Abstract:
A magnetic resonance imaging apparatus is provided. The apparatus includes an imaging unit applying a gradient magnetic field and a radio frequency pulse to an inspection body in an magnetostatic field and generating a magnetic resonance signal, a bed having a top panel for placing the inspection body thereon and sliding the top panel in a longitudinal direction, a radio frequency coil for detecting the magnetic resonance signal, a display unit displaying a positioning image, a determining unit determining an ROI (a region of interest) on the basis of designation on the positioning image, a comparing unit comparing the ROI with an available FOV (a field of view) defined by the magnetostatic field, a calculating unit calculating a plurality of FOVs including the ROI when the comparing unit determines that the size of the ROI is greater than that of the available FOV, and a control unit controlling the imaging unit, the bed, and the radio frequency coil so as to perform an imaging operation on each of the FOVs.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-317284, filed Oct. 31, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a magnetic resonance imaging apparatus in which an image related to a range of interest designated by an operator is obtained.  
         [0004]     2. Description of the Related Art  
         [0005]     In a known magnetic resonance imaging (MRI) apparatus, positioning of a field of view (FOV) is performed by determining a range of interest (ROI) which is designated on a reference image for positioning. Since the FOV available in a single imaging operation is limited in the MRI apparatus, it is only possible to designate the ROI in a range that does not exceed the available FOV.  
         [0006]     Recently, a method in which a plurality of images obtained through a plurality times of imaging operations are connected to each other so as to obtain a wider range of image has been contemplated. In this case, the operator has to determine the FOV by designating the ROI at every imaging operation.  
         [0007]     Examples of an FOV setting method are disclosed in JP-A-1-166750, JP-A-2003-250775, JP-A-2004-97826, JP-A-2000-308627, JP-UM-A-6-66629, and JP-T-2004-527301, for example.  
         [0008]     However, in the known MRI apparatus described above, when the operator desires to image a sectional region exceeding the FOV available in a single imaging operation, the operator has to suitably designate the ROIs in correspondence with the desired sectional region. As the number of the imaging operation increases, the accompanying workload increases accordingly, thereby complicating the work.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     It is therefore desirable to reduce burdens imposed on the operator when the operator desires to obtain an image related to a region exceeding the available FOV.  
         [0010]     According to an aspect of the invention, there is provided a magnetic resonance imaging apparatus which includes an imaging unit applying a gradient magnetic field and a radio frequency pulse to an inspection body in an magnetostatic field and generating a magnetic resonance signal; a bed having a top panel for placing the inspection body thereon and sliding the top panel in a longitudinal direction; a radio frequency coil for detecting the magnetic resonance signal; a display unit displaying a positioning image; a determining unit determining an ROI (a region of interest) on the basis of designation on the positioning image; a comparing unit comparing the ROI with an available FOV (a field of view) defined by the magnetostatic field; a calculating unit calculating a plurality of FOVs including the ROI when the comparing unit determines that the size of the ROI is greater than that of the available FOV; and a control unit controlling the imaging unit, the bed, and the radio frequency coil so as to perform an imaging operation on each of the FOVs.  
         [0011]     According to another aspect of the invention, there is provided a magnetic resonance imaging apparatus which includes an imaging unit applying a gradient magnetic field and a radio frequency pulse to an inspection body in an magnetostatic field and generating a magnetic resonance signal; a bed having a top panel for placing the inspection body thereon and sliding the top panel in a longitudinal direction; a radio frequency coil for detecting the magnetic resonance signal; a display unit displaying a positioning image; a determining unit determining a plurality of ROIs (a region of interest), the size of each of which is smaller than that of an available FOV (a field of view) defined by the magnetostatic field, on the basis of designation on the positioning image; a moving unit moving at least one of the ROIs on the basis of the designation on the positioning image and moving an ROI other than the moved ROI to be in a predetermined state with respect to the moved ROI; a fixing unit fixing the plurality of ROIs; and a control unit controlling the imaging unit, the bed, and the radio frequency coil so as to perform an imaging operation on each of the ROIs fixed by the fixing unit.  
