JP4528389B2 - Magnetic resonance diagnostic equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic resonance diagnostic apparatus that uses a magnetic resonance phenomenon to obtain morphological information such as a slice image of a subject (living body) and functional information such as spectroscopy, and in particular, magnetism caused by nonuniformity of a static magnetic field distribution. The present invention relates to a magnetic resonance diagnostic apparatus capable of suppressing deterioration of a resonance spectrum and measuring a magnetic resonance spectrum in a local region at high speed.
[0002]
[Prior art]
In the magnetic resonance imaging (MRI) apparatus and the magnetic resonance spectroscopy (MRS) apparatus, the uniformity of the static magnetic field greatly affects the quality and accuracy of the MR image and the MR spectrum, and therefore very high uniformity is required. Particularly, in the ¹ H (metabolite) -MRS apparatus, since the range of chemical shift is narrow, only magnetic field inhomogeneities of about 0.1 ppm at the maximum are allowed. For this reason, in the magnetic resonance diagnostic apparatus, in addition to the main magnet that generates a static magnetic field, a plurality of correction coils (called shim coils) for canceling the static magnetic field inhomogeneity are provided, and the value of the current flowing through the shim coil is adjusted. By doing so, the inhomogeneity of the static magnetic field is compensated.
[0003]
However, even if shim coils are used, if the subject is composed of multiple components such as a living body and has a non-uniform distribution / component, the static magnetic field uniformity as described above should be realized in the entire region of the subject. Is extremely difficult. This is because, in the case of the human body, the magnetic field inhomogeneity of the second or higher order component often occurs.
[0004]
For this reason, a method for improving the magnetic field uniformity only in a local region of interest has been considered. As a specific example, a magnetic resonance signal is generated from a local region by a pulse sequence of the stimulated echo (STE) method described in JP-A-4-227232, and the time constant of attenuation of the signal is the most. There is a method of determining the primary shim current so as to be longer. This is based on the fact that the more homogeneous the magnetic field, the faster the signal decays.
[0005]
However, this method also has drawbacks. That is, it takes adjustment time to calculate the optimum current value by sequentially changing the shim current. Furthermore, when the MR spectrum of another local region is measured, it is necessary to perform the same adjustment again from the beginning.
[0006]
On the other hand, as described in JP-A-4-208133, a method is also conceivable in which the magnetic field inhomogeneity is obtained from the phase information of the MR image, and the shim current is calculated for each local region according to the obtained inhomogeneity. ing. In this method, magnetic field measurement is performed once in a wide range including a local region, and a shim current is calculated from the local magnetic field distribution. As a calculation method, the measured static magnetic field inhomogeneous distribution is developed into a magnetic field component that can be generated by a shim coil, and orthogonal function expansion is often used for this expansion. At this time, what should be noted is the accuracy of the expansion, and the number of data points needs to be increased (the resolution is made finer or a wide area is measured) as the number of expansion terms increases. This leads to extension of the photographing time at the stage of acquiring the MR image. On the contrary, when the number of expansion terms is reduced, instead of shortening the imaging time, the line width of the spectrum becomes wider due to the above-described magnetic field inhomogeneity of the second and higher order components, and S / N Has the disadvantage of deteriorating.
[0007]
[Problems to be solved by the invention]
As described above, in the conventional magnetic resonance diagnostic apparatus, a shim coil generates a magnetic field that locally compensates for the non-uniform distribution of the static magnetic field, and the shim current is adjusted to increase the uniformity of the static magnetic field locally. There was a problem that it took time.
[0008]
An object of the present invention is to provide a magnetic resonance diagnostic apparatus that can improve the uniformity of a static magnetic field in a local region in a short time with high accuracy and collect magnetic resonance data with high accuracy.
[0009]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, the present invention uses the following means.
[0010]
(1) A magnetic resonance diagnostic apparatus according to an aspect of the present invention includes a main magnet that generates a substantially uniform static magnetic field in an imaging space in which a subject can be inserted, and a magnetic field for correcting non-uniformity of the static magnetic field. A magnetic resonance diagnostic apparatus comprising: a plurality of shim coils for generating a shim; and a shim power supply for supplying a shim current to the plurality of shim coils; and means for measuring a magnetic field distribution in a first region in the imaging space; Means for calculating a first shim current set from the magnetic field distribution of the region, and setting the first shim current set to a shim power source, and the first shim current set is used to include the first shim current set in the imaging region is a means for measuring the magnetic field distribution of the second area including the first area is smaller than the local region, and calculates the second shim current set using only the magnetic field distribution of the local region, the first Is the shim current set and the second shim current set? Calculating a third shim current set, it is characterized in that a third shim current set and means for setting the shim power supply.
