Phase correction method, phase correction apparatus, and magnetic resonance imaging apparatus

Abstract

To perform phase correction for reducing a phase difference in a region of interest between data whose polarities are inverted to each other in reading directions in a k-space.SOLUTION: A phase correction method includes: acquiring first k-space data collected in a first reading direction and second k-space data collected in a second reading direction which is a direction opposite to the first reading direction; generating first adjustment data and second adjustment data by performing, on a first real space data and second real space data obtained by performing one-dimensional Fourier transformation on the first k-space data and the second k-space data, respectively, a predetermined weighting so that weight is low in regions corresponding to positions in the reading directions and has phase difference dispersion larger than predetermined dispersion; calculating a correction amount for correcting a phase difference between the first adjustment data and the second adjustment data; and, on the basis of the correction amount, correcting a phase difference between data collected in different reading directions.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A magnetic resonance imaging (MRI) device is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field with radio frequency (RF) signals at the Larmor frequency, and generates images by reconstructing the MR signals generated from the subject in response to the excitation.

[0003] One of the pulse sequences for imaging a subject in an MRI device is the echo planar imaging (EPI) method. In the EPI method, MR signal data is collected while reversing the polarity of the readout gradient magnetic field. In this case, a phase difference occurs between MR signal data with the polarity of the readout gradient magnetic field reversed due to eddy currents and magnetic field inhomogeneity. If adjacent k-spaces are filled with a phase difference between MR signal data, N / 2 artifacts may occur.

[0004] Therefore, in order to reduce the N / 2 artifact, the Ahn-Cho method, which performs 1st and 0th order phase correction, and other multi-order phase correction methods are known. However, with the conventional phase correction methods, phase correction is not performed appropriately, which can cause image degradation in the region of interest in diagnosis or examination. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2011 / 234221 [Patent Document 2] U.S. Pat. No. 1,106,1098 [Non-patent literature]

[0006] [Non-Patent Document 1] CB AHN et al., “A New Phase Correction Method in NMR Imaging Based on Autocorrelation and Histogram Analysis”, IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. MI-6, NO. 1, MARCH 1987 Summary of the Invention [Problem to be solved by the invention]

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to perform phase correction to reduce the phase difference in the region of interest between data whose polarity is inverted in the readout direction of the k-space. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0008] A phase correction method according to one embodiment acquires first k-space data collected in a first readout direction and second k-space data collected in a second readout direction opposite to the first readout direction, generates first adjusted data and second adjusted data in first real space data and second real space data obtained by one-dimensional Fourier transform of the first k-space data and the second k-space data, respectively, which correspond to a position in the readout direction and are weighted with a predetermined weight such that the weight is low in an area where the variance of the phase difference is larger than a predetermined variance, calculates a correction amount for correcting the phase difference between the first adjusted data and the second adjusted data, and corrects the phase difference between data having different readout directions based on the correction amount. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a phase correction device according to an embodiment. [Diagram 2] FIG. 1 is an explanatory diagram of the phase difference between k-space and real space. [Diagram 3] FIG. 13 is an explanatory diagram of data whose polarity is inverted in the readout direction of k-space and real space data that has been subjected to one-dimensional Fourier transform. [Figure 4] FIG. 13 shows an example of poor phase correction in a region of interest. [Diagram 5] 4 is a flowchart showing an example of operation of a phase correction method according to the embodiment. [Figure 6] FIG. 1 is an explanatory diagram of phase lines and the readout direction of k-space data. [Figure 7] FIG. 4 is an explanatory diagram of adjustment data according to the embodiment. [Figure 8] 4A to 4C are diagrams showing first to third examples of weighting according to the first embodiment. [Figure 9] 4A to 4C are diagrams showing a first example and an application example of weighting according to the first embodiment. [Figure 10] 6A to 6C are diagrams showing a second example and an application example of weighting according to the first embodiment. [Figure 11] FIG. 11 is a diagram showing a fourth example of weighting according to the first embodiment. [Figure 12] FIG. 11 is a diagram showing an example of phase correction using a fourth example of weighting according to the first embodiment. [Figure 13] FIG. 11 is a diagram showing an example of weighting in a phase correction method according to the second embodiment. [Figure 14] 1 is a schematic diagram showing an example of the overall configuration of a magnetic resonance imaging apparatus according to an embodiment; [Figure 15] 1 is a schematic diagram showing an example of the configuration of a magnetic resonance imaging apparatus including a phase correction device according to an embodiment; [Figure 16] 5 is a flowchart showing a first operation example of the magnetic resonance imaging apparatus according to the embodiment. [Figure 17] 6 is a flowchart showing a second operation example of the magnetic resonance imaging apparatus according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of a phase correction method, a phase correction device, and a magnetic resonance imaging device will be described in detail with reference to the drawings.

[0011] (Phase correction device) 1 is a schematic diagram showing an example of the configuration of a phase correction device 4 according to an embodiment. The phase correction device 4 performs phase correction to reduce a phase difference in a region of interest, such as diagnosis or examination, between data whose polarity is inverted in the readout direction of the k-space. As shown in FIG. 1, the phase correction device 4 includes a processing circuit 41 and a storage circuit 42. The phase correction device 4 may further include an input interface 43, a network interface 44, and a display 45.

[0012] The display 45 is configured with a general display device such as, for example, a liquid crystal display, an OLED (Organic Light Emitting Diode) display panel, a plasma display panel, an organic EL (Electro Luminescence) panel, etc. The display 45 displays various information under the control of the processing circuit 41. The display 45 is a display device, and may also be, for example, a GUI (Graphical User Interface) that can receive various operations from a user, such as a touch panel.