         [0012]     According to a further aspect of the invention, there is provided an imaging method in a magnetic resonance imaging apparatus having an imaging unit applying a gradient magnetic field and a radio frequency pulse to an inspection body in an magnetostatic field and generating a magnetic resonance signal, a bed having a top panel for placing the inspection body thereon and sliding the top panel in a longitudinal direction, a radio frequency coil for detecting the magnetic resonance signal, and a display unit displaying a positioning image, the method including: determining an ROI (a region of interest) on the basis of designation of the positioning image; comparing the ROI with an available FOV (a field of view) defined by the magnetostatic field; calculating a plurality of FOVs including the ROI when it is determined by the comparing unit that the size of the ROI is greater than that of the available FOV; and controlling the imaging unit, the bed, and the radio frequency coil so as to perform an imaging operation on each of the FOVs.  
         [0013]     According to a still further aspect of the invention, there is provided an imaging method in a magnetic resonance imaging apparatus having an imaging unit applying a gradient magnetic field and a radio frequency pulse to an inspection body in an magnetostatic field and generating a magnetic resonance signal, a bed having a top panel for placing the inspection body thereon and sliding the top panel in a longitudinal direction, a radio frequency coil for detecting the magnetic resonance signal, and a display unit displaying a positioning image, the method including: determining a plurality of ROIs (a region of interest), the size of each of which is smaller than that of an available FOV (a field of view) defined by the magnetostatic field, on the basis of designation on the positioning image; moving at least one of the ROIs on the basis of the designation on the positioning image and moving an ROI other than the moved ROI to be in a predetermined state with respect to the moved ROI; fixing the plurality of ROIs; and controlling the imaging unit, the bed, and the radio frequency coil so as to perform an imaging operation on each of the fixed ROIs.  
         [0014]     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0015]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0016]      FIG. 1  is a block diagram showing a magnetic resonance imaging (MRI) apparatus in accordance with embodiments of the invention.  
         [0017]      FIG. 2  is a flowchart showing operations performed by a calculation unit shown in  FIG. 1  in accordance with a first embodiment of the invention.  
         [0018]      FIG. 3  is a diagram showing an example of a reference image.  
         [0019]      FIG. 4  is a diagram showing an example of displaying a range of interest (ROI) in accordance with the first embodiment.  
         [0020]      FIG. 5  is a diagram showing an example of setting a field of view (FOV) in accordance with the first embodiment.  
         [0021]      FIG. 6  is a flowchart showing operations performed by a calculation unit shown in  FIG. 1  in accordance with a second embodiment of the invention.  
         [0022]      FIG. 7  is a diagram showing an example of a setting state of the ROI in accordance with the second embodiment.  
         [0023]      FIG. 8  is a diagram showing an example of changing the ROI in accordance with the second embodiment.  
         [0024]      FIG. 9  is a diagram showing another example of changing the ROI in accordance with the second embodiment.  
         [0025]      FIG. 10  is a diagram showing an example of a setting state of the ROI in accordance with a third embodiment of the invention.  
         [0026]      FIG. 11  is a diagram showing an example of changing the ROI in accordance with the third embodiment.  
         [0027]      FIG. 12  is a diagram showing another example of changing the ROI in accordance with the third embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     Hereinafter, the embodiments of the invention will be described with reference to drawings.  
         [0029]      FIG. 1  is a block diagram showing a magnetic resonance imaging (MRI) apparatus in accordance with embodiments of the invention. The MRI apparatus functionally includes a magnet unit for generating a magnetostatic field, a gradient magnetic field generating unit for generating a gradient magnetic field for providing positional information to the magnetostatic field, a transceiver unit for magnetic excitation and a nuclear magnetic resonance (NMR) signal reception, and a control and calculating unit for system control and data processing.  
         [0030]     Specifically, as illustrated in  FIG. 1 , the magnet unit includes a normal conduction type magnet  1 , for example, and a magnetostatic field electric current source  2  supplying a current to the magnet  1 . The magnet unit generates a magnetostatic field H 0  in a z-axis direction of an opening unit through which an inspection body P is inserted.  
