Magnetic resonance imaging device, subject alignment device, and subject alignment method

Abstract

The present invention provides a magnetic resonance imaging apparatus, a subject alignment apparatus, and a subject alignment method that automatically align the imaging target portion of a subject with the imaging space without the use of additional hardware. A receiving coil positioned at the imaging target portion of the subject receives nuclear magnetic resonance signals and calculates the position of the receiving coil. The bed carrying the subject is moved so that the position of the receiving coil aligns with the imaging space of the magnetic resonance imaging apparatus. This aligns the imaging target portion of the subject with the imaging space of the magnetic resonance imaging apparatus.

Description

Technical Field

[0001] The present invention relates to a magnetic resonance imaging (hereinafter referred to as "MRI") apparatus, and more particularly to a technique for improving the workflow of an operator when setting up a subject. Background Art

[0002] An MRI device measures the NMR signals generated by the spins of the nuclei of the tissues that make up a subject, particularly the human body, and produces two- or three-dimensional images of the morphology and function of the head, abdomen, limbs, and other parts of the subject. During imaging, the subject is placed in a uniform static magnetic field generated by the MRI device's static magnetic field magnet. High-frequency magnetic field pulses are applied from the transmitting coil, and gradient magnetic field pulses are applied from the gradient magnetic field coil. The nuclei of the subject's tissues, exposed to the high-frequency magnetic field pulses, generate NMR signals, and the gradient magnetic field pulses impart phase and frequency encoding to the NMR signals. The NMR signals are measured as time-series data by the receiving coils. The measured NMR signals are reconstructed into images using a two- or three-dimensional Fourier transform.

[0003] The imaging space of an MRI apparatus is designed to create a uniform static magnetic field with a predetermined accuracy and to be able to apply a predetermined gradient magnetic field pulse. Therefore, the operator must arrange the subject's imaging target area within the imaging space.

[0004] Traditionally, the operator positioned the patient in the imaging space as follows. First, the patient lay on the MRI bed, and the operator moved the bed so that the imaging target area was positioned near the center of the static magnetic field. Next, the operator illuminated the patient with the MRI laser. While visually confirming the laser's irradiation area, the operator further moved the bed, making fine adjustments to position the imaging target area at the center of the static magnetic field.

[0005] However, the visual alignment of the bed becomes a burden on the operator. In addition, when the same person being examined is examined multiple times for observation, there is also a problem that the position of the person being examined is subtly different for each examination. In addition, as an incidental problem, there is a risk that the laser used for position adjustment will enter the eyes of the person being examined. In addition, when using laser for alignment, the bed needs to be moved slightly multiple times, which sometimes makes the person being examined feel uncomfortable. Therefore, in recent years, there has been an increasing demand for improving the efficiency and reproducibility of video recording. One of these is the automation of the setting of the person being examined.

[0006] Patent Document 1 proposes a positioning method that calculates the position where a bed should be placed based on the height of the person being examined, and then moves the bed to the calculated position. Specifically, first, based on the examination information (age, gender, and imaging target area) selected by the operator, the bed position for placing the imaging target area in the imaging space is roughly calculated based on learning data. Next, a sensor is used to measure the height and weight of the person being examined, and the measurement results are used to calculate the correction amount for the bed position. The bed is then moved to the bed position determined by the above process.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: U.S. Patent Application Publication No. 2017 / 0311842

[0010] Patent Document 1 discloses a technique for calculating the movement amount of a bed for placing an imaging target part in an imaging space of an MRI apparatus based on the height and weight of the subject. However, this technique does not consider the positional relationship between a receiving coil mounted on the subject and the imaging space.

[0011] Specifically, the operator positions the receiving coil close to the imaging target area so that its sensitivity area encompasses the actual imaging target area. Therefore, the actual imaging target area is the area where the receiving coil is mounted. For example, a body coil, a receiving coil for use on the anterior side of the body, can be mounted at a desired location on the body using space on the bed's top plate. The operator then positions the body coil above the imaging target area.

[0012] Therefore, the actual imaging target area may be offset from the imaging target area calculated based on the subject's height and weight. Therefore, it is preferable to position the receiving coil at the center of the static magnetic field (the center of the imaging space). However, conventional techniques do not take the position of the receiving coil into account, resulting in the possibility that a portion of the receiving coil's sensitivity area may be offset from the imaging space, making it impossible to generate an image of that portion.

[0013] Furthermore, in the technology of Patent Document 1, since sensors for measuring the height and weight of the subject are used, the MRI apparatus needs to be equipped with the sensors in advance, which increases the cost. Summary of the Invention

[0014] Therefore, an object of the present invention is to automatically align an imaging target portion of a subject in an imaging space without using additional hardware.

[0015] Technical solutions to problems

[0016] To achieve the above-mentioned object, the magnetic resonance imaging apparatus of the present invention comprises: a static magnetic field generator for generating a static magnetic field in an imaging space; a receiving coil for receiving nuclear magnetic resonance signals emitted from a subject; a bed for carrying the subject and moving the bed into the imaging space; and a subject positioning unit for aligning and placing an imaging target portion of the subject in the imaging space by controlling the movement of the bed. The subject positioning unit calculates the position of the receiving coil using the nuclear magnetic resonance signals received by the receiving coil when the receiving coil is positioned at the imaging target portion of the subject, and moves the bed so that the position of the receiving coil aligns with the imaging space, thereby aligning the imaging target portion with the imaging space.

[0017] Effects of the Invention

[0018] According to the present invention, the position of the receiving coil is determined using nuclear magnetic resonance signals received by a receiving coil positioned at the imaging target portion of the subject, and the position of the receiving coil is aligned with the imaging space. This allows the imaging target portion of the subject to be automatically aligned with the imaging space without the use of additional hardware. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a diagram for explaining the overall configuration of an MRI apparatus according to an embodiment of the present invention.