[0013] The network interface 44 implements various information communication protocols according to the form of the network. The network interface 44 has a function of performing communication control according to various protocols and connecting to the network by wire or wirelessly. The network interface 44 can exchange various data, such as MR signal data of a subject, between the network and the storage circuitry 42, for example.

[0014] The input interface 43 includes an input device that can be operated by a user, and an input circuit that inputs a signal from the input device. The input device can be realized by, for example, a trackball, a switch, a mouse, a keyboard, a touchpad that performs an input operation by touching the scanning surface, a touchscreen in which a display screen and a touchpad are integrated, a non-contact input device using an optical sensor, a voice input device, etc. When the input device is operated by a user, the input circuit generates a signal according to the operation and outputs it to the processing circuit 41. Note that the input interface 43 may be a touch panel in which the input device is integrated with a display.

[0015] The memory circuitry 42 is configured with a processor-readable storage medium, such as a semiconductor memory element such as a random access memory (RAM) or a flash memory, a hard disk, or an optical disk. The memory circuitry 42 may be configured with a portable medium, such as a universal serial bus (USB) memory or a digital video disk (DVD). The memory circuitry 42 can transmit and receive various data, such as MR signal data of a subject, via the portable medium. The memory circuitry 42 also stores various processing programs used in the processing circuitry 41, data required for executing the programs, and the like.

[0016] The processing circuit 41 realizes a function of overall control of the phase correction device 4. The processing circuit 41 is a processor that realizes various functions by reading and executing various processing programs stored in the storage circuit 42 or directly incorporated in the processing circuit 41. The processor of the processing circuit 41 realizes each function such as an acquisition function F1, an adjustment function F2, and a correction function F3.

[0017] Here, the phase difference between the k-space and the real space will be described with reference to Fig. 2, comparing the k-space data with the real space data. Fig. 2(b) and Fig. 2(d) are real space data obtained by one-dimensional Fourier transform of the MR signal data in the k-space of Fig. 2(a) and Fig. 2(c), respectively. Fig. 2(c) shows a state in which the center of the echo in the k-space is shifted by the shift amount Shift in formula (1) compared to Fig. 2(a). Here, the phase difference (or phase shift) in the real space refers to a phase difference caused by the influence of eddy currents, magnetic field inhomogeneity, etc. between data collected in a first readout direction and data collected in a second readout direction opposite to the first readout direction.

[0018]

number

[0019] Fig. 2(e) shows the zeroth-order and first-order phase differences in real space. By inversely multiplying the linear phase shown in formula (2) based on the zeroth-order and first-order phase differences in real space (i.e., by multiplying the real-space data by the complex conjugate of the linear phase shown in formula (2)), phase correction of the real-space data is possible. Furthermore, since this correction process can be performed after data collection is completed, there is no need to adjust the phase difference before data collection or collect additional data for correction.

[0020]

number

[0021] The echo shift occurring in the k-space between multiple MR signal data is caused by eddy currents and magnetic field inhomogeneity of the magnetic resonance imaging device in the EPI method, which collects MR signal data while reversing the polarity of the readout gradient magnetic field to fill the k-space, for example. If the adjacent k-space is filled in a state where an echo shift occurs in the k-space data, this causes N / 2 artifacts to occur in the MR image.

[0022] In order to reduce the N / 2 artifact, for example, the Ahn-Cho method is known, which performs zero-order and first-order phase correction. Each arrow in FIG. 3(a) with a different direction indicates the k-space data repeatedly collected over time t while reversing the readout direction. FIG. 3(b) shows the real space data obtained by one-dimensional Fourier transform of the k-space data in FIG. 3(a) over time t. In the real space data in FIG. 3(b), F2i(x) and F2i+1(x) represent data whose polarities are reversed with respect to each other in the readout direction of the k-space.

[0023] For example, the phase coefficient θ1 (φ1 = θ1·x) corresponding to the first-order phase difference φ1 in real space is calculated using real space data in the readout direction (X direction) as shown in equation (3). The zeroth-order phase difference φ0 in real space is estimated from the offset at the center position 0 in real space after the first-order phase difference is corrected.

[0024]

number

[0025] In equation (3), real space data F2i(x) represents the signal value (complex signal value) of the 2i-th pixel in the time t direction and the x-th pixel in the real space X direction (see Fig. 3(b)). Also, conj(F) represents the complex conjugate value of the complex signal value F, and angle[] represents the operation of calculating the phase of the complex number in [].

[0026] As shown in formula (3), the phase coefficient θ1 corresponding to the first-order phase difference φ1 is obtained by calculating the phase of the correlation function of the signal values ​​of pixels adjacent to each other in the time t direction and the real space X direction. In general, an imaging target part having a larger signal value is often a region of interest that has useful information for correction processing. However, for example, when a larger signal value is present at a position where the magnetic field uniformity is low or where the phase changes sharply, phase correction may not be performed appropriately. In addition, image degradation may occur in the region of interest due to phase correction not being performed appropriately.

