Patent Publication Number: US-2023152402-A1

Title: Magnetic resonance imaging apparatus and magnetic resonance imaging method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of and claims benefit under 35 U.S.C. § 120 to U.S. application Ser. No. 17/305,677 filed on Jul. 13, 2021, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a magnetic resonance imaging apparatus and a magnetic resonance imaging method. 
     BACKGROUND 
     Perfusion techniques are used for rendering hemodynamics of capillaries in a tissue by using an Arterial Spin Labeling (ASL) method by which a Radio Frequency (RF) pulse is radiated onto blood vessels so as to invert blood spins and to use the inverted spins as an endogenous tracer. Known examples of the perfusion techniques include a Flow-sensitive Alternating Inversion Recovery (FAIR) method, a Continuous Arterial Spin Labeling (CASL) method, and a pulsed-Continuous Arterial Spin Labeling (pCASL) method. 
     The FAIR method is basically a two-dimensional imaging method by which an imaging process is performed by applying a spatially selective pulse to a Region Of Interest (ROI) slice. Although the FAIR method has an advantage of achieving a high Signal-to-Noise Ratio (SNR), a problem remains where, when a spatially selective IR pulse has repeatedly been applied, the perfusion curve fails to return to the original baseline thereof. 
     Further, by continuously applying a spatially selective pulse, the pCASL method is able to achieve a high SNR similarly to the FAIR method. However, the pCASL method has the problem where, when a spatially selective IR pulse has repeatedly been applied, the perfusion curve fails to return to the original baseline thereof. In addition, another problem arises where it is necessary to suppress the Magnetization Transfer (MT) effect, especially in brain. 
     For the reasons stated above, with the perfusion techniques using an ASL method, how to suppress the MT effect is important. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating a magnetic resonance imaging apparatus according to an embodiment; 
         FIG.  2    is a flowchart illustrating a processing procedure performed by the magnetic resonance imaging apparatus according to a first embodiment; 
         FIGS.  3 A and  3 B  are charts for explaining pulse sequences executed by the magnetic resonance imaging apparatus according to the first embodiment; 
         FIG.  3 C  is a drawing for explaining application regions of Radio Frequency (RF) pulses applied by the magnetic resonance imaging apparatus according to the first embodiment; 
       FIG. 3D is a drawing for explaining changes in longitudinal magnetization caused by the RF pulses applied by the magnetic resonance imaging apparatus according to the first embodiment; 
         FIG.  3 E  is a drawing for explaining k-space data acquisition performed by the magnetic resonance imaging apparatus according to the first embodiment; 
         FIG.  4    is a drawing for explaining a Graphical User Interface (GUI) related to the magnetic resonance imaging apparatus according to the first embodiment; 
         FIG.  5    is a chart for explaining a process performed by the magnetic resonance imaging apparatus according to the first embodiment; 
         FIGS.  6 A,  6 B, and  6 C  are charts for explaining pulse sequences executed by a magnetic resonance imaging apparatus according to a modification example of the first embodiment; 
         FIG.  7    is a flowchart illustrating a processing procedure performed by a magnetic resonance imaging apparatus according to a second embodiment; 
         FIG.  8    is a chart for explaining pulse sequences executed by the magnetic resonance imaging apparatus according to the second embodiment; and 
         FIGS.  9 A and  9 B  are drawings for explaining a process performed by the magnetic resonance imaging apparatus according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A magnetic resonance imaging apparatus according to an embodiment includes sequence controlling circuitry and processing circuitry. The sequence controlling circuitry is configured to execute (i) a first pulse sequence in which a spatially selective inversion recovery (IR) pulse and a spatially non-selective IR pulse are applied, and subsequently a Cartesian acquisition is performed when a first Inversion Time (TI) period has elapsed, and a radial acquisition is performed after the Cartesian acquisition and (ii) a second pulse sequence in which the spatially non-selective IR pulse is applied without applying the spatially selective IR pulse, and subsequently a Cartesian acquisition is performed when the first TI period has elapsed, and a radial acquisition is performed after the Cartesian acquisition, while varying the first TI period, with respect to a plurality of first TI periods. The processing circuitry is configured to calculate a second TI period to be used in a third pulse sequence and a fourth pulse sequence, based on data obtained from the first pulse sequence and the second pulse sequence executed by the sequence controlling circuitry. The sequence controlling circuitry executes (iii) the third pulse sequence in which the spatially selective IR pulse and the spatially non-selective IR pulse are applied, and subsequently a Cartesian acquisition is performed when the second TI period has elapsed, and a radial acquisition is performed after the Cartesian acquisition and (iv) the fourth pulse sequence in which the spatially non-selective IR pulse is applied without applying the spatially selective IR pulse, and subsequently a Cartesian acquisition is performed when the second TI period has elapsed, and a radial acquisition is performed after the Cartesian acquisition. The processing circuitry generates a magnetic resonance image of an imaged region based on data obtained from the third pulse sequence and the fourth pulse sequence. 
     Exemplary embodiments of the present disclosure will be explained below with reference to the accompanying drawings. In the following sections, some of the constituent elements having mutually the same configurations will be referred to by using the same reference characters, and duplicate explanations thereof will be omitted. 
     First Embodiment 
       FIG.  1    is a block diagram illustrating a magnetic resonance imaging apparatus  100  according to a first embodiment. As illustrated in  FIG.  1   , the magnetic resonance imaging apparatus  100  includes a static magnetic field magnet  101 , a static magnetic field power supply (not illustrated), a gradient coil  103 , a gradient power supply  104 , a couch  105 , couch controlling circuitry  106 , a transmission coil  107 , transmitter circuitry  108 , a reception coil  109 , receiver circuitry  110 , sequence controlling circuitry  120  (a sequence controlling unit), and an image processing device  130 . The magnetic resonance imaging apparatus  100  does not include an examined subject (hereinafter, “patient”) P (e.g., a human body). Further, the configuration illustrated in  FIG.  1    is merely an example. For instance, any of the functional units in the sequence controlling circuitry  120  and the image processing device  130  may be integrated together or separated as appropriate. 