         [0031]     The gradient magnetic field generating unit includes a gradient magnetic field electric current source which is constituted by a triplet of gradient magnetic field coils  4  mounted on the magnet  1  in x-, y-, z-directions, a driving circuit  5  supplying a current to the gradient magnetic field coils  4 , and a gradient magnetic field control unit  6 . The gradient magnetic field control unit  6  activates the drive circuit  5  in accordance with a pulse sequence supplied from a main control unit  7 . Then, a linear magnetic field is superimposed on the magnetostatic field H 0  in order to provide positional information for imaging, thereby forming the gradient magnetic field.  
         [0032]     The transceiver unit includes a transmitting coil  8   a  and a receiving coil  8   b  disposed in the opening unit of the magnet  1  so as to face the inspection body P, and a transmitter  9  and a receiver  10  connected respectively to the transmitting coil  8   a  and the receiving coil  8   b . The transmitter  9  generates a radio frequency pulse for NMR excitation on the basis of instructions from the control unit  7 . The receiver  10  detects and amplifies the NMR signal obtained by the receiving coil  8   b  and sends the NMR signal to a memory unit  11  on the basis of the instructions from the control unit  7 .  
         [0033]     The control and calculating unit includes the control unit  7 , the memory unit  11 , a calculating unit  12 , a display unit  13 , and an input unit  14 . The memory unit  11  memorizes the NMR signal. The calculating unit  12  provides an operational instruction to the control unit  7 . Moreover, the calculating unit  12  subjects the NMR signal memorized in the memory unit  11  to a calculation processing including a Fourier transformation, for example, so as to generate image data. The display unit  13  displays an image represented by the image data generated by the calculating unit  12  or displays various kinds of information that is to be notified to the operator under the control of the calculating unit  12 . The input unit  14  includes a keyboard or a mouse, for example, and the operator inputs various designation using the input unit  14 .  
         [0034]     The MRI apparatus according to the embodiments of the invention has the above-mentioned basic construction.  
       First Embodiment  
       [0035]     In a first embodiment, the calculating unit  12  further includes several functions described later. A first function is a function of determining a range of interest (ROI) designated by manipulations in the input unit  14 . The first function allows designation of the ROI regardless of a field of view (FOV) available in a single imaging operation. A second function is a function of determining a point of interest by designating the point of interest in the ROI by manipulations in the input unit  14 . A third function is a function of setting a plurality of FOVs so as to include the whole ROI when the size of the designated ROI is greater than that of the available FOV. In the third function, when the point of interest is designated, the plurality of FOVs is set so that the point of interest is positioned in the middle of a single FOV. A fourth function is a function of instructing the control unit  7  to perform an imaging operation on each of the FOVs, and connecting a plurality of images obtained through a plurality times of imaging operations, thereby generating image data related to the ROI.  
         [0036]     Hereinafter, operations of the MRI apparatus according to the first embodiment having the above-mentioned construction will be described.  
         [0037]      FIG. 2  is a flowchart showing operations performed by a calculation unit  12  in accordance with a first embodiment.  
         [0038]     In step Sa 1 , the calculating unit  12  displays a reference image prepared in advance as illustrated in  FIG. 3 , for example, on the display unit  13 . The reference image is reorganized on the basis of the NMR signal collected in a high speed from a wide range while changing the position of a bed, for example.  
         [0039]     The operator designates a region requiring a high-definition imaging operation as the ROI by observing the reference image and manipulating the input unit  14 . In step Sa 2 , the calculating unit  12  determines the designated ROI on the basis of output information from the input unit  14 . In this case, the calculating unit  12  does not put restrictions on the size of the ROI. The calculating unit  12  superimposes the determined ROI on the reference image as illustrated by numeral  21  in  FIG. 4 , for example.  
