JP2015104489A - Magnetic resonance apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MR apparatus that acquires a plurality of diffusion weighted images that differ in MPG (motion probing gradient) application directions avoiding extension of a scan time as much as possible.SOLUTION: An MR apparatus includes a plurality of gradient pulse generating means for generating gradient pulses applied in an x-axis direction, a y-axis direction and a z-axis direction. By combining the gradient pulses generated by at least two of the gradient pulse generating means of the plurality of the gradient pulse generating means, an MPG to be applied to a plurality of axes (r1' axis, r2' axis, r3' axis, r4' axis, r5' axis, and r6' axis) respectively is caused to be generated. The plurality of axes (r1' axis, r2' axis, r3' axis, r4' axis, r5' axis, and r6' axis) are set based on the magnetic field generating efficiency of the plurality of the gradient pulse generating means.

Description

  The present invention relates to a magnetic resonance apparatus that generates gradient pulses.

  In recent years, diffusion tensor imaging has been used for visualization of white matter nerve fiber bundles (see Patent Document 1).

JP 2012-157687 A

  In diffusion tensor imaging, the application direction of MPG (Motion Probing Gradient) is changed, and a scan for acquiring a plurality of diffusion weighted images having different application directions of MPG is executed. The magnetic resonance apparatus generally has a gradient coil for x-axis, a gradient coil for y-axis, and a z-axis so that gradient pulses can be applied in the x-axis direction, the y-axis direction, and the z-axis direction. For use with gradient coils. Therefore, the application direction of MPG can be adjusted by adjusting the magnitude of the gradient pulse applied in each axial direction. After acquiring a plurality of diffusion-weighted images having different MPG application directions, a tensor analysis can be performed based on these diffusion-weighted images, thereby creating a diffusion tensor image.

  However, in diffusion tensor imaging, a sequence for generating MPG may be executed by applying gradient pulses only in the x-axis direction without applying gradient pulses in the y-axis direction and z-axis direction. In this sequence, since gradient pulses for MPG are applied only in the x-axis direction, the load is concentrated on the x-axis amplifier that outputs current to the gradient coil for the x-axis, and the amount of heat generated by the x-axis amplifier increases. There is. Therefore, when performing diffusion tensor imaging, a rest period for reducing the load on the amplifier is provided between the sequences. By providing such rest time, the sequence can be repeatedly executed even when the load is concentrated on a specific amplifier.

  However, the x-axis gradient coil, the y-axis gradient coil, and the z-axis gradient coil may have different magnetic field generation efficiencies due to differences in coil patterns. For example, the magnetic field generation efficiency of the x-axis gradient coil may be lower than the magnetic field generation efficiency of the z-axis gradient coil. In this case, the x-axis amplifier needs to supply a larger coil current to the gradient coil for the x-axis in order to compensate for the difference in magnetic field generation efficiency. Therefore, there is a problem that the amount of heat generated by the x-axis amplifier increases. As a method for dealing with an increase in the amount of heat generated by the amplifier, it is conceivable to increase the rest time between sequences. However, if the rest time is increased, there is a problem that the scan time is extended.

  Therefore, it is desired to acquire a plurality of diffusion weighted images with different MPG application directions without extending the scan time as much as possible.

One aspect of the present invention is a plurality of gradient pulse generating means for generating gradient pulses applied in different directions, wherein at least two of the plurality of gradient pulse generating means are generated. A plurality of gradient pulse generating means for generating MPG applied to each of a plurality of axes by synthesizing gradient pulses;
The plurality of axes is a magnetic resonance apparatus set based on the magnetic field generation efficiency of the plurality of gradient pulse generating means.

  Since the MPG axis is set based on the magnetic field generation efficiency of the gradient pulse generating means, diffusion emphasis can be performed without concentrating the load on the specific gradient pulse generating means. Therefore, since the load on each gradient pulse generating means can be reduced, the rest time between sequences can be shortened, and the scan time can be shortened.

