Magnetic resonance imaging apparatus and magnetic resonance imaging method

Abstract

To improve the image quality.SOLUTION: A magnetic resonance imaging device according to an embodiment comprises a sequence control unit and a generation unit. The sequence control unit executes a first pulse sequence of applying a region selection IR pulse and a region non-selection IR pulse and a second pulse sequence of performing radial collection after applying the region non-selection IR pulse, for a plurality of first TI times. The generation unit calculates a second TI time in a third pulse sequence and a fourth pulse sequence on the basis of data obtained from the first pulse sequence and the second pulse sequence. The sequence control unit executes the third pulse sequence and the fourth pulse sequence. The generation unit generates a magnetic resonance image in an imaging region on the basis of data obtained from the third pulse sequence and the fourth pulse sequence.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments disclosed in this specification and the drawings relate to a magnetic resonance imaging apparatus and a magnetic resonance imaging method. [Background technology]

[0002] A perfusion technique that uses an RF pulse to irradiate blood vessels, inverting the spin of the blood, and then using this as an endogenous tracer, the ASL (Arterial Spin Labeling) method, is used to visualize the blood flow dynamics in the capillaries of tissues. Examples of perfusion techniques include the FAIR (flow-sensitive alternating inversion recovery) method, the CASL (Continuous arterial spin Labeling) method, and the pCASL (pulsed-continuous arterial spin labeling) method.

[0003] The FAIR method is essentially a two-dimensional imaging method in which region-selective pulses are applied to ROI slices to perform imaging. Although the FAIR method has the advantage of achieving a high SNR, it has the problem that the perfusion curve does not return to the original baseline when region-selective IR pulses are repeatedly applied.

[0004] In addition, the pCASL method can obtain a high SNR similar to the FAIR method by continuously applying region-selective pulses, but there is a problem that when region-selective IR pulses are repeatedly applied, the perfusion curve does not return to the original baseline, and there is also a problem that the MT (Magnetization Transfer) effect needs to be suppressed.

[0005] Therefore, in perfusion techniques using the ASL method, it is important to know how to suppress the MT effect. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Kim Seng-G, "Quantification of relative cerebral blood flow change by Flow-sensitive Alternating Inversion Recovery (FAIR) technique: application to functional mapping", Magn Reson Med, 1995, Vol. 34, p 293-301 [Non-patent document 2] Robert R Edelman et al., "Qualitative mapping of cerebral blood flow and functional localization with echo-planar MR imaging and signal targeting with alternating frequency", Radiology, 1994, Vol. 192, p 513-520 [Non-patent document 3] Dai W, Garcia D, de Bazelaire C, Alsop DC, "Continuous flow driven inversion for arterial spin labeling using pulsed radiofrequency and gradient fields", Magn Reson Med, 2008, Vol. 60, p1488-1497 Summary of the Invention [Problem to be solved by the invention]

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve image quality. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems. [Means for solving the problem]

[0008] A magnetic resonance imaging apparatus according to an embodiment includes a sequence controller and a generator. The sequence controller executes a first pulse sequence in which a region-selective IR (Inversion Recovery) pulse and a region-non-selective IR pulse are applied, followed by a Cartesian acquisition when a first TI (Inversion Time) has elapsed, and a radial acquisition is performed after the Cartesian acquisition. The sequence controller also executes a second pulse sequence in which the region-non-selective IR pulse is applied without applying the region-selective IR pulse, followed by a Cartesian acquisition when the first TI has elapsed, and a radial acquisition is performed after the Cartesian acquisition, for a plurality of first TIs while varying the first TI. The generator calculates second TIs for third and fourth pulse sequences based on data obtained from the first and second pulse sequences executed by the sequence controller. The sequence controller executes the third pulse sequence in which, after applying the region-selective IR pulse and the region-non-selective IR pulse, the Cartesian acquisition is performed when the second TI has elapsed, and the radial acquisition is performed after the Cartesian acquisition, and the fourth pulse sequence in which, after applying the region-selective IR pulse but not the region-selective IR pulse, the Cartesian acquisition is performed when the second TI has elapsed, and the radial acquisition is performed after the Cartesian acquisition. The generator generates a magnetic resonance image of an imaging region based on data obtained from the third pulse sequence and the fourth pulse sequence. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a magnetic resonance imaging apparatus according to an embodiment. [Figure 2] FIG. 2 is a flowchart showing the procedure of the processing performed by the magnetic resonance imaging apparatus according to the first embodiment. [Figure 3A]FIG. 3A is a diagram illustrating a pulse sequence executed by the magnetic resonance imaging apparatus according to the first embodiment. [Figure 3B] FIG. 3B is a diagram illustrating a pulse sequence executed by the magnetic resonance imaging apparatus according to the first embodiment. [Figure 3C] FIG. 3C is a diagram illustrating an application region of an RF (Radio Frequency) pulse applied by the magnetic resonance imaging apparatus according to the first embodiment. [Figure 3D] FIG. 3D is a diagram illustrating a change in longitudinal magnetization due to an RF pulse applied by the magnetic resonance imaging apparatus according to the first embodiment. [Figure 3E] FIG. 3E is a diagram illustrating the acquisition of k-space data performed by the magnetic resonance imaging apparatus according to the first embodiment. [Figure 4] FIG. 4 is a diagram illustrating a GUI (Graphical User Interface) related to the magnetic resonance imaging apparatus according to the first embodiment. [Figure 5] FIG. 5 is a diagram illustrating the processing performed by the magnetic resonance imaging apparatus according to the first embodiment. [Figure 6A] FIG. 6A is a diagram illustrating a pulse sequence executed by a magnetic resonance imaging apparatus according to a modification of the first embodiment. [Figure 6B] FIG. 6B is a diagram illustrating a pulse sequence executed by a magnetic resonance imaging apparatus according to a modification of the first embodiment. [Figure 6C] FIG. 6C is a diagram illustrating a pulse sequence executed by a magnetic resonance imaging apparatus according to a modification of the first embodiment. [Figure 7] FIG. 7 is a flowchart showing the procedure of processing performed by the magnetic resonance imaging apparatus according to the second embodiment. [Figure 8] FIG. 8 is a diagram illustrating a pulse sequence executed by the magnetic resonance imaging apparatus according to the second embodiment. [Figure 9A]FIG. 9A is a diagram illustrating processing performed by a magnetic resonance imaging apparatus according to another embodiment. [Figure 9B] FIG. 9B is a diagram illustrating processing performed by a magnetic resonance imaging apparatus according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, common reference numerals are used to designate the same components, and duplicated descriptions will be omitted.

