Inspection apparatus using nuclear magnetic resonance

• US 5,928,146 A
• Filed: 03/11/1997
• Issued: 07/27/1999
• Est. Priority Date: 03/15/1996
• Status: Expired due to Term

• Current Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Inventors: Itagaki, Hiroyuki, Okajima, Kenichi, Takiguchi, Kenji, Takahashi, Tetsuhiko
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): MANTIS MERCADER, ELENI M
• Application Number:
  US08/815,069
• Time in Patent Office: 868 Days
• Field of Search: 600/410, 600/413, 324/307, 324/309
• US Class Current: 600/410
• CPC Class Codes: G01R 33/56554 caused by acquiring plural, differently encoded echo signals after one RF excitation, e.g. correction for readout gradients of alternating polarity in EPI

Abstract

An inspection apparatus using nuclear magnetic resonance having arithmetic and control means for controlling a pulse sequence for detecting a nuclear magnetic resonance signal from a target to be inspected and calculating the detected signal. The arithmetic and control means controls an echo planar pulse sequence for acquiring a plurality of images of a predetermined same region of the target to be inspected; and arranges echo signal data obtained by measuring the inspection target by the echo planar pulse sequence and forms an EPI data set; designates a plurality of data points in k-space as observed points; designates a predetermined EPI data set to reference data for body motion for correcting influence by the body motion of the inspection target and calculates a reference phase as a phase of the body motion reference data at the observed points; calculates the phase of the EPI data set at the observed points; calculates a body motion correcting value expressing the influence by the body motion of the inspection target by using the phase difference between the phase of the EPI data set and the reference phase; and executes a process for eliminating the influence by the body motion of the inspection target by removing the phase difference of the EPI data set of the target to be inspected by using the body motion correction values.

Claims

1. An inspection apparatus using nuclear magnetic resonance, comprising:

static magnetic field generating means for generating a static magnetic field;

gradient magnetic field generating means for generating gradient magnetic fields in three directions, respectively;

radio frequency magnetic field generating means for generating a radio frequency magnetic field for exciting nuclear magnetization of a target to be inspected;

detection means for detecting a nuclear magnetic resonance signal from the target to be inspected; and

arithmetic and control means for calculating a detection signal of the signal detection means, exciting the nuclear magnetization in a predetermined cross section of the target to be inspected and controlling a pulse sequence for detecting the nuclear magnetic resonance signal,

wherein the arithmetic and control means;

(a) controls an echo planar pulse sequence for acquiring a plurality of images of a predetermined same region of the target to be inspected; and

(b) (1) arranges echo signal data in a k-space, obtained by measuring the target to be inspected using the echo planar pulse sequence and forms an EPI data set corresponding to each image;

(2) designates a plurality of coordinate points in the k-space as observed points for detecting the body motion, the observed points being arranged in parallel with one of the coordinate axes in the k-space or being arranged in parallel with two or more coordinate axes, respectively, selected from the coordinate axes;

(3) designates a predetermined one of the EPI data sets to reference data for body motion for correcting influence by the body motion of the target to be inspected and calculates reference phase as a phase of the reference data for body motion at each observed point;

(4) calculates the phase of the EPI data set at each observed point;

(5) calculates a body motion correction value expressing the influence by the body motion of the target to be inspected by using the phase difference between the phase of the EPI data set and the reference phase; and

(6) executes a process for eliminating the influence by body motion of the target to be inspected by eliminating the phase difference of the EPI data set by using the body motion correction value.

2. The apparatus according to claim 1, wherein in (3), the reference data for body motion is acquired either synchronously with respiration of the target to be inspected, synchronously with electrocardiogram waveform of the target to be inspected, or in a state where the target to be inspected holds his/her breath.

3. The apparatus according to claim 1, wherein (5) includes processes for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and for deriving the correction value for body motion at each observed point from the phase difference at each observed point and the coordinate value in the k-space.

4. The apparatus according to claim 1, wherein (4) includes processes for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and for obtaining at least one approximate linear line by a least-square method from the phase difference at each observed point and the coordinate values in the k-space.

