US-20260126507-A1 - MAGNETIC RESONANCE IMAGING APPARATUS, MAGNETIC RESONANCE IMAGING METHOD, AND COMPUTER-READABLE NON-VOLATILE STORAGE MEDIUM STORING MAGNETIC RESONANCE IMAGING PROGRAM

US20260126507A1US 20260126507 A1US20260126507 A1US 20260126507A1US-20260126507-A1

Abstract

A magnetic resonance imaging apparatus according to an embodiment includes processing circuitry. The processing circuitry is configured to, in readout of magnetic resonance data in imaging of a subject, read out the magnetic resonance data for a position along a first direction in k-space and a position along a second direction in the k-space different from the first direction in a batch without applying a refocusing pulse, apply the refocusing pulse and perform phase encoding to reset readout positions of the magnetic resonance data, and read out the magnetic resonance data in a batch such that a total readout time with regard to the readout of the magnetic resonance data does not exceed a predetermined reference time that depends on a spatial resolution.

Inventors

Hidenori Takeshima

Assignees

CANON MEDICAL SYSTEMS CORPORATION

Dates

Publication Date: 20260507
Application Date: 20251103
Priority Date: 20241106

Claims (8)

1 . A magnetic resonance imaging apparatus comprising processing circuitry configured to: in readout of magnetic resonance data in imaging of a subject, read out the magnetic resonance data for a position along a first direction in k-space and a position along a second direction in the k-space different from the first direction in a batch without applying a refocusing pulse; apply the refocusing pulse and perform phase encoding to reset readout positions of the magnetic resonance data; and read out the magnetic resonance data in a batch such that a total readout time with regard to the readout of the magnetic resonance data does not exceed a predetermined reference time that depends on a spatial resolution.
2 . The magnetic resonance imaging apparatus according to claim 1 , wherein a readout line of the magnetic resonance data formed by the position along the first direction and the position along the second direction has an S-shape or an inverted S-shape in the k-space.
3 . The magnetic resonance imaging apparatus according to claim 1 , wherein the processing circuitry collects first correction data for the position along the first direction in a region including a center of the k-space in a batch without applying a refocusing pulse, and wherein the processing circuitry corrects a position of the magnetic resonance data in the k-space using the first correction data.
4 . The magnetic resonance imaging apparatus according to claim 3 , wherein the processing circuitry collects second correction data for the position along the first direction and the position along the second direction in the region including the center of the k-space in a batch without applying a refocusing pulse, wherein a readout line of the second correction data formed by the position along the first direction and the position along the second direction has an S-shape and an inverted S-shape in the region including the center of the k-space, and wherein the processing circuitry corrects the position of the magnetic resonance data in the k-space using at least one of the first correction data and the second correction data.
5 . The magnetic resonance imaging apparatus according to claim 4 , wherein the processing circuitry collects at least one of the first correction data and the second correction data a plurality of times in the region including the center of the k-space, and wherein the processing circuitry applies the refocusing pulse and executes phase encoding in each of the plurality of times of collection of at least one of the first correction data and the second correction data, thereby to reset readout positions of at least one of the first correction data and the second correction data.
6 . The magnetic resonance imaging apparatus according to claim 4 , wherein the processing circuitry collects at least one of the first correction data and the second correction data at a higher density than a density of collection of the magnetic resonance data in the k-space.
7 . A magnetic resonance imaging method, comprising: in readout of magnetic resonance data in imaging of a subject, reading out the magnetic resonance data for a position along a first direction in k-space and a position along a second direction in the k-space different from the first direction in a batch without applying a refocusing pulse; applying the refocusing pulse and performing phase encoding to reset readout positions of the magnetic resonance data; and repeatedly performing reading out of the magnetic resonance data and resetting of the readout positions over a predetermined range in the k-space, wherein reading out the magnetic resonance data in a batch refers to reading out the magnetic resonance data in a batch such that a total readout time with regard to the readout of the magnetic resonance data does not exceed a predetermined reference time that depends on a spatial resolution.
