Magnetic resonance imaging apparatus and magnetic resonance imaging method

Patent metadata

Field	Value
Publication number	US-10024943-B2
Application number	US-201514968332-A
Country	US
Kind code	B2
Filing date	Dec 14, 2015
Priority date	Jun 14, 2013
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

According to one embodiment, an MRI apparatus includes a gradient coil, an RF coil, an RF receiver, and processing circuitry which controls these components to perform each pulse sequence. The processing circuitry sets a main-scan pulse sequence, a first pulse sequence which includes application of a gradient magnetic field in a readout direction, and a second pulse sequence which includes application of the gradient magnetic field in a readout direction, and whose acquisition region is shifted from the first pulse sequence. The processing circuitry reconstructs image data of the main scan, based on magnetic resonance signals acquired by the main-scan pulse sequence and phase difference data in the readout direction between first k-space data generated from the magnetic resonance signals acquired by the first pulse sequence and second k-space data generated from the magnetic resonance signals acquired by the second pulse sequence.

First claim

What is claimed is:

1. A magnetic resonance imaging apparatus comprising:
a gradient coil configured to apply a gradient magnetic field in accordance with a pulse sequence;
an RF coil configured to transmit RF pulses causing nuclear magnetic resonance and receive nuclear magnetic resonance signals in accordance with the pulse sequence;
an RF receiver configured to acquire the nuclear magnetic resonance signals received by the RF coil in accordance with the pulse sequence; and
processing circuitry configured to control the gradient coil, the RF coil, and the RF receiver to perform a first pulse sequence, a second pulse sequence, and a main-scan pulse sequence,
wherein the processing circuitry is configured to
(a) set the first pulse sequence in which application of a gradient magnetic field in a readout direction is included, in such a manner that the nuclear magnetic resonance signals are acquired from a first acquisition region including at least a part of an imaging region of a main scan,
(b) set the second pulse sequence in which application of the gradient magnetic field in the readout direction is included, in such a manner that the nuclear magnetic resonance signals are acquired from a second acquisition region including at least a part of the imaging region and being shifted from the first acquisition region,
(c) set the main-scan pulse sequence in which application of the gradient magnetic field in the readout direction and a gradient magnetic field in a phase encode direction is included, in such a manner that the nuclear magnetic resonance signals from the imaging region are acquired,
(d) generate first k-space data including a plurality of matrix elements, by sampling the nuclear magnetic resonance signals acquired by the first pulse sequence,
(e) generate second k-space data including a plurality of matrix elements, by sampling the nuclear magnetic resonance signals acquired by the second pulse sequence,
(f) calculate phase difference data indicative of phase difference in the readout direction between the first k-space data and the second k-space data,
(g) generate main scan k-space data based on the nuclear magnetic resonance signals acquired by the main-scan pulse sequence and the phase difference data, and
(h) reconstruct image data of the imaging region based on the main scan k-space data.

2. The magnetic resonance imaging apparatus according to claim 1 ,
wherein the processing circuitry is configured to
(a) calculate the phase difference data as a function of elapsed time when the gradient magnetic field in the readout direction is applied,
(b) calculate a waveform of the gradient magnetic field in the readout direction based on the phase difference data,
(c) generate the main-scan k-space data based on the nuclear magnetic resonance signals acquired by the main-scan pulse sequence and the waveform of the gradient magnetic field in the readout direction, so that each time integral value up to each sampling period corresponding to each of the matrix elements is equally-spaced, and
(d) reconstruct the image data by performing image reconstruction processing including Fourier transformation on the main-scan k-space data.

3. The magnetic resonance imaging apparatus according to claim 2 ,
wherein the processing circuitry is configured to calculate the phase difference data based on (a) data corresponding to a nuclear magnetic resonance signal acquired at a timing of effective echo time of the first k-space data and (b) data corresponding to a nuclear magnetic resonance signal acquired at a timing of effective echo time of the second k-space data.

