Magnetic resonance imaging apparatus, and method for correcting measurement-space coordinates

Patent metadata

Field	Value
Publication number	US-9714994-B2
Application number	US-201113881207-A
Country	US
Kind code	B2
Filing date	Oct 28, 2011
Priority date	Nov 9, 2010
Publication date	Jul 25, 2017
Grant date	Jul 25, 2017

Abstract

In order to approximate the gradient magnetic field pulse waveform shape with high accuracy and improve the image quality at the time of imaging cross-section change or oblique imaging, an MRI apparatus of the present invention divides the waveform shape of the gradient magnetic field pulse into a plurality of sections, defines an approximation function for each section, and corrects the k-space coordinates at which the echo signal is arranged using the parameter of the approximation function. In addition, an optimal parameter of the approximation function of the waveform shape of the gradient magnetic field pulse is searched for using the measured signal.

First claim

The invention claimed is:

1. A magnetic resonance imaging apparatus comprising:
a static magnetic field generation unit;
a gradient magnetic field generation unit that gives a magnetic field gradient to a static magnetic field generated by the static magnetic field generation unit;
a signal transmission unit that irradiates an examination target placed in the static magnetic field with a high-frequency magnetic field;
a signal receiving unit that receives an echo signal emitted from the examination target due to nuclear magnetic resonance; and
a signal processing unit that processes the echo signal to reconstruct an image of the examination target, wherein
the signal processing unit includes an approximation function generation unit that generates an approximation function that, for each of at least two temporally divided sections of a gradient magnetic field pulse waveform to which the magnetic field gradient is given by the gradient magnetic field generation unit, approximates the gradient magnetic field pulse waveform and a correction unit that corrects measurement-space coordinates, at which the echo signal is arranged, using the approximation function.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein at least the two approximation functions include different kinds of approximation functions.

3. The magnetic resonance imaging apparatus according to claim 2 , wherein, among the approximation functions including the different kinds of approximation functions, at least one approximation function is an exponential function and at least one approximation function is a linear function.

4. The magnetic resonance imaging apparatus according to claim 1 , wherein the approximation function generation unit includes a parameter calculation unit that approximates the approximation function by calculating a parameter, which expresses the approximation function, using the echo signal.

5. The magnetic resonance imaging apparatus according to claim 4 , wherein the measured echo signal is obtained by executing a preliminary measurement pulse sequence for measuring a gradient magnetic field pulse waveform shape for gradient magnetic fields of a plurality of axes, and the approximation function generation unit calculates a parameter of an approximation function for each of gradient magnetic field pulse waveforms of the plurality of axes.

6. The magnetic resonance imaging apparatus according to claim 4 , wherein parameters of at least the two approximation functions are changed according to imaging conditions.

7. The magnetic resonance imaging apparatus according to claim 4 , wherein the parameter calculation unit includes an evaluation value calculation unit that calculates an evaluation value, which is for evaluating a degree of improvement of image quality of the image, from the image and a determination unit that determines an optimum value of a parameter on the basis of the evaluation value calculated by the evaluation value calculation unit.

8. The magnetic resonance imaging apparatus according to claim 7 , wherein the parameter calculation unit sets a region of interest in the image, calculates the evaluation value on the basis of a signal value of the region of interest, and determines the optimum value of the parameter from relationship between the evaluation value and a value of a parameter used when generating the image.

9. The magnetic resonance imaging apparatus according to claim 1 , wherein at least the two approximation functions have the same inclination between adjacent sections.

10. A method for correcting measurement-space coordinates of an echo signal measured by a magnetic resonance imaging apparatus, the measurement-space coordinate correction method comprising:
a step of approximating a gradient magnetic field pulse waveform shape with at least two approximation functions;
a step of storing a parameter of each approximation function in a storage unit; and
a step of correcting the measurement-space coordinates of the echo signal using the parameter stored in the storage unit and the measured echo signal.

11. The measurement-space coordinate correction method according to claim 10 , wherein, in the approximation step, an approximation function is set for each of a plurality of different gradient magnetic field pulse waveform shapes corresponding to a plurality of imaging conditions.

12. The measurement-space coordinate correction method according to claim 10 , wherein the approximation step includes a step of optimizing a parameter of an approximation function.

13. The measurement-space coordinate correction method according to claim 12 , wherein, in the optimization step, an optimum value of a parameter is calculated by repeating an image reconstruction step of reconstructing an image using measurement-space coordinates, which are corrected using an initial value of a parameter, and the measured echo signal while changing the initial value of the parameter.

14. The measurement-space coordinate correction method according to claim 13 , wherein the optimization step includes an evaluation value calculation step of calculating an evaluation value, which is for evaluating a degree of improvement of image quality of the image, from the image and a determination step of determining an optimum value of a parameter on the basis of the calculated evaluation value after the image reconstruction step.

Assignees

• Takizawa Masahiro
• Takahashi Tetsuhiko
• Kawamura Miyuki
• Hitachi Ltd

Inventors

• Takizawa Masahiro
• Takahashi Tetsuhiko
• Kawamura Miyuki

Classifications

• G01R33/28

  Details of apparatus provided for in groups G01R33/44 - G01R33/64 · CPC title

• G01R33/48 Primary

  NMR imaging systems · CPC title

• G01R33/56572 Primary

  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

• G01R33/4824

  using a non-Cartesian trajectory · CPC title