JP6867876B2 - Magnetic resonance imaging device and body motion correction method - Google Patents

Description

The present invention relates to a magnetic resonance imaging (MRI) device, and more particularly to a body motion correction technique.

The MRI apparatus is a medical diagnostic imaging apparatus that uses a nuclear magnetic resonance phenomenon in which hydrogen nuclei (protons) placed in a static magnetic field resonate with a high-frequency magnetic field of a specific frequency, and images the distribution in a non-invasive manner. In the MRI apparatus, in order to give position information to the nuclear magnetic resonance signal generated from the inspection target, a gradient magnetic field is applied in the biaxial or triaxial directions, and the nuclear magnetic resonance signal is measured while changing the gradient magnetic field strength. The nuclear magnetic resonance signal is arranged in a measurement space (hereinafter, referred to as k space) about the axis of the gradient magnetic field.

When the subject moves during the measurement of the nuclear magnetic resonance signal, the gradient magnetic field is applied to a position different from the position where the gradient magnetic field is originally applied, and the data arranged in the k-space includes the deviation. Become. In the case of orthogonal sampling in which the k-space is sampled along its axis, the deviation appears mainly in the phase encoding direction. As a result, body motion artifacts appear in the phase encoding direction of the image reconstructed from k-space to real space, and the image quality deteriorates.

In order to prevent this deterioration of image quality, some body motion correction methods in MRI have been proposed. One is a method of tracking the movement of a marker attached to a subject using hardware such as a camera installed around the device to detect the amount of body movement and correct the position at the time of measurement (for example, Non-Patent Document 1). Is. The second is a method using a sequence to which a sampling method resistant to body movement is applied (for example, Non-Patent Document 2). Third, an additional echo signal (called a navigator echo) is measured in addition to the signal used for imaging. Then, it is a method of detecting the amount of body movement from the navigator echo and correcting the position at the time of measurement (for example, Non-Patent Document 3).

Although the method of Non-Patent Document 1 can detect and correct body movement with high accuracy, there is a problem that additional hardware is required. Further, since it is necessary to control the measurement system in real time to correct the measurement position, there is a problem that an advanced measurement control means is required.

In the method of Non-Patent Document 2, a band-shaped signal called Blade, which is collected so that the center of k-space becomes the signal center, is radially sampled (called radial sampling). Then, the signals in each blade are phase-corrected, and all the blades are added together. As a result, the body movement artifacts are averaged and the body movement is corrected by multiple sampling the low frequency region of the k-space that affects the image quality. However, there is a problem that the imaging time is extended in order to obtain the same spatial resolution as orthogonal sampling, which is a general imaging method.

The method of Non-Patent Document 3 does not require additional hardware and does not extend the imaging time, but it requires advanced measurement control means because it is necessary to control the measurement system in real time to correct the measurement position. There is a problem of becoming. Further, since it is necessary to measure the navigator echo, there is a problem that only an imaging method having a sufficient time for measuring the navigator echo can be applied. Furthermore, there are problems such as being unable to sufficiently cope with random body movements such as coughing and swallowing that occur mainly in the head and body movements of non-rigid bodies.

As a method for solving the problems in the above method, a method of correcting the body movement only by post-processing by utilizing the difference in the sensitivity of the receiving coil has been proposed (for example, Patent Document 1). This is a method of regenerating a measurement signal by utilizing the difference in sensitivity of a plurality of receiving coils, and comparing the regenerated signal (hereinafter referred to as a regenerated signal) with the measurement signal, and the body of the measurement signals. This is a method that combines a method of detecting a signal affected by motion (hereinafter referred to as a body motion signal) and replacing the body motion signal with zero or an arbitrary value (for example, the regenerated signal itself). Patent Document 1 uses the GRAPPA (Generalized Auto-Calibration Partially Parallell Acquisition) method as a signal regeneration method (Non-Patent Document 4). This method does not require additional hardware, does not extend the imaging time, and can correct the movement of non-rigid bodies.

U.S. Pat. No. 9649579

Maclaren Jet al, Measurement and direction of magnetic head motion daring magnetic resonance imaging of the brain, PLos One8 Pipe, James G.M. "Motion direction with PROPELLER MRI: application to head motion and free-breathing cardiac imaging." Magnetic Resonance in Medical White, Nathan, et al. "PROMO: Real-time projective motion correction in MRI imaging-based tracking." Magnetic Resonance in Medicine 63.1 (2010): 91-105. 42.5 (1999): 963-969. Grishold, Mark A. , Et al. “Generalyzed autocalibrating partially parallell acquisitions (GRAPPA).” Magnetic response in medicine 47.6 (2002): 1202-1210.

In the method described in Patent Document 1, when generating a regenerated signal, a region for calculating a weighting coefficient corresponding to a sensitivity portion of each receiving coil (hereinafter referred to as a reference signal region) is a low frequency in k-space. Set to the area. However, when body movement is mixed in the reference signal region, an error due to body movement also occurs in the weighting coefficient calculated using the signal in the reference signal region. Therefore, when the regenerated signal is calculated using the weighting coefficient in which the error due to body movement is mixed, an error occurs in the entire regenerated signal, and the error propagates to the measurement signal to be corrected. As a result, there is a problem that a sufficient image quality improvement effect cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a body motion correction method capable of obtaining a high image quality improvement effect even if a body motion signal is mixed in a reference signal region.

In order to solve the above problems, the present invention first sets a reference signal area for k space data (measurement signals arranged in the measurement space) measured by a plurality of receiving coils, and includes the reference signal area in the reference signal area. The error caused by body movement is corrected for the measured signal (reference signal). Then, the entire measurement space area is corrected based on the corrected reference signal area. In the body motion correction of the reference signal region, the reference signal is corrected by repeating the correction process while updating the conditions for calculating the weighting coefficient.

Specifically, the MRI apparatus of the present invention uses a static magnetic field generating magnet that generates a static magnetic field in the space where the subject is placed, a transmission unit that transmits a high-frequency magnetic field pulse to the subject, and irradiation of the high-frequency magnetic field pulse. A receiving unit provided with two or more receiving coils for receiving the nuclear magnetic resonance signal generated from the subject, a gradient magnetic field application unit for applying a gradient magnetic field for adding position information to the nuclear magnetic resonance signal, and the transmission. A unit, a computer that controls the operation of the gradient magnetic field applying unit and the receiving unit, and performs arithmetic processing on the received nuclear magnetic resonance signal. The computer includes a measurement control unit that controls the operations of the transmission unit, the gradient magnetic field application unit, and the reception unit to arrange nuclear magnetic resonance signals received by the two or more reception coils in the measurement space, and the measurement space. It is provided with a body motion correction processing unit that corrects body motion with respect to the measurement signal of the above, and an image reconstruction unit that reconstructs an image using the measurement signal corrected by the body motion correction processing unit. Then, the body motion correction processing unit sets at least one region of the measurement space as a reference signal region, and sets the measurement signal in the reference signal region as a reference signal, and the reference signal region setting unit and the reference signal. Based on the reference signal body motion correction unit that corrects the body motion and the reference signal after the body motion correction corrected by the reference signal body motion correction unit, the body motion correction is performed on the measurement signals in the entire area of the measurement space. It is provided with an all-area correction unit for performing the operation.

According to the present invention, a high image quality improvement effect can be obtained even when the body movement is mixed in the reference signal region, and the body movement is corrected by using only the acquired image itself without the need for additional hardware or real-time measurement control. Therefore, a high-quality image can be obtained without extending the measurement time.