         [0040]     In steps Sa 3  to Sa 5 , the calculating unit  12  waits for the occurrence of any one of events: a change of the ROI, a designation of the point of interest, and a start of the imaging.  
         [0041]     The operator changes the once-designated ROI by manipulating the input unit  14  in accordance with necessity. When an operation of changing the ROI is performed, the calculating unit  12  returns to step Sa 2  from step Sa 3  and determines the changed ROI.  
         [0042]     The operator may designate the point of interest in the ROI by manipulating the input unit  14 . When an operation of designating the point of interest is performed, the calculating unit  12  proceeds from step Sa 4  to step Sa 6 . In step Sa 6 , the calculating unit  12  determines the designated point of interest. Thereafter, the calculating unit  12  returns to a waiting state from steps Sa 3  to Sa 5 .  
         [0043]     After finishing the designation of the ROI, the operator instructs to start an imaging operation by manipulating the input unit  14 . In response to the imaging start instruction, the calculating unit  12  proceeds from step Sa 5  to step Sa 7 . In step Sa 7 , the calculating unit  12  determines whether the size of the ROI determined at that moment is greater than that of the available FOV. When the size of the ROI is greater than that of the available FOV, the calculating unit  12  proceeds from step Sa 7  to step Sa 8 . In step Sa 8 , the calculating unit  12  sets a plurality of FOVs so as to include the whole ROI. If the calculating unit  12  has determined the designated point of interest in step Sa 6 , the calculating unit  12  sets the FOVs so that the point of interest is positioned in the middle of a single FOV. It is desirable to partly superimpose adjacent FOVs on each other.  FIG. 5  is a diagram showing an example of setting the FOV related to the designated ROI as illustrated in  FIG. 4 . Three FOVs  31 ,  32 , and  33  are set in  FIG. 5 . Moreover, the FOV  31  and the FOV  32  or the FOV  32  and the FOV  33  are partly superimposed on each other, respectively.  
         [0044]     In step Sa 9 , the calculating unit  12  sends instructions to the control unit  7  to perform an imaging operation on each of the FOVs set in step Sa 8 . In step Sa 10 , the calculating unit  12  reorganizes images in each of the FOVs on the basis of the collected NMR signal and connects the reorganized images to each other, thereby generating a reorganized image corresponding to the ROI.  
         [0045]     On the other hand, when the size of the ROI is smaller than that of the available FOV, the calculating unit  12  proceeds from step Sa 7  to step Sa 11 . In step Sa 11 , the calculating unit  12  sets the ROI as it is as the FOV.  
         [0046]     In step Sa 12 , the calculating unit  12  sends instructions to the control unit  7  to perform an imaging operation on the FOV set in step Sa 11 . In step Sa 13 , the calculating unit  12  reorganizes images in the FOV on the basis of the collected NMR signal.  
         [0047]     According to the first embodiment, even when the operator desires to obtain a reorganized image related to a region exceeding the available FOV, the operator needs only to designate a single ROI. Accordingly, it is possible to reduce burdens imposed on the operator compared to the case of designating a plurality of ROIs.  
         [0048]     In addition, according to the first embodiment, it is possible to remarkably increase throughputs of a positioning scanning. That is, since a plurality of FOVs is set by dividing a single ROI into a plurality of ROIs, it is possible to suitably maintain relative positions of the plurality of FOVs when connecting the reorganized images related to each of the FOVs to each other, thereby increasing connection precision.  
       Second Embodiment  
       [0049]     In a second embodiment, the calculating unit  12  further includes several functions described later. A first function is a function of determining a plurality of ROIs designated to be parallel to each other by manipulations in the input unit  14 . The first function restricts designation of the ROIs so that one of the ROIs does not exceed the available FOV. A second function is a function of moving one of the ROIs in accordance with designation of movement by manipulations in the input unit  14 . Moreover, the second function moves an ROI other than the moved ROI in a direction parallel to the moving direction of the moved ROI in the same state as being determined by the first function. A third function is a function of instructing the control unit  7  to perform an imaging operation on each of the plurality of FOVs, and connecting a plurality of images obtained through a plurality times of imaging operations, thereby generating image data related to the ROI.  
