JP5487253B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention magnetically excites a nuclear spin of a subject with a radio frequency (RF) signal having a Larmor frequency, and reconstructs an image from a magnetic resonance (MR) signal generated by the excitation. The present invention relates to a magnetic resonance imaging apparatus, and more particularly, to a magnetic resonance imaging apparatus that collects MR signals using an RF coil having a plurality of surface coils.

  Magnetic Resonance Imaging (MRI) magnetically excites the nuclear spin of a subject placed in a static magnetic field with an RF signal of Larmor frequency, and re-images the MR signal generated by this excitation. It is the imaging method to comprise.

  In the field of magnetic resonance imaging, a high-speed imaging technique has been devised in which an RF coil is configured using a multi-coil having a plurality of surface coils, and MR signals are collected using each surface coil. This imaging using a plurality of surface coils is called parallel imaging (Parallel Imaging). Parallel imaging includes Subencoding method, SENSE (sensitivity encoding) method that performs unfolding (development) processing, thumb of square (SoS: sum of square) PILS (Partially Parallel Imaging With Localized Sensitivities) method.

  In Parallel Imaging, special imaging such as spiral imaging may be performed, but in general, the number of data acquisitions in the phase encoding direction is reduced, and the resulting aliasing in the image data is the sensitivity distribution of each surface coil. It is unfolded using the independence of. There are various multi-coil shapes for Parallel Imaging depending on the part to be imaged, and some are specialized for research.

  FIG. 24 is a diagram showing a shape example of a conventional ladder type multi-coil in which four surface coils are arranged in the Z-axis direction, and FIG. 25 is a diagram of a conventional multi-type in which two surface coils are arranged coaxially in the Z-axis direction. FIG. 26 is a diagram showing an example of the shape of a coil, and FIG. 26 is a diagram showing a shape example of a conventional ladder type multi-coil in which 12 surface coils are arranged in a plurality of directions.

  For example, a ladder type (ladder type) multi-coil as shown in FIG. 24 is used only for the heart. Some multi-coils that are practically used are not necessarily sufficient in the number of surface coils, such as those having two surface coils around the subject P as shown in FIG. On the other hand, there are also provided a sufficient number of surface coils, such as the multi-coil shown in FIG. 26, and surface coils arranged spatially around the subject P in a plurality of directions in order to improve the degree of freedom of the imaging section. is there. When the Z direction is set to the encode direction, the multi-coil shown in FIG. 24 has a structure in which four surface coils are arranged in the encode direction. In the multi-coils shown in FIGS. The structure is arranged in the encoding direction. Such multi-coils having various shapes are used as RF coils for data reception.

  However, in Parallel Imaging, unfolding processing is appropriate when the subject to be imaged is larger than the field of view (FOV) set in the phase encode (PE) direction (hereinafter referred to as “set FOV”). However, there is a problem that the portion where the set FOV protrudes in the PE direction, that is, the folded portion appears as a folded artifact near the center of the image. For example, when a coronal cross-sectional image is captured, if there is a subject to be captured at the set FOV end in the longitudinal direction, the unfolding process cannot be performed properly, and artifacts remain. Especially when the receiving multi-coil has a small number of element coils, such as a volume coil, and the sensitivity spread of one element coil is large, unfolding is not performed properly, and artifacts tend to remain. It is in.

  FIG. 27 is a schematic diagram showing the sensitivity distribution of a conventional multi-coil having two surface coils in the Z-axis direction as shown in FIG. 25 and FIG.

  In FIG. 27, the horizontal axis indicates the PE direction (Z-axis direction), and the vertical axis indicates the sensitivity of each surface coil. Moreover, the solid line in FIG. 27 shows the sensitivity distribution of each surface coil. As shown in FIG. 27, the sensitivity of each surface coil increases near the center position of each surface coil, and decreases at a position away from the vicinity of the center position of each surface coil.

  When collecting data using these surface coils, in order to properly unfold the collected data and completely remove aliasing artifacts, a signal from the subject is received at the set FOV. There is a need. Therefore, as shown in FIG. 27, it is necessary to set the set FOV at the time of the photographing plan so as to include the sensitivity range of each surface coil. However, when an excessively wide setting FOV is set, there is a problem that the spatial resolution is lowered.

  Conversely, if the set FOV is too narrowed to improve the spatial resolution, aliasing artifacts will occur due to the influence of signals received outside the set FOV.

  FIG. 28 is a diagram for explaining a portion where artifacts occur when the set FOV is narrowed down in the data collection using the conventional multi-coil having the sensitivity distribution shown in FIG.

  In FIG. 28, the horizontal axis indicates the PE direction (Z-axis direction), and the vertical axis indicates the sensitivity of each surface coil. Moreover, the solid line in FIG. 28 shows the sensitivity distribution of each surface coil.

  As shown in FIG. 28, when signals are collected by setting a setting FOV that is narrower than the sensitivity range of each surface coil in order to maintain the necessary spatial resolution, signals from three points in the original space (real space) are obtained. Fold to 1 point. For example, signals from three points A1, A2, and A3 in FIG. 28 are folded to one point. For this reason, in Parallel Imaging using a multi-coil having only two independent surface coils in the PE direction, unfolding processing cannot be performed properly, and signals that are not necessary for the protruding portion R0 are folded back. And artifacts occur.

  In this way, the aliasing artifact due to the signal from the portion R0 that protrudes from the set FOV appears near the center of the image. However, since the setting FOV is set so that the lesion to be normally photographed is located near the center of the image, there is a possibility that the interpretation of the image may be hindered. Therefore, in the PE direction, when the photographing target is larger than the set FOV, it is important to set the set FOV so as to include the sensitivity distribution of each surface coil.

  On the other hand, the occurrence of aliasing artifacts can also be prevented by setting the setting FOV so that the object to be imaged becomes smaller than the setting FOV in the PE direction. Therefore, it is important to set the setting FOV so that the shooting target is smaller than the setting FOV in the shooting plan.

  Further, even if a folding artifact appears, the setting FOV can be set smaller if it is an area that does not affect interpretation such as a lesion. Further, it is possible to improve the spatial resolution, reduce the amount of data collected, and reduce the data processing time. Therefore, it is effective to grasp the position of the folding artifact before photographing. However, the position at which the aliasing artifact appears changes depending on the speed-up rate PI, which is one of the imaging parameters in Parallel Imaging.

  FIG. 29 is a diagram showing the appearance position of the folding artifact when the speed-up rate is 2 in the conventional Parallel Imaging.

  For example, when a coronal cross-sectional image of the body of the subject P is captured, a set FOV with a PEFOV width of PEFOV as shown in FIG. Here, if there is a protruding region R0 of the subject that protrudes from the set FOV in the PE direction, a folding artifact occurs.

  As shown in FIG. 29 (a), when photographing is performed with a setting FOV in which the width in the PE direction is PEFOV, image data in which the width in the PE direction is PEFOV / PI is obtained as shown in FIG. 29 (b). Here, since PI = 2, the width of the folded image data in the PE direction is PEFOV / 2.

  Next, a range of PEFOV × (1-1 / PI) / 2 from each end in the PE direction of the folded image data is set as an unfolded area. Here, since PI = 2, all the areas of the folded image data are unfolded areas. In addition, the protruding region R0 shown in FIG. 29A is folded at each position adjacent to the outside of each unfolded region boundary. Since the boundary of each unfolded region is adjacent in the center of the folded image, each data from the two protruding regions R0 is also adjacent in the center of the folded image.

  When the image data in the unfolded area is unfolded, a display image having a PEFOV width in the PE direction as shown in FIG. 29C is generated. However, since the data from the protruding area R0 remains in the display image without being unfolded, the image of the protruding area R0 appears as an artifact at the center of the image. Therefore, there is a risk that artifacts overlap the lesion.

  On the other hand, the position of the artifact can be shifted in the PE direction by changing the acceleration rate PI.

  FIG. 30 is a diagram showing the appearance position of the folding artifact when the speed-up rate is 1.5 in the conventional Parallel Imaging.

  For example, when a coronal cross-sectional image of the body of the subject P is captured, a setting FOV in which the width in the PE direction is PEFOV is set in the state where the protruding region R0 exists as shown in FIG. The

  As shown in FIG. 30A, when photographing is performed with a setting FOV in which the width in the PE direction is PEFOV, image data in which the width in the PE direction is PEFOV / PI is obtained as shown in FIG. 30B. Here, since PI = 1.5, the width of the folded image data in the PE direction is PEFOV / 1.5.

  Next, a range of PEFOV × (1-1 / PI) / 2 from each end in the PE direction of the folded image data is set as an unfolded area. Here, since PI = 1.5, the two regions near both ends in the PE direction of the folded image data are respectively unfolded regions. Further, the protruding region R0 shown in FIG. 30A is folded at each position adjacent to the outside of the boundary of each unfolded region. Since the boundary of each unfolded region is a position shifted from the center of the folded image by a distance corresponding to the acceleration rate, each data from the two protruding regions R0 is also increased from the center of the folded image to the acceleration rate. The position is shifted by the corresponding distance.

  When the image data in the unfolded area is unfolded, a display image having a PEFOV width in the PE direction as shown in FIG. 30C is generated. However, since the data from the protruding area R0 remains in the display image without being unfolded, the image of the protruding area R0 appears as an artifact at a position shifted from the center of the image by a distance corresponding to the speed-up rate. .

  Thus, when the speed-up rate is changed, the position of the folding artifact can be changed in the PE direction. However, since the position of the folding artifact changes depending on the speed-up rate, it is difficult for the operator to predict. Therefore, it is also difficult to set the minimum, that is, the optimal setting FOV at which no aliasing artifacts occur in the lesion, at the time of the imaging plan.

  Under such a background, a folding prevention function (No Wrap function) that reduces folding artifacts in the PE direction has been devised regardless of the positional relationship between the set FOV and the shooting target during shooting plan (for example, patent document) 1, Patent Document 2, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3).

  In this technique, a FOV wider than the set FOV at the time of shooting plan is set as a developed FOV for unfold processing, and an image of the developed FOV is generated once by the unfold processing. Then, the set FOV image is cut out from the developed FOV image to be a display image.