It is the schematic of the magnetic resonance apparatus of one form of this invention. It is a figure which shows an example of the matrix D showing the some axis | shaft of MPG. 6 is an explanatory diagram of the first row (d ₁₁ , 0, 0) of the matrix D. FIG. Is an explanatory view of the second row of the matrix _{D (d 21, d 22,} 0). It is an explanatory view of the third row of the matrix _{D (d 31, d 32,} d 33). Fourth row of the matrix _{D (d 41, -d 42,} -d 43) is an explanatory view of. Fifth row of the matrix _{D (d 51, -d 52,} d 53) is an explanatory view of. Sixth row of the matrix _{D (-d 61, -d 62,} d 63) is an explanatory view of. It is a figure which shows the positional relationship of vector V1-V6. It is a figure which shows an example of the scan for acquiring a diffusion tensor image using sequence AF. It is a figure which shows the matrix D 'schematically. It is a figure which shows the matrix P schematically. It is a figure which shows the maximum value M of each element of the matrix P1-Pw. It is an illustration of a first row of the matrix _{Dj' (d 11, j d 12} , j -d 13, j). It is an explanatory view of the second row of the matrix _{Dj' (d 21, j d 22} , j d 23, j). Is an explanatory view of the third row of the matrix _{Dj' (d 31, j -d 32} , j d 33, j). Is an explanatory view of a fourth row of the matrix _{Dj' (d 41, j -d 42} , j -d 43, j). Is an explanatory view of a fifth row of the matrix _{Dj' (d 51, j -d 52} , j -d 53, j). Is an explanatory view of a sixth row of the matrix _{Dj' (d 61, j -d 62} , j d 63, j). It is a figure which shows the positional relationship of vector V1'-V6 '.

  Hereinafter, although the form for inventing is demonstrated, this invention is not limited to the following forms.

FIG. 1 is a schematic view of a magnetic resonance apparatus according to one embodiment of the present invention.
A magnetic resonance apparatus (hereinafter referred to as “MR apparatus”, MR: Magnetic Resonance) 100 includes a magnet 2, a table 3, a receiving coil 4, and the like.

  The magnet 2 has a bore 21 in which the subject 12 is accommodated. The magnet 2 includes gradient coils 22x, 22y and 22z for applying gradient pulses. The gradient coil 22x applies a gradient pulse in the X-axis direction, the gradient coil 22y applies a gradient pulse in the Y-axis direction, and the gradient coil 22z applies a gradient pulse in the Z-axis direction.

  The table 3 has a cradle 3 a that supports the subject 12. The cradle 3a is configured to be able to move into the bore 21. The subject 12 is transported to the bore 21 by the cradle 3a.

  The receiving coil 4 is attached to the subject 12. The receiving coil 4 receives a magnetic resonance signal from the subject 12.

  The MR apparatus 100 further includes a gradient power supply 5, a transmitter 7, a receiver 8, a control unit 9, an operation unit 10, a display unit 11, and the like.

  The gradient power supply 5 supplies a gradient magnetic field signal to the amplification unit 6. The amplifying unit 6 includes an X-axis amplifier 6x, a Y-axis amplifier 6y, and a Z-axis amplifier 6z. Each amplifier 6x, 6y, 6z amplifies the signal from the gradient power supply 5 and supplies a coil current to the gradient coils 22x, 22y, 22z. The gradient coils 22x, 22y, and 22z generate a magnetic field corresponding to the supplied coil current. A combination of the x-axis amplifier 6x and the gradient coil 22x, a combination of the y-axis amplifier 6y and the gradient coil 22y, and a combination of the z-axis amplifier 6z and the gradient coil 22z are gradient pulse generating means. It corresponds to.

  The transmitter 7 supplies current to an RF coil (not shown). The receiver 8 performs signal processing such as detection on the signal received from the receiving coil 4.

  The control unit 9 transmits necessary information to the display unit 11 and reconstructs an image based on the data received from the receiver 8 so as to realize various operations of the MR apparatus 100. Control the operation of each part.

  The operation unit 10 is operated by an operator and inputs various information to the control unit 9. The display unit 11 displays various information.

In this embodiment, the magnetic field generation efficiencies of the gradient coils 22x, 22y, and 22z are different. The following table shows an example of the magnetic field generation efficiency.

The magnetic field generation efficiency values shown in Table 1 are values when a current of 100 A is supplied to each of the gradient coils 22x, 22y, and 22z. Comparing the magnetic field generation efficiency, it can be seen that the magnetic field generation efficiency gx in the x-axis direction and the magnetic field generation efficiency gy in the y-axis direction are lower by 5 mT / m than the magnetic field generation efficiency gz in the z-axis direction.
The MR apparatus 100 is configured as described above.

  In this embodiment, an example in which diffusion tensor imaging is executed using the MR apparatus 100 will be described.

  When performing diffusion tensor imaging, it is necessary to set a plurality of axes representing the application direction of MPG. Therefore, first, a plurality of axes representing the MPG application direction will be described.

FIG. 2 is a diagram illustrating an example of a matrix D representing a plurality of axes of MPG.
Each of the first to sixth rows of the matrix D corresponds to an axis representing the MPG application direction. Below, the 1st line-the 6th line of the matrix D are demonstrated in order, referring FIGS. 3-8.

