Method for imaging using magnetic resonance imaging apparatus

Abstract

To reduce examination time in an examination performed with a magnetic resonance imaging apparatus.SOLUTION: A method for imaging using a magnetic resonance imaging apparatus according to one embodiment sets imaging conditions and scan regions for each of a plurality of main scans, calculates an execution order of the plurality of main scans based on an SAR (Specific Absorption Rate) waiting time defined as a waiting time when the scan regions partially or entirely overlap among the plurality of main scans and a couch-moving time, and executes the plurality of main scans in the calculated execution order while accompanying movement of a couch on which a subject is placed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The embodiments disclosed in this specification and the drawings relate to an imaging method using a magnetic resonance imaging (MRI) device. [Background technology]

[0002] An MRI device is an imaging device that performs a scan to excite the nuclear spins of a subject placed in a static magnetic field with radio frequency (RF) pulses at the Larmor frequency and collects magnetic resonance (MR) signals generated from the subject as a result of the excitation, and generates MR images based on the MR signals collected by the scan.

[0003] For safety reasons, when scanning with an MRI device, the IEC (International Electronics Commission) standard sets an upper limit for the SAR (Specific Absorption Rate), which is an index of the amount of energy absorbed by a subject irradiated with RF pulses.

[0004] To comply with safety limits on SAR values ​​based on IEC standards, a predetermined waiting time may be inserted between consecutive scans during an MRI examination. This waiting time is called the SAR waiting time. Accumulation of SAR waiting time during an examination leads to an extension of the examination time. The SAR waiting time can be shortened by changing the imaging conditions, but the image quality of the generated MR images may be degraded by doing so. The SAR waiting time may also be shortened by changing the order in which multiple scans are performed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-143235 Summary of the Invention [Problem to be solved by the invention]

[0006] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to shorten the examination time in an examination using an MRI apparatus. 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]

[0007] An imaging method using a magnetic resonance imaging apparatus according to one embodiment sets imaging conditions and scan areas for each of a plurality of main scans, calculates the execution order of the plurality of main scans based on a Specific Absorption Rate (SAR) waiting time, which is defined as the waiting time when the scan areas of the plurality of main scans partially or entirely overlap, and on the bed movement time, and executes the plurality of main scans in accordance with the execution order while moving the bed on which the subject is placed. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a block diagram showing the overall configuration of an MRI apparatus according to an embodiment. [Figure 2] 4 is a flowchart showing an example of the operation of an imaging method in the MRI apparatus according to the embodiment. [Figure 3] 10A and 10B are diagrams showing examples of setting scan areas for multiple main scans according to the embodiment. [Figure 4] FIG. 10 is a diagram showing an example of the execution order of a plurality of main scans according to a comparative example. [Figure 5] 10 is a flowchart showing an example of an algorithm for a phase for determining the first main scan in calculating the execution order of a plurality of main scans according to the embodiment. [Figure 6]FIG. 10 is an explanatory diagram of an algorithm for a phase that determines the first main scan in calculating the execution order of a plurality of main scans according to the embodiment. [Figure 7] 10 is a flowchart showing an example of an algorithm for a phase for determining the second and subsequent main scans in calculating the execution order of a plurality of main scans according to the embodiment. [Figure 8] FIG. 10 is an explanatory diagram of an algorithm for a phase that determines the second and subsequent main scans in calculating the execution order of a plurality of main scans according to the embodiment. [Figure 9] FIG. 10 is a diagram showing an example of the execution order of a plurality of main scans according to the embodiment. [Figure 10] 10A and 10B are diagrams showing examples of display screens of protocol lists according to a comparative example and an embodiment; [Figure 11] FIG. 10 is a view showing an example of a display screen for setting status information of a plurality of main scans according to the embodiment. [Figure 12] 10A and 10B are diagrams showing an example of a display screen for setting status information before and after cancellation of a specific main scan in the execution order of multiple main scans according to the embodiment. [Figure 13] 10A and 10B are diagrams showing an example of a display screen for setting status information before and after switching the execution order between specific main scans in the execution order of a plurality of main scans according to the embodiment. [Figure 14] 10 is a flowchart showing an example of an algorithm for a phase for determining the second and subsequent main scans in calculating the execution order of a plurality of main scans according to a first modified example of an embodiment. [Figure 15] FIG. 10 is a first explanatory diagram of an algorithm for a phase that determines the second and subsequent main scans in calculating the execution order of a plurality of main scans according to a first modified example of an embodiment. [Figure 16] FIG. 10 is a second explanatory diagram of the algorithm for the phase that determines the second and subsequent main scans in calculating the execution order of a plurality of main scans according to the first modified example of the embodiment. [Figure 17] FIG. 10 is a diagram showing an example of the execution order of a plurality of main scans according to a first modified example of the embodiment. [Figure 18]10 is a flowchart showing an example of an algorithm for a phase for determining the second and subsequent main scans in calculating the execution order of a plurality of main scans according to a second modified example of the embodiment. [Figure 19] FIG. 10 is an explanatory diagram of an algorithm for a phase that determines the second and subsequent main scans in calculating the execution order of a plurality of main scans according to a second modified example of the embodiment. [Figure 20] FIG. 10 is a diagram showing an example of the execution order of a plurality of main scans according to a second modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of an imaging method using a magnetic resonance imaging apparatus will be described with reference to the drawings. In each drawing, the same elements are given the same reference numerals, and duplicated explanations will be omitted.

[0010] (Overall configuration of MRI device) 1 is a block diagram showing the overall configuration of an MRI apparatus 1 according to an embodiment. The MRI apparatus 1 includes a gantry device 100, a control cabinet 300, a console 400, and a bed 500.

[0011] The gantry 100 has a static magnetic field magnet 10, a gradient magnetic field coil 11, and a whole body (WB) coil 12. These components are housed in a cylindrical housing.

