MAGNETIC RESONANCE IMAGING SYSTEM AND METHOD

• US 20100134107A1
• Filed: 04/17/2008
• Published: 06/03/2010
• Est. Priority Date: 04/27/2007
• Status: Active Grant

• Current Assignee: FUJIFILM Healthcare Corp. (Fujifilm Holdings Corporation)
• Original Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Inventors: Kitamoto, Naoya
• Granted Patent: US 8,148,980 B2
• Time in Patent Office: Days
• US Class Current: 324/309
• CPC Class Codes: G01R 33/5602 by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse
• CPC Class Codes: G01R 33/5607 by reducing the NMR signal of a particular spin species, e.g. of a chemical species for fat suppression, or of a moving spin species for black-blood imaging
• CPC Class Codes: G01R 33/5615 Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
• CPC Class Codes: G01R 33/5617 using RF refocusing, e.g. RARE
• CPC Class Codes: G01R 33/565 Correction of image distortions, e.g. due to magnetic field inhomogeneities
• CPC Class Codes: G01R 33/56563 caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 G01R33/56509, G01R33/56518, G01R33/56536 take precedence
• CPC Class Codes: G01R 33/56572 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 Class Codes: G01R 33/5659 caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field G01R33/56509, G01R33/56518, G01R33/56536 take precedence

Abstract

A magnetic resonance imaging system is characterized in that a control unit executes, as pulse sequences, a first sequence for obtaining data of a predetermined 2-dimensional region in a k-space and a second sequence for obtaining data required for reconstruction of an image by irradiating an object to be examined with an inversion recovery pulse and corrects the phase of the data obtained by the second sequence with the data of the 2-dimensional region obtained by the first sequence, and in that a signal processing unit reconstructs a real component image with corrected data.

Upon execution of the first sequence, the control unit obtains the data of the predetermined 2-dimensional region in the k-space while varying a phase encoding amount.

Claims

1. A magnetic resonance imaging apparatus comprising:

a static magnetic field generation unit configured to generate a static magnetic field in an imaging space;

a gradient magnetic field generation unit configured to apply a gradient magnetic field pulse to an object to be examined who is placed in the imaging space;

a high-frequency irradiation unit configured to irradiate a high-frequency magnetic field pulse to the object;

a reception unit configured to acquire nuclear magnetic resonance signals produced from the object;

a signal processing unit configured to execute arithmetic processing on the signals acquired by the reception unit for reconstructing an image; and

a control unit configured to control the operation of the high-frequency irradiation unit, gradient magnetic field generation unit and reception unit so as to execute a predetermined pulse sequence, wherein;

the control unit executes a first sequence for obtaining the data in a predetermined 2-dimensional region in a k-space as the pulse sequence and a second sequence for obtaining the data necessary for imaging reconstruction by irradiating an IR pulse to the object, and corrects the phase of the data obtained in the second sequence using the data of the 2-dimensional region obtained in the first sequence; and

the signal processing unit reconstructs a real component image using the data after being corrected,

characterized in that the control unit obtains the data of a predetermined 2-dimensional region in the k-space while varying the phase encoding amount upon executing the first sequence.

2. The magnetic resonance imaging apparatus according to claim 1, characterized in that the first sequence obtains the data in a predetermined low-frequency region which includes the spatial frequency “

0”

in a k-space as a predetermined 2-dimensional region in the k-space.

3. The magnetic resonance imaging apparatus according to claim 2, wherein the control unit allocates “

0”

as the data value in the high-frequency region which is outside of the low-frequency region in the k-space to be obtained by the first sequence, so as to execute the correction.

4. The magnetic resonance imaging apparatus according to claim 1, wherein the control unit generates a 2-dimensional phase correction map by performing 2-dimensional Fourier transform-ation on the data in the k-space obtained by the first sequence, and corrects the phase of the data obtained by the second sequence using the generated map.

5. The magnetic resonance imaging apparatus according to claim 4, wherein:

the reception unit includes a plurality of reception coils which are disposed in the imaging space simultaneously for acquiring nuclear magnetic resonance signals respectively; and

the control unit generates the 2-dimensional phase correction map for each of the plurality of reception coils using the nuclear magnetic resonance signal acquired by the plurality of reception coils respectively in the first sequence, and corrects the signal data received by the plurality of reception coils respectively in the second sequence using the generated maps.

6. The magnetic resonance imaging apparatus according to claim 1, wherein:

the second sequence includes an IR pulse and a signal collecting pulse sequence for collecting nuclear magnetic resonance signals from the nuclear magnetization which is inverted by the IR pulse; and

the first sequence includes the pulse sequence which is the same as the signal collecting pulse sequence.

7. A magnetic resonance imaging method that obtains a real component image using the inversion recovery method that applies an IR pulse before acquiring image data comprising:

a step of executing a first sequence for acquiring the data of a predetermined 2-dimensional region in a k-space;

a step of executing a second sequence for acquiring the data necessary for imaging reconstruction by irradiating an IR pulse to the object;

a step of correcting the phase of the data acquired in the second sequence using the data of the 2-dimensional region acquired in the first sequence; and

a step of reconstructing a real component image using the corrected data,

characterized in that the first sequence acquires the data of a predetermined 2-dimensional region in the k-space while performing phase encode.

8. The magnetic resonance imaging method according to claim 7, wherein the first sequence obtains the data of the preset low-frequency region including spatial frequency “

0”

in a k-space as a predetermined 2-dimensional region in the k-space.

9. The magnetic resonance imaging method according to claim 8, wherein the correction is executed by allocating “

0”

as the data value in the high-frequency region which is outside of the low-frequency region in the k-space to be acquired in the first sequence.

10. The magnetic resonance imaging method according to claim 7, characterized in including:

a step of generating a 2-dimensional phase correction map by performing 2-dimensional Fourier transformation on the data in the k-space by the first sequence; and

a step of correcting the phase of the data acquired in the second sequence using the 2-dimensional phase correction map.

11. The magnetic resonance imaging method according to claim 7, characterized in that the 2-dimensional phase correction map is generated for each of the plurality of reception coils using the nuclear resonance signals respectively acquired by the plurality of reception coils in the first sequence, and the correction is executed using the generated map on the signal data received by the plurality of reception coils in the second sequence.

12. The magnetic resonance imaging method according to claim 7, wherein:

the second sequence includes an IR pulse and a signal collecting pulse sequence for collecting nuclear magnetic resonance signals from the nuclear magnetization which is inverted by the IR pulse; and

the first sequence includes the pulse sequence which is the same as the signal collecting pulse sequence.