FIG. 3 is an explanatory diagram of the first row (d ₁₁ , 0, 0) of the matrix D.
FIG. 3A shows a vector V1 representing the x-axis component of (d ₁₁ , 0, 0). The vector V1 has a magnitude “d ₁₁ ” in the x-axis direction. Since the y-axis component and the z-axis component have zero values, (d ₁₁ , 0, 0) is represented by the vector V1. The x-axis where the vector V1 is located defines the MPG application direction.

FIG. 3B schematically shows a sequence A for applying MPG on the x-axis. In a sequence A, gradient pulse Qx1 amplitude k · _{d 11} is applied to the x-axis direction (k is a coefficient). It represents MPG to which the gradient pulse Qx1 is applied on the x-axis. Data acquisition is performed after applying the gradient pulse Qx1. In addition to the gradient pulse Qx1, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 4 is an explanatory diagram of the second row (d ₂₁ , d ₂₂ , 0) of the matrix D.
FIG. 4A shows two vectors Vx2 and Vy2 representing (d ₂₁ , d ₂₂ , 0). The vector Vx2 has a size “d ₂₁ ” in the x-axis direction, and the vector Vy2 has a size “d ₂₂ ” in the y-axis direction. Since the z-axis component has a value of zero, (d ₂₁ , d ₂₂ , 0) is represented by vectors Vx2 and Vy2. FIG. 4B shows a vector V2 obtained by combining the vectors Vx2 and Vy2. In FIG. 4B, the axis that defines the direction of the vector V2 is indicated by the symbol “r2”. The r2 axis defines the MPG application direction.

FIG. 4C schematically shows a sequence B for applying MPG on the r2 axis. In the sequence B, a gradient pulse Qx2 having an amplitude k · d ₂₁ is applied in the x-axis direction, and a gradient pulse Qy2 having an amplitude k · d ₂₂ is applied in the y-axis direction. A synthesized magnetic field obtained by synthesizing these gradient pulses Qx2 and Qy2 represents MPG applied on the r2 axis. Data acquisition is performed after applying the gradient pulses Qx2 and Qy2. In addition to the gradient pulses Qx2 and Qy2, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 5 is an explanatory diagram of the third row (d ₃₁ , d ₃₂ , d ₃₃ ) of the matrix D.
In FIG. 5 _(a), has been shown to _{(d 31, d 32, d} 33) 3 single vectors representing the Vx3, Vy3, Vz3. The vector Vx3 has a magnitude “d ₃₁ ” in the x-axis direction, the vector Vy3 has a magnitude “d ₃₂ ” in the y-axis direction, and the vector Vz3 has a magnitude “d ₃₃ ” in the z-axis direction. "have. FIG. 5B shows a vector V3 obtained by combining the vectors Vx3, Vy3, and Vz3. In FIG. 5B, the axis that defines the direction of the vector V3 is indicated by the reference numeral “r3”. The r3 axis defines the MPG application direction.

FIG. 5C schematically shows a sequence C for applying MPG on the r3 axis. In the sequence C, a gradient pulse Qx3 having an amplitude k · d ₃₁ is applied in the x-axis direction, a gradient pulse Qy3 having an amplitude k · d ₃₂ is applied in the y-axis direction, and a gradient pulse having an amplitude k · d ₃₃ is applied in the z-axis direction. Qz3 is applied. A synthesized magnetic field obtained by synthesizing these gradient pulses Qx3, Qy3, and Qz3 represents MPG applied on the r3 axis. After applying the gradient pulses Qx3, Qy3, and Qz3, data acquisition is performed. In addition to the gradient pulses Qx3, Qy3, and Qz3, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 6 is an explanatory diagram of the fourth row (d ₄₁ , −d ₄₂ , −d ₄₃ ) of the matrix D.
In FIG. 6 _(a), has been shown to _{(d 41, -d 42, -d} 43) 3 single vectors representing the Vx4, Vy4, Vz4. The vector Vx4 has a magnitude “d ₄₁ ” in the x-axis direction, the vector Vy4 has a magnitude “d ₄₂ ” in the −y-axis direction, and the vector Vz4 has a magnitude “d” in the −z-axis direction. d ₄₃ ”. FIG. 6B shows a vector V4 obtained by combining the vectors Vx4, Vy4, and Vz4. In FIG. 6B, the axis that defines the direction of the vector V4 is indicated by the symbol “r4”. The r4 axis defines the MPG application direction.

