Patent Publication Number: US-2019170838-A1

Title: Coil apparatus, magnetic resonance imaging apparatus, and method of controlling the coil apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2017-0164252, filed on Dec. 1, 2017 in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     The disclosure relates to a coil apparatus, a Magnetic Resonance Imaging (MRI) apparatus, and a method of controlling the coil apparatus, and more particularly, to a technique for controlling a coil apparatus for transmitting a Radio Frequency (RF) signal onto an object and receiving an excited Magnetic Resonance (MR) signal from the object to normally operate corresponding to a direction of a magnetic field formed in a MRI apparatus. 
     2. Description of the Related Art 
     In general, a medical imaging apparatus is an apparatus for providing information about a patient as an image. Examples of a medical imaging apparatus are an X-ray apparatus, an ultrasonic diagnostic apparatus, a computer tomography (CT) scanner, a Magnetic Resonance Imaging (MRI) apparatus, etc. 
     an MRI apparatus holds an important position in the field of medical imaging diagnosis because image-taking conditions are relatively free and it can provide excellent contrast and various diagnosis information images for soft tissue. 
     MRI causes nuclear magnetic resonance (NMR) in the hydrogen atomic nuclei of the human body using a magnetic field harmless to humans as well as RF, which is non-ionizing radiation, to thus image the densities and physical or chemical characteristics of the atomic nuclei. 
     An MRI apparatus may include an RF transmitting coil for transmitting RF pulses, and an RF receiving coil for receiving electromagnetic waves, that is, Magnetic Resonance (MR) signals emitted from excited atomic nuclei. 
     Also, an MRI apparatus may receive MR signals excited in an object from a local coil apparatus including a plurality of RF receiving coils, as an external apparatus which assists the MRI apparatus and is independent from the MRI apparatus. 
     For the coils transmitting and receiving RF signals and the local coil apparatus to properly operate to receive excited MR signals from an object, the coils need to be installed in a correct direction with respect to a direction of a magnetic field formed in the MRI apparatus. 
     SUMMARY 
     Therefore, it is an aspect of the present disclosure to provide a coil apparatus for determining a direction of a magnetic field formed in a Magnetic Resonance Imaging (MRI) apparatus, and changing a phase of an RF signal that is applied to an RF coil to thereby operate the RF coil normally in the magnetic field formed in the MRI apparatus regardless of a position of the coil apparatus, a MRI apparatus, and a method of controlling the coil apparatus. 
     Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure. 
     In accordance with an aspect of the present disclosure, there is provided a coil apparatus including a radio frequency (RF) coil configured to transmit an RF transmission signal onto an object; a sensor configured to detect a static magnetic field formed in a magnetic resonance imaging (MRI) apparatus; a processor configured to determine a direction of the static magnetic field, determine an orientation direction of the coil apparatus with respect to the determined direction of the static magnetic field, and transmit a control signal for controlling a phase of an RF signal that is applied to the RF coil, based on the orientation direction of the coil apparatus; and a switch configured to change the phase of the RF signal that is applied to the RF coil, based on the control signal. 
     Based on determining that the orientation direction of the coil apparatus is opposite to a predetermined direction with respect to the determined direction of the static magnetic field, the processor may be further configured to transmit a control signal for changing the phase of the RF signal, and based on determining that the orientation direction of the coil apparatus is the predetermined direction, the processor transmits a control signal for not changing the phase of the RF signal. 
     Based on determining that the orientation direction of the coil apparatus is opposite to a predetermined direction, the processor may be further configured to transmit a control signal for changing the phase of the RF signal that is transmitted by the RF coil by 90°. 
     The processor may be further configured to determine the orientation direction of the coil apparatus based on a rotation direction of a B1 field formed in a direction that is perpendicular to the static magnetic field by the RF signal that is applied to the RF coil. 
     Based on determining that that the rotation direction of the B1 field is opposite to a predetermined rotation direction, the processor may be further configured to determine that the orientation direction of the coil apparatus is opposite to the predetermined direction. 
     The sensor may be further configured to detect a hall voltage based on the static magnetic field formed in the MRI apparatus. 
     The processor may be further configured to determine the direction of the static magnetic field based on a polarity of the detected hall voltage, and the polarity of the hall voltage may change according to a direction of a potential difference generated based on the static magnetic field. 
     The switch may be further configured to change the phase of the RF signal by 90° according to the control signal, and to apply the RF signal to the RF coil. 
     The coil apparatus may further include a DC conductor configured to detect a hall voltage based on the static magnetic field formed in the MRI apparatus. 
     The RF coil may include an RF transmitting coil configured to transmit the RF transmission signal onto the object, and an RF receiving coil configured to receive an excited Magnetic Resonance (MR) signal from the object. 
     The RF coil may include a birdcage coil. 
     In accordance with an aspect of the present disclosure, there is provided a method of controlling a coil apparatus, including detecting a static magnetic field formed in a Magnetic Resonance Imaging (MRI) apparatus; determining a direction of the static magnetic field; determining an orientation direction of the coil apparatus with respect to the determined direction of the static magnetic field; transmitting a control signal for controlling a phase of a Radio Frequency (RF) signal that is applied to an RF coil, based on the orientation direction of the coil apparatus; and changing the phase of the RF signal that is applied to the RF coil, based on the control signal. 
     The transmitting of the control signal for controlling the phase of the RF signal that is applied to the RF coil may include transmitting a control signal for changing the phase of the RF signal based on determining that the orientation direction of the coil apparatus is opposite to a predetermined direction; and transmitting a control signal for not changing the phase of the RF signal based on determining that the orientation direction of the coil apparatus is the predetermined direction. 
     In accordance with an aspect of the present disclosure, there is provided a magnetic resonance imaging (MRI) apparatus including a static magnetic field generator configured to form a static magnetic field in an inner space of the MRI apparatus; a Radio Frequency (RF) coil configured to transmit an RF transmission signal onto an object; a magnetic field sensor configured to detect the static magnetic field; a controller configured to determine a direction of the static magnetic field based on the detected static magnetic field, determine an orientation direction of the RF coil with respect to the determined direction of the static magnetic field, and transmit a control signal for controlling a phase of an RF signal that is applied to the RF coil, based on the orientation direction of the RF coil; and a switch configured to change the phase of the RF signal that is applied to the RF coil, based on the control signal. 
     The RF coil may include an RF transmitting coil configured to transmit the RF transmission signal onto the object, and an RF receiving coil configured to receive an excited Magnetic Resonance (MR) signal from the object. 
     Based on determining that an orientation direction of the RF transmitting coil is opposite to a predetermined direction with respect to the determined direction of the static magnetic field, the controller may be further configured to transmit a control signal for changing the phase of the RF signal, and based on determining that the orientation direction of the RF transmitting coil is the predetermined direction, the controller may be further configured to transmit a control signal for not changing the phase of the RF signal. 
     Based on determining that an orientation direction of the RF transmitting coil is opposite to a predetermined direction with respect to the determined direction of the static magnetic field, the controller may be further configured to transmit a control signal for changing the phase of the RF signal that is applied to the RF coil by 90°. 