[0012] The control cabinet 300 has a gradient magnetic field power supply 31, an RF receiver 32, an RF transmitter 33, and a sequence controller 34. Under the control of the sequence controller 34, the gradient magnetic field power supply 31 supplies current to the gradient magnetic field coil 11, causing the gradient magnetic field coil 11 to generate gradient magnetic fields along the X-axis, Y-axis, and Z-axis.

[0013] The static magnetic field magnet 10 of the gantry 100 has a roughly cylindrical shape and generates a static magnetic field within a bore into which a patient to be examined is carried. The bore refers to the examination space inside the cylinder of the static magnetic field magnet 10. The static magnetic field magnet 10 incorporates a superconducting coil, which is cooled to an extremely low temperature by liquid helium. In the excitation mode, the static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power supply (not shown) to the superconducting coil. Thereafter, when the static magnetic field magnet 10 transitions to the persistent current mode, the static magnetic field power supply is disconnected. Once the static magnetic field magnet 10 transitions to the persistent current mode, it continues to generate a strong static magnetic field for a long period of time, for example, for more than one year. Note that the static magnetic field magnet 10 may be configured as a permanent magnet.

[0014] The gradient magnetic field coil 11 has a roughly cylindrical shape and is fixed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 generates a gradient magnetic field when supplied with current from a gradient magnetic field power supply 31. Specifically, the gradient magnetic field coil 11 has three coils corresponding to the X-axis, Y-axis, and Z-axis that are orthogonal to each other. The three coils of the gradient magnetic field coil 11 generate a gradient magnetic field whose magnetic field strength changes along each of the X-axis, Y-axis, and Z-axis.

[0015] The WB coil 12 has a roughly cylindrical shape and is fixed so as to surround the subject inside the gradient magnetic field coil 11. The WB coil 12 transmits RF pulses from an RF transmitter 33 to the subject, and receives MR signals emitted from the subject due to excitation of hydrogen nuclei.

[0016] The bed 500 has a bed body 50 and a top board 51. The subject is placed on the top board 51. The bed body 50 is capable of moving the top board 51 in the vertical and horizontal directions. Before imaging, the bed body 50 moves the top board 51, on which the subject is placed, to a predetermined height and then moves it into the bore. In this specification, moving the bed means moving the top board 51 in the horizontal direction.

[0017] The MRI apparatus 1 may have a local coil 20 in addition to the WB coil 12. The local coil 20 is an RF coil disposed close to the subject and receives MR signals emitted from the subject at a position close to the subject. The local coil 20 may transmit RF pulses transmitted from an RF transmitter 33 to the subject. The local coil 20 is composed of, for example, multiple element coils. There are various types of local coils 20 depending on the imaging region of the subject, such as for the head, chest, spine, lower limbs, and whole body. FIG. 1 illustrates an example of a local coil 20 for the chest.

[0018] The RF transmitter 33 generates RF pulses based on command signals from a sequence controller 34. The generated RF pulses are transmitted to the WB coil 12 or the local coil 20 and applied to the subject. The RF receiver 32 detects MR signals received by the WB coil 12 or the local coil 20, converts the detected MR signals into analog-to-digital (AD) signals, and outputs the converted signals to the sequence controller 34. The digitized MR signals are called raw data.

[0019] The sequence controller 34 executes a scan of the subject by driving the gradient magnetic field power supply 31, the RF transmitter 33, and the RF receiver 32 under the control of the console 400. The sequence controller 34 receives raw data from the RF receiver 32 by the scan and transmits it to the console 400.

[0020] The sequence controller 34 includes a processing circuit (not shown). This processing circuit is configured with hardware such as a processor that executes a predetermined program, an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit).

[0021] The console 400 includes a processing circuit 41, a memory circuit 42, an input interface 43, and a display 45. The console 400 may also include a network interface 44.

[0022] The memory circuitry 42 is a storage medium including a ROM (Read Only Memory), a RAM (Random Access Memory), and an external storage device such as an HDD (Hard Disk Drive), an optical disk device, etc. The memory circuitry 42 stores various information and data, and stores various programs executed by the processor of the processing circuitry 41.

[0023] The input interface 43 includes various input devices for the user to input various information and data, and an input circuit for processing signals from the input devices. The input devices include, for example, a trackball, a switch, a mouse, a keyboard, a touchpad, a touchscreen, a non-contact input device using an optical sensor, and a voice input device. When an input device is operated, the input circuit generates a signal corresponding to the operation and outputs it to the processing circuit 41.

[0024] The network interface 44 communicates with various devices connected to the network via wired or wireless means, and exchanges various types of information and data.

[0025] The display 45 is a display device such as a liquid crystal display panel, a plasma display panel, an organic EL panel, etc. The display 45 displays various information and data under the control of the processing circuit 41, and may also be a GUI (Graphical User Interface) that functions as an input device.

[0026] The processing circuitry 41 is a circuit including, for example, a CPU or a dedicated or general-purpose processor. The processor executes various programs stored in the memory circuitry 42 to realize a condition setting function F1, an area setting function F2, a calculation function F3, a scanning function F4, a display control function F5, and an image generation function F6.

[0027] Using these components, the console 400 controls the entire MRI apparatus 1. Specifically, the processing circuitry 41 receives instructions regarding imaging conditions and various other information through operations by a user, such as a medical technician, via the input interface 43. The processing circuitry 41 then causes the sequence controller 34 to execute a scan based on the input imaging conditions, and reconstructs an MR image based on the raw data received from the sequence controller 34. The reconstructed MR image is displayed on the display 45 and stored in the memory circuitry 42.

[0028] (Operation flow of the embodiment) 2 is a flowchart showing an example of the operation of the imaging method in the MRI apparatus 1 according to the embodiment. The MRI apparatus 1 executes multiple main scans depending on the examination contents of the subject. As will be described later, each of the multiple main scans differs in either the imaging conditions or the scan area.