  FIG. 31 is a diagram showing the appearance position of the folding artifact when the No Wrap function is used in the conventional Parallel Imaging.

  For example, when a coronal cross-sectional image of the body of the subject P is captured, a setting FOV in which the width in the PE direction is PEFOV is set in the state where the protruding region R0 exists as shown in FIG. The In the shooting plan, a magnification NoWrap of the developed FOV with respect to the set FOV is also set.

  As shown in FIG. 31 (a), when shooting is performed with the FOV set to a PEFOV width of PEFOV, as shown in FIG. 31 (b), folded image data with a PE direction width of PEFOV × NoWrap / PI is obtained. . For example, when PI = 2 and NoWrap = 2, the width of the folded image data in the PE direction is PEFOV.

  Next, a range of PEFOV × NoWrap × (1-1 / PI) / 2 from both ends in the PE direction of the folded image data is set as an unfolded region. Here, when PI = 2 and NoWrap = 2, the range of PEFOV / 2 from each end in the PE direction is an unfolded region, and therefore the entire range of the set FOV is the target of unfolding processing. Further, the protruding area shown in FIG. 31 (a) is folded to each position shifted from the boundary of each unfolded area by a distance corresponding to the magnification NoWrap of the developed FOV. Accordingly, the boundary of each unfolded region is the center of the folded image, but the protruding region R0 is not the center of the folded image.

  Next, when the unfolded area of the folded image data is unfolded, a developed image having a developed FOV whose width in the PE direction is PEFOV × NoWrap as shown in FIG. 31C is generated. Therefore, if the value of NoWrap is sufficiently large, the unfolding process is performed without leaving data from the protruding area R0. When NoWrap = 2, the width of the developed image in the PE direction is PEFOV × 2.

  Then, the display image of the setting FOV is cut out from the developed image of the developed FOV and displayed. As a result, occurrence of aliasing artifacts due to the protruding region R0 can be prevented by appropriately setting the value of NoWrap.

JP 2004-329613 A US Patent Application Publication No. 2004/0263167

Y. Machida, S. Uchizono, N. Ichinose “Fold-Over Aliasing Artifact Suppression Technique in MR Parallel Imaging: Considerations of Role of FOV in Image Formation Procedure”, Proc. Intl. Soc. Mag. Reson. Med. 13 (2005 ), p506 J.W. Goldfarb, M. Shinnar “Field-of-view Restrictions for Artifact-free SENSE Imaging”, Proc. Intl. Soc. Mag. Reson. Med. 10 (2002), (abstract 2412) J.W.Goldfarb “The SENSE Ghost: Field-of-view Restrictions for SENSE Imaging”, J. Magn. Reson. Imaging 2004; 20: 1046-1051

  As described above, when setting the FOV that is narrower than the sensitivity range of each surface coil in order to maintain the required spatial resolution and collecting the signal, unfolding was not performed properly, and the set FOV protruded in the PE direction. There is a problem that the part appears as a folded artifact. This is a significant problem especially when there is a target at the set FOV end of the phase encoding direction or when the number of element coils is small.

  Further, grasping the position of the folding artifact before photographing is effective in preventing the appearance of the folding artifact. However, there is a problem that the position at which the folding artifact appears is difficult to predict because it changes depending on the acceleration rate PI, which is one of the imaging parameters in Parallel Imaging. In particular, when the No Wrap function, which is a conventional anti-folding function in the encoding direction, is used, the development FOV that is the target of unfolding processing is different from the set FOV, so the prediction of the appearance position of the folding artifact becomes more complicated. .

  The present invention has been made to cope with such a conventional situation, and provides a magnetic resonance imaging apparatus capable of preventing the appearance of a folding artifact by easily grasping the position of the folding artifact before photographing. It is to be.

A magnetic resonance imaging apparatus according to the present invention includes a data collection unit that collects a magnetic resonance signal from a subject, an image data generation unit that generates image data from the magnetic resonance signal collected by the data collection unit, and imaging. A region display means for calculating a region where a magnetic resonance signal causing a folding artifact on the image data based on a condition as a folding attention region, and displaying the obtained folding attention region on a display device; The area display means includes the aliasing attention area based on an imaging condition including an enlargement factor that is a parameter of a aliasing prevention function that performs aliasing removal processing on an imaging field that is enlarged with respect to a set imaging field. It is characterized by being configured to calculate .

  In the magnetic resonance imaging apparatus according to the present invention, the appearance of the folding artifact can be prevented by easily grasping the position of the folding artifact before imaging.

1 is a configuration diagram of a magnetic resonance imaging apparatus according to a first embodiment of the present invention. The figure which shows an example of the detailed structure of RF coil shown in FIG. The cross-sectional schematic diagram which shows the example of arrangement | positioning of the WB coil and phased array coil which are shown in FIG. The functional block diagram of the computer shown in FIG. The schematic diagram which shows the saturation area | region by the presaturation pulse set by the signal suppression condition setting part shown in FIG. The schematic diagram which shows the example which selected each slice used as the application object of an excitation pulse and a refocusing pulse so that an unnecessary signal may not generate | occur | produce by the signal suppression condition setting part shown in FIG. The schematic diagram which shows an example of the sensitivity map of the surface coil preserve | saved at the sensitivity map database shown in FIG. The schematic diagram which shows an example of the sensitivity map of the surface coil preserve | saved at the assumed sensitivity database shown in FIG. FIG. 5 is a diagram illustrating an example of a aliasing removal process in the aliasing removal processing unit illustrated in FIG. 4 and an example of a weighting function for weighting addition in a weighting addition unit 52; The flowchart which shows an example of the flow in the case of performing Parallel Imaging with the magnetic resonance imaging apparatus shown in FIG. The figure which shows the example which synthesize | combines the intermediate | middle image data produced | generated by unfolding with respect to the folded image data, and the folded image data as it is by weighted addition The functional block diagram of the computer with which the magnetic resonance imaging apparatus which concerns on the 2nd Embodiment of this invention is provided. The flowchart which shows an example of the flow in the case of performing Parallel Imaging with the magnetic resonance imaging apparatus shown in FIG. FIG. 13 is a diagram illustrating a folding attention area displayed by the folding attention area display unit illustrated in FIG. 12 when the acceleration rate PI = 2 and the enlargement ratio NoWrap = 1 are set. FIG. 13 is a diagram illustrating a folding attention area displayed by the folding attention area display unit illustrated in FIG. 12 when the speed increase rate PI = 1.5 and the enlargement ratio NoWrap = 1. FIG. 13 is a diagram showing a folding attention area displayed by the folding attention area display unit shown in FIG. 12 when the speed increase rate PI = 1 and the enlargement ratio NoWrap = 1. FIG. 13 is a diagram showing a folding attention area displayed by the folding attention area display unit shown in FIG. 12 when the speed increase rate PI = 1 and the enlargement ratio NoWrap = 2. FIG. 13 is a diagram illustrating a folding attention area displayed by the folding attention area display unit illustrated in FIG. 12 when the speed increase rate PI = 2 and the enlargement ratio NoWrap = 2 are set. FIG. 13 is a diagram showing a folding attention area displayed by the folding attention area display unit shown in FIG. 12 when speeding rate PI = 2 and enlargement ratio NoWrap = 1.2 are set. FIG. 13 is a diagram illustrating a folding attention area displayed by the folding attention area display unit illustrated in FIG. 12 when the speed increase rate PI = 1.2 and the enlargement ratio NoWrap = 1.2 are set. FIG. 13 is a diagram illustrating a folding attention area displayed by the folding attention area display unit illustrated in FIG. 12 when the speed increase rate PI = 1.2 and the enlargement ratio NoWrap = 1.5 are set. FIG. 13 is a diagram illustrating a folding attention area displayed by the folding attention area display unit illustrated in FIG. 12 when the speed increase rate PI = 1 and the enlargement ratio NoWrap = 1.2 are set. When the speed increase rate PI = 1.5 and the enlargement rate NoWrap = 1 are set, information for determining the appearance position of each folding artifact corresponding to a plurality of folding attention areas is displayed by the folding attention area display unit shown in FIG. The figure which shows the example displayed with the return caution area | region. The figure which shows the example of a shape of the conventional ladder type multi coil which has arrange | positioned four surface coils to the Z-axis direction. The figure which shows the example of the shape of the conventional multi-coil which arrange | positioned two surface coils coaxially to the Z-axis direction. The figure which shows the example of a shape of the conventional ladder type multi-coil which arrange | positioned 12 surface coils in the several direction. The schematic diagram which shows the sensitivity distribution of the conventional multi coil provided with two surface coils in the Z-axis direction like FIG. 25 and FIG. The figure explaining the part which an artifact generate | occur | produces when setting FOV is narrowed down in the data collection using the conventional multicoil which has a sensitivity distribution shown in FIG. The figure which shows the appearance position of the folding | turning artifact when the speed-up rate is 2 in the conventional Parallel Imaging. The figure which shows the appearance position of the folding | turning artifact in the case where the speed-up rate is 1.5 in the conventional Parallel Imaging. The figure which shows the appearance position of the folding | turning artifact in the case of using the No Wrap function in the conventional Parallel Imaging.

  Embodiments of a magnetic resonance imaging apparatus and a control method of the magnetic resonance imaging apparatus according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram of a magnetic resonance imaging apparatus according to the first embodiment of the present invention.

  The magnetic resonance imaging apparatus 20 does not show a cylindrical static magnetic field magnet 21 that forms a static magnetic field, and a shim coil 22, a gradient magnetic field coil unit 23, and an RF coil 24 provided inside the static magnetic field magnet 21. It is built in the gantry.

  In addition, the magnetic resonance imaging apparatus 20 includes a control system 25. The control system 25 includes a static magnetic field power supply 26, a gradient magnetic field power supply 27, a shim coil power supply 28, a transmitter 29, a receiver 30, a sequence controller 31, and a computer 32. The gradient magnetic field power source 27 of the control system 25 includes an X-axis gradient magnetic field power source 27x, a Y-axis gradient magnetic field power source 27y, and a Z-axis gradient magnetic field power source 27z. In addition, the computer 32 includes an input device 33, a display device 34, an arithmetic device 35, and a storage device 36.

