JP2018148995A5

JP2018148995A5 -

Info

Publication number: JP2018148995A5
Application number: JP2017045952A
Authority: JP
Filing date: 2017-03-10
Publication date: 2020-02-27
Anticipated expiration: 2037-03-10

Description

図９（Ａ）は、金属シム７２ｂの配置前の、Ｚ軸方向における磁場Ｂ_Ｚの分布の一例を示す。磁場Ｂ_Ｚは、ハーモニクスＡ_２ ^０ _＿bare（Ａ_２ ^０ _＿bare＞０）を比例定数とする、Ｚ位置の２乗に比例する関数として表される。Ａ_２ ^０ _＿bareは、ハーモニクスＡ_ｎ ^ｍ _＿bareの一要素である。図９（Ａ）は、パッシブシミング前であるため、磁場の不均一性は、最終的に収まるべき磁場不均一性の許容範囲Ｂｄに収まっていない。 9 (A) is a front arrangement of the metal shim 72 b, shows an example of the distribution of the magnetic field _{B Z} in the Z axis direction. Magnetic field _{B Z} is represented harmonics _{_A} ² ₀ _{_bare} the _{_(A} ² ₀ _{_bare>} ₀₎ is a proportional constant, as a function proportional to the square of the Z position. _A ₂ ⁰ _bare is an element of harmonic _{_A} ⁿ _m _{_bare.} In FIG. 9A, before the passive shimming, the non-uniformity of the magnetic field does not fall within the allowable range Bd of the magnetic field non-uniformity to be finally reduced.

図１１（Ａ）は、金属シム７２ｂの配置前の、Ｚ軸方向における磁場Ｂ_Ｚの分布の一例を示す。図１１（Ａ）は、図９（Ａ）と同一である。図１１（Ｂ）は、図１１（Ａ）に対し、分布Ｓ_１，１〜Ｓ_{２４，１５}に従って金属シム７２ｂが配置された場合の、Ｚ軸方向における磁場Ｂ_Ｚの分布の一例を示す。 11 (A) is a front arrangement of the metal shim 72 b, shows an example of the distribution of the magnetic field _{B Z} in the Z axis direction. FIG. 11A is the same as FIG. 9A. FIG. 11 (B) with respect to FIG. 11 (A), the case where the metal shim 72b is disposed according to the distribution _{_S} 1,1 _{~S 24,15,} shows an example of the distribution of the magnetic field _{B Z} in the Z axis direction.

図１４（Ａ）は、金属シム７２ｂの配置前の、Ｚ軸方向における磁場Ｂ_Ｚの分布の一例を示す。磁場Ｂ_Ｚは、比例定数がハーモニクスの項Ａ_２ ^０ _＿bare（Ａ_２ ^０ _＿bare＜０）であり、Ｚ位置の２乗に比例する関数として表される。図１４（Ｂ）は、図１４（Ａ）に対し、Ｚ^２チャンネルのシムコイル１１ｅで磁場補正された場合の、Ｚ軸方向における磁場Ｂ_Ｚの分布の一例を示す。 14 (A) is a front arrangement of the metal shim 72 b, shows an example of the distribution of the magnetic field _{B Z} in the Z axis direction. Magnetic field _{B Z} is a proportionality constant is the harmonic term _{^{_{_{^{_{A 2 0 _bare (A 2 0}}}}}} _bare <0), expressed as a function proportional to the square of the Z position. FIG. 14 (B) to FIG. 14 (A), the case where the magnetic field corrected by shim coil 11e of ^{Z 2} channels, shows an example of the distribution of the magnetic field _{B Z} in the Z axis direction.

Claims

A static magnetic field magnet for generating a static magnetic field,
A metal shim in which a predetermined number is arranged at each position in the static magnetic field,
A coil that generates a magnetic field by supplying power and corrects the uniformity of the static magnetic field by active shimming,
The arrangement of the metal shim is determined under conditions that prioritize the suppression of the center frequency shift over the uniformity of the static magnetic field,
The coil corrects a static magnetic field formed by the arrangement of the metal shims so that the static magnetic field has a predetermined uniformity.
Magnetic resonance imaging device.

The metal shim is arranged at a position far from the center position of the static magnetic field with respect to the arrangement of the metal shim when the uniformity of the magnetic field satisfies a predetermined standard.
The magnetic resonance imaging apparatus according to claim 1.

The arrangement of the metal shim is determined so that the center frequency shift falls within a predetermined range, regardless of whether or not the uniformity of the magnetic field satisfies a predetermined criterion.
The magnetic resonance imaging apparatus according to claim 1.

Placement of the metal shim, to placement of the metal shim when the uniformity of the magnetic field meets the predetermined criteria, the metal shim far position from the center of the static magnetic field is added arranged ,
The magnetic resonance imaging apparatus according to claim 3 .

The degree of influence on the center frequency shift differs depending on each position where the metal shim is arranged ,
The arrangement of the metal shim is an arrangement in which the metal shim is added at a position where the degree of influence is negative ,
The magnetic resonance imaging apparatus according to claim 4 .

The arrangement of the metal shim is
While allowing the uniformity of the magnetic field at passive shimming by arrangement of the metal shim does not satisfy the predetermined criteria, the correction which combines the passive shimming and said active shimming the uniformity of the magnetic field is predetermined It is an arrangement in which the metal shim is added so as to satisfy the criterion and suppress the center frequency shift .
A magnetic resonance imaging apparatus according to claim 5 .

The degree of influence on the center frequency shift differs depending on each position where the metal shim is arranged ,
In the active shimming before the passive shimming due to the arrangement of the metal shim, the characteristic of the static magnetic field is converted so that the metal shim is arranged more in a position where the influence degree is negative in the passive shimming .
The magnetic resonance imaging apparatus according to claim 3 .

A predetermined number of metal shims are placed at each position in the static magnetic field generated by the static magnetic field magnet , and the coil for correcting the static magnetic field receives the supply of electric power to generate a magnetic field, so that the uniformity of the magnetic field is predetermined. A static magnetic field correction method for correcting the static magnetic field so as to satisfy the criteria of
The arrangement of the metal shim is determined under conditions that prioritize the suppression of the center frequency shift over the uniformity of the static magnetic field,
By the coil, the static magnetic field formed by the arrangement of the metal shim is corrected to be a static magnetic field of a predetermined uniformity,
Static magnetic field correction method.