[0029] In the following description, an actual scan is a scan that acquires MR signals for generating MR images that are mainly used for diagnosis and examination. A locator scan is a so-called positioning scan that acquires MR signals for generating MR images that are used to set a scan region for the actual scan. Note that MR images generated from MR signals acquired in an actual scan may be used for positioning, or MR images generated from MR signals acquired in a locator scan may be used for examination and diagnosis.

[0030] The imaging condition elements include condition elements necessary for executing a scan, such as the orientation of an anatomical plane, such as an axial plane, a coronal plane, or a sagittal plane, the type of pulse sequence, the imaging region (FOV: Field Of View), the overlap region, and imaging parameters. The imaging parameters include, for example, the repetition time (TR: Repetition Time), the echo time (TE: Echo Time), the inversion time (TI: Inversion Time), the slice thickness, the number of data in the frequency direction and the phase direction, the reception bandwidth, and the number of additions. The imaging region is an area imaged as an MR image and may be a two-dimensional area or a three-dimensional area. Hereinafter, a set of imaging condition elements necessary for executing one scan will be referred to as "one imaging condition," and one imaging condition will be set for one scan.

[0031] In step ST1, the condition setting function F1 sets imaging conditions for the locator scan. The imaging conditions for the locator scan are set, for example, by input by a user via the input interface 43, by reading out imaging conditions for the locator scan stored in the memory circuitry 42, or by a combination of these.

[0032] The imaging region of the locator scan, which is the region to be imaged as an MR image and set as an imaging condition, may be a part of the subject or the whole body. The imaging region of the locator scan may be set to include the imaging region of interest of the subject. The imaging region of interest is a region including an imaging region required depending on the examination content and diagnostic region of the subject, and is a region including all of the imaging regions set for each of the multiple main scans in step ST4. The locator scan may use imaging conditions that enable MR images of a wide range to be acquired in a short scan time.

[0033] In step ST2, the region setting function F2 sets a scan region for the locator scan based on the imaging conditions for the locator scan. The scan region is a region where a scan for collecting MR signals is performed, and may be the same region as the imaging region or may be a region larger than the imaging region and including the imaging region. The scan region may be a region including the overlap region and the imaging region.

[0034] In step ST3, the scan function F4 causes the MRI apparatus 1 to execute a locator scan.

[0035] In step ST4, the condition setting function F1 sets imaging conditions for each of the multiple main scans. The imaging conditions for the multiple main scans are set, for example, by user input via the input interface 43, by reading out imaging conditions for each of the multiple main scans stored in the memory circuitry 42, or by a combination of these. The imaging conditions are set according to the examination content and diagnostic region so that a desired contrast-enhanced image, such as T1-weighted, T2-weighted, or diffusion-weighted, is generated. The imaging conditions for the multiple main scans also include an imaging area. For example, the user may set the imaging area for each of the multiple main scans by referring to an MR image of the subject from a locator scan displayed on the display 45.

[0036] During one examination period in which multiple main scans are performed, two or more imaging conditions are used. When the main imaging condition elements match between multiple main scans, it is said that the imaging conditions are the same. The main imaging condition elements are condition elements that cause differences in contrast enhancement, such as T1-weighted, T2-weighted, and diffusion-weighted, between the generated MR images. The main imaging condition elements are, for example, the type of pulse sequence, such as fast spin echo, inversion recovery, and diffusion-weighted echo planar. The main imaging condition elements may include various imaging parameters that cause differences in contrast enhancement depending on the type of pulse sequence. Note that "the imaging conditions are the same" also includes cases in which all imaging condition elements match between multiple main scans. The condition setting function F1 sets one imaging condition for each of multiple main scans.

[0037] The process of step ST4 is not limited to being performed after step ST3, but may be performed after step ST1 or step ST2.

[0038] In step ST5, the region setting function F2 sets a scan region for each of the plurality of main scans based on the imaging conditions for each of the plurality of main scans.

[0039] The region setting function F2 divides the imaging region of interest of the subject in the longitudinal direction of the bed 500 according to the number of main scans with the same type of imaging conditions, thereby setting scan regions for each of the main scans with the same type of imaging conditions.

[0040] FIG. 3(A) shows an example of setting scan areas for multiple main scans. FIG. 3(B) shows an example of setting scan areas for multiple main scans in FIG. 3(A), divided into three imaging conditions Pa, Pb, and Pc. In the example shown in FIGS. 3(A) and 3(B), the multiple main scans are shown as a total of 15 main scans, consisting of five main scans Sa corresponding to the five scan areas Sa1 to Sa5 under imaging condition Pa, six main scans Sb corresponding to the six scan areas Sb1 to Sb6 under imaging condition Pb, and four main scans Sc corresponding to the four scan areas Sc1 to Sc4 under imaging condition Pc. In this way, the area setting function F2 collectively sets scan areas for multiple main scans with the same imaging conditions.

[0041] For each main scan, the bed on which the subject is placed is moved as necessary, and the longitudinal center position of the bed 500 of the scan area for each main scan is moved to the magnetic field center (isocenter). Therefore, from the viewpoint of ensuring the image quality of MR images, the scan areas for multiple main scans may be adjusted according to the orientation of the anatomical cross section and the type of pulse sequence set. For example, when a pulse sequence (e.g., diffusion-weighted echo-planar imaging) is set that is likely to cause distortion in MR images when a scan is performed at a position away from the magnetic field center where the magnetic field is inhomogeneous, it is desirable to set a smaller scan area than when a pulse sequence that is less likely to cause distortion is set.

[0042] When an axial section is set as an imaging condition, it is desirable to set a smaller scan area in the longitudinal direction of the bed 500 than when a coronal section or a sagittal section is set as an imaging condition. When the scan area in the longitudinal direction of the bed 500 is set small, scans in both end areas of the scan area in the longitudinal direction of the bed 500 are performed at positions close to the magnetic field center where magnetic field uniformity is high.

[0043] 3(A) and 3(B), the same imaging region of interest (in this example, the whole body region from head to toes excluding both arms) is set between the main scans under the three imaging conditions Pa, Pb, and Pc. The imaging region of interest may be the same between the imaging conditions, or may be different for each imaging condition.