[0020] Figure 2 This is a flowchart showing the processing of the subject positioning unit 81 according to the first embodiment.

[0021] Figure 3 This is a flowchart showing a modified example of the processing of the subject positioning unit 81 according to the first embodiment.

[0022] Figure 4 This is a screen example showing a screen for selecting an imaging target site and a display screen for recommended receiving coils in the first, second, third, and fourth embodiments.

[0023] Figure 5 This is an explanatory diagram showing the distance from a reference position of the human body to a target examination site in the first embodiment.

[0024] Figure 6 (a) is an explanatory diagram showing the arrangement of elements of the array-shaped receiving coil in the first embodiment. Figure 6 (b) is a table showing the relative positions of components.

[0025] Figure 7 This is a table showing the relationship among gender, age, and height that is predetermined in the first embodiment.

[0026] Figure 8This is a list showing the distances from a predetermined reference position (cervical curvature) to the target examination site in the first embodiment by height.

[0027] Figure 9 (a) shows the pulse sequence used for the object alignment in embodiments 1, 2, 3, and 4. Figure 9 (b) is a flowchart showing the processing of the acquired NMR signals.

[0028] Figure 10 (a) is an explanatory diagram showing the arrangement of elements of the array-shaped receiving coil in the first embodiment. Figure 10 (b-1) is shown using Figure 10 (a) is a graph showing the signal intensity profile of the absolute value image obtained for each element of the receiving coil based on the NMR signal of the uniform phantom. Figure 10 (b-2) is used Figure 10 (a) is a graph showing the distribution of signal intensity of an absolute value image obtained for each element by the receiving coil based on the NMR signal of the subject.

[0029] Figure 11 (a) is an explanatory diagram showing the arrangement of elements of the array-shaped receiving coil and the central element in the first embodiment. Figure 11 (b) is based on the use of Figure 11 (a) is an explanatory diagram for determining the boundary position of the element from the distribution of the signal intensity of the absolute value image obtained by the receiving coil.

[0030] Figure 12 This is a flowchart showing the processing of the subject positioning unit 81 according to the second embodiment.

[0031] Figure 13 This is an explanatory diagram showing the structure of a receiving coil including one element in the second embodiment and the distribution of signal intensity of an absolute value image obtained from NMR signals of a uniform phantom using the receiving coil.

[0032] Figure 14 This is an explanatory diagram showing a receiving coil including one element, the center of the static magnetic field, and the centroid of the distribution of the signal intensity of the absolute value image in the second embodiment.

[0033] Figure 15 This is a flowchart showing the processing of the subject positioning unit 81 according to the third embodiment.

[0034] Figure 16 This is an explanatory diagram showing the configuration of an array-shaped receiving coil in the third embodiment and the distribution of signal intensity in the X-axis direction of an absolute value image obtained from NMR signals of a uniform phantom using the receiving coil.

[0035] Figure 17 This is an explanatory diagram showing the arrangement of elements of the array-shaped receiving coil in the third embodiment, the center element, and the boundary positions of the elements obtained from the distribution of signal intensities of the obtained absolute value image.

[0036] Figure 18 This is a flowchart showing the processing of the subject positioning unit 81 according to the fourth embodiment.

[0037] Figure 19 It is an explanatory diagram showing the movement of the bed and the actual corrected movement amount in the fourth embodiment.

[0038] Description of Reference Numerals

[0039] 1: Subject, 2: Static magnetic field generating system, 3: Gradient magnetic field generating system, 4: Sequencer, 5: Transmitting system, 6: Receiving system, 7: Signal processing system, 8: Central processing unit (CPU), 9: Gradient magnetic field coil, 10: Gradient magnetic field power supply, 11: High-frequency oscillator, 12: Modulator, 13: High-frequency amplifier, 14a: High-frequency coil (transmitting coil), 14b: High-frequency coil (receiving coil), 15: Signal amplifier, 16: Quadrature phase detector, 17: A / D converter, 18: Magnetic disk, 19: Optical disk, 20: Display, 21: ROM, 22: RAM, 23: Trackball or mouse, 24: Keyboard, 81: Alignment unit, 82: Image reconstruction unit. DETAILED DESCRIPTION

[0040] Hereinafter, embodiments of the MRI apparatus of the present invention will be described in detail with reference to the accompanying drawings. In the following description, elements having the same functions are denoted by the same reference numerals, and their repeated descriptions are omitted.

[0041] First, according to Figure 1 An overall overview of an example of an MRI apparatus according to this embodiment will be described. Figure 1 This is a block diagram showing the overall configuration of the MRI apparatus according to this embodiment.

[0042] MRI devices use NMR phenomena to obtain cross-sectional images of the subject. Figure 1 As shown, the system includes a static magnetic field generating system 2 , a gradient magnetic field generating system 3 , a transmitting system 5 , a receiving system 6 , a signal processing system 7 , a sequencer 4 , and a central processing unit (CPU) 8 .

[0043] The static magnetic field generating system 2 is configured with a static magnetic field generating source of a permanent magnet type, a normal conductor type, or a superconducting type, disposed around the subject 1. The static magnetic field generating source generates a uniform static magnetic field in the space surrounding the subject 1 in a direction perpendicular to the subject's body axis in the case of a vertical magnetic field type, and generates a uniform static magnetic field in the direction of the subject's body axis in the case of a horizontal magnetic field type.