     The static magnetic field magnet  101  is a magnet formed to have a hollow and substantially circular cylindrical shape and is configured to generate a static magnetic field in the space on the inside thereof. For example, the static magnetic field magnet  101  is a superconductive magnet or the like and is magnetically excited by receiving a supply of an electric current from the static magnetic field power supply. The static magnetic field power supply is configured to supply the electric current to the static magnetic field magnet  101 . In another example, the static magnetic field magnet  101  may be a permanent magnet. In that situation, the magnetic resonance imaging apparatus  100  does not have to include a static magnetic field power supply. Further, the static magnetic field power supply may be provided separately from the magnetic resonance imaging apparatus  100 . 
     The gradient coil  103  is a coil formed to have a hollow and substantially cylindrical shape and is arranged on the inside of the static magnetic field magnet  101 . The gradient coil  103  is formed by combining together three coils corresponding to X-, Y-, and Z- axes that are orthogonal to one another. By individually receiving a supply of an electric current from the gradient power supply  104 , each of the three coils is configured to generate a gradient magnetic field of which the magnetic field intensity changes along the corresponding one of the X-, Y-, and Z- axes. The gradient magnetic fields generated by the gradient coil  103  along the X-, Y-, and Z-axes are referred to as, for example, a slice gradient magnetic field Gs, a phase encode gradient magnetic field Ge, and a readout gradient magnetic field Gr. The gradient power supply  104  is configured to supply the electric current to the gradient coil  103 . 
     The couch  105  includes a couchtop  105   a  on which the patient P is placed. Under control of the couch controlling circuitry  106 , the couchtop  105   a  is inserted into the hollow (an image taking opening) of the gradient coil  103 , while the patient P is placed thereon. Normally, the couch  105  is installed so that the longitudinal direction thereof extends parallel to the central axis of the static magnetic field magnet  101 . Under control of the image processing device  130 , the couch controlling circuitry  106  is configured to drive the couch  105  so as to move the couchtop  105   a  in longitudinal directions and up-and-down directions. 
     The transmission coil  107  is arranged on the inside of the gradient coil  103  and is configured to generate a radio frequency magnetic field by receiving a supply of an RF pulse from the transmitter circuitry  108 . The transmitter circuitry  108  is configured to supply the RF pulse corresponding to a Larmor frequency determined by the type of targeted atoms and the magnetic field intensity, to the transmission coil  107 . 
     The reception coil  109  is arranged on the inside of the gradient coil  103  and is configured to receive magnetic resonance signals (which hereinafter may be referred to as “MR signals” as necessary) emitted from the patient P due to influence of the radio frequency magnetic field. Upon receipt of the magnetic resonance signals, the reception coil  109  is configured to output the received magnetic resonance signals to the receiver circuitry  110 . 
     The transmission coil  107  and the reception coil  109  described above are merely examples. The configuration may be realized by using one or a combination of two or more selected from among: a coil having only transmitting functions, a coil having only receiving functions, and a coil having transmitting and receiving functions. 
     The receiver circuitry  110  is configured to detect the magnetic resonance signals output from the reception coil  109  and to generate magnetic resonance data based on the detected magnetic resonance signals. More specifically, the receiver circuitry  110  is configured to generate the magnetic resonance data by performing a digital conversion on the magnetic resonance signals output from the reception coil  109 . Further, the receiver circuitry  110  is configured to transmit the generated magnetic resonance data to the sequence controlling circuitry  120 . Alternatively, the receiver circuitry  110  may be provided so as to belong to a gantry device including the static magnetic field magnet  101 , the gradient coil  103 , and the like. 
     The sequence controlling circuitry  120  is configured to perform an imaging process on the patient P, by driving the gradient power supply  104 , the transmitter circuitry  108 , and the receiver circuitry  110 , based on sequence information transmitted thereto from the image processing device  130 . In this situation, the sequence information is information defining a procedure for performing the imaging process. The sequence information defines: the intensity of the electric current to be supplied by the gradient power supply  104  to the gradient coil  103  and the timing with which the electric current is to be supplied; the intensity of the RF pulse to be supplied by the transmitter circuitry  108  to the transmission coil  107  and the timing with which the RF pulse is to be applied; the timing with which the magnetic resonance signal is detected by the receiver circuitry  110 ; and the like. For example, the sequence controlling circuitry  120  may be an integrated circuit such as an Application Specific Integrated Circuit (ASIC) or a Field Programmable Gate Array (FPGA) or an electronic circuit such as a Central Processing Unit (CPU) or a Micro Processing Unit (MPU). Details of pulse sequences executed by the sequence controlling circuitry  120  will be explained later. 
     Further, upon receipt of the magnetic resonance data from the receiver circuitry  110  as a result of the imaging process performed on the patient P by driving the gradient power supply  104 , the transmitter circuitry  108 , and the receiver circuitry  110 , the sequence controlling circuitry  120  is configured to transfer the received magnetic resonance data to the image processing device  130 . 
     The image processing device  130  is configured to control the entirety of the magnetic resonance imaging apparatus  100 , to generate images, and the like. The image processing device  130  includes a memory  132 , an input device  134 , a display  135 , and processing circuitry  150 . The processing circuitry  150  includes an interface function  131 , a controlling function  133 , and a generating function  136 . 
     In the first embodiment, the processing functions performed by the interface function  131 , the controlling function  133 , and the generating function  136  are stored in the memory  132  in the form of computer-executable programs. The processing circuitry  150  is a processor configured to realize the functions corresponding to the programs, by reading and executing the programs from the memory  132 . In other words, the processing circuitry  150  that has read the programs has the functions illustrated within the processing circuitry  150  in  FIG.  1   . Although the example is explained with reference to  FIG.  1    in which the single processing circuit (i.e., the processing circuitry  150 ) realizes the processing functions performed by the interface function  131 , the controlling function  133 , and the generating function  136 , it is also acceptable to structure the processing circuitry  150  by combining together a plurality of independent processors, so that the functions are realized as a result of the processors executing the programs. In other words, each of the abovementioned functions may be structured as a program, so that the single processing circuit (the processing circuitry  150 ) executes the programs. In another example, one or more specific functions may each be installed in a dedicated and independent program executing circuit. Further, in  FIG.  1   , the interface function  131 , the controlling function  133 , and the generating function  136  are examples of a receiving unit, a controlling unit, and a generating unit, respectively. Further, the sequence controlling circuitry  120  is an example of a sequence controlling unit. 