In the figure which shows the appearance of the MRI apparatus to which this invention is applied, (a) is a horizontal magnetic field type MRI apparatus, (b) is a vertical magnetic field type MRI apparatus, and (c) is a tunnel type magnet obliquely. It is a tilted MRI device. It is a functional block diagram of the MRI apparatus to which this invention is applied. It is a functional block diagram of the computer of 1st Embodiment. It is a flowchart of the computer of 1st Embodiment. It is a figure for demonstrating an example of the spin echo type pulse sequence adopted in 1st Embodiment. It is the flowchart of the body motion correction processing part of 1st Embodiment. (A) to (d) are conceptual diagrams for explaining the reference signal region set in the first embodiment. It is a functional block diagram of the reference signal body motion correction part of the 1st Embodiment. It is the flowchart of the reference signal body motion correction part of 1st Embodiment. It is a conceptual diagram for demonstrating the convolution integral range set in 1st Embodiment. It is a functional block diagram of the body movement position detection part of 1st Embodiment. It is the flowchart of the body movement position detection part of 1st Embodiment. It is a flowchart of the whole area correction part of 1st Embodiment. It is a functional block diagram of the whole area correction part of 1st Embodiment. In the figure which shows the effect of the method of 1st Embodiment, (a) is an absolute value image of a reference phantom, (b) is an absolute value image corrected by the conventional method, (c) is the 1st Embodiment. The absolute value image corrected by the form, (d) is an absolute value image to which a body motion signal is applied, (e) is an absolute value image of the difference between (a) and (b) of this figure, and (f) is this figure (f). The difference absolute value image between a) and (c) is shown. It is a figure which shows the k-space data of the 2nd Embodiment. It is a functional block diagram of the computer of the third embodiment. It is a figure which shows the processing flow of the 3rd Embodiment. It is a figure which shows the k-space data of the 3rd Embodiment. (A) and (b) are diagrams showing embodiments of display, respectively.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings for explaining the embodiment, those having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted. Further, the present invention is not limited to the following forms.

[Device configuration]
The present invention can be applied to various known MRI devices regardless of the form and type of the device. FIG. 1 illustrates some of them. FIG. 1A is a horizontal magnetic field type MRI apparatus 100 using a tunnel type magnet that generates a static magnetic field with a solenoid coil. FIG. 1B is a hamburger type (open type) perpendicular magnetic field type MRI apparatus 120 in which magnets are separated vertically in order to enhance the feeling of openness. Further, FIG. 1 (c) is an MRI apparatus 130 using the same tunnel type magnet as in FIG. 1 (a), shortening the depth of the magnet, and tilting the magnet diagonally to enhance the feeling of openness. In this embodiment, any MRI apparatus having these appearances can be used. The following description will be described as a generalized MRI apparatus 100.

As shown in the functional block diagram of FIG. 2, the MRI apparatus 100 mainly generates a static magnetic field in the space where the subject 101 is placed, for example, a static magnetic field generating magnet such as a static magnetic field coil (hereinafter referred to as a static magnetic field coil). ) 102, a shim coil 104 that adjusts the static magnetic field distribution, a high-frequency transmission coil 105 that transmits a high-frequency magnetic field to the measurement region of the subject 101 (hereinafter, simply referred to as a transmission coil), and nuclear magnetic resonance generated from the subject 101. In order to add position information to the receiving high-frequency coil 106 (hereinafter, simply referred to as the receiving coil) that receives the signal and the nuclear magnetic resonance signal generated from the subject 101, gradient magnetic fields are applied in the x-direction, y-direction, and z-direction, respectively. It includes a gradient magnetic field coil 103 to be applied, a transmitter 107, a receiver 108, a computer 109, a gradient magnetic field power supply unit 112, a shim power supply unit 113, and a sequence control device 114.

As the static magnetic field coil 102, various forms are adopted according to the structures of the MRI devices 100, 120, and 130 shown in FIGS. 1 (a), 1 (b), and 1 (c), respectively. ..

The transmitter coil 105 and the transmitter 107 function as a transmitter, and a high-frequency magnetic field is irradiated from the transmitter coil by transmitting a high-frequency signal generated by the transmitter 107 to the transmitter coil 105. The nuclear magnetic resonance signal detected by the receiving coil 106 is sent to the computer 109 through the receiver 108. In the present embodiment, the sensitivity distribution information of a plurality of receiving coils is used to regenerate a signal that is not affected by body movement. Therefore, the receiving coil 106 of the present embodiment includes at least two receiving coils. When a plurality of receiving coils are collectively referred to as a receiving coil or a multi-coil, each receiving coil is also referred to as a channel of the receiving coil.

The gradient magnetic field coil 103 and the shim coil 104 are driven by the gradient magnetic field power supply unit 112 and the shim power supply unit 113, respectively.

The sequence control device 114 includes a gradient magnetic field power supply unit 112 which is a drive power source for the gradient magnetic field coil 103, a shim power supply unit 113 which is a drive power source for the shim coil 104, a transmitter 107, and a receiver 108 (collectively, these are used). It controls the operation of the measuring unit), and controls the timing of application of the gradient magnetic field and high-frequency magnetic field and reception of the nuclear magnetic resonance signal. The control time chart is called a pulse sequence, is set in advance according to the measurement, and is stored in a storage device or the like provided in the computer 109 described later.

The computer 109 controls the operation of the entire MRI apparatus 100 and performs various arithmetic processes on the received nuclear magnetic resonance signal. In the present embodiment, the computer 109 performs calculations for body motion correction and the like in addition to general image reconstruction calculations. Therefore, as shown in FIG. 3, it has a measurement control unit 310, a body motion correction processing unit 320, and an image reconstruction unit 330.

The computer 109 is an information processing device including a CPU, a memory, a storage device, and the like, and the control and calculation performed by the computer 109 are realized by the CPU executing a predetermined program. However, a part of the calculation can be realized by hardware such as ASIC (Application Specific Integrated Circuit) and FPGA (Field Programmable Gate Array). Further, at least one of the various functions realized by the computer 109 is an information processing device independent of the MRI device 100, and is realized by an information processing device capable of transmitting and receiving data to and from the MRI device 100. You may.

A display 110, an external storage device 111, an input device 115, and the like are connected to the computer 109. The display 110 is an interface for displaying the result obtained by the arithmetic processing to the operator. The input device 115 is an interface for the operator to input conditions, parameters, and the like necessary for the measurement and arithmetic processing performed in the present embodiment. In the input device 115 of the present embodiment, the user can input measurement parameters such as the number of echoes to be measured, the reference echo time (TE), the echo interval, and the FOV (Field of View). The external storage device 111, together with the storage device, holds data used for various arithmetic processes executed by the computer 109, data obtained by the arithmetic processing, input conditions, parameters, and the like.

[Operation of MRI device]
The outline of the operation of the above-mentioned MRI apparatus will be described with reference to FIG.

<Measurement step S1001>
When the imaging is started, the measurement control unit 310 operates the sequence control device 114 according to a pulse sequence set based on the parameters input by the user via the input device 115. The sequence control device 114 controls the operation of the measurement unit, collects a nuclear magnetic resonance signal (hereinafter referred to as an echo signal) generated by the subject 101 at a predetermined echo time (TE), and stores the collected echo signal in a memory. Store in the measurement space inside.

The pulse sequence executed in step S1001 is not particularly limited, and a known pulse sequence can be adopted. However, FIG. 5 shows an orthogonal sampling type spin echo pulse sequence 510 sampled in Cartesian coordinates as an example.

In this pulse sequence 510, the echo signal is measured by the following procedure within one repetition time. First, the RF pulse 511 is irradiated to excite the spin of the subject 101. At this time, a slice selection gradient magnetic field (Gs) 512 is applied at the same time as the RF pulse 511 in order to select a specific slice of the subject 101. Subsequently, a phase-encoded gradient magnetic field (Gp) 513 for phase-encoding the echo signal is applied, and an RF pulse 514 for further inverting the spin is applied together with the slice-selective gradient magnetic field (Gs) 515. Then, after time TE from the first RF pulse 511 irradiation, a readout gradient magnetic field (Gr) 516 is applied to measure the echo signal 517. This process is repeated until all the preset desired k-space regions are filled.

The spin echo pulse sequence shown in FIG. 5 is an example of a pulse sequence executed by the measurement control unit 310, and the present embodiment is not limited to this, and various changes can be made. For example, a gradient echo pulse sequence may be used, or a high-speed spin echo sequence that measures a plurality of echo signals by repeating RF pulse and phase-encoded magnetic field application during one repetition time may be used for measurement. Further, although the imaging sequence in FIG. 5 is a pulse sequence for 2D, the imaging sequence may be a pulse sequence for 3D imaging.

