US-12625210-B2 - Magnetic resonance imaging apparatus, magnetic resonance imaging method, and non-transitory computer readable medium

US12625210B2US 12625210 B2US12625210 B2US 12625210B2US-12625210-B2

Abstract

According to one embodiment, a magnetic resonance imaging apparatus includes processing circuitry. The processing circuitry is configured to design a pulse sequence including a plurality of refocus pulses and a plurality of crusher gradient fields, in such a manner that a first crusher gradient field to be applied after a first refocus pulse group and a second crusher gradient field to be applied before a second refocus pulse group after the first refocus pulse group overlap one another at least partially. The processing circuitry is configured to acquire magnetic resonance spectroscopic signals by executing the designed pulse sequence.

Inventors

Hidenori Takeshima

Assignees

CANON MEDICAL SYSTEMS CORPORATION

Dates

Publication Date: 20260512
Application Date: 20230724
Priority Date: 20220727

Claims (12)

1 . A magnetic resonance imaging apparatus, comprising: processing circuitry configured to: design a pulse sequence including a plurality of refocus pulses and a plurality of crusher gradient fields, in such a manner that a first crusher gradient field and a second crusher gradient field, each to be applied between adjacent refocus pulses of the plurality of refocus pulses, are combined into one; and acquire magnetic resonance spectroscopic signals by executing the designed pulse sequence, wherein the pulse sequence includes six refocus pulses.
2 . The magnetic resonance imaging apparatus according to claim 1 , wherein a second refocus pulse and a fourth refocus pulse are included in the six refocus pulses, a third refocus pulse and a fifth refocus pulse are included in the six refocus pulses, and a time interval between the second refocus pulse and the third refocus pulse and a time interval between the fourth refocus pulse and the fifth refocus pulse are each shorter than a time interval between other refocus pulses.
3 . The magnetic resonance imaging apparatus according to claim 2 , wherein the processing circuitry is further configured to continuously apply, as the first crusher gradient field and the second crusher gradient field combined into one, a region selective gradient field regarding the second refocus pulse and the third refocus pulse, for the time interval between the second refocus pulse and the third refocus pulse.
4 . The magnetic resonance imaging apparatus according to claim 2 , wherein the processing circuitry is further configured to continuously apply, as the first crusher gradient field and the second crusher gradient field combined into one, a region selective gradient field regarding the fourth refocus pulse and the fifth refocus pulse, for the time interval between the fourth refocus pulse and the fifth refocus pulse.
5 . The magnetic resonance imaging apparatus according to claim 2 , wherein the processing circuitry is further configured to design a time interval between the second refocus pulse and the third refocus pulse and a time interval between the fourth refocus pulse and the fifth refocus pulse to be longer as a required crusher intensity increases.
6 . The magnetic resonance imaging apparatus according to claim 2 , wherein the processing circuitry is further configured to design a time interval between the second refocus pulse and the third refocus pulse and a time interval between the fourth refocus pulse and the fifth refocus pulse to be longer as a size of a volume of interest (VOI) in an axial direction increases.
7 . The magnetic resonance imaging apparatus according to claim 1 , wherein the processing circuitry is further configured to apply a MEGA pulse between a third refocus pulse and a fourth refocus pulse, and apply the MEGA pulse after a sixth refocus pulse, the MEGA pulse being a frequency selection pulse, the third refocus pulse, the fourth refocus pulse, and the sixth refocus pulse being included in the six refocus pulses.
8 . The magnetic resonance imaging apparatus according to claim 1 , wherein each of the six refocus pulses is designed to have a pulse length from 2.6 milliseconds to 3.4 milliseconds and have a pulse band from 2 kHz to 5 kHz.
9 . A magnetic resonance imaging comprising: processing circuitry configured to: design a pulse sequence including a plurality of refocus pulses and a plurality of crusher gradient fields, in such a manner that a first crusher gradient field and a second crusher gradient field, each to be applied between adjacent refocus pulses of the plurality of refocus pulses, are combined into one; and acquire magnetic resonance spectroscopic signals by executing the designed pulse sequence, wherein the pulse sequence is a localization by adiabatic selective refocusing (LASER) pulse sequence.
10 . The magnetic resonance imaging apparatus according to claim 9 , wherein the processing circuitry is further configured to adjust a time interval between refocus pulses in the LASER pulse sequence and the first and second crusher gradient fields according to a size of a volume of interest (VOI).
11 . A magnetic resonance imaging method, comprising: designing a pulse sequence including a plurality of refocus pulses and a plurality of crusher gradient fields, in such a manner that a first crusher gradient field and a second crusher gradient field, each to be applied between adjacent refocus pulses of the plurality of refocus pulses, are combined into one; and acquiring magnetic resonance spectroscopic signals by executing the designed pulse sequence, wherein the pulse sequence includes six refocus pulses.