  The static magnetic field magnet 21 is connected to a static magnetic field power supply 26 and has a function of forming a static magnetic field in the imaging region by a current supplied from the static magnetic field power supply 26. In many cases, the static magnetic field magnet 21 is composed of a superconducting coil, and is connected to the static magnetic field power supply 26 at the time of excitation and supplied with current. It is common. In some cases, the static magnetic field magnet 21 is composed of a permanent magnet and the static magnetic field power supply 26 is not provided.

  A cylindrical shim coil 22 is coaxially provided inside the static magnetic field magnet 21. The shim coil 22 is connected to the shim coil power supply 28, and is configured such that a current is supplied from the shim coil power supply 28 to the shim coil 22 to make the static magnetic field uniform.

  The gradient magnetic field coil unit 23 includes an X-axis gradient magnetic field coil 23 x, a Y-axis gradient magnetic field coil 23 y, and a Z-axis gradient magnetic field coil 23 z, and is formed in a cylindrical shape inside the static magnetic field magnet 21. A bed 37 is provided inside the gradient coil unit 23 as an imaging region, and the subject P is set on the bed 37. The RF coil 24 may not be built in the gantry but may be provided near the bed 37 or the subject P.

  The gradient magnetic field coil unit 23 is connected to a gradient magnetic field power supply 27. The X axis gradient magnetic field coil 23x, the Y axis gradient magnetic field coil 23y, and the Z axis gradient magnetic field coil 23z of the gradient magnetic field coil unit 23 are respectively an X axis gradient magnetic field power source 27x, a Y axis gradient magnetic field power source 27y, and a Z axis. It is connected to the gradient magnetic field power supply 27z.

  The X-axis gradient magnetic field power source 27x, the Y-axis gradient magnetic field power source 27y, and the Z-axis gradient magnetic field power source 27z are supplied with currents supplied to the X-axis gradient magnetic field coil 23x, the Y-axis gradient magnetic field coil 23y, and the Z-axis gradient magnetic field coil 23z, respectively. In the imaging region, a gradient magnetic field Gx in the X-axis direction, a gradient magnetic field Gy in the Y-axis direction, and a gradient magnetic field Gz in the Z-axis direction can be formed, respectively.

  The RF coil 24 is connected to the transmitter 29 and the receiver 30. The RF coil 24 receives the high frequency signal from the transmitter 29 and transmits it to the subject P, and receives the NMR signal generated by the excitation by the high frequency signal of the nuclear spin inside the subject P and receives it to the receiver 30. Has the function to give.

  2 is a diagram showing an example of a detailed configuration of the RF coil 24 shown in FIG. 1, and FIG. 3 is a schematic sectional view showing an arrangement example of the WB coil 24a and the phased array coil 24b shown in FIG.

  The RF coil 24 includes, for example, a transmission RF coil 24 and a reception RF coil 24. A whole body (WB) 24a coil is used for the RF coil 24 for transmission, while a phased array coil 24b is used for the RF coil 24 for reception. The phased array coil 24b includes a plurality of surface coils 24c, and each surface coil 24c is individually connected to the receiving system circuit 30a.

  In addition, the surface coils 24c of the phased array coil 24b are arranged symmetrically around the Z axis that is around the cross section L including the specific region of interest of the subject P, for example. Further, a WB coil 24a is provided outside the phased array coil 24b. The high frequency signal is transmitted to the subject P by the WB coil 24a, while each surface coil 24c of the WB coil 24a or the phased array coil 24b receives the NMR signal from the cross section L including the specific region of interest in multiple channels. The receiver 30 is configured to be provided to each reception system circuit 30a.

  On the other hand, the sequence controller 31 of the control system 25 is connected to the gradient magnetic field power source 27, the transmitter 29, and the receiver 30. The sequence controller 31 has control information necessary for driving the gradient magnetic field power supply 27, the transmitter 29, and the receiver 30, for example, operation control information such as the intensity, application time, and application timing of the pulse current to be applied to the gradient magnetic field power supply 27. And the gradient magnetic field power source 27, the transmitter 29, and the receiver 30 are driven according to the stored predetermined sequence to drive the X-axis gradient magnetic field Gx, the Y-axis gradient magnetic field Gy, and the Z-axis gradient magnetic field. It has the function of generating Gz and high frequency signals.

  The sequence controller 31 is configured to receive raw data, which is complex data obtained by detection of the NMR signal and A / D conversion in the receiver 30, and supply the raw data to the computer 32.

  For this reason, the transmitter 29 is provided with a function of applying a high frequency signal to the RF coil 24 based on the control information received from the sequence controller 31, while the receiver 30 detects the NMR signal received from the RF coil 24. Then, by executing required signal processing and A / D conversion, a function of generating raw data that is digitized complex data and a function of supplying the generated raw data to the sequence controller 31 are provided.

  Further, the computer 32 is provided with various functions by executing the program stored in the storage device 36 of the computer 32 by the arithmetic unit 35. However, the computer 32 may be configured by providing a specific circuit regardless of the program.

  FIG. 4 is a functional block diagram of the computer 32 shown in FIG.

  The computer 32 functions as a sequence controller control unit 40, a k-space database 41, an imaging condition setting unit 42, a signal suppression condition setting unit 43, an image reconstruction unit 44, a real space database 45, and a post-processing unit 46 according to programs. The post-processing unit 46 includes a signal suppression determination unit 47, a development processing unit 48, a aliasing removal processing unit 49, a sensitivity map database 50, an assumed sensitivity database 51, and a weighted addition unit 52.

  The sequence controller control unit 40 has a function of controlling driving by giving a pulse sequence to the sequence controller 31 based on information from the input device 33 or other components. That is, the sequence controller control unit 40 has a function of executing an arbitrary imaging scan including Parallel Imaging. The sequence controller control unit 40 has a function of receiving raw data from the sequence controller 31 and arranging it as k-space data in a k-space (Fourier space) formed in the k-space database 41.

  For this reason, each raw data generated in the receiver 30 is stored in the k-space database 41 as k-space data.

  The imaging condition setting unit 42 has a function of setting imaging conditions in accordance with an instruction from the input device 33 and giving a pulse sequence to the signal suppression condition setting unit 43 as imaging conditions. In particular, the imaging condition setting unit 42 is configured to be able to set imaging conditions for Parallel Imaging such as the number of phase encodings and the setting FOV corresponding to the number of surface coils 24c in the PE direction.

  The signal suppression condition setting unit 43 sets a signal suppression condition for suppressing an MR signal from a specific spatial region that causes a folding artifact in Parallel Imaging, for the pulse sequence acquired from the imaging condition setting unit 42. And a function of giving a pulse sequence after setting the signal suppression condition to the sequence controller control unit 40 and the post-processing unit 46. An arbitrary method can be adopted as a signal suppression method for suppressing the MR signal.

  The site causing the folding artifact varies depending on conditions such as the number, arrangement, and sensitivity distribution of the surface coils 24c. Here, for simplicity of explanation, the simplest phased array in which the two surface coils 24c are arranged in the PE direction. A case where imaging is performed using the coil 24b will be described.

  When imaging is performed using the phased array coil 24b in which the two surface coils 24c are arranged in the PE direction, a portion that protrudes from the set FOV in the PE direction becomes a space part that causes the occurrence of folding artifacts. Therefore, it can be said that the signal from the portion protruding from the set FOV in the PE direction is an unnecessary signal. As a method for suppressing unnecessary signals from a specific space, for example, a method of applying a presaturation pulse for suppressing unnecessary signals or a slice to which an excitation pulse or a refocus pulse is applied so that unnecessary signals are not generated. The method of selecting is mentioned.

  FIG. 5 is a schematic diagram showing a saturation region by a presaturation pulse set by the signal suppression condition setting unit 43 shown in FIG.

  In FIG. 5, the horizontal axis indicates the PE direction, and the vertical axis indicates the sensitivity of the two surface coils 24c. Moreover, the solid line in FIG. 5 shows the sensitivity distribution of each surface coil 24c.

  As shown in FIG. 5, when the set FOV is set within a range in which each surface coil 24c has sensitivity, a signal from outside the set FOV becomes an unnecessary signal that causes the occurrence of aliasing artifacts. Therefore, ideally, a signal from outside the set FOV can be made almost non-signaled by saturating the region R1 where an unnecessary signal outside the set FOV is generated by the presaturation pulse. In other words, by applying a pre-saturation pulse so that the signal from the FOV end in the PE direction is suppressed, it functions as a sensitivity filter that suppresses the sensitivity in the region R1 from the FOV end in the PE direction to the outside of the FOV. Can be made.

  By applying such a presaturation pulse, signals from the point A1 in the PE direction near the center of the set FOV and the point A2 in the set FOV near the set FOV end are collected, and outside the set FOV near the set FOV end. The signal from the point A3 is not obtained.

  FIG. 6 is a schematic diagram showing an example in which the slices to be applied with the excitation pulse and the refocus pulse are selected by the signal suppression condition setting unit 43 shown in FIG. 4 so that unnecessary signals are not generated.

  In FIG. 6, the horizontal axis indicates the PE direction, and the vertical axis indicates the sensitivity of the two surface coils 24c. Moreover, the solid line in FIG. 5 shows the sensitivity distribution of each surface coil 24c.

  When the slice selected at the time of applying the excitation pulse and the slice selected at the time of applying the refocus pulse are crossed, a signal can be generated only from the common portion R2. This corresponds to suppressing signals from other than the common portion R2 to which both the excitation pulse and the refocus pulse are applied. Therefore, by setting the slice selected when the refocus pulse is applied in the PE direction, it is possible to suppress signal generation from a region where an unnecessary signal is generated from the FOV end to outside the FOV as shown in FIG. . That is, the sensitivity filter of the two surface coils 24c can be formed by controlling the position of the common part R2 to which both the excitation pulse and the refocus pulse are applied.

  The signal suppression condition setting unit 43 is configured to set a slice that is excited and refocused by the presaturation pulse, the excitation pulse, and the refocus pulse described above for the pulse sequence acquired from the imaging condition setting unit 42. The

  The image reconstruction unit 44 has a function of reconstructing image data of the subject P, which is real space data, by acquiring k space data from the k space database 41 and performing image reconstruction processing such as Fourier transform. A function of writing the obtained image data into the real space database 45.