[0011] (First embodiment) FIG. 1 is a block diagram showing a magnetic resonance imaging apparatus 100 according to a first embodiment. As shown in FIG. 1, the magnetic resonance imaging apparatus 100 includes a static magnetic field magnet 101, a static magnetic field power supply (not shown), a gradient magnetic field coil 103, a gradient magnetic field power supply 104, a bed 105, a bed control circuit 106, a transmission coil 107, a transmission circuit 108, a reception coil 109, a reception circuit 110, a sequence control circuit 120 (sequence control unit), and an image processing device 130. Note that the magnetic resonance imaging apparatus 100 does not include a subject P (e.g., a human body). The configuration shown in FIG. 1 is merely an example. For example, the components in the sequence control circuit 120 and the image processing device 130 may be configured as integrated or separated as appropriate.

[0012] The static magnetic field magnet 101 is a magnet formed in a hollow, approximately cylindrical shape, and generates a static magnetic field in the internal space. The static magnetic field magnet 101 is, for example, a superconducting magnet, and is excited by receiving a current from a static magnetic field power supply. The static magnetic field power supply supplies a current to the static magnetic field magnet 101. As another example, the static magnetic field magnet 101 may be a permanent magnet, in which case the magnetic resonance imaging apparatus 100 may not be provided with a static magnetic field power supply. Furthermore, the static magnetic field power supply may be provided separately from the magnetic resonance imaging apparatus 100.

[0013] The gradient magnetic field coil 103 is a hollow, approximately cylindrical coil and is disposed inside the static magnetic field magnet 101. The gradient magnetic field coil 103 is formed by combining three coils corresponding to the mutually orthogonal X, Y, and Z axes, and these three coils are individually supplied with current from a gradient magnetic field power supply 104 to generate gradient magnetic fields whose magnetic field strengths change along the X, Y, and Z axes. The gradient magnetic fields of the X, Y, and Z axes generated by the gradient magnetic field coil 103 are, for example, a slicing gradient magnetic field Gs, a phase encoding gradient magnetic field Ge, and a readout gradient magnetic field Gr. The gradient magnetic field power supply 104 supplies current to the gradient magnetic field coil 103.

[0014] The bed 105 includes a top plate 105a on which the subject P is placed, and under the control of a bed control circuit 106, the top plate 105a is inserted into the cavity (imaging port) of the gradient magnetic field coil 103 with the subject P placed thereon. The bed 105 is usually installed so that its longitudinal direction is parallel to the central axis of the static magnetic field magnet 101. Under the control of the image processing device 130, the bed control circuit 106 drives the bed 105 to move the top plate 105a in the longitudinal direction and the up-down direction.

[0015] The transmitting coil 107 is disposed inside the gradient magnetic field coil 103, and generates a high-frequency magnetic field upon receiving RF pulses from a transmitting circuit 108. The transmitting circuit 108 supplies the transmitting coil 107 with RF pulses corresponding to a Larmor frequency determined by the type of atom of interest and the magnetic field strength.

[0016] The receiving coil 109 is disposed inside the gradient magnetic field coil 103, and receives magnetic resonance signals (hereinafter referred to as "MR signals" as necessary) emitted from the subject P due to the influence of the high frequency magnetic field. Upon receiving the magnetic resonance signals, the receiving coil 109 outputs the received magnetic resonance signals to the receiving circuit 110.

[0017] The above-described transmitting coil 107 and receiving coil 109 are merely examples. They may be configured by combining one or more of a coil having only a transmitting function, a coil having only a receiving function, or a coil having a transmitting and receiving function.

[0018] The receiving circuit 110 detects the magnetic resonance signal output from the receiving coil 109 and generates magnetic resonance data based on the detected magnetic resonance signal. Specifically, the receiving circuit 110 generates the magnetic resonance data by digitally converting the magnetic resonance signal output from the receiving coil 109. The receiving circuit 110 also transmits the generated magnetic resonance data to the sequence control circuit 120. The receiving circuit 110 may be provided on the gantry side including the static magnetic field magnet 101, the gradient magnetic field coil 103, etc.

[0019] The sequence control circuit 120 drives the gradient magnetic field power supply 104, the transmission circuit 108, and the reception circuit 110 based on sequence information transmitted from the image processing device 130, thereby imaging the subject P. Here, the sequence information is information that defines a procedure for performing imaging. The sequence information defines the strength of the current that the gradient magnetic field power supply 104 supplies to the gradient magnetic field coil 103 and the timing of supplying the current, the strength of the RF pulse that the transmission circuit 108 supplies to the transmission coil 107 and the timing of applying the RF pulse, and the timing of detecting a magnetic resonance signal by the reception circuit 110. For example, the sequence control circuit 120 is an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), or an electronic circuit such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). Details of the pulse sequence executed by the sequence control circuit 120 will be described later.

[0020] Furthermore, when the sequence control circuit 120 receives magnetic resonance data from the receiving circuit 110 as a result of driving the gradient magnetic field power supply 104, the transmitting circuit 108, and the receiving circuit 110 to image the subject P, the sequence control circuit 120 transfers the received magnetic resonance data to the image processing device 130.

[0021] The image processing device 130 performs overall control of the magnetic resonance imaging apparatus 100 and generates images. The image processing device 130 includes a memory 132, an input device 134, a display 135, and a processing circuit 150. The processing circuit 150 includes an interface function 131, a control function 133, and a generation function 136.