[0044] The gradient magnetic field generation system 3 is configured to include: gradient magnetic field coils 9 for applying gradient magnetic fields Gx, Gy, and Gz in the three axes of X, Y, and Z, which serve as the coordinate system (stationary coordinate system) of the MRI apparatus; and a gradient magnetic field power supply 10 for driving each gradient magnetic field coil. The gradient magnetic field power supply 10 selectively supplies drive current to the gradient magnetic field coils in the X, Y, and Z directions in accordance with commands from a sequencer 4, described later, thereby applying one or more of the gradient magnetic fields Gx, Gy, and Gz. For example, during imaging, a slice-direction gradient magnetic field pulse (Gs) is applied in a direction orthogonal to the slice plane (imaging section) to set the slice plane relative to the subject 1. Gradient magnetic field pulses (Gp) in the phase encoding direction and gradient magnetic field pulses (Gf) in the frequency encoding direction are applied in the remaining two directions, which are orthogonal to the slice plane and mutually orthogonal to each other. This allows position information in each direction to be encoded in the echo signal.

[0045] The transmission system 5 comprises a high-frequency oscillator 11, a modulator 12, a high-frequency amplifier 13, and a high-frequency coil (transmitting coil) 14a on the transmitting side. To induce nuclear magnetic resonance in the atomic nuclear spins of the biological tissue of the subject 1, the subject 1 is irradiated with high-frequency magnetic field pulses (hereinafter referred to as "RF pulses"). Specifically, the modulator 12 amplitude-modulates the RF pulses output from the high-frequency oscillator 11 at a timing based on instructions from the sequencer 4. After amplification by the high-frequency amplifier 13, the amplitude-modulated RF pulses are supplied to the high-frequency coil 14a positioned near the subject 1, thereby irradiating the subject 1 with the RF pulses. This generates nuclear magnetic resonance in the atomic nuclear spins of the tissue of the subject 1, emitting an echo signal (NMR signal).

[0046] The receiving system 6 is configured to include a high-frequency receiving coil (receiving coil) 14b on the receiving side, a signal amplifier 15, a quadrature phase detector 16, and an A / D converter 17. It detects echo signals (NMR signals) emitted by the subject 1. Specifically, the receiving coil 14b is positioned close to the subject 1, receives the echo signals emitted by the subject 1, and converts them into electrical signals. The signal amplifier 15 amplifies the echo signals, and the quadrature phase detector 16 splits the echo signals into two orthogonal signals based on timing instructions from the sequencer 4. The two signals are converted to digital quantities by the A / D converter 17 and transmitted to the signal processing system 7.

[0047] The signal processing system 7 includes storage devices such as an optical disk 19, a magnetic disk 18, a ROM 21, and a RAM 22, and a display 20 including a CRT. The CPU 8 constitutes a portion of the signal processing system 7 and, by reading and executing programs pre-stored on the optical disk 19, etc., implements functions such as a subject alignment unit 81 that automatically aligns (position-matches) the subject 1 with the imaging space 40, an image reconstruction unit 82 that performs image reconstruction, and a data processing unit (not shown) that performs various data processing.

[0048] Specifically, the subject positioning unit 81 automatically positions the imaging target portion of the subject 1 placed on the bed 30 at the center of the imaging space 40 (center of the static magnetic field).

[0049] When the image reconstruction unit 82 receives data from the receiving system 6 , the CPU 8 performs signal processing, image reconstruction, and other processing, and displays the resulting tomographic image of the subject 1 on the display 20 and records it on the disk 18 of the external storage device.

[0050] The sequencer 4 is a control unit that causes the transmission system 6 and the gradient magnetic field generation system 3 to irradiate and apply RF pulses and gradient magnetic field pulses, respectively, at predetermined timings, and causes the reception system 6 to execute a pulse sequence at predetermined timings for detecting echo signals from the subject 1. The sequencer 4 operates under the control of the CPU 8 and issues commands to each component to execute the pulse sequence, thereby collecting the data (echo signals) required for reconstructing a tomographic image of the subject 1.

[0051] The operation unit 25 inputs various control information for the MRI apparatus and control information for processing performed by the signal processing system 7, and includes a trackball or mouse 23 and a keyboard 24. The operation unit 25 is disposed near the display 20, and is configured so that the operator can interactively control various processing of the MRI apparatus through the operation unit 25 while viewing the display 20.

[0052] MRI imaging targets hydrogen nuclei (protons), the primary structural material of the subject, and is a common clinical target. By visualizing information related to the spatial distribution of proton density and the spatial distribution of relaxation times in excited states, MRI allows for two- or three-dimensional imaging of the morphology and function of the human head, abdomen, limbs, and other areas.

[0053] The receiving coil 14 b is installed by the operator so as to face or surround the imaging target portion of the subject 1 .

[0054] Hereinafter, a process of automatically aligning the imaging target portion of the subject 1 placed on the bed 30 to the center (static magnetic field center) of the imaging space 40 by the subject positioning unit 81 will be described using Embodiments 1 to 4.

[0055] <<Implementation Method 1>>

[0056] Next, use Figure 2 The process of the object positioning unit 81 according to the first embodiment of the present invention is described below.

[0057] (Step 101)

[0058] The operator inputs the subject information through the operation unit 25, and the subject positioning unit 81 receives the input subject information. As the subject information, "image target part", "body position", "gender" and "age" are required input items. Figure 4 An example of a display screen showing various selectable imaging target areas is shown. Figure 4 The imaging target part can be input by selecting the imaging target part in the display screen. Figure 4 The display screen may be configured to display the type of the receiving coil 14b recommended according to the selected imaging target part.