[0011]
(2) magnetic resonance diagnostic apparatus according to another aspect of the present invention, a main magnet for generating a substantially uniform static magnetic field can be inserted shooting space object, for correcting the non-uniformity of the static magnetic field A magnetic resonance diagnostic apparatus comprising: a plurality of shim coils that generate a magnetic field; and a shim power supply that supplies current to the plurality of shim coils; a first unit that measures a magnetic field distribution in a first region in an imaging space; Means for calculating a first shim current set from the magnetic field distribution of the region, and setting the first shim current set to a shim power source, and the first shim current set is used to include the first shim current set in the imaging region Means for measuring the magnetic field distribution of the second region to be stored, storing the magnetic field distribution of the second region, designating means for designating a local region smaller than the first region, and the local region designated by the designating means Is included in the second region Or a determination unit, when the determination means determines that the local region is included in the second region, and calculates the second shim current set using only the magnetic field distribution of the local region, the Means for calculating a third shim current set from one shim current set and a second shim current set and setting the third shim current set to a shim power source is provided.
[0012]
(3) A magnetic resonance diagnostic apparatus according to another aspect of the present invention is the magnetic resonance diagnostic apparatus according to (1) or (2) above, wherein the spatial resolution of the magnetic field distribution of the first region is that of the second region. It is characterized by being coarser than the spatial resolution of the magnetic field distribution.
[0013]
(4) A magnetic resonance diagnostic apparatus according to another aspect of the present invention is the magnetic resonance diagnostic apparatus according to any one of (1) to (3), wherein the number of channels of the second shim current set is the first shim. Less than the number of channels in the current set, and among the third shim current sets, the shim current of the channel corresponding to the second shim current set is the first shim current of the channel corresponding to the value of the second shim current set. The shim currents of the remaining channels of the third shim current set are determined only by the first shim currents of the corresponding channels.
[0014]
(5) A magnetic resonance diagnostic apparatus according to another aspect of the present invention is the magnetic resonance diagnostic apparatus according to any one of (1) to (4), wherein the first shim current set is from the first to the higher order. This is a shim current for magnetic field distribution correction, and the second shim current set is a shim current for primary magnetic field distribution correction.
[0016]
According to such a magnetic resonance diagnostic apparatus, in a magnetic resonance diagnostic apparatus that detects and analyzes a magnetic resonance signal from a local region, it is possible to perform high-precision magnetic field uniformity adjustment without extending the imaging time. .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a magnetic resonance diagnostic apparatus according to the present invention will be described below with reference to the drawings.
[0018]
First Embodiment FIG. 1 is a block diagram showing a configuration of a magnetic resonance diagnostic apparatus according to a first embodiment of the present invention. In a gantry (not shown), a main magnet 10 for generating a main magnetic field (static magnetic field), 3 for generating a gradient magnetic field having a linear gradient magnetic field distribution in the directions of three orthogonal axes x, y, and z. A gradient coil system 12 composed of two gradient coils, a shim coil system 14 composed of a plurality of shim coils for canceling out the non-uniformity of the static magnetic field generated by the main magnet 10, and an RF coil 16 are provided. The main magnet 10 as a static magnetic field generator is configured using, for example, a superconducting coil, a normal conducting coil, or a permanent magnet. The RF coil 16 is used to generate radio frequency (RF) pulses and to detect echo signals generated by magnetic resonance. Note that transmission of RF pulses and reception of echo signals may be performed by separate transmission coils and reception coils.
[0019]
The main magnet 10 is driven by a main magnet power supply 18. The RF coil 16 is driven by the transmitter 24 when magnetic resonance is excited, and is coupled to the receiver 26 when detecting an echo signal. The gradient magnetic field coil system 12 is driven by a gradient magnetic field power supply 20 (gradient magnetic field current), and the shim coil system 14 is driven by a shim coil power supply 22 (shim current).