[0027] FIG. 4 is a diagram showing an example of poor phase correction in a region of interest. FIG. 4(a) shows the phase difference before correction, the correction amount, and the phase difference after correction in the readout direction. The phase difference after correction is the phase difference obtained by correcting the phase difference before correction by the correction amount. FIG. 4(b) is a generated image after the phase correction of FIG. 4(a). As shown in FIG. 4, for example, when there is a locally large signal value at the end of an image region with low magnetic field uniformity (P1 in FIG. 4(b)), the phase correction at P2 in FIG. 4(a) may not be performed appropriately due to the phase correction at P1 in FIG. 4(a). If the phase correction is not performed appropriately, image degradation such as shading may occur in the center of an image region with a relatively small signal value (for example, P2 in FIG. 4(b)).

[0028] Therefore, in the phase correction device 4 of the embodiment, in order to obtain an image in which the region of interest is well depicted, phase correction is performed between data whose polarity is inverted in the readout direction of k-space to reduce the phase difference in the region of interest.

[0029] (First embodiment) The processing circuit 41 of the phase correction device 4 has an acquisition function F1, an adjustment function F2, and a correction function F3. The functions and operations of the processing circuit 41 of the phase correction device 4 will be described with reference to the flowchart of FIG.

[0030] In step ST10, the acquisition function F1 acquires first k-space data collected in a first readout direction. The acquisition function F1 may acquire one piece of first k-space data, or may acquire a plurality of pieces of first k-space data. The first k-space data may be acquired via the network interface 44, or may be acquired from the storage circuitry 42.

[0031] In step ST20, the acquisition function F1 acquires second k-space data collected in a second readout direction. The acquisition function F1 may acquire one piece of second k-space data or may acquire multiple pieces of second k-space data. The second k-space data may be acquired via the network interface 44 or from the storage circuitry 42.

[0032] Here, the readout direction of the first k-space data and the second k-space data will be described with reference to FIG. 6. The first k-space data and the second k-space data may be at least one set of data collected on the same phase line. As shown in FIG. 6, for example, the first k-space data and the second k-space data are collected on the same phase line L1 in the direction of the arrow A1 and the direction of the arrow A2 opposite to the arrow A1. Note that, although FIG. 6 shows a phase line with zero phase in the ky direction as the same phase line L1, it may be a phase line that is not zero phase in the ky direction, such as another phase line L2.

[0033] Also, the first k-space data and the second k-space data may be at least one set of data acquired at adjacent phase lines. As shown in Fig. 6, for example, the first k-space data and the second k-space data are acquired at adjacent phase lines L3 and L2 in the ky direction in the direction of the arrow A3 and the direction of the arrow A4 opposite to the arrow A3, respectively. Note that the adjacent phase lines are not limited to the phase lines L3 and L2, and may be other adjacent phase lines.

[0034] Furthermore, the first k-space data and the second k-space data need only be at least one set of data whose polarity is inverted in the readout direction of the k-space, and they do not have to be data of adjacent phase lines or data of the same phase line.

[0035] The plurality of first k-space data and the plurality of second k-space data are a plurality of data acquired over time t as shown in Fig. 2(a). The plurality of first k-space data and the plurality of second k-space data may be a plurality of sets of data acquired on the same phase line.

[0036] The first k-space data and the second k-space data may be a plurality of sets of data acquired at adjacent phase lines. In the case of adjacent phase line data, the data may be data acquired by repeatedly acquiring one adjacent phase line (e.g., phase line L3 and phase line L2 in FIG. 6). The data may be data acquired by acquiring a plurality of adjacent phase lines, such as phase line L2 and phase line L3, phase line L4 and phase line L5 in FIG. 6.

[0037] Furthermore, the plurality of first k-space data and the plurality of second k-space data may be configured by a combination of at least one set of data on the same phase line and at least one set of data on adjacent phase lines.

[0038] In step ST30, the adjustment function F2 generates first real space data and second real space data by performing one-dimensional Fourier transform on the first k-space data and the second k-space data, respectively. Here, Fig. 7(a) is the same as Fig. 3(a), and data with polarity inverted in the readout direction of the k-space along time t is collected. Fig. 7(b) is real space data along time t obtained by performing one-dimensional Fourier transform on the k-space data of Fig. 7(a).

[0039] In step ST40, the adjustment function F2 generates first adjustment data and second adjustment data with a predetermined weighting corresponding to the position in the readout direction for the first real space data and the second real space data. When a plurality of first k-space data and a plurality of second k-space data are acquired, the adjustment function F2 may generate a plurality of first adjustment data and a plurality of second adjustment data with a predetermined weighting corresponding to the position in the readout direction for the plurality of first real space data and the plurality of second real space data obtained by one-dimensional Fourier transforming the plurality of first k-space data and the plurality of second k-space data, respectively.

[0040] Fig. 7(b) differs from Fig. 3(b) in that first and second adjusted data are generated by applying a predetermined weighting Weight(x) corresponding to the position in the readout direction (i.e., x direction) to the first and second real space data. As shown in formula (4), the adjusted data G(x) is obtained from the real space data F(x) and a predetermined weighting Weight(x). In the real space data of Fig. 7(b), F2i(x) and F2i+1(x) represent data whose polarities are inverted with each other in the readout direction of the k-space.

[0041]

number

[0042] Here, the predetermined weighting corresponding to the position in the readout direction used by the phase correction device 4 will be described with reference to Figs. 8 to 10. The shape of the predetermined weighting Weight(x) is given according to the image position (i.e., the position x in the readout direction), and the larger the weighting value, the heavier it is treated as a factor of phase correction. In other words, the correction effect is greater at image positions with a large predetermined weighting Weight(x). Therefore, it is advisable to optimize and set the predetermined weighting Weight(x) so that the weighting of the region of interest in which it is desired to prioritize image quality in the imaging region is large.