[0044] Here, Fig. 4 shows an example of the execution order of multiple main scans according to a comparative example. In the comparative example, multiple main scans are executed starting from the subject's head in the order that minimizes the bed movement time within one examination period. In Fig. 4, the execution order of the first to fifteenth main scans is indicated by the numbers (1) to (15) that indicate the imaging numbers. The bed movement time is the time it takes for the top plate 51 of the bed 500 to move from the scan start point to the scan area of ​​the first main scan, or between consecutive main scans in the second and subsequent main scans.

[0045] The scan start point is a predetermined position in the longitudinal direction of the bed 500. The scan start point may be a position outside the subject's region of interest for imaging in the longitudinal direction of the bed 500, or may be a position within the subject's region of interest for imaging, regardless of the direction in which the subject is carried in. The scan start point may be set by the user as an imaging condition. Before imaging, the subject is carried into the gantry device 100 head first (head first) or feet first (feet first).

[0046] 4, the scan area Sb1 in the first main scan (1) and the scan area Sa1 in the second main scan (2) overlap. This makes it necessary to provide an SAR wait time after the first main scan (1). In the comparative example, the scan areas of all 15 consecutively performed main scans partially or entirely overlap, making it necessary to provide an SAR wait time after each main scan.

[0047] The SAR wait time is a predetermined wait time provided between two consecutive main scans to satisfy the safety limit for the SAR value set by the IEC standard. The SAR value is an index of the amount of energy absorbed by a subject irradiated with an RF pulse. In this specification, the SAR wait time is defined as the wait time that occurs when the scan regions of two consecutive main scans partially or completely overlap.

[0048] During one examination period in which multiple main scans are performed, the SAR wait time may accumulate, potentially extending the examination time. In this specification, the examination time refers to the length of time from the time of issuing a command to start the first of multiple main scans to the time of completion of the last main scan. In an examination using the MRI apparatus 1 according to this embodiment, the process of step ST6 is performed to shorten the examination time.

[0049] In step ST6, calculation function F3 calculates the execution order of multiple main scans based on the SAR wait time and the bed movement time. Calculation function F3 may calculate the execution order so that the total interval time between multiple main scans is shorter than the total SAR wait time when multiple main scans are executed in the order that minimizes the bed movement time within one examination period (i.e., the total SAR wait time in the comparative example described above). The interval time is the time between two consecutive main scans, from the end time of the previous main scan to the start time of the next main scan, and is generated by the SAR wait time or the bed movement time.

[0050] The calculation of the execution order by calculation function F3 in step ST6 includes a phase for determining the first main scan among multiple main scans and a phase for determining the second and subsequent main scans. Fig. 5 is a flowchart showing an example of an algorithm for the phase for determining the first main scan, and Figs. 6(A), 6(B), 6(C), and 6(D) are explanatory diagrams of the algorithm for the phase for determining the first main scan. Fig. 7 is a flowchart showing an example of an algorithm for the phase for determining the second and subsequent main scans, and Figs. 8(A), 8(B), and 8(C) are explanatory diagrams of the algorithm for the phase for determining the second and subsequent main scans.

[0051] 5, a scan start point Sp0 is determined and an execution order list is initialized. The execution order list is a list showing the execution order of multiple main scans to be performed within one examination period.

[0052] In step ST102, the examination time Tex0 is calculated by adding up the scan times of multiple main scans. Figure 6(A) shows the initialized execution order list and examination times. In step ST102, there are no main scans registered in the execution order list.

[0053] FIG. 6(B) shows the selection of the first main scan. In step ST103, scan areas in multiple main scans are selected as a search section group for determining the execution order list. In the following description of the algorithm, the scan areas of all main scans within one examination period are collectively referred to as the "total scan area," and the scan areas of each main scan, which are elements of the "total scan area," are referred to as a "section." The search section group is a set of scan areas in main scans that are not registered in the execution order list and are a set of scan areas that can be selected as the next imaging section when determining the execution order list. The next imaging section is the scan area of ​​the main scan that will be executed after the main scan of the current section. The current section is the scan area of ​​the main scan that is latest in the execution order list at the current time, i.e., the scan area of ​​the main scan that was last registered in the incomplete execution order list.

[0054] In Fig. 6(B), the search section group is the entire scan area. In step ST104, the main scan of the search section whose center position is closest to the scan start point Sp0 among the search sections is selected as the main scan to be executed first in the execution order, i.e., as the main scan of the first next imaging section. In Fig. 6(B), the main scan of the scan area Sb1 is selected and executed first in the execution order.

[0055] FIG. 6(C) shows the registration of the execution order list. In step ST105, the main scan of the next imaging section selected in step ST104 is registered in the execution order list as the main scan to be executed first. In step ST106, the interval time from the examination start time to the scan start time of the first next imaging section is added to the examination time. Since the main scan of the first next imaging section is the start of multiple consecutive main scans, the SAR wait time is 0. Therefore, in FIG. 6(C), the interval time Tin(Sb1) from the examination start time to the scan start time of the first next imaging section is the bed movement time TB(Sb1,Sp0) from the scan start point Sp0 to the center position of the first next imaging section (i.e., the scan area Sb1). The examination time is calculated as Tex0 + Tin(Sb1).

[0056] FIG. 6(D) shows how the current section is determined. In step ST107, the scan area of ​​the first main scan, i.e., the next imaging section corresponding to the main scan registered in the execution order list in the immediately preceding step ST105, is excluded from the search section group. The search section group obtained by excluding the scan area of ​​the first main scan from the entire scan area becomes the search section group for determining the second main scan. In this way, the scan area of ​​the main scan registered in the execution order list is excluded from the search section group. In step ST108, the next imaging section corresponding to the main scan registered in the execution order list in the immediately preceding step ST105 is determined as the current section. In other words, when determining the second main scan, the main scan that serves as the basis for calculating the bed movement time and SAR wait time is determined as the main scan of the current section.