     The term “processor” used in the above explanations denotes, for example, a Central Processing Unit (CPU), a 
     Graphical Processing Unit (GPU), or a circuit such as an Application Specific Integrated Circuit (ASIC) or a programmable logic device (e.g., a Simple Programmable Logic Device [SPLD], a Complex Programmable Logic Device [CPLD], or a Field Programmable Gate Array [FPGA]). The one or more processors are configured to realize the functions by reading and executing the programs saved in the memory  132 . 
     Further, instead of saving the programs in the memory  132 , it is also acceptable to directly incorporate the programs in the circuits of the one or more processors. In that situation, the one or more processors realize the functions by reading and executing the programs incorporated in the circuits thereof. Similarly, the couch controlling circuitry  106 , the transmitter circuitry  108 , the receiver circuitry  110 , and the like are each also configured by using an electronic circuit like the abovementioned processor. 
     By employing the interface function  131 , the processing circuitry  150  is configured to transmit the sequence information to the sequence controlling circuitry  120  and to receive the magnetic resonance data from the sequence controlling circuitry  120 . Further, upon receipt of the magnetic resonance data, the processing circuitry  150  including the interface function  131  is configured to store the received magnetic resonance data into the memory  132 . 
     The magnetic resonance data stored in the memory  132  is arranged in a k-space by the controlling function  133 . As a result, the memory  132  stores therein k-space data. 
     The memory  132  is configured to store therein the magnetic resonance data received by the processing circuitry  150  including the interface function  131 , the k-space data arranged in the k-space by the processing circuitry  150  including the controlling function  133 , image data generated by the processing circuitry  150  including the generating function  136 , and the like. For example, the memory  132  may be a semiconductor memory element such as a Random Access Memory (RAM) or a flash memory, or a hard disk, an optical disk, or the like. 
     The input device  134  is configured to receive various types of instructions and inputs of information from an operator. For example, the input device  134  is a pointing device such as a mouse or a trackball, a selecting device such as a mode changing switch, and/or an input device such as a keyboard. Under control of the processing circuitry  150  including the controlling function  133 , the display  135  is configured to display a Graphical User Interface (GUI) used for receiving an input of an image taking condition, images generated by the processing circuitry  150  including the generating function  136 , and the like. For example, the display  135  is a display such as a liquid crystal display monitor. 
     By employing the controlling function  133 , the processing circuitry  150  is configured to control the entirety of the magnetic resonance imaging apparatus  100  and to control image taking processes, image generating processes, image displaying processes, and the like. For example, the processing circuitry  150  including the controlling function  133  is configured to receive the input of the image taking condition (e.g., an image taking parameter) through the GUI and to generate the sequence information according to the received image taking condition. Further, the processing circuitry  150  including the controlling function  133  is configured to transmit the generated sequence information to the sequence controlling circuitry  120 . 
     By employing the generating function  136 , the processing circuitry  150  is configured to generate an image by reading the k-space data from the memory  132  and performing a reconstructing process such as a Fourier transform on the read k-space data. 
     Next, a background of an embodiment will briefly be explained. 
     Perfusion techniques are used for rendering hemodynamics of capillaries in a tissue by using an Arterial Spin Labeling (ASL) method by which an RF pulse is radiated onto blood vessels so as to invert blood spins and to use the inverted spins as an endogenous tracer. Known examples of the perfusion techniques include a Flow-sensitive Alternating Inversion Recovery (FAIR) method, a Continuous Arterial Spin Labeling (CASL) method, and a pulsed-Continuous Arterial Spin Labeling (pCASL) method. 
     The FAIR method is basically a two-dimensional imaging method by which an imaging process is performed by applying a spatially selective pulse to a ROI slice. Although the FAIR method has an advantage of achieving a high SNR, a problem remains where, when a spatially selective IR pulse has repeatedly been applied, the perfusion curve fails to return to the original baseline thereof. 
     Further, by continuously applying a spatially selective pulse, the pCASL method is able to achieve a high SNR similarly to the FAIR method. However, the pCASL method has the problem where, when a spatially selective IR pulse has repeatedly been applied, the perfusion curve fails to return to the original baseline thereof. In addition, another problem arises where it is necessary to suppress the Magnetization Transfer (MT) effect. 
     For the reasons stated above, with the perfusion techniques using an ASL method, how to suppress the MT effect is important. 
     In relation to the above, among ASL methods, configurations to apply a spatially non-selective IR pulse have not been mainstream methods, because spatially non- selective IR pulses can easily lower the SN ratios of images. However, we have discovered that applying a spatially non- selective IR pulse significantly suppresses the MT effect. One of the reasons is that, although a larger MT effect is exerted on magnetization while spins are aligned along the direction of a magnetic field (+Mz), a smaller MT effect is exerted on longitudinal magnetization of longitudinal magnetization in the opposite direction (-Mz). 
     Accordingly, the magnetic resonance imaging apparatus  100  according to an embodiment is configured to execute two pulse sequences, namely, a pulse sequence in which a spatially non-selective pulse is applied, and subsequently an acquisition sequence is executed and another pulse sequence in which a spatially non-selective pulse and a spatially selective pulse are applied and subsequently an acquisition sequence is executed and is configured to generate a magnetic resonance image by calculating a difference between pieces of data acquired from the two pulse sequences. In this situation, as the acquisition sequence, the sequence controlling circuitry  120  performs a Cartesian acquisition and subsequently performs a radial acquisition, in an example. 
     As a result, it is possible to suppress the MT effect and to apply ASL to a site other than the heart, which has hitherto been considered difficult. It is therefore possible to perform four-dimensional (4D) non-contrast-enhanced ASL imaging on, for example, a region in the brain, a muscle, or a kidney, a region including a region having microvascularization, or a region including a region having microcirculation. 
     In addition, it is possible to perform a preliminary imaging process with respect to a plurality of TI values and to determine an optimal TI value based on the results thereof. It is therefore possible to improve throughput of medical examinations. 