4. The magnetic resonance imaging apparatus according to claim 3 ,
wherein the processing circuitry is configured to
(a) set the first pulse sequence to acquire the nuclear magnetic resonance signals by repeating inversion of polarity of the gradient magnetic field in the readout direction,
(b) set the second pulse sequence to acquire the nuclear magnetic resonance signals by repeating inversion of polarity of the gradient magnetic field in the readout direction, and
(c) set a pulse sequence of echo planar imaging in which inversion of polarity of the gradient magnetic field in the readout direction is repeated, as the main-scan pulse sequence.

5. The magnetic resonance imaging apparatus according to claim 4 ,
wherein the processing circuitry is configured to shift the second acquisition region from the first acquisition region, by shifting a detection frequency of the RF receiver in the second pulse sequence from a detection frequency of the RF receiver in the first pulse sequence.

6. The magnetic resonance imaging apparatus according to claim 5 ,
wherein the processing circuitry is configured to
(a) set the first pulse sequence to acquire the nuclear magnetic resonance signals from an acquisition region which is expanded in the readout direction from an acquisition region of the nuclear magnetic resonance signals of the main-scan pulse sequence, and
(b) set the second pulse sequence to acquire the nuclear magnetic resonance signals from an acquisition region which is expanded in the readout direction from the acquisition region of the nuclear magnetic resonance signals of the main-scan pulse sequence.

7. The magnetic resonance imaging apparatus according to claim 6 ,
wherein the processing circuitry is configured to
(a) set a third pulse sequence in which application of the gradient magnetic field in the readout direction is included, in such a manner that the nuclear magnetic resonance signals are acquired from a third acquisition region including at least a part of the imaging region,
(b) set each of the first pulse sequence and the second pulse sequence in such a manner that polarity of the gradient magnetic field in the readout direction at effective echo time becomes opposite to polarity of the gradient magnetic field in the readout direction at effective echo time of the third pulse sequence,
(c) control the gradient coil, the RF coil, and the RF receiver to perform the third pulse sequence in addition to the first pulse sequence, the second pulse sequence, and the main-scan pulse sequence,
(d) generate third k-space data including a plurality of matrix elements, by sampling the nuclear magnetic resonance signals acquired by the third pulse sequence, and
(e) reconstruct the image data by correcting phase error included in the nuclear magnetic resonance signals acquired by the main-scan pulse sequence, based on phase correction data obtained from the first k-space data and the third k-space data.

8. The magnetic resonance imaging apparatus according to claim 4 ,
wherein the processing circuitry is configured to
(a) set unequally-spaced sampling periods, so that each time integral value, whose back end of integral interval is a representative time of each of sampling periods for the nuclear magnetic resonance signals, is equally-spaced, and
(b) generate the main-scan k-space data by sampling the nuclear magnetic resonance signals acquired by the main-scan pulse sequence based on the unequally-spaced sampling periods.

9. The magnetic resonance imaging apparatus according to claim 4 ,
wherein the processing circuitry is configured to
(a) generate the main-scan k-space data by sampling the nuclear magnetic resonance signals acquired by the main-scan pulse sequence at equally-spaced intervals,
(b) perform rearrangement on the main-scan k-space data so that each time integral value whose back end of integral interval is a representative time of each sampling period corresponding to each matrix element of the main-scan k-space data is placed at equal intervals, and
(c) reconstruct the image data by performing image reconstruction

Assignees

• Toshiba Medical Sys Corp

Inventors

• Machii Yutaka
• Kusahara Hiroshi
• Kassai Yoshimori

Classifications

• G01R33/56572

  caused by a distortion of a gradient magnetic field, e.g. non-linearity of a gradient magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title

• G01R33/56554

  caused by acquiring plural, differently encoded echo signals after one RF excitation, e.g. correction for readout gradients of alternating polarity in EPI · CPC title

• G01R33/5618

  using both RF and gradient refocusing, e.g. GRASE · CPC title

• G01R33/5616

  using gradient refocusing, e.g. EPI · CPC title

• G01R33/34

  Constructional details, e.g. resonators {, specially adapted to MR} · CPC title