiment, a magnet using a superconducting coil is used for the static magnetic field source  101 . At least a part or a whole of a vacuum container accommodating a first refrigerant container accommodating the superconducting coil is covered with the second refrigerant chamber  300  accommodating a superconducting antenna. In the fourth embodiment, description of things in common with the aforementioned embodiments is omitted. Effects of the present configuration are as described above. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.