     Further, by combining the 4D non-contrast-enhanced ASL imaging with Magnetic Resonance Angiography (MRA), it is expected possible to predict of a stenosis or an occlusion of a blood vessel with a high level of precision. 
     A configuration to realize this example will be explained with reference to  FIGS.  2  to  5   . 
       FIG.  2    is a flowchart for explaining a flow in a process performed by the magnetic resonance imaging apparatus according to the first embodiment. 
     To begin with, at step S 100 , the sequence controlling circuitry  120  executes: a first pulse sequence in which a spatially selective IR pulse and a spatially non-selective IR pulse are applied and subsequently a radial acquisition is performed; and a second pulse sequence in which a spatially non-selective IR pulse is applied without applying a spatially selective IR pulse, and subsequently a radial acquisition is performed. 
     This procedure will be explained with reference to  FIGS.  3 A to  3 E . 
       FIG.  3 A  illustrates the first pulse sequence in which the spatially selective IR pulse and the spatially non-selective IR pulse are applied, and subsequently the radial acquisition is performed.  FIG.  3 B  illustrates the second pulse sequence in which, without applying a spatially selective IR pulse, the radial acquisition is performed. The first pulse sequence in which the spatially selective IR pulse and the spatially non-selective IR pulse are applied, and subsequently the radial acquisition is performed may be referred to as a Tag-ON sequence. In contrast, the second pulse sequence in which, without applying a spatially selective IR pulse, the radial acquisition is performed may be referred to as a Tag-OFF sequence. 
     In the following sections, an example will be explained with reference to  FIGS.  3 A and  3 B  in which the acquisition sequences executed by the sequence controlling circuitry  120  at step S 100  are for minimizing acoustic noise utilizing Ultrashort Echo Time (mUTE). Usually, the sequence controlling circuitry  120  is configured to link together the Tag-ON sequence in  FIG.  3 A  and the Tag-OFF sequence in  FIG.  3 B , so as to execute the linked sequences as a set of acquisitions. 
     As illustrated in  FIG.  3 A , the sequence controlling circuitry  120  performs a magnetic resonance imaging process on an imaged region, by executing the first pulse sequence in which a spatially non-selective IR pulse  4 , which is an RF pulse to invert nuclear spins in a wider region, is applied to a wider region including the imaged region, and subsequently, a spatially selective IR pulse  5 , which is an RF pulse to invert nuclear spins in a specific region, is applied to a smaller region than the application region of the spatially non-selective IR pulse  4 , and when a prescribed time period has elapsed, the acquisition sequence to acquire data is executed. 
     At first, the application regions of the spatially non-selective IR pulse  4  and the spatially selective IR pulse  5  will be explained, with reference to  FIG.  3 C . In this situation, a region  8  denotes the imaged region, which is the region subject to the imaging process and the region from which the data is to be acquired with the acquisition sequence executed by the sequence controlling circuitry  120  after the spatially non-selective IR pulse  4  and the spatially selective IR pulse  5  are applied. Further, a region  6  denotes the region to which the spatially non-selective IR pulse is applied by the sequence controlling circuitry  120 . The sequence controlling circuitry  120  is configured to apply the spatially non-selective IR pulse  4  to the wider region  6  including the region  8  serving as the imaged region. Further, a region  7  denotes the region to which the spatially selective IR pulse  5  is applied by the sequence controlling circuitry  120 . The sequence controlling circuitry  120  is configured to apply the spatially selective IR pulse  5  to the region  7 , which is a relatively smaller region. The region  7  to which the spatially selective IR pulse  5  is applied by the sequence controlling circuitry  120  is, for example, selected on the upstream side of the region  8  serving as the imaged region. In other words, blood that is present in the region  7  at the time of applying the spatially selective IR pulse  5  and is present in the region  8  at the time of executing the acquisition sequence is labeled. 
     Next, changes in longitudinal magnetization of spins caused by the applications of the spatially non-selective IR pulse  4  and the spatially selective IR pulse  5  will be explained, with reference to FIG. 3D. FIG. 3D is a drawing for explaining temporal changes in the longitudinal magnetization of the spins. 
     The plotline  14  indicates temporal changes in the longitudinal magnetization of the spins in a location to which both the spatially non-selective IR pulse  4  and the spatially selective IR pulse  5  are applied. The plotline  13  indicates temporal changes in the longitudinal magnetization of the spins in a location to which only the spatially non- selective IR pulse  4  is applied, while the spatially selective IR pulse  5  is not applied. 
     Both the spatially non-selective IR pulse  4  and the spatially selective IR pulse  5  invert the longitudinal magnetization of the location to which the RF pulse is applied. Accordingly, in the location to which both the spatially non-selective IR pulse  4  and the spatially selective IR pulse  5  are applied, i.e., the labeled location, the longitudinal magnetization is inverted twice so that the longitudinal magnetization returns to the original value and exhibits a high signal, as indicated by the plotline  14 . 
     In contrast, in the location to which only the spatially non-selective IR pulse  4  is applied, while the spatially selective IR pulse  5  is not applied, i.e., the location such as a background part, the signal of the longitudinal magnetization is inverted by the RF pulse only once, and the signal gradually relaxes, as indicated by the plotline  13 . In this situation, the longitudinal magnetization value is equal to zero at a null point  15 . Accordingly, when the sequence controlling circuitry  120  executes the acquisition sequence in the vicinity of the null point  15 , because the blood labeled by the spatially selective IR pulse  5  exhibits a high signal, it is possible to perform the imaging process while suppressing background signals. A purpose of the spatially non-selective IR pulse  4  and the spatially selective pulse  5  applied by the sequence controlling circuitry  120  has thus been explained. 