5. The apparatus according to claim 4, wherein in the process for obtaining the approximate linear lines, data points having a high signal intensity among the EPI data set are used as the observed points and the phase difference between data points having a low signal intensity among the EPI data set and the reference phase are obtained from the approximate linear lines and the coordinate values in the k-space.

6. The apparatus according to claim 1, wherein (5) includes processes for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and for obtaining at least one approximate linear line by a least-square method from the phase difference at each observed point and the coordinated values in the k-space, and also a process for deriving a body motion correction value at each coordinate value from the approximate linear lines and the coordinate values in the k-space.

7. The apparatus according to claim 6, wherein in the process for obtaining the approximate linear lines, data points having a high signal intensity among the EPI data set are used as the observed points and the phase difference between data points having a low signal intensity among the EPI data set and the reference phase are obtained from the approximate linear lines and the coordinate values in the k-space.

8. The apparatus according to claim 1, wherein (6) includes a process for removing the phase difference at each coordinate value in the k-space from the EPI data set of the target to be inspected, the phase difference being calculated from the approximate linear lines obtained from the process in (5) for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and forming the approximate linear lines from the phase difference at each observed point and the coordinate values in the k-space.

9. The apparatus according to claim 1, wherein (6) includes a process for removing inclination of the approximate linear lines from the EPI data set of the target to be inspected, the approximate linear lines being obtained from the process in (5) for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and forming the approximate linear lines from the phase difference at each observed point and the coordinate values in the k-space.

10. The apparatus according to claim 1, wherein (6) includes a process for removing offset components and inclinations of the approximate linear lines of the phase difference from the EPI data set of the target to be inspected, the approximate linear lines being obtained from the process in (5) for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and forming the approximate linear lines from the phase difference at each observed point and the coordinate values in the k-space.

11. The apparatus according to claim 1, wherein (5) includes a process for inverting a sign of a phase difference between the phase of the EPI data set and the reference phase and removing it from the EPI data set of the target to be inspected.

12. The apparatus according to claim 1, wherein (6) is implemented after a value for correcting phase distortion caused by eddy currents is derived.

13. An inspecting apparatus using nuclear magnetic resonance, comprising:

static magnetic field generating means for generating a static magnetic field;

gradient magnetic field generating means for generating gradient magnetic fields in three directions, respectively;

radio frequency magnetic field generating means for generating a radio frequency magnetic field for exciting nuclear magnetization of a target to be inspected;

detection means for detecting a nuclear magnetic resonance signal from the target to be inspected; and

arithmetic and control means for calculating a detection signal of the signal detection means, exciting the nuclear magnetization in a predetermined cross section of the target to be inspected and controlling a pulse sequence for detecting the nuclear magnetic resonance signal,

wherein the arithmetic and control means;

(a) controls an echo planar pulse sequence for acquiring a plurality of images of a predetermined same region of the target to be inspected; and

(b) (1) calculates a value for correcting phase distortion occurring when an EPI pulse sequence is implemented from an echo signal obtained by measuring the target to be inspected at least in a part of the EPI pulse sequence;

(2) arranges the echo signals obtained by measuring the target to be inspected using the EPI pulse sequence in a k-space, thereby forming an EPI data set corresponding to each image;

(3) designates a plurality of data points in the k-space as observed points for detecting the body motion, the observed points being arranged in parallel to one of the coordinate axes in the k-space or being arranged in parallel to two or more coordinate axes, respectively, selected from the coordinate axes;

(4) designates a predetermined one of the EPI data sets to reference data for body motion for correcting influence by the body motion of the target to be inspected and calculates a reference phase as a phase of the reference data for body motion at each observed point;

(5) calculates a phase of the EPI data set at each observed point;

(6) calculates a body motion correction value expressing the influence by the body motion of the target to be inspected by using the phase difference between the phase of the EPI data set and the reference phase;

(7) removes the influence by the body motion of the target to be inspected by removing the phase difference of the EPI data set by using the body motion correction value; and

(8) executes a process for reconstructing an image by using the EPI data set in which the influence by the body motion of the target to be inspected is removed.

