Magnetic resonance imaging apparatus and flip angle determination method

Patent metadata

Field	Value
Publication number	US-9541623-B2
Application number	US-201214116228-A
Country	US
Kind code	B2
Filing date	May 23, 2012
Priority date	Jun 9, 2011
Publication date	Jan 10, 2017
Grant date	Jan 10, 2017

Abstract

The purpose of the present invention is to obtain an image with a desired contrast while minimizing specific absorption rate and without deteriorating image quality in a variable refocus flip angle sequence. To this end, Teequiv specified by a signal decay pattern SSP obtained by a flip angle changing pattern FAP is compared with a designated Teequiv, and the flip angle changing pattern FAP is changed according to the comparison result to search for the flip angle changing pattern FAP which gives a desired contrast. Then, the flip angle changing pattern FAP which is capable of realizing the designated Teequiv is determined. Then, imaging is performed using each flip angle constitutes the determined flip angle changing pattern FAP.

First claim

The invention claimed is:

1. A magnetic resonance imaging apparatus comprising:
static magnetic field generating unit configured to generate a static magnetic field;
gradient magnetic field application unit configured to apply a gradient magnetic field to an object to be examined that is placed in the static magnetic field;
high-frequency magnetic field application unit configured to apply a high-frequency field magnetic pulse for exciting magnetization of the object at a predetermined flip angle;
signal receiving unit configured to receive echo signals emitted from the object by nuclear magnetic resonance;
image reconstruction unit configured to reconstruct an image from the received echo signal;
control unit configured to control the gradient magnetic field application unit, high-frequency magnetic field application unit, signal receiving unit and image reconstruction unit in accordance with an imaging sequence; and
input receiving unit configured to receive input of imaging conditions to be used by the control unit,
wherein:
the imaging conditions include contrast information for specifying a desired contrast;
the control unit comprises sequence generation unit configured to generate an imaging sequence using the imaging condition and a pulse sequence;
the pulse sequence is for applying plural refocus high-frequency magnetic field pulses after applying one excitation high-frequency magnetic field pulse;
the sequence generation unit comprises flip-angle determination unit configured to determine each flip angle of the plural refocus high-frequency magnetic field pulses; and
the flip angle determination unit searches flip angles capable of acquiring an image with a desired contrast which is specified by the contrast information by changing each flip angle of the plural refocus high-frequency magnetic field pulses, and determines the acquired flip angles as the respective flip angles of the plural refocus high-frequency magnetic field pulses to be used in the imaging sequence, and

wherein the flip angle determining unit changes each flip angle of the plural refocus high-frequency magnetic field pulses so that a calculated echo time which determines the contrast of a reconstruction image which can be obtained by the flip angles from the signal intensity of echo signals which can be acquired by the respective flip angles of the plural refocus high-frequency magnetic field pulses falls within the effective range of a desired echo time which determines the desired contrast
wherein the flip angle determining unit, as the result of comparing the calculated echo time and the desired echo time, makes the change of flip angles of stabilization pulses among the plural refocus high-frequency magnetic field pulses gradual when the calculated echo time is shorter than the desired echo time, and makes the change of flip angles of the stabilization pulses steep when the calculated echo time is longer than the desired echo time.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein the flip angle determining unit compares the calculated echo time and the desired echo time, increases all flip angles of the plural refocus high-frequency magnetic field pulses with respect to a predetermined reference value at equal rate when the calculated echo time is shorter than the desired echo time, and all flip angle of the plural refocus high-frequency magnetic field pulses are reduced with respect to a predetermined reference value at equal rate when the calculated echo time is longer than the desired echo time.

3. A magnetic resonance imaging apparatus comprising:
static magnetic field generating unit configured to generate a static magnetic field;
gradient magnetic field application unit configured to apply a gradient magnetic field to an object to be examined that is placed in the static magnetic field;
high-frequency magnetic field application unit configured to apply a high-frequency field magnetic pulse for exciting magnetization of the object at a predetermined flip angle;
signal receiving unit configured to receive echo signals emitted from the object by nuclear magnetic resonance;
image reconstruction unit configured to reconstruct an image from the received echo signal;
control unit configured to control the gradient magnetic field application unit, high-frequency magnetic field application unit, signal receiving unit and image reconstruction unit in accordance with an imaging sequence; and
input receiving unit configured to receive input of imaging conditions to be used by the control unit,
wherein:
the imaging conditions include contrast information for specifying a desired contrast;
the control unit comprises sequence generation unit configured to generate an imaging sequence using the imaging condition and a pulse sequence;
the pulse sequence is for applying plural refocus high-frequency magnetic field pulses after applying one excitation high-frequency magnetic field pulse;
the sequence generation unit comprises flip-angle determination unit configured to determine each flip angle of the plural refocus high-frequency magnetic field pulses; and
the flip angle determination unit searches flip angles capable of acquiring an image with a desired contrast which is specified by the contrast information by changing each flip angle of the plural refocus high-frequency magnetic field pulses, and determines the acquired flip angles as the respective flip angles of the plural refocus high-frequency magnetic field pulses to be used in the imaging sequence, and

wherein the flip angle determining unit changes each flip angle of the plural refocus high-frequency magnetic field pulses so that a calculated echo time which determines the contrast of a reconstruction image which can be obtained by the flip angles from the signal intensity of echo signals which can be acquired by the respective flip angles of the plural refocus high-frequency magnetic field pulses falls within the effective range of a desired echo time which determines the desired contrast
wherein the flip angle determining unit, when the calculated echo time and the desired echo time are compared and the calculated echo time is shorter than the desired echo time, sets all flip angles having the same value as a predetermined minimum value or smaller at the minimum value.

4. A magnetic resonance imaging apparatus comprising:
static magnetic field generating unit configured to generate a static magnetic field;
gradient magnetic field application unit configured to apply a gradient magnetic field to an object to be examined that is placed in the static magnetic field;
high-frequency magnetic field application unit configured to apply a high-frequency field magnetic pulse for exciting magnetization of the object at a predetermined flip angle;
signal receiving unit configured to receive echo signals emitted from the object by nuclear magnetic resonance;
image reconstruction unit configured to reconstruct an image from the received echo signal;
control unit configured to control the gradient magnetic field application unit, high-frequency magnetic field application unit, signal receiving unit and image reconstruction unit in accordance with an imaging sequence, and
input receiving unit configured to receive input of imaging conditions to be used by the control unit,
wherein:
the imaging conditions include contrast information for specifying a desired contrast;
the control unit comprises sequence generation unit configured to generate an imaging sequence using the imaging condition and a pulse sequence;
the pulse sequence is for applying plural refocus high-frequency magnetic field pulses after applying one excitation high-frequency magnetic field pulse;
the sequence generation unit comprises flip-angle determination unit configured to determ

Assignees

• Hoshino Yusuke
• Kaneta Akiko
• Kurokawa Shinji
• Hitachi Ltd

Inventors

• Hoshino Yusuke
• Kaneta Akiko
• Kurokawa Shinji

Classifications

• G01R33/56 Primary

  Image enhancement or correction, e.g. subtraction or averaging techniques {, e.g. improvement of signal-to-noise ratio and resolution} · CPC title

• G01R33/5617 Primary

  using RF refocusing, e.g. RARE · CPC title

• G01R33/583

  Calibration of signal excitation or detection systems, e.g. for optimal RF excitation power or frequency (G01R33/246 takes precedence) · CPC title