     Next, with reference back to  FIG.  3 A , the acquisition sequence executed by the sequence controlling circuitry  120  will be explained. In the first embodiment, the sequence controlling circuitry  120  performs a 4D acquisition. In this situation, the 4D acquisition denotes performing a three- dimensional (3D) acquisition on the k-space while varying the TI periods, so as to perform acquisition four-dimensionally in total. In other words, by varying the TI period to be different values, the sequence controlling circuitry  120  is configured to acquire data with respect to a plurality of TI periods each of which denotes the time since the spatially non-selective pulse  4  or the spatially selective pulse  5  is applied. In this situation, for example, the sequence controlling circuitry  120  acquires the data by using a mUTE sequence as the acquisition sequence. In other words, in the first embodiment, the acquisition sequence executed by the sequence controlling circuitry  120  includes: acquisitions in a plurality of Cartesian segments such as Cartesian acquisitions  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  performed on a central part of the space; and a radial acquisition  16  performed on an outside part of the k-space. In other words, after applying the spatially non-selective IR pulse  4  and the spatially selective IR pulse  5 , the sequence controlling circuitry  120  performs the Cartesian acquisition  15   a  when time  16   a  has elapsed, performs the Cartesian acquisition  15   b  when time  16   b  has elapsed, performs the Cartesian acquisition  15   c  when time  16   c  has elapsed, performs the Cartesian acquisition  15   d  when time  16   d  has elapsed, similarly performs the Cartesian acquisitions  15   e  and  15   f , and subsequently performs the radial acquisition  16 . 
       FIG.  3 E  illustrates a relationship between the Cartesian acquisitions and the radial acquisition performed by the sequence controlling circuitry  120 .  FIG.  3 E  three-dimensionally illustrates the region of the k-space where the data acquisition is performed. A region  60  represents the central part of the k-space where the Cartesian acquisitions are performed. Each of the line segments such as a line segment  61  indicates the radial acquisition performed by the sequence controlling circuitry  120 . In other words, in the executed acquisition sequence, the sequence controlling circuitry  120  at first performs the Cartesian acquisitions  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f , on the region  60  in the central part of the k-space while varying the TI value, and subsequently performs the radial acquisition  16  on the region outside the region  60  positioned in the central part of the k-space, toward the outside from the center of the k-space, for example. In this manner, the sequence controlling circuitry  120  has executed the first pulse sequence. 
     At step S 110  explained later, by employing the generating function  136 , the processing circuitry  150 , for example, generates data related to TI=TI 1  being the TI corresponding to the time  16   a  by using the acquisition from the cartesian acquisition  15   a  and the radial acquisition  16 , further generates data related to TI=TI 2  being the TI corresponding to the time  16   b  by using the acquisition from the cartesian acquisition  15   b  and the radial acquisition  16 , and generates data related to TI=TI 3  being the TI corresponding to the time  16   c  by using the acquisition from the cartesian acquisition  15   c  and the radial acquisition  16 . 
     Similarly as illustrated in  FIG.  3 B , in the second pulse sequence, after applying only the spatially non-selective IR pulse  4  without applying the spatially selective IR pulse  5 , the sequence controlling circuitry  120  performs a cartesian acquisition  15   a  when the time  16   a  has elapsed, performs a cartesian acquisition  15   b  when the time  16   b  has elapsed, performs a Cartesian acquisition  15   c  when the time  16   c  has elapsed, performs a Cartesian acquisition  15   d  when the time  16   d  has elapsed, similarly performs Cartesian acquisitions  15   e  and  15   f , and subsequently performs a radial acquisition  16 . The only difference between the first pulse sequence and the second pulse sequence is the presence/absence of the application of the spatially selective pulse  5 , and the other processes are the same. 
     In  FIGS.  3 A and  3 B , the time TI 1 , TI 2 , TI 3 , TI 4  and so on, which denote the time from the application of the spatially non-selective pulse  4  or the spatially selective pulse  5  to the execution of the Cartesian acquisitions  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f , are variable and may arbitrarily be set in accordance with instructions from the user.  FIG.  4    illustrates an example of a GUI for this purpose. 
     By employing the controlling function  133 , the processing circuitry  150  receives a change made to TI 1 , i.e., an input of the time  16   a  in  FIGS.  3 A and  3 B , via the input device  134  and buttons  21  and  22  on an input panel  20  of the display  135 . Further, by employing the controlling function  133 , the processing circuitry  150  receives a change made to an increment of the TI, e.g., an input of the increment from TI 1  to TI 2  illustrated in  FIGS.  3 A and  3 B , via the input device  134  and buttons  23  and  24  on the input panel  20  of the display  135 . Further, by employing the controlling function  133 , the processing circuitry  150  receives a change made to the number of cartesian acquisition segments, via the input device  134  and buttons  25  and  26  on the input panel  20  of the display  135 . In this situation, the number of Cartesian acquisition segments denotes the number of Cartesian acquisition segments corresponding to mutually-different TI values. In the example illustrated in  FIGS.  3 A and  3 B , the number of Cartesian acquisition segments is six. Further, by employing the controlling function  133 , the processing circuitry  150  receives a change made to a Cartesian acquisition interval via the input device  134  and buttons  27  and  28  on the input panel  20  of the display  135 . In this situation, the Cartesian acquisition interval denotes the interval between the Cartesian acquisitions performed by the sequence controlling circuitry  120 . An interval  17  illustrated in  FIG.  3 B  is the Cartesian acquisition interval. 
     Subsequently, at step S 120 , by employing the generating function  136 , the processing circuitry  150  generates a magnetic resonance image in which the MT effect is suppressed, based on the data obtained from the first pulse sequence and the second pulse sequence executed by the sequence controlling circuitry  120  at step S 100 . More specifically, by employing the generating function  136 , the processing circuitry  150  generates a first image (a Tag-ON image) by performing a Fourier transform on first k-space data obtained by executing the first pulse sequence being a Tag-ON sequence. 
     For example, by employing the generating function  136 , the processing circuitry  150  generates data related to TI =TI 1 , based on the data obtained from the Cartesian acquisition  15   a  and the data obtained from the radial acquisition  16  in  FIG.  3 A . Similarly, by employing the generating function  136 , the processing circuitry  150  generates data related to TI=TI 2 , based on the data obtained from the Cartesian acquisition  15   b  and the data obtained from the radial acquisition  16  in  FIG.  3 A . Further, by employing the generating function  136 , the processing circuitry  150  generates data related to TI =TI 3 , based on the data obtained from the Cartesian acquisition  15   c  and the data obtained from the radial acquisition  16  in  FIG.  3 A . In this manner, the processing circuitry  150  generates the pieces of data related to the plurality of TI values, based on the pieces of data obtained by executing the first pulse sequence. 