     The magnetic field sensor may be further configured to detect a hall voltage based on the static magnetic field formed in the MRI apparatus. 
     The controller may be further configured to determine the direction of the static magnetic field based on a polarity of the detected hall voltage, and the polarity of the hall voltage may change according to a direction of a potential difference generated based on the static magnetic field. 
     The switch may be configured to change the phase of the RF signal by 90° according to the control signal, and applies the RF signal to the RF transmitting coil. 
     In accordance with an aspect of the present disclosure, there is provided a coil apparatus including a radio frequency (RF) coil configured to transmit an RF transmission signal onto an object; a sensor configured to detect a static magnetic field formed in a magnetic resonance imaging (MRI) apparatus; a processor configured to determine a direction of the static magnetic field, determine a relationship between an orientation direction of the coil apparatus and the determined direction of the static magnetic field, and a switch configured to change a phase of an RF signal that is applied to the RF coil, based on the determined relationship. 
     Based on the processor determining that the orientation direction of the coil apparatus is opposite to the determined direction of the static magnetic field, the switch may be further configured to change the phase of the RF signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiment of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic view of a Magnetic Resonance Imaging (MRI) apparatus according to an embodiment; 
         FIG. 2 ,  FIG. 3 , and  FIG. 4  show outer appearances of coil apparatuses according to embodiments; 
         FIG. 5  is a conceptual view showing directions of static magnetic fields formed in a MRI apparatus and a coil apparatus positioned in correspondence to the directions of the static magnetic fields, according to an embodiment; 
         FIG. 6  shows a B1 field formed in a coil apparatus in a direction that is perpendicular to a static magnetic field formed in a MRI apparatus, according to an embodiment; 
         FIG. 7  is a control block diagram of a coil apparatus according to an embodiment; 
         FIG. 8  shows a sensor according to an embodiment that detects a hall voltage based on a static magnetic field; 
         FIG. 9  is a view for describing a case of not changing a phase of a Radio Frequency (RF) signal that is applied to an RF coil, according to an embodiment; 
         FIG. 10  is a view for describing a case of changing a phase of a RF signal that is applied to an RF coil, according to an embodiment; 
         FIG. 11  and  FIG. 12  are flow charts illustrating a coil apparatus controlling method according to an embodiment; 
         FIG. 13  is a block diagram showing a control flow of a MRI apparatus according to an embodiment; and 
         FIG. 14  shows a structure of a scanner according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, like reference numerals will refer to like components throughout this specification. This specification does not describe all components of the embodiments, and general information in the technical field to which the present disclosure belongs or overlapping information between the embodiments will not be described. As used herein, the terms “portion”, “part, “module, “member” or “block” may be implemented as software or hardware, and according to embodiments, a plurality of “portions”, “parts, “modules, “members” or “blocks” may be implemented as a single component, or a single “portion”, “part, “module, “member” or “block” may include a plurality of components. 
     Also, it will be understood that when a certain part “includes” a certain component, the part does not exclude another component but can further include another component, unless the context clearly dictates otherwise. 
     Also, it will be understood that, although the terms first, second, etc. may be used herein to describe various components, these components should not be limited by these terms. These terms are only used to distinguish one component from another. 
     Also, it is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. 
     In this specification, the term “image” may mean multi-dimensional data configured with discrete image elements, for example, pixels in a 2-Dimensional (2D) image and voxels in a 3-Dimensional (3D) image. For example, an image may include a medical image of an object, acquired by an X-ray imaging apparatus, a Computed Tomography (CT) apparatus, a Magnetic Resonance Imaging (MRI) apparatus, an ultrasonic apparatus, and other medical imaging systems. 
     In this specification, the term “object” may be a human, an animal, or a part of a human or an animal. For example, the object may include an organ, such as skin, liver, heart, uterus, brain, breasts, abdomen, etc., or blood vessels. Also, the term “object” may be a phantom. The phantom means a material having a volume that is very close to the density and effective atomic number of a living thing, and may include a spherical phantom having similar properties to the human body. 
     In this specification, the term “user” may be a medical specialist including a doctor, a nurse, a medical technologist, and a radiological technologist, and may also be an engineer who repairs medical equipment. However, the user is not limited to the above-mentioned persons. 
     A Magnetic Resonance Imaging (MRI) system is a system for acquiring a Magnetic Resonance (MR) signal and reconstructing the MR signal as an image. The MR signal is a Radio Frequency (RF) signal emitted from an object. 
     In the MRI system, a main magnet forms a static magnetic field, and the MRI system aligns a magnetic dipole moment direction of specific atomic nuclei of an object located in the static magnetic field in the direction of the static magnetic field. A gradient magnetic field coil applies a gradient signal to the static magnetic field to form a gradient magnetic field, thereby inducing different resonance frequencies for different regions of the object. 
     A RF coil irradiates an RF signal corresponding to a resonance frequency of a target region from which an image will be acquired. Also, as the gradient magnetic field is formed, the RF coil receives MR signals of different resonance frequencies emitted from the object&#39;s various regions. Then, the MRI system acquires an image from the MR signals using an image reconstruction technique. 
     Hereinafter, the operation principle and embodiments will be described with reference to the accompanying drawings. 
       FIG. 1  is a schematic view of a MRI apparatus. 
     Referring to  FIG. 1 , a MRI apparatus  1  may include an operating module  10 , a controller  30 , and a scanner  50 . Herein, the controller  30  may be, as shown in  FIG. 1 , implemented independently. In an embodiment, the controller  30  may be divided to a plurality of components to be respectively included in individual components of the MRI apparatus  1 . Hereinafter, the individual components of the MRI apparatus  1  will be described in detail. 
     The scanner  50  may be implemented in a shape, for example, a bore shape, whose inside space is empty and into which an object may be inserted. In the inside space of the scanner  50 , a static magnetic field and a gradient magnetic field may be formed, and a RF signal may be irradiated. 
     The scanner  50  may include a static magnetic field generator  51 , a gradient magnetic field generator  52 , an RF coil portion  53 , a transfer table  55 , and a display  56 . The static magnetic field generator  51  may form a static magnetic field for aligning a magnetic dipole moment direction of atomic nuclei included in the object in a direction of the static magnetic field. The static magnetic field generator  51  may be implemented as a permanent magnet or a superconductive magnet using a cooling coil. 
     The gradient magnetic field generator  52  may be connected to the controller  30 . The gradient magnetic field generator  52  may apply a gradient to the static magnetic field according to a control signal received from the controller  30  to form a gradient magnetic field. The gradient magnetic field generator  52  may include X, Y, and Z coils for forming gradient magnetic fields in X-, Y-, and Z-axis directions that are orthogonal to each other, and generate a gradient signal in correspondence to a scanning location so as to induce different resonance frequencies for the object&#39;s different parts. 