[0020]
The gradient magnetic field power supply 20, the shim coil power supply 22, and the transmitter 24 are driven by a sequence controller 32 according to a predetermined sequence, and an x-axis gradient magnetic field Gx, a y-axis gradient magnetic field Gy, a z-axis gradient magnetic field Gz, and a radio frequency (RF) pulse are predetermined. It occurs in the pulse sequence. In this case, the x-axis gradient magnetic field Gx, the y-axis gradient magnetic field Gy, and the z-axis gradient magnetic field Gz are mainly used as, for example, a read gradient magnetic field Gr, a phase encode gradient magnetic field Ge, and a slice gradient magnetic field Gs, respectively. The computer system 28 drives and controls the sequence controller 32 and takes in an echo signal as an echo signal received by the receiver 26 and applies a predetermined signal processing to thereby perform magnetic resonance spectroscopy or magnetic resonance spectrum of the subject. The stereoscopic imaging is reconstructed and displayed on the display unit 30.
[0021]
FIG. 2 is a flowchart of the sequence controller 32 that adjusts the magnetic field inhomogeneity prior to the collection of the magnetic resonance spectrum according to the first embodiment. First, a local region where a magnetic resonance spectrum is to be observed is set from an image acquired in advance (see FIG. 3). In the present embodiment, in addition to the local region, a second region including the local region and a first region substantially including the second region are set.
[0022]
In step S1, the magnetic field distribution in the first region is measured. The measurement of the magnetic field distribution can be realized by a known measurement method using a spin echo (SE) method, a field echo (FE) method, or a chemical shift imaging method. Here, the FE method imaging as shown in FIG. According to the sequence, the inhomogeneous distribution of the magnetic field is obtained using the fact that the phase information of the reconstructed image reflects the influence of the inhomogeneity of the magnetic field. The magnetic field distribution is obtained by reconstructing the echo signals E1 and E2, respectively, taking the difference between the phase images, and multiplying by an appropriate coefficient. FIG. 4 shows a pulse sequence for obtaining a magnetic field distribution in a specific slice plane, but measurement in 3D space such as a multi-slice method can be easily realized based on the same principle.
[0023]
In step S2, the magnetic field distribution of the first region measured in this way is developed into a magnetic field component that can be generated by the shim coil system 14, and based on this, it is necessary to cancel the magnetic field inhomogeneity corresponding to the local region. A first shim current set is calculated. The calculation method of the shim current set is realized by a generally known fitting calculation such as a least square method. Since the magnetic field distribution generated by the shim coil is often in the form of an orthogonal function such as a Legendre function, it is common to expand the magnetic field distribution with the orthogonal function system (especially spherical expansion).
[0024]
In step S 3, the first shim current set is set to the shim coil power supply 22.
[0025]
In step S4, the magnetic field distribution in the second region is measured with the first shim current set flowing from the shim coil power supply 22 to the shim coil system 14. Similarly to the measurement of the magnetic field distribution in the first region in step S1, the measurement of the magnetic field distribution in the second region also obtains the magnetic field distribution based on the phase information of the reconstructed image. However, the spatial resolution of the measurement of the magnetic field distribution in the second region is higher than the spatial resolution of the measurement of the magnetic field distribution in the first region.
[0026]
In step S5, a second shim current set is calculated using a part of the magnetic field distribution in the second region. The calculation of the second shim current set also uses orthogonal function expansion in the same manner as the calculation of the first shim current set in step S2.
[0027]
In step S6, a third shim current set is calculated from the sum of the first shim current set and the second shim current set.
[0028]
In step S 7, the third shim current set is set in the shim coil power supply 22. This third shim current set improves the magnetic field uniformity in the local region. After correcting the non-uniformity of the static magnetic field in this way, collection of the magnetic resonance spectrum is started.
[0029]
Steps S1 to S7 can be performed continuously, or an MR imaging operation can be added along the way.