[0059] (Step 102)

[0060] The operator places the reference position of the body of the subject 1 (e.g., the neck bend) as Figure 5 The vehicle is placed on the bed 30 so as to coincide with a predetermined position of the bed 30 (the position of the arrow, which is a mark provided on the bed 30 ).

[0061] Furthermore, the operator sets the receiving coil 14b at the imaging target part of the subject 1. In addition, the cable of the receiving coil 14b is connected to the connector provided on the bed 30, thereby connecting to the signal amplifier 15. Here, as an example, Figure 6 As shown in FIG. 1 ( a ), an array coil in which a plurality of coils are arranged in the HF (Head Foot) direction (body axis direction) of the subject 1 is used as the receiving coil 14 b . Figure 6 The receiving coil 14 b also includes a plurality of coils arranged in the width direction of the subject 1 .

[0062] Then, when the operator presses the bed movement start button, the subject positioning unit 81 accepts this and proceeds to step 103 .

[0063] (Steps 103 and 104)

[0064] In step 103, the subject positioning unit 81 determines whether the "height" of the subject information has not been input in step 101. If not, the process proceeds to step 104, and estimates the height based on the "sex" and "age" information input in step 101 by referring to a table showing the relationship between sex, age, and height. The table showing the relationship between sex, age, and height is, for example, Figure 7 As shown, this is a table prepared in advance based on statistical data of height by age and stored in ROM 21, etc.

[0065] Furthermore, the accuracy of the height estimation in step 104 can be improved by using height data by age or race.

[0066] In step 103 , when the subject positioning unit 81 has completed inputting the “height” of the subject information in step 101 , the process directly proceeds to step 105 .

[0067] (Step 105)

[0068] In step 105 , the subject positioning unit 81 calculates the bed movement amount for positioning the imaging target part at the center of the static magnetic field based on the imaging target part and the body height.

[0069] First, the subject positioning unit 81 refers to the following data based on the imaging subject part and height received in step 101: Figure 8 The distance from the curved part of the neck to the imaging site is obtained using a predetermined table or the like shown in FIG. Figure 8 The table is based on statistical data by height, etc. Figure 5 As shown in FIG. 1 , the distances from the curved part of the neck to each imaging site are predetermined for each body height and stored in the ROM 21 or the like.

[0070] When the center of the static magnetic field is used as the origin, the position of the imaging target site on the bed (target bed position) can be expressed as in equation (1).

[0071] [Formula 1]

[0072] TargetTablePosition=DefaultTablePosition+ShiftPosition…(1)

[0073] Here, TargetTablePosition indicates the target bed position, DefaultTablePosition indicates the bed position of the cervical flexure, and ShiftPosition indicates the distance from the cervical flexure to the input imaging target site.

[0074] The subject positioning unit 81 calculates the position of the imaging target part (target bed position) using the calculated distance from the cervical curvature to the imaging site, the current bed position of the cervical curvature, and equation (1). This allows calculation of the bed movement amount required to move the imaging target part (target bed position) to the center (origin) of the static magnetic field.

[0075] Then, the subject positioning unit 81 moves the bed 30 by an amount corresponding to the calculated bed movement amount, and places the imaging target site at the center of the static magnetic field.

[0076] (Step 106)

[0077] If the CPU 8 (the object alignment unit 81) recognizes that the conditions for RF pulse irradiation are met (for example, the door of the shielded room equipped with the MRI device is closed and a fixed time has passed), the CPU 8 (the object alignment unit 81) starts the sequencer 4 and, under the control of the sequencer 4, executes a predetermined pulse sequence for aligning the receiving coil 14b.

[0078] The pulse sequence and the flow of a series of processing after receiving NMR signals by the pulse sequence are shown in FIG. Figure 9 (a) Figure 9 (b).

[0079] like Figure 9 As shown in (a), the pulse sequence for positioning is a sequence of selecting a slice (sagittal or coronal plane) containing the HF direction (body axis direction) of the subject 1, exciting its spin, and using the HF direction as the reading direction to receive the released NMR signal through the receiving coil 14b.

[0080] Specifically, slice selection gradient magnetic field pulses 803 and 804 are applied to select slices including the HF direction (body axis direction), RF pulses 801 and 802 are irradiated to excite spins, and frequency encoding gradient magnetic field pulses 805 are applied in the HF direction. At the same time, echo signals 806 are received by each element of the array coil serving as the receiving coil 14b (the read-out direction is the HF direction).

[0081] The receiving system 6 transmits the NMR signals received by the respective elements constituting the receiving coil 14 b to the signal processing system 7 .

[0082] like Figure 9 As shown in (b), the object positioning unit 81 of the signal processing system 7 divides the NMR signals (signals in k-space) received by each array coil into real signals and imaginary signals, performs Fourier transform on each of them, generates real signal images and imaginary signal images, and adds the two images to generate an absolute value (intensity) image for each element of the array coil.

[0083] (Step 107)

[0084] The object positioning unit 81 determines the element of the receiving coil 14b to be arranged at the center of the static magnetic field according to the "image target part". Figure 6 In the example of the receiving coil of (a), any one of the center elements EL5 to EL8 in the HF direction is set as the element to be arranged at the center of the static magnetic field. Figure 6 In the example of the receiving coil of (a), since elements are also arranged in the left-right direction of the subject, it is preferable to set the central element EL6 or EL7 closest to the HF direction (body axis) as the element to be arranged at the center of the static magnetic field in the HF direction. Figure 10 As shown in (a), EL6 is arranged at the center of the static magnetic field with respect to the HF direction (body axis).

[0085] In addition, to define the center element in the HF direction of the receiving coil, Figure 6 For each receiving coil shown in (b), relative position information of each element relative to the center position of the receiving coil is defined in advance and stored in the ROM 21 or the like.