Further, when executing the pulse sequence of the present embodiment, the order of applying the phase-encoded gradient magnetic field (Gp) can be determined in consideration of the appearance of the body motion signal in the k-space. The example shown in FIG. 5 is a case of continuous measurement in order, but measurement may be performed in a random order or in an order of application at arbitrary intervals. When the application order is continuous, if continuous body movement is mixed, the body movement signal appears continuously even in k-space. On the other hand, when the application order is discontinuous (for example, a random phase encoding application order), if continuous body motion is mixed, the body motion signal appears randomly in the k-space. In this way, even if the body movements are the same, the positions of the body movement signals in the k-space differ depending on the imaging order, and different artifacts appear when reconstructed. In the body motion correction described later, the reference region, the convolution calculation range, and the like to be set at the time of correction may be determined in consideration of the application order of the phase-encoded gradient magnetic field.

The computer 109 arranges the echo signal stored in the measurement space in the k-space data defined by the measurement parameters. The receiver 108 of the MRI apparatus of this embodiment is a multi-channel using a plurality of receiving coils, and in the measurement step S1001, k-space data is collected for each channel.

<Body movement correction step S1002>
The computer 109 (body movement correction processing unit 320) corrects an error caused by body movement for a plurality of k-space data (body movement correction step S1002). In this step, basically, a signal (regenerated signal) obtained by regenerating an echo signal based on sensitivity information of a plurality of receiving coils is calculated from the measured echo signal. Then, a signal affected by body movement (body movement signal) is detected from the regenerated signal and the echo signal, and a process of replacing the detected body movement signal with the regenerated signal is executed. Here, the "signal" is a variety of concepts including not only one echo measured by a pulse sequence (for example, the echo signal 517 in FIG. 5) but also data on each line in k-space or a part thereof.

In order to obtain sensitivity information of a plurality of receiving coils used for the above basic processing, in the present embodiment, first, a part region of k-space (hereinafter referred to as a reference signal region) is set, and this reference signal region is set. On the other hand, the body motion correction calculation is performed to correct the reference signal region. Then, the weighting coefficient is calculated using the measured signal in the corrected reference signal region. The regenerated signal is calculated based on the weighting coefficient calculated in this way, and the body motion signal is detected and corrected using the regenerated signal. Therefore, the body motion correction processing unit 320 includes a reference signal area setting unit 321, a reference signal body motion correction unit 322, and an entire area correction unit 323 as functional units. The functions of each of these parts will be described in detail in the description of the embodiments described later, together with the specific processing of the body movement correction step S1002.

<Image reconstruction step S1003>
Next, the computer 109 (image reconstruction unit 330) performs inverse Fourier transform and multi-coil image synthesis on the k-space data including the echo signal corrected in step S1002 to create a motion-corrected reconstruction image. .. The image is displayed on the display 110. If necessary, an image or the like created from the regenerated signal calculated in step S1002 may be displayed on the display 110.

According to the MRI apparatus of the present embodiment, since the body motion signal mixed in the reference signal region is corrected and then the entire region of the k-space is corrected, a high image quality improvement effect can be obtained.

Next, a specific embodiment of the body motion correction process executed by the MRI apparatus of the present embodiment will be described.

[First Embodiment]
As shown in FIG. 6, the body motion correction process of the present embodiment includes a process of setting a reference signal region (S1101) and a process of correcting the reference signal region to make the reference signal region substantially free of the body motion signal. (S1102) includes a process (S1103) in which the sensitivity distribution of the receiving coil is calculated using the corrected reference signal, the weighting coefficient is determined, and the body motion correction is performed for the entire region using the weighting coefficient. In the processing of S1102 and S1103, the signal at the predetermined position is regenerated by the convolution operation of the signal in the surrounding area to acquire the regenerated signal, and the measurement signal at the predetermined position is compared with the regenerated signal. It includes the process of detecting and correcting body movements. Hereinafter, each process will be described in detail.

<Reference signal area setting: S1101>
The reference signal region setting unit 321 sets the measurement signal in at least one or more k-space regions used for calculating the sensitivity distribution of the receiving coil as the reference signal region.
The reference signal area set in this step is an initial value of the subsequent processing, is corrected in step S1102, and is updated as necessary. By widening the reference signal region, it is possible to improve the calculation accuracy of the weighting coefficient based on the sensitivity distribution, but it becomes easier to include the body motion signal and the calculation time becomes longer. Therefore, the reference signal area set as the initial value is set to a relatively narrow range.

FIG. 7A shows an example of the reference signal region set in this step. In the figure, the horizontal direction is the frequency encoding direction, the vertical direction is the phase encoding direction, and the direction perpendicular to the paper surface is the slicing direction. In the illustrated example, the region 801 near the center of the k-space is set as the reference signal region with respect to the desired k-space region 800 set in advance. As an example, the entire k-space region is set as the initial value in the frequency encoding direction, and, for example, 27 points are set as the initial values in the phase encoding direction.

In the example shown in FIG. 7A, the entire k-space region is set as the reference signal region with respect to the frequency encoding direction, but only a part of the frequency encoding may be set as the reference signal region. When the entire k-space region is set as the reference signal region with respect to the frequency encoding direction, the number of simultaneous equations used when calculating the weighting coefficient described later can be increased to improve the calculation accuracy. On the other hand, when only a part of the frequency encoding is set as the reference signal region, the calculation time can be shortened.

<Reference signal body motion correction processing: S1102>
The reference signal body motion correction unit 322 performs a process of correcting the body motion signal mixed in the set reference signal region. Specifically, the regenerated signal of the reference signal area set by the reference signal area setting unit 321 is created based on the sensitivity information of the receiving coil. After that, the position of the body motion signal is detected by performing a difference comparison between the measured signal in the reference signal region and the regenerated signal. Then, by replacing the measurement signal at the detected position with the regenerated signal, a measurement signal corrected for the influence of body movement can be obtained.

At this time, in order to obtain a sufficient correction effect, the iterative operation is performed while updating the reference signal region or the region for forming the regenerated signal set inside this region (referred to as the convolution integration range). By performing the iterative calculation, it becomes possible to perform the correction again using the reference signal corrected at the first time, and the body motion signal mixed in the reference signal region is corrected according to the repetition.

FIG. 8 shows a functional block diagram of the reference signal body motion correction unit 322 that realizes such a function. As shown in the figure, the reference signal body motion correction unit 322 includes a convolution integration range setting unit 410, a weighting coefficient calculation unit 420, a regeneration reference signal calculation unit 430, a body motion position detection unit 440, and a reference signal replacement unit 450. A setting area update unit 460 and an iterative calculation processing unit 470 are provided. The convolution integration range setting unit 410 sets the range of the measurement space used for calculating the weighting coefficient based on the sensitivity distribution of the receiving coil as the convolution integration range. The weighting coefficient calculation unit 420 calculates the weighting coefficient of the convolution integration range by using the reference signal and the measurement signal of the convolution integration range. The regeneration reference signal calculation unit 430 regenerates the reference signal for each reference signal in the reference signal region by using the reference signal and the weighting coefficient. The body movement position detection unit 440 detects a signal position with body movement in the reference signal region from the reference signal and the regeneration reference signal calculated by the regeneration reference signal calculation unit. The reference signal replacement unit 450 replaces the reference signal at a position with body movement detected by the body movement position detection unit with the regenerated reference signal.

The iterative calculation processing unit 470 repeats the processing of each unit of the reference signal body motion correction unit at least once according to a predetermined end condition. At this time, the reference signal after replacement is set as a new reference signal by the reference signal replacement unit. In addition, the setting area update unit 460 updates one or both of the reference signal area and the convolution integration range at least once in the iterative process.

Hereinafter, the details of the processing (FIG. 6: step S1102) performed by each functional unit of the reference signal body motion correction unit 322 will be described with reference to FIG.
<< S1201 >>
First, the convolution integration range setting unit 410 sets the convolution integration range required to regenerate the measurement signal based on the sensitivity information of the receiving coil. FIG. 10 shows a conceptual diagram of the convolution integration range set in the present embodiment. The horizontal direction in this figure is the frequency encoding direction, the vertical direction is the phase encoding direction, and the direction perpendicular to the paper surface is the slicing direction.

For example, in the k-space region 810, in the example shown in FIG. 10A, one point is set in the frequency encoding direction and three points are set in the phase encoding direction in the convolution integration range 811. At this time, the signal 813 regenerated by the convolution integration is regenerated using the measurement signals of two points excluding the measurement signals of the points to be regenerated from the three points surrounded by the convolution integration range 811. .. In the example shown in FIG. 10B, three points are set in the convolution integration range 812 in the frequency encoding direction and the phase encoding direction, respectively. In the illustrated example, the convolution integration range 811 and 812 are set as the convolution integration range centered on the signal 813 regenerated by the convolution integration, but the convolution integration range may not be set in the symmetry region. Further, although one convolution integration range is set, a plurality of convolution integration ranges may be set.