     The RF coil portion  53  may be connected to the controller  30 . The RF coil portion  53  may irradiate an RF signal onto the object according to a control signal received from the controller  30 , and receive a MR signal emitted from the object. The RF coil portion  53  may transmit an RF signal of the same frequency as that of precession to the object toward atomic nuclei that perform the precession, then stop transmitting the RF signal, and receive a MR signal emitted from the object. 
     The RF coil portion  53  may be implemented as an RF transmitting coil for generating electronic waves having a radio frequency corresponding to the kind of atomic nuclei, and an RF receiving coil for receiving electronic waves emitted from the atomic nuclei, or the RF coil portion  53  may be implemented as a single RF transmitting and receiving coil having both a transmitting function and a receiving function. 
     The RF transmitting coil may be implemented as a whole-volume coil for transmitting an RF pulse to the entire of the object, and the RF receiving coil may also be implemented as a whole-volume coil for receiving an excited MR signal from the entire of the object. The whole-volume coil may also be referred to as a body coil. 
     Also, the RF receiving coil may be provided in an external apparatus, hereinafter referred to as a coil apparatus  300 , that may be independent from the scanner  50 , and mounted on the object. The coil apparatus  300  may be connected to the scanner  50 , the controller  30 , and the operating module  10  through a signal transceiver such as a cable, and transmit data about a MR signal generated from atomic nuclei to an image processor  11 . The coil apparatus  300  may be implemented as a dedicated coil, such as a head coil, a spine coil, a torso coil, and a knee coil, according to a region that is to be scanned or a region on which it is mounted. The coil apparatus  300  shown in  FIG. 1  may be implemented as a knee coil. 
     The coil apparatus  300  may function as both the RF transmitting coil and the RF receiving coil, or may function as the RF receiving coil. 
     On at least one of an inner or an outer surface of the scanner  50 , a display  56  may be provided. The display  56  may be controlled by the controller  30 , and provide a user or an object with information related to medical image scanning. 
     Also, the scanner  50  may include an object monitor for acquiring monitoring information about the object&#39;s state and transmitting the monitoring information. For example, the object monitor may acquire monitoring information about an object from a camera for photographing a motion, a location, etc. of the object, a spirometer for measuring a breath of the object, an electrocardiogram (ECG) system for measuring an electrocardiogram of the object, or a thermometer for measuring a temperature of the object, and transfer the monitoring information to the controller  30 . Accordingly, the controller  30  may control an operation of the scanner  50  using the monitoring information about the object. Hereinafter, the controller  30  will be described. 
     The controller  30  may control overall operations of the scanner  50 . 
     The controller  30  may control sequences of signals formed in the inside of the scanner  50 . The controller  30  may control the gradient magnetic field generator  52  and the RF coil portion  53  according to a pulse sequence received from the operating module  10  or a designed pulse sequence. 
     The pulse sequence may include all information required for controlling the gradient magnetic field generator  52  and the RF coil portion  53 . For example, the pulse sequence may include information about strength of a pulse signal that is applied to the gradient magnetic field generator  52 , a time for which the pulse signal is applied, a timing at which the pulse signal is applied, etc. 
     The controller  30  may control a waveform generator for generating a gradient waveform, that is, a current pulse according to a pulse sequence, and a gradient amplifier for amplifying the current pulse and transferring the amplified current pulse to the gradient magnetic field generator  52 , thereby controlling the gradient magnetic field generator  52  to form a gradient magnetic field. 
     The controller  30  may control operations of the RF coil portion  53 . For example, the controller  30  may supply an RF pulse of a resonance frequency to the RF coil portion  53  to irradiate an RF signal, and receive a MR signal received by the RF coil portion  53 . At this time, the controller  30  may control an operation of a switch, for example, a T/R switch, capable of adjusting a transmitting or receiving direction, through a control signal, to irradiate an RF signal and to receive a MR signal according to an operation mode. The switch will be described in detail, later. 
     The controller  30  may control a movement of the transfer table  55  on which the object is placed. Before scanning is performed, the controller  30  may move the transfer table  55  in advance to correspond to the object&#39;s region to be scanned. 
     The controller  30  may control the display  56 . For example, the controller  30  may control an on/off function of the display  56  or a screen to be displayed on the display  56 , through a control signal. 
     The controller  30  may control the coil apparatus  300 . For example, the controller  30  may control an operation of a switch, for example, an on/off switch, for receiving or not receiving a MR signal, through a control signal, thereby receiving or not receiving a MR signal of the coil apparatus  300  according to an operation mode. 
     The controller  30  may be implemented with a memory that stores algorithms for controlling operations of components in the MRI apparatus  1 , and data of program formats, and a processor that performs the above-described operations using the data stored in the memory. The memory and the processor may be implemented as separate chips. In an embodiment, the memory and the processor may be implemented as a single chip. 
     The operating module  10  may control overall operations of the MRI apparatus  1 . The operating module  10  may include the image processor  11 , an input device  12 , and an output device  13 . 
     The image processor  11  may store a MR signal received from the controller  30  using the memory, and apply an image reconstruction method to the MR signal using the processor to thereby create an image about the object from the MR signal. 
     For example, the image processor  11  may fill digital data in a k-space, which may also referred to as a Fourier space or a frequency space, of the memory, and when k-space data is completed, the image processor  11  may apply various image reconstruction methods, for example, Inverse Fourier Transform, to the k-space data through the processor to reconstruct the k-space data as an image. 
     Also, various signal processes which the image processor  11  applies to the MR signal may be performed in parallel. For example, the image processor  11  may perform signal-processing in parallel on a plurality of MR signals received by a multi-channel RF coil to reconstruct the MR signals as an image. Meanwhile, the image processor  11  may store the reconstructed image in the memory, or the controller  30  may store the reconstructed image in an external server through a communicator  60 , which will be described later. 
     The input device  12  may receive a control command for overall operations of the MRI apparatus  1  from a user. For example, the input device  12  may receive object information, parameter information, a scan condition, information about a pulse sequence, etc. from the user. The input device  12  may be implemented as a keyboard, a mouse, a trackball, a voice recognizer, a gesture recognizer, a touch screen, etc. 
     The output device  13  may output an image created by the image processor  11 . Also, the output device  13  may output a user interface (UI) configured to receive a control command for the MRI apparatus  1  from the user. The output device  13  may be implemented as a speaker, a printer, a display, etc., and the display may include the display  56  disposed on at least one of the outer or inner surface of the scanner  50 . An embodiment described below relates to a case in which the output device  13  is implemented as a display, however, embodiments are not limited to this. 
     The display may be a Cathode Ray Tube (CRT), a Digital Light Processing (DLP) panel, a Plasma Display Panel (PDP), a Liquid Crystal Display (LCD) panel, an Electro Luminescence (EL) panel, an Electrophoretic Display (EPD) panel, an Electrochromic Display (ECD) panel, a Light Emitting Diode (LED) display, or an Organic Light Emitting Diode (OLED) panel, although it is not limited to these. 