[0057] 7, it is determined whether or not the search section group is empty. If the search section group is not empty (that is, NO in step ST201), the process proceeds to step ST202.

[0058] FIG. 8(A) shows the selection of the second main scan. In step ST202, the bed movement time from the center position of the current section to each center position of the search section group is calculated. In step ST203, the SAR latency time when each main scan of the search section group is performed after the main scan of the current section is calculated. FIG. 8(A) shows the SAR latency and bed movement time when a main scan of scan area Sa1, Sb2, or Sc1 is performed after the main scan of scan area Sb1, but the SAR latency and bed movement time are calculated for all main scans in the search section group.

[0059] In step ST204, based on the SAR waiting time and the bed movement time, each interval time from the scan end time of the current section to the scan start time of each main scan in the search section group is calculated. In step ST205, from among the interval times calculated in step ST204, a search section whose interval time is equal to or less than a predetermined value is selected as the next imaging section. For example, for all main scans in the search section group, i.e., all main scans not registered in the execution order list, the longer of the SAR waiting time and the bed movement time may be calculated as each interval time, and the one main scan with the shortest interval time may be selected as the main scan of the next imaging section.

[0060] In this way, the calculation function F3 registers the first main scan in the execution order in the execution order list based on the scan starting point, and then repeats the following two processes to complete the execution order list. That is, the calculation function F3 repeats a first process of calculating the interval between the last main scan registered in the incomplete execution order list and each unregistered main scan, and a second process of registering the unregistered main scan whose interval is equal to or shorter than a predetermined value or is the shortest as the next main scan in the execution order in the execution order. The interval may be calculated as the longer of the SAR waiting time or the bed movement time.

[0061] FIG. 8(B) shows the registration of the execution order list. In step ST206, the main scan of the next imaging section is registered in the execution order list. In FIG. 8(B), the main scan of the second next imaging section (i.e., scan area Sc1) is added to the execution order list as the second main scan. In step ST207, the interval time from the scan end time of the current section to the scan start time of the next imaging section is added to the examination time.

[0062] 8(B), the interval time Tin(Sc1) from the end time of the first main scan to the start time of the second main scan is calculated based on two points: the SAR waiting time TC(Sc1,Sb1) when the main scan of scan area Sc1 is executed after the main scan of scan area Sb1, and the time it takes to move the bed from the center position of scan area Sb1 to the center position of scan area Sc1 of the next imaging section. The examination time is calculated as Tex0 + Tin(Sb1) + Tin(Sc1).

[0063] Each interval time is added to the examination time until all main scans are registered in the execution order list. In other words, the examination time for a subject for which all main scans are performed is calculated by adding up the scan time for each of the multiple main scans and the interval time between two consecutive main scans.

[0064] FIG. 8(C) shows how the current section is determined. In step ST208, the next imaging section is excluded from the group of search sections. In step ST209, the next imaging section is determined as the current section. In FIG. 8(C), the scan area Sb2 is the current section. After step ST209, the process returns to step ST201. The processes of steps ST201 to ST209 are repeated until the group of search sections becomes empty (i.e., YES in step ST201) and the execution order list is completed.

[0065] 9 shows an example of the execution order of multiple main scans according to the embodiment, determined as described above. The execution order example in FIG. 9 differs from the execution order example of multiple main scans according to the comparative example in FIG. 4.

[0066] Returning to FIG. 2, in step ST7 of FIG. 2, the display control function F5 reflects the execution order of the multiple main scans calculated in step ST6 in a protocol list and displays it on the display 45. FIG. 10(A) shows an example of a display screen of a protocol list according to the comparative example of FIG. 4. FIG. 10(B) shows an example of a display screen of a protocol list according to the embodiment of FIG. 9. A protocol list is a list in which all scans performed within one examination period are displayed on the display 45 in the order of execution together with the imaging conditions. In the protocol list, all scans are arranged in an execution order that reflects the execution order list of the multiple main scans. In the display screen examples of FIGS. 10(A) and 10(B), a protocol list in which a locator scan and multiple main scans are arranged in the order of imaging numbers is displayed together with comments and scan times, but the information displayed as the protocol list is not limited to this.

[0067] The display control function F5 accepts cancellation of execution of actual scans or change of execution order on the protocol list display screen. The display control function F5 also reflects the cancellation of execution of specific actual scans or change of execution order accepted on the protocol list display screen on the screen displaying setting status information of multiple actual scans in step ST9. The setting status information is, for example, information regarding the position of each scan area of ​​the multiple actual scans in the longitudinal direction of the bed 500 and the execution order.

[0068] In step ST8, the scan function F4 causes the MRI apparatus 1 to perform a plurality of main scans in accordance with the execution order of step ST6, while moving the bed on which the subject is placed.

[0069] In step ST9, the display control function F5 displays the setting status information for multiple main scans on the display 45. Figures 11(A) and 11(B) show examples of display screens for setting status information for multiple main scans. Figure 11(A) shows that the first main scan is currently being performed, and Figure 11(B) shows that the fourth main scan is currently being performed. Each scan area is assigned an imaging number in accordance with the order of execution and is displayed.

[0070] The display control function F5 may display the position of each scan area in the longitudinal direction of the bed 500 so that it can be identified for each imaging condition. The imaging conditions may be displayed so that it can be identified which contrast-enhanced image is being produced, for example, "T1 weighted," "T2 weighted," or "diffusion weighted (DWI)." The display control function F5 may use hatching or chromatic color shading to distinguish between scan areas of completed main scans, scan areas of main scans currently being performed, and main scans that have not yet been performed. For scan areas currently being scanned, "imaging," "scanning," or "executing" may be displayed. The display control function F5 may distinguish between scan areas of main scans currently being performed and other scan areas by flashing the scan areas.

[0071] The display control function F5 accepts cancellation of execution of main scans or change of execution order on the display screen of setting status information of multiple main scans. The display control function F5 also reflects cancellation of execution of specific main scans or change of execution order accepted on the display screen of setting status information on the display screen of protocol list. The calculation function F3 recalculates the examination time when main scans are canceled or their execution order is changed.