FIG. 6C schematically shows a sequence D for applying MPG on the r4 axis. In sequence D, a positive gradient pulse Qx4 having an amplitude k · d _{41 in} the x-axis direction is applied, a negative gradient pulse Qy4 having an amplitude k · d ₄₂ is applied in the y-axis direction, and an amplitude k · d in the z-axis direction. ₄₃ negative gradient pulses Qz4 are applied. A synthesized magnetic field obtained by synthesizing these gradient pulses Qx4, Qy4, and Qz4 represents MPG applied on the r4 axis. Data acquisition is performed after applying the gradient pulses Qx4, Qy4, and Qz4. In addition to the gradient pulses Qx4, Qy4, and Qz4, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 7 is an explanatory diagram of the fifth row (d ₅₁ , −d ₅₂ , d ₅₃ ) of the matrix D.
FIG. 7A shows three vectors Vx5, Vy5, and Vz5 representing (d ₅₁ , −d ₅₂ , d ₅₃ ). The vector Vx5 has a magnitude “d ₅₁ ” in the x-axis direction, the vector Vy4 has a magnitude “d ₅₂ ” in the −y-axis direction, and the vector Vz4 has a magnitude “d” in the z-axis direction. ₅₃ ". FIG. 7B shows a vector V5 obtained by combining the vectors Vx5, Vy5, and Vz5. In FIG. 7B, the axis that defines the direction of the vector V5 is indicated by the symbol “r5”. The r5 axis defines the application direction of MPG.

FIG. 7C schematically shows a sequence E for applying MPG on the r5 axis. In sequence E, a positive gradient pulse Qx5 having an amplitude k · d _{51 in} the x-axis direction is applied, a negative gradient pulse Qy5 having an amplitude k · d ₅₂ is applied in the y-axis direction, and an amplitude k · d in the z-axis direction. ₅₃ positive gradient pulses Qz5 are applied. A synthesized magnetic field obtained by synthesizing these gradient pulses Qx5, Qy5, and Qz5 represents MPG applied on the r5 axis. After applying the gradient pulses Qx5, Qy5, and Qz5, data acquisition is performed. In addition to the gradient pulses Qx5, Qy5, and Qz5, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 8 is an explanatory diagram of the sixth row (−d ₆₁ , −d ₆₂ , d ₆₃ ) of the matrix D.
FIG. 8A shows three vectors Vx6, Vy6, and Vz6 representing (−d ₆₁ , −d ₆₂ , d ₆₃ ). The vector Vx6 has a magnitude “d ₆₁ ” in the −x axis direction, the vector Vy6 has a magnitude “d ₆₂ ” in the −y axis direction, and the vector Vz6 has a magnitude “d” in the z axis direction. d ₆₃ ”. FIG. 8B shows a vector V6 obtained by combining the vectors Vx6, Vy6, and Vz6. In FIG. 8B, the axis that defines the direction of the vector V6 is indicated by the symbol “r6”. The r6 axis defines the MPG application direction.

FIG. 8C schematically shows a sequence F for applying MPG on the r6 axis. In the sequence F, a negative gradient pulse Qx6 with an amplitude k · d ₆₁ is applied in the x-axis direction, a negative gradient pulse Qy6 with an amplitude k · d ₆₂ is applied in the y-axis direction, and an amplitude k · d in the z-axis direction. ₆₃ positive gradient pulses Qz6 are applied. A synthesized magnetic field obtained by synthesizing these gradient pulses Qx6, Qy6, and Qz6 represents MPG applied on the r6 axis. After applying the gradient pulses Qx6, Qy6, and Qz6, data acquisition is performed. In addition to the gradient pulses Qx6, Qy6, and Qz6, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

  Therefore, it can be seen that sequences A to F perform diffusion weighting on the axes (x axis, r2 axis, r3 axis, r4 axis, r5 axis, r6 axis) represented by vectors V1 to V6. FIG. 9 shows the positional relationship between the vectors V1 to V6. From FIG. 9, it can be seen that the directions of the vectors V1 to V6 are different from each other.

FIG. 10 is a diagram illustrating an example of a scan for acquiring a diffusion tensor image using sequences A to F.
FIG. 10 shows an example in which sequences A to F are executed on a plurality of slices set on the head. In FIG. 10, for convenience of explanation, it is assumed that the number of slices is three.

  First, in the period P1, the sequence A is sequentially executed on the slices SL1 to SL3. Thereby, diffusion weighted images W11, W21, and W31 that have been subjected to diffusion weighting in the x-axis direction (see FIG. 3) are obtained.

  Next, in the period P2, the sequence B is sequentially performed on the slices SL1 to SL3. Thereby, diffusion weighted images W12, W22, and W32 on which diffusion weighting in the r2 axis direction (see FIG. 4) is performed are obtained.

  Similarly, the sequences C, D, E, and F are executed for each slice. Thereby, the diffusion-weighted images of 6 axes (x axis, r2 axis, r3 axis, r4 axis, r5 axis, r6 axis) shown in FIGS. 3 to 8 can be obtained. After obtaining these diffusion-weighted images, by performing tensor analysis for each slice, a diffusion tensor image TN1 of slice SL1, a diffusion tensor image TN2 of slice SL2, and a diffusion tensor image TN3 of slice SL3 can be obtained.