     Meanwhile, in  FIG. 1 , the operating module  10  and the controller  30  are shown as separated components, however, the operating module  10  and the controller  30  may be included in a single device. Also, processes that are performed by the operating module  10  and the controller  30  may be performed by another device. For example, the image processor  11  may convert a MR signal received from the controller  30  to a digital signal, or the controller  30  may itself convert a MR signal to a digital signal. 
     Also, at least one component may be added or deleted in correspondence to the performances of the components of the MRI apparatus  1  shown in  FIG. 1 . Also, it will be easily understood to one of ordinary skill in the art that the relative positions of the components may be changed in correspondence to the performance or structure of the MRI apparatus  1 . 
     Meanwhile, each of the components shown in  FIG. 1  may be a software component and/or a hardware component, such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC). 
     Hereinafter, the coil apparatus  300  according to an embodiment will be described. The coil apparatus  300  which will be described below may include an RF transmitting coil for irradiating an RF signal onto an object, and an RF receiving coil for receiving an excited MR signal from the object, wherein the RF receiving coil is assumed to receive an excited MR signal from a region of the object. 
       FIGS. 2 to 4  show outer appearances of coil apparatuses according to various embodiments. 
     As shown in  FIG. 2 , the coil apparatus  300  may be implemented as a coil apparatus  300   a , which may be a head coil apparatus for scanning an object&#39;s head and receiving an excited MR signal from the object&#39;s head. 
     In the coil apparatus  300   a , a plurality of RF transmitting coils and a plurality of RF receiving coils may be installed, and the plurality of RF transmitting coils may irradiate an RF signal onto the object&#39;s head. The plurality of RF receiving coils may receive an echo signal, that is, a MR signal generated from the object&#39;s head, and transmit data about the MR signal to the image processor  11  of the MRI apparatus  1  through a signal transceiver TR such as a cable to acquire an MR image about the object&#39;s head. 
     Also, as shown in  FIG. 3 , the coil apparatus  300  may be implemented as a coil apparatus  300   b  for scanning an object&#39;s localized region and receiving an excited MR signal from the object&#39;s localized region. Herein, the object&#39;s localized region may be one of the object&#39;s various regions, such as an arm, a leg, etc. 
     In the coil apparatus  300   b , likewise, a plurality of RF transmitting coils and a plurality of RF receiving coils may be installed, and the plurality of RF transmitting coils may irradiate an RF signal onto the object&#39;s localized region. The plurality of RF receiving coils may receive an echo signal, that is, a MR signal generated from the object&#39;s localized region to acquire a MR image about the object&#39;s localized region. The coil apparatus  300   b  may also include a hall sensor  301   b , which may correspond to hall sensor  301   c  described in greater detail below. 
     When the coil apparatus  300  is connected to the MRI apparatus  1  through a signal transceiver TR such as a cable, the RF receiving coils included in the coil apparatus  300  may be electrically connected to the scanner  50 , the controller  30 , and the image processor  11  of the MRI apparatus  1 . 
     As shown in  FIG. 4 , the coil apparatus  300  may be implemented as a coil apparatus  300   c , which may be a knee coil apparatus for scanning an object&#39;s knee and receiving an excited MR signal from the object&#39;s knee. 
     In the coil apparatus  300   c , likewise, a plurality of RF transmitting coils and a plurality of RF receiving coils may be installed, and the plurality of RF transmitting coils may irradiate an RF signal onto the object&#39;s knee. The plurality of RF receiving coils may receive an echo signal, that is, a MR signal generated from the object&#39;s knee, and transmit data about the MR signal to the image processor  11  of the MRI apparatus  1  through a signal transceiver TR such as a cable to thereby acquire a MR image about the object&#39;s knee. 
     Referring to  FIG. 4 , the coil apparatus  300   c  may be manufactured in a circular shape to scan an object&#39;s knee, and have a cavity into which the object&#39;s knee is inserted. 
     Even after the object&#39;s knee is inserted into and fixed at the coil apparatus  300   c , the direction of the coil apparatus  300   c  may change due to the object&#39;s movement. To prevent the problem, the coil apparatus  300   c  may include a hall sensor  301   c . The MRI apparatus  1  may determine whether the coil apparatus  300   c  is properly fixed or whether a direction in which the coil apparatus  300   c  is coupled is a proper direction, based on a detection value transferred from the hall sensor  301   c . The hall sensor  301   c  may be installed in the inside or outside of the coil apparatus  300   c , although not limited thereto. 
     Also, in embodiments, the coil apparatus  300  may be implemented as a torso coil apparatus for scanning an object&#39;s chest or abdomen and receiving an excited MR signal from the object&#39;s chest or abdomen. 
     The above-described coil apparatus  300  may include a birdcage coil, a surface foil, and a TEM coil, according to the structure of coils. 
     The coil apparatus  300  shown in  FIGS. 2 to 4  may include a birdcage coil. The coil apparatus  300  may be influenced by a direction of a magnetic field formed in the MRI apparatus  1 , and in the case of a birdcage coil, when an alignment of the coil apparatus  300  does not correspond to a direction of a magnetic field formed in the MRI apparatus  1 , the coil apparatus  300  may not operate properly. 
     That is, when an alignment of the coil apparatus  300  is different from a predetermined direction with respect to a direction of a magnetic field formed in the MRI apparatus  1 , the quality of a MR image acquired by the coil apparatus  300  may deteriorate. Accordingly, it may be necessary to readjust the position of the coil apparatus  300 . 
     Hereinafter, an example in which the coil apparatus  300  according to an embodiment is the coil apparatus  300   c  shown in  FIG. 4  will be described. As discussed above, coil apparatus  300   c  may be, for example, a knee coil apparatus. However, the type of the coil apparatus  300  to which an embodiment is applied is not limited. 
       FIG. 5  is a conceptual view showing directions of static magnetic fields formed in a MRI apparatus and a coil apparatus positioned in correspondence to the directions of the static magnetic fields, according to embodiments.  FIG. 6  shows a B1 field formed in a coil apparatus in a direction that is perpendicular to a static magnetic field formed in a MRI apparatus, according to an embodiment. 
     Referring to  FIG. 5 , the MRI apparatus  1  may form a static magnetic field by the static magnetic field generator  51 , as described above. The static magnetic field is also referred to as a B0 field. 
     The MRI apparatus  1  may form a static magnetic field by a main magnet, and a direction of the static magnetic field may depend on the polarity of the main magnet. As described above, the coil apparatus  300  may be influenced by a direction of a magnetic field formed in the MRI apparatus  1 , and when an alignment of the coil apparatus  300  does not correspond to a direction of a magnetic field formed in the MRI apparatus  1 , the coil apparatus  300  may not operate properly. 
     That is, a directivity of the coil apparatus  300  with respect to a static magnetic field formed by the MRI apparatus  1  may be important to the operation of the coil apparatus  300  and the MRI apparatus  1 . 
     In the MRI apparatus  1  shown in (a) of  FIG. 5 , a direction of a static magnetic field (B0 field) is an A direction, and in the MRI apparatus  1  shown in (b) and (c) of  FIG. 5 , a direction of a static magnetic field (B0 field) is a B direction. 
