Magnetic resonance imaging method and device

• US 6,885,885 B1
• Filed: 05/26/2000
• Issued: 04/26/2005
• Est. Priority Date: 05/26/1999
• Status: Expired due to Fees

• Current Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Inventors: Takizawa, Masahiro, Takahashi, Tetsuhiko
• Primary Examiner(s): ROBINSON, DANIEL LEON
• Application Number:
  US09/979,241
• Time in Patent Office: 1,796 Days
• Field of Search: 600/410, 600/411, 600/407, 600/436, 600/419, 324/307, 324/308, 324/309
• US Class Current: 600/410
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/11 Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb for measuring pulse A61B5/02 ;A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721
• CPC Class Codes: G01R 33/56509 due to motion, displacement or flow, e.g. gradient moment nulling G01R33/567 takes precedence
• 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 33/5676 Gating or triggering based on an MR signal, e.g. involving one or more navigator echoes for motion monitoring and correction

Abstract

A magnetic resonance imaging apparatus has means for detecting the movement of an object so as to correct the variation of the non-uniformity of static magnetic field because of the movement of the object and thereby to improve the quality of the MR image. When actually measured data is corrected by using a signal for correcting the static magnetic field obtained in a preliminary measurement, the influence of the non-uniformity of static magnetic field is eliminated from the image based on the information from the body movement detecting means by using a correcting signal measured at the same time phase of the periodic movement as that of the actually measured signal. A navigation echo measured during the same repetition time as that of the actually measured signal is used for detection of time phase by detecting means. As a result, the quality of image is not deteriorated by the variation of the non-uniformity of static magnetic field due to the movement of the body of the object, realizing imaging of high quality image.

Claims

1. Magnetic resonance imaging method comprising,

(a) step for applying static magnetic field, slice selective gradient magnetic field, gradient magnetic field for reading out a signal to an object placed within a measurement space with a defined pulse sequence, and for acquiring signal showing non-uniformity distribution of said static magnetic field in selected slice of said object,

(b) step for applying said static magnetic field, slice selective gradient magnetic field, phase encode gradient magnetic field, gradient magnetic field for reading out said signal to said object placed in said measurement space with said defined pulse sequence, and for acquiring signal showing image information in said selected slice of said object,

(c) step for making signal showing real image information of said object by calculating between signal showing image information acquired in said step (b) and signal showing static magnetic field non-uniformity acquired in said step (a),

(d) step for reconstructing image of said object from signal showing real image information of said object.

5. A magnetic resonance imaging method according to claims 1 or 4, wherein said signal that shows static magnetic field non-uniformity being acquired in plural number of time phase over one period of a periodical motion of said object is used to correct signal of said same time phasing in said signal expressing imaging information.

6. A magnetic resonance imaging method according to claims 1 or 4, wherein the signal expressing static magnetic field non-uniformity is measured in plural number of time phasing over one period of a motion of said object, and the signal expressing image information is measured continuously to the plural number of images.

7. A magnetic resonance imaging method according to claims 1 or 4, wherein static magnetic field non-uniformity correction is performed after one-dimensional transforming said signal showing static magnetic field non-uniformity and signal expressing image information.

13. The magnetic resonance imaging method according to claim 1 or claim 4, wherein

said signal showing non-uniformity distribution of said static magnetic field is acquired by continuously alternating the polarity of the read out gradient magnetic field without applying the phase encode gradient magnetic field, and

said signal showing real image information is acquired by continuously alternating the polarity of the read out gradient magnetic field, with the phase encode gradient magnetic field being applied discretely.