[0043] 8(a), 8(b), and 8(c) respectively show a first weighting example Weight1, a second weighting example Weight2, and a third weighting example Weight3 as examples of the predetermined weighting Weight(x). For example, as shown in the first weighting example Weight1 in FIG. 8(a) and the second weighting example Weight2 in FIG. 8(b), the predetermined weighting Weight(x) may be weighted higher in a central region in the readout direction than in an outer region outside the central region.

[0044] Here, Fig. 9(a) is the same as Fig. 8(a), and Fig. 9(b) is an application example of the first weighting example Weight1 of Fig. 9(a). For example, as in the spine image of Fig. 9(b), when the central region in the imaging region is the region of interest and it is desired to emphasize the image quality of the central region, it is preferable to set the weighting so that the phase of the central region of the image is corrected.

[0045] Also, Fig. 10(a) is the same as Fig. 8(b), and Fig. 10(b) is an application example of the second weighting example Weight2 of Fig. 10(a). The second weighting example Weight2 is a weighting having two peaks. For example, as in the chest image of Fig. 10(b), when the region of interest exists in two or more separate regions within the imaging region, it is preferable to set the weighting so that phase correction is performed in each of the regions of interest.

[0046] As shown in Figures 9 and 10, the predetermined weighting may be weighting that gives a higher weight to the region of interest than to regions of non-interest. Information on the region of interest specified by the user may be acquired, and the predetermined weighting may be set based on the information on the region of interest. The information on the region of interest may be, for example, information on a region to be weighted higher or information on a region to be weighted lower. The region that can be specified by the information on the region of interest is not limited to a region, and may be a point or a line, and may be not limited to one, but may be multiple. The information on the region of interest is acquired, for example, via the input interface 43.

[0047] FIG. 11 shows a fourth example of weighting, Weight4. The fourth example of weighting, Weight4, in FIG. 11 is weighting where p=0.6 and q=0 in Equation (5). The predetermined weighting may be weighting using a Hamming window function with the center of the position in the readout direction for acquiring the first k-space data and the second k-space data as the line symmetric axis. The Hamming window function is a window function that does not set both ends of the FOV (Field Of View) that is the imaging region to 0. Therefore, when the Hamming window function is set for the FOV as the predetermined weighting, the weighting will not become 0 in the inner region of the FOV. In other words, the information in the imaging region will not be completely lost.

[0048] Furthermore, the predetermined weighting may be a weighting that sets a predetermined value, such as 0 or a value close to 0, in the region outside the FOV. The region outside the FOV is not a region of interest, so the phase difference does not need to be corrected.

[0049]

number

[0050] FIG. 12 is a diagram showing an example of phase correction using the fourth example of weighting, Weight4. FIG. 12(a) shows the phase difference before correction, the correction amount, and the phase difference after correction in the readout direction. The phase difference after correction is the phase difference before correction corrected by the correction amount. FIG. 12(b) is a generated image after the phase correction of FIG. 12(a). Since P1 and P2 in FIG. 12(a) are outside the imaging region where the magnetic field uniformity is low, the variance of the phase difference tends to be larger than in the central region.

[0051] Therefore, in order to make the correction amount of the phase difference less susceptible to the influence of the variance of the phase difference, the predetermined weighting may be such that the weighting is low in the region where the variance of the phase difference is larger than the predetermined variance. With such weighting, even if the magnetic field uniformity is low and the variance of the phase difference between the first real space data and the second real space data is larger than the predetermined variance and the signal value is locally large at the end of the image region (P1 in FIG. 12(b)) as shown in FIG. 12, the phase correction at P2 in FIG. 12(a) is appropriately performed without being influenced by the phase correction at P1 in FIG. 12(a), and the image quality of the center part of the image, which is the region of interest (for example, P2 in FIG. 12(b)), is also maintained. The predetermined weighting may be such that the weighting is high in the region of interest and low in the region where the variance of the phase difference is large.

[0052] Also, when a plurality of first k-space data and a plurality of second k-space data are acquired, the predetermined weighting may be such that the weighting is low in an area where the variance of the phase difference is larger than the predetermined variance.

[0053] In step ST50, the correction function F3 calculates a correction amount for correcting the phase difference between the first adjustment data and the second adjustment data.

[0054] For example, the phase coefficient θ1 corresponding to the first-order phase difference φ1 in the real space is calculated using the adjusted data after a predetermined weighting corresponding to the position in the readout direction is performed as shown in Equation (6). The zeroth-order phase difference φ0 in the real space is estimated from the offset at the center position 0 after the first-order phase difference is corrected.

[0055]

number

[0056] In equation (6), the adjustment data G2i(x) represents the signal value (complex signal value) of the 2i-th pixel in the time t direction and the x-th pixel in the real space X direction (see FIG. 12(b)). As shown in equation (6), the phase coefficient θ1 corresponding to the first-order phase difference φ1 can be obtained by calculating the phase of the correlation function of the signal values ​​of pixels adjacent to each other in the time t direction and the real space X direction.

[0057] In step ST60, the correction function F3 corrects the phase difference between the data read in different directions based on the correction amount.

[0058] Here, the phase coefficient θ1 corresponding to the first-order phase difference φ1 in the real space has been described. However, as shown in FIG. 12(a) where the correction amount is shown by a curve rather than a straight line, the phase correction device 4 can also correct higher-order phase differences in the real space, such as second-order, third-order, fourth-order, etc.