     In one example, a case in which the coil apparatus  300   c  operates properly when a direction of a static magnetic field formed in the MRI apparatus  1  is the A direction is assumed. In this example, when the coil apparatus  300   c  is disposed in the MRI apparatus  1  shown in (a) of  FIG. 5  in the state in which it is positioned at a fixed location in a direction shown in  FIG. 5 , the coil apparatus  300   c  may operate properly to acquire a MR signal. 
     Meanwhile, because a direction of a static magnetic field formed in the MRI apparatus  1  shown in (b) and (c) of  FIG. 5  is the B direction that is opposite to the A direction, the coil apparatus  300   c  may not operate properly when the coil apparatus  300   c  is disposed in the MRI apparatus  1  shown in (b) and (c) of  FIG. 5  in the state in which the coil apparatus  300   c  is positioned at the fixed location in the direction shown in  FIG. 5 . 
       FIG. 6  is a perspective view showing an internal structure of the coil apparatus  300   c  shown in  FIG. 5 . As discussed above, coil apparatus  300   c  may be an example of coil apparatus  300 . 
     When an RF signal is applied to the coil apparatus  300   c , a RF field may be formed in a direction that is perpendicular to a static magnetic field B0 formed in the MRI apparatus  1  in the inside of the cavity of the coil apparatus  300   c . That is, the RF field formed in the direction that is perpendicular to the static magnetic field B0 may be a B1 field, and the B1 field may rotate by the RF signal applied to the coil apparatus  300   c , as shown in  FIG. 6 . 
     The RF signal applied to the coil apparatus  300   c  may be applied to the coil apparatus  300   c  through an RF applier  140  (as shown, for example, in  FIG. 7 ) of the MRI apparatus  1 . At this time, a plurality of RF signals may be applied from the MRI apparatus  1  to the coil apparatus  300   c  with phase differences of 90°. 
     The rotation direction of the B1 field may change according to a phase of an RF signal applied to the coil apparatus  300   c . The quality of a MR image according to a MR signal may vary depending on the rotation direction of the B1 field. 
     For example, as shown in  FIG. 6 , when the direction of the static magnetic field B0 formed in the MRI apparatus  1  is the A direction, the coil apparatus  300   c  may need to be aligned in a predetermined direction with respect to the A direction of the static magnetic field B0, and when the coil apparatus  300   c  is positioned in the predetermined direction, a B1 field formed in the knee coil apparatus  300  may rotate in a direction shown in  FIG. 6  to acquire a MR image. 
     However, when the coil apparatus  300   c  is positioned in a direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B1, the B1 field formed in the coil apparatus  300   c  may rotate in a direction that is opposite to the direction shown in  FIG. 6 . Accordingly, no MR image may be acquired, or the quality of a MR image may deteriorate. 
     A direction in which the B1 field rotates with respect to the direction of the static magnetic field B0 to acquire a MR image may change by cases. 
     Accordingly, when the alignment direction of the coil apparatus  300   c  is opposite to the predetermined direction with respect to the direction of the static magnetic field B0, it may be necessary to change the position of the coil apparatus  300   c  or to change a wiring of a cable connected to the coil apparatus  300   c  and transmitting an RF signal to change the phase of an RF signal that is applied to the coil apparatus  300   c . However, changing the position of the coil apparatus  300   c  or changing the wiring of the cable may require additional time and cost. 
     In the coil apparatus according to an embodiment and the control method thereof, by determining a direction of a static magnetic field formed in the MRI apparatus  1  and changing a phase of an RF signal that is applied to the coil apparatus  300   c , the coil apparatus  300   c  may operate normally in a magnetic field formed in the MRI apparatus  1  regardless of its position. 
       FIG. 7  is a control block diagram of a coil apparatus according to an embodiment.  FIG. 8  shows a sensor according to an embodiment that detects a hall voltage based on a static magnetic field.  FIG. 9  is a view for describing a case of not changing a phase of a RF signal that is applied to an RF coil, according to an embodiment.  FIG. 10  is a view for describing a case of changing a phase of a RF signal that is applied to an RF coil, according to an embodiment. 
     Referring to  FIG. 7 , the coil apparatus  300  according to an embodiment may include a sensor  310  for detecting a hall voltage based on a static magnetic field, a processor  320  for controlling components of the coil apparatus  300 , a switch  330  for changing a phase of an RF signal that is applied to an RF coil  340 , the RF coil  340  for irradiating an RF signal onto an object and receiving an excited MR signal from the object, and a memory  350  for storing data related to operations of the coil apparatus  300 . 
     The sensor  310  may detect a hall voltage based on a static magnetic field formed in the MRI apparatus  1 , and transfer the hall voltage to the processor  320 . The sensor  310  may be, as an example of a magnetic field sensor, a Hall effect sensor that detects a magnetic field based on the Hall effect. 
     The sensor  310  may be attached on the inside or outside surface of the coil apparatus  300 . That is, the sensor  310  may be attached on an RF transmitting coil  341  or an RF receiving coil  342  of the RF coil  340 , or may be an embedded type. Hereinafter, for convenience of description, the sensor  310  is assumed to be a hall sensor attached on the RF transmitting coil  341 . 
     When the coil apparatus  300  including the RF transmitting coil  341  enters the inside of a gantry of the MRI apparatus  1 , the sensor  310  may detect a hall voltage value caused by a static magnetic field formed in the inside of the gantry, and transfer the hall voltage value to the processor  320 . Also, even when the coil apparatus  300  does not enter the inside of the gantry, the sensor  310  may detect a hall voltage caused by a static magnetic field formed in the MRI apparatus  1 . 
     The processor  320  may determine a direction of the static magnetic field formed in the MRI apparatus  1  based on the hall voltage detected by the sensor  310 . 
     The Hall effect may refer to a phenomenon in which a potential difference is generated. More specifically, the Hall effect may refer to a phenomenon in which, when a magnetic field is formed perpendicular to a direction of current flowing in a conductor, a potential difference (an electric field) is generated in the conductor. 
     In  FIG. 8 , a plurality of arrows connecting the N pole of a magnet with the S pole may form a magnetic field. The N pole and the S pole may correspond to the static magnetic field generator  51  of the MRI apparatus  1 , and the plurality of arrows connecting the N pole with the S pole may indicate a static magnetic field. 
     When the sensor  310  receives power from a power source  360 , current may flow from a negative (−) pole of the power source  360  to a positive (+) pole of the power source  360 . That is, current may flow in an x-axis direction of  FIG. 8 . At this time, a potential difference may be generated in a y-axis direction in a conductor  175  through which the current flows. 
     The sensor  310  may detect the potential difference generated in the y-axis direction, that is, a hall voltage, wherein the hall voltage may change by a magnetic field. Accordingly, the sensor  310  may detect an intensity of an external magnetic field, and also may be used to detect direct current or alternating current through the intensity of the external magnetic field. Also, the sensor  310  may be applied to detect a rotation of a rotating body. 