[0086] (Step 108)

[0087] In step 108 , the subject positioning unit 81 calculates the center positions of the center elements EL5 to EL8 (here, EL6 ) in the HF direction based on the signal intensity data of the absolute value (intensity) image of each element of the receiving coil 14 b obtained in step 106 .

[0088] Specifically, for Figure 10 (b-1), Figure 10 The element column (EL2, EL6, EL10) arranged in the Z-axis (HF) direction shown in (b-2) is used to create a signal intensity distribution of the absolute value (intensity) image of each element, and the center position of the element EL6 in the HF direction is calculated based on the distribution.

[0089] At this time, if the subject 1 is not of the same shape and composition as the human body, it will not be the same as Figure 10 The ideal signal intensity distribution shown in (b-1) is obtained as Figure 10 Therefore, it is difficult to calculate the center position of element EL6 based on the peak position of the signal intensity distribution. Therefore, in this embodiment, based on the signal intensity distribution of the absolute value image of each element, the signals of the adjacent elements (EL2, EL6, EL10) in the HF direction are compared, as shown in FIG. Figure 11 (a) Figure 11As in (b), positions Z1 and Z2 in the HF direction (Z direction) where the signal intensity distribution values ​​between the elements are equal (i.e., the distributions intersect) are determined. This allows detection of the boundary positions (positions Z1 and Z2) between the elements.

[0090] In addition, the Z-axis direction is the same direction as the static magnetic field and is the longitudinal direction of the bed.

[0091] If Figure 11 Taking the element arrangement of (a) as an example, the position Z where the values ​​of the signal intensity distribution are equal can be expressed as in equation (2).

[0092] [Formula 2]

[0093] EL2 Signal(i)=EL6 Signal(i), EL6 Signal(j)=EL10 Signal(j)…(2)

[0094] Where i≠j

[0095] The center position CorrectionPosition of the element EL6 can be calculated by using the boundary positions between the elements (positions Z1 and Z2) according to Formula (3).

[0096] [Formula 3]

[0097] CorrectionPosition=(Z2+Z1) / 2…(3)

[0098] Z1, Z2: Indicates the coordinate positions of two points in the Z direction that constitute the boundary.

[0099] The center position of element EL6 obtained by formula (3) is the center value of the coordinate positions of the two points (positions Z1 and Z2) serving as boundary positions, and represents the distance from the center of the static magnetic field (Z = 0.0). Therefore, the subject positioning unit 81 uses this value as the bed movement amount to move the bed 30, thereby enabling the center of element EL6 of the receiving coil 14b to be arranged at the center of the static magnetic field in the Z-axis direction.

[0100] Thus, the operator can arrange the receiving coil 14b attached to the imaging target site at the center of the static magnetic field in the HF direction, thereby automatically arranging the receiving coil 14b and the imaging target site in the imaging space 40. Therefore, the entire imaging target site can be imaged.

[0101] In addition, in this embodiment, no additional sensors are used. Instead, the distance from the reference position of the human body to the target imaging part is calculated based on the input subject information, and the approximate bed movement position is determined and the bed is moved. Then, the readout is set in the HF direction, and the NMR signal obtained by applying the slice selection gradient magnetic field and the frequency encoding gradient magnetic field is used to obtain the signal intensity distribution of the absolute value image of the element in the Z-axis (HF) direction. The boundaries between the elements are detected, and the center position of the element can be calculated based on the boundary position. The center position of the element is treated as the distance from the center of the static magnetic field, and the calculated center value is used as the bed movement amount to move the bed, so that the desired element can be configured toward the center of the static magnetic field.

[0102] In addition, if Figure 3 As shown, the subject alignment unit 81 may also execute step 109 after moving the bed 30 through steps 101 to 108 to position the desired receiving coil 14b element at the center of the static magnetic field, thereby more accurately positioning the desired element at the center of the static magnetic field. In step 109, the subject alignment unit 81 determines whether the position of the desired receiving coil 14b element is within a predetermined range (e.g., less than 1.5 cm) from the center of the static magnetic field. If the position of the receiving coil 14b element is within the predetermined range from the center of the static magnetic field, automatic subject alignment is complete. If not, the process returns to step 106 and automatic subject alignment is repeated.

[0103] In the first embodiment, the description is given using a bed in which the cervical curvature is used as the reference position of the human body and a mark indicating the reference position of the cervical curvature is provided on the bed. However, other parts of the human body may be used as the reference position.

[0104] The following are examples of the effects of the MRI apparatus according to the first embodiment.

[0105] 1. The burden on the user (device operator) caused by the work of setting the worktable position can be reduced.

[0106] 2. Since it does not use lasers like the existing technology, the risk of laser entering the eyes can be avoided.

[0107] 3. It can reduce the discomfort caused to the person being tested due to the movement of the bed during laser alignment in the prior art.

[0108] 4. The desired sensitivity area of ​​the receiving coil can be automatically moved to the center of the static magnetic field.

[0109] 5. Since no additional hardware is required, the manufacturing cost can be suppressed.

[0110] <<Implementation Method 2>>

[0111] Next, use Figure 12 The process of the subject positioning unit 81 according to the second embodiment of the present invention is described.

[0112] In the second embodiment, a case where the number of elements of the receiving coil 14b is one will be described. Hereinafter, only the processes that are different from those in the first embodiment will be described, and descriptions of the same processes will be omitted.

[0113] (Steps 201 to 205)

[0114] Since steps 101 to 105 are the same as those in the first embodiment, their description will be omitted.