[0022] In the first embodiment, the processing functions performed by the interface function 131, the control function 133, and the generation function 136 are stored in the memory 132 in the form of computer-executable programs. The processing circuit 150 is a processor that reads and executes the programs from the memory 132 to realize the functions corresponding to the programs. In other words, the processing circuit 150, after reading the programs, has the functions shown in the processing circuit 150 in FIG. 1 . Note that FIG. 1 illustrates the processing functions performed by the interface function 131, the control function 133, and the generation function 136 being realized by a single processing circuit 150. However, the processing circuit 150 may be configured by combining multiple independent processors, and each processor may execute a program to realize the function. In other words, each of the above functions may be configured as a program, and a single processing circuit 150 may execute each program. As another example, a specific function may be implemented in a dedicated, independent program execution circuit. Note that in FIG. 1, the interface function 131, the control function 133, and the generation function 136 are examples of a reception unit, a control unit, and a generation unit, respectively. The sequence control circuit 120 is an example of a sequence control unit.

[0023] The term "processor" used in the above description refers to circuits such as a CPU (Central Processing Unit), a GPU (Graphical Processing Unit), an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). The processor realizes its functions by reading and executing programs stored in memory 132.

[0024] Furthermore, instead of storing the program in the memory 132, the program may be directly embedded in the processor circuitry. In this case, the processor performs its functions by reading and executing the program embedded in the circuitry. The bed control circuitry 106, the transmission circuitry 108, the reception circuitry 110, etc. are also similarly configured using electronic circuits such as the processor.

[0025] The processing circuitry 150 transmits sequence information to the sequence control circuitry 120 via the interface function 131, and receives magnetic resonance data from the sequence control circuitry 120. Furthermore, upon receiving the magnetic resonance data, the processing circuitry 150 having the interface function 131 stores the received magnetic resonance data in the memory 132.

[0026] The magnetic resonance data stored in the memory 132 is arranged in k-space by the control function 133. As a result, the memory 132 stores the k-space data.

[0027] The memory 132 stores magnetic resonance data received by the processing circuitry 150 having the interface function 131, k-space data arranged in k-space by the processing circuitry 150 having the control function 133, image data generated by the processing circuitry 150 having the generation function 136, etc. For example, the memory 132 is a semiconductor memory element such as a RAM (Random Access Memory), a flash memory, a hard disk, an optical disk, etc.

[0028] The input device 134 accepts various instructions and information input from an operator. The input device 134 is, for example, a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard. The display 135, under the control of the processing circuit 150 having the control function 133, displays a GUI (Graphical User Interface) for accepting input of imaging conditions, an image generated by the processing circuit 150 having the generation function 136, and the like. The display 135 is, for example, a display device such as a liquid crystal display.

[0029] The processing circuitry 150 performs overall control of the magnetic resonance imaging apparatus 100 using the control function 133, and controls imaging, image generation, image display, etc. For example, the processing circuitry 150 having the control function 133 accepts input of imaging conditions (imaging parameters, etc.) on a GUI and generates sequence information according to the accepted imaging conditions. In addition, the processing circuitry 150 having the control function 133 transmits the generated sequence information to the sequence control circuit 120.

[0030] The processing circuitry 150 uses the generation function 136 to read out the k-space data from the memory 132 and perform reconstruction processing such as Fourier transform on the read out k-space data to generate an image.

[0031] Next, the background of the embodiment will be briefly described.

[0032] A perfusion technique that uses an RF pulse to irradiate blood vessels, inverting the spin of the blood, and then using this as an endogenous tracer, the ASL (Arterial Spin Labeling) method, is used to visualize the blood flow dynamics in the capillaries of tissues. Examples of perfusion techniques include the FAIR (flow-sensitive alternating inversion recovery) method, the CASL (Continuous arterial spin Labeling) method, and the pCASL (pulsed-continuous arterial spin labeling) method.

[0033] The FAIR method is essentially a two-dimensional imaging method in which region-selective pulses are applied to ROI slices to perform imaging. Although the FAIR method has the advantage of achieving a high SNR, it has the problem that the perfusion curve does not return to the original baseline when region-selective IR pulses are repeatedly applied.

[0034] In addition, the pCASL method can obtain a high SNR similar to the FAIR method by continuously applying region-selective pulses, but there is a problem that when region-selective IR pulses are repeatedly applied, the perfusion curve does not return to the original baseline, and there is also a problem that the MT (Magnetization Transfer) effect needs to be suppressed.

[0035] Therefore, in perfusion techniques using the ASL method, it is important to know how to suppress the MT effect.

[0036] Here, the application of non-region-selective IR pulses in the ASL method has not been mainstream because the non-region-selective IR pulses tend to reduce the signal-to-noise ratio of the image. However, we found that the application of non-region-selective IR pulses significantly suppresses the MT effect. This is partly because the MT effect is large for magnetization in which the spins are aligned in the direction of the magnetic field (+Mz), but is small for longitudinal magnetization in the opposite direction (-Mz).

[0037] Therefore, the magnetic resonance imaging apparatus 100 according to the embodiment executes two pulse sequences, one of which applies a non-region-selective pulse and then executes an acquisition sequence, and the other of which applies a non-region-selective pulse and a region-selective pulse and then executes an acquisition sequence, and generates a magnetic resonance image by subtracting data obtained by the two pulse sequences. Here, the sequence control circuit 120, as an example, executes Cartesian acquisition followed by radial acquisition as an acquisition sequence.

[0038] This allows the MT effect to be suppressed, enabling the application of ASL to areas other than the heart, which has previously been considered difficult, such as areas of the brain, muscle, or kidney, areas containing microvasculature, and areas containing microcirculation, to be subjected to 4D non-contrast ASL imaging.

[0039] Additionally, preliminary imaging can be performed for multiple TIs and the optimum TI can be determined based on the results, thereby improving the throughput of the inspection.

[0040] In addition, it is expected that combining 4D non-contrast ASL imaging with MRA will enable more accurate prediction of vascular stenosis and blockage.

[0041] This configuration will be described with reference to FIGS.

[0042] FIG. 2 is a flowchart illustrating the flow of processing performed by the magnetic resonance imaging apparatus according to the first embodiment.