     A value detected by the sensor  310  provided in the RF transmitting coil  341  may be used to determine a position of the coil apparatus  300  with respect to a direction of a static magnetic field, that is, a directivity of the coil apparatus  300 . 
     The sensor  310  may be included in the coil apparatus  300  together with various other components, and the position and number of the sensor  310  are not limited. 
     More specifically, the processor  320  may determine a direction of a static magnetic field formed in the MRI apparatus  1 , based on the hall voltage detected by the sensor  310 . That is, because a polarity of a hall voltage detected by the sensor  310  changes according to a direction of a potential difference generated based on a static magnetic field, as described above, the processor  320  may determine a direction of a static magnetic field according to a direction of a potential difference causing a polarity of a hall voltage. 
     The coil apparatus  300  according to an embodiment may determine a direction of a static magnetic field based on a hall voltage detected by the sensor  310 . However, the coil apparatus  300  may determine a direction of a static magnetic field based on a hall voltage detected by a DC conductor included in the coil apparatus  300 , separately from the sensor  310 . That is, the coil apparatus  300  may include a DC conductor therein, and the DC conductor may detect a hall voltage generated by a static magnetic field, and transfer the hall voltage to the processor  320 . 
     The processor  320  may determine a direction of a static magnetic field formed in the MRI apparatus  1  based on a hall voltage detected by the sensor  310 , and determine whether the coil apparatus  300  is positioned in a predetermined direction with respect to the determined direction of the static magnetic field. 
     That is, the processor  320  may determine whether the coil apparatus  300  is positioned in a predetermined direction with respect to a rotation direction of a B1 field formed in a direction that is perpendicular to a static magnetic field B0 by a RF signal that is applied to the RF coil  340 . 
     As described above with reference to  FIGS. 5 and 6 , the rotation direction of the B1 field may change according to a phase of a RF signal that is applied to the RF coil  340 , and when the coil apparatus  300  is positioned in the predetermined direction with respect to the direction of the static magnetic field B0, a MR image acquired by the rotating B1 field may have high quality. 
     Accordingly, the processor  320  may determine whether the coil apparatus  300  is positioned in the predetermined direction with respect to the direction of the static magnetic field B0 formed in the MRI apparatus  1 , based on the rotation direction of the B1 field of the coil apparatus  300 . 
     That is, the processor  320  may determine whether a rotation direction of a B1 field is a predetermined rotation direction with respect to the direction of the static magnetic field B0, and when the rotation direction of the B1 field is opposite to the predetermined rotation direction, the processor  320  may determine that the coil apparatus  300  is positioned in a direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0. 
     Referring to  FIGS. 9 and 10 , when static magnetic fields B0 are formed in the same direction in the MRI apparatus  1 , a B1 field formed in the coil apparatus  300   c  of  FIG. 9  may rotate in a clockwise direction, and a B1 field formed in the coil apparatus  300   c  of  FIG. 10  may rotate in a counterclockwise direction. 
     The processor  320  may determine whether coil apparatus  300   c  is positioned in a predetermined direction with respect to the direction of the static magnetic field B0 among the rotation direction of the B1 field formed in the coil apparatus  300   c  of  FIG. 9  and the rotation direction of the B1 field formed in the coil apparatus  300   c  of  FIG. 10 , based on a hall voltage detected by the sensor  310 . 
     The memory  350  may store data about a proper direction of the coil apparatus  300  with respect to a direction of a static magnetic field B0 formed in the MRI apparatus  1 , and the processor  320  may determine whether the coil apparatus  300  is positioned in a predetermined direction, that is, the proper direction, based on the data stored in the memory  350 . 
     The memory  350  may store data related to operations and control of the coil apparatus  300 . 
     The memory  350  may be implemented as at least one of a non-volatile memory device, for example, a cache, Read Only Memory (ROM), Programmable ROM (PROM), Erasable Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), and flash memory, a volatile memory device, for example, Random Access Memory (RAM), or a storage medium, such as Hard Disk Drive (HDD) and Compact Disc Read Only Memory (CD-ROM), although not limited to these. The memory  350  may be implemented as a separate chip from the processor  320  described above, or the memory  350  and the processor  320  may be integrated into a single chip. 
     When the processor  320  determines that the coil apparatus  300  is positioned in a direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0, the processor  320  may transmit a control signal for changing a phase of an RF signal that is applied to the RF coil  340 . 
     That is, when the coil apparatus  300  is positioned in the direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0, the phase of the RF signal that is applied to the RF coil  340  may need to change since the rotation direction of the B1 field is opposite to the predetermined rotation direction. 
     More specifically, the processor  320  may transmit a control signal for changing the phase of the RF signal that is applied to the RF coil  340  by 90°. As shown in  FIG. 6 , the processor  320  may transmit a control signal for changing the phases of all RF signals that are applied to the RF coil  340  by 90°. That is, the processor  320  may change the phase of an RF signal having a phase of 0° to 90°, and the phase of an RF signal having a phase of 90° to 0°, among a plurality of RF signals that are applied to the RF coil  340 . 
     The switch  330  may change the phase of the RF signal that is applied to the RF coil  340 , based on the control signal transmitted from the processor  320 . The switch  330  may be one of various types of switches, such as a T/R switch. However, the switch  330  may be any type of switch as long as it can change the phase of an input signal. 
     Referring to  FIG. 9 , when the rotation direction, for example a clockwise direction, of the B1 field formed in the coil apparatus  300   c  with respect to the direction of the static magnetic field B0 matches with the predetermined rotation direction, the processor  320  may determine that the coil apparatus  300   c  is positioned in the predetermined direction with respect to the direction of the static magnetic field B0. 
     Accordingly, the processor  320  may transmit a control signal for not changing the phase of an RF signal that is applied from the RF applier  140  to the RF coil  340 , and the switch  330  may not change the phase of the RF signal that is applied to the RF coil  340 , based on the control signal from the processor  320 . 
     Referring to  FIG. 10 , when the rotation direction, for example a counterclockwise direction, of the B1 field formed in the coil apparatus  300   c  with respect to the direction of the static magnetic field B0 is opposite to the predetermined rotation direction, the processor  320  may determine that the coil apparatus  300   c  is positioned in the direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0. 
     Accordingly, the processor  320  may transmit a control signal for changing the phase of an RF signal that is applied from the RF applier  140  to the RF coil  340  by 90°, and the switch  330  may change the phase of the RF signal that is applied to the RF coil  340  by 90°, based on the control signal from the processor  320 . 
     That is, as shown in  FIG. 10 , the switch  330  may change the phase of an RF signal having a phase of 0° to 90°, and the phase of an RF signal having a phase of 90° to 0°, among a plurality of RF signals that are applied to the RF coil  340 , and the rotation direction of the B1 field formed in the coil apparatus  300   c  may change to the clockwise direction by the changed RF signals. 
     Accordingly, when the coil apparatus  300   c  is positioned in the direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0, the rotation direction of the B1 field may change by changing the phase of the RF signal through the switch  330 , so that a MR signal may be acquired. 
       FIGS. 11 and 12  are flow charts illustrating a coil apparatus controlling method according to an embodiment. 