  For this reason, the real space database 45 stores image data obtained by scanning.

  The post-processing unit 46 reads the image data in the folded state collected by Parallel Imaging from the real space database 45 and generates the unfolded image data, and the display device 34 displays the unfolded image data. It has a function to display.

  The sensitivity map database 50 of the post-processing unit 46 stores a sensitivity map of the surface coil 24c in the setting FOV required when unfolding the image data in the folded state.

  FIG. 7 is a schematic diagram showing an example of the sensitivity map of the surface coil 24c stored in the sensitivity map database 50 shown in FIG.

  In FIG. 7, the horizontal axis indicates the PE direction, and the vertical axis indicates the sensitivity of the surface coil 24c. Moreover, the solid line in FIG. 7 shows the sensitivity distribution of the surface coil 24c. As shown in FIG. 7, the sensitivity map S <b> 1 of the surface coil 24 c in the PE direction setting FOV is stored in the sensitivity map database 50.

  The assumed sensitivity database 51 stores an assumed sensitivity map of the surface coil 24c that is assumed after being substantially filtered by the application of the presaturation pulse and the control of the common part to which the excitation pulse and the refocus pulse are applied.

  FIG. 8 is a schematic diagram showing an example of a sensitivity map of the surface coil 24c stored in the assumed sensitivity database 51 shown in FIG.

  In FIG. 8, the horizontal axis indicates the PE direction, and the vertical axis indicates the sensitivity of the surface coil 24c. Moreover, the solid line in FIG. 8 shows the sensitivity distribution of the surface coil 24c. As shown in FIG. 8, an assumed sensitivity map S2 of the surface coil 24c in the set FOV in which the sensitivity at the set FOV end in the PE direction is 0 is stored in the assumed sensitivity database 51.

  The signal suppression determination unit 47 has a function of determining whether or not the image data in the folded state read from the real space database 45 is obtained in a state where unnecessary signals are sufficiently suppressed, and an unnecessary signal Is determined to have been sufficiently suppressed, the folded image data is provided to the expansion processing unit 48, whereas when it is determined that the unnecessary signal is not sufficiently suppressed, the folded image data is folded. It has a function to be given to the removal processing unit 49.

  As a method for determining whether or not the image data in the folded state is obtained in a state where unnecessary signals are sufficiently suppressed, for example, whether or not suppression of unnecessary signals is sufficient for each shooting condition in advance. There is a method of associating these in advance. In this case, the signal suppression determination unit 47 refers to the signal suppression condition based on the pulse sequence acquired from the signal suppression condition setting unit 43. When the image data in the folded state is collected according to a signal suppression condition that does not sufficiently suppress unnecessary signals, it is determined that the unnecessary signals are not sufficiently suppressed on the image data.

  However, a method for determining whether or not the unnecessary signal is sufficiently suppressed is arbitrary. For example, in the folded image data, the signal from the region to be suppressed is compared with a threshold set in advance to a noise level, and an unnecessary signal is detected when a signal with a non-negligible intensity exceeding the threshold is detected. May be determined not to be sufficiently suppressed. Further, the image data in the folded state or the reference image data obtained from the image data is displayed on the display device 34, and the user determines whether or not the unnecessary signal is sufficiently suppressed by visual observation. Also good. In this case, a determination result by the user as to whether or not the unnecessary signal is sufficiently suppressed is given from the input device 33 to the signal suppression determination unit 47.

  The unfolding processing unit 48 performs the unfolding process on the image data in the folded state acquired from the signal suppression determination unit 47, thereby obtaining the unfolded image data, and the unfolded image. It has a function of displaying data on the display device 34. Further, when executing the unfolding process, the development processing unit 48 refers to the sensitivity map of the surface coil 24c stored in the sensitivity map database 50 so that an inverse transformation matrix can be created for the unfolding process from the sensitivity map. Composed. The unfolding process using the inverse transformation matrix obtained from the sensitivity map has been widely known in the past. Ra JB, Rim CY. “Fast imaging using subencoding data sets from multiple detectors.” Magn Reson Med 1993; 30: 142-145, KP Pruessmann, M. Weiger, MB Scheidegger, P. Boesiger, “SENSE: Sensitivity encoding for fast MRI” MRM 42: 952-962 (1999).

  Here, if the unnecessary signal is sufficiently suppressed, the image data in the folded state is information that there is no signal from the region outside the set FOV even if the portion of the subject P exists outside the set FOV. The unfolding process can be appropriately executed based on the above. For example, as shown in FIG. 5, the signal in the folded state from the point A1 in the PE direction near the center of the setting FOV and the point A2 in the setting FOV near the setting FOV end is expressed as a signal from the point A3 outside the setting FOV. It becomes possible to unfold based on the information that there is no.

  Therefore, the expansion processing unit 48 is configured to refer to the signal suppression condition based on the pulse sequence acquired from the signal suppression condition setting unit 43 and obtain information indicating the no-signal area. Thereby, even if the site of the subject P exists outside the set FOV, it is possible to acquire a full FOV image unfolded from the half-matrix data by the development processing unit 48.

  On the other hand, signal suppression by applying a pre-saturation pulse or the like is not necessarily performed completely. In actual photographing, there may be a signal remaining in a region where unnecessary signals are generated. In such a case, the signal suppression determination unit 47 determines that the unnecessary signal is not sufficiently suppressed. Therefore, the post-processing unit 46 is provided with a function of performing processing for removing the non-negligible influence caused by the residual signal on the image data in the folded state where the unnecessary signal is not sufficiently suppressed.

  The aliasing removal processing unit 49 performs a plurality of different aliasing removal processings on the folded image data acquired from the signal suppression determination unit 47 and unfolded generated by each aliasing removal processing. It has a function of giving a plurality of intermediate image data in a state to the weighted addition unit 52.

  The weighting addition unit 52 performs a weighted addition of a plurality of intermediate image data after the aliasing removal processing acquired from the aliasing removal processing unit 49, thereby generating final single image data, and the generated image. It has a function of displaying data on the display device 34.

  FIG. 9 is a diagram illustrating the aliasing removal processing in the aliasing removal processing unit 49 illustrated in FIG. 4 and an example of a weighting function for weighting addition in the weighting addition unit 52.

  In the graph of FIG. 9, the horizontal axis indicates the PE direction, and the vertical axis indicates the sensitivity of the surface coil 24c. The solid line indicates the sensitivity distribution of the surface coil 24c.

  When suppression of unnecessary signals in the region R1 in FIG. 9 is insufficient, when the signal from the point A1 near the center in the setting FOV and the signal from the point A2 near the FOV end in the setting FOV are unfolded, The influence of the signal from the point A3 in the vicinity of the FOV end outside the set FOV remains slightly. Similarly, if the signal from point B1 near the center in the setting FOV and the signal from point B2 near the FOV end in the setting FOV are unfolded, the signal from point B3 near the FOV end outside the setting FOV will be affected. It will remain a little.

  At this time, the influence of the absolute signal intensity due to the unnecessary signal from the points A3 and B3 near the FOV end outside the set FOV is slight, but due to the unnecessary signal from the points A3 and B3 near the center of the unfolded image. There is a possibility that a difference in signal intensity may cause a step in the image. That is, the absolute amount of unnecessary signals from the points A3 and B3 mixed in the signals from the points A1 and B1 are often not so large as to hinder diagnosis. However, the step of the image due to the residual unnecessary signal from the points A3 and B3 may cause a problem in diagnosis.

  For this reason, at the points A1 and B1 near the center of the image, it is important to reduce the level difference rather than calculating the absolute signal intensity with high accuracy. Therefore, it is assumed that the signal contribution from points A1 and B1 is dominant near the center of the set FOV, and the image is assumed to have little influence of the signal from the vicinity of the FOV end although the accuracy is slightly reduced as the signal strength. If this is created, artifacts of steps appearing near the center of the image can be reduced.

  Conversely, in calculating the signal value at points A2 and B2 near the FOV end in the set FOV, in order to obtain the signal strength more accurately, the absolute strength from points A1 and B1 near the center in the set FOV It is desirable to remove the influence of a large signal by a normal unfolding process. At this time, the signal values at the points A2 and B2 near the FOV end in the set FOV obtained by the calculation remain affected by the residual unnecessary signals from the points A3 and B3 near the FOV end outside the set FOV. However, the residual signal from points A3 and B3 is not limited to Parallel Imaging, but only affects natural folding that occurs in various imaging, and is equivalent to artifacts caused by imaging for full FOV other than Parallel Imaging. Stay in the artifact.

  Therefore, in response to the above diagnostic request, the aliasing removal processing unit 49 and the weighting addition unit 52 each perform a plurality of different aliasing processes so that different aliasing removal processing is performed depending on the position of the image data before aliasing removal. A removal process and a weighted addition process are configured to be executed. As a specific example, image data in the vicinity of the center (for example, points A1 and B1) in the set FOV in which inconsistency on the image due to folding from the FOV end prevents diagnosis is read from the assumed sensitivity database 51. The unfolding process is performed using the inverse transformation matrix created from the assumed sensitivity map S2 in which the sensitivity near the FOV end is zero.

  On the other hand, for the image data near the FOV end (for example, points A2 and B2) in the set FOV, an inverse transformation matrix created from the sensitivity map S1 of the original surface coil 24c read from the sensitivity map database 50 is used. Unfold processing is performed. That is, the image data is inversely converted using a sensitivity matrix whose coefficients are changed according to the position in the set FOV.

  Then, the folding removal processing unit 49 performs a plurality of different folding removal processings on the folded image data before the folding removal so that the above-described folding removal processing is performed, and a plurality of pieces obtained by the respective folding removal processing. The intermediate image data is provided to the weighted addition unit 52. On the other hand, the weighting addition unit 52 is configured to perform weighting addition of the plurality of intermediate image data created by the aliasing removal processing unit 49 so as to match the diagnostic request.