2. Magnetic resonance imaging method comprising,

(e) step for applying static magnetic field, slice selective gradient magnetic field, gradient magnetic field for reading out said signal to an object placed in measurement space with defined pulse, and for acquiring signal showing static magnetic field non-uniformity in said selected slice of said object,

(f) step for detecting motion of said object and for setting plural number of time phase in one period of a motion of said object, and for acquiring MR signal that shows said motion of said object in these every time phase,

(g) step for applying static magnetic field, slice selective gradient magnetic field, phase encode gradient magnetic field, gradient magnetic field for reading out said signal with the defined pulse sequence to said object placed in said measurement space in each time phase of said one period of said motion of said object, and for acquiring signal that shows image information in said selected slice of said object,

(h) step for removing static magnetic field non-uniformity signal including static magnetic field non-uniformity from said signal showing image information of said object being acquired in said step (g) in each time phase by using said signal showing static magnetic field acquired in said step (e) and said signal showing said motion of object acquired in said step (f),

(i) step for reconstructing image by using said signal being removed static magnetic field non-uniformity in said step (h).

12. The magnetic resonance imaging method according to claim 2, wherein correction for motion in step (h) does not adversely affect the correction for the static magnetic field non-uniformity.

3. Magnetic resonance imaging method comprising,

(j) step for detecting motion of an object and for setting several time phase in one period of said motion of said object,

(k) step for applying static magnetic field, slice selective gradient magnetic field, gradient magnetic field for reading out said signal to said object placed in said measurement space with said defined pulse sequence per each time phase, and for acquiring signal expressing motion of said object and signal of static field non-uniformity distribution of said selected slice,

(l) step for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal with said defined pulse sequence to said object placed in said measurement space per each time phasing, and acquiring signal showing said motion of said object and image information in said selected slice,

(m) step for removing static magnetic field non-uniformity signal comprising static field non-uniformity by said motion of said object from signal showing image information of said object per each time phase acquired in said step (1), using signal expressing motion of said object acquired in said step (k) and signal showing non-uniformity distribution of said static magnetic field in said selected slice and signal expressing motion of said object acquired by said step (1), and

(n) step for performing image reconstruction by using signal of which static magnetic field non-uniformity is removed in said step (m).

4. Magnetic resonance imaging method comprising,

(o) step for detecting motion of an object, and for setting plural number of time phase in one period interval of a motion of said object,

(p) step for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal to said object placed in the measurement space with said defined pulse, and for acquiring signal expressing motion of said object and signal showing non-uniformity distribution of said static magnetic field in said selected slice,

(q) step for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal to the object placed in the measurement space with said defined pulse sequence in every time phase being set, and for acquiring signal expressing said motion of said object and signal showing image information in said selected slice,

(r) step for detecting signal showing irregular motion of said object from said signal expressing motion of said object acquired by said step (p) or step (q) and for removing this detected irregular motion signal from image information acquired in said step (q),

(s) step removing static magnetic field non-uniformity signal from signal having be removed irregular motion signal in said step (r) by using signal expressing motion of said object acquired by said step (p) and step (q) and signal showing static magnetic field non-uniformity distribution in said selected slice and signal expressing said motion of said object per every time phasing being set, and

(t) step for image reconstructing signal acquired in said step (s).

8. A magnetic resonance imaging apparatus comprising,

magnetic field generation means for generating static magnetic field and gradient magnetic field and high frequency magnetic field to measuring space that an object is placed, detecting means for detecting nuclear magnetic resonance signal generated from said object, signal processing means for signal processing nuclear magnetic resonance signal detected by said detecting means,

means for image reconstructing signal processed by this signal processing means,

image display means for displaying the reconstructed image, means for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal to said object placed in said measurement space with said defined pulse sequence and for acquiring signal showing non-uniformity of said static magnetic field in said selected slice of said object,

means for applying static magnetic field and slice selective gradient magnetic field and phase encode gradient magnetic field and gradient magnetic field for reading out said signal to said object placed in said measurement space with said defined pulse sequence and for acquiring signal showing image information in said selected slice of said object,

means for removing signal showing said static magnetic field non-uniformity from signal showing said image information and for making signal expressing real image information of said object, and

means for reconstructing image of said object from said signal expressing real image information of said object.