[0059] When a plurality of first k-space data and a plurality of second k-space data are acquired, the correction function F3 calculates a plurality of correction amounts for correcting the phase difference between the plurality of first adjusted data and the plurality of second adjusted data, and corrects the phase difference between a plurality of data in different readout directions based on the plurality of correction amounts. For example, the correction amount may be calculated for each combination of the first adjusted data G0 and the second adjusted data G1, the first adjusted data G2 and the second adjusted data G3, ..., the first adjusted data G2i and the second adjusted data G2i+1, ..., and correction may be performed so that the sum of the phase differences after correction is minimized.

[0060] According to the phase correction method and the phase correction device of the first embodiment, it is possible to perform phase correction to reduce the phase difference in the region of interest between data whose polarity is inverted in the readout direction of the k-space. Even in the case where the k-space is filled while inverting the polarity in the readout direction of the k-space like an EPI image, stable phase correction is performed, and it is possible to reduce image quality defects in the region of interest.

[0061] Second embodiment The phase correction device 4 according to the second embodiment differs from the phase correction device 4 according to the first embodiment in that the predetermined weighting is selected from a plurality of types of weighting. Otherwise, the configuration, function, and operation are not substantially different from those of the phase correction device 4 according to the first embodiment, so that a duplicated description will be omitted. In the second embodiment, in step ST40 of FIG. 5, the adjustment function F2 acquires a plurality of types of weighting and selects one predetermined weighting from the acquired plurality of types of weighting. For example, the one predetermined weighting is selected based on the phase difference after correction to which the correction amount is applied by calculating a correction amount for each of the plurality of types of weighting.

[0062] FIG. 13 shows four weights obtained by changing p=0, p=0.2, p=0.6, and p=1.0 with q=0 in the weighting using the Hamming window function of equation (4). As shown in FIG. 13, a plurality of weights Weight(x) can be obtained by changing the value of p. The predetermined weight is set to a weight that minimizes the sum of phase differences between data in different read directions among the plurality of weights. For example, the sum of the phase differences after correction is obtained using the correction evaluation Metric of equation (7) for the phase differences after correction after the plurality of weights. The weight that minimizes the sum of the phase differences after correction may be selected from the plurality of weights as the predetermined weight.

[0063]

number

[0064] In addition, the weightings may be obtained by changing the variables of one arithmetic expression, or may be obtained from a plurality of arithmetic expressions, a data table relating to a plurality of weightings, or both one or a plurality of arithmetic expressions and a data table. At least one of the one or a plurality of arithmetic expressions and the data table for generating the weightings is stored in, for example, the memory circuit 42.

[0065] According to the phase correction method and the phase correction device of the second embodiment, the same effects as those of the phase correction method and the phase correction device of the first embodiment can be obtained. In the second embodiment, by using correction evaluation or the like to evaluate the phase correction error when the weighting is applied, a more optimal weighting can be selected from a plurality of types of weighting, and therefore, more stable phase correction than that of the first embodiment can be achieved.

[0066] (Overall configuration of magnetic resonance imaging device) A magnetic resonance imaging (MRI) apparatus 1 according to the embodiment is configured to include a phase correction device 4. The MRI apparatus 1 may be configured to communicate with the phase correction device 4 via a network and include the phase correction device 4. The MRI apparatus 1 is capable of using magnetic resonance imaging technology. FIG. 14 is a schematic diagram showing an example of the overall configuration of the MRI apparatus 1 according to the embodiment. The MRI apparatus 1 is configured to include a magnet stand 100, a control cabinet 300, an image processing device 400 such as a console, and a bed 500.

[0067] The magnet gantry 100 and the bed 500 are arranged, for example, in a shielded room called an examination room. On the other hand, the control cabinet 300 is arranged, for example, in a machine room, and the image processing device 400 is arranged, for example, in an operation room. Note that the image processing device 400 may be connected to the MRI apparatus 1 via a network and installed in a remote location away from the operation room.

[0068] The magnet gantry 100 includes a static magnetic field magnet 10, a gradient magnetic field coil 11, and a WB (Whole Body) coil 12. The static magnetic field magnet 10 of the magnet gantry 100 is broadly classified into a cylindrical type in which the magnet has a cylindrical magnetic structure, and an open type in which a pair of magnets are arranged above and below with an imaging space in between. Here, an MRI device 1 with a cylindrical magnet gantry 100 will be described, but an open type MRI device may also be used. Note that the open type MRI device has the same configuration as the cylindrical type MRI device 1, except that the static magnetic field magnet, gradient magnetic field coil, and WB coil that constitute the magnet gantry are parallel plate-shaped.

[0069] The static magnetic field magnet 10 has a roughly cylindrical shape and generates a static magnetic field in a bore into which the subject P is transported. The bore is the space inside the cylinder of the magnet gantry 100. The static magnetic field magnet 10 is composed of, for example, a housing for holding liquid helium, a refrigerator for cooling the liquid helium to an extremely low temperature, and a superconducting coil inside the housing. The static magnetic field magnet 10 may be composed of a permanent magnet. Below, a case where the static magnetic field magnet 10 has a superconducting coil will be described.

[0070] The static magnetic field magnet 10 has a built-in superconducting coil, which is cooled to an extremely low temperature by liquid helium. In the excitation mode, the static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power supply to the superconducting coil. After that, when the mode is switched to the persistent current mode, the static magnetic field power supply is disconnected. Once in the persistent current mode, the static magnetic field magnet 10 continues to generate a static magnetic field for a long time, for example, for more than one year.