     Further, by employing the generating function  136 , the processing circuitry  150  generates a second image (a Tag-OFF image) by performing a Fourier transform on second k-space data obtained by executing the second pulse sequence being a Tag-OFF sequence. Subsequently, the processing circuitry  150  generates a magnetic resonance image in which the background signal and the MT effect are suppressed by performing a difference calculating process between the first image (the Tag-ON image) and the second image (the Tag-OFF image). 
     For example, by employing the generating function  136 , the processing circuitry  150  generates data related to TI being equal to TI 1 , based on the data obtained from the Cartesian acquisition  15   a  and the data obtained from the radial acquisition  16  in  FIG.  3 B . Similarly, by employing the generating function  136 , the processing circuitry  150  generates data related to TI being equal to TI 2 , based on the data obtained from the Cartesian acquisition  15   b  and the data obtained from the radial acquisition  16  in  FIG.  3 B . Further, by employing the generating function  136 , the processing circuitry  150  generates data related to TI being equal to TI 3 , based on the data obtained from the Cartesian acquisition  15   c  and the data obtained from the radial acquisition  16  in  FIG.  3 B . In this manner, the processing circuitry  150  has generated the pieces of data related to the plurality of TI values, based on the pieces of data obtained by executing the first pulse sequence. 
     As explained above, in the magnetic resonance imaging apparatus  100  according to the first embodiment, the 4D ASL sequence is executed by applying the spatially non-selective IR pulse. As a result, it is possible to suppress the MT effect and is therefore possible to apply ASL to a site other than the heart, which has hitherto been considered difficult. For example, it is possible to perform the imaging process on an imaged region such as a region in the brain, a muscle, or a kidney, a region including a region having microvascularization, or a region including a region having microcirculation. 
     The example was explained with reference to  FIGS.  3 A and  3 B  in which the radial acquisition  16  is performed after the Cartesian acquisitions  15   a  to  15 f; however, possible embodiments are not limited to this example. The radial acquisition  16  may be performed before the Cartesian acquisitions  15   a  to  15 f. In other words, the radial acquisition  16  may be performed before the application of the ASL pulse. 
     In addition, by further analyzing the magnetic resonance image generated at step S 110 , the processing circuitry  150  is capable of distinguishing a normal blood flow from a blood vessel having a stenosis, being ischemic, having an occlusion, having an infarct, or having been revascularized/treated. 
     In an example, by employing the generating function  136 , the processing circuitry  150  is configured to calculate, with respect to the imaged region, at least one of a peak signal value, a peak flow time, arterial transit time, and a blood flow volume, as an index, based on the data obtained from the first pulse sequence and the second pulse sequence executed by the sequence controlling circuitry  120  at step S 100  and is configured to further perform the analysis based on the calculated index. 
       FIG.  5    illustrates an example of the analysis.  FIG.  5    illustrates temporal changes in signal values observed after the difference calculating process performed between the first image and the second image, in various status of blood vessels, with respect to a given imaged region. More specifically, the curve  50  indicates temporal changes in the signal value of a normal blood flow. The curve  51  indicates temporal changes in the signal value of a blood flow in a blood vessel in a stenosed/ischemic state. The curve  52  indicates temporal changes in the signal value of a blood flow in a blood vessel having a tighter stenosis. The curve  53  indicates temporal changes in the signal value of a blood flow in a blood vessel in an occluded/infarct state. The curve  54  indicates temporal changes in the signal value of a blood flow in a blood vessel that has been revascularized/treated. 
     In this situation, as for the peak flow time at which the signal value of a blood flow exhibits a maximum value, it is observed in comparison with a peak flow time  55  of the signal value of the blood flow in the normal blood vessel, the peak flow time of the curve  51  indicating the signal value of the blood flow in the blood vessel in the stenosis/ischemic state has the TI shifted to later and thus has a slower blood flow. Further, the peak flow time of the curve  52  indicating the signal value of the blood flow in the blood flow having a tighter stenosis is further later than the peak flow time of the curve  51 . Conversely, the peak flow time of the curve  54  indicating the signal value of the blood flow in the blood vessel that has been revascularized/treated is shifted in the direction of smaller TI values, compared to the peak flow time  55  of the signal value of the blood flow in the normal blood vessel. As explained herein, the processing circuitry  150  is able to predict the degree of a stenosis or an occlusion of the blood vessel while employing the generating function  136 , by utilizing the notion that the peak flow time of the signal value varies depending on the degree of a stenosis or an occlusion in the blood vessel. In other words, by employing the generating function  136 , the processing circuitry  150  is able to predict the degree of the stenosis or the occlusion in the blood vessel, based on the index acquired based on the data obtained from the first pulse sequence and the second pulse sequence executed by the sequence controlling circuitry  120  at step S 100 . 
     The example was explained above in which, by employing the generating function  136 , the processing circuitry  150  is configured to predict the degree of the stenosis or the occlusion of the blood vessel by using the peak flow time as an index; however, possible embodiments are not limited to this example. In other examples, by employing the generating function  136 , the processing circuitry  150  may predict the degree of a stenosis or an occlusion of the blood vessel by using, as an index, a peak signal value, arterial transit time (ATT)  56 , or a blood flow volume obtained by calculating the area of the part defined by the curve and the horizontal axis (the time axis). For example, a tighter stenosis exhibits a delayed peak flow time, a smaller peak signal value, and longer ATT, the sequence controlling circuitry  120  is able to predict the degree of a stenosis or an occlusion of the blood vessel based on these characteristics. In particular, the magnetic resonance imaging apparatus  100  according to the embodiment is capable of efficiently eliminating the background signal and the MT signal by performing the difference calculating process on the images obtained from the two pulse sequences executed with the application of the spatially non-selective IR pulse. Consequently, by employing the generating function  136 , the sequence controlling circuitry  120  is able to detect even a tight stenosis equal to or smaller than 50% of the diameter of the blood vessel, based on the index. 