     Referring to  FIG. 11 , the sensor  310  may detect a static magnetic field formed in the MRI apparatus  1 , and according to an embodiment, the sensor  310  may detect a hall voltage based on a static magnetic field formed in the MRI apparatus  1 , in operation  1000 . A principle by which the sensor  310  detects a hall voltage has been described above with reference to  FIG. 8 , and accordingly, overlapping descriptions thereof are omitted. 
     The processor  320  may determine a direction of the static magnetic field based on the hall voltage detected by the sensor  310 , in operation  1100 . 
     That is, because the polarity of the hall voltage detected by the sensor  310  depends on a direction of a potential difference generated based on the static magnetic field formed in the MRI apparatus  1 , the processor  320  may determine a direction of the static magnetic field based on the polarity of the hall voltage detected by the sensor  310 . 
     The processor  320  may determine whether the coil apparatus  300  is positioned in a predetermined direction with respect to the determined direction of the static magnetic field, in operation  1200 . More specifically, the processor  320  may determine whether a rotation direction of a B1 field formed in the coil apparatus  300  is a predetermined rotation direction with respect to the direction of the static magnetic field, in operation  1210 . 
     When the processor  320  determines that the rotation direction of the B1 field is opposite to the predetermined rotation direction, the processor  320  may determine that the coil apparatus  300  is positioned in a direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field, in operation  1220 . 
     Also, when the processor  320  determines that the rotation direction of the B1 field is the predetermined rotation direction, the processor  320  may determine that the coil apparatus  300  is positioned in the predetermined direction with respect to the direction of the static magnetic field, in operation  1230 . 
     When the processor  320  determines that the coil apparatus  300  is positioned in a direction that is opposite to the predetermined direction, the processor  320  may transmit a control signal for changing a phase of an RF signal that is applied to the RF coil  340  by 90°, in operation  1300 . 
     The switch  330  may change the phase of the RF signal that is applied to the RF coil  340  by 90°, based on the control signal from the processor  320 , in operation  1400 . 
     Hereinafter, technical features of the coil apparatus  300  according to an embodiment, and a case of applying the coil apparatus control method to the components included in the MRI apparatus  1  will be described. 
       FIG. 13  is a block diagram showing a control flow of a MRI apparatus according to an embodiment. 
     Referring to  FIG. 13 , the MRI apparatus  1  according to an embodiment may include the scanner  50  for forming a magnetic field and generating a resonance phenomenon for atomic nuclei, the controller  30  for controlling operations of the scanner  50 , determining a direction in which the RF coil portion  53  is positioned, and transmitting a control signal for changing a phase of an RF signal that is applied to the RF coil portion  53 , the image processor  16  for generating a MR image based on an echo signal generated from the atomic nuclei, that is, a MR signal, the RF transmitting coil  57  for irradiating an RF signal onto an object, the RF receiving coil  58  for receiving a MR signal generated by the scanner  50  of the MRI apparatus  1  and transferring the MR signal to the image processor  16 , a magnetic field sensor  59  for detecting a hall voltage based on a static magnetic field formed by the static magnetic field generator  51 , and a switch  150  for changing a phase of an RF signal that is applied to the RF coil portion  53 . 
     The scanner  50  may include the static magnetic field generator  51  for forming a static magnetic field in the inside space, and the gradient magnetic field generator  52  for generating a gradient in a static magnetic field to form a gradient magnetic field. That is, when an object is located in the inside space of the scanner  50 , a static magnetic field, a gradient magnetic field, and an RF pulse may be applied to the object. Atomic nuclei constructing the object may be excited by the applied RF pulse, and accordingly, an echo signal may be generated from the object. 
     The RF receiving coil  58  may receive an RF signal (that is, a MR signal) emitted from the excited atomic nuclei. More specifically, the RF receiving coil  58  may transmit an RF signal of the same frequency as that of precession to the object toward atomic nuclei that perform the precession, then stop transmitting the RF signal to the object, and receive a MR signal emitted from the object. 
     Generally, the RF receiving coil  58  may be a type fixed on a gantry or a type removably attached on a gantry. When the RF receiving coil  58  is a type removably attached on a gantry, the RF receiving coil  58  may include an RF coil for a part of the object, such as a head coil, a chest RF coil, a leg RF coil, a neck RF coil, a shoulder RF coil, a wrist RF coil, and an ankle RF coil, as described above with reference to  FIGS. 2 to 4 . 
     Meanwhile, the RF coil portion  53  according to the present disclosure may include the magnetic field sensor  59 . The magnetic field sensor  59  may be a sensor that detects a magnetic field applied by the scanner  50 . 
     More specifically, for example, the magnetic field sensor  59  may detect a hall voltage based on a static magnetic field formed by the static magnetic field generator  51 , and transfer the hall voltage to the controller  30 . The magnetic field sensor  59  may be, for example, a hall sensor that detects a magnetic field based on the Hall effect. 
     The magnetic field sensor  59  may be attached on the inner or outer surface of the RF coil portion  53 . That is, the magnetic field sensor  59  may be attached on the RF transmitting coil  57  or the RF receiving coil  58  of the RF coil portion  53 , or may be an embedded type. Hereinafter, for convenience of description, the magnetic field sensor  59  is assumed to be a hall sensor attached on the RF transmitting coil  57 . 
     The controller  30  may include a static magnetic field controller  31  for controlling an intensity and direction of a static magnetic field formed by the static magnetic field generator  51 , a pulse sequence controller  32  for designing a pulse sequence and controlling the gradient magnetic field generator  52  and the RF transmitting coil  57  according to the pulse sequence, and a transfer controller  33  for controlling the transfer table  55  for transferring the object. 
     The transfer controller  33  may control the transfer table  55  on which the object lies, according to an input signal that a user inputs through a control console. 
     Meanwhile, the controller  30  may be a processor for controlling overall operations of the MRI apparatus  1 . In the current embodiment, the configuration of the controller  30  is divided to the static magnetic field controller  31 , the pulse sequence controller  32 , and the transfer controller  33 , for convenience of description, however, the static magnetic field controller  31 , the pulse sequence controller  32 , and the transfer controller  33  may be integrated into a single System On Chip (SOC) in hardware. 
     Also, the controller  30  may be implemented with a memory that stores algorithms for controlling operations of components in the MRI apparatus  1 , and data for programs embodying the algorithms, and a processor that performs the above-described operations using the data stored in the memory. The memory and the processor may be implemented as separate chips or a single chip. 
     The MRI apparatus  1  may include a gradient applier  130  for applying a gradient signal to the gradient magnetic field generator  52 , and an RF applier  140  for applying an RF signal to the RF transmitting coil  57 . The gradient applier  130  and the RF applier  140  may adjust a gradient magnetic field formed in the inside space of the scanner  50  and an RF applied to atomic nuclei through the control of the pulse sequence controller  32 . 
