Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2003-01-17
2004-04-13
Shrivastav, Brij (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000
Reexamination Certificate
active
06720767
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Japanese Application No. 2002-014286 filed Jan. 23, 2002.
BACKGROUND OF THE INVENTION
The present invention relates to a method of measuring the phase offset of an FID (free induction decay) signal, a method of measuring the phase offset of SE (spin echo)/STE (stimulated echo) signals, an MR (magnetic resonance) imaging method, and an MRI (magnetic resonance imaging) apparatus, and more particularly to a method of measuring the phase offset of an FID signal caused by static magnetic field inhomogeneity, a method of measuring the phase offset of SE/STE signals (SE signal and STE signal) caused by static magnetic field inhomogeneity, an MR imaging method in which the phase offset of the FID signal and the phase offset of the SE/STE signals caused by static magnetic field inhomogeneity are corrected, and an MRI apparatus capable of conducting such methods.
Japanese Patent No. 2,898,329 discloses an MR imaging method comprising:
(1) repeatedly conducting data collection in an SSFP (steady state free precession) state with a successively varying amount of phase encoding to acquire data ƒ&ngr;(
0
) for individual views &ngr; that together fill a k-space;
(2) repeatedly conducting data collection in the SSFP state with the successively varying amount of phase encoding and with an RF phase alternated by 180° to acquire data ƒ&ngr;(
1
) for individual views &ngr; that together fill the k-space;
(3) generating data A&ngr; by addition processing or subtraction processing on ƒ&ngr;(
0
) and ƒ&ngr;(
1
) as given by:
A&ngr;=
0.5
×F&ngr;
(0)+0.5
×F
&ngr;(1)
or
A&ngr;=
0.5
×F
&ngr;(0)−0.5
×F
&ngr;(1); and
(4) reconstructing an image from the resulting data A&ngr;.
The data collected in the SSFP state as in the MR imaging method above contain both components of FID signals and components of SE/STE signals.
It is known that when an image is produced from data collected in the SSFP state as in the MR imaging method disclosed in Japanese Patent No. 2,898,329, static magnetic field inhomogeneity, if any, gives rise to band artifacts in the image.
The generation of band artifacts is caused by phase offsets in the FID signals and SE/STE signals due to static magnetic field inhomogeneity, which results in mutual interference between the FID and SE/STE signals.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention is to provide a method of measuring the phase offset of an FID signal caused by static magnetic field inhomogeneity, a method of measuring the phase offset of SE/STE signals caused by static magnetic field inhomogeneity, an MR imaging method in which the phase offset of the FID signal and the phase offset of the SE/STE signals caused by static magnetic field inhomogeneity are corrected, and an MRI apparatus capable of conducting such methods.
In accordance with a first aspect, the present invention provides a method of measuring the phase offset of an FID signal characterized in comprising: adding a crusher for resetting the phase of SE/STE signals to a pulse sequence that is repeated for conducting data collection in an SSFP state, and omitting a phase encoding axis pulse therefrom; collecting phase-offset-measurement data in the SSFP state by repeating the resulting pulse sequence; and measuring the phase offset of the FID signal from the phase-offset-measurement data obtained.
In the method of measuring the phase offset of an FID signal of the first aspect, since the phase of the SE/STE signals is reset by adding a crusher, the phase-offset-measurement data obtained exhibits the phase offset of the FID signal component. Therefore, the phase offset of the FID signal can be measured from the phase-offset-measurement data obtained.
In accordance with a second aspect, the present invention provides the method of measuring the phase offset of an FID signal having the aforementioned configuration, characterized in that: said crusher for resetting the phase of SE/STE signals is a gradient pulse that is applied to at least one of a phase encoding axis and a read axis at a time after a data collection period.
In the method of measuring the phase offset of an FID signal of the second aspect, since a gradient pulse is applied to at least one of a phase encoding axis and a read axis at a time after a data collection period, the phase of the SE/STE signals can be reset without affecting the phase of the FID signal component.
In accordance with a third aspect, the present invention provides a method of measuring the phase offset of SE/STE signals characterized in comprising: adding a crusher for resetting the phase of an FID signal to a pulse sequence that is repeated for conducting data collection in an SSFP state, and omitting a phase encoding axis pulse therefrom; collecting phase-offset-measurement data in the SSFP state by repeating the resulting pulse sequence; and measuring the phase offset of the SE/STE signals from the phase-offset-measurement data obtained.
In the method of measuring the phase offset of FID signal of the third aspect, since the phase of the FID signal is reset by adding a crusher, the phase-offset-measurement data obtained exhibits the phase offset of the SE/STE signal component. Therefore, the phase offset of the SE/STE signals can be measured from the phase-offset-measurement data obtained.
In accordance with a fourth aspect, the present invention provides the method of measuring the phase offset of SE/STE signals having the aforementioned configuration, characterized in that: said crusher for resetting the phase of an FID signal is a gradient pulse that is applied to at least one of a phase encoding axis and a read axis at a time after an RF pulse and before a data collection period.
In the method of measuring the phase offset of an FID signal of the fourth aspect, since a gradient pulse is applied to at least one of a phase encoding axis and a read axis at a time after an RF pulse and before a data collection period, the phase of the FID signal can be reset without affecting the phase of the SE/STE signal component.
In accordance with a fifth aspect, the present invention provides an MR imaging method characterized in comprising: adjusting the phase of an RF pulse in a pulse sequence that is repeated for conducting data collection in an SSFP state to correct the phase offsets of an FID signal and SE/STE signals; collecting imaging data in the SSFP state by repeating the resulting pulse sequence; and producing an image from the imaging data obtained.
In the MR imaging method of the fifth aspect, since the zeroth-order phase offsets of the FID signal and SE/STE signals can be corrected by adjusting the phase of the RF pulse, band artifacts caused by static magnetic field inhomogeneity can be reduced.
In accordance with a sixth aspect, the present invention provides an MR imaging method characterized in comprising: adding a correction pulse for correcting the phase offsets of an FID signal and SE/STE signals to a pulse sequence that is repeated for conducting data collection in an SSFP state; collecting imaging data in the SSFP state by repeating the resulting pulse sequence; and producing an image from the imaging data obtained.
In the MR imaging method of the sixth aspect, since the first-order phase offsets of the FID signal and SE/STE signals can be corrected by adding a correction pulse, band artifacts caused by static magnetic field inhomogeneity can be reduced.
In accordance with a seventh aspect, the present invention provides an MR imaging method characterized in comprising: adjusting the phase of an RF pulse in a pulse sequence that is repeated for conducting data collection in an SSFP state and adding a correction pulse for correcting the phase offsets of an FID signal and SE/STE signals to correct the phase offsets of the FID signal and SE/STE signals; collecting imaging data in the SSFP state by repeating the resulting pulse sequence; and producing an image from the imaging data obtained.
In th
Armstrong Teasdale LLP
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
Shrivastav Brij
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