  However, the MPG for performing diffusion weighting has a larger magnetic field strength than a lead gradient pulse or the like. Therefore, when the sequences A to F having MPG are executed, the amount of heat generated by the amplification unit 6 also increases. Therefore, when the scan shown in FIG. 10 is executed, a rest time Δt for reducing the load on the amplification unit 6 is provided between the sequences. By providing the rest time Δt, the sequences A to F can be repeatedly executed even if the heat generation amount of the amplification unit 6 is large.

  However, in the period P1, the sequence A (see FIG. 3) in which MPG is applied only to the x axis is executed, so the load concentrates on the x axis. Accordingly, the amount of heat generated by the x-axis amplifier 6x becomes considerably large, and therefore it is necessary to increase the rest time Δt between sequences.

  On the other hand, since the sequences B to F (see FIGS. 4 to 8) in which MPG is applied in the biaxial direction or the triaxial direction are executed in the periods P2 to P6, two or three loads are applied to the amplifying unit 6. Can be distributed to two amplifiers. Therefore, the calorific value of each amplifier can be reduced, so that the rest time Δt can be shortened. However, if the rest time Δt is changed for each period, TR varies and the image quality deteriorates. Therefore, the rest time Δt when executing the sequences B to F needs to coincide with the rest time Δt when executing the sequence A so that the TR does not vary, and there is a problem that the scan time becomes long. . Therefore, in this embodiment, the matrix D is optimized so that the scan time can be shortened. Hereinafter, how the matrix D is optimized in this embodiment will be described.

First, consider that the matrix D is rotated about the x, y, and z axes by rotation angles α, β, and γ, respectively.
The matrix D ′ after the matrix D is rotated about the x-axis, the y-axis, and the z-axis can be expressed by the following expression.

  Here, the rotation angles (α, β, γ) are changed in the range of 0 ° ≦ α, β, γ <360 °, respectively, and a matrix D ′ corresponding to each (α, β, γ) is calculated. . FIG. 11 schematically shows the calculated matrix D ′. In FIG. 11, matrices D ′ = D1 ′ and Dj ′ obtained when (α, β, γ) = (α1, β1, γ1), (αj, βj, γj), (αw, βw, γw). , Dw ′ is representatively shown.

After calculating the matrix D ′ for each value of (α, β, γ), a matrix P in consideration of the magnetic field generation efficiency is calculated for each matrix D ′. The matrix P can be calculated by the following formula.

  The matrix G represents the reciprocal of the magnetic field generation efficiency gx, gy, gz. Therefore, the matrix P can be calculated by substituting the value of D ′ and the values of the magnetic field generation efficiencies gx, gy, and gz into Equation (2). FIG. 12 schematically shows the matrix P calculated using the equation (2). FIG. 12 shows matrices P1, Pj, and Pw obtained by substituting D1 ′, Dj ′, and Dw ′ for D ′ in Expression (2), respectively.

  Elements 1 / gx, 1 / gy, and 1 / gz of the matrix G represent reciprocals of the magnetic field generation efficiency. Therefore, by multiplying the matrix D by G, the matrix P reflecting the magnitude of the coil current necessary for generating the gradient pulse can be calculated.

After obtaining the matrix P = P1 to Pw, the absolute value of each element of the matrix P1 to Pw is obtained, and the maximum value M of the absolute value of the element is specified for each of the matrices P1 to Pw. FIG. 13 shows the maximum absolute value M of the identified elements. In FIG. 13, the maximum value M of the absolute value of the element is surrounded by a circle. For example, the maximum value M of the absolute value of the matrix P1 at element _{M = | d} 22,1 / gy _| a is, the matrix _{Pj M = | -d 53, j} / gz | a is, the matrix Pw M = | d _{41, w} / gx |.

After specifying the maximum value M of the absolute values of the elements for each of the matrices P1 to Pw, a matrix having the smallest maximum value M is selected from the matrices P1 to Pw. Here, the maximum value _M = the absolute value of the elements of the matrix _{P1~Pw | d 22,1 / gy | ~} | d 41, w / gx | among the maximum value of the absolute values of the elements of the matrix Pj M = | Let −d _{53, j} / gz | be the smallest. Therefore, the matrix Pj is selected.

  The matrix Pj reflects the magnitude of the coil current with respect to the matrix Dj ′. Therefore, by using the matrix Dj ′ among the matrices D1 ′ to Dw ′, the load applied to the amplifying unit 6 can be most efficiently distributed to the three amplifiers.

  Therefore, in this embodiment, the MPG axis is defined based on the matrix Dj ′. Below, the axis | shaft of MPG prescribed | regulated by the matrix Dj 'is demonstrated.