[0043] First, in step S100, the sequence control circuit 120 executes a first pulse sequence in which a region-selective IR pulse and a region-non-selective IR pulse are applied, followed by radial collection, and a second pulse sequence in which a region-non-selective IR pulse is applied without applying the region-selective IR pulse, followed by radial collection.

[0044] Such a configuration will be described with reference to FIGS. 3A to 3E.

[0045] Figure 3A shows a first pulse sequence in which radial acquisition is performed after applying a region-selective IR pulse and a non-region-selective IR pulse, and Figure 3B shows a second pulse sequence in which radial acquisition is performed without applying a region-selective IR pulse. The first pulse sequence in which radial acquisition is performed after applying a region-selective IR pulse and a non-region-selective IR pulse is also called the Tag-On sequence, and the second pulse sequence in which radial acquisition is performed without applying a region-selective IR pulse is also called the Tag-Off sequence.

[0046] 3A and 3B, the case where the acquisition sequence executed by the sequence control circuit 120 in step S100 is mUTE (minimizing acoustic noise utilizing UTE) will be described. Normally, the sequence control circuit 120 links the Tag-ON sequence in FIG. 3A and the Tag-OFF sequence in FIG. 3B and executes them as one set of acquisition.

[0047] As shown in FIG. 3A, in the first pulse sequence, the sequence control circuit 120 applies a non-region-selective IR pulse 4, which is an RF pulse that inverts nuclear spins in a wide region, to a wide region including the imaging region, and then applies a region-selective IR pulse 5, which is an RF pulse that inverts nuclear spins in a specific region, to a narrower region than the application region of the non-region-selective IR pulse 4. After a predetermined time has elapsed, the sequence control circuit 120 then executes an acquisition sequence to acquire data and performs magnetic resonance imaging of the imaging region.

[0048] First, referring to FIG. 3C , the application regions of the region-non-selective IR pulse 4 and the region-selective IR pulse 5 will be described. Here, region 8 is the imaging region, i.e., the region to be imaged, and is the region from which data is collected in the acquisition sequence executed by the sequence control circuit 120 after application of the region-non-selective IR pulse 4 and the region-selective IR pulse 5. Region 6 is the region to which the sequence control circuit 120 applies the region-non-selective IR pulse. The sequence control circuit 120 applies the region-non-selective IR pulse 4 to a wide region 6 that includes region 8, which is the imaging region. Region 7 is the region to which the sequence control circuit 120 applies the region-selective IR pulse 5. The sequence control circuit 120 applies the region-selective IR pulse 5 to region 7, which is a relatively narrow region. Region 7 to which the sequence control circuit 120 applies the region-selective IR pulse 5 is selected, for example, upstream of region 8, which is the imaging region. In other words, blood that is in region 7 when the region-selective IR pulse 5 is applied and that is present in region 8 when the acquisition sequence is executed is labeled.

[0049] Next, a change in the longitudinal magnetization of spins due to application of the region non-selective IR pulse 4 and the region selective IR pulse 5 will be described with reference to Fig. 3D. Fig. 3D is a diagram illustrating the change over time in the longitudinal magnetization of spins.

[0050] Graph 14 shows the change over time in the longitudinal magnetization of spins at a location where both the region non-selective IR pulse 4 and the region selective IR pulse 5 are applied, and graph 13 shows the change over time in the longitudinal magnetization of spins at a location where only the region non-selective IR pulse 4 is applied and no region selective IR pulse 5 is applied.

[0051] Both the region-nonselective IR pulse 4 and the region-selective IR pulse 5 invert the longitudinal magnetization at the location where the RF pulse is applied. Therefore, at the location where both the region-nonselective IR pulse 4 and the region-selective IR pulse 5 are applied, i.e., the location where labeling is performed, the longitudinal magnetization is inverted twice, as shown in graph 14, and the longitudinal magnetization returns to its original value, resulting in a high signal.

[0052] On the other hand, in areas where only the region-non-selective IR pulse 4 is applied and the region-selective IR pulse 5 is not applied, i.e., areas such as the background, the RF pulse inverts the longitudinal magnetization signal only once, and the signal gradually relaxes, as shown in graph 13. Here, at the null point 15, the value of the longitudinal magnetization becomes 0. Therefore, by having the sequence control circuit 120 execute an acquisition sequence near the null point 15, blood labeled by the region-selective IR pulse 5 becomes a high signal, enabling imaging with suppressed background signals. This is the purpose of the sequence control circuit 120 applying the region-non-selective IR pulse 4 and the region-selective pulse 5.

[0053] Next, returning to FIG. 3A , the acquisition sequence executed by the sequence control circuit 120 will be described. In the first embodiment, the sequence control circuit 120 performs 4D acquisition. Here, 4D acquisition means that k-space is acquired in 3D and acquired in a total of four dimensions while changing the TI time. That is, the sequence control circuit 120 acquires data for multiple TI times while varying the TI time, which is the time after the region non-selective pulse 4 or the region selective pulse 5 is applied. Here, the sequence control circuit 120 performs data acquisition using, for example, a mUTE sequence as an acquisition sequence. That is, in the first embodiment, the acquisition sequence executed by the sequence control circuit 120 consists of acquisition in multiple Cartesian segments consisting of Cartesian acquisitions 15a, 15b, 15c, 15d, 15e, 15f, etc., performed in the central part of the space, and radial acquisition 16 performed in the outer part of the k-space. That is, after applying the region non-selective IR pulse 4 and the region selective IR pulse 5, the sequence control circuit 120 performs Cartesian collection 15a after time 16a has passed, performs Cartesian collection 15b after time 16b has passed, performs Cartesian collection 15c after time 16c has passed, performs Cartesian collection 15d after time 16d has passed, ... performs Cartesian collections 15e and 15f, and then performs radial collection 16.