[0115] (Step 206)

[0116] If the CPU 8 (the object alignment unit 81) recognizes that the conditions for irradiating the RF pulse are met (for example, the door of the shielded room is closed and a fixed time has passed), the CPU 8 (the object alignment unit 81) starts the sequencer 4 and, through the control of the sequencer 4, executes a predetermined pulse sequence for aligning the receiving coil 14b.

[0117] This pulse sequence is similar to that of the first embodiment. Figure 9 The pulse sequence is the same as that of (a), but the sequencer 4 does not apply the slice selection gradient magnetic fields 803 and 804, but applies the frequency encoding gradient magnetic field 805 while receiving the echo signal 806 through one element of the receiving coil 14b (the readout direction is the HF direction).

[0118] The processing after receiving the echo signal is the same as step 106 in the first embodiment, and an absolute value image for one element constituting the receiving coil 14 b is generated.

[0119] (Step 207)

[0120] The object positioning unit 81 determines the element to be placed at the center of the static magnetic field according to the "image target part". Figure 4 As shown, the operator is presented with a recommended receiving coil according to the imaging site, and the elements of the presented recommended receiving coil are set so as to be arranged at the center of the static magnetic field.

[0121] (Step 208)

[0122] The object positioning unit 81 generates an absolute value image of one element of the receiving coil 14b in step 206, as shown in FIG. Figure 13 In this way, a signal intensity distribution of an absolute value image in the Z-axis (HF) direction is created (here, the Z-axis direction is the same direction as the static magnetic field and is the longitudinal direction of the bed).

[0123] Next, the object alignment unit 81 is configured to generate a signal intensity distribution of the element, such as Figure 14 Calculate the center of gravity Z in the Z direction G If Figure 13 as well as Figure 14 As an example of the component configuration, the center of gravity Z G It can be calculated by formula (4).

[0124] [Formula 4]

[0125] Z G =∑(S i ×Z i ) / ∑S i …(4)

[0126] When the center position of the static magnetic field is Z=0.0, the center of gravity Z G The coordinate position of represents the distance from the center of the static magnetic field, so the object positioning unit 81 calculates the center of gravity Z G The coordinates of the bed are used as the bed movement amount, and the bed 30 is moved, thereby the center of gravity Z of the element can be moved to the G Arranged toward the center of the static magnetic field.

[0127] According to the second embodiment, even if the receiving coil 14b has only one element, the center of gravity of the element can be automatically positioned at the center of the static magnetic field.

[0128] <<Implementation Method 3>>

[0129] Next, use Figure 15 The process of the object positioning unit 81 in embodiment 3 is described.

[0130] The processing of the third embodiment is the same as that of the first embodiment, but differs in that the bed 30 is moved in the X direction (short side direction = RL (body width) direction of the subject). Below, only the processing that differs from the first embodiment is described, and the description of the same processing is omitted.

[0131] Furthermore, an MRI apparatus having a structure capable of moving the bed 30 in the X direction is generally limited to an MRI apparatus having a vertical magnetic field.

[0132] (Steps 301 to 305)

[0133] Since steps 101 to 105 are the same as those in the first embodiment, their description will be omitted.

[0134] (Step 306)

[0135] When the CPU 8 (object alignment unit 81) recognizes that the RF pulse irradiation conditions are met (for example, the door of the shielded room is closed and a fixed time has passed), the CPU 8 (object alignment unit 81) starts the sequencer 4 and executes a predetermined pulse sequence for aligning the receiving coil 14b under the control of the sequencer 4. This pulse sequence is the same as that of the embodiment 1. Figure 9 The pulse sequence is the same as that of (a) in Embodiment 1, but differs from that of Embodiment 1 in that the slices are set along the RL direction of the subject 1, and the readout direction is also in the RL direction. Specifically, RF pulses 801 and 802 are irradiated while slice selection gradient magnetic fields 803 and 804 are applied to select slices along the RL direction of the subject 1. Furthermore, echo signals 806 are received by the receiving coil 14b while a frequency encoding gradient magnetic field 805 is applied (the readout direction is in the RL direction).

[0136] The processing after receiving the echo signal is the same as step 106 in the first embodiment, and an absolute value image is generated for each of the plurality of elements constituting the receiving coil 14 b .

[0137] (Step 307)

[0138] The object alignment unit 81 determines the element to be placed at the center of the static magnetic field according to the "imaging part". Figure 4 As shown, the recommended receiving coil is presented to the operator according to the imaging site, and the center element EL6 (or EL7) in the RL direction of the presented recommended receiving coil is set so as to be arranged at the center of the static magnetic field.

[0139] (Step 308)

[0140] The object positioning unit 81 generates the absolute value images of the plurality of elements of the receiving coil 14b generated in step 306, as shown in FIG. Figure 16 Thus, for the plurality of elements EL5 to EL8 arranged in the X-axis (RL) direction, a signal intensity distribution of an absolute value image in the X-axis (RL) direction is created (here, the X-axis direction is perpendicular to the static magnetic field and is the short side direction of the bed).

[0141] Based on the signal intensity distribution generated for each element EL5 to EL8, the signal intensities of adjacent elements EL5 to EL8 in the RL direction are compared to find the positions in the X direction where the signal values ​​between the elements are equal, thereby detecting the boundaries X1 and X2 between the elements.

[0142] If Figure 17 Taking the element configuration as an example, the position in the X direction where the signal values ​​between the elements are equal can be calculated using formula (5).

[0143] [Formula 5]

[0144] EL5 Signal(i)=EL6 Signal(i), EL6 Signal(j)=EL7 Signal(j)…(5)

[0145] Where i≠j

[0146] The center position CorrectionPosition of the element EL6 can be calculated by using the boundary positions between the elements (positions X1 and X2) using Formula (6).