14 to 19 are explanatory diagrams of the axis of the MPG defined by the matrix Dj ′.
Hereinafter, FIGS. 14 to 19 will be described in order.

FIG. 14 is an explanatory diagram of the first row (d _{11, j} d _{12, j} −d _{13, j} ) of the matrix Dj ′.
FIG _{14 (a), (d 11} , j d 12, j -d 13, j) 3 single vector Vx1' representing the, Vy1', Vz1' is shown. The vector Vx1 ′ has a magnitude “d _{11, j} ” in the x-axis direction, the vector Vy1 ′ has a magnitude “d _{12, j} ” in the y-axis direction, and the vector Vz1 ′ is −z It has a size “d _{13, j} ” in the axial direction. FIG. 14B shows a vector V1 ′ obtained by combining the vectors Vx1 ′, Vy1 ′, and Vz1 ′. In FIG. 14B, the axis that defines the direction of the vector V1 ′ is indicated by the symbol “r1 ′”. The r1 ′ axis defines the MPG application direction.
FIG. 14C schematically shows a sequence A ′ for applying MPG on the r1 ′ axis. In a sequence A', positive gradient pulse Qx1' amplitude k _{· d 11, j} is applied to the x-axis direction, positive gradient pulse Qy1' amplitude k _{· d 12, j} is applied to the y-axis direction, z A negative gradient pulse Qz1 ′ having an amplitude k · d _{13, j} is applied in the axial direction. A synthesized magnetic field obtained by synthesizing these gradient pulses Qx1 ′, Qy1 ′, and Qz1 ′ represents MPG applied on the r1 ′ axis. After applying gradient pulses Qx1 ′, Qy1 ′, and Qz1 ′, data collection is performed. In addition to the gradient pulses Qx1 ′, Qy1 ′, and Qz1 ′, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 15 is an explanatory diagram of the second row (d _{21, j} d _{22, j} d _{23, j} ) of the matrix Dj ′.
FIG _{15 (a), (d 21} , j d 22, j d 23, j) 3 single vector Vx2' representing the, Vy2', Vz2' is shown. The vector Vx2 ′ has a magnitude “d _{21, j} ” in the x axis direction, the vector Vy2 ′ has a magnitude “d _{22, j} ” in the y axis direction, and the vector Vz2 ′ has a z axis. It has a size “d _{23, j} ” in the direction. FIG. 15B shows a vector V2 ′ obtained by combining the vectors Vx2 ′, Vy2 ′, and Vz2 ′. In FIG. 15B, the axis that defines the direction of the vector V2 ′ is indicated by the symbol “r2 ′”. The r2 ′ axis defines the MPG application direction.
FIG. 15C schematically shows a sequence B ′ for applying MPG on the r2 ′ axis. In the sequence B ′, a positive gradient pulse Qx2 ′ having an amplitude k · d _{21, j} is applied in the x-axis direction, a positive gradient pulse Qy2 ′ having an amplitude k · d _{22, j} is applied in the y-axis direction, and z A positive gradient pulse Qz2 ′ having an amplitude k · d _{23, j} is applied in the axial direction. A combined magnetic field obtained by combining these gradient pulses Qx2 ′, Qy2 ′, and Qz2 ′ represents the MPG applied on the r2 ′ axis. After applying gradient pulses Qx2 ′, Qy2 ′, and Qz2 ′, data collection is performed. In addition to the gradient pulses Qx2 ′, Qy2 ′, and Qz2 ′, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 16 is an explanatory diagram of the third row (d _{31, j} −d _{32, j} d _{33, j} ) of the matrix Dj ′.
FIG _{16 (a), (d 31} , j -d 32, j d 33, j) 3 single vector Vx3' representing the, Vy3', Vz3' is shown. The vector Vx3 ′ has a magnitude “d _{31, j} ” in the x-axis direction, the vector Vy3 ′ has a magnitude “d _{32, j} ” in the −y-axis direction, and the vector Vz3 ′ has z It has a size “d _{33, j} ” in the axial direction. FIG. 16B shows a vector V3 ′ obtained by combining the vectors Vx3 ′, Vy3 ′, and Vz3 ′. In FIG. 16B, the axis that defines the direction of the vector V3 ′ is indicated by the symbol “r3 ′”. The r3 ′ axis defines the MPG application direction.
FIG. 16C schematically shows a sequence C ′ for applying MPG on the r3 ′ axis. In the sequence C ′, a positive gradient pulse Qx3 ′ having an amplitude k · d _{31, j in} the x-axis direction is applied _, a negative gradient pulse Qy3 ′ having an amplitude k · d _{32, j} is applied in the y-axis direction, and z A positive gradient pulse Qz3 ′ having an amplitude k · d _{33, j} is applied in the axial direction. A synthesized magnetic field obtained by synthesizing these gradient pulses Qx3 ′, Qy3 ′, and Qz3 ′ represents MPG applied on the r3 ′ axis. After applying the gradient pulses Qx3 ′, Qy3 ′, and Qz3 ′, data collection is performed. In addition to the gradient pulses Qx3 ′, Qy3 ′, and Qz3 ′, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 17 is an explanatory diagram of the fourth row (d _{41, j} −d _{42, j} −d _{43, j} ) of the matrix Dj ′.
FIG _{17 (a), (d 41} , j -d 42, j -d 43, j) 3 single vector Vx4' representing the, Vy4', Vz4' is shown. The vector Vx4 ′ has a magnitude “d _{41, j} ” in the x-axis direction, the vector Vy4 ′ has a magnitude “d _{42, j} ” in the −y-axis direction, and the vector Vz4 ′ has − It has a size “d _{43, j} ” in the z-axis direction. FIG. 17B shows a vector V4 ′ obtained by combining the vectors Vx4 ′, Vy4 ′, and Vz4 ′. In FIG. 17B, the axis that defines the direction of the vector V4 ′ is indicated by the symbol “r4 ′”. The r4 ′ axis defines the MPG application direction.
FIG. 17C schematically shows a sequence D ′ for applying MPG on the r4 ′ axis. In the sequence D ′, a positive gradient pulse Qx4 ′ having an amplitude k · d _{41, j} is applied in the x-axis direction, a negative gradient pulse Qy4 ′ having an amplitude k · d _{42, j} is applied in the y-axis direction, and z A negative gradient pulse Qz4 ′ having an amplitude k · d _{43, j} is applied in the axial direction. A synthesized magnetic field obtained by synthesizing these gradient pulses Qx4 ′, Qy4 ′, and Qz4 ′ represents MPG applied on the r4 ′ axis. After applying the gradient pulses Qx4 ′, Qy4 ′, and Qz4 ′, data collection is performed. In addition to the gradient pulses Qx4 ′, Qy4 ′, and Qz4 ′, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 18 is an explanatory diagram of the fifth row (d _{51, j} −d _{52, j} −d _{53, j} ) of the matrix Dj ′.
FIG _{18 (a), (d 51} , j -d 52, j -d 53, j) 3 single vector Vx5' representing the, Vy5', Vz5' is shown. The vector Vx5 ′ has a magnitude “d _{51, j} ” in the x-axis direction, the vector Vy5 ′ has a magnitude “d _{52, j} ” in the −y-axis direction, and the vector Vz5 ′ has − It has a size “d _{53, j} ” in the z-axis direction. FIG. 18B shows a vector V5 ′ obtained by combining the vectors Vx5 ′, Vy5 ′, and Vz5 ′. In FIG. 18B, the axis that defines the direction of the vector V5 ′ is indicated by a symbol “r5 ′”. The r5 ′ axis defines the MPG application direction.
FIG. 18C schematically shows a sequence E ′ for applying MPG on the r5 ′ axis. In the sequence E ′, a positive gradient pulse Qx5 ′ having an amplitude k · d _{51, j} is applied in the x-axis direction, a negative gradient pulse Qy5 ′ having an amplitude k · d _{52, j} is applied in the y-axis direction, and z A negative gradient pulse Qz5 ′ having an amplitude k · d _{53, j} is applied in the axial direction. A combined magnetic field obtained by combining these gradient pulses Qx5 ′, Qy5 ′, and Qz5 ′ represents the MPG applied on the r5 ′ axis. After applying the gradient pulses Qx5 ′, Qy5 ′, and Qz5 ′, data collection is performed. In addition to the gradient pulses Qx5 ′, Qy5 ′, and Qz5 ′, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