Here, if the convolution calculation range is wide, the amount of calculation in the weighting coefficient calculation step described later becomes large. In addition, there is a high possibility that signals affected by body movement will enter positions with different convolution calculation ranges. In the process (S1102) of the present embodiment, the convolution integration range is updated and the calculation is repeated. Therefore, the convolution integration range set as the initial value is set to a relatively narrow range as shown in FIG. It is desirable to adopt a method of expanding the range.

<< S1202 >>
The weighting coefficient calculation unit 420 calculates the weighting coefficient used when regenerating the measurement signal. The weighting coefficient is calculated based on the sensitivity information of each receiving coil. The specific calculation method will be described below.

Generally, when synthesizing one k-space data from echo signals (k-space data) acquired by receiving coils of a plurality of channels, each echo signal is multiplied by the weighting coefficient of each receiving coil and convoluted and integrated. One echo signal (k-space data) can be regenerated. In the present embodiment, this is used to calculate the weighting coefficient.

That is, the reference signal of an arbitrary k-space position ki in the reference signal region of the receiving coil of the nth channel is y (ki, n), and it is within the convolution integration range excluding the position ki of the receiving coil of the mth channel. When the signal of the k-space position kr is A (kr, m) and the weighting coefficient corresponding to A (kr, m) is w (kr, m), the reference signal y (ki, n) is expressed by the following equation (ki, n). It is represented by 1).

When the equation of the equation (1) is expressed in a matrix form as a simultaneous equation for all pixels in the reference signal region, it is expressed by the equation (2).

ここで、ｗ_０（ｍ）はｙとＡｗとの差を最小にする重み係数を示す。 The weighting coefficient can be calculated by solving equation (2) with respect to w. This simultaneous equation can be solved by, for example, the least squares method shown in Eq. (3).

Here, w ₀ (m) indicates a weighting coefficient that minimizes the difference between y and Aw.

In general, as the number of simultaneous equations increases, the fitting accuracy in the least squares method improves, so that a highly accurate weighting coefficient can be calculated, but the calculation time increases. Further, when a body motion signal is added to the simultaneous equations, the fitting accuracy is lowered. By convolving a relatively narrow range as the initial value and setting it as the integration range, the calculation time is reduced and the possibility of adding a body motion signal is reduced.

ｇは再生成信号を示し、ここでは参照信号領域内の任意の位置ｋｉの再生成信号である。 << S1203, S1204 >>
The regeneration reference signal calculation unit 430 calculates the regeneration signal based on the sensitivity information of the receiving coil only for the measurement signal in the reference signal region by using the weighting coefficient calculated in step S1202 (step S1203). .. The regenerated signal can be calculated using the same equation (4) as the equation (1).

g represents a regenerated signal, which here is a regenerated signal at any position ki within the reference signal region.

The regeneration processing of steps S1202 to S1203 is executed for all channels of the multicoil used for measurement, and the regeneration signals for all channels are calculated.

<< S1205 >>
The body movement position detection unit 440 compares the measurement signal with the regenerated signal and detects the position of the body movement signal. In the region where there is no body motion signal, the measurement signal and the regenerated signal are equal within the error range, but around the body motion signal, as a result of the convolution integration, the error of the body motion signal exudes to the surroundings. Become. Therefore, when the difference between the measurement signal and the regenerated signal is compared, the circumference of the body motion signal has a locally high value. Therefore, the position of the body motion signal can be acquired by detecting the maximum value of this difference signal.

In order to realize this function, the body movement position detection unit 440 includes a difference signal calculation unit 610, a projection signal calculation unit 620, a maximum value calculation unit 630, and a body movement signal position setting unit, as shown in FIG. 640 and.

式（５）、ｓは差分信号、ｆは計測信号、ｇは再生成信号であり、これら信号の変数（ｘ，ｙ，ｃｈ）は、ｘが位相エンコード軸、ｙが周波数エンコード軸、ｃｈが受信コイルのチャンネルである（以下、同じ）。 Hereinafter, the processing flow of each part of the body movement position detection unit 440 will be described with reference to FIG.
First, the difference signal calculation unit 610 calculates the difference between the measurement signal and the regenerated signal (step S1401). The difference signal is represented by the equation (5).

Equation (5), s is a difference signal, f is a measurement signal, g is a regeneration signal, and the variables (x, y, ch) of these signals are x for the phase encoding axis, y for the frequency encoding axis, and ch for the frequency encoding axis. This is the channel of the receiving coil (the same applies hereinafter).

ここで、ｐ（ｘ）は位相エンコード軸の位置ｘでの差分信号の投影値（以下、投影信号と呼ぶ）を示す。投影信号ｐに対して、例えば移動平均フィルターやウェブレットフィルターなどの、フィルタリング処理を施してもよい。 Next, the projection signal calculation unit 620 projects the difference signal s in the phase encoding axis direction in which the influence of body movement appears (step S1402). The projection of the difference signal is represented by the equation (6).

Here, p (x) indicates a projected value (hereinafter, referred to as a projected signal) of the difference signal at the position x of the phase encoding axis. The projected signal p may be subjected to a filtering process such as a moving average filter or a wavelet filter.

The maximum value calculation unit 630 performs a maximum value search for the projected signal p (x) (step S1403). A known method can be adopted for the maximum value search. For example, a method of searching for a value larger than an adjacent sample as a maximum value can be used. At this time, an arbitrary constraint may be provided on the maximum value, for example, the unique height of the maximum value is calculated and discrimination is performed using a preset threshold value. Further, a method of discriminating the maximum value using an arbitrarily set threshold value may be used.

The body motion signal position setting unit 640 acquires the position of the maximum value detected in step S1403 on the phase encoding axis (step S1404).
By the above procedure, the position of the body motion signal is detected from the measurement signal and the regenerated signal. That is, the process (step S1205) by the body movement position detection unit 440 of FIG. 9 is completed.

<< S1206 >>
The reference signal replacement unit 450 replaces the body motion signal detected in step S1205 with the regenerated signal. The regenerated signal corresponding to the position of the detected body motion signal is a signal that is not affected by the body motion from the result of the convolution integration unless there is another body motion signal around it. Therefore, in the replacement process performed in this step, a measurement signal (hereinafter referred to as a correction signal) in which the influence of body movement is corrected can be obtained.

<< S1207 >>
The iterative calculation processing unit 470 repeatedly executes the processes from step S1202 to step S1206 at least once. Various methods can be adopted for the determination of the end of the repetition. For example, the end determination is performed based on the number of iterations, and 10 iterations are performed as a preset number of times. Alternatively, a method may be adopted in which an image quantitative value such as the square root (Root Mean Square Error) or image entropy of the mean square error is calculated, and a threshold value is set for the amount of change in the value to determine the end.

式（７）中、Ｉ、Ｇはそれぞれ計測信号と補正後計測信号からマルチコイル合成により得た画像を示し、ｉは各画像の画素の位置を示す（以下、同じ）。 When RMSE is used, specifically, the square root (RMSE) of the mean square error is calculated from the image obtained by inverse Fourier transforming the measurement signal and the corrected measurement signal and synthesizing the multicoils by the following equation.

In the formula (7), I and G represent images obtained by multi-coil synthesis from the measurement signal and the corrected measurement signal, respectively, and i indicates the position of the pixel of each image (hereinafter, the same applies).

This RMSE is 0 for the same image, and shows a larger value as the difference increases. The time when this value becomes equal to or less than a predetermined threshold value is defined as the end point of the iterative process.

この画像エントロピーＥは、小さな値を取るほど体動アーチファクトが低減されていること示す。従ってＥが所定の閾値以下となったときを繰り返し処理の終了時点とする。 When the image entropy is used for the end determination, the image entropy E is calculated from the following equation (8).

This image entropy E indicates that the smaller the value, the smaller the movement artifact. Therefore, the time when E becomes equal to or less than a predetermined threshold value is set as the end point of the iterative process.