12 . A non-transitory computer readable medium including computer executable instructions, wherein the instructions, when executed by a processor, cause the processor to perform a method comprising: designing a pulse sequence including a plurality of refocus pulses and a plurality of crusher gradient fields, in such a manner that a first crusher gradient field to be applied after a first refocus pulse group and a second crusher gradient field and a second crusher gradient field, each to be applied between adjacent refocus pulses of the plurality of refocus pulses, are combined into one; and acquiring magnetic resonance spectroscopic signals by executing the designed pulse sequence using a magnetic resonance imaging apparatus, wherein the pulse sequence includes six refocus pulses.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-119877, filed Jul. 27, 2022, the entire contents of which are incorporated herein by reference. FIELD Embodiments described herein relate generally to a magnetic resonance imaging apparatus, a magnetic resonance imaging method, and a non-transitory computer readable medium. BACKGROUND Of the major techniques for magnetic resonance spectroscopic (MRS) imaging sequences such as point resolved spectroscopy (PRESS), image-selected in vivo spectroscopy (ISIS), and localization by adiabatic selective refocusing (LASER), the LASER technique has high volume of interest (VOI) selection precision due to a low amount of contamination of unwanted signals beyond a region of interest to be excited. However, the LASER technique has a problem that two refocus pulses need to be transmitted with respect to each of the gradient fields Gx, Gy, and Gz, namely, six refocus pulses in total need to be transmitted, resulting in an increase in the TE. Thus, semi-LASER, in which four refocus pulses in total are applied, is often used as an alternative to LASER; however, in semi-LASER, only a gradient field for normal slice selection is applied (a gradient field for the refocus pulses is not applied) with respect to an axis. Thus, there is a problem of deterioration in slice characteristics with respect to the axial direction in which a gradient field for normal slice selection is applied. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a magnetic resonance imaging apparatus according to the present embodiment. FIG. 2 is a flowchart showing an operation of the magnetic resonance imaging apparatus according to the present embodiment. FIG. 3 is a diagram showing a first design example of a pulse sequence according to the present embodiment. FIG. 4 is a diagram showing a second design example of the pulse sequence according to the present embodiment. FIG. 5 is a diagram showing a third design example of the pulse sequence according to the present embodiment. DETAILED DESCRIPTION In general, according to one embodiment, a magnetic resonance imaging apparatus includes processing circuitry. The processing circuitry is configured to design a pulse sequence including a plurality of refocus pulses and a plurality of crusher gradient fields, in such a manner that a first crusher gradient field to be applied after a first refocus pulse group and a second crusher gradient field to be applied before a second refocus pulse group after the first refocus pulse group overlap one another at least partially. The processing circuitry is configured to acquire magnetic resonance spectroscopic signals by executing the designed pulse sequence. Hereinafter, a magnetic resonance imaging apparatus, a magnetic resonance imaging method, and a program according to the present embodiment will be described with reference to the accompanying drawings. In the embodiments to be described below, elements assigned the same reference symbols are assumed to perform similar operations, and redundant descriptions will be omitted where unnecessary. An embodiment will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration example of a magnetic resonance imaging apparatus 1 according to the present embodiment. As shown in FIG. 1, the magnetic resonance imaging apparatus 1 includes a gantry 11, a bed 13, a gradient field power supply 21, transmission circuitry 23, reception circuitry 25, a bed driving unit 27, sequence control circuitry 29, and a medical information processor (host computer) 50. The gantry 11 includes a static field magnet 41 and a gradient field coil 43. The static field magnet 41 and the gradient field coil 43 are accommodated in a housing of the gantry 11. A hollow-shaped bore is formed in the housing of the gantry 11. In the bore of the gantry 11, a transmitter coil 45 and a receiver coil 47 are disposed. The static field magnet 41 has a hollow, substantially cylindrical shape, and produces a static field in the interior of the substantial cylinder. Examples of the static field magnet 41 that may be used include a permanent magnet, a superconducting magnet, a normal conducting magnet, etc. It is assumed herein that the central axis of the static field magnet 41 is defined as a Z axis, that an axis vertically orthogonal to the Z axis is defined as a Y axis, and that an axis horizontally orthogonal to the Z axis is defined as an X axis. The X, Y, and Z axes configure an orthogonal three-dimensional coordinate system. The gradient field coil 43 is a coil unit attached to the inside of the static field magnet 41 and formed in a hollow, substantially cylindrical shape. The gradient field coil 43 produces a gradient field upon receiving a current supply from the gradient field power supply 21. More specifically, the gradient field coil 43 inc