  When two intermediate image data are obtained from the image data collected using the two surface coils 24c having the sensitivity distribution shown in the upper part of FIG. 9 by the aliasing removal process, the PE direction as shown in the lower part of FIG. The two intermediate image data are weighted and added to each other by the weighting functions W1 and W2 that depend on the position of. That is, in the vicinity of the center of the image data obtained by weighted addition, the components of the intermediate image data obtained by creating the inverse transformation matrix from the assumed sensitivity map S2 with the sensitivity of 0 and performing the unfolding process increase. Thus, the weight function W2 is determined. Conversely, in the vicinity of the FOV end of the image data obtained by the weighted addition, the weight is set so that the components of the intermediate image data obtained by creating the inverse transformation matrix from the original sensitivity map S1 and performing the unfolding process increase. A function W1 is determined.

  Then, by combining the plurality of intermediate image data obtained by the different aliasing removal processes in the weighting and adding unit 52, it is possible to obtain final image data having a higher quality with less artifacts than in the past. It becomes.

  Next, the operation and action of the magnetic resonance imaging apparatus 20 will be described.

  FIG. 10 is a flowchart showing an example of the flow in the case where Parallel Imaging is performed by the magnetic resonance imaging apparatus 20 shown in FIG. 1, and the reference numerals with numerals in the figure indicate the steps of the flowchart.

  First, the subject P is set on the bed 37 in advance. Further, a static magnetic field is formed in the imaging region of the static magnetic field magnet 21 (superconducting magnet) excited by the static magnetic field power supply 26. Further, a current is supplied from the shim coil power supply 28 to the shim coil 22, and the static magnetic field formed in the imaging region is made uniform.

  In step S1, instruction information is given to the imaging condition setting unit 42 by operating the input device 33, and imaging conditions for Parallel Imaging such as the number of phase encodings and the set FOV corresponding to the number of surface coils 24c in the PE direction are set. Is set. That is, the number of phase encodings is set to be smaller than that of imaging that is not Parallel Imaging, and the setting FOV as narrow as possible is set so as not to cause aliasing artifacts. Then, the set imaging condition is given from the imaging condition setting unit 42 to the signal suppression condition setting unit 43 as a pulse sequence.

  Next, in step S <b> 2, the signal suppression condition setting unit 43 generates an unnecessary signal generated from a region from the set FOV end to the outside of the set FOV that causes the aliasing artifact with respect to the pulse sequence acquired from the imaging condition setting unit 42. Slices to be selected at the time of applying a presaturation pulse or applying an excitation pulse and a refocusing pulse are set. The pulse sequence after setting the signal suppression condition is given from the signal suppression condition setting unit 43 to the sequence controller control unit 40 and the post-processing unit 46.

  Next, when Parallel Imaging is given to the sequence controller control unit 40 by operating the input device 33 in Step S3, imaging for Parallel Imaging is executed. That is, the sequence controller control unit 40 gives the pulse sequence received from the signal suppression condition setting unit 43 to the sequence controller 31.

  The sequence controller 31 drives the gradient magnetic field power source 27, the transmitter 29, and the receiver 30 according to the pulse sequence received from the sequence controller control unit 40, thereby forming a gradient magnetic field in the imaging region in which the subject P is set, A high frequency signal is generated from the RF coil 24.

  Therefore, an NMR signal generated by nuclear magnetic resonance in the subject P is received by each surface coil 24 c of the RF coil 24 and given to each receiving system circuit 30 a in the receiver 30. Each receiving system circuit 30a receives the NMR signal from each surface coil 24c of the RF coil 24, performs necessary signal processing, and then performs A / D conversion to generate raw data that is an NMR signal of digital data. To do. The receiver 30 gives the generated raw data to the sequence controller 31. The sequence controller 31 provides the raw data to the sequence controller control unit 40, and the sequence controller control unit 40 arranges the raw data as k-space data in the k-space formed in the k-space database 41.

  Next, the image reconstruction unit 44 reconstructs the image data of the subject P, which is real space data, by capturing k space data from the k space database 41 and performing image reconstruction processing such as Fourier transform, The obtained image data is written into the real space database 45. As a result, image data obtained by scanning is stored in the real space database 45. However, since the image data is collected by Parallel Imaging, it is in a folded state.

  Next, in step S4, the signal suppression determination unit 47 determines whether the image data in the folded state read from the real space database 45 is obtained in a state where unnecessary signals are sufficiently suppressed. judge. This determination is performed, for example, when the signal suppression determination unit 47 refers to a determination table that associates whether or not shooting conditions and unnecessary signals are sufficiently suppressed. However, it may be determined whether or not the unnecessary signal is sufficiently suppressed by visual observation of the image by the user and threshold processing for the intensity of the unnecessary signal.

  When the signal suppression determination unit 47 determines that the unnecessary signal has been sufficiently suppressed, the signal suppression determination unit 47 provides the unfolded image data to the development processing unit 48.

  Then, in step S5, the development processing unit 48 refers to the sensitivity map of the surface coil 24c stored in the sensitivity map database 50, and creates an inverse transformation matrix for unfolding processing from the sensitivity map. Then, the expansion processing unit 48 performs unfolding processing on the image data in the folded state acquired from the signal suppression determination unit 47 using an inverse transformation matrix. As a result, the unfolded image data is given from the development processing unit 48 to the display device 34 and displayed.

  Since the image data created in this manner is generated in a state in which unnecessary signals that cause folding artifacts are sufficiently suppressed, an image in which folding artifacts are suppressed is obtained. For this reason, the user can make a diagnosis based on a higher quality image.

  On the other hand, when the signal suppression determination unit 47 determines in step S4 that the unnecessary signal is not sufficiently suppressed, the folded image processing unit 49 is supplied with the folded image data.

  Then, in step S <b> 6, the aliasing removal processing unit 49 performs different aliasing removal processing on the folded image data. Specifically, the aliasing removal processing unit 49 refers to the sensitivity map of the surface coil 24c stored in the sensitivity map database 50, and uses the sensitivity map for unfolding processing for the vicinity of the FOV end of the folded image data. Create an inverse transformation matrix. Further, the aliasing removal processing unit 49 refers to the assumed sensitivity map of the surface coil 24c in which the sensitivity at the FOV end stored in the assumed sensitivity database 51 is 0, and unfolds the image data in the folded state near the center. An inverse transformation matrix is created from the assumed sensitivity map for processing.

  Then, the aliasing removal processing unit 49 applies the inverse transformation created from the original sensitivity map and the assumed sensitivity map in which the sensitivity at the FOV end is 0 to the folded image data. Unfold processing is executed using both of the matrices. The two intermediate image data obtained in this way are given from the aliasing removal processing unit 49 to the weighting addition unit 52.

  Next, in step S <b> 7, the weighted addition unit 52 generates final single image data by performing weighted addition of the two intermediate image data acquired from the aliasing removal processing unit 49, and displays the display device 34. To display. At this time, the weighting function used for the weighted addition is obtained by creating an inverse transformation matrix from the assumed sensitivity map in which the sensitivity is set to 0 in the vicinity of the center of the image data obtained by the weighted addition and performing the unfolding process. In contrast, the intermediate image data obtained by unfolding by creating an inverse transformation matrix from the original sensitivity map near the FOV end of the image data obtained by weighted addition increases. The data components are determined so as to increase.

  Therefore, a step due to folding is suppressed near the center of the image data, and the signal intensity is obtained with high accuracy near the FOV end of the image data. Further, although unnecessary signals are not sufficiently suppressed, they are suppressed to some extent, so that an image with reduced aliasing artifacts can be used for diagnosis.

  That is, the magnetic resonance imaging apparatus 20 as described above actively suppresses the generation of MR signals in a specific spatial region when a subject is present outside the set FOV in Parallel Imaging, and the signal suppression region is known. By using it as information, an image without aliasing artifacts is obtained. More specifically, the magnetic resonance imaging apparatus 20 uses a signal suppression method such as application of a pre-saturation pulse or setting of an excitation range to specify a specific spatial position such as a FOV end in the PE direction that causes aliasing artifacts in Parallel Imaging. The MR signal is suppressed. Further, the magnetic resonance imaging apparatus 20 creates a plurality of intermediate images with different generation conditions according to the spatial position in consideration of the possibility of incomplete signal suppression, and synthesizes the created plurality of intermediate images. Thus, a final image is obtained.

  For this reason, according to the magnetic resonance imaging apparatus 20, it is possible to acquire a good image free from aliasing artifacts by using Parallel Imaging even when there is a target at the FOV end in the PE direction or when the number of element coils is small. Can do. And a diagnostic image with higher reliability can be provided.

  In the above-described example, when unnecessary signal suppression is insufficient, different aliasing removal processing is performed and weighted addition is performed. However, unnecessary signal suppression is not limited to the case where unnecessary signal suppression is insufficient. Depending on the situation and the target diagnostic image, the folded image data may be subjected to different aliasing removal processing to generate intermediate image data, and then the intermediate image data may be synthesized by weighted addition. In the above-described example, two intermediate image data are created by unfolding processing in which the coefficient of the sensitivity matrix is changed, but other aliasing removal processing may be performed.

  Examples of aliasing removal processing include multiple unfolding processes using an inverse transformation matrix created from a sensitivity map and unfolding processes using an inverse transformation matrix created from an assumed sensitivity map. In addition to unfolding processing, processing such as processing other than unfolding processing, such as thumb of square processing, can be mentioned. These processes are appropriately selected according to the relationship between the image data in the folded state and the image data after the aliasing removal to be created for diagnosis.

  FIG. 11 is a diagram showing an example in which intermediate image data generated by unfolding the folded image data and the folded image data are directly combined by weighted addition.

  In FIG. 11, the horizontal axis indicates the PE direction, and the vertical axis indicates the signal value. For example, signals are collected in a state where signals outside the set FOV are suppressed as indicated by a dotted line D1 in FIG. In this case, the signal near the set FOV end is folded back to the position indicated by the broken line D2. As a result, since the signal value of the folded image data is the sum of the signal indicated by the broken line D2 and the signal indicated by the dotted line D1 that are folded back in the unfolded region, the signal value is indicated by the solid line D3.

  In such a case, the image data in the vicinity of the center R3 of the unfolded region can be used as it is, whereas the image data at the end R4 of the unfolded region needs to be developed by unfolding processing. Therefore, the intermediate image data generated by the unfold process and the image data in the folded state are weighted and added, and the components of the folded image data increase near the center of the set FOV, and the end of the set FOV What is necessary is just to synthesize | combine so that the component of the intermediate image data produced | generated by the unfold process may increase in the vicinity.