It should be noted that if a sufficient body motion correction effect is obtained by the iterative calculation and no change occurs in the iterative calculation, the same value will be shown even if the RMSE or image entropy is repeated. At this time, the iterative calculation may be terminated when the value falls below the preset change amount threshold value. In addition, other image quantitative values may be used for the end determination, and when it is determined that the correction signal contains more artifacts than the measurement signal before correction, such as an increase in the image quantitative value due to repetition. You may end the iteration in this step.

<< S1208 >>
The setting area update unit 460 updates the reference signal area and the convolution integration range used for signal regeneration based on the sensitivity information of the receiving coil.

Generally, when the number of simultaneous equations calculated by the equation (3) is small, a fitting error occurs due to the influence of noise. Further, if the signal-to-noise ratio (Signal to Noise Ratio; SNR) of the measurement signals used in the simultaneous equations is low, the fitting accuracy is lowered. In addition, a fitting error also occurs when a body motion signal is mixed in the reference signal region.
Here, if the reference signal region is large, the number of simultaneous equations increases, but a large number of body motion signals are included, so that a fitting error occurs. Further, if the convolution integration range is small, the number of simultaneous equations increases, but the weighting coefficient cannot sufficiently reflect the sensitivity information of the receiving coil, so that a fitting error occurs.

Therefore, in the present embodiment, first, in step S1101, a small region is set as the reference signal region so that the reference signal region does not include a large amount of body motion signals. The decrease in the number of simultaneous equations due to the small reference signal region is compensated for by reducing the convolution integration range set in step S1201. In the setting area update (this step S1208) accompanying the subsequent iterative calculation, the convolution integral range is expanded in the direction of widening, and the decrease in the number of simultaneous equations accompanying it is compensated by expanding the reference signal area.

An example of updating the reference signal region will be described again with reference to FIG. 7. In the example shown in FIG. 7B, the reference signal region 801 (FIG. 7A) set in step S1101 is extended in the phase encoding direction (802). For example, the reference signal in the phase encoding axis direction is extended from 27 points to 45 points.

As shown in FIG. 7A, when the reference signal in the frequency encoding axis direction is set in the entire k-space region, the frequency encoding axis direction is not updated, but in step S1101. When the reference signal in the frequency encoding axis direction is not set as the entire k-space region, the frequency encoding axis direction may be updated in this step S1208.

Further, the reference signal area after the update does not have to include the reference signal area before the update. For example, when the reference signal region before updating includes the body motion signal, as shown in FIG. 7C, the region 803 that does not include the k-space center different from the region 801 set in step S1101. May be used as the reference signal area after updating. Further, as shown in FIG. 7D, the two reference signal regions 803 and 804 may be used as the updated reference signal regions, excluding the region including the body motion signal. The reference signal region may be a region symmetrical from the center of k-space or may be asymmetric with respect to the center of k-space.

An example of updating the convolution integral range will be described again with reference to FIG. For example, in the first setting (S1201), as shown in FIG. 10A, the number of points in the frequency encoding direction of the convolution integration range 811 is set to 1, and at the time of updating, as shown by reference numeral 813 in FIG. 10B. , The number of points in the frequency encoding direction is expanded to 3 points. The extension in the phase encoding direction may be performed instead of or in combination with the extension in the frequency encoding direction.

As described above, the size and shape of the reference signal region and the convolution integration range are arbitrary.
The reference signal area and the convolution integration range may be updated at the same time or separately. When performed separately, the body motion can be corrected without reducing the number of simultaneous equations in the equation (3) by expanding the reference signal region and repeating it, and then expanding the convolution integration range.

<< S1209 >>
After updating the reference signal region or the convolution integration range, the iterative calculation processing unit 470 further performs a process of repeating the steps S1201 to S1208 at least once. For example, iterative processing is performed twice. In the iterative process, since the reference signal region and the convolution integration range are updated in step S1208, a regenerated signal different from that before step S1208 is obtained can be obtained. When the reference signal area is updated in step S1208, since the body motion signal of the initial value reference signal area is corrected in step S1207, the measurement signal newly set as the reference signal is mainly corrected. To.

In the repetition, for example, when the setting area is updated only a desired number of times preset and the present step is performed more than that, the update may not be performed and step S1208 may be skipped. The repetition end determination is not the number of iterations as described above, but is the same as the end determination in step S1207. For example, an image quantitative value such as RMSE or image entropy is calculated, and a threshold value is set for the amount of change in the value. A method of determining the end may be taken. Further, limits such as an upper limit may be set in advance in the reference signal region or the convolution integration range, and the process may be repeated until these limits are reached.

By the above procedures S1201 to S1209, the reference signal area correction process (S1102) shown in FIG. 6 is completed, and a measurement signal in which the body motion signal in the reference signal area is corrected is obtained.

<All area correction processing: S1103>
The whole area correction unit 322 corrects the body movement signal mixed in the whole area of the k-space by using the measurement signal of the reference signal area in which the body movement signal is corrected. This process is the same as the body motion correction for the reference signal region (FIGS. 9: S1202 to S1206) except that the body motion correction is used as the reference signal region, and the weighting coefficient is set as shown in FIG. Calculation process (S1301), calculation process to calculate regenerated signal (S1302), process to repeat steps S1301 and S1302 for all channels (S1303), process to detect body movement position (S1304), and process to replace measurement signal. (S1305) is included.

In order to realize such processing, as shown in FIG. 14, the whole area correction unit 323 includes a weight coefficient calculation 710, a regeneration measurement signal calculation unit 720, a body movement position detection unit 730, and a measurement signal replacement unit. 740 and.

Hereinafter, in step S1103 of FIG. 6, processing will be described for each functional unit of the total area correction unit 322 to perform.

<< S1301 >>
The weighting coefficient calculation unit 710 calculates the weighting coefficient based on the sensitivity information of the receiving coil using the corrected reference signal. This process is the same as in step S1202 described above, and the weighting coefficient is calculated by solving simultaneous equations (equation (2)) for all pixels in the reference signal region. Here, since the weighting coefficient is calculated using the reference signal region corrected by the reference signal body motion correction unit 322, the weighting coefficient with less error can be calculated. The convolution integration range for calculating the reference signal may be the same as or different from step S1202.

<< S1302, S1303 >>
The regeneration measurement signal calculation unit 720 regenerates the measurement signal over the entire k-space using the weighting coefficient calculated in step S1301. The calculation of the regenerated signal is the same as in step S1203, and is performed using the equation (4). However, in step S1203, the regenerated signal was calculated only in the reference signal region, but in this step, the regenerated signal g in the entire k-space is calculated.
The regenerated measurement signal calculation unit 720 repeats the processes of steps S1301 and S1302 for each receiving coil.

<< S1304 >>
The body movement position detection unit 730 detects the body movement by the same method as in step S1205. That is, the difference signal between the regenerated signal and the actually measured measurement signal is calculated, the maximum position is searched from the projection in the phase encoding axis direction, and that is used as the body movement position. However, in the whole area body motion correction process S1103, since the measurement signal is regenerated in the entire k-space in step S1303, the body motion detection in this step is also performed in the entire k-space.

<< S1305 >>
In the measurement signal replacement unit 740, the measurement signal at the position where the body movement is detected is replaced with the regenerated signal, as in step S1206. By the above procedures S1301 to S1305, a measurement signal in which the body motion signal in the entire k-space is corrected can be obtained (FIG. 6: S1103).

In the body motion correction processing of the reference signal area shown in FIG. 9, the reference signal area and the convolution integration range were updated and the iterative processing was performed. However, in the whole area body motion correction processing, the reference signal area after the body motion correction was performed. Since the weighting coefficient is obtained using, it is not necessary to perform iterative processing.

The body movement correction process (FIG. 3: S1002) in the present embodiment is completed by the processes of steps S1101 to S1103 described above. After that, the image reconstruction unit 330 reconstructs the image using the measurement signals after the body motion correction of each channel. That is, the image reconstruction unit 330 reconstructs the k-space data for each channel including the measurement signal corrected by the full area correction unit 323 into a real space image by inverse Fourier transform, and the image of each receiving coil. To calculate the final image. The combined final image is displayed on the display 110 as, for example, an absolute value image.
If necessary, the regenerated image calculated in step S1002 may be appropriately displayed on the display 110.