[0071] The gradient magnetic field coil 11 has a roughly cylindrical shape like the static magnetic field magnet 10, and is placed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 is composed of three gradient magnetic field coils for the X-axis, Y-axis, and Z-axis. Each gradient magnetic field coil is supplied with a gradient magnetic field current (power) from a gradient magnetic field power supply 31 (31x for the X-axis, 31y for the Y-axis, and 31z for the Z-axis), thereby generating gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions and applying them to the subject P. Here, the Z-axis direction is the direction along the static magnetic field, the Y-axis direction is the vertical direction, and the X-axis direction is the direction perpendicular to the Z-axis and Y-axis.

[0072] The WB coil 12 is also called a whole-body coil, and is disposed inside the gradient magnetic field coil 11 in a generally cylindrical shape so as to surround the subject P. The WB coil 12 functions as a transmitting coil. That is, the WB coil 12 transmits RF pulses to the subject P in accordance with radio frequency (RF) signals transmitted from the RF transmitter 32. Meanwhile, the WB coil 12 may also function as a receiving coil in addition to functioning as a transmitting coil that transmits RF pulses. In that case, the WB coil 12 serves as a receiving coil to receive MR signals emitted from the subject P due to excitation of atomic nuclei.

[0073] The MRI apparatus 1 may include a local coil 20 in addition to the WB coil 12. The local coil 20 is placed close to the body surface of the subject P. The local coil 20 may include a plurality of coil elements. There are several types of local coils 20, such as a head coil, a chest coil, an abdominal coil, a spine coil, and a knee coil. Note that, although FIG. 1 shows a case where the local coil 20 is a chest coil, the present invention is not limited to this case.

[0074] The local coil 20 functions as a receiving coil. That is, the local coil 20 receives the above-mentioned MR signal. The local coil 20 may be a transmitting / receiving coil having a function as a transmitting coil that transmits RF pulses in addition to the function as a receiving coil that receives MR signals. That is, the local coil 20 may be a transmitting-only coil, a receiving-only coil, or a coil for both transmitting and receiving.

[0075] The bed 500 includes a bed body 50 and a tabletop 51. The bed body 50 can move the tabletop 51 in the vertical and horizontal directions, and moves the subject P placed on the tabletop 51 to a predetermined height before imaging. Thereafter, during imaging, the tabletop 51 is moved horizontally to move the subject P into the bore.

[0076] The control cabinet 300 includes gradient magnetic field power supplies 31 (for the X-axis 31x, for the Y-axis 31y, and for the Z-axis 31z), an RF transmitter 32, an RF receiver 33, and a sequence controller .

[0077] The gradient magnetic field power supply 31 includes gradient magnetic field power supplies 31x, 31y, and 31z for each channel that drive coils that generate gradient magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The gradient magnetic field power supplies 31x, 31y, and 31z output required currents independently for each channel in response to a command from a sequence controller 34.

[0078] The RF transmitter 32 generates a high-frequency signal based on an instruction from a sequence controller 34. The RF transmitter 32 transmits the generated high-frequency signal to the WB coil 12 and the local coil 20.

[0079] The MR signals received by the WB coil 12 and the local coil 20 are transmitted to the RF receiver 33. The RF receiver 33 performs analog-to-digital (AD) conversion on the MR signals from the WB coil 12 and the local coil 20 and outputs them to a sequence controller 34. The digitally converted MR signals are sometimes called raw data.

[0080] The sequence controller 34, under the control of the image processing device 400, drives the gradient magnetic field power supply 31, the RF transmitter 32, and the RF receiver 33 to image the subject P. When raw data is received from the RF receiver 33 by imaging, the sequence controller 34 transmits the raw data to the image processing device 400.

[0081] The sequence controller 34 includes a processing circuit (not shown). This processing circuit is configured with hardware such as a processor that executes a predetermined program, a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC).

[0082] Next, the image processing device 400 will be described. The image processing device 400 includes a processing circuitry 410, a storage circuitry 420, an input interface 430, and a display 450. The image processing device 400 may further include a network interface 440. Fig. 15 is a schematic diagram showing an example of the configuration of an MRI apparatus 1 including a phase correction device 4 according to an embodiment.

[0083] The display 450 has the same configuration as the display 45 of the phase correction device 4, and therefore a duplicated description will be omitted. The display 450 further displays various information under the control of the processing circuit 410.

[0084] The network interface 440 has the configuration of the network interface 44 of the phase correction device 4, and therefore a duplicated description will be omitted. The network interface 440 can exchange various data, such as MR signal data of a subject, between a network and the storage circuitry 420, for example.

[0085] The input interface 430 has the same configuration as the input interface 43 of the phase correction device 4, and therefore a duplicated description will be omitted.

[0086] The memory circuitry 420 has the same configuration as the memory circuitry 42 of the phase correction device 4, and therefore a duplicated description will be omitted. The memory circuitry 420 further stores various processing programs used in the processing circuitry 410, data required for executing the programs, and medical images.

[0087] The processing circuit 41 realizes a function of controlling the phase correction device 4. The processing circuit 41 is a processor that realizes various functions by reading and executing various processing programs stored in the memory circuit 42. The processor of the processing circuit 41 realizes each function such as an acquisition function F1, an adjustment function F2, and a correction function F3.

[0088] The processing circuitry 410 has the configuration of the processing circuitry 41 of the phase correction device 4, and therefore a duplicated description will be omitted. The processing circuitry 410 is a processor that realizes various functions by reading and executing various processing programs stored in the storage circuitry 420 or directly incorporated in the processing circuitry 410. The image processing device 400 centrally controls the entire MRI apparatus 1 using these components.