  In the above-described embodiment, an example in which signals are collected using the two surface coils 24c has been described. However, even when signals are collected using three or more surface coils 24c, the cause of occurrence of aliasing artifacts is also the same. Can be suppressed by a desired signal suppression method. Furthermore, when collecting signals using the surface coil 24c having a three-dimensional sensitivity distribution, or when collecting signals using the three-dimensionally arranged surface coil 24c, spatial aliasing artifacts can be obtained. It is possible to specify a region where an unnecessary signal that causes generation is generated, and to suppress unnecessary signals from the specified region. And it becomes possible to perform an appropriate aliasing removal process using the known information that the signal in a specific space part is 0.

  FIG. 12 is a functional block diagram of a computer provided in the magnetic resonance imaging apparatus according to the second embodiment of the present invention.

  In the magnetic resonance imaging apparatus 20A shown in FIG. 12, the function of the computer 32A is different from that of the magnetic resonance imaging apparatus 20 shown in FIG. Since other configurations and operations are not substantially different from those of the magnetic resonance imaging apparatus 20 shown in FIG. 1, only the functional block diagram of the computer 32A is shown, and the same components are denoted by the same reference numerals and description thereof is omitted.

  The computer 32A of the magnetic resonance imaging apparatus 20A includes a sequence controller control unit 40, a k-space database 41, an imaging condition setting unit 42, a folding attention area display unit 60, an image reconstruction unit 44, a real space database 45, and an image processing unit. It functions as 61.

  The sequence controller control unit 40 has a function of controlling driving by giving an imaging pulse sequence including Parallel Imagin to the sequence controller 31 based on information from the input device 33 or other components. The sequence controller control unit 40 has a function of receiving raw data from the sequence controller 31 and arranging it as k-space data in a k-space (Fourier space) formed in the k-space database 41.

  The shooting condition setting unit 42 has a function of setting shooting conditions such as a setting FOV in accordance with an instruction from the input device 33 and a function of giving the set shooting conditions to the sequence controller control unit 40 as a pulse sequence. In particular, the imaging condition setting unit 42 is configured to be able to set imaging conditions for Parallel Imaging using a plurality of surface coils 24c. Specific examples of imaging conditions for Parallel Imaging include an enlargement ratio NoWrap, which is a parameter for the speed-up ratio PI and the anti-folding function in the PE direction. The acceleration rate PI can be set from 1 to the maximum number of surface coils 24c. The number of general-purpose surface coils 24c is about 4 to 8.

  The anti-folding function can also be used in normal imaging other than Parallel Imaging. The parameter NoWrap of the anti-folding function is an expansion rate of the developed FOV after the unfolding process with respect to the setting FOV set by the user at the time of the shooting plan.

  Further, the photographing condition setting unit 42 has a function of giving the set attention FOV, the speed-up rate PI, and the anti-folding function enlargement rate NoWrap to the turn-around attention area display unit 60.

  The loopback caution area display unit 60 obtains boundaries in the PE direction of the loopback caution area, the unfolded area, and the unfolded area based on the setting FOV, the acceleration rate PI, and the enlargement rate NoWrap received from the imaging condition setting unit 42. And the obtained folding attention area, unfolded area, and boundary of the unfolded area in the PE direction are displayed on the display device 34 together with the set FOV.

  Here, the aliasing attention area is a signal generation area that may cause aliasing artifacts. The unfold area is an area to be subjected to unfold processing, which is post-processing after data collection in Parallel Imaging. In addition, a folding artifact appears near the boundary of the unfolded area due to a signal from the folding attention area.

  Further, the folding attention area display unit 60 is configured to create information indicating the appearance position of the folding artifact corresponding to a signal from a certain folding attention area and display the information on the display device 34 as necessary.

  The image reconstruction unit 44 has a function of reconstructing image data of the subject P, which is real space data, by acquiring k space data from the k space database 41 and performing image reconstruction processing such as Fourier transform. A function of writing the obtained image data into the real space database 45.

  The image processing unit 61 has a function of performing necessary image processing such as projection processing and cross-section conversion processing on the image data read from the real space database 45 and displaying the image data on the display device 34.

  Next, the operation and action of the magnetic resonance imaging apparatus 20A will be described.

  FIG. 13 is a flowchart showing an example of the flow in the case where Parallel Imaging is performed by the magnetic resonance imaging apparatus 20A shown in FIG. 12, and the reference numerals with numerals in the figure indicate each step of the flowchart.

  First, the subject P is set on the bed 37 in advance. Further, a static magnetic field is formed in the imaging region of the static magnetic field magnet 21 (superconducting magnet) excited by the static magnetic field power supply 26. Further, a current is supplied from the shim coil power supply 28 to the shim coil 22, and the static magnetic field formed in the imaging region is made uniform.

  In step S10, shooting condition instruction information is given to the shooting condition setting unit 42 by operating the input device 33, and the setting FOV, the parallel imaging speed increase rate PI, and the anti-folding function enlargement rate NoWrap are temporarily set. . The imaging condition setting unit 42 gives the temporarily set FOV, the acceleration rate PI, and the enlargement rate NoWrap to the caution area display unit 60.

  Next, in step S11, the folding attention area display unit 60 determines whether the folding attention area, the unfold area, and the unfold area are based on the setting FOV, the acceleration rate PI, and the enlargement rate NoWrap received from the imaging condition setting unit 42. Find the boundary in the PE direction. Then, the folding attention area display unit 60 causes the display device 34 to display the calculated folding attention area, the unfolded area, and the boundary in the PE direction of the unfolded area.

  FIG. 14 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the acceleration rate PI = 2 and the enlargement ratio NoWrap = 1 are set.

  As shown in FIG. 14, for example, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P to be imaged. Note that the width of the set FOV in the direction perpendicular to the PE direction is also arbitrarily set and becomes the set width.

  When the enlargement ratio NoWrap = 1, that is, when the anti-folding function is not used, the area outside the set FOV in the PE direction is the anti-aliasing area R5. The return caution area R5 is displayed on the display device 34 so as to be identifiable by diagonal lines or other arbitrary methods as shown in FIG. Therefore, the protrusion area R6 of the subject P protruding in the PE direction from the set FOV overlaps with the folding attention area R5. If Parallel Imaging is executed under this condition, the folding artifact of the protrusion area R6 appears in advance. I can confirm.

  Further, the unfolded region R7 in the case of the enlargement ratio NoWrap = 1 is a region having a width B1 from the boundary on both sides in the PE direction of the set FOV toward the set FOV. Here, the width B1 of the unfolded region R7 in the case of the enlargement ratio NoWrap = 1 can be calculated by Expression (1).

[Equation 1]
B1 = PEFOV × (1-1 / PI) (1)
Here, since the speed-up rate PI = 2, the unfold region R7 is all the regions in the set FOV. Further, the part where the folding artifact appears is a boundary R8 in the PE direction of the unfolded region R7. Therefore, in addition to the unfolded region R7, the position of the boundary R8 of the unfolded region R7 is also displayed on the display device 34 so that it can be identified. As a result, not only the fact that the folding artifact of the protruding region R6 appears, but also the appearance position of the folding artifact can be easily grasped in advance.

  FIG. 15 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the speed increase rate PI = 1.5 and the enlargement ratio NoWrap = 1 are set.

  As shown in FIG. 15, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P. Since the enlargement ratio NoWrap = 1, the area outside the set FOV in the PE direction is displayed on the display device 34 so as to be identifiable as the folding attention area R5. Since the protrusion area R6 of the subject P protruding in the PE direction from the set FOV overlaps with the folding attention area R5, it can be confirmed in advance by Parallel Imaging that the folding artifact of the protrusion area R6 appears.

  Further, in equation (1), since the speed increase rate PI = 1.5, the unfold region R7 is a region having a width B1 = PEFOV / 3 from both ends of the set FOV. Therefore, the position of the boundary R8 of the unfolded region R7 where the folding artifact of the protruding region R6 appears is the position of the distance PEFOV / 3 from both ends of the set FOV.

  Furthermore, the folding attention area R5 can be obtained and displayed on the display device 34 even when normal imaging other than Parallel Imaging is performed without using the folding prevention function. The photographing conditions in this case are the speed-up rate PI = 1 and the enlargement rate NoWrap = 1.

  FIG. 16 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the acceleration rate PI = 1 and the enlargement ratio NoWrap = 1 are set.

  As shown in FIG. 16, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P. Since the enlargement ratio NoWrap = 1, the area outside the set FOV in the PE direction is displayed on the display device 34 so as to be identifiable as the folding attention area R5. Since the protrusion area R6 of the subject P protruding in the PE direction from the set FOV overlaps with the folding attention area R5, it can be confirmed in advance that the folding artifact of the protrusion area R6 appears by imaging.

  Further, since the speed-up rate PI = 1, the unfolded region R7 and the boundary R8 of the unfolded region R7 are not displayed.

  On the other hand, when the enlargement ratio NoWrap> 1, that is, when the anti-folding function is used, it is further outside the shift position by the distance GAP corresponding to the enlargement ratio NoWrap from the edge of the setting FOV in the PE direction toward the outside of the setting FOV. Is the turn-around attention area R5. The distance GAP at this time can be calculated by equation (2).

[Equation 2]
GAP = PEFOV (NoWrap-1) / 2 (PI ≧ 2NoWrap / (1 + NoWrap))
= PEFOV (NoWrap-1) / PI (PI <2NoWrap / (1 + NoWrap))
= PEFOV (NoWrap-1) (PI = 1) (2)
Further, when the enlargement ratio NoWrap> 1, the unfold region R7 is an area having a width B from the shift position by the distance GAP from the boundary on both sides in the PE direction of the setting FOV toward the outside of the setting FOV. Become. Here, the width B of the unfolded region R7 in the case of the enlargement ratio NoWrap> 1 can be calculated by Expression (3). Expression (3) is an expression including the case where the enlargement ratio NoWrap = 1.

[Equation 3]
B = PEFOV × NoWrap × (1-1 / PI) (3)
FIG. 17 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the acceleration rate PI = 1 and the enlargement ratio NoWrap = 2 are set.