[0030]
In this embodiment, since the spatial resolution of the measurement of the magnetic field distribution of the second region in step S4 is higher than the spatial resolution of the measurement of the magnetic field distribution of the first region in step S1, the magnetic field uniformity in the local region is improved. Can be made. This effect is achieved even if the number of terms (number of channels) in the first shim current set is equal to the number of terms in the second shim current set. Conventionally, the magnetic field distribution is measured with high spatial resolution only in the second region, but in reality, the magnetic field distribution in the surrounding first region is also necessary. The uniformity could not be corrected and the degree of uniformity was low. However, according to the present embodiment, in addition to the measurement of the magnetic field distribution in the first region, the measurement of the high spatial resolution of the magnetic field distribution in the narrow second region is performed. Since the first and second shim current sets that cancel the non-uniformity up to the next are obtained, and the final shim current set is obtained by adding them, the first shim current set is corrected and the first shim current set is corrected. The distribution of the area 2 is obtained, and the measurement accuracy of nonuniformity is improved. Furthermore, since the number of magnetic field data in the local region is increased, the accuracy of fitting is improved. Therefore, the magnetic field uniformity in the local region can be improved.
[0031]
According to the inventor's study, in the magnetic resonance diagnostic apparatus equipped with the primary shim coil (3 channels), the spectrum half-width of the human head is adjusted from 1.47 ppm before adjustment to 0.30 ppm by the configuration of the first embodiment. Improved. This is because there is a second or higher order magnetic field inhomogeneity due to the living body, and the larger the magnetic field distribution measurement region from which the shim current is calculated, the larger the error in the first-order expansion. In support of this, it was confirmed that in the magnetic resonance diagnostic apparatus having up to the secondary shim coils (5 channels), the spectrum half-width of the human head is further improved to about 0.18 ppm.
[0032]
The adjustment time in this embodiment will be described. About 20 seconds in the magnetic field distribution measurement step of the first region in step S1, 1 minute in the magnetic field distribution measurement step of the second region in step S4, and these imaging conditions ( It took about 20 seconds, a total of 1 minute and 40 seconds, to set the slice thickness and the number of matrices. In the method of monitoring signal attenuation by the STE method described in the prior art, an adjustment time of about 3 minutes is required. From this, it can be seen that the effect of time reduction according to the present embodiment is great.
[0033]
As described above, according to the first embodiment, the magnetic field distribution of the second region including the local region where the spectrum is to be measured and the first region including the second region is changed by changing the spatial resolution (second The spatial resolution of the region is increased), and the shim current set is obtained by performing first-order and second-order function expansions, respectively, so that the magnetic field uniformity in the local region can be improved.
[0034]
Hereinafter, other embodiments of the magnetic resonance diagnostic apparatus according to the present invention will be described. In the description of the other embodiments, the same parts as those in the first embodiment are denoted by the same reference numerals, and the detailed description thereof is omitted.
[0035]
Second Embodiment The second embodiment relates to an improvement of the first embodiment. In the first embodiment, the number of channels of the first shim current set (correcting the second-order nonuniformity) and the second shim current set (correcting the first-order nonuniformity) are equal. The embodiment is characterized in that the number of channels of the second shim current set is smaller than the number of channels of the first shim current set. The overall configuration and operation are the same as those of the first embodiment shown in FIGS. 1 and 2, except for the calculation of the third shim current set in step S6 of FIG. As shown in FIG. 5, it is assumed that the first shim current set has three channels A, B, and C, and the second shim current set has only two channels A and B. The third shim current set (three channels) is the first and second shim current sets for the two channels (channel A and channel B) common to the first and second shim current sets, as in the first embodiment. For one channel (channel C) that has only the first shim current set, the current value of channel C of the first shim current set is set as it is.
[0036]
Since the primary component is mainly used for the magnetic field inhomogeneity in the local region, in the second embodiment, it has been found that the following adjustment may be performed in the case of the human head. Consider a case where a shim coil is composed of three primary distribution channels and five secondary distribution channels. In step S1 of FIG. 2, the magnetic field distribution of the first region is measured so as to cover the head widely, and in step S2, the second spherical expansion is performed to perform the first shim current set (primary and secondary). Distribution 8 channels) is calculated. In step S3, this value is set in the shim coil power supply 22. In step S4, magnetic field measurement is performed with a higher spatial resolution than the measurement in step S1 in a second region that includes a local region of interest and is narrower than the first region measured in step S1. Of the magnetic field distribution obtained here, use the magnetic field distribution of the region that is almost the same as the local region of interest (the meaning of almost the same is because the data is discrete, Since there is a case where there is no data), in step S5, the first spherical expansion is performed to calculate the second shim current set (for the primary distribution of three channels). The primary distribution 3 channels of the third shim current set are calculated as the sum of the primary distribution 3 channels of the first shim current set and the second shim current set (for the primary distribution 3 channels). In addition, the secondary distribution 5 channels of the third shim current set is set to a value equal to the secondary 5 channels of the first shim current set.