FIG. 19 is an explanatory diagram of the sixth row (d _{61, j} −d _{62, j} d _{63, j} ) of the matrix Dj ′.
FIG _{19 (a), (d 61} , j -d 62, j d 63, j) 3 single vector Vx6' representing the, Vy6', Vz6' is shown. The vector Vx6 ′ has a magnitude “d _{61, j} ” in the x-axis direction, the vector Vy6 ′ has a magnitude “d _{62, j} ” in the −y-axis direction, and the vector Vz6 ′ has z It has a size “d _{63, j} ” in the axial direction. FIG. 19B shows a vector V6 ′ obtained by combining the vectors Vx6 ′, Vy6 ′, and Vz6 ′. In FIG. 19B, the axis that defines the direction of the vector V6 ′ is indicated by the symbol “r6 ′”. The r6 ′ axis defines the MPG application direction.
FIG. 19C schematically shows a sequence F ′ for applying MPG on the r6 ′ axis. In the sequence F ′, a positive gradient pulse Qx6 ′ having an amplitude k · d _{61, j} is applied in the x-axis direction, a negative gradient pulse Qy6 ′ having an amplitude k · d _{62, j} is applied in the y-axis direction, and z A positive gradient pulse Qz6 ′ having an amplitude k · d _{63, j} is applied in the axial direction. A combined magnetic field obtained by combining these gradient pulses Qx6 ′, Qy6 ′, and Qz6 ′ represents the MPG applied on the r6 ′ axis. After applying the gradient pulses Qx6 ′, Qy6 ′, and Qz6 ′, data acquisition is performed. In addition to the gradient pulses Qx6 ′, Qy6 ′, and Qz6 ′, various pulses are applied before data collection, but gradient pulses that are not related to MPG are not shown.