14. The apparatus according to claim 13, wherein in (4), the reference data for body motion is acquired either synchronously with respiration of the target to be inspected, synchronously with electrocardiogram of the target to be inspected, or in a state where the target to be inspected holds his/her breath.

15. The apparatus according to claim 13, wherein (6) includes processes for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and for deriving the body motion correction value at each observed point from the phase difference at every coordinate point and the coordinate values in the k-space.

16. The apparatus according to claim 13, wherein (6) includes processes for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and for obtaining at least one approximate linear line by a least-square method from the phase difference at each observed point and the coordinate values in the k-space.

17. The apparatus according to claim 16, wherein in the process for obtaining the approximate linear lines, data points having a high signal intensity among the EPI data set are used as the observed points and the phase difference between data points having a low signal intensity among the EPI data set and the reference phase are obtained from the approximate linear lines and the coordinate values in the k-space.

18. The apparatus according to claim 13, wherein (6) includes processes for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and for obtaining at least one approximate linear line by a least-square method from the phase differences at each observed point and the coordinate values in the k-space, and also includes a process for deriving a body motion correction value at each coordinate value from the approximate linear lines and the coordinate values in the k-space.

19. The apparatus according to claim 18, wherein in the process for obtaining the approximate linear lines, data points having a high signal intensity among the EPI data set are used as the observed points and the phase difference between data points having a low signal intensity among the EPI data set and the reference phase are obtained from the approximate linear lines and the coordinate values in the k-space.

20. The apparatus according to claim 13, wherein (7) includes a process for removing the phase difference at each coordinate value in the k-space from the EPI data set of the target to be inspected, the phase difference being calculated from the approximate linear lines obtained from the process in (6) for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and forming the approximate linear lines from the phase difference at each observed point and the coordinate values in the k-space.

21. The apparatus according to claim 13, wherein (7) includes a process for removing an inclination of the approximate linear lines from the EPI data set of the target to be inspected, the inclination obtained from the process in (6) for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and the coordinate values in the k-space.

22. The apparatus according to claim 13, wherein (7) includes a process for removing offset components of an inclination of the approximate linear lines of the phase difference from the EPI data set of the target to be inspected, the approximate linear lines being obtained from the process in (6) for calculating the phase difference between the phase of the EPI data set and the reference phase at every corresponding observed point and forming the approximate linear lines from the phase difference at each observed point and the coordinate values in the k-space.

23. The apparatus according to claim 13, wherein (6) includes a process for inverting a sign of a phase difference between the phase of the EPI data set and the reference phase and removing it from the EPI data set of the target to be inspected.

24. The apparatus according to claim 13, wherein (7) is implemented after a value for correcting phase distortion caused by eddy currents is derived.

25. An inspection apparatus using nuclear magnetic resonance, comprising:

static magnetic field generating means for generating a static magnetic field;

gradient magnetic field generating means for generating gradient magnetic fields in three directions, respectively;

radio frequency magnetic field generating means for generating a radio frequency magnetic field for exciting nuclear magnetization of a target to be inspected;

detection means for detecting a nuclear magnetic resonance signal from the target to be inspected; and

arithmetic and control means for calculating a detection signal of the signal detection means, exciting the nuclear magnetization in a predetermined cross section of the target to be inspected and controlling a pulse sequence for detecting the nuclear magnetic resonance signal,

wherein the arithmetic and control means;

(a) controls a predetermined pulse sequence for acquiring a plurality of images of a predetermined same region of the target to be inspected a plurality of times by an echo planar imaging; and

(b) (1) arranges echo signal data in a k-space, obtained by measuring the target to be inspected using the echo planar pulse sequence and forms an EPI data set corresponding to each image;

(2) estimates a phase rotation amount of the a zero-encode echo signal in which a phase encoding amount by a phase encoding gradient magnetic field pulse is zero in the EPI data set and a time difference between the center of the zero-encode echo signal and the center of a radio frequency pulse, and detects fluctuation in the phase rotation amount between the images from the estimated phase rotation amount;

(3) determines a phase correction amount for each echo signal in the EPI data set; and

(4) corrects the phase of each echo signal in the EPI data set.