[0072] 12(A) and 12(B) show examples of the display screen of setting status information before and after the cancellation of a specific main scan. First, the currently set execution order is displayed on the display 45, for example, as a number, according to the execution order list completed by the processing circuitry 41. If the user selects and cancels the scan area Sc3, which is the fifth main scan, on the display screen of setting status information, the main scan of scan area Sc3 is deleted. Then, when the main scan of scan area Sc3 is deleted, the scan area Sb3, which was the sixth main scan in FIG. 12(A), becomes the fifth main scan in FIG. 12(B), and the execution order of subsequent main scans is also moved up. In other words, if the execution of at least one main scan among multiple main scans displayed on the display 45 is canceled, the execution of at least one canceled main scan is deleted, and the execution order of the main scans after the deleted main scan is moved up. In this way, the execution order of the main scans is updated.

[0073] 13(A) and 13(B) show example display screens of setting status information before and after swapping the execution order between specific main scans. For example, the user swaps the execution order between scan area Sb6, which is the twelfth main scan, and scan area Sc3, which is the fifth main scan, by dragging the mouse. As a result of the swapping of the execution order in FIG. 13(A), in FIG. 13(B), the main scan with scan area Sb6 becomes the fifth main scan, and the main scan with scan area Sc3 becomes the twelfth main scan. In other words, when the execution order of the first and second main scans among the multiple main scans displayed on display 45 is swapped, the actual execution order of the first and second main scans is also swapped.

[0074] In step ST10, the image generating function F6 generates a plurality of MR images based on a plurality of MR signals acquired by executing a plurality of main scans.

[0075] In step ST11, the image generation function F6 generates a stitched image of the subject's ROI by stitching together the MR images while adjusting distortion and brightness differences between the MR images. For example, the stitched image is generated from multiple MR images generated by performing multiple main scans under the same imaging conditions but with different scan regions.

[0076] In step ST12, the image generation function F6 generates a fusion image of the imaging region of interest of the subject based on the multiple MR images. The fusion image is generated based on the multiple MR images so as to obtain necessary clinical findings according to the contents of the examination or diagnosis. Note that the fusion image may be generated based on a stitched image.

[0077] (First Modification) In a first modified example of the embodiment, the process of Fig. 14 is performed after the phase of determining the first main scan in Fig. 5. Fig. 14 shows an example of the phase of determining the second and subsequent main scans. In the above-described embodiment, the examination time is shortened by shortening the total time interval calculated from the SAR waiting time and the bed moving time, but in the first modified example, the examination time is shortened by prioritizing elimination of the influence of the SAR waiting time over the bed moving time.

[0078] Figures 15(A), 15(B), and 15(C) show the case in which, in the first modified example, the first next imaging section (1) is selected, and then the second next imaging section (2) is selected.

[0079] In step ST301, it is determined whether the search section group is empty or not. If the search section group is not empty (that is, NO in step ST301), the process proceeds to step ST302.

[0080] FIG. 15(A) shows the selection of a comparison section. In step ST302, the search section of the search section group whose center position is closest to the scan starting point Sp0 is selected as the comparison section. In FIG. 15(A), the search section group is the remaining 14 scan areas after excluding the scan area of ​​the first main scan (1) from all scan areas. Here, the first comparison section is scan area Sa1, whose center position is closest to the scan starting point Sp0.

[0081] In step ST303, the bed movement time from the center position of the current section to the center position of the comparison section is calculated. In FIG. 15(A), the current section is the scan area Sb1. In step ST304, the SAR waiting time when the main scan of the comparison section is executed after the main scan of the current section is calculated. In step ST305, it is determined whether the bed movement time is equal to or greater than the SAR waiting time. If the bed movement time is shorter than the SAR waiting time (i.e., NO in step ST305), the process proceeds to step ST306.

[0082] In FIG. 15(A), the bed movement time TB(Sa1, Sb1) from the center position of the current section (i.e., the scan area Sb1 of the first main scan) to the center position of the first comparison section (i.e., the scan area Sa1) is shorter than the SAR waiting time TC(Sa1, Sb1) when the main scan of the first comparison section is performed after the main scan of the current section, so processing proceeds to step ST306.

[0083] In step ST306, the search section whose center position is closest to the scan starting point Sp0 after the comparison section is selected as the new comparison section. In Figure 15(A), scan area Sc1 is selected as the second comparison section because it is closest to the scan starting point Sp0 after the center position of the first comparison section (i.e., scan area Sa1).

[0084] After step ST306, the process returns to step ST302, and steps ST303 to ST305 are repeated until the bed movement time becomes equal to or longer than the SAR waiting time (i.e., YES in step ST305). In Figure 15(A), the bed movement time TB(Sc1,Sb1) from the center position of scan area Sb1 to the center position of the second comparison section (i.e., scan area Sc1) is shorter than the SAR waiting time TC(Sc1,Sb1) when a main scan of scan area Sc1 is performed after a main scan of scan area Sb1, so the process proceeds to step ST306. Then, scan area Sb2 is selected as the third comparison section.

[0085] 15(A), the bed movement time TB(Sb2, Sb1) from the center position of scan area Sb1 to the center position of the third comparison section (i.e., scan area Sb2) is equal to or longer than the SAR waiting time TC(Sb2, Sb1) when the main scan of scan area Sb2 is performed after the main scan of scan area Sb1, so the determination is YES in step ST305. If the bed movement time is equal to or longer than the SAR waiting time (i.e., YES in step ST305), the process proceeds to step ST307.

[0086] After registering the main scan that is first in the execution order based on the scan starting point in the incomplete execution order list in this way, the calculation function F3 repeats the following process to complete the execution order list. That is, the calculation function F3 repeats the process of registering one main scan that will result in a bed movement time equal to or greater than the SAR waiting time when executed after the main scan that was last registered in the incomplete execution order list, preferentially registering it in the incomplete execution order list, starting with the main scan whose scan area is closest to the scan starting point Sp0.