[0089] Specifically, imaging conditions and other various information and instructions are received by a user such as an examiner operating an input interface 430 such as a mouse and a keyboard. The processing circuitry 410 then causes the sequence controller 34 to execute a scan based on the input pulse sequence such as the EPI method and imaging conditions, while reconstructing an MR image based on data transmitted from the sequence controller 34. The reconstructed MR image is displayed on a display 450 or stored in the memory circuitry 420.

[0090] The processing circuit 410 includes the processing circuit 41 of the phase correction device 4, and realizes an acquisition function F1, an adjustment function F2, and a correction function F3. The functions and operations of the acquisition function F1, the adjustment function F2, and the correction function F3 will not be described again. The processing circuit 410 of the MRI device 1 differs from the processing circuit 41 of the phase correction device 4 in that it further realizes an acquisition function F4 and an image generation function F5.

[0091] FIG. 16 is a flow chart showing a first operation example of the MRI apparatus 1. In the first operation example, a pre-scan is started before step ST10. The pre-scan is a calibration scan performed before a main imaging scan for generating an MR image. In the first operation example, the processes of steps ST10 to ST50 are performed during the pre-scan to calculate a correction amount. That is, the first k-space data and the second k-space data are acquired during the pre-scan of the magnetic resonance imaging. An acquisition function F4 acquires the first k-space data and the second k-space data.

[0092] After step ST50, the actual imaging scan is started. The acquisition function F4 acquires MR image data for generating an MR image during the actual imaging scan. The image generation function F5 generates an MR image from the MR image data corrected based on the correction amount calculated in step ST50. In the first operation example, the correction amount is calculated from the first k-space data and the second k-space data acquired in the pre-scan, and phase correction is performed on the MR image data collected in the actual imaging scan.

[0093] 17 is a flow chart showing a second operation example of the MRI apparatus 1. In the second operation example, a main imaging scan is started before step ST10. In the second operation example, the processes of steps ST10 to ST50 are performed during the main imaging scan to calculate the correction amount. That is, the first k-space data and the second k-space data are collected during the main imaging scan of the magnetic resonance imaging. The collection function F4 collects the first k-space data and the second k-space data.

[0094] Moreover, the acquisition function F4 acquires MR image data for generating an MR image during the actual imaging scan. The image generation function F5 generates an MR image from the MR image data corrected based on the correction amount calculated in step ST50. In the second operation example, the correction amount is calculated from the first k-space data and the second k-space data acquired in the actual imaging scan, and phase correction is performed on the MR image data collected in the actual imaging scan.

[0095] According to at least one of the phase correction methods, phase correction devices, and magnetic resonance imaging apparatuses described above, phase correction can be performed to reduce the phase difference in a region of interest between data whose polarity is inverted in the readout direction of k-space.

[0096] In the above embodiment, the term "processor" refers to a circuit such as a dedicated or general-purpose CPU (Central Processing Unit), GPU (Graphics Processing Unit) or an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)).

[0097] When the processor is, for example, a CPU, the processor realizes various functions by reading and executing a program stored in a memory circuit. When the processor is, for example, an ASIC, instead of storing a program in a memory circuit, a function corresponding to the program is directly built into the circuit of the processor as a logic circuit. In this case, the processor realizes various functions by hardware processing that reads and executes the program built into the circuit. Alternatively, the processor can realize various functions by combining software processing and hardware processing.

[0098] In the above embodiment, an example was shown in which a single processor of the processing circuit realizes each function, but a processing circuit may be configured by combining multiple independent processors, and each processor may realize each function. In addition, when multiple processors are provided, a memory circuit for storing a program may be provided for each processor, or one memory circuit may collectively store programs corresponding to the functions of all the processors.

[0099] In addition, the acquisition function F1, adjustment function F2, correction function F3, collection function F4, and image generation function F5 in the description of the embodiment are examples of the acquisition unit, adjustment unit, correction unit, collection unit, and image generation unit, respectively, as described in the claims.

[0100] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0101] 1...Magnetic resonance imaging (MRI) device 11...Gradient magnetic field coil F1...Acquisition function F2...Adjustment function F3...Correction function F4...Acquisition function F5...Image generation function

Claims

1. acquiring first k-space data acquired in a first readout direction and second k-space data acquired in a second readout direction opposite the first readout direction; generating first real space data and second real space data obtained by one-dimensional Fourier transform of the first k-space data and the second k-space data, respectively, which correspond to a position in a readout direction and are weighted by a predetermined weighting so that the weighting is low in an area where the variance of the phase difference is larger than a predetermined variance; calculating a correction amount for correcting a phase difference between the first adjustment data and the second adjustment data, and correcting a phase difference between data having different read directions based on the correction amount; Phase correction method.

2. The first k-space data and the second k-space data are At least one set of data collected on the same phase line; The phase correction method according to claim 1 .

3. The first k-space data and the second k-space data are At least one set of data collected at adjacent phase lines; The phase correction method according to claim 1 .

4. The first k-space data and the second k-space data are Data collected during a pre-scan of a magnetic resonance imaging system. The phase correction method according to claim 1 .

5. The first k-space data and the second k-space data are The data collected during the magnetic resonance imaging scan The phase correction method according to claim 1 .