According to the present embodiment, in a technique of performing body motion correction by comparing / replacing a regenerated signal created using sensitivity information with an actually measured measurement signal, a k-space region (reference signal) for acquiring sensitivity information. The area) is first corrected for body motion, and then sensitivity information is obtained from the corrected reference signal area, and the body motion correction for the entire area is performed using the information. Therefore, the sensitivity information obtained from the reference signal area is obtained. The accuracy of the image can be improved, and a high image quality improvement effect can be obtained. Further, according to the present embodiment, in the body motion correction of the reference signal region, the correction accuracy of the reference signal region is improved by performing the iterative calculation while updating the convolution integration range for obtaining the reference signal region or the regenerated signal. be able to.

[Example of the first embodiment]
In order to confirm the effect of body movement correction by the first embodiment, the following imaging experiment was carried out.
Using a magnetic resonance imaging device of the type shown in FIG. 1 (a) with a static magnetic field strength of 3 tesla and a receiving coil equipped with 15 channels, the pulse sequence shown in FIG. 5 was executed to obtain a cylindrical phantom (nickel chloride aqueous solution). The magnetic resonance signal was measured.

In order to mix the body movement signal in a simulated manner, the phantom measured in the normal arrangement and the one measured by inserting a cushion of about 3 cm on the neck side and shifting the position are acquired, and the measurement signal in k-space is acquired. By exchanging, a measurement signal was created in a simulated state in which body movements were mixed. In this embodiment, the measurement signals of the phase encode axis specified in the phase encode axis direction at a 6-point period are replaced.

The method (Example) described in the first embodiment and the correction of the reference signal area, that is, the iterative calculation and the setting area update shown in FIG. 9 are not performed on the measured signal in which the body movement is mixed, which is simulated. The method of correcting the entire area (comparative example) was applied to the body movement correction. For the reference signal region of the comparative example, the same conditions as those used in the final iterative calculation of the example were set. Therefore, the body motion signal is mixed in the reference signal region.

The results are shown in FIG. In FIG. 15, (a) is an absolute value image 1501 (reference image) before applying body motion, (b) is an absolute value image 1502 in which body motion correction is performed according to a comparative example, and (c) is body motion correction according to an example. The absolute value image 1503, (d) is the absolute value image 1504 (body movement image) after the body movement is applied, and (e) is the difference absolute value obtained by displaying the difference between the absolute value images 1501 and 1502 on a scale of 100 times. Images 1505 and (f) show a difference absolute value image 1506 in which the difference between the absolute value images 1501 and 1503 is displayed on a scale of 100 times.

As can be seen from the result of FIG. 15, in the body motion corrected absolute value image 1502 of the comparative example, the artifact remains at the position indicated by the arrow 1507, for example, whereas the body motion corrected absolute value image of the example is used. It can be seen that the artifacts are reduced in 1503. Further, in the difference absolute value image 1505 of the comparative example, the difference from the absolute value image 1501 before the body movement is strongly left, whereas in the difference absolute value image 1506 of the example, the absolute value before the body movement is applied is absolute. It can be seen that there is almost no difference from the value image 1501.
From the above results, it was confirmed that the method described in the first embodiment can obtain a high image quality improving effect.

[Second Embodiment]
In the first embodiment, the case where the signal measurement in the k-space is orthogonally sampled has been described, but in the present embodiment, the signal measurement of the non-orthogonal sampling is performed. The configuration of the apparatus is the same as that of the first embodiment, but the pulse sequence used is different, and the function of the computer 109 is changed accordingly. Hereinafter, only the points different from the first embodiment will be described.

Non-orthogonal sampling includes radial sampling in which k-space 820 is sampled radially and spiral sampling in which k-space 830 is sampled in a spiral shape, as shown in FIGS. 16A and 16B. Further, although not shown, as a modification of radial sampling, there is also sampling called a propeller that samples radiation at the same angle in a band shape. Any of the present embodiments can be applied. The signals measured by these non-orthogonal samplings are interpolated to the same Cartesian coordinate type as the orthogonal sampling (hereinafter referred to as gridting process).

Therefore, as shown in FIG. 17, the body motion correction processing unit 320 of the present embodiment further includes a gripping processing unit 340 that interpolates the non-orthogonally sampled signal into the orthogonal sampling. The processing performed by the gripping processing unit 340 is known, and description thereof will be omitted here. Since the measurement signal subjected to this gripping process has the same coordinate system as that of the first embodiment, the body motion correction process is performed by the same procedure as that of the first embodiment.

[Third Embodiment]
In the first embodiment, the case where the phase-encoded gradient magnetic field (Gp) is applied so that the desired k-space region set in advance is completely filled and the echo signal is measured has been described, but in the present embodiment, the period The application of the phase-encoded gradient magnetic field (Gp) is thinned out, and the measurement is performed so that the k-space region is thinned out periodically (parallel imaging).

Hereinafter, the processing of the present embodiment will be described with reference to FIG.
<Step S1701>
The measurement control unit 310 performs parallel imaging imaging according to a predetermined thinning rate or double speed rate (R-factor) and other measurement conditions set in advance, and acquires measurement data for each channel.

FIG. 19 shows an example of measurement data 840 by parallel imaging. As shown in FIG. 19A, in parallel imaging, not all signals in the preset k-space are measured, but some signals are thinned out for measurement. In FIG. 19A, the signal measured in the k-space is shown by a solid line, and the position of the unmeasured signal is shown by a dotted line. Here, the case where the thinning rate is 1/2, that is, the case where the measurement is thinned out every other line is shown, but the thinning rate is not limited to the one shown in the figure.

<Step S1702>
Next, as shown in FIG. 19B, the area thinned out from such k-space data 840 is excluded, and k-space data 850 smaller than the desired k-space area set in advance is created.

<Step S1703>
After that, the reduced k-space data 850 is subjected to body motion correction processing. The body motion correction process is the same as the process of the first embodiment. First, a reference signal area is set in the k-space data 850, and the body motion correction process is performed on the reference signal area by the iterative calculation shown in FIG.

<Step S1704>
Next, the body motion correction process for the entire k-space 850 is performed using the signal in the reference signal region after the body motion correction. That is, the weighting coefficient of each receiving coil is calculated from the reference region signal after the body motion correction, and the regenerated signal is generated for the entire k-space using the weighting coefficient. The generated regenerated signal is compared with the actually measured measurement signal, the body movement position is detected, and the measurement signal at the detected position is corrected. As a result, the body motion correction of the k-space data 850 composed of the actually measured measurement signals is completed.

<Step S1705>
After that, the k-space data 850 is returned to the original size (k-space data 840), and for the unmeasured signal, a known signal interpolation method such as SENSE (Sensitivity Encoding), SMASH (Simultaneus Acquisition of Spatial Harmonics), or Image reconstruction is performed using GRAPPA (Generialized Autocharibrating Partially Parallell Acquisitions). In this step S1705, the sensitivity information of each receiving coil is required, and as this sensitivity information, the sensitivity information of the receiving coil and the weighting coefficient calculated in step S1704 can be used. Since the reconstructed image uses the k-space data of each channel corrected for body movement, the influence of body movement is reduced, and an image without body movement artifacts can be obtained.

[Display Embodiment]
The pulse sequence, sampling method, measurement order of k-space (application order of gradient magnetic field), and imaging conditions described in the above-described embodiments may be set in advance with the imaging method, but GUI (Graphic) may be used. It can be set by the user through User Interface) or the like. Further, the processing by the body motion correction processing unit executed in each embodiment may be automatically started, for example, when a site where a body motion artifact is expected is set as an imaging site, or the user may use the process. If necessary, it is also possible to determine the necessity of body motion correction before imaging or after confirming the image after imaging, and set the necessity of processing and the processing conditions via the input device 115. is there.

FIG. 20 shows an example of an interface screen (GUI) when the user interactively sets conditions and the like. In FIG. 20A, the screen 900 in which the user sets the pulse sequence and the imaging parameter prior to the start of measurement accepts the input of the necessity of the body motion correction process. On this screen 900, for example, it is possible to accept selection of an imaging method (pulse sequence) and setting of ordering (k-space measurement order) in consideration of body movement. When parallel imaging is selected, input of imaging parameters such as R factor is accepted.