  Therefore, the sequences A ′ to F ′ apply diffusion weighting to the axes defined by the vectors V1 ′ to V6 ′ (r1 ′ axis, r2 ′ axis, r3 ′ axis, r4 ′ axis, r5 ′ axis, r6 ′ axis). I know what to do. FIG. 20 shows the positional relationship between the vectors V1 ′ to V6 ′. FIG. 20 shows that the directions of the vectors V1 ′ to V6 ′ are different from each other.

  In this embodiment, an axis that defines the application direction of MPG is set based on a matrix Dj ′ that can most efficiently disperse the load applied to the amplifier 6 to the three amplifiers. Therefore, since the heat generation of each amplifier can be reduced, the rest time Δt (see FIG. 10) between the sequences can be shortened.

  In this embodiment, the case where the gradient pulse generation efficiency in the x-axis direction and the y-axis direction is lower than the gradient pulse generation efficiency in the z-axis direction is described. However, the present invention can be applied when the gradient pulse generation efficiency in any one of the three axial directions is lower than the gradient pulse generation efficiency in the other axial directions.

  In this embodiment, an example in which six axes are set as the MPG application direction is described. However, the present invention is not limited to six axes, and can be applied when it is necessary to set a plurality of MPG application directions.

2 Magnet 3 Table 3a Cradle 4 Receiving coil 5 Gradient power supply 7 Transmitter 8 Receiver 9 Control unit 10 Operation unit 11 Display unit 12 Subject 21 Bore 22x, 22y, 22z Gradient coil

Claims (12)

A plurality of gradient pulse generating means for generating gradient pulses applied in different directions, wherein the gradient pulses generated by at least two of the plurality of gradient pulse generating means are synthesized; A plurality of gradient pulse generating means for generating MPG applied to each of a plurality of axes;
The plurality of axes are set based on magnetic field generation efficiency of the plurality of gradient pulse generating means. In the plurality of gradient pulse generating means,
First gradient pulse generating means for generating gradient pulses applied in a first direction;
Second gradient pulse generating means for generating a gradient pulse applied in the second direction;
Third gradient pulse generating means for generating a gradient pulse applied in the third direction;
The magnetic resonance apparatus according to claim 1, comprising: Each of the plurality of axes is
Provided obliquely with respect to at least two of the first axis representing the first direction, the second axis representing the second direction, and the third axis representing the third direction. The magnetic resonance apparatus according to claim 2.   The plurality of axes includes a plurality of other axes around a first rotation angle, a second rotation angle, and a third rotation around the first axis, the second axis, and the third axis. The magnetic resonance apparatus according to claim 3, wherein the magnetic resonance apparatus is calculated by rotating each of the rotation angles of the magnetic resonance apparatus.   The magnetic resonance apparatus according to claim 4, wherein the first rotation angle, the second rotation angle, and the third rotation angle are determined based on the magnetic field generation efficiency. The magnetic resonance apparatus according to claim 4 or 5, wherein the plurality of axes are obtained using the following determinant.
  A first matrix representing the plurality of axes is selected from matrices D ′ = D1 ′,..., Dw ′ obtained by changing the values of the rotation angles α, β, and γ. The magnetic resonance apparatus according to claim 6.   The first matrix is selected based on the matrix P = P1,... Pw in which the magnetic field generation efficiency is considered for each of the matrices D ′ = D1 ′,. The magnetic resonance apparatus according to claim 7. The magnetic resonance apparatus according to claim 8, wherein the matrix P is obtained using the following determinant.
  The magnetic resonance apparatus according to claim 9, wherein the first matrix is selected based on a maximum absolute value of each element of the matrix P = P1, ... Pw.   The said 1st matrix is selected based on the 2nd matrix from which the maximum value of the absolute value of the said element becomes the minimum among the said matrix P = P1, ... Pw. Magnetic resonance device. The magnetic resonance apparatus according to claim 4, wherein the plurality of other axes includes the first axis.