[0054] FIG. 3E illustrates the relationship between Cartesian acquisition and radial acquisition performed by the sequence control circuit 120. FIG. 3E is a three-dimensional diagram illustrating the region of k-space where data acquisition is performed. Region 60 represents the central portion of k-space where Cartesian acquisition is performed, and each line segment, such as line segment 61, represents a radial acquisition performed by the sequence control circuit 120. In other words, in the acquisition sequence to be performed, the sequence control circuit 120 first performs Cartesian acquisitions 15a, 15b, 15c, 15d, 15e, 15f, etc., for region 60 in the central portion of k-space while changing the TI, and then performs radial acquisition 16 for a region outside region 60 in the central portion of k-space, e.g., from the center of k-space toward the outside. In this manner, the sequence control circuit 120 executes the first pulse sequence.

[0055] In step S110 described later, the processing circuit 150 uses the generation function 136 to generate data relating to TI=TI1, which is the TI corresponding to time 16a, for example, using the collection obtained by Cartesian collection 15a and the radial collection 16, generates data relating to TI=TI2, which is the TI corresponding to time 16b, using the collection obtained by Cartesian collection 15b and the radial collection 16, and generates data relating to TI=TI3, which is the TI corresponding to time 16c, using the collection obtained by Cartesian collection 15c and the radial collection 16.

[0056] 3B, in the second pulse sequence, the sequence control circuit 120 applies only the region-non-selective IR pulse 4, then does not apply the region-selective IR pulse 5, and then performs Cartesian acquisition 15a after time 16a has passed, performs Cartesian acquisition 15b after time 16b has passed, performs Cartesian acquisition 15c after time 16c has passed, performs Cartesian acquisition 15d after time 16d has passed, ... performs Cartesian acquisitions 15e and 15f, and then performs radial acquisition 16. The only difference between the first and second pulse sequences is whether or not the region-selective pulse 5 is applied, and the other processing is the same.

[0057] 3A and 3B, TI1, TI2, TI3, TI4, etc., which are the times from when the region non-selective pulse 4 or the region selective pulse 5 is executed until when the Cartesian acquisition 15a, 15b, 15c, 15d, 15e, 15f, etc. is executed, can be made variable and can be freely set according to the user's request. An example of the GUI according to FIG. 4 is shown.

[0058] The processing circuit 150 accepts, via the control function 133, a change in the input of TI1, i.e., the time 16a in FIGS. 3A and 3B, via buttons 21 and 22 on the input panel 20 of the display 135, through the input device 134. The processing circuit 150 also accepts, via the control function 133, a change in the input of the increment of TI, for example, the increment from TI1 to TI2 in FIGS. 3A and 3B, through buttons 23 and 24 on the input panel 20 of the display 135. The processing circuit 150 also accepts, via the control function 133, a change in the number of Cartesian acquisition segments via buttons 25 and 26 on the input panel 20 of the display 135. Here, the number of Cartesian acquisition segments refers to the number of Cartesian acquisition segments with different TIs, and in the case of FIGS. 3A and 3B, the number of Cartesian acquisition segments is six. Furthermore, the processing circuit 150 accepts a change in the Cartesian collection interval via the input device 134 and buttons 27 and 28 on the input panel 20 of the display 135 using the control function 133. Here, the Cartesian collection interval refers to the interval between Cartesian collections performed by the sequence control circuit 120, and the interval 17 in FIG. 3B is the Cartesian collection interval.

[0059] Subsequently, in step S120, 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 control circuitry 120 in step S100, using the generation function 136. Specifically, the processing circuitry 150 generates a first image (Tag-ON image) by using the generation function 136 to Fourier transform the first k-space data obtained by executing the first pulse sequence, which is a Tag-ON sequence.

[0060] For example, the processing circuitry 150 generates data relating to TI=TI1 based on data acquired by Cartesian acquisition 15a in FIG. 3A and data acquired by radial acquisition 16, using the generation function 136. Similarly, the processing circuitry 150 generates data relating to TI=TI2 based on data acquired by Cartesian acquisition 15b in FIG. 3A and data acquired by radial acquisition 16, using the generation function 136. Furthermore, the processing circuitry 150 generates data relating to TI=TI3 based on data acquired by Cartesian acquisition 15c in FIG. 3A and data acquired by radial acquisition 16, using the generation function 136. In this manner, the processing circuitry 150 generates data relating to multiple TIs based on data acquired by execution of the first pulse sequence.

[0061] Furthermore, the processing circuitry 150 generates a second image (Tag-OFF image) by Fourier transforming the second k-space data obtained by executing the second pulse sequence, which is the Tag-OFF sequence, using the generation function 136. Subsequently, the processing circuitry 150 performs differential processing between the first image (Tag-ON image) and the second image (Tag-OFF image) to generate a magnetic resonance image in which background signals and the MT effect are suppressed.

[0062] For example, the processing circuitry 150 generates data having a TI of TI1 based on data acquired by Cartesian acquisition 15a in FIG. 3B and data acquired by radial acquisition 16, using the generation function 136. Similarly, the processing circuitry 150 generates data having a TI of TI2 based on data acquired by Cartesian acquisition 15b in FIG. 3B and data acquired by radial acquisition 16, using the generation function 136. Furthermore, the processing circuitry 150 generates data having a TI of TI3 based on data acquired by Cartesian acquisition 15c in FIG. 3B and data acquired by radial acquisition 16, using the generation function 136. In this manner, the processing circuitry 150 generates data having a plurality of TIs based on data acquired by execution of the first pulse sequence.

[0063] In this way, the magnetic resonance imaging apparatus 100 according to the first embodiment applies a region-non-selective IR pulse to execute a 4D ASL sequence. This makes it possible to suppress the MT effect and apply ASL to regions other than the heart, which has been considered difficult in the past. For example, it has become possible to perform imaging of regions of the brain, muscle, or kidney, regions including microvascular regions, and regions including microcirculation regions as imaging regions.

[0064] 3A and 3B, the radial collection 16 is performed after the Cartesian collections 15a to 15f, but the embodiment is not limited to this, and the radial collection 16 may be performed before the Cartesian collections 15a to 15f. In other words, the radial collection 16 may be performed before the application of the ASL pulse.