8 . A computer-readable non-volatile storage medium storing a magnetic resonance imaging program for causing a computer to: in readout of magnetic resonance data in imaging of a subject, read out the magnetic resonance data for a position along a first direction in k-space and a position along a second direction in the k-space different from the first direction in a batch without applying a refocusing pulse; apply the refocusing pulse and perform phase encoding to reset readout positions of the magnetic resonance data; and repeatedly perform reading out of the magnetic resonance data and resetting of the readout positions over a predetermined range in the k-space, wherein reading out the magnetic resonance data in a batch refers to reading out the magnetic resonance data in a batch such that a total readout time with regard to the readout of the magnetic resonance data does not exceed a predetermined reference time that depends on a spatial resolution.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2024-194199, filed on Nov. 6, 2024, 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 computer-readable non-volatile storage medium storing a magnetic resonance imaging program. BACKGROUND There is conventionally a high-speed imaging method called Echo Planar Imaging (hereinafter referred to as EPI) in which all data in k-space is collected without a refocusing pulse. In EPI, since a refocusing pulse is not used, B0 shifts including chemical shift are accumulated. Therefore, in EPI, chemical shift artifacts appear in the phase encoding direction. There is also a high-speed imaging method called Fast Spin Echo (hereinafter referred to as FSE). In FSE, a refocusing pulse is applied for each line along the frequency encoding direction in k-space to collect magnetic resonance data. Therefore, in FSE, the B0 shifts are reset with each collection of one line of magnetic resonance data. However, FSE requires a longer imaging time than EPI due to the application of a refocusing pulse. Another high-speed imaging method is Gradient and Spin Echo (GRASE). GRASE is an imaging method in which a refocusing pulse is applied every N lines (where N is a natural number equal to or greater than 2) in the phase encoding direction, and magnetic resonance data is collected while interleaving. In this case, the B0 shifts are reset with each collection of N lines of magnetic resonance data. GRASE is positioned as an intermediate method between EPI and FSE. EPI is required to quickly capture an image of a subject. However, in EPI, chemical shift appears in the phase encoding direction. Since fat signals appear in different pixels due to the chemical shift, a clear image cannot be obtained in EPI unless fat is suppressed. More specifically, in normal EPI, the sampling interval along the phase encoding direction is longer (slower) than the sampling interval along the frequency encoding direction, so that chemical shift artifacts that depend on the phase encoding direction appear in a magnetic resonance image. As described above, the chemical shift artifacts are reduced in GRASE as compared to EPI because the sampling interval in GRASE is inversely proportional to an interleaving factor (factor that determines the interleaving of readouts in the phase encoding direction). However, even in GRASE, because the sampling interval in the phase encoding direction is shorter than that in the frequency encoding direction, chemical shift appears in the phase encoding direction. The fundamental reason for the short sampling interval in GRASE is that the total readout time with regard to the frequency encoding direction (a time interval between two temporally adjacent refocusing pulses) is excessively long. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating a configuration of a magnetic resonance imaging (MRI) apparatus according to an embodiment; FIG. 2 is a diagram illustrating an example of batch readout of magnetic resonance (MR) data according to the embodiment; FIG. 3 is a diagram illustrating an example of readout by Fast Spin Echo (FSE) and Echo Planar Imaging (EPI) as a comparative example; FIG. 4 is a diagram illustrating an example of sequence information (sequence) according to the embodiment; and FIG. 5 is a flowchart illustrating an example of a procedure for a sampling interval reduction imaging process according to the embodiment. DETAILED DESCRIPTION A magnetic resonance imaging apparatus according to an embodiment includes processing circuitry. The processing circuitry is configured to, in readout of magnetic resonance data in imaging of a subject, read out the magnetic resonance data for a position along a first direction in k-space and a position along a second direction in the k-space different from the first direction in a batch without applying a refocusing pulse, apply the refocusing pulse and perform phase encoding to reset readout positions of the magnetic resonance data, and read out the magnetic resonance data in a batch such that a total readout time with regard to the readout of the magnetic resonance data does not exceed a predetermined reference time that depends on a spatial resolution. Various Embodiments will be described hereinafter with reference to the accompanying drawings. The contents described in each embodiment can be similarly applied to other embodiments in principle. In the following embodiments, the same reference numerals denote the same parts, and a repetitive description thereof will be omitted as appropriate. Embodiment FIG. 1 is a block diagram illustrating a configuration of a magnetic resonance imaging (MRI) apparatus 100 according to an embodiment. As illustrated in FIG. 1, the