[0147] [Formula 6]

[0148] CorrectionPositoin=(X2+X1) / 2…(6)

[0149] X1, X2: Indicates the coordinate positions of two points in the X direction that serve as the boundary.

[0150] The center position of the element EL6 obtained by formula (6) is the center value of the coordinate positions of the two points (positions X1 and X2) as the boundary positions, and represents the distance from the center of the static magnetic field (X=0.0). Therefore, the subject positioning unit 81 uses this value as the bed movement amount to move the bed 30, thereby being able to Figure 17 In this way, the element EL6 at the center of the receiving coil 14b is arranged at the center of the static magnetic field with respect to the X-axis direction.

[0151] The above-mentioned embodiment 3 is a process of arranging the element at the center of the receiving coil 14b in the X (RL) direction at the center of the static magnetic field. Therefore, by combining it with the process of arranging the element at the center of the receiving coil 14b in the Z (HF) direction at the center of the static magnetic field in embodiments 1 and 2, the center of the receiving coil 14 in the X (RL) direction and the Z (HF) direction can be aligned with the center of the static magnetic field.

[0152] For example, after performing the processing of embodiments 1 and 2 to calculate the bed movement amount in the Z direction and execute the bed movement in the Z direction, the calculation of the bed movement amount in the X direction and the execution of the bed movement in the X direction based on embodiment 3 are performed, thereby enabling bed control to align the center of the receiving coil set at the imaging target area of ​​the subject with the center of the static magnetic field.

[0153] Furthermore, it is of course possible to perform bed control in the order of performing bed movement in the X direction and then the Z direction.

[0154] Furthermore, by performing excitation in the coronal plane, the bed movement amounts in the Z direction and the X direction can be calculated simultaneously, and efficient bed movement such as simultaneous control of the bed movement in the Z direction and the X direction can be performed.

[0155] Furthermore, as is common to Embodiments 1, 2, and 3, the excitation slice profile and slice thickness can also be optimized according to the imaging site and body position. For example, in imaging sites such as extremities, the object may not be contained within the imaging space 40. Therefore, full excitation can be performed to acquire NMR signals without applying a slice-selective gradient magnetic field.

[0156] <<Implementation Method 4>>

[0157] Next, use Figure 18 、 Figure 19 Embodiment 4 is explained. In Embodiments 1, 2, and 3, respectively, the bed is moved by a predetermined bed movement amount (preset amount) in accordance with the imaging subject's body part and height, with reference to a predetermined table, etc., in steps 101 to 105, 201 to 205, and 301 to 305. However, in Embodiment 4, these processes are not performed. In Embodiment 4, the bed 30 is moved in the HF direction at a constant speed, and NMR signals are acquired at fixed intervals, while the desired receiving coil element is moved toward the center of the static magnetic field. Figure 18 The process is described in detail.

[0158] (Step 401)

[0159] The operator inputs the subject information through the operation unit 25, and the subject positioning unit 81 receives the input subject information. As the subject information, "imaging part" is a required input item. Figure 4 An example of a display screen showing various selectable imaging target areas is shown.

[0160] (Step 402)

[0161] The object positioning unit 81 determines the element of the receiving coil 14b to be arranged at the center of the static magnetic field according to the "image target part". Figure 6 In the example of the receiving coil of (a), any one of the central elements EL5 to EL8 in the HF direction (for example, EL6) is set as the element to be arranged at the center of the static magnetic field.

[0162] (Step 403)

[0163] The operator makes the subject 1 lie on a bed and sets the receiving coil 14b on the imaging target part of the subject 1. The cable of the receiving coil 14b is connected to a connector provided on the bed 30, thereby connecting to the signal amplifier 15.

[0164] When the operator presses the bed movement start button, the patient positioning unit 81 starts the sequencer 4, and the bed 30 starts moving into the MRI apparatus under the control of the sequencer 4. The moving speed is set to a fixed speed (for example, v [mm / s]), and the bed is moved continuously (see Figure 19 ).

[0165] (Step 404)

[0166] While the bed 30 is moving at a constant speed, the subject positioning unit 81 executes a pulse sequence similar to step 106 of the first embodiment, and the receiving coil 14b receives NMR signals (echo signals) through all elements. The subject positioning unit 81 generates an absolute value image for each element of the receiving coil 14b and generates the following: Figure 10 The signal intensity distribution of the absolute value image as shown in (b-2).

[0167] (Steps 405, 406)

[0168] The object positioning unit 81 executes the first half of step 108 of embodiment 1 and detects the position of the element of the receiving coil 14b based on the boundary values ​​Z1 and Z2 of the signal intensity distribution (step 405). In step 405, it is determined whether the position of the element of the receiving coil 14b can be detected. If so, the process proceeds to step 407. Whether the element position can be detected can be determined, for example, by comparing the signal strength of the coordinates of the two points at the boundary values ​​Z1 and Z2 used in calculating the element position with a predetermined threshold. If the threshold is exceeded, the determination is made that the element position can be detected.

[0169] If detection is not possible, the object positioning unit 81 returns to step 404 and executes the pulse sequence again.