[0065] Furthermore, the processing circuitry 150 can further analyze the magnetic resonance image generated in step S110 to distinguish between normal blood flow and stenosis, ischemic, occlusion, infarct, or revascularized / treated blood vessels.

[0066] As an example, the processing circuit 150 uses the generation function 136 to calculate at least one of the peak signal value, peak flow time, arterial transit time, and blood flow volume in the imaging area as an index based on the data obtained from the first pulse sequence and the second pulse sequence executed by the sequence control circuit 120 in step S100, and performs analysis based on this.

[0067] An example of such analysis is shown in Figure 5. Figure 5 shows the time variation of signal values ​​in a given imaging region after subtraction processing between a first image and a second image for various vascular conditions. Specifically, curve 50 shows the time variation of signal values ​​of normal blood flow, curve 51 shows the time variation of signal values ​​of blood flow in a blood vessel in a stenotic / ischemic state, curve 52 shows the time variation of signal values ​​of blood flow in a blood vessel in a tighter stenosis, curve 53 shows the time variation of signal values ​​of blood flow in a blood vessel in an occluded / infarcted state, and curve 54 shows the time variation of signal values ​​of blood flow in a revascularized / treated blood vessel.

[0068] Considering the peak flow time, which is the time when the signal value of blood flow reaches its maximum value, it can be seen that the peak flow time of curve 51, which represents the signal value of blood flow in a stenotic / ischemic blood vessel, is later in TI compared to peak flow time 55, which represents the signal value of blood flow in a normal blood vessel, and therefore the blood flow is slower. Furthermore, the peak flow time of curve 52, which represents the signal value of blood flow in a narrow stenotic blood vessel, is even later than the peak flow time of curve 51. Conversely, the peak flow time of curve 54, which represents the signal value of blood flow in a revascularized / treated blood vessel, is shifted toward a smaller TI compared to peak flow time 55, which represents the signal value of blood flow in a normal blood vessel. By utilizing this difference in the peak flow time of the signal value depending on the degree of stenosis or occlusion of the blood vessel, processing circuit 150 can predict the degree of stenosis or occlusion of the blood vessel using generation function 136. That is, the processing circuit 150 can predict the degree of stenosis or occlusion of blood vessels based on the index obtained based on the data obtained from the first pulse sequence and the second pulse sequence executed by the sequence control circuit 120 in step S100 using the generation function 136.

[0069] In the above example, the processing circuitry 150 predicts the degree of stenosis or occlusion of a blood vessel using the peak flow time as an index by the generation function 136. However, the embodiment is not limited to this. As an example, the processing circuitry 150 may predict the degree of stenosis or occlusion of a blood vessel using the peak signal value, the arterial transit time (ATT) 56, and the blood flow volume calculated by determining the area enclosed by the curve and the horizontal axis (time axis) as indexes by the generation function 136. For example, since a narrow stenosis is characterized by a delayed peak flow time, a small peak signal value, and a large ATT, the sequence control circuit 120 can predict the degree of stenosis or occlusion of a blood vessel based on these characteristics. In particular, in the magnetic resonance imaging apparatus 100 according to the embodiment, it is possible to efficiently remove background signals and MT signals by performing differential processing on images obtained from two pulse sequences executed with the application of non-region-selective IR pulses, and therefore the sequence control circuit 120 can detect even a narrow stenosis, for example, a stenosis of 50% or less of the blood vessel diameter, based on the index using the generation function 136.

[0070] As described above, the magnetic resonance imaging apparatus according to the first embodiment can obtain perfusion signals in which the MT effect is suppressed.

[0071] (Modification of the first embodiment) In the first embodiment, the sequence control circuit 120 executes mUTE (minimizing acoustic noise utilizing UTE (ultrashort echo)). However, the embodiment is not limited to this, and the sequence control circuit 120 may execute various 2D or 3D acquisition sequences such as FSE (Fast Spin Echo) method, FASE (Fast Asymmetric Spin Echo) method, bSSFP (balanced Steady State Free Precession), UTE (Ultrashort Echo) method, and EPI (Echo Planar Imaging) method.

[0072] Furthermore, the sequence control circuit 120 may perform electrocardiographic synchronization when taking an image.

[0073] Such examples are shown in Figures 6A, 6B, and 6C. As schematically shown in Figure 6A, when the sequence control circuit 120 performs ECG synchronization, the sequence control circuit 120 alternately executes Tag-ON sequence 1 and Tag-OFF sequence 2 in synchronization with an electrocardiogram 10. Here, Figure 6B is an example of TAG-ON sequence 1, and Figure 6C is an example of TAG-OFF sequence 2. Here, with respect to processing other than ECG synchronization, the sequence control circuit 120 and the processing circuit 150 perform processing similar to that of the first embodiment.

[0074] That is, as shown in FIG. 6B, the sequence control circuit 120 applies a region non-selective pulse 4 at a time when a predetermined time 11 has elapsed since the R wave 3, and then executes an acquisition sequence 16 after a predetermined time 12 has elapsed since the application of the region non-selective pulse 4.

[0075] Also, as shown in FIG. 6C, the sequence control circuit 120 applies a region non-selective pulse 4 and a region selective pulse 5 at a time when a predetermined time 11 has elapsed since the R wave 3, and then executes an acquisition sequence 16 after a predetermined time 12 has elapsed since the application of the region non-selective pulse 4 and the region selective pulse 5.

[0076] (Second embodiment) In the second embodiment, as in the first embodiment, imaging is performed while the sequence control circuit 120 applies region non-selective pulses to both the Tag-ON sequence and the Tag-OFF sequence, but an example will be described in which, before the actual imaging, a preparatory scan is performed multiple times with different TI times to determine an appropriate TI time. This makes it possible to perform the actual imaging with the TI time that is most suitable for the purpose of imaging.

[0077] This processing will be described with reference to Fig. 7. Fig. 7 is a flowchart showing the procedure of processing performed by the magnetic resonance imaging apparatus according to the second embodiment. Note that in Fig. 7, repeated description of the parts performing the same processing as in the first embodiment will be omitted.