  As shown in FIG. 17, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P. Since the speed increase rate PI = 1 and the enlargement rate NoWrap = 2, the area far from the setting FOV is identified as the caution area R5 for the position shifted from the setting FOV by the distance GAP (= PEFOV) in the PE direction. It is displayed on the display device 34 as possible. In the example of FIG. 17, since the protrusion region R6 of the subject P that protrudes in the PE direction from the set FOV does not overlap with the folding attention region R5, it is confirmed beforehand by imaging that the folding artifact of the protrusion region R6 does not appear. it can. In other words, it can be confirmed that the appearance of the folding artifact can be prevented by the folding prevention function.

  Further, since the speed-up rate PI = 1, the unfolded region R7 and the boundary R8 of the unfolded region R7 are not displayed.

  FIG. 18 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the acceleration rate PI = 2 and the enlargement ratio NoWrap = 2 are set.

  As shown in FIG. 18, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P. Since the speed-up rate PI = 2 and the enlargement rate NoWrap = 2, the region on the side far from the set FOV is the return attention region R5 with respect to the position shifted by the distance GAP (= PEFOV / 2) in the PE direction from the set FOV. Are displayed on the display device 34 in an identifiable manner. In the example of FIG. 18, since the protrusion region R6 of the subject P protruding in the PE direction from the set FOV does not overlap with the folding attention region R5, it is confirmed beforehand by imaging that the folding artifact of the protrusion region R6 does not appear. it can. In other words, it can be confirmed that the appearance of the folding artifact can be prevented by the folding prevention function.

  Further, since the speed increase rate PI = 2 and the enlargement rate NoWrap = 2, the unfold region R7 is within the set FOV from the shift position by the distance GAP from the boundary on both sides in the PE direction of the set FOV toward the outside of the set FOV. It becomes an area of width B (= PEFOV) toward. The unfolded region R7 and the boundary R8 of the unfolded region R7 located at the center of the set FOV are displayed on the display device 34 in an identifiable manner. For this reason, if there is a signal from the folding attention area R5, the position of the folding artifact that appears by the signal can be grasped.

  FIG. 19 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the acceleration rate PI = 2 and the enlargement ratio NoWrap = 1.2 are set.

  As shown in FIG. 19, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P. Since the speed increase rate PI = 2 and the enlargement rate NoWrap = 1.2, the region on the side far from the set FOV is turned back at the position shifted by the distance GAP (= PEFOV / 10) in the PE direction from the set FOV. Are displayed on the display device 34 in an identifiable manner.

  In the example of FIG. 19, since the protrusion area R6 of the subject P protruding in the PE direction from the set FOV does not overlap with the folding attention area R5, it is confirmed beforehand by imaging that the folding artifact of the protrusion area R6 does not appear. it can. In other words, it can be confirmed that the appearance of the folding artifact can be prevented by the folding prevention function. Further, in the example of FIG. 19, since the unfolded region R7 is set narrower than the example of FIG. 18, in the case of the acceleration rate PI = 2, the enlargement rate NoWrap = 2 from the viewpoint of preventing an increase in shooting time. It can be seen that the enlargement ratio NoWrap = 1.2 is better than In other words, when the speed increase rate PI = 2, it can be said that the enlargement rate NoWrap = 1.2 is sufficient.

  Further, since the speed increase rate PI = 2 and the enlargement rate NoWrap = 1.2, the unfold region R7 is within the set FOV from the shift position by the distance GAP from the boundary on both sides in the PE direction of the set FOV toward the outside of the set FOV. It becomes an area of width B (= 0.6 × PEFOV) toward. The unfolded region R7 and the boundary R8 of the unfolded region R7 located at the center of the set FOV are displayed on the display device 34 in an identifiable manner. For this reason, if there is a signal from the folding attention area R5, the position of the folding artifact that appears by the signal can be grasped.

  FIG. 20 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the speed increase rate PI = 1.2 and the enlargement ratio NoWrap = 1.2 are set.

  As shown in FIG. 20, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P. Since the speed increase rate PI = 1.2 and the enlargement rate NoWrap = 1.2, the region on the side far from the set FOV is turned back from the position shifted by the distance GAP (= PEFOV / 10) in the PE direction from the set FOV. Are displayed on the display device 34 in an identifiable manner.

  In the example of FIG. 20, since the protrusion area R6 of the subject P protruding in the PE direction from the set FOV does not overlap with the folding attention area R5, it is confirmed beforehand by imaging that the folding artifact of the protrusion area R6 does not appear. it can.

  Further, since the speed increase rate PI = 1.2 and the enlargement rate NoWrap = 1.2, the unfold region R7 is within the set FOV from the shift position by the distance GAP from the boundary on both sides in the PE direction of the set FOV toward the outside of the set FOV. It becomes an area of width B (= PEFOV / 5) toward. The unfolded region R7 and the boundary R8 of the unfolded region R7 located near both ends of the set FOV are displayed on the display device 34 in an identifiable manner. For this reason, if there is a signal from the folding attention area R5, the position of the folding artifact that appears by the signal can be grasped.

  FIG. 21 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the speed increase rate PI = 1.2 and the enlargement rate NoWrap = 1.5 are set.

  As shown in FIG. 21, a set FOV whose width in the PE direction is PEFOV is set in the body of the subject P. When the acceleration rate PI = 1.2 and the enlargement rate NoWrap = 1.5, PI <2NoWrap / (1 + NoWrap) in equation (2). If the enlargement ratio NoWrap is solved, NoWrap> PI / (2-PI). Accordingly, an area on the side away from the set FOV with respect to a position shifted by the distance GAP (≈0.4 × PEFOV) in the PE direction from the set FOV is displayed on the display device 34 so as to be identifiable as a turn-around attention area R5.

  In the example of FIG. 21, since the protrusion area R6 of the subject P protruding in the PE direction from the set FOV does not overlap with the folding attention area R5, it is confirmed in advance that the folding artifact of the protrusion area R6 does not appear by imaging. it can.

  When the speed increase rate PI = 1.2 and the enlargement rate NoWrap = 1.5, the unfold region R7 is positioned outside the set FOV in terms of calculation. Therefore, it is not necessary to display the unfolded region R7 and the unfolded region R7 boundary R8 on the display device 34.

  Further, even when the anti-folding function is used in normal imaging other than Parallel Imaging, the anti-aliasing region R5 can be displayed on the display device 34.

  FIG. 22 is a diagram illustrating a folding attention area displayed by the folding attention area display unit 60 illustrated in FIG. 12 when the acceleration rate PI = 1 and the enlargement ratio NoWrap = 1.2 are set.

  As shown in FIG. 22, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P. Since the speed increase rate PI = 1 and the enlargement rate NoWrap = 1.2, the region on the side far from the set FOV is turned back at the position shifted by the distance GAP (= 0.2 × PEFOV) in the PE direction from the set FOV. Are displayed on the display device 34 in an identifiable manner.

  In the example of FIG. 22, since the protrusion area R6 of the subject P protruding in the PE direction from the set FOV does not overlap with the folding attention area R5, it is confirmed beforehand by imaging that the folding artifact of the protrusion area R6 does not appear. it can. Further, according to the examples shown in FIGS. 16, 22, and 17, it can be seen that, when Parallel Imaging is not performed, aliasing artifacts appear unless the aliasing prevention function is used. Therefore, in order to prevent the appearance of the aliasing artifact, it is necessary to use the aliasing prevention function. However, it can be seen that the shooting time can be shortened by setting the enlargement ratio NoWrap = 1.2 rather than the enlargement ratio NoWrap = 2.

  Further, since the speed-up rate PI = 1, the unfolded region R7 and the boundary R8 of the unfolded region R7 are not displayed.

  Furthermore, in addition to the folding attention area R5, the unfolding area R7, and the boundary R8 of the unfolding area R7, the signal area that causes the folding artifact and the appearance position of the folding artifact can be displayed in association with each other.

  In FIG. 23, when the speed increase rate PI = 1.5 and the enlargement rate NoWrap = 1, the return attention area display unit 60 shown in FIG. 12 determines the appearance position of each return artifact corresponding to a plurality of return attention areas. It is a figure which shows the example which displayed the information for doing with a return attention area.

  As shown in FIG. 23, a set FOV whose width in the PE direction is PEFOV is set in the body portion of the subject P. Since the enlargement ratio NoWrap = 1, the area outside the PE direction of the set FOV is displayed on the display device 34 so as to be identifiable as the folding attention areas R5A and R5B. However, one folding attention area R5A is colored by COLOR1 so that the color gradually becomes lighter as the distance from the end of the set FOV increases. The other caution area R5B is colored so that the color gradually becomes lighter as it moves away from the end of the set FOV by COLOR2 different from COLOR1.

  In this case, since the two protruding regions R6A and R6B of the subject P protruding from the set FOV in the PE direction overlap with the respective folding attention regions R5A and R5B, each of the protruding regions corresponds to the protruding regions R6A and R6B by Parallel Imaging. It can be confirmed in advance that two folding artifacts appear.

  Further, since the speed increase rate PI = 1.5, the unfold regions R7A and R7B are regions of width B1 = PEFOV / 3 from both ends of the set FOV. Accordingly, the positions of the boundaries R8A and R8B of the unfolded regions R7A and R7B where the folding artifacts corresponding to the protruding regions R6A and R6B appear are the positions of the distance PEFOV / 3 from both ends of the set FOV, respectively. Therefore, the appearance position of the folding artifact corresponding to the protruding area R6A in the folding attention area R5A colored by COLOR1, that is, from the boundary R8A of the unfolded area R7A on the side farther from the folding attention area R5A colored by COLOR1. The region R9A toward the return attention region R5A colored by COLOR1 is also colored so that the color gradually becomes lighter as it moves away from the boundary R8A of the unfolded region R7A by COLOR1.

  Similarly, the appearance position of the folding artifact corresponding to the protruding area R6B in the folding attention area R5B colored by COLOR2, that is, the boundary R8B of the unfolded area R7B on the side farther from the folding attention area R5B colored by COLOR2. The region R9B, which is colored from COLOR2 to the turn-around attention region R5B, is also colored by COLOR2 so that the color gradually becomes lighter as it moves away from the boundary R8B of the unfolded region R7B.