[0037]
An example of the human head is introduced. FIG. 6 shows the magnetic field distribution obtained in step S4 by adjusting step S2 and step S3. Although the degree of inhomogeneity has been reduced, magnetic field inhomogeneities still cannot be ignored. When attention is paid to the area A in FIG. 6, the remaining non-uniformity is almost linear in the area A. Therefore, in step S5, it is shown that it is sufficient to perform spherical expansion for only the first three channels. FIG. 7 shows the magnetic field distribution realized by the third shim current set obtained in step S7, which is substantially horizontal (= uniform) in the region A. As a result of the inventor's experiment, in the same local region tested in the first embodiment, a spectral line width of 0.14 ppm (0.18 ppm in the first embodiment) is realized by this embodiment, and the magnetic resonance spectrum is highly accurate. Magnetic field uniformity up to a level that can be measured quickly has been improved.
[0038]
Third Embodiment A third embodiment relates to a modification of both the first embodiment and the second embodiment, and FIG. 8 shows a flow of processing based on the first embodiment.
[0039]
In step S11, the magnetic field distribution in the first area, which is a large area, is measured with low spatial resolution.
[0040]
In step S12, a first shim current set from the magnetic field distribution of the first region to the second order is calculated.
[0041]
In step S <b> 13, the first shim current set is set to the shim coil power supply 22.
[0042]
In step S14, the magnetic field distribution of the second region, which is a narrow region, is measured with high spatial resolution using the first shim current set.
[0043]
In step S15, the magnetic field distribution of the second region obtained in step S14 is stored.
[0044]
In step S16, positioning for collecting MR spectrum data is started. In step S17, a local region for collecting spectrum data is designated. In step S18, it is determined whether or not the local region is included in the second region. If the local region is included in the second region, a second shim current set is calculated in step S19 using a part of the magnetic field distribution of the second region stored in step S15. In step S20, a third shim current set is calculated from the first shim current set and the second shim current set. In step S21, the third shim current set is set to the shim coil power source 22. In step S22, collection of MR spectra in the local region is started. In step S18, if the local area is not included in the second area, a warning is issued in step S23, the second area is reset, and the adjustment operation (steps S11 to S11) is performed again. Alternatively, the local region is reset and the determination in step S18 is repeated.
[0045]
In this way, as long as the local region specified in step S17 is included in the second region, an optimum shim current value corresponding to the location can be calculated. This process is merely a numerical calculation process, and the calculation time is negligibly short. Therefore, as the number of local regions in which the spectrum is to be measured increases, the proportion of the magnetic field uniformity adjustment process in the total imaging time can be significantly reduced.
[0046]
Note that the size of the local area specified in step S17 is preferably substantially the same as the local area of the first embodiment. This is because if the specified local region is very small, the signal-to-noise ratio of the magnetic field distribution is low and function fitting calculation may not be possible. In step S18, it is also preferable to determine whether the local region is too small or the signal-to-noise ratio of the magnetic field data is low, and issue a warning message such as “data is insufficient”. Alternatively, the amount of data may be automatically increased instead of issuing a warning. That is, it can be considered that the data area used in step S19 is a range in which the local area is enlarged by a predetermined amount. The conditions for executing this enlargement process are determined from the viewpoint of whether the number of data points has reached a required number, or whether a sufficiently accurate shim current can be obtained at the time of expansion.
[0047]
Further, when the signal-to-noise ratio of the magnetic field distribution is poor, the magnetic field distribution may be smoothed. Thereby, the determination accuracy of the shim current can be improved.
[0048]
Further, the third embodiment is not limited to the flow shown in FIG. 8, and may be based on the second embodiment in which the number of channels of the second shim current set is smaller than the number of channels of the first shim current set.
[0049]
The present invention is not limited to the embodiment described above, and can be implemented with various modifications. For example, although the above description has been made with respect to MR spectrum measurement, the present invention can be similarly applied to MR imaging. In addition, although the first shim current set is corrected to the second order magnetic field non-uniformity, it may be corrected to the third order or higher order non-uniformity. In that case, an area other than the first and second areas may be set. For example, a third region that is smaller than the second region and includes a local region is set, and third and second shim current sets are obtained in the first and second regions, respectively, and the first region is obtained in the third region. The shim current set up to may be obtained.