         [0050]     Hereinafter, operations of the MRI apparatus according to the second embodiment having the above-mentioned construction will be described.  
         [0051]      FIG. 6  is a flowchart showing operations performed by a calculation unit  12  in accordance with the second embodiment.  
         [0052]     In step Sb 1 , the calculating unit  12  displays a reference image prepared in advance as illustrated in  FIG. 3 , for example, on the display unit  13 .  
         [0053]     The operator designates a region requiring a high-definition imaging operation as the ROI by observing the reference image and manipulating the input unit  14 . In step Sb 2 , the calculating unit  12  determines the designated ROI on the basis of output information from the input unit  14 . In this case, the calculating unit  12  restricts the size of the ROI so as not to exceed the available FOV.  
         [0054]     Subsequently, the calculating unit  12  proceeds to a waiting state from steps Sb 3  to Sb 5 . In the waiting state, the calculating unit  12  waits for the occurrence of any one of events: a change of the ROI, a designation of a new ROI, and a start of the imaging.  
         [0055]     The operator changes the once-designated ROI by manipulating the input unit  14  in accordance with necessity. When an operation of changing the ROI is performed, the calculating unit  12  returns to step Sb 2  from step Sb 3  and determines the changed ROI.  
         [0056]     The operator designates a new ROI by manipulating the input unit  14  in accordance with necessity. When an operation of designating the new ROI is performed, the calculating unit  12  proceeds from step Sb 4  to step Sb 6 . In step Sb 6 , the calculating unit  12  determines the newly designated ROI on the basis of output information from the input unit  14 .  
         [0057]     Thereafter, the calculating unit  12  returns to a waiting state from steps Sb 7  to Sb 9 . In the waiting state, the calculating unit  12  waits for the occurrence of any one of events: a change of the ROI, a designation of a new ROI, and a start of the imaging.  
         [0058]     The operator may designate another new ROI by manipulating the input unit  14  in accordance with necessity. When an operation of designating the new ROI is performed, the calculating unit  12  returns to step Sb 6  from step Sb 8  and determines the newly designated ROI. The number of ROIs that can be designated in the invention may be restricted so as not to exceed a threshold number of ROIs.  
         [0059]     The operator changes one of the designated ROIs by manipulating the input unit  14  in accordance with necessity. When an operation of changing the ROI is performed, the calculating unit  12  proceeds from step Sb 7  to step Sb 10 . In step Sb 10 , the calculating unit  12  determines a changed ROI. Subsequently, in step Sb 11 , the calculating unit  12  changes an ROI other than the changed ROI so as to be parallel to the changed ROI. For example, it is assumed that the ROI  42  is rotated as illustrated in  FIG. 8  from the state where three ROIs  41 ,  42 , and  43  are set as illustrated in  FIG. 7 . In this case, the calculating unit  12  rotates and moves the ROIs  41  and  43  so that the ROIs  41  and  43  are parallel to the ROI  42  and aligned in a state as illustrated in  FIG. 9 . In this case, when the original ROIs  41 ,  42 , and  43  are superimposed on each other as illustrated in  FIG. 7 , the calculating unit  12  reproduces the superimposition as illustrated in  FIG. 9 . After finishing the designation of the whole ROIs, the calculating unit  12  returns to a waiting state from steps Sb 6  to Sb 8 .  
         [0060]     In addition, the calculating unit  12  displays the designated ROIs so that the designated ROIs are superimposed on the reference image as illustrated in FIGS.  7  to  9 , for example.  
         [0061]     After finishing the designation of the ROI, the operator instructs to start an imaging operation by manipulating the input unit  14 . When the calculating unit  12  is instructed to start an imaging operation during a waiting state from steps Sb 7  to Sb 9 , the calculating unit  12  proceeds from step Sb 9  to step Sb 12 . In step Sb 12 , the calculating unit  12  sets each of the ROIs determined at that moment as the FOV.  