[0078] First, in step S200, the sequence control circuit 120 executes a first pulse sequence, which is a Tag-ON pulse sequence, and a second pulse sequence, which is a Tag-OFF pulse sequence, for a plurality of TI times while applying a region-non-selective IR pulse and changing the TI time.

[0079] Such an example is shown in Fig. 8. As shown in Fig. 8, the sequence control circuit 120 executes a Tag-ON sequence 1, which is a first pulse sequence that applies a region-selective IR pulse 5 and a region-non-selective IR pulse 4, and then performs data acquisition 16 when a first TI has elapsed, and a Tag-OFF sequence 2, which is a second pulse sequence that applies a region-non-selective IR pulse 4 without applying the region-selective IR pulse 5, and then performs data acquisition 16 when the TI has elapsed, for a plurality of TIs, for example, TIs 16a, 16b, etc., while changing the TI. Here, the sequence control circuit 120 executes, for example, a Tag-ON pulse sequence 1, which is a first pulse sequence that applies a region-selective IR pulse 5 and a region-non-selective IR pulse 4, then performs Cartesian collection when TI has elapsed, and then performs radial collection after the Cartesian collection, and a Tag-OFF sequence 2, which is a second pulse sequence that applies a region-non-selective IR pulse without applying a region-selective IR pulse, then performs Cartesian collection when TI has elapsed, and then performs radial collection after the Cartesian collection, for a plurality of TI times, for example, TI times 16a, 16b, etc., while changing the TI time.

[0080] Next, in step S210, the processing circuitry 150 uses the generation function 136 to calculate, based on data obtained from the first pulse sequence and the second pulse sequence, a TI time or a set of TI times for a third pulse sequence that is a Tag-ON sequence and a fourth pulse sequence that is a Tag-OFF sequence executed by the sequence control circuit 120 in step S220. Here, an example of the pulse sequence executed as the third pulse sequence that is a Tag-ON sequence executed by the sequence control circuit 120 in step S220 is, for example, the pulse sequence of FIG. 3A described in the first embodiment. Also, an example of the pulse sequence executed as the fourth pulse sequence that is a Tag-OFF sequence executed by the sequence control circuit 120 in step S230 is, for example, the pulse sequence of FIG. 3B described in the first embodiment.

[0081] As a method of calculating the TI or a set of TI in the third pulse sequence and the fourth pulse sequence, for example, the processing circuitry 150 may use the control function 133 to receive an input from a user via the input device 134. As another example, the processing circuitry 150 may use the control function 133 to calculate indices such as a peak signal value in the imaging region, a peak flow time, an arterial transit time, and a blood flow volume based on the first pulse sequence and the second pulse sequence, as described in the first embodiment, and calculate the TI or a set of TI in the third pulse sequence and the fourth pulse sequence based on the calculated indices.

[0082] Subsequently, in step S220, the sequence control circuit 120 executes a third pulse sequence which is a Tag-ON sequence and a fourth pulse sequence which is a Tag-OFF sequence for the TI time or the set of TI times calculated in step S210 while applying a non-region-selective IR pulse. As an example, the sequence control circuit 120 executes the third pulse sequence in which, after applying a region-selective IR pulse and a non-region-selective pulse, Cartesian acquisition is performed when the TI time (or the set of TI times) calculated in step S210 has elapsed, and radial acquisition is performed after the Cartesian acquisition, and the fourth pulse sequence in which, after applying a non-region-selective IR pulse without applying a region-selective IR pulse, Cartesian acquisition is performed when the TI time (or the set of TI times) has elapsed, and radial acquisition is performed after the Cartesian acquisition.

[0083] Subsequently, in step 230, processing circuitry 150 generates, via generation function 136, a magnetic resonance imaging image of the imaging region based on data obtained from the third and fourth pulse sequences.

[0084] The processing in steps S220 and S230 is the same as in the first embodiment, and therefore a repeated description will be omitted.

[0085] As in the first embodiment, the magnetic resonance imaging apparatus 100 according to the embodiment applies a non-region-selective pulse in step S220, thereby suppressing the MT effect, and therefore the imaging region can be a region other than the heart, such as a brain, muscle, or kidney region, a region including microvessels, a region including microcirculation, etc. Also, as in the first embodiment, the processing circuitry 150 can calculate, using the generation function 136, indices such as a peak signal value, peak flow time, arterial transit time, and blood flow volume in the imaging region based on data obtained from the third pulse sequence and the fourth pulse sequence, and can predict the degree of vascular stenosis or occlusion, perforator artery abnormalities, etc. based on the calculated indices.

[0086] (Other embodiments) The magnetic resonance imaging apparatus 100 according to the embodiment may predict the degree of stenosis or occlusion of a blood vessel or an abnormality in a perforating branch based on, for example, an image of a blood vessel obtained by MRA (Magnetic Resonance Angiography) imaged by a TOF (Time Of Flight) method and the indices such as a peak signal value in an imaging region, a peak flow time, an arterial transit time, and a blood flow volume described in the first embodiment.

[0087] Such an example will be described using FIGS. 9A and 9B. FIGS. 9A and 9B are magnetic resonance angiography (MRA) images obtained using the 3D TOF method. FIG. 9A is a coronal image of the brain, and FIG. 9B is an axial image of the brain. In FIG. 9A, a low-signal-intensity region 40 in the MRA signal is observed. However, because microvessels inherently have low signal intensity, it may be difficult to determine, for example, perforating artery abnormalities using MRA data alone. However, for example, if a magnetic resonance signal obtained by executing the pulse sequence according to the first or second embodiment in the thalamus 41, which is a region associated with the blood vessels in the low-signal-intensity region 40 in the MRA signal, is a hypoperfusion signal, it is possible to predict perforating artery abnormalities. That is, the magnetic resonance imaging apparatus 100 according to the embodiment can predict the degree of vascular stenosis or occlusion and perforating artery abnormalities by integrating the indices calculated by the generation function 136 of the processing circuitry 150 with the MRA image and making a comprehensive judgment. In other words, the magnetic resonance imaging apparatus 100 according to the embodiment can identify the location of blood vessels that affect the normality / abnormality of the brain parenchyma, for example, based on the relationship between the location of the brain parenchyma and vascular information obtained from MRA images, etc., and can predict, for example, the progression of a disease.