9. A magnetic resonance imaging apparatus comprising,

magnetic field generation means for generating static magnetic field and gradient magnetic field and high frequency magnetic field to measuring space in which an object is placed,

detecting means for detecting nuclear magnetic resonance signal being generated from said object,

signal processing means for signal processing nuclear magnetic resonance signal detected by said detecting means,

image reconstruction means for image reconstructing said signal processed by said signal processing means,

image display means for displaying image reconstructed by said image reconstructing means,

means for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal to said object placed in said measurement space with said defined pulse sequence and for acquiring signal showing non-uniformity distribution of said static magnetic field in said selected slice of said object,

means for detecting motion of said object by setting plural number of time phase in one period interval of said motion of said object and acquiring an MR signal showing motion of said object per these each time phasing,

means for applying static magnetic field and slice selective gradient magnetic field and phase encode gradient magnetic field and gradient magnetic field for reading out to said object placed in said measurement space in each time phase in one period interval of said motion of said object with said defined pulse sequence and for acquiring signal showing image information in said selected slice of said object,

means for removing static magnetic field non-uniformity signal including static magnetic field non-uniformity of said motion of said object from signal showing image information of said object in each time phasing by using said signal showing static magnetic field non-uniformity and signal showing motion of said object, and

means for performing image reconstruction using signal that the static field non-uniformity signal is removed.

10. A magnetic resonance imaging apparatus comprising,

magnetic field generation means for respectively generating static magnetic field and gradient magnetic field and high frequency magnetic field to measuring space in which an object is placed,

detecting means for detecting nuclear magnetic resonance signal generated from said object,

signal processing means for signal processing said nuclear magnetic resonance signal detected by said detecting means,

means for image reconstructing said signal processed by said signal processing means, image display means for displaying reconstructed image,

means for detecting said motion of said object and setting plural number of time phase in one period interval of said motion of said object,

means for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal to said object placed in said measurement space with said defined pulse sequence in each time phase that is set and for acquiring signal expressing motion of said object and signal showing non-uniformity distribution of said static magnetic field in said selected slice,

means for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal to said object placed in said measurement space with said defined pulse sequence per time phase that is set and for acquiring said signal expressing said motion of said object and said signal showing said image information in said selected slice,

means for removing static magnetic field non-uniformity signal including static magnetic field non-uniformity by said motion of said object from said signal showing image information of said object in each time phase by using signal expressing motion of said object and signal showing non-uniformity distribution of said static magnetic field in said selected slice and signal expressing motion of said object that is acquired together with said imaging signal, and

means for performing image reconstructing by using signal that said static magnetic field non-uniformity signal is removed.

11. A magnetic resonance imaging apparatus comprising,

magnetic field generation means for generating static magnetic field and gradient magnetic field and high frequency magnetic field respectively to measuring space in which an object is placed,

detecting means for detecting nuclear magnetic resonance signal generated from said object,

signal processing means for signal processing said nuclear magnetic resonance signal detected by said detecting means,

means for image reconstructing said signal processed by said signal processing means,

image display means for displaying reconstructed image,

means for detecting motion of said object and setting plural number of time phase in one period interval of said motion of said object,

means for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal with said defined pulse sequence in each time phase that is set and acquiring signal expressing motion of said object and non-uniformity distribution of said static magnetic field in said selected slice,

means for applying static magnetic field and slice selective gradient magnetic field and gradient magnetic field for reading out said signal with said defined pulse sequence in each time phase set and acquiring signal expressing motion of said object and signal showing image information in said selected slice,

means for detecting signal showing an irregular motion of said motion from signal expressing said motion of said object and removing said detected irregular motion signal from information, means for removing static magnetic field non-uniformity signal from image signal that said irregular motion signal is removed by using signal expressing motion of said object and signal showing non-uniformity distribution of said static magnetic field in said selected slice and signal expressing motion of said object in each time phase that is set, and means for image reconstructing from signal that the static field non-uniformity signal is removed.