[0087] FIG. 15(B) shows the registration of the execution order list. In step ST307, the comparison section is determined as the next imaging section, and the main scan of the comparison section is registered in the execution order list. In FIG. 15(B), the main scan of the third comparison section (i.e., scan area Sb2) is added to the execution order list as the second main scan. In step ST308, the interval time from the scan end time of the current section to the scan start time of the next imaging section is added to the examination time. In FIG. 15(B), the examination time is calculated as Tex0 + Tin(Sb1) + Tin(Sb2), which is the sum of the scan time of each of the multiple main scans and the interval time between the multiple main scans.

[0088] Figure 15(C) shows how the current section is determined. In step ST309, the next imaging section is excluded from the search section group. In step ST310, the next imaging section is determined as the current section. In Figure 15(C), the main scan of scan area Sb2 is determined as the current section.

[0089] 16(A), 16(B), and 16(C) show the case where, in the first modified example, the third imaging section (3) is selected, and then the fourth imaging section (4) is selected.

[0090] In Fig. 16(A), the search section group consists of the remaining 12 scan areas excluding the scan areas of the first to third main scans (1) to (3) from the total scan area. Here, the first comparison section is scan area Sa1, whose center position is closest to the scan start point Sp0. In Fig. 16(A), the bed movement time TB(Sa1, Sb3) from the center position of the current section (i.e., scan area Sb3) to the center position of the first comparison section (i.e., scan area Sa1) is equal to or longer than the SAR waiting time TC(Sa1, Sb3) when the main scan of scan area Sa1 is performed after the main scan of the current section, so the process does not proceed to step ST306.

[0091] In Figure 16(B), the main scan of the first comparison section (i.e., scan area Sa1) is added to the execution order list as the fourth main scan, and the inspection time is calculated as Tex0 + Tin(Sb1) + Tin(Sb2) + Tin(Sb3) + Tin(Sa1). In Figure 16(C), scan area Sa1 is determined as the current section.

[0092] After step ST310, the process returns to step ST301, and steps ST301 to ST310 are repeated until the search section group becomes empty (i.e., YES in step ST301) and the execution order list is completed. Fig. 17 shows an example of the execution order of multiple main scans according to the first modified example determined as described above.

[0093] (Second Modification) In a second modified example of the embodiment, the processing of FIG. 18 is performed after the phase of determining the first main scan in FIG. 5. FIG. 18 shows an example algorithm for the phase of determining the second and subsequent main scans. In the second modified example of FIG. 18, the processing of steps ST402 and ST406 is performed instead of the processing of steps ST302 and ST306 in the first modified example of FIG. 14. In the first modified example, a comparison section is selected from a position close to the scan start point Sp0, whereas in the second modified example, a comparison section is selected from a position close to the current section.

[0094] Figure 19(A) shows the selection of a comparison section. In step ST402, the search section of the search section group whose center position is closest to the current section is selected as the comparison section. In Figure 19(A), the search section group consists of the remaining 12 scan areas excluding the scan areas of the first to third main scans (1) to (3) from all scan areas. Here, the first comparison section is scan area Sc2, whose center position is closest to the center position of the current section (i.e., scan area Sb3).

[0095] 19A, in step ST305, the first comparison section has a bed movement time TB(Sc2, Sb3) that is shorter than the SAR waiting time TC(Sc2, Sb3). Therefore, the determination in step ST305 in FIG. 18 is NO, and the process proceeds to step ST406.

[0096] In step ST406, the search section that is next closest to the current section after the comparison section is selected as the new comparison section. In Figure 19(A), the scan area Sa3, whose center position is closest to the current section after the first comparison section (i.e., scan area Sc2), is selected as the second comparison section.

[0097] After step ST406, the process returns to step ST402, and the processes of steps ST303, ST304, and ST305 are repeated until the bed movement time is equal to or longer than the SAR waiting time (that is, YES in step ST305).

[0098] 19(A), the third comparison section is selected because the bed movement time TB(Sa3,Sb3) is also shorter than the SAR waiting time TC(Sa3,Sb3) in the second comparison section.Furthermore, the fourth comparison section is selected because the bed movement time TB(Sa3,Sb3) is also shorter than the SAR waiting time TC(Sa3,Sb3) in the third comparison section.

[0099] In this way, after registering the main scan that is first in the execution order based on the scan starting point in the incomplete execution order list, the calculation function F3 repeats the following process to complete the execution order list. That is, the calculation function F3 repeats the process of registering one main scan that will result in a bed movement time equal to or greater than the SAR wait time when executed after the main scan that was last registered in the incomplete execution order list in the incomplete execution order list, giving priority to the main scan whose scan area is closest to the last main scan.

[0100] FIG. 19(B) shows the registration of the execution order list. FIG. 19(C) shows the determination of the current section. In FIGS. 19(B) and 19(C) according to the second modified example, unlike FIGS. 16(B) and 16(C) according to the first modified example, the main scan of scan area Sb4 is selected as the fourth main scan. FIG. 20 shows an example of the execution order of multiple main scans according to the second modified example of the embodiment determined as described above.

[0101] (others) The embodiment, the first modification, and the second modification differ in the algorithm for calculating the execution order in the phase for determining the second and subsequent main scans, which includes step ST6 in Fig. 2. Therefore, the calculation function F3 may have a step of selecting an algorithm for calculating an appropriate execution order so as to further shorten the examination time. That is, the calculation function F3 selects whether to calculate the execution order based on (a) only the bed movement time, (b) only the SAR wait time, or (c) both the SAR wait time and the bed movement time.

[0102] The execution order may be calculated by selecting the main scans in order of scan area closest to the scan start point Sp0, i.e., based only on the bed movement time. Alternatively, the execution order may be calculated so that the main scans whose scan areas do not completely overlap are consecutive, so that no SAR wait time occurs between consecutive main scans. Alternatively, the execution order may be calculated based on the SAR wait time and the bed movement time, as in the embodiment, the first modified example, and the second modified example.