     The image processor  16  may include a data collector  161  for receiving data for a spin echo signal, that is, a MR signal generated from atomic nuclei, and processing the data to create a MR image, a data storage device  162  for storing the data received by the data collector  161 , and a data processor  163  for processing the stored data to create a MR image. 
     Also, the MRI apparatus  1  may include a user controller for receiving a control command for overall operations of the MRI apparatus  1  from a user. Particularly, the MRI apparatus  1  may receive a command for a scan sequence from a user, and generate a pulse sequence according to the command. 
     The user controller may include a control console for enabling the user to control the system, a display  112  for displaying a control state and displaying an image created by the image processor  16  to enable the user to diagnose an object&#39;s health state, and a sound output device  113  for transferring information to the user. 
     The display  112  may display an image created by the image processor  16 , and display an output screen related to a control of the MRI apparatus  1 . 
     The coil apparatus  300  and the control method described above with reference to  FIGS. 1 to 12  may be applied in the same manner to the MRI apparatus  1 . 
       FIG. 14  shows a structure of a scanner according to an embodiment. 
     Referring to  FIG. 14 , the MRI apparatus  1  may include the static magnetic field generator  51  for forming a static magnetic field in the inside space of the scanner  50 , and the RF coil portion  53  for irradiating an RF signal onto an object. 
     The RF coil portion  53  shown in  FIG. 14  may correspond to the internal structure of the coil apparatus  300  described above with reference to  FIG. 6 . 
     That is, when an RF signal is applied to the RF coil portion  53 , a B1 field may be formed in the cavity of the RF coil portion  53  in a direction that is perpendicular to a static magnetic field B0 formed in the MRI apparatus  1 . Also, by the RF signal applied to the RF coil portion  53 , the B1 field may rotate, as described above with reference to  FIG. 6 . 
     The RF signal applied to the RF coil portion  53  may be applied to the RF transmitting coil  57  of the RF coil portion  53  through the RF applier  140 . At this time, a plurality of RF signals that are applied from the MRI apparatus  1  to the RF coil portion  53  may be applied to the RF transmitting coil  57  with phase differences of 90°. 
     A rotation direction of the B1 field may change according to a phase of an RF signal that is applied to the RF coil portion  53 . The quality of a MR image according to a MR signal may vary depending on the rotation direction of the B1 field. 
     The MRI apparatus  1  according to an embodiment may determine a direction of a static magnetic field formed in the MRI apparatus  1  and change a phase of an RF signal that is applied to the RF coil portion  53  to thereby operate the RF coil portion  53  normally in a magnetic field formed in the MRI apparatus  1  regardless of a position of the RF coil portion  53 . 
     More specifically, the magnetic field sensor  59  according to an embodiment may detect a hall voltage based on a static magnetic field formed in the MRI apparatus  1 , and transfer the hall voltage to the controller  30 . 
     The controller  30  may determine a direction of the static magnetic field formed in the MRI apparatus  1  based on the hall voltage detected by the magnetic field sensor  59 . That is, because the polarity of the hall voltage detected by the magnetic field sensor  59  depends on a direction of a potential difference generated based on the static magnetic field formed in the MRI apparatus  1 , the controller  30  may determine a direction of the static magnetic field based on the polarity of the hall voltage detected by the magnetic field sensor  59 . This operation has been described above with reference to  FIG. 8 , and accordingly, overlapping descriptions thereof are omitted. 
     The controller  30  may determine whether the RF coil portion  53  is positioned in a predetermined direction with respect to the determined direction of the static magnetic field. That is, the controller  30  may determine whether the RF coil portion  53  is positioned in a predetermined direction, based on a rotation direction of a B1 field formed in a direction that is perpendicular to the static magnetic field B by an RF signal applied to the RF coil portion  53 . 
     As described above with reference to  FIGS. 5 and 6 , the rotation direction of the B1 field may change according to a phase of an RF signal that is applied to the RF coil portion  53 , and when the RF coil portion  53  is positioned in the predetermined direction with respect to the direction of the static magnetic field B0, a MR image acquired by the rotating B1 field may have high quality. 
     Accordingly, the controller  30  may determine whether the rotation direction of the B1 field is the predetermined rotation direction with respect to the direction of the static magnetic field B0, and when the controller  30  determines that the rotation direction of the B1 field is a direction that is opposite to the predetermined rotation direction, the controller  30  may determine that the RF coil portion  53  is positioned in a direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0. 
     Also, when the controller  30  determines that the rotation direction of the B1 field is the predetermined rotation direction, the controller  30  may determine that the RF coil portion  53  is positioned in the predetermined direction with respect to the direction of the static magnetic field B0. 
     When the controller  30  determines that the RF coil portion  53  is positioned in the direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0, the controller  30  may transmit a control signal for changing a phase of an RF signal that is applied to the RF coil portion  53 . 
     That is, when the RF coil portion  53  is positioned in the direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0, the phase of the RF signal that is applied to the RF coil portion  53  may need to change since the rotation direction of the B1 field is opposite to the predetermined rotation direction. 
     More specifically, the controller  30  may transmit a control signal for changing the phase of the RF signal that is applied to the RF coil portion  53  by 90°. As shown in  FIG. 10 , the controller  30  may transmit a control signal for changing the phases of all RF signals that are applied to the RF coil portion  53  by 90°. That is, the controller  30  may change the phase of an RF signal having a phase of 0° to 90°, and the phase of an RF signal having a phase of 90° to 0°, among a plurality of RF signals that are applied to the RF coil portion  53 . 
     The switch  150  may change the phase of the RF signal that is applied to the RF coil portion  53  by 90°, based on the control signal from the controller  30 . That is, the switch  150  may change the phase of an RF signal having a phase of 0° to 90°, and the phase of an RF signal having a phase of 90° to 0°, among a plurality of RF signals that are applied to the RF coil portion  53 , so that the rotation direction of the B1 field formed in the RF coil portion  53  may change to the opposite direction by the changed RF signals. 
     Accordingly, when the RF coil portion  53  is positioned in the direction that is opposite to the predetermined direction with respect to the direction of the static magnetic field B0, the rotation direction of the B1 field may change by changing the phase of an RF signal through the switch  150 , so that a MR signal of high quality may be acquired. 
     Therefore, by determining a direction of a static magnetic field formed in the MRI apparatus and changing a phase of an RF signal that is applied to the RF coil, the RF coil may operate normally in a magnetic field formed in the MRI apparatus regardless of its position. Accordingly, it may be possible to reduce time and cost required for adjusting a wrong position of the RF coil, and to prevent an unnecessary waste of scan time. 
     Meanwhile, the disclosed embodiments may be implemented in the form of a recording medium that stores instructions executable by a computer. The instructions may be stored in the form of program codes, and when executed by a processor, the instructions may create a program module to perform operations of the disclosed embodiments. The recording medium may be implemented as a computer-readable recording medium. 
     The computer-readable recording medium may include all kinds of recording media storing instructions that can be interpreted by a computer. For example, the computer-readable recording medium may be ROM, RAM, a magnetic tape, a magnetic disc, a flash memory, an optical data storage device, etc. 
     Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.