  In this way, by coloring the appearance positions of the folding attention areas R5A and R5B using different colors, the user can grasp the appearance positions of the artifacts corresponding to the folding attention areas R5A and R5B. Further, the direction of the folding artifact can be indicated by coloring the folding attention areas R5A, R5B and the artifact appearance areas R9A, R9B so that the color gradually becomes lighter.

  The return attention areas R5A and R5B and the corresponding return artifact appearance areas R9A and R9B may be identified and directed by methods other than color and gradation. For example, patterns and symbols may be displayed.

  The return attention area, the unfold area, the boundary between the unfold area and the appearance position of the return artifact corresponding to the return attention area corresponding to the imaging conditions as described above are displayed on the display device 34 in an identifiable manner. For this reason, the user can determine in advance whether or not the temporarily set shooting conditions are appropriate. That is, the user can confirm whether or not the folding artifact may appear at a position where the diagnosis is disturbed, whether or not the imaging time is prolonged due to excessive data collection, and the like.

  If the user determines that the temporarily set shooting condition is not appropriate and needs to be corrected, the shooting condition instruction information is given to the shooting condition setting unit 42 by operating the input device 33 again in step S10. It is done. Then, a new setting FOV, speed-up rate PI, and enlargement rate NoWrap are temporarily set.

  In this way, the provisional setting of the setting FOV, the speed-up rate PI, and the enlargement rate NoWrap, and the display of the folding attention area, etc. are repeatedly performed, so that the shooting conditions are corrected to more appropriate conditions. For example, the user can arbitrarily change the enlargement ratio NoWrap so that the folding attention area displayed on the display device 34 does not overlap the protrusion area, and can set a smaller enlargement ratio NoWrap. That is, the enlargement ratio NoWrap can be optimized so as to shorten the shooting time.

  When the user determines that the set shooting conditions are appropriate, the temporarily set shooting conditions are determined by operating the input device 33.

  Then, in step S <b> 12, the imaging condition setting unit 42 determines that the imaging conditions have been established, and gives imaging conditions such as a pulse sequence to the sequence controller control unit 40.

  In step S13, when an instruction to start imaging is given from the input device 33 to the sequence controller control unit 40, the sequence controller control unit 40 sets the imaging conditions such as a pulse sequence received from the imaging condition setting unit 42 to the sequence controller 31. To give. For this reason, data collection according to imaging conditions is performed by control of the gradient magnetic field power source 27, the transmitter 29, and the receiver 30 of the sequence controller 31. The collected raw data is arranged in the k space formed in the k space database 41 as k space data.

  Next, the image reconstruction unit 44 reconstructs the image data of the subject P, which is real space data, by capturing k space data from the k space database 41 and performing image reconstruction processing such as Fourier transform, The obtained image data is written into the real space database 45. Further, the image processing unit 61 performs necessary image processing such as projection processing and cross-section conversion processing on the image data read from the real space database 45 and causes the display device 34 to display the image data.

  Since the image displayed in this manner is captured in advance under imaging conditions that do not cause folding artifacts and the imaging time is shortened, it can be obtained in higher quality and in a shorter time. Then, the user can make a diagnosis using an image that does not have the intended folding artifact in advance.

  That is, the above-described magnetic resonance imaging apparatus 20A displays the boundary region between the unfolded region, the unfolded region, and the unfolded region in which the folding artifact appears in the PE direction of the preset FOV when performing the imaging plan of Parallel Imaging. It is something that can be done.

  This makes it easy to perform a shooting plan in which the appearance position of the folding artifact is predicted in advance. That is, it is possible to select an optimal minimum setting FOV and an optimal Parallel Imaging speedup rate PI. In addition, attention to aliasing artifacts in Parallel Imaging can be alerted to the user. As a result, it is possible to avoid misdiagnosis and re-imaging due to the appearance of unintended folding artifacts.

  The Parallel Imaging unfolding process can be performed not only in the PE direction but also in the slice encode (SE) direction. For this reason, the magnetic resonance imaging apparatus 20A may be configured to display the return risk area, the unfold area, the boundary of the unfold area, and the appearance position of the return artifact corresponding to the return risk area in the SE direction. In addition, when using the anti-folding function in the encoding direction in general imaging other than Parallel Imaging, the magnetic resonance imaging apparatus 20A may be configured to display the folding risk area. Further, even when Parallel Imaging is performed using three or more surface coils 24c and the speed-up rate PI> 2, the folding risk area, the unfolding area, the boundary of the unfolding area, and the folding risk area by the method described above. The appearance position of the folding artifact corresponding to can be displayed.

  In the above-described example, the user has manually optimized the enlargement ratio NoWrap. However, the return attention area display unit 60 may be provided with a function for optimizing the enlargement ratio NoWrap and may be automated. In this case, a function for detecting a protruding area from the set FOV is provided in the loop-back attention area display unit 60. The protrusion area can be detected by threshold processing, for example. Then, the folding attention area display section 60 sets a minimum enlargement ratio NoWrap that provides a necessary gap between the protruding area and the folding attention area detected by the folding attention area display section 60.

  It is also possible to provide a magnetic resonance imaging apparatus having the functions of both the magnetic resonance imaging apparatuses 20 and 20A in the above embodiments. For example, the magnetic resonance imaging apparatus can be provided with both a display function of a folding attention area and a function of suppressing unwanted signals that cause folding artifacts. In this case, whether or not there is a possibility that signals that cause aliasing artifacts may be collected even if the shooting conditions are set in advance so that aliasing artifacts do not occur as much as possible by the display function of the aliasing attention area. Can be judged. Then, it is possible to estimate a spatial part where an unnecessary signal is generated by the display function of the return attention area, and to suppress the unnecessary signal in the estimated spatial part by the function of suppressing the unnecessary signal.

20 Magnetic Resonance Imaging Device 21 Magnet for Static Magnetic Field 22 Shim Coil 23 Gradient Magnetic Field Coil Unit 24 RF Coil 24a WB Coil 24b Phased Array Coil 24c Surface Coil 25 Control System 26 Static Magnetic Field Power Supply 27 Gradient Magnetic Field Power Supply 28 Shim Coil Power Supply 29 Transmitter 30 Receiver 31 Sequence Controller 32 Computer 33 Input Device 34 Display Device 35 Computing Device 36 Storage Device 37 Bed 40 Sequence Controller Control Unit 41 k Space Database 42 Imaging Condition Setting Unit 43 Signal Suppression Condition Setting Unit 44 Image Reconstruction Unit 45 Real Space Database 46 Processing unit 47 Signal suppression determination unit 48 Development processing unit 49 Folding removal processing unit 50 Sensitivity map database 51 Assumed sensitivity database 52 Weighting addition unit 60 Folding attention area display unit 61 Image processing unit P Test body

Claims (6)

Data collection means for collecting magnetic resonance signals from the subject;
Image data generating means for generating image data from the magnetic resonance signals collected by the data collecting means;
A region display means for calculating a region where a magnetic resonance signal causing a folding artifact on the image data based on a photographing condition may be generated as a folding attention region, and displaying the obtained folding attention region on a display device;
Have
The area display means calculates the aliasing attention area based on an imaging condition including an enlargement factor that is a parameter of a aliasing prevention function that performs aliasing removal processing on an imaging field that is enlarged with respect to a set imaging field. Composed of,
Magnetic resonance imaging apparatus characterized by. Data collection means for collecting magnetic resonance signals from the subject;
Image data generating means for generating image data from the magnetic resonance signals collected by the data collecting means;
A region display means for calculating a region where a magnetic resonance signal causing a folding artifact on the image data based on a photographing condition may be generated as a folding attention region, and displaying the obtained folding attention region on a display device;
Have
While the data collection means is configured to collect the magnetic resonance signal by Parallel Imaging using a plurality of coils,
The area display means is configured to calculate the aliasing attention area based on imaging conditions including a speed-up rate that is a parameter of the Parallel Imaging.
A magnetic resonance imaging apparatus. Data collection means for collecting magnetic resonance signals from the subject;
Image data generating means for generating image data from the magnetic resonance signals collected by the data collecting means;
A region display means for calculating a region where a magnetic resonance signal causing a folding artifact on the image data based on a photographing condition may be generated as a folding attention region, and displaying the obtained folding attention region on a display device;
Have
While the data collection means is configured to collect the magnetic resonance signal by Parallel Imaging using a plurality of coils,
The area display means calculates an area to be subjected to unfolding processing of the folded image data having the folding generated by the image data generation means as an unfolded area, and causes the display device to display the unfolded area. Composed,
A magnetic resonance imaging apparatus. Data collection means for collecting magnetic resonance signals from the subject;
Image data generating means for generating image data from the magnetic resonance signals collected by the data collecting means;
A region display means for calculating a region where a magnetic resonance signal causing a folding artifact on the image data based on a photographing condition may be generated as a folding attention region, and displaying the obtained folding attention region on a display device;
Have
While the data collection means is configured to collect the magnetic resonance signal by Parallel Imaging using a plurality of coils,
The region display unit is configured to calculate a boundary of a region to be subjected to unfolding processing of the folded image data having the folding generated by the image data generation unit, and to display the boundary on a display device.
A magnetic resonance imaging apparatus. Data collection means for collecting magnetic resonance signals from the subject;
Image data generating means for generating image data from the magnetic resonance signals collected by the data collecting means;
A region display means for calculating a region where a magnetic resonance signal causing a folding artifact on the image data based on a photographing condition may be generated as a folding attention region, and displaying the obtained folding attention region on a display device;
Have
The region display means is configured to display on the display device each appearance region of the folding artifact caused by each magnetic resonance signal from the plurality of folding attention areas so that the correspondence relationship with the plurality of folding attention areas can be identified. Ru is,
A magnetic resonance imaging apparatus. Data collection means for collecting magnetic resonance signals from the subject;
Image data generating means for generating image data from the magnetic resonance signals collected by the data collecting means;
A region display means for calculating a region where a magnetic resonance signal causing a folding artifact on the image data based on a photographing condition may be generated as a folding attention region, and displaying the obtained folding attention region on a display device;
Have
The region display means, the occurrence region of the folding artifacts due to the magnetic resonance signals from the folded note region, Ru is configured to display on the display device so that the direction is visible in the folded artifact,
A magnetic resonance imaging apparatus.

Images