[0103] According to the imaging method of the MRI apparatus according to at least one of the embodiments described above, the examination time can be reduced.

[0104] In the above embodiments, the term "processor" refers to circuits such as a dedicated or general-purpose CPU (Central Processing Unit), GPU (Graphics Processing Unit) or Application Specific Integrated Circuit (ASIC), programmable logic device (e.g., Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA)).

[0105] If the processor is, for example, a CPU, the processor realizes various functions by reading and executing programs stored in a memory circuit. If the processor is, for example, an ASIC, instead of storing a program in a memory circuit, the functions corresponding to the program are directly incorporated into the processor's circuit as logic circuits. In this case, the processor realizes various functions through hardware processing that reads and executes the program incorporated in the circuit. Alternatively, the processor can realize various functions by combining software processing and hardware processing.

[0106] In addition, although the above embodiment shows an example in which a single processor of a processing circuit realizes each function, a processing circuit may be configured by combining multiple independent processors, and each processor may realize each function. Furthermore, when multiple processors are provided, a memory circuit for storing programs may be provided separately for each processor, or a single memory circuit may collectively store programs corresponding to the functions of all processors.

[0107] In addition, the condition setting function F1, area setting function F2, calculation function F3, scan function F4, display control function F5, and image generation function F6 in the description of the embodiment are examples of a condition setting unit, area setting unit, calculation unit, scan unit, display control unit, and image generation unit, respectively.

[0108] Although several embodiments of the present invention 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, and modifications 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 described in the claims and their equivalents. [Explanation of symbols]

[0109] 1...Magnetic Resonance Imaging (MRI) device F1...Condition setting function F2...Area setting function F3...Calculation function F4...Scan function F5...Display control function F6...Image generation function

Claims

1. 1. An imaging method using a magnetic resonance imaging apparatus that performs a plurality of main scans while moving a bed on which a subject is placed, comprising: setting imaging conditions and a scan area for each of the plurality of main scans; calculating an execution order of the plurality of main scans based on a specific absorption rate (SAR) waiting time, which is defined as a waiting time when the scan regions of the plurality of main scans partially or entirely overlap each other, and a bed movement time; performing the plurality of main scans in accordance with the execution order; An imaging method using a magnetic resonance imaging apparatus.

2. setting one imaging condition selected from two or more imaging conditions for each of the plurality of main scans; dividing the imaging interest region of the subject in the longitudinal direction of the bed according to the number of main scans having the same imaging conditions, thereby setting scan regions for each of the main scans having the same imaging conditions; An imaging method using the magnetic resonance imaging apparatus according to claim 1.

3. calculating the execution order so that the total interval time between the plurality of main scans is shorter than the total SAR waiting time when the plurality of main scans are executed in an order that minimizes the bed movement time within one examination period; An imaging method using the magnetic resonance imaging apparatus according to claim 1.

4. calculating an examination time for the subject when all of the main scans are performed by summing the scan time of each of the plurality of main scans and the interval time between two successive main scans; An imaging method using the magnetic resonance imaging apparatus according to claim 1.

5. Select whether the calculation of the execution order is based on (a) only the bed movement time, (b) only the SAR waiting time, or (c) both the SAR waiting time and the bed movement time. An imaging method using the magnetic resonance imaging apparatus according to claim 1.

6. After registering the first scan in the execution order based on the scan start point in the execution order list, the execution order is calculated by repeating a first process of calculating interval times between the main scan registered last in the execution order list and each unregistered main scan, and a second process of registering an unregistered main scan, from among the interval times, whose interval time is equal to or less than a predetermined value, in the execution order list as the next main scan in the execution order; An imaging method using the magnetic resonance imaging apparatus according to claim 1.

7. (a) Selecting the main scan to be executed first in order of the main scan having the scan area closest to the scan starting point; (b) after registering the first main scan in the execution order based on the scan starting point in the execution order list, repeating a process of registering one main scan in the execution order list, in which the bed movement time will be equal to or longer than the SAR waiting time when executed after the main scan last registered in the execution order list, preferentially registering the main scan whose scan area is closest to the scan starting point in the execution order list, (c) after registering the main scan that is the first in the execution order based on the scan starting point in the execution order list, repeating a process of registering in the execution order list one main scan whose bed movement time will be equal to or longer than the SAR wait time when executed after the main scan that is last registered in the execution order list, preferentially registering the main scan whose scan area is closest to the last main scan; and (d) after registering the main scan that is to be executed first in the execution order list based on the scan starting point, repeating a first process of calculating, as each interval time, the longer of the SAR waiting time and the bed movement time between the main scan that is last registered in the execution order list and each unregistered main scan, and a second process of registering, in the execution order list, the unregistered main scan that has the shortest interval time among the interval times, as the main scan that is to be executed next; Calculating the execution order by any one of the following: An imaging method using the magnetic resonance imaging apparatus according to claim 1.

8. displaying on a display the position of each scan area of ​​the plurality of main scans in the longitudinal direction of the bed and information about the execution order; 5. An imaging method using the magnetic resonance imaging apparatus according to claim 1.

9. When the execution of at least one of the main scans displayed on the display is canceled, In the execution order, at least one main scan whose execution has been canceled is deleted, and at least one main scan and subsequent main scans are moved up. An imaging method using the magnetic resonance imaging apparatus according to claim 8.

10. When the execution order of the first main scan and the second main scan among the plurality of main scans displayed on the display is exchanged, the order of the first main scan and the second main scan is exchanged; An imaging method using the magnetic resonance imaging apparatus according to claim 8.

11. generating a plurality of magnetic resonance images based on a plurality of magnetic resonance signals acquired by performing the plurality of main scans; generating at least one of a stitched image and a fused image of the imaging region of interest of the subject based on the plurality of magnetic resonance images; An imaging method using the magnetic resonance imaging apparatus according to claim 2.

Images