[0170] (Step 407)

[0171] The subject positioning unit 81 stops the movement of the bed 30 and calculates the distance from the position of the element EL6 of the receiving coil 14b detected in step 405 to the center of the static magnetic field. At this time, considering that the bed is continuously moving during and after the execution of the pulse sequence in step 404, the distance from the current position of the element to the center of the static magnetic field is calculated. Specifically, Figure 9 In the pulse sequence (a), if the irradiation timing of the RF pulse 801 is set to time 0 [s], for example, and the time from when the receiving coil 14b receives the NMR signal until the subject positioning unit 81 performs the analysis of the device position is set to t [s], the bed 30 moves vt [mm] during the elapsed time t [s] (see Figure 19). The position of the element detected in step 405 (the center value of the boundary values ​​Z1 and Z2) is the position at time 0 [s]. Therefore, considering the bed movement amount vt [mm] during the time t [s], the bed movement amount (actual correction movement amount) CorrectionPosition for aligning the element EL6 of the receiving coil 14b with the center of the static magnetic field can be calculated by formula (7): Figure 19 ).

[0172] [Formula 7]

[0173] CorrectionPosition=(Z2+Z1) / 2-vt…(7)

[0174] The subject positioning unit 81 moves the bed 30 by the bed movement amount (actual correction movement amount) CorrectionPosition obtained by equation (7), thereby arranging the center of the element EL6 of the receiving coil 14b at the center of the static magnetic field in the Z-axis direction.

[0175] Thus, the operator can arrange the receiving coil 14b attached to the imaging target site at the center of the static magnetic field in the HF direction, thereby automatically arranging the receiving coil 14b and the imaging target site in the imaging space 40. Therefore, the entire imaging target site can be imaged.

[0176] In addition, in this embodiment 4, since the processing of steps 101 to 105 of embodiment 1 is not performed, and the bed is moved by a predetermined bed movement amount (preset amount) with reference to a predetermined table, etc., there is the following advantage, namely, there is no need to prepare a table in advance, and the operator does not need to input his height.

[0177] Furthermore, since the bed 30 is continuously moved toward the center of the static magnetic field even during the execution of the pulse sequence, the bed movement amount in step 407 is small, and the subject can be quickly positioned at the center of the static magnetic field.

[0178] As mentioned above, although embodiment of this invention was described, this invention is not limited to the structure and process of embodiment.

Claims

1. A magnetic resonance imaging device, characterized in that The apparatus comprises: a static magnetic field generating unit for generating a static magnetic field in an imaging space; a gradient magnetic field generating unit for applying a gradient magnetic field superimposed on the static magnetic field; a transmitting coil for irradiating a high-frequency magnetic field to a subject arranged in the imaging space; a receiving coil for receiving nuclear magnetic resonance signals emitted from the subject; a bed for carrying the subject and moving the subject to the imaging space; and a subject positioning unit for positioning the imaging target part of the subject in the imaging space by controlling the movement of the bed. The receiving coil is a structure having a plurality of elements arranged at least in a given direction. The object positioning portion, According to a given pulse sequence, a high-frequency magnetic field is irradiated to the subject in the imaging space, and while applying the gradient magnetic field in a given direction, the nuclear magnetic resonance signals emitted from the subject are received by the elements of the receiving coil arranged in the imaging target part of the subject. Performing Fourier transform on the nuclear magnetic resonance signal received by the element, reconstructing an absolute value image for each element, and calculating the distribution of signal intensity of the absolute value image for each element. calculating the position of a specific element among the plurality of elements according to the positions where the distribution of the signal strength of each element intersects in the given direction, The position of the specific element is used as the position of the receiving coil, and the bed is moved so that the position of the receiving coil coincides with the imaging space, thereby aligning the imaging target site with the imaging space.

2. The magnetic resonance imaging apparatus according to claim 1, wherein The point between two positions where the distribution of the specific element intersects with the distributions of the elements adjacent to both sides of the specific element in the given direction is calculated as the position of the specific element.

3. The magnetic resonance imaging apparatus according to claim 1, wherein The subject positioning unit calculates the distribution also for a direction intersecting the given direction, and calculates the position of the receiving coil also for a direction intersecting the given direction, so that the position of the receiving coil matches the imaging space.

4. The magnetic resonance imaging apparatus according to claim 1, wherein Before determining the position of the receiving coil, the subject positioning unit moves the imaging target site into the imaging space using the height of the subject and / or the imaging target site input by the operator.

5. The magnetic resonance imaging apparatus according to claim 1, wherein The subject positioning unit calculates the position of the receiving coil by executing the pulse sequence while continuously moving the bed toward the imaging space.

6. The magnetic resonance imaging apparatus according to claim 1, wherein The subject positioning unit calculates the movement amount of the bed for aligning the position of the receiving coil with the imaging space by subtracting the movement amount of the bed during the execution of the pulse sequence and / or the calculation of the position of the receiving coil.

7. A method for positioning a subject in a magnetic resonance imaging apparatus, wherein the magnetic resonance imaging apparatus includes a subject positioning unit, wherein: receiving a nuclear magnetic resonance signal received by a receiving coil disposed at an imaging target portion of a subject and calculating a position of the receiving coil; The bed on which the subject is placed is moved so that the position of the receiving coil coincides with the imaging space of the magnetic resonance imaging apparatus, thereby aligning the imaging target part with the imaging space. The receiving coil is a structure having a plurality of elements arranged at least in a given direction. The nuclear magnetic resonance signals received by the elements of the receiving coil are nuclear magnetic resonance signals emitted from the subject in the imaging space by irradiating the subject with a high-frequency magnetic field according to a given pulse sequence while applying a gradient magnetic field in a given direction. The object positioning portion, Performing Fourier transform on the nuclear magnetic resonance signal received by the element, reconstructing an absolute value image for each element, and calculating the distribution of signal intensity of the absolute value image for each element. calculating the position of a specific element among the plurality of elements according to the positions where the distribution of the signal strength of each element intersects in the given direction, The position of the specific element is used as the position of the receiving coil, and the bed is moved so that the position of the receiving coil coincides with the imaging space, thereby aligning the imaging target site with the imaging space.

Images