[0050]
【The invention's effect】
As described above, according to the present invention, in a magnetic resonance diagnostic apparatus that detects and analyzes a magnetic resonance signal from a local region, it is possible to perform high-precision magnetic field uniformity adjustment without increasing the imaging time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration of a first embodiment of a magnetic resonance diagnostic apparatus according to the present invention.
FIG. 2 is a flowchart showing the magnetic field uniformity adjustment operation of the first embodiment of the magnetic resonance diagnostic apparatus according to the present invention.
FIG. 3 is a schematic diagram showing an example of setting a local area, first area, and second area in the present invention.
FIG. 4 is a diagram showing a pulse sequence of an FE method for measuring a magnetic field.
FIG. 5 is a schematic diagram showing calculation of a third shim current set in the second embodiment of the present invention.
FIG. 6 is a diagram showing magnetic field inhomogeneity before adjustment according to the second embodiment.
FIG. 7 is a diagram showing magnetic field inhomogeneity after adjustment according to the second embodiment.
FIG. 8 is a flowchart showing the magnetic field uniformity adjustment operation of the third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Main magnet 12 ... Gradient magnetic field coil system 14 ... Shim coil system 16 ... RF coil 18 ... Main magnet power supply 20 ... Gradient magnetic field power supply 22 ... Shim coil power supply 24 ... Transmitter 26 ... Receiver 32 ... Sequence controller

Claims (5)

A main magnet for generating a substantially uniform static magnetic field can be inserted shooting space object, a plurality of shim coils for generating a magnetic field for correcting the non-uniformity of the static magnetic field, shim current to the plurality of shim coils In a magnetic resonance diagnostic apparatus comprising a shim power supply for supplying
Means for measuring the magnetic field distribution of the first region in the imaging space;
Means for calculating a first shim current set from the magnetic field distribution of the first region and setting the first shim current set to a shim power source;
Means for measuring a magnetic field distribution of a second region that is included in the first region within the imaging region using a first shim current set and includes a local region smaller than the first region ;
A second shim current set is calculated using only the magnetic field distribution in the local region, a third shim current set is calculated from the first shim current set and the second shim current set, and the third shim current set is calculated. Means to set the shim power,
A magnetic resonance diagnostic apparatus comprising: A main magnet for generating a substantially uniform static magnetic field can be inserted shooting space object, a plurality of shim coils generates a magnetic field for correcting the non-uniformity of the static magnetic field, a current to the plurality of shim coils In a magnetic resonance diagnostic apparatus comprising a shim power supply to supply,
Means for measuring the magnetic field distribution of the first region in the imaging space;
Means for calculating a first shim current set from the magnetic field distribution of the first region and setting the first shim current set to a shim power source;
Means for measuring a magnetic field distribution of a second region included in the first region in the imaging region using a first shim current set, and storing the magnetic field distribution of the second region;
Designating means for designating a local region smaller than the first region ;
Determining means for determining whether or not the local area specified by the specifying means is included in the second area;
When the determination unit determines that the local region is included in the second region, a second shim current set is calculated using only the magnetic field distribution of the local region, and the first shim current set and the first shim current set Means for calculating a third shim current set from the two shim current sets and setting the third shim current set to a shim power supply;
A magnetic resonance diagnostic apparatus comprising:   3. The magnetic resonance diagnostic apparatus according to claim 1, wherein the spatial resolution of the magnetic field distribution in the first region is coarser than the spatial resolution of the magnetic field distribution in the second region. The number of channels of the second shim current set is less than the number of channels of the first shim current set;
Of the third shim current set, the shim current of the channel corresponding to the second shim current set is calculated by the sum of the value of the second shim current set and the first shim current of the corresponding channel, 4. The magnetic resonance diagnostic apparatus according to claim 1, wherein the shim current of the remaining channels of the set of shim currents is determined only by the first shim current of the corresponding channel. 5. .   The first shim current set is a shim current for correcting the magnetic field distribution from the first order to the higher order, and the second shim current set is a shim current for correcting the primary magnetic field distribution. The magnetic resonance diagnostic apparatus according to any one of claims 1 to 4.

Images