6. acquiring a plurality of first k-space data and a plurality of second k-space data; generating a plurality of first real space data and a plurality of second real space data obtained by performing a one-dimensional Fourier transform on the plurality of first k-space data and the plurality of second k-space data, respectively, a plurality of first adjustment data and a plurality of second adjustment data that correspond to positions in a readout direction and are weighted in a predetermined manner so that the weight is low in an area where the variance of the phase difference is larger than a predetermined variance; calculating a plurality of correction amounts for correcting a phase difference between the plurality of first adjustment data and the plurality of second adjustment data, and correcting a phase difference between a plurality of data in different read directions based on the plurality of correction amounts; The phase correction method according to claim 1 .

7. The predetermined weighting is a weighting that is higher in a central region in the position of the readout direction than in an outer region that is outside the central region. The phase correction method according to claim 1 .

8. The predetermined weighting is a weighting that is set to a predetermined value in an area outside a field of view (FOV). The phase correction method according to claim 1 .

9. The predetermined weighting is weighting using a Hamming window function with a center of a position in a readout direction for acquiring the first k-space data and the second k-space data as a line symmetric axis. The phase correction method according to claim 1 or 8.

10. The predetermined weighting is a weighting that gives a higher weight to an area of ​​interest than to an area of ​​non-interest. The phase correction method according to claim 5 .

11. Obtaining information about a user-specified area of ​​interest; The predetermined weighting is a weighting set based on information about the region of interest. The phase correction method according to claim 10.

12. storing at least one of one or more arithmetic expressions and data tables for generating a plurality of types of weighting; The predetermined weighting is a weighting that minimizes a sum of phase differences between data in different read directions among the plurality of weightings. The phase correction method according to claim 1 or 5.

13. an acquisition unit that acquires first k-space data acquired in a first readout direction and second k-space data acquired in a second readout direction opposite to the first readout direction; an adjustment unit that generates first adjusted data and second adjusted data, which are obtained by performing one-dimensional Fourier transform on the first k-space data and the second k-space data, respectively, and which are weighted in a predetermined manner so that the weight is lowered in a region where the variance of the phase difference is larger than a predetermined variance, corresponding to a position in a readout direction; a correction unit that calculates a correction amount for correcting a phase difference between the first adjustment data and the second adjustment data, and corrects a phase difference between data having different read directions based on the correction amount. Phase correction device.

14. The acquisition unit acquires a plurality of first k-space data and a plurality of second k-space data; the adjustment unit generates a plurality of first adjustment data and a plurality of second adjustment data, the first adjustment data and the second adjustment data being weighted in a predetermined manner so that the weight is lower in a region where the variance of the phase difference is larger than a predetermined variance, in the plurality of first real space data and the plurality of second real space data obtained by performing a one-dimensional Fourier transform on the plurality of first k-space data and the plurality of second k-space data, respectively, corresponding to a position in a readout direction; the correction unit calculates a plurality of correction amounts for correcting phase differences between the plurality of first adjustment data and the plurality of second adjustment data, and corrects the phase differences between a plurality of data in different read directions based on the plurality of correction amounts so that a sum of the phase differences is minimized. The phase correction device according to claim 13.

15. Further comprising a storage unit that stores at least one of one or more arithmetic expressions and a data table for generating a plurality of types of weighting.

15. A phase correction device according to claim 13 or 14.

16. A gradient coil for generating a gradient magnetic field; an acquisition unit that applies the gradient magnetic field to acquire k-space data, which is an MR signal in a readout direction; an acquisition unit that acquires first k-space data acquired in a first readout direction and second k-space data acquired in a second readout direction opposite to the first readout direction, the first k-space data being acquired by the acquisition unit; an adjustment unit that generates first adjusted data and second adjusted data, which are obtained by performing one-dimensional Fourier transform on the first k-space data and the second k-space data, respectively, and which are weighted in a predetermined manner so that the weight is lowered in a region where the variance of the phase difference is larger than a predetermined variance, corresponding to a position in a readout direction; a correction unit that calculates a correction amount for correcting a phase difference between the first adjustment data and the second adjustment data, and corrects a phase difference between data having different read directions based on the correction amount. Magnetic resonance imaging device.

17. An image generating unit is further provided, the acquisition unit acquires the first k-space data and the second k-space data during a pre-scan, and acquires MR image data for generating an MR image during a main imaging scan; the image generating unit generates an MR image from the MR image data corrected based on the correction amount.

17. A magnetic resonance imaging apparatus according to claim 16.

18. An image generating unit is further provided, The acquisition unit acquires the first k-space data, the second k-space data, and MR image data for generating an MR image during a main imaging scan; the image generating unit generates an MR image from the MR image data corrected based on the correction amount.

17. A magnetic resonance imaging apparatus according to claim 16.

19. The acquisition unit acquires a plurality of first k-space data and a plurality of second k-space data; the adjustment unit generates a plurality of first adjustment data and a plurality of second adjustment data, the first adjustment data and the second adjustment data being weighted in a predetermined manner so that the weight is lower in a region where the variance of the phase difference is larger than a predetermined variance, in the plurality of first real space data and the plurality of second real space data obtained by performing a one-dimensional Fourier transform on the plurality of first k-space data and the plurality of second k-space data, respectively, corresponding to a position in a readout direction; the correction unit calculates a plurality of correction amounts for correcting phase differences between the plurality of first adjustment data and the plurality of second adjustment data, and corrects the phase differences between a plurality of data in different read directions based on the plurality of correction amounts so that a sum of the phase differences is minimized.

17. A magnetic resonance imaging apparatus according to claim 16.

Images