The user selects the body motion correction by checking the box 901 for inputting the "necessary" of the body motion correction process in consideration of the imaging site and whether the selected imaging method is a pulse sequence that is vulnerable to body motion artifacts. To do. If the body movement correction process is involved, the processing time until image reconstruction will be extended, so if you want to check the reconstructed image as soon as possible, check the "No" box.

Alternatively, as shown on the screen 910 (b), the box 901 instructing the body motion correction process is displayed together with the image display unit 905, and the body motion artifact appearing in the final image 905 displayed on the image display unit 905 is taken into consideration. , You may enter the "required" of the body movement correction process in the box. Although not shown in FIG. 20, the user may be able to set the type of image to be displayed on the display as the final image of the screen 910, the necessity of displaying the image reconstructed from the regenerated signal, and the like.

The computer 109 performs the process according to FIG. 4 and the like only when the body motion correction process “necessary” is selected, and based on the set imaging method and pulse sequence, the process of any of the above-described embodiments. To execute. According to this embodiment, the range of user settings can be expanded.

As described above, the MRI apparatus 100 of the present embodiment includes a static magnetic field generating magnet 102 that generates a static magnetic field in the space where the subject is placed, and a transmission unit (105, 107) that transmits a high-frequency magnetic field pulse to the subject. ), The receiving unit (106, 108) including two or more receiving coils 106 that receive the nuclear magnetic resonance signal generated from the subject by irradiation with the high-frequency magnetic field pulse, and the position information is added to the nuclear magnetic resonance signal. The operation of the gradient magnetic field application unit (103, 112) for applying the gradient magnetic field for the purpose, the transmission unit, the gradient magnetic field application unit, and the reception unit is controlled, and arithmetic processing is performed on the received nuclear magnetic resonance signal. A computer (109) for performing is provided. The computer (109) controls the operations of the transmitting unit, the gradient magnetic field applying unit, and the receiving unit, and arranges the nuclear magnetic resonance signals received by the two or more receiving coils in the measurement space (310). ), A body motion correction processing unit (320) that corrects the body motion of the measurement signal in the measurement space, and an image reconstruction unit that reconstructs an image using the measurement signal corrected by the body motion correction processing unit. (330) and. The body motion correction processing unit (320) includes a reference signal area setting unit (321) that sets at least one region of the measurement space as a reference signal region and sets a measurement signal in the reference signal region as a reference signal. Measurement of the entire area of the measurement space based on the reference signal body motion correction unit (322) that corrects the body motion of the reference signal and the reference signal after the body motion correction corrected by the reference signal body motion correction unit. It is provided with an all-area correction unit (323) that corrects body motion for a signal.

Further, the body motion correction method of the present embodiment is a body that corrects a signal affected by body motion included in the measurement signal with respect to a measurement signal acquired by a magnetic resonance imaging device provided with two or more receiving coils. In the dynamic correction method, a reference signal region setting step for setting a signal in at least one or more regions as a reference signal region in the measurement signals acquired by the at least two or more receiving coils, and a body in the reference signal region. Reference signal body motion correction step to correct the dynamic signal, and
The reference signal includes an all-area correction step for correcting the measured body movement in the entire area based on the body movement-corrected reference signal corrected by the body movement correction unit.

According to the present embodiment, even when a body motion signal is mixed in the reference signal region, iterative calculation is performed in advance while updating the setting when regenerating the measurement signal using the sensitivity distribution information of a plurality of receiving coils. By performing this on the reference area, a high body movement correction effect can be obtained.

100: MRI device, 101: subject, 102: static magnetic field coil, 103: gradient magnetic field coil, 104: shim coil, 105: transmit coil, 106: receive coil, 107: transmitter, 108: receiver, 109: computer, 110: Display, 111: External storage device, 112: Power supply unit for gradient magnetic field, 113: Power supply unit for shim, 114: Sequence control device, 115: Input device, 120: MRI device, 130: MRI device, 310: Measurement control Unit, 320: Body motion correction processing unit, 330: Image reconstruction unit, 340: Gridding processing unit, 410: Folding integration range setting unit, 420: Weight coefficient calculation unit, 430: Regeneration reference signal calculation unit, 440: Body movement position detection unit, 450: Reference signal replacement unit, 460: Setting area update unit, 470: Repetitive calculation processing unit, 510: Spin echo system pulse sequence, 610: Difference signal calculation unit, 620: Projection signal calculation unit, 630 : Maximum value calculation unit, 640: Body movement signal position setting unit, 710: Weight coefficient calculation unit, 720: Regeneration measurement signal calculation unit, 730: Body movement position detection unit, 740: Measurement signal replacement unit.

Claims (14)