     As explained above, the magnetic resonance imaging apparatus according to the first embodiment is able to obtain a perfusion signal in which the MT effect is suppressed. Modification Examples of First Embodiment 
     In the first embodiment, the example was explained in which the sequence controlling circuitry  120  implements the process of minimizing acoustic noise utilizing Ultrashort Echo Time (mUTE); however, possible embodiments are not limited to this example. The sequence controlling circuitry  120  may execute any of various types of 2D and 3D acquisition sequences, such as a Fast Spin Echo (FSE) method, a Fast Asymmetric Spin Echo (FASE) method, balanced Steady State Free Precession (bSSFP), an Ultrashort Echo Time (UTE) method, an Echo Planar Imaging (EPI) method, or the like. 
     Further, for the imaging process, the sequence controlling circuitry  120  may implement electrocardiographic synchronization. 
       FIGS.  6 A,  6 B, and  6 C  illustrate examples thereof. As schematically illustrated in  FIG.  6 A , when the sequence controlling circuitry  120  is configured to implement the electrocardiographic synchronization, the sequence controlling circuitry  120  alternately executes a Tag-ON sequence  1  and a Tag-OFF sequence  2  in synchronization with an electrocardiogram  10 . In this situation,  FIG.  6 B  illustrates an example of the Tag-ON sequence  1 , whereas  FIG.  6 C  illustrates an example of the Tag-OFF sequence  2 . In this situation, as for the processes other than the electrocardiographic synchronization, the sequence controlling circuitry  120  and the processing circuitry  150  perform the same processes as those in the first embodiment. 
     In other words, as illustrated in  FIG.  6 B , the sequence controlling circuitry  120  applies the spatially non-selective pulse  4  when a prescribed time period  11  has elapsed since an R-wave  3  and executes an acquisition sequence  16  when a prescribed time period  12  has elapsed since the application of the spatially non-selective pulse  4 . 
     Further, as illustrated in  FIG.  6 C , the sequence controlling circuitry  120  applies the spatially non-selective pulse  4  and the spatially selective pulse  5  when the prescribed time period  11  has elapsed since an R-wave  3  and executes an acquisition sequence  16  when the prescribed time period  12  has elapsed since the application of the spatially non-selective pulse  4  and the spatially selective pulse  5 . 
     Second Embodiment 
     In a second embodiment, an example will be explained in which, similarly to the first embodiment, the sequence controlling circuitry  120  performs an imaging process while applying the spatially non-selective pulse in both a Tag-ON sequence and a Tag-OFF sequence, but performs prior to a main imaging process, a preliminary scan multiple times for understanding an optimal TI period while varying the TI period. As a result, it is possible to perform the main imaging process by using the TI period that is most appropriate for the purpose of the imaging process. 
     Next, this process will be explained with reference to  FIG.  7   .  FIG.  7    is a flowchart illustrating a processing procedure performed by a magnetic resonance imaging apparatus according to the second embodiment. In  FIG.  7   , duplicate explanations of the parts having the same processes as those in the first embodiment will be omitted. 
     To begin with, at step S 200 , the sequence controlling circuitry  120  executes the first pulse sequence being a Tag-ON pulse sequence and the second pulse sequence being a Tag-OFF pulse sequence, while applying the spatially non-selective IR pulse and varying the TI period, with respect to a plurality of TI periods. 
       FIG.  8    illustrates an example of this process. As illustrated in  FIG.  8   , the sequence controlling circuitry  120  executes: the Tag-ON sequence  1  being the first pulse sequence in which the spatially selective IR pulse  5  and the spatially non-selective IR pulse  4  are applied, and subsequently, a data acquisition  16  is performed when the first TI period has elapsed; and the Tag-OFF sequence  2  being the second pulse sequence in which the spatially non- selective IR pulse  4  is applied without applying the spatially selective IR pulse  5 , and subsequently, a data acquisition  16  is performed when the TI period has elapsed, while varying the TI period, with respect to a plurality of TI periods e.g., TI periods  16   a ,  16   b , and so on. In this situation, for example, the sequence controlling circuitry  120  executes: the Tag-ON sequence  1  being the first pulse sequence in which the spatially selective IR pulse  5  and the spatially non-selective IR pulse  4  are applied, and subsequently, a Cartesian acquisition is performed when the TI period has elapsed, and a radial acquisition is performed after the Cartesian acquisition; and the Tag-OFF sequence  2  being the second pulse sequence in which the spatially non- selective IR pulse is applied without applying the spatially selective IR pulse, and subsequently, a Cartesian acquisition is performed when the TI period has elapsed, and a radial acquisition is performed after the Cartesian acquisition, while varying the TI period, with respect to the plurality of TI periods e.g., the TI periods  16   a ,  16   b , and so on. 
     After that, at step S 210 , by employing the generating function  136 , the processing circuitry  150  calculates, based on data obtained from the first pulse sequence and the second pulse sequence, a TI period or a set of TI periods to be used in a third pulse sequence being a Tag-ON sequence and a fourth pulse sequence being a Tag-OFF sequence that will be executed by the sequence controlling circuitry  120  at step S 220 . In this situation, an example of the pulse sequence executed as the third pulse sequence being the Tag-ON sequence to be executed by the sequence controlling circuitry  120  at step S 220  is the pulse sequence in  FIG.  3 A  explained in the first embodiment. Further, an example of the pulse sequence executed as the fourth pulse sequence being the Tag-OFF sequence to be executed by the sequence controlling circuitry  120  at step S 230  is the pulse sequence in  FIG.  3 B  explained in the first embodiment. 
     As a method for calculating the TI period or the set of TI periods to be used in the third pulse sequence and the fourth pulse sequence, for example, the processing circuitry  150  may receive an input from the user via the input device  134  by employing the controlling function  133 . As another method, by employing the controlling function  133 , the processing circuitry  150  may calculate an index such as a peak signal value, a peak flow time, arterial transit time, a blood flow volume, or the like of the imaged region based on the first pulse sequence and the second pulse sequence, as explained in the first embodiment, so as to further calculate the TI period or the set of TI periods to be used in the third pulse sequence and the fourth pulse sequence based on the calculated index. 