[0088] Furthermore, in the first embodiment, the 4D imaging method is not limited to the case where 3D acquisition is performed while changing the TI, and may be, for example, 3D Coine acquisition.

[0089] (program) Furthermore, the instructions shown in the processing procedures described in the above-described embodiments can be executed based on a software program. A general-purpose computer can store this program in advance and, by loading this program, achieve the same effects as those achieved by the magnetic resonance imaging apparatus 100 of the above-described embodiments. The instructions described in the above-described embodiments can be recorded as a computer-executable program on a magnetic disk (e.g., a flexible disk, a hard disk), an optical disk (e.g., a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD±R, a DVD±RW), a semiconductor memory, or a similar recording medium. The storage medium may take any storage format as long as it is readable by a computer or an embedded system. The computer can achieve the same operations as the magnetic resonance imaging apparatus 100 of the above-described embodiments by loading the program from the recording medium and having the CPU execute the instructions described in the program based on the program. Furthermore, the computer may acquire or load the program via a network.

[0090] Furthermore, an operating system (OS), database management software, network middleware, or the like running on a computer based on instructions from a program installed on the computer or embedded system from a storage medium may execute some of the processes for implementing the above-described embodiments. Furthermore, the storage medium is not limited to a medium independent of the computer or embedded system, but also includes a storage medium that stores or temporarily stores a program downloaded via a local area network (LAN), the internet, or the like. Furthermore, the storage medium is not limited to one medium; even when the processes in the above-described embodiments are executed from multiple media, the storage medium in the embodiments may have any configuration.

[0091] The computer or embedded system in the embodiments is for executing each process in the above-described embodiments based on a program stored in a storage medium, and may be configured as any of a device consisting of a single device such as a personal computer or a microcomputer, or a system in which multiple devices are connected to a network. Furthermore, the computer in the embodiments is not limited to a personal computer but also includes an arithmetic processing unit, a microcomputer, etc. included in information processing equipment, and is a general term for equipment or devices that can realize the functions in the embodiments by a program.

[0092] According to at least one of the embodiments described above, image quality can be improved.

[0093] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0094] 120 Sequence control circuit 134 Input Device 135 Display 150 Processing Circuit

Claims

1. a sequence control unit that executes a first pulse sequence in which a region-selective IR (Inversion Recovery) pulse and a region-non-selective IR pulse are applied, and then a Cartesian collection is performed when a first TI (Inversion Time) has elapsed, and then a radial collection is performed after the Cartesian collection; and a second pulse sequence in which the region-non-selective IR pulse is applied without applying the region-selective IR pulse, and then the Cartesian collection is performed when the first TI has elapsed, and then the radial collection is performed after the Cartesian collection, for a plurality of first TIs while changing the first TI; a generating unit that calculates a second TI time 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 control unit, the sequence control unit executes the third pulse sequence in which, after applying the region-selective IR pulse and the region-non-selective IR pulse, the Cartesian collection is performed when the second TI has elapsed, and the radial collection is performed after the Cartesian collection; and the fourth pulse sequence in which, after applying the region-non-selective IR pulse without applying the region-selective IR pulse, the Cartesian collection is performed when the second TI has elapsed, and the radial collection is performed after the Cartesian collection; the generation unit generates a magnetic resonance image of a brain region that is an imaging region, based on data obtained from the third pulse sequence and the fourth pulse sequence, calculates at least one of a peak signal value, a peak flow time, an arterial transit time, and a blood flow volume in the imaging region as an index, based on the data obtained from the third pulse sequence and the fourth pulse sequence, and predicts a degree of at least one of vascular stenosis and occlusion, based on an MRA (Magnetic Resonance Angiography) image and the index.

2. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the imaging region is a region of the brain, muscle, or kidney.

3. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the imaging region includes a region of microvascularization or microcirculation.

4. The magnetic resonance imaging apparatus according to claim 1 , wherein the generating unit detects a stenosis of 50% or less of a blood vessel diameter based on the index.

5. A magnetic resonance imaging apparatus as described in claim 1, wherein the generation unit predicts perforating branch abnormalities based on the index.

6. A magnetic resonance imaging method performed by a magnetic resonance imaging apparatus, comprising: a first pulse sequence in which a sequence control unit applies a region-selective IR (Inversion Recovery) pulse and a region-non-selective IR pulse, then performs Cartesian acquisition when a first TI (Inversion Time) has elapsed, and then performs radial acquisition after the Cartesian acquisition; a second pulse sequence in which the region-non-selective IR pulse is applied without applying the region-selective IR pulse, and then the Cartesian acquisition is performed when the first TI has elapsed, and the radial acquisition is performed after the Cartesian acquisition; and the second pulse sequence is executed for a plurality of the first TIs while changing the first TIs; a generating unit calculating second TI times in a third pulse sequence and a fourth pulse sequence based on data obtained from the first pulse sequence and the second pulse sequence; The sequence control unit executes the third pulse sequence in which, after applying the region-selective IR pulse and the region-non-selective IR pulse, the Cartesian collection is performed when the second TI has elapsed, and the radial collection is performed after the Cartesian collection, and the fourth pulse sequence in which, after applying the region-non-selective IR pulse without applying the region-selective IR pulse, the Cartesian collection is performed when the second TI has elapsed, and the radial collection is performed after the Cartesian collection, generating a magnetic resonance image of a brain region that is an imaging region based on data obtained from the third pulse sequence and the fourth pulse sequence by the generating unit; a magnetic resonance imaging method for predicting a degree of at least one of vascular stenosis and occlusion based on an MRA (Magnetic Resonance Angiography) image and the index, the method comprising: calculating, as an index, at least one of a peak signal value, a peak flow time, an arterial transit time, and a blood flow volume in the imaging region based on data obtained from the third pulse sequence and the fourth pulse sequence;

Images