A magnet that generates a static magnetic field in the space where the subject is placed, and a magnet that generates a static magnetic field.
A transmitter that transmits a high-frequency magnetic field pulse to the subject,
A receiver having two or more receiving coils that receive the nuclear magnetic resonance signal generated from the subject by irradiation with a high-frequency magnetic field pulse, and a receiver.
A gradient magnetic field application unit that applies a gradient magnetic field for adding position information to the nuclear magnetic resonance signal, and a gradient magnetic field application unit.
A computer that controls the operations of the transmitting unit, the gradient magnetic field applying unit, and the receiving unit, and performs arithmetic processing on the received nuclear magnetic resonance signal.
It is a magnetic resonance imaging apparatus equipped with
The calculator
A measurement control unit that controls the operations of the transmission unit, the gradient magnetic field application unit, and the reception unit to arrange the nuclear magnetic resonance signals received by the two or more reception coils in the measurement space.
A body motion correction processing unit that corrects body motion for the measurement signal in the measurement space,
An image reconstruction unit that reconstructs an image using the measurement signal corrected by the body motion correction processing unit is provided.
The body movement correction processing unit
A reference signal area setting unit that sets at least one area of the measurement space as a reference signal area and sets a measurement signal in the reference signal area as a reference signal.
A reference signal body motion correction unit that corrects the body motion of the reference signal,
Based on the reference signal after the body motion correction corrected by the reference signal body motion correction unit, the whole area correction unit that corrects the body motion for the measurement signal in the entire area of the measurement space is provided .
The reference signal body motion correction unit
A convolution integral range setting unit that sets the range of the measurement space used to calculate the weighting coefficient based on the sensitivity distribution of the receiving coil as the convolution integral range, and a convolution integral range setting unit.
A weighting coefficient calculation unit that calculates a weighting coefficient of the convolutional integration range using the reference signal and the measurement signal of the convolutional integration range, and a weighting coefficient calculation unit.
For each reference signal in the reference signal region, a regenerated reference signal calculation unit that regenerates the reference signal using the reference signal and the weighting coefficient, and
From the reference signal and the regenerated reference signal calculated by the regenerated reference signal calculation unit, a body movement position detecting unit that detects a signal position with body movement in the reference signal region, and a body movement position detecting unit.
A reference signal replacement unit that replaces a reference signal at a position with body movement detected by the body movement position detection unit with the regenerated reference signal, and a reference signal replacement unit.
Magnetic resonance imaging apparatus comprising: a. The magnetic resonance imaging apparatus according to claim 1.
The reference signal body motion correction unit
A setting area update unit that updates one or both of the reference signal area and the convolution integration range at least once, and
An iterative calculation processing unit that repeats each processing of the setting area updating unit, the weighting coefficient calculation unit, the body movement position detecting unit, and the reference signal replacement unit at least once.
A magnetic resonance imaging apparatus characterized by further comprising. The magnetic resonance imaging apparatus according to claim 2.
The setting area updating unit is a magnetic resonance imaging apparatus characterized in that the setting area updating unit is updated so as to expand the reference signal area. The magnetic resonance imaging apparatus according to claim 2.
The setting area updating unit is a magnetic resonance imaging apparatus characterized in that the setting area updating unit is updated so as to widen the convolution integration range. The magnetic resonance imaging apparatus according to claim 1.
The reference signal body motion correction unit
The reference signal after replacement is set as a new reference signal by the reference signal replacement unit, and each of the weight coefficient calculation unit, the regeneration reference signal calculation unit, the body movement position detection unit, and the reference signal replacement unit. A magnetic resonance imaging apparatus further comprising a repetitive arithmetic processing unit that repeats processing at least once. The magnetic resonance imaging apparatus according to claim 2 or 5.
The iterative calculation processing unit is a magnetic resonance imaging apparatus characterized by performing iterative calculations a preset number of times. The magnetic resonance imaging apparatus according to claim 2 or 5.
The iterative calculation processing unit performs iterative calculation until the amount of change in the quantitative value calculated from the image reconstructed by the image reconstruction unit using the reference signal replaced by the reference signal replacement unit falls below a preset threshold value. A magnetic resonance imaging apparatus characterized in that the above is performed. The magnetic resonance imaging apparatus according to claim 1.
The body movement position detection unit
A difference signal calculation unit that calculates a difference signal by differentiating the reference signal and the regenerated reference signal,
A projection signal calculation unit that calculates the projection signal by projecting the difference signal in the phase encoding direction,
A maximum value calculation unit that calculates the maximum value of the projected signal, and
A body motion signal position setting unit that sets a position corresponding to the maximum value as a body motion signal position,
A magnetic resonance imaging apparatus comprising. A magnet that generates a static magnetic field in the space where the subject is placed, and a magnet that generates a static magnetic field.
A transmitter that transmits a high-frequency magnetic field pulse to the subject,
A receiver having two or more receiving coils that receive the nuclear magnetic resonance signal generated from the subject by irradiation with a high-frequency magnetic field pulse, and a receiver.
A gradient magnetic field application unit that applies a gradient magnetic field for adding position information to the nuclear magnetic resonance signal, and a gradient magnetic field application unit.
A computer that controls the operations of the transmitting unit, the gradient magnetic field applying unit, and the receiving unit, and performs arithmetic processing on the received nuclear magnetic resonance signal.
It is a magnetic resonance imaging apparatus equipped with
The calculator
A measurement control unit that controls the operations of the transmission unit, the gradient magnetic field application unit, and the reception unit to arrange the nuclear magnetic resonance signals received by the two or more reception coils in the measurement space.
A body motion correction processing unit that corrects body motion for the measurement signal in the measurement space,
An image reconstruction unit that reconstructs an image using the measurement signal corrected by the body motion correction processing unit is provided.
The body movement correction processing unit
A reference signal area setting unit that sets at least one area of the measurement space as a reference signal area and sets a measurement signal in the reference signal area as a reference signal.
A reference signal body motion correction unit that corrects the body motion of the reference signal,
Based on the reference signal after the body motion correction corrected by the reference signal body motion correction unit, the whole area correction unit that corrects the body motion for the measurement signal in the entire area of the measurement space is provided.
The whole area correction unit
A weighting coefficient calculation unit that calculates a weighting coefficient using the measurement signal and the body movement-corrected reference signal corrected by the reference signal body movement correction unit, and a weighting coefficient calculation unit.
A regenerated measurement signal calculation unit that regenerates the measurement signal using the measurement signal and the weighting coefficient,
Using the measurement signal and the regeneration measurement signal generated by the regeneration measurement signal calculation unit, a body movement position detection unit that detects a signal position with body movement in the measurement space, and a body movement position detection unit.
A measurement signal replacement unit that replaces the measurement signal at a position with body movement detected by the body movement position detection unit with the regenerated measurement signal, and a measurement signal replacement unit.
A magnetic resonance imaging apparatus comprising. A magnet that generates a static magnetic field in the space where the subject is placed, and a magnet that generates a static magnetic field.
A transmitter that transmits a high-frequency magnetic field pulse to the subject,
A receiver having two or more receiving coils that receive the nuclear magnetic resonance signal generated from the subject by irradiation with a high-frequency magnetic field pulse, and a receiver.
A gradient magnetic field application unit that applies a gradient magnetic field for adding position information to the nuclear magnetic resonance signal, and a gradient magnetic field application unit.
A computer that controls the operations of the transmitting unit, the gradient magnetic field applying unit, and the receiving unit, and performs arithmetic processing on the received nuclear magnetic resonance signal.
It is a magnetic resonance imaging apparatus equipped with
The calculator
A measurement control unit that controls the operations of the transmission unit, the gradient magnetic field application unit, and the reception unit to arrange the nuclear magnetic resonance signals received by the two or more reception coils in the measurement space.
A body motion correction processing unit that corrects body motion for the measurement signal in the measurement space,
An image reconstruction unit that reconstructs an image using the measurement signal corrected by the body motion correction processing unit is provided.
The body movement correction processing unit
A reference signal area setting unit that sets at least one area of the measurement space as a reference signal area and sets a measurement signal in the reference signal area as a reference signal.
A reference signal body motion correction unit that corrects the body motion of the reference signal,
Based on the reference signal after the body motion correction corrected by the reference signal body motion correction unit, the whole area correction unit that corrects the body motion for the measurement signal in the entire area of the measurement space is provided.
The measurement control unit is a magnetic resonance imaging device characterized in that the measurement space is orthogonally sampled. A magnet that generates a static magnetic field in the space where the subject is placed, and a magnet that generates a static magnetic field.
A transmitter that transmits a high-frequency magnetic field pulse to the subject,
A receiver having two or more receiving coils that receive the nuclear magnetic resonance signal generated from the subject by irradiation with a high-frequency magnetic field pulse, and a receiver.
A gradient magnetic field application unit that applies a gradient magnetic field for adding position information to the nuclear magnetic resonance signal, and a gradient magnetic field application unit.
A computer that controls the operations of the transmitting unit, the gradient magnetic field applying unit, and the receiving unit, and performs arithmetic processing on the received nuclear magnetic resonance signal.
It is a magnetic resonance imaging apparatus equipped with
The calculator
A measurement control unit that controls the operations of the transmission unit, the gradient magnetic field application unit, and the reception unit to arrange the nuclear magnetic resonance signals received by the two or more reception coils in the measurement space.
A body motion correction processing unit that corrects body motion for the measurement signal in the measurement space,
An image reconstruction unit that reconstructs an image using the measurement signal corrected by the body motion correction processing unit, and an image reconstruction unit.
With
The body movement correction processing unit
A reference signal area setting unit that sets at least one area of the measurement space as a reference signal area and sets a measurement signal in the reference signal area as a reference signal.
A reference signal body motion correction unit that corrects the body motion of the reference signal,
Based on the reference signal after the body motion correction corrected by the reference signal body motion correction unit, the whole area correction unit that corrects the body motion for the measurement signal in the entire area of the measurement space, and the whole area correction unit.
With
The measurement control unit samples the measurement space in a non-orthogonal manner.
The body motion correction processing unit is a magnetic resonance imaging apparatus further comprising a gridding processing unit that converts a non-orthogonally sampled measurement signal into a measurement signal of orthogonal sampling by a gridding process. The magnetic resonance imaging apparatus according to claim 1.
The measurement control unit performs parallel imaging in which the measurement space is thinned out for measurement.
The body motion correction processing unit is a magnetic resonance imaging apparatus characterized in that the measurement space is reduced to a measurement space composed of only measurement signals, and the body motion correction is performed on the reduced measurement space. The magnetic resonance imaging apparatus according to claim 1.
A magnetic resonance imaging apparatus further comprising an input unit that receives the necessity of processing by the body motion correction processing unit. It is a body motion correction method that corrects a signal affected by body motion included in the measurement signal with respect to a measurement signal acquired by a magnetic resonance imaging device provided with two or more receiving coils.
In the measurement signal acquired by each of the two or more receiving coils, a reference signal area setting step for setting a signal in at least one or more areas as a reference signal area, and a reference signal area setting step.
A reference signal body motion correction step for correcting a body motion signal in the reference signal region, and
The whole area correction step of correcting the body movement of the measured whole area based on the body motion corrected reference signal corrected in the reference signal body movement correction step is included.
The reference signal body motion correction step
The step of setting the range of the measurement space used to calculate the weighting coefficient based on the sensitivity distribution of the receiving coil as the convolution integration range, and
A step of calculating the weighting coefficient of the convolution integration range by using the reference signal which is a signal of the reference signal region and the measurement signal of the convolution integration range, and
For each reference signal in the reference signal region, a step of regenerating the reference signal using the reference signal and the weighting coefficient, and
A step of detecting a signal position with body movement in the reference signal region from the reference signal and the regenerated reference signal, and
A step of replacing the detected reference signal at the signal position with the body movement with the regenerated reference signal, and
A body movement correction method characterized by including.

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