         [0062]     In step Sb 13 , the calculating unit  12  sends instructions to the control unit  7  to perform an imaging operation on each of the FOVs set in step Sb 12 . In step Sb 14 , the calculating unit  12  reorganizes images in each of the FOVs on the basis of the collected NMR signal and connects the reorganized images to each other, thereby generating a reorganized image corresponding to the ROI.  
         [0063]     On the other hand, when the calculating unit  12  is instructed to start an imaging operation during a waiting state from steps Sb 3  to Sb 5 , the calculating unit  12  proceeds from step Sb 5  to step Sb 15 . In step Sb 15 , the calculating unit  12  sets the ROI as it is as the FOV.  
         [0064]     In step Sb 16 , the calculating unit  12  sends instructions to the control unit  7  to perform an imaging operation on the FOV set in step Sb 15 . In step Sb 17 , the calculating unit  12  reorganizes images in the FOV on the basis of the collected NMR signal.  
         [0065]     According to the second embodiment, when the operator desires to obtain a reorganized image related to a region exceeding the available FOV, the operator needs to designate a plurality of ROIs. However, since the ROIs are automatically aligned parallel to each other, the operator does not need to manually adjust the position of the ROIs. Accordingly, it is possible to reduce burdens imposed on the operator compared to the case of requiring such a task.  
         [0066]     In addition, according to the second embodiment, it is possible to remarkably increase throughputs of a positioning scanning. That is, since a plurality of ROIs are automatically aligned parallel to each other, it is possible to suitably maintain relative positions of the plurality of ROIs when connecting the reorganized images related to each of the FOVs to each other, thereby increasing connection precision.  
       Third Embodiment  
       [0067]     In a third embodiment, the calculating unit  12  further includes several functions described later. A first function is a function of determining a plurality of ROIs designated to be parallel to each other by manipulations in the input unit  14 . The first function restricts designation of the ROIs so that one of the ROIs does not exceed the available FOV. A second function is a function of moving one of the ROIs in accordance with designation of movement by manipulations in the input unit  14 . Moreover, the second function changes an ROI other than the moved ROI to keep track of the movement of a reference point in a region superimposed by the moved ROI. A third function is a function of instructing the control unit  7  to perform an imaging operation on each of the plurality of FOVs, and connecting a plurality of images obtained through a plurality times of imaging operations, thereby generating image data related to the ROI.  
         [0068]     Hereinafter, operations of the MRI apparatus according to the third embodiment having the above-mentioned construction will be described.  
         [0069]     The processing sequence of the calculating unit  12  in the third embodiment is the same as that of the second embodiment as illustrated in  FIG. 6 , excepting that the operation in step Sb 11  of the third embodiment is different from that of the second embodiment. That is, in step Sb 11 , the calculating unit  12  changes an ROI other than the moved ROI to keep track of the movement of a reference point in a region superimposed by the moved ROI. For example, it is assumed that the ROI  52  is moved as illustrated in  FIG. 11  from the state where three ROIs  51 ,  52 , and  53  are set as illustrated in  FIG. 10 . In this case, the calculating unit  12  moves the ROIs  51  and  53  so that the ROIs  51  and  53  keep track of the movement of reference points  61  and  62  and are aligned in a state as illustrated in  FIG. 12 . In addition, the reference points  61  and  62  may be designated by the operator, or a center position of the superimposed region of the ROIs may be automatically set as the reference point.  
         [0070]     According to the third embodiment, when the operator desires to obtain a reorganized image related to a region exceeding the available FOV, the operator needs to designate a plurality of ROIs. However, since the ROIs are automatically aligned to keep the partly superimposed state between the ROIs, the operator does not need to manually adjust the position of the ROIs even when one of the ROIs is changed. Accordingly, it is possible to reduce burdens imposed on the operator compared to the case of requiring such a task.  
         [0071]     Various modifications can be made to the embodiments of the invention in the following manner.  
         [0072]     In the first embodiment, it may be possible to set the FOV so as not to include a portion of the ROIs.  
         [0073]     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.