     Subsequently, at step S 220 , the sequence controlling circuitry  120  executes the third pulse sequence being a Tag-ON sequence and the fourth pulse sequence being a Tag-OFF sequence, while applying the spatially non-selective IR pulse, with respect to the TI period or the set of TI periods calculated at step S 210 . In an example, the sequence controlling circuitry  120  executes: the third pulse sequence in which the spatially selective IR pulse and the spatially non-selective pulse are applied, and subsequently, a Cartesian acquisition is performed when the TI period (or the set of TI periods) calculated at step S 210  has elapsed, and a radial acquisition is performed after the Cartesian acquisition; and the fourth pulse sequence in which the spatially non-selective IR pulse is applied without applying the spatially selective IR pulse, and subsequently, a Cartesian acquisition is performed when the TI period (or the set of TI periods) has elapsed, and a radial acquisition is performed after the Cartesian acquisition. 
     After that, at step S 230 , by employing the generating function  136 , the processing circuitry  150  generates a magnetic resonance imaging image of the imaged region based on data obtained from the third pulse sequence and the fourth pulse sequence. 
     The process at step S 220  and the process at step S 230  are the same as the processes in the first embodiment. Accordingly, duplicate explanations thereof will be omitted. 
     Similarly to the first embodiment, by applying the spatially non-selective pulse at step S 220 , the magnetic resonance imaging apparatus  100  according to the embodiment is able to suppress the MT effect. It is therefore possible to use, as the imaged region, a region other than the heart such as a region in the brain, a muscle, or a kidney, a region including microvascularization, a region including microcirculation, or the like. Further, similarly to the first embodiment, by employing the generating function  136 , the processing circuitry  150  is able to calculate the peak signal value, the peak flow time, the arterial transit time, the blood flow volume, or the like of the imaged region as the index, based on the data obtained from the third pulse sequence and the fourth pulse sequence. It is therefore possible to predict the degree of a stenosis or an occlusion of the blood vessel, an abnormality in a perforator branch, or the like based on the calculated index. 
     Other Embodiments 
     Possible embodiments are not limited to the above examples. 
     The magnetic resonance imaging apparatus  100  according to an embodiment may, for example, predict the degree of a stenosis or an occlusion of a blood vessel or an abnormality in a perforator branch, based on an image of the blood vessel obtained by Magnetic Resonance Angiography (MRA) implemented with a Time of Flight (TOF) method, together with the index of the imaged region explained in the first embodiment such as a peak signal value, a peak flow time, arterial transit time, a blood flow volume, or the like. 
     This example will be explained, with reference to  FIGS.  9 A and  9 B .  FIGS.  9 A and  9 B  illustrate images of Magnetic Resonance Angiography (MRA) using a 3D TOF method.  FIG.  9 A  illustrates a coronal image of the brain, whereas  9 B illustrates an axial image of the brain. In  FIG.  9 A , although a low-signal region  40  of an MRA signal is observed, it may be difficult in some situations, for example, to judge an abnormality in a perforator branch or the like from the MRA data alone, because microvascularization naturally has a low signal. To cope with this situation, for example, it is possible to predict an abnormality in a perforator branch, when a hypoperfusion signal is obtained as the magnetic resonance signal obtained by executing the pulse sequences in the first or the second embodiment on the thalamus  41 , which is a region related to the blood vessels in the low-signal region  40  of the MRA signal. In other words, the magnetic resonance imaging apparatus  100  according to the embodiment is able to predict the degree of a stenosis or an occlusion of the blood vessel or an abnormality in a perforator branch, by performing a comprehensive evaluation using the index calculated by the processing circuitry  150  while employing the generating function  136 , together with the MRA image. In other words, based on a relationship between the position of the parenchyma of the brain and blood vessel information obtained from the MRA image or the like, for example, the magnetic resonance imaging apparatus  100  according to the embodiment is able to identify the position of a blood vessel that affects the normal/abnormal state of the parenchyma of the brain and is thus able to predict the status of progress of a disease or the like, for example. 
     Further, in the first embodiment, the 4D imaging method is not limited to performing a 3D acquisition while varying the TI value and may be a 3D Cine acquisition, for example. Computer Programs 
     The instructions in the processing procedure described in the above embodiments may be executed based on a computer program (hereinafter “program”) realized with software. As a result of a general-use computer storing therein the program in advance and reading the program, it is possible to achieve the same advantageous effects as those achieved by the magnetic resonance imaging apparatus  100  according to any of the above embodiments. The instructions described in the above embodiments may be recorded as a computer-executable program on a magnetic disk (e.g., a flexible disk or a hard disk), an optical disk (e.g., a Compact Disk Read-Only Memory [CD-ROM], a CD Recordable [CD-R], a CD ReWritable [CD-RW], a Digital Versatile Disk Read-Only Memory [DVD-ROM], a DVD Recordable [DVD±R], DVD ReWritable [DVD±RW]), a semiconductor memory, or a similar recording medium. Any storage format may be used as long as the storage medium is readable by a computer or an embedded system. By reading the program from the recording medium and causing a CPU to execute the instructions written in the program based on the read program, the computer is able to realize the same operations as those performed by the magnetic resonance imaging apparatus  100  according to any of the above embodiments. Further, when the computer obtains or reads the programs, the program may be obtained or read via a network. 
     Further, based on the instructions in the program installed in the computer or the embedded system from the storage medium, an Operating System (OS) working in the computer or Middleware such as database management software or a network may execute a part of the processes for realizing any of the above embodiments. Further, the storage medium does not necessarily have to be independent of the computer or the embedded system and may be a storage medium storing therein or temporarily storing therein the program transmitted via a Local Area Network (LAN), the Internet, or the like and downloaded. Further, the storage medium does not necessarily have to be singular. Possible embodiments of the storage medium include the situation where the processes of the above embodiments are executed from two or more media. It is possible to use any configuration for the one or more media. 
     The computer or the embedded system according to the above embodiments is configured to execute the processes in the above embodiments based on the program stored in the one or more storage media and may be configured as a single apparatus such as a personal computer or a microcomputer or as a system in which a plurality of apparatuses is connected together via a network. Further, the “computer” according to the embodiments does not necessarily have to be a personal computer and may be an arithmetic processing device included in an information processing device or a microcomputer. The term “computer” is a generic name for any device or apparatus capable of realizing the functions of the embodiments by using the program. 
     According to at least one aspect of the embodiments